© Author(s) 2024. CC Atribution 4.0 License
Geologic structure and origin of the Zadlog karst polje 
Geološka zgradba in nastanek kraškega polja Zadlog
Jože ČAR¹ & Ela ŠEGINA²*
1Beblerjeva 4, SI-5280 Idrija, Slovenija; e-mail: joze.car@siol.net
2Geološki zavod Slovenije, Dimičeva ulica 14, SI-1000 Ljubljana, Slovenija; *corresponding author: ela.segina@geo-zs.si
Prejeto / Received 29. 2. 2024; Sprejeto / Accepted 20. 8. 2024; Objavljeno na spletu / Published online 16. 12. 2024
Key words: karst polje, thrust and fault tectonics, dolomite, hydrogeology, Zadlog, Zadloško polje
Ključne besede: kraško polje, narivna in prelomna tektonika, dolomit, hidrogeologija, Zadlog, Zadloško polje
Abstract
In the wider Idrija area in western Slovenia, several large plains formed along the thrusts within the dolomite and at the 
contact of dolomite and limestone. The purpose of this paper is to present the detailed structural-geological background 
of one such plain, namely the Zadlog plain, and based on these findings, to provide new starting points for analyzing 
the genetic conditions of other karst poljes in Notranjska. The Zadloško polje was formed in a wider near-fault crushed 
zone at the contact of two structural units within the Upper Triassic Norian-Rhaetian dolomite, with the thrust crossing 
the polje in its central part. The initially lowered area at the thrust represented a morphological basis, and the crushed 
zones in the dolomite played a hydrological retention role inducing the stagnation of surface water and, as a result, the 
formation of the karst polje. Younger fault tectonics then established efficient drainage of surface water and the erosion of 
sediments to the karst underground. Besdies this, slope equilibration leads us to conclude that the karst polje capability of 
hydrologic retention is recently decreased. The example of Zadloško polje shows that the thrust structures and associated 
hydrological conditions are the key elements for the formation of karst poljes in the dissected karst surface. Further 
detailed structural-geological mapping will reveal whether similar structural-geological conditions are the basis for the 
formation of other karst poljes in the region.
Izvleček
Vzdolž narivov znotraj dolomita in narivov na kontaktu dolomita in apnenca so na Idrijskem v zahodni Sloveniji 
mestoma nastale večje izravnave. Namen tega prispevka je predstaviti podrobno strukturno-geološko ozadje ene takih 
izravnav, in sicer Zadloške uravnave in na podlagi teh ugotovitev podati nova izhodišča za prevetritev genetskih razmer 
tudi drugih kraških polj na Notranjskem. Zadloško polje je tako nastalo v razširjeni obprelomni zdrobljeni coni ob stiku 
dveh strukturnih enot znotraj zgornjetriasnega norijsko-retijskega dolomita, pri čemer narivnica prečka polje v njegovem 
osrednjem delu. Začetna obnarivna izravnava je predstavljala morfološko zasnovo, zdrobljeni coni v dolomitu pa sta 
imeli ključno vodno-zadrževalno vlogo pri zastajanju površinske vode in posledično pri nastanku kraškega polja. Mlajša 
prelomna tektonika je nato vzpostavila efektivno odvajanje voda in odnašanje sedimentov v kraško podzemlje. Prav tako 
opazujemo uravnavanje pobočij izravnave, zaradi česar menimo, da je vodno-zadrževalna sposobnost kraškega polja 
recentno zmanjšana. Primer Zadloškega polja kaže, da so narivna zgradba in z njo povezane hidrološke razmere ključni 
element za oblikovanje kraškega polja v razčlenjenem kraškem površju. Ali so podobne strukturno-geološke razmere 
osnova nastanka tudi ostalih kraških polj v regiji, bo razkrilo nadaljnje podrobno strukturno-geološko kartiranje.
GEOLOGIJA 67/2, 249-271, Ljubljana 2024
https://doi.org/10.5474/geologija.2024.012
Introduction
On the extensive Črni Vrh plateau, northwest of 
Črni Vrh above Idrija, lies a 2 km long and up to 
800 m wide plain, which locals simply call Zadlog 
but sometimes also Zadloško polje (Fig. 1A, B). On 
the plain lies the dispersed settlement of Zadlog 
with many names for the different parts of the pol-
je. The Zadlog plain is surrounded by higher eleva-
Uvod
Na obsežni Črnovrški planoti severozahodno 
od Črnega Vrha nad Idrijo leži 2 km dolga in 
do 800 m široka izravnava, ki ji domačini reče-
jo preprosto Zadlog (v Zadlogu), včasih pa tudi 
Zadloško polje (sl. 1A, B). Na izravnavi leži raz-
treseno naselje Zadlog, s številnimi imeni posa-
meznih predelov polja. Zadloška izravnava je z 
250 Jože ČAR & Ela ŠEGINA
tions on all sides and is therefore often referenced 
as Zadloška kotlina (Zadlog basin) on geographical 
maps. Leaving aside different geographical defini-
tions, the term Zadloško polje or just Zadlog will be 
used hereinafter.
On a printed geological map of Idrija at the 
scale of 1:25000, the structure of the Zadloško 
polje area and its surroundings appears to be sim-
ple and uncomplicated (Mlakar & Čar 2009, Fig. 
1). The conditions are logically and, according to 
the figures, adequately explained. The geological 
structure of Zadlog seems very simple for the oth-
erwise complex territory of Idrija. However, a quick 
geological examination of the central part of Zad-
loško polje revealed that the geological conditions 
are quite different. This was indeed reason enough 
for a renewed, more detailed geological survey of 
Zadlog and its surrounding area. It revealed that 
Zadloško polje and its surroundings have a more 
complex structural-geological composition than 
previously believed, which is hardly recognizable 
due to the naturally level terrain, continuous farm-
ing and extensive land improvement works. There 
are few discussions of the Zadlog polje: before the 
results of detailed fieldwork presented in this re-
search and the identification of complex structur-
al-tectonic conditions, Zadlog was on a geological 
map represented only in his general features. Al-
though the hydrological conditions were general-
ly known, no one had yet considered them in the 
wider hydrological context. The findings of the new 
structural-geological mapping presented here can 
be used to explain the position of the polje with-
in the broader structural situation of the area, the 
formation of the karst polje, the position and for-
mation of swallets, and to explain general hydro-
logical and morphological features and how it fits 
into the broader geological structure of the Črni 
Vrh plateau and wider Idrija region. The formation 
of the initial plain of the karst polje is in the exist-
ing karst literature often associated with tension 
conditions (Gams 1978, Vrabec, 1994; Gracia et al., 
2003; Doğan et al., 2017), while the formation of 
the karst polje in the context of thrust tectonics has 
not yet been discussed. 
General features of Zadloško polje
The geographical features of Zadloško polje 
were discussed in 1968 by Habič in his PhD thesis 
(Habič, 1968). Only some data from his work that 
is relevant to this discussion is summarised here.
The extensive plain of Zadlog is located on the 
western edge of the Črni Vrh plateau at an alti-
tude of between 716 and 720 m. To the north and 
east towards the Idrijca valley, Idrijski Log and 
vseh strani obdana z v išjim vzpetinami, zato je 
na geografskih kartah večkrat označena tudi kot 
Zadloška kotlina. Ne glede na različne geograf-
ske opredelitve bomo v nadaljevanju uporabljali 
poimenovanje Zadloško polje, ali pa samo Zad-
log.
Pogled na natisnjeno idrijsko geološko karto 
v merilu 1 : 25.000 kaže, da ima območje Zad-
loškega polja z okolico preprosto in enostavno 
zgradbo (Mlakar & Čar, 2009, sl. 1). Razmere so 
logično in, glede na podatke, primerno razlože-
ne. Za sicer geološko zapleteno idrijsko ozemlje 
izgleda geološka zgradba Zadloga zelo enostavna. 
Vendar je že hiter geološki ogled osrednjega dela 
Zadloškega polja pokazal, da so geološke razmere 
očitno drugačne. Seveda je bil to zadosten razlog 
za ponovno, natančnejše geološko kartiranje Za-
dloga in okolice. Pokazalo se je, da ima Zadloško 
polje z okolico bolj zapleteno strukturno-geološko 
zgradbo od predhodno razumljene, ki je zaradi 
naravne izravnave terena, stalnega kmetovanja in 
obsežnih melioracijskih del težje prepoznavna. O 
Zadloški izravnavi obstaja le malo razprav. Pred, 
v tej raziskavi predstavljenimi rezultati podrob-
nega terenskega dela in ugotovitvijo zapletenih 
strukturno-tektonskih razmer, je bil Zadlog na 
geoloških kartah izrisan samo v svojih splošnih 
potezah. Hidrološke razmere so bile sicer v splo-
šnem znane, toda nihče jih še ni obravnaval v 
širšem hidrološkem kontekstu. Na podlagi ugo-
tovitev tukaj predstavljenih rezultatov struktur-
no-geološkega kartiranja pa se da dobro razložiti 
lego polja v širši strukturni zgradbi ozemlja, na-
stanek kraškega polja, lego in nastanek ponikev 
in pojasniti splošne hidrološke in morfološke zna-
čilnosti ter vpetost v širšo geološko strukturo Čr-
novrške planote in Idrijskega ozemlja. Nastanek 
začetne uravnave kraškega polja se v obstoječi 
krasoslovni literaturi pogosto povezuje z natezni-
mi razmerami (Gams, 1978; Vrabec, 1994; Gracia 
et al., 2003; Doğan et al., 2017), medtem ko na-
stanek kraškega polja v okviru narivne tektonike 
še ni bil obravnavan. 
Splošne značilnosti Zadloškega polja
Geografske značilnosti Zadloškega polja je ob-
ravnaval Habič v svojem doktoratu leta 1968 (Ha-
bič, 1968). Iz njegovega dela povzemamo le nekaj, 
za naše razpravljanje pomembnih podatkov.
Obsežna zadloška uravnava na zahodnem ob-
robju Črnovrške planote leži na višini med 716 
in 720 m. Na severu in vzhodu proti dolini Idrij-
ce, Idrijskemu Logu in Koševniku je obrobljena 
z nižjim grebenom s številnimi manjšimi dolina-
mi, ki se iztekajo na eni strani proti Zadlogu, na 
251Geologic structure and origin of the Zadlog karst polje
Koševnik, it is lined by a lower ridge with numer-
ous smaller valleys leading towards Zadlog on one 
side and Idrijski Log on the other (Fig. 1A, B). The 
ridge, which runs only some 40 m above the pres-
ent-day base of the plain, is interrupted by a num-
ber of indistinct peaks rising up to no more than 
100 m above the base of Zadloško polje. The lowest 
points of the ridge are the distinct pass close to the 
Podtisov Vrh peak at 724 m, where a forest road 
from the Belca valley leads to Zadlog, and the pass 
near Kočar (above Ivanšek) (735 m), where the road 
from Zadlog leads to Idrijski Log and Idrijska Bela. 
On the southern edge of Zadlog, there are steep 
and poorly dissected slopes with ca. 1100 m high 
peaks. The only notch in the slope is the Bukovska 
Rovna ledge (782 m) extending into a distinctly dry 
and heavily karstified lowered area towards Mrzli 
Log and the pass near Šoštar, where the main road 
leads to Črni Vrh. Here is also the lowest point of 
the edge of Zadloško polje at an altitude of 718 m. 
Given the above-mentioned data, Zadlog could in-
deed be referred to as a shallow basin. 
Geographers and geologists alike write about 
how the Idrijca, the Belca and the Kanomljica 
once probably f lowed together across the Zad-
loško polje, the Črni Vrh plateau and further along 
the Hotenjsko podolje valley system towards the 
Ljubljanica (Savnik, 1959; Melik, 1963; Mlakar, 
2002). The f low of the watercourses in Idrija to-
wards the Ljubljanica river was discussed in great 
detail and supported by geomorphological data 
by Mlakar (2002). Such an assessment is not sup-
ported by any material evidence. Habič (1968) had 
already determined that on the Zadlog-Črni Vrh 
plateau and the Hotenjsko podolje area between 
drugi strani pa proti Idrijskemu Logu (sl. 1A, B). 
Greben, ki poteka le kakih 40 m nad današnjim 
dnom izravnave, je prekinjen z nekaj neizraziti-
mi vrhovi, ki se vzpenjajo največ do 100 m nad 
dnom Zadloškega polja. Najnižji točki grebena 
sta izrazita prehod pri Podtisovem Vrhu na višini 
724 m, kjer je na Zadlog speljana gozdna cesta 
iz doline Belce, in prelaz pri Kočarju (nad Ivan-
škom) (735 m), kjer poteka cesta iz Zadloga proti 
Idrijskemu Logu in Idrijski Beli. Na južnem ob-
robju Zadloga ležijo strma in slabo razčlenjena 
pobočja z vrhovi na višini okrog 1100 m. Zarezo 
v pobočju predstavlja le polica Bukovska Rovna 
(782 m), ki se podaljša v izrazito suho in močno 
zakraselo znižanje proti Mrzlemu Logu, ter pre-
hod pri Šoštarju, kjer poteka glavna cesta proti 
Črnemu Vrhu. Tu je tudi najnižja točka obrobja 
Zadloškega polja na višini 718 m. Iz zgornjih po-
datkov izhaja, da ima Zadlog značilnosti plitve 
kotline. 
O tem, da naj bi nekdaj Idrijca, Belca in Ka-
nomljica združeno tekale čez Zadloško polje, Čr-
novrško planoto in dalje po Hotenjskem podolju 
proti Ljubljanici, so pisali tako starejši geogra-
f i kot tudi geologi (Savnik, 1959; Melik, 1963; 
Mlakar, 2002). Še posebej podrobno in podprto 
z geološkimi in morfološkimi podatki je pretok 
idrijskih vodotokov proti Ljubljanici obravna-
val Mlakar (2002). Materialnih dokazov za tako 
mnenje ne navaja. Že Habič (1968) je ugotovil, 
da na Zadloško-Črnovrški planoti in Hotenjskem 
podolju med Godovičem in Hotedršico ni sledov 
rečne erozije ali prodov, ki bi vsekakor morali biti 
A B
Fig. 1. A – Location and basic topographic features of the Zadloško polje area. B – View on Zadloško polje during floods (18. 12. 2009). Photo: 
Bojana Zagoda.
Sl. 1. A – Lokacija in osnovne topografske značilnosti območja Zadloškega polja. B – Pogled na Zadloško polje v času poplav (18. 12. 2009). 
Foto: Bojana Zagoda.
252 Jože ČAR & Ela ŠEGINA
Godovič and Hotedršica there are no traces of f lu-
vial erosion or cobble, which should certainly have 
been preserved, even if only here and there and in 
marginal amounts. Zadloško polje is covered by an 
unevenly thick yellowish dolomitic clayey eluvium 
with rare, small and irregular millimetre-sized 
chert clasts showing no signs of transport. The 
clasts were not studied in detail, however, they 
represent sparingly soluble residue and certainly 
originate from the parent rock. The thickness of 
eluvium is locally increased in some lower parts of 
the terrain. The internal texture shows that it was 
transported for only a short distance.
The entire Zadloško polje was artificially lev-
elled (ameliorated) to a considerable extent. To get 
land for farming, the lower dolomite outcrops were 
mostly levelled out. At the northern and central 
parts of Zadloško polje, however, there are still do-
lomite hummocks rising about 1.5 to some metres 
from the plain that mainly run northwest to south-
east and are aligned with strata of dolomite. They 
are either bare or covered with shallow turf, shrub-
bery, individual trees or sparse woods. Nowadays it 
is impossible to deduce how many dolines and other 
karst formations have been filled. Given the condi-
tions elsewhere on the dolomitic part of the Črni 
Vrh plateau (Črni Vrh, Predgriže, Koševnik and Id-
rijski Log), which has comparable structural com-
position (Zagoda, 2004), it can be concluded that 
the Upper Triassic dolomite in Zadlog is also rela-
tively poorly karstified, which is as well supported 
by geological mapping of the same kind of dolomite 
in a comparable structural position in Idrijski Log 
and Predgriže. However, there are some morpho-
logically distinctive sinking areas with ponors on 
Zadloško polje. 
The inf luence of the Pleistocene glaciation on the 
morphology of Zadlog has not yet been studied and 
is currently unknown. Undoubtedly, such cold cli-
matic conditions inf luenced the faster denudation of 
dolomites in the hinterland and more intense trans-
port of the weathered material to the karst polje.
Geological structure of Zadloško polje
Earlier data
Existing geological maps (Buser et al., 1967; 
Mlakar, 1969; Pleničar, 1970; Mlakar & Čar, 2009) 
suggest that the structure of Zadloško polje and 
its wider surroundings is very simple. The Posto-
jna sheet from the Basic geological map (Osnovna 
geološka karta, OGK) and the interpreter to this 
sheet (Pleničar et al., 1970) show that Zadlog and 
its wider surroundings are made of thinly to mod-
erately stratified Upper Triassic Norian-Rhaetian 
ohranjeni, pa čeprav le tu in tam in v neznatnih 
sledovih. Zadloško polje sicer prekriva neena-
komerno debela dolomitna rumenkasta glinasta 
preperina z redkimi, majhnimi in nepravilnimi 
klasti roženca milimetrskih dimenzij, ki ne kaže-
jo znakov premeščanja, saj so povsem nepravil-
nih oblik. Klastov na tem mestu nismo razisko-
vali, vendar predstavljajo težje topni ostanek in 
zagotovo izhajajo iz matične kamnine. Preperina 
je na nekaterih nižje ležečih predelih lokalno de-
belejša. Notranja tekstura kaže, da je preložena le 
na kratko razdaljo.
Celotno Zadloško polje je bilo s posegi v 
dobršni meri umetno izravnano (meliorirano). 
Za potrebe kmetovanja so bile izravnane predv-
sem nižje dolomitne golice. V severnem in osred-
njem delu Zadloškega polja pa še vedno štrle iz 
izravnave od 1,5 do nekaj metrov visoke dolo-
mitne grbine, ki potekajo v glavnem v smeri se-
verozahod – jugovzhod, skladno s slemenitvijo 
dolomitnih plasti. So gole ali pa pokrite s plitvo 
rušo, grmovjem, posameznimi drevesi ali red-
kim gozdom. Koliko je v podlagi zasutih vrtač 
in drugih kraških oblik ni raziskano. Iz razmer 
drugod na dolomitnem delu Črnovrške planote 
(Črni Vrh, Predgriže, Koševnik in Idrijski Log), 
ki ima primerljivo strukturno zgradbo (Zagoda, 
2004), lahko sklepamo, da je zgornjetriasni do-
lomit tudi v Zadlogu razmeroma slabo zakrasel.
To podpira tudi geološko kartiranje enakega do-
lomita v primerljiv i strukturni legi v Idrijskem 
Logu in Predgrižah. Se pa na Zadloškem polju 
nahaja nekaj morfološko izrazitih ponikalnih 
območij. 
Vpliv pleistocenske poledenitve na morfologijo 
Zadloga še ni bil preučen in ga ta hip ne pozna-
mo. Nedvomno pa so hladnejše podnebne raz-
mere vplivale na hitrejšo denudacijo dolomitov v 
zaledju polja in intenzivnejše površinsko premeš-
čanje preperine na izravnavo. 
Geološka zgradba Zadloškega polja
Starejši podatki
Pogled na dosedanje geološke karte (Buser 
et al., 1967; Mlakar, 1969; Pleničar, 1970; Mla-
kar & Čar, 2009) pokaže, da naj bi bilo Zadlo-
ško polje s širšo okolico zelo preprosto zgrajeno. 
Glede na OGK list Postojna in tolmača k temu 
listu (Pleničar et al., 1970) vidimo, da Zadlog 
s širšo okolico gradi tanko do srednje plastnati 
zgornjetriasni norijsko-retijski (ti. glavni) do-
lomit. Dno zadloške uravnave v celoti pokriva-
jo kvartarni sedimenti – nanosi rek in potokov 
(Pleničar et al., 1970). Od terciarne tektonike je 
253Geologic structure and origin of the Zadlog karst polje
dolomite (so-called main dolomite). The base of the 
Zadlog plain is entirely covered by quaternary sed-
iments – river and stream deposits (Pleničar et al., 
1970). Regarding tertiary tectonics, only the thrust 
line between the Lower Cretaceous limestone of the 
first ‘slice’ (today: Koševnik nappe slice) and the 
Upper Triassic dolomite of the second ‘slice’ (today: 
Čekovnik thrust slice) running north and east of 
Zadlog along the plain of Idrijski Log and Koševnik 
is delineated. No other potential tectonic elements 
have been identified.
Zadloško polje was not remapped during the pro-
duction of the new 1:25,000 scale geological map 
(Mlakar & Čar, 2009). The conditions thus remain 
nearly identical as when delineated and described 
by Mlakar on his 1969 geological map, while the 
new map includes corrections of thrust unit desig-
nations. According to Placer’s (Placer, 1981, 2008) 
thrust dissection of western Slovenia and his recent 
oral proposal, the Hrušica nappe lies in the deeper 
bedrock of the territory of Idrija, and over it follow 
the Koševnik, Čekovnik and Kanomlje interjacent 
slice (nappe slice in this paper), covered by the 
Lower thrust block of Trnovo nappe, which is now-
adays divided into four internal overthrust bodies 
(Mlakar & Čar, 2009; Čar, 2010; Čar et al., 2021). 
The entire Zadloško polje and its wider surround-
ings consist of two thrust packages of Upper Trias-
sic Norian-Rhaetian dolomite. The northern border 
of Zadloško polje and a large portion of the central 
part belong to the Čekovik nappe slice. The Upper 
Triassic dolomite has a normal stratigraphic posi-
tion according to recent findings (Čar, 2010). The 
southern slopes towards Špičasti vrh (822 m), Mrzli 
Log and Špik also consist of the Norian–Rhaetian 
dolomite, but it belongs to the Trnovo nappe over-
thrust unit, i.e. the Tičnica inner thrust sheet (Čar, 
2010). The thrust line between the two units should 
run along the southern edges of Zadlog, the same 
way as it is delineated on Mlakar’s map (1969). Two 
fault lines are delineated on the map: the first one 
runs from Mrzli Log across Bukovska Rovna, inter-
sects Zadloško polje and continues across Kotenjski 
rob (along the location Kot) into the Belca valley, 
while the second fault intersects the eastern part 
of Zadloško polje. It enters the polje in Plestenice 
and continues past Klančar and across Koševnik 
into the Idrijca valley. This map dating in 1969 also 
shows that the base of Zadloško polje is covered by 
alluvial deposits (Mlakar & Čar, 2009).
Previous geological maps (Pleničar, 1970; 
Mlakar, 1969; Mlakar & Čar, 2009) did not take 
into account the hydrological conditions in Zad-
log and the remarks on the coverage of the polje 
f loor already observed and written down by Habič 
izr isana le narivnica med spodnjekrednim ap-
nencem prve luske (danes: Koševniška krovna 
luska) in zgornjetriasnim dolomitom druge lus-
ke (danes: Čekovniška krovna luska), ki pote-
ka severno in vzhodno od Zadloga po uravnavi 
Idrijskega Loga in Koševnika. Drugi tektonski 
elementi niso bili ugotovljeni.
Pri izdelavi nove geološke karte v merilu 1: 25 
000 (Mlakar & Čar, 2009). Zadloškega polja nis-
mo na novo kartirali. Razmere zato ostajajo sko-
raj enake, kot jih je izrisal in opisal Mlakar na 
svoji geološki karti iz leta 1969, vendar s poprav-
ki poimenovanja narivnih enot. Soglasno s Pla-
cerjevo narivno razčlenitvijo zahodne Slovenije 
in njegovim novejšim ustnim predlogom (Placer, 
1981, 2008) leži v globlji podlagi Idrijskega ozem-
lja Hrušiški pokrov, nad njim si sledijo Košev-
niška, Čekovniška in Kanomeljska krovna luska, 
pokriva jih spodnji narivni blok Trnovskega po-
krova, ki je danes razdeljen na štiri notranje na-
rivne grude (Mlakar & Čar, 2009; Čar, 2010; Čar 
et al., 2021). Celotno Zadloško polje in njegovo 
širšo okolico gradita dva narivna paketa zgornje-
triasnega norijsko-retijskega dolomita. Severno 
obrobje Zadloškega polja in velik delež osrednje-
ga dela pripada Čekovniški krovni luski. Zgor-
njetriasni dolomit ima po novejših ugotovitvah 
normalno stratigrafsko lego (Čar, 2010). Južna 
pobočja proti Špičastemu vrhu (822 m), Mrzlemu 
Logu in Špiku gradi prav tako norijsko-retijski 
dolomit, le da pripada narivni enoti Trnovskega 
pokrova in sicer Tičenski notranji narivni grudi 
(Čar, 2010). Narivnica med obema enotama naj bi 
potekala po južnem obrobju Zadloga, enako kot je 
izrisana na Mlakarjevi karti (1969). Na karti sta 
izrisani dve prelomni liniji: prva poteka iz Mrzle-
ga Loga čez Bukovsko Rovno, seka Zadloško polje 
in se nadaljuje čez Kotenjski rob (po lokaciji Kot) 
v dolino Belce, drugi prelom pa seka vzhodni del 
Zadloškega polja. Na polje prihaja v Plestenicah 
in se nadaljuje mimo Klančarja in čez Koševnik 
v dolino Idrijce. Tudi na tej karti iz leta 1969 je 
izrisano, da prekrivajo dno Zadloškega polja alu-
vialni nanosi (Mlakar & Čar, 2009).
Pri izdelavi dosedanjih geoloških kart (Ple-
ničar, 1970; Mlakar 1969; Mlakar & Čar, 2009) 
niso upoštevane hidrološke razmere v Zadlogu in 
pripombe o pokritosti dna polja, ki jih je ugoto-
vil in zapisal že Habič (1968). To je bil povod za 
podrobnejše geološko kartiranje Zadloga z obrob-
jem v merilu 1 : 5000.
254 Jože ČAR & Ela ŠEGINA
Prelomna tektonika
Za lažjo razlago in boljše razumevanja na-
rivnih in obnarivnih deformacij na Zadloškem 
polju in njegovem obrobju obravnavamo najprej 
prelomno tektoniko. Poimenovanje pretrtosti ob 
prelomih in narivih ter njihovo spreminjanje v 
horizontalni in vertikalni smeri je soglasno z no-
menklaturo v Čarjevi razpravi (2018). Predsta-
vljeni podatki so rezultat podrobnega struktur-
no-geološkega kartiranja, ki je bilo izvedeno za 
namene te raziskave.
V zahodnem delu Zadloškega polja sledijo od 
njegovega obrobja proti vzhodu Figarjev, Podti-
sov in Zadloški prelom (sl. 2). Prelomi so des-
no-zmični, različno močni in imajo smer seve-
rozahod – jugovzhod. Združujemo jih v zahodni 
zadloški prelomni snop. Na skrajnem zahodnem 
obrobju Zadloškega polja poteka do 300 m ši-
rok, iz štir ih ožjih zdrobljenih con in močnih 
vmesnih porušenih con zgrajen Figarjev pre-
lom s splošnim  vpadom 80° proti jugozahodu 
(sl. 2). Jugozahodni del prelomne cone prehaja 
v strmem pobočju južnega obrobja Zadloga v 
široko razpoklinsko cono, značilno za vzdolžno 
spreminjanje prelomnih con (Čar, 2018). Seve-
rovzhodni del poteka vzdolž vznožja Špičastega 
vrha in se v nadaljevanju priključi na Zadloški 
prelom. Čez sedlo Podtisov Vrh poteka iz doli-
ne Belce dvojni Podtisov prelom z okrog 150 m 
široko prelomno cono. Sedlo Podtisov Vrh se je 
oblikovalo v zdrobljenih conah z vpadom 80° 
proti jugozahodu (sl. 3A). Prelomna cona poteka 
čez zahodni del Zadloškega polja in se v nada-
ljevanju priključi na močan Zadloški prelom, ki 
poteka iz doline Belce do roba Zadloškega polja 
pri Gozdniku in se nadaljuje čez polje do Buko-
vske Rovne (sl. 2). Močna prelomna cona Zadlo-
škega preloma je široka do 200 m in se nadaljuje 
proti Mrzlemu Logu in Kanjemu Dolu. V njej se 
je oblikovala poglobljena, morfološko razgiba-
na, močno zakrasela in znižana cona, ki poteka 
med Bukovsko Rovno in Mrzlim Logom. Stopnja 
pretrtosti kamnin se vzdolž cone spreminja od 
zdrobljenih do širokih porušenih con, v zunanjih 
prelomnih conah opazujemo različno močne raz-
poklinske cone.
Tudi vzhodni del Zadloškega polja in njeno 
obrobje prav tako seka niz prelomov, združujemo 
jih v vzhodni zadloški prelomni snop.  Od zahoda 
proti vzhodu si sledijo: Plesteniški, Klančarjev, 
Črnovrški, Abrahtov (ime po kmetiji) in močnej-
ši  Predgriški prelom (sl. 2). Plesteniški prelom je 
v severnem delu Zadloga usmerjen od severoza-
hoda proti jugovzhodu, v nadaljevanju se pribli-
žuje močni in široki coni Zadloškega preloma in 
(1968). This prompted a more detailed geologi-
cal mapping of Zadlog and its edges at a scale of 
1:5,000.
Fault tectonics
For an easier interpretation and a better under-
standing of the thrust and thrust–shear deforma-
tions on Zadloško polje and its edges, fault tectonics 
are discussed first. The fault and thrust fracturing 
nomenclature below and their variability in hori-
zontal and vertical directions is in line with the 
one published in the discussion by Čar (2018). The 
data presented are the result of detailed structur-
al-geological mapping, which was carried out for 
the purposes of the present research.
In the western part of Zadloško polje, from its 
edges eastwards follow the Figar, Podtis and Za-
dlog faults (Fig. 2). The faults are dextral strike-
slips of varying strength and are oriented north-
west–southeast. They are grouped together in the 
western Zadlog set of faults. The Figar fault is up 
to 300 m wide, consists of four narrow crushed 
zones and strong interjacent broken zones, has a 
general 80° dip to the southwest and runs over the 
far western edge of Zadloško polje (Fig. 2). The 
southwestern part of the fault zone transitions 
over the steep slope on the southern edges of Za-
dlog into a wide fissure zone, which is typical of 
the longitudinal changes in fault zones (Čar, 2018). 
The northeastern part runs along the foot of the 
Špičasti vrh and later joins the Zadlog fault. The 
double Podtis fault with an approximately 150 m 
wide fault zone leads from Belca valley across 
the Podtisov Vrh saddle. The Podtisov Vrh saddle 
formed in crushed zones with an 80° dip to the 
southwest (Fig. 3 A). The fault zone runs across 
the western part of Zadloško polje and joins the 
strong Zadlog fault, which runs from the Belca 
valley to the edge of Zadloško polje at Gozdnik and 
then progresses across the polje all the way to Bu-
kovska Rovna (Fig. 2). The strong fault zone of the 
Zadlog fault is up to 200 m wide and progresses 
towards Mrzli Log and Kanji Dol. Within this zone 
formed a deepened, morphologically dissected, 
strongly karstified and lowered zone which leads 
between Bukovska Rovna and Mrzli Log. The de-
gree of rock fracturing varies along the zone from 
crushed to widely fractured, and fissured zones of 
varying strength can be observed in the outer fault 
zones.
The eastern part of Zadloško polje and its edges 
are also intersected by a series of faults, grouped to-
gether in the eastern Zadlog set of faults. Running 
from west to east: Plestenice, Klančar, Črni Vrh, 
Abraht (named after a farm) and stronger Pred-
255Geologic structure and origin of the Zadlog karst polje
griže fault (Fig. 2). The Plestenice fault runs north-
west to southeast in the northern part of Zadlog, 
and then it approaches the strong and wide Zad-
log fault zone and joins it southeast of Mrzli Log 
outside of this map. Other faults have NNW-SSE 
direction in the northern part of the geologic map 
and later turn to NW-SE direction and predom-
inantly appear as relatively wide broken and fis-
sured zones in the dolomite. The fractured zones 
in both of the examined Zadlog set of faults are 
densely stacked with only 100 to 300 m distanc-
es in-between on average. All faults are dextral 
strike-slips. The displacements along these faults 
would need to be determined more precisely, but 
we estimate that they are relatively small. 
se nanjo priključi jugovzhodno od Mrzlega Loga 
izven okvir ja naše karte. Ostali prelomi imajo 
na severnem delu geološke karte smer SSZ-JJV, 
nato pa povijejo v smer SZ-JV in se kažejo pred-
vsem kot sorazmerno široke porušene in razpok-
linske cone v dolomitu. V obeh obravnavanih 
prelomnih snopih se pretrte cone nizajo na go-
sto, med njimi so razdalje v povprečju le od 100 
do 300 m. Pri vseh prelomih gre za desne zmi-
ke. Kakšni so premiki ob njih, bi bilo potrebno 
natančnejše ugotoviti, vendar ocenjujemo, da so 
relativno majhni. 
A
B
20
20
90
80
90
Trebče
Črni Vrh20
20
20
250/15
80
80
25
60
60
60
90
90
4030
80
90
80
80 90
90
90
70
60/90
60/90
Klančar
Ivanšk
Šoštar
Plestenice
Hudi kot
Na Sredi
ZADLOG
Podtisov 
vrh Gozdnik
Figar
Špičasti vrh
E
DAC
B
230/20
230/20
240/20
230/20
220/20
220/30
220/20 230/10
220/20
230/10
220/10
230/20
250/30245/10
230/30
200/20
220/20
215/10
210/20
230/30
210/20
270/45
250/20
270/20
250/25
250/30210/50
220/50
230/30
240/15 200/30
220/20
220/25
210/20
210/20
240/80
Mrzli Log
270/20
230/20
240/10
230/20
240/20
230/20
230/35160/25
220/15
210/20
220/10
Kot
250/10
220/15
2
2,3
2,3
3
3
Model zadloškega tlačnega klina/
Model of the Zadlog compression 
wedge 
δ1
δ1
P
lesten
iški p
relo
m
/P
lesten
ice fau
lt
Zadloški prelom
/Zadlog fault
δ1
Legenda/Legend
smer glavne napetosti/
direction of the main tension
relativna smer zmika/
relative direction of the 
displacement
smer premikanja/direction of 
movement
dvignjeni blok/uplifted block
reverzni prleom/reverse fault
240/30
KKL
TP/1
ČKL
230/15
Zajeti izvir
Predgriže
Figarjev prelom
/
Figar fault
Podtisov 
P
le
ste
n
iški p
re
lo
m
/P
le
ste
n
ice
 fa
u
lt
K
la
n
ča
rje
v p
re
lo
m
/K
la
n
ča
r fa
u
lt
Č
rnovrški prelom
/Č
rni V
rh fault
Abrahtov prelom
/Abraht fault
Predgriški prelom
/Predgriže fault
prelom
 
Sušni 
vrh
Mala 
Suša
Kotenjski prelom
/Kot fault
Zadloški prelom
/Zadlog fault
Fig
arj
ev
 
pre
lom
/
Fig
ar 
fau
lt
Po
dt
iso
v 
pr
el
om
/
Po
dt
is 
fa
ul
t
HP
Za
ho
dn
i z
ad
lo
šk
i p
re
lo
m
ni
 sn
op
/ 
W
es
t Z
ad
lo
g 
se
t o
f f
au
lts
 
Vzh
odn
i za
dloš
ki p
relo
mni
 sno
p/
Eas
t Za
dlog
 set
 of f
ault
s
Ko
te
nj
sk
i s
no
p 
pr
el
om
ov
/
Ko
t s
et
 o
f f
au
lts Klo
b
u
ča
rje
v p
re
lo
m
/
K
lo
b
u
ča
r fa
u
lt
Kotenjski 
rob
Bukovska 
rovna
/Podtis fault
/Tectonics
/Stratigraphy
/Hydrology
/Thrust border between nappes
/Thrust border between 
                 nappe slices
/Major slip fault
/Minor slip fault
/Reverse fault
/flisch
/bright grey limestone
/layered dolomite
/layered dolomite with rare
           shaly intercalations 
/Temporary spring
/Permanent spring
/Water reservoir
F
Obseg maksimalnih poplav /Maximal flood extent 0 0.5 1 Km
Zadloški prelom
/Zadlog fault
Idr
ijsk
i Lo
g
Občasno medplastno izvirno območje /Temporary interbed-
ded inflow  
Fig. 2. Structural-geological map of Zadloško polje. The AB profile is shown in Figure 4. HP – Hrušica nappe, TP/1 – Lower thrust block of 
Trnovo nappe, ČKL – Čekovnik nape slice, KKL – Koševnik nappe slice. Ponor zones: A – Štefkova rupa, B – Ponikva, C – Ponor at Cigale 
farm, D – Štirnska rupa, E – no name ponor zone, F – Figar ponor zone.
Sl. 2. Strukturno-geološka karta Zadloškega polja. Profil AB je prikazan na sliki 4. HP – Hrušiški pokrov, TP/1 – Spodnji narivni blok 
Trnovskega pokrova, ČKL – Čekovniška krovna luska, KKL – Koševniška krovna luska. Ponikalna območja: A – Štefkova rupa, B – Ponikva, 
C – Ponikva pri kmetiji Cigale, D – Štirnska rupa, E – ponikalno območje brez imena, F – Figarjevo ponikalno območje.
256 Jože ČAR & Ela ŠEGINA
The central part of Zadlog, which is loctated 
between the Zadlog and Plestenice faults, is about 
1300 m wide at the northwestern edge of the polje 
and gradually becomes narrower towards the south-
east (Fig. 2). It encompasses Hudi Kot on the south-
ern edges of the polje, the central part of the polje Na 
Sredi and the levelled extensions between numerous 
dolomite outcrops towards Sušni vrh, Mala Suša and 
Kot in the northwest. The faults intersecting the cen-
tral part of Zadloško polje are genetically distinct. 
The eastern faults branch off the Plestenice fault 
in the area of Kot and Mala Suša, and lean on the 
approximately 300 m long area of the Zadlog fault 
at the Na Sredi site. This is the ‘Kotenjski niz’ (af-
ter the hamlet of Kot) set of three morphologically 
less distinct, reverse faults in the north–south direc-
tion. According to the geological data, they are the 
result of secondary pressure conditions between the 
Plestenice fault on the one hand and the Zadlog fault 
on the other. Both dextral strike-slip faults are rel-
atively strong and, as already mentioned, converge 
and merge towards the southeast. A pressure wedge 
has formed between them where weak and branched 
reverse faults formed due to intense dextral strike-
slips (Zadlog compression wedge model, Fig. 2). 
They dip about 60° to the east, which is in line with 
their origin. Along these there are slightly uplifted 
eastern blocks. The western set consists of several 
weaker branched out strike-slip faults of Kot with 
narrow fault zones. On the northwestern edges of Za-
dloško polje they run in the NW–SE direction, then 
gently bend in the SSW–SSE direction, intertwine 
with eastern set of reverse faults zones at location 
Na Sredi and lean on the Zadlog fault at the same 
section as the reverse faults. The entwinement at Na 
Sredi shows that reverse faults are slightly older as 
they are intersected by strike-slip faults (Fig. 2). In-
tersections of reverse and strike-slip fault zones are 
connected to the sinking zones at Na Sredi (Fig. 2).
Thrust tectonics
Ref lecting on the hitherto inconsistent desig-
nation of the different types of thrust units, as well 
as the differing graphic tracing of thrust contacts 
between them on geological maps, a table with the 
subdivision and designation of individual thrust 
elements was presented in 2021 (Čar et al., 2021). 
The deeper bedrock of the Idrija territory con-
tains Upper Cretaceous limestones and through ero-
sion overlying Palaeocene-Eocene f lysch rocks of 
the Hrušica nappe (HP) (Fig. 4), which are visible at 
the southern margin of the Strug tectonic window. 
According to older literature, the above-mentioned 
thrust unit is believed to be native bedrock of the Idri-
ja territory (Mlakar, 1969, Fig. 5; Placer, 1973, 1981). 
Osrednji del Zadloga med Zadloškim in 
Plesteniškim prelomom je na severozahodnem 
robu polja širok okrog 1300 m, proti jugovzhodu 
pa se postopno oži (sl. 2). Zaobjema Hudi Kot 
na južnem obrobju polja, osrednji del polja Na 
Sredi in izravnane podaljške med številnimi 
dolomitnimi izdanki proti Sušnemu vrhu, Mali 
Suši in Kotu na severozahodu. Prelomi, ki sekajo 
osrednji del Zadloškega polja, so genetsko raz-
l ični. Vzhodni se odcepijo od Plesteniškega pre-
loma na območju Kota in Male Suše, in se nasla-
njajo v okrog 300 m dolgem območju na Zadloški 
prelom na lokaciji Na Sredi. Gre za Kotenjski (po 
zaselku Kot) niz treh morfološko manj izrazitih, 
reverznih prelomov v smeri sever-jug. Glede na 
geološke podatke ugotavljamo, da so rezultat 
sekundarnih t lačnih razmer med Plesteniškim 
prelomom na eni in Zadloškim na drugi strani. 
Oba desno zmična preloma sta razmeroma moč-
na in se proti jugovzhodu, kot smo že omenili, 
približujeta in združita. Med njima je nastal 
t lačni klin, v katerem so ob intenzivnih desnih 
zmikih nastali šibki reverzni prelomi (Model 
zadloškega t lačnega klina, sl. 2). Vpadajo okrog 
60° proti vzhodu, kar je v soglasju z njihovim 
nastankom. Ob njih so vzhodni bloki nekoliko 
dvignjeni. Zahodnejši snop sestavlja več šibkej-
ših in razvejanih Kotenjskih zmičnih prelomov 
z ozkimi prelomnimi conami. Na severozaho-
dnem obrobju Zadloškega polja potekajo v smeri 
SZ-JV,  nato povijejo rahlo v smer SSZ-JJV. Na 
lokaciji Na Sredi se prepletejo s conami vzhod-
nega reverznega prelomnega snopa in naslanjajo 
na Zadloški prelom na istem odseku kot reverzni 
prelomi. Pri prepletanju Na Sredi v idimo, da so 
reverzni prelomi nekoliko starejši, saj jih zmič-
ni prelomi sekajo (sl. 2). Na sekanje omenjenih 
reverznih in zmičnih prelomnih con so vezana 
ponikalna območja Na Sredi (sl. 2). 
Narivna tektonika
Ob premisleku o doslej neenotnem poimeno-
vanju različnih tipov narivnih enot, kot tudi zara-
di različnih grafičnih izrisov narivnih stikov med 
njimi na geoloških kartah smo leta 2021 podali 
preglednico razčlenitve in poimenovanje posame-
znih narivnih elementov (Čar et al., 2021). 
V globlji podlagi idr ijskega območja ležijo 
zgornjekredni apnenci in erozijsko na njih pa-
leocensko-eocenske f l išne kamnine Hrušiške-
ga pokrova (HP) (sl. 4), ki se na obravnavanem 
območju pojavijo v južnem obrobju Tektonskega 
okna Strug. Po starejši l iteraturi naj bi bi la ome-
njena narivna enota avtohtona podlaga idrijske-
ga območja (Mlakar, 1969, sl. 5; Placer, 1973, 
257Geologic structure and origin of the Zadlog karst polje
In the Idrija area, Lower and Upper Cretaceous lime-
stone of the Koševnik nappe slice (KKL) is thrust onto 
the rocks of the Hrušica nappe in a normal position 
and measures 100 to 500 m in thickness (Fig. 4). In 
view of the geological conditions in the Strug tectonic 
window and Idrijska Bela, the Koševnik nappe slice 
underneath Zadloško polje mainly consists of Upper 
Cretaceous limestone, but may deeper down already 
continuously transition into Lower Cretaceous lime-
stones with rare intercalations of early diagenetic 
dolomite. Along the thrust line, soft f lysch rocks are 
often pushed out in such a way that Upper Creta-
ceous limestones of the Hrušica nappe are directly 
overlain by Lower or Upper Cretaceous limestones 
of the Koševnik nappe slice (Fig. 4). The Koševnik 
nappe slice is covered by Norian-Rhaetian dolomite 
of the Čekovnik nappe slice (ČKL) in its normal posi-
tion. The morphologically very distinctive thrust line 
between the two nappe units runs along the northern 
preiphery of Idrijski Log (Zagoda, 2004) (Fig. 2) and 
then crosses Predgriško polje east of Črni Vrh (Mlakar 
& Čar, 2009). The northern edges and northern part 
of Zadloško polje consist of Upper Triassic dolomite 
of the Čekovnik nappe slice. The remaining part of 
Zadlog as well as its southern and western edges con-
sist of the Trnovo nappe Norian-Rhaetian dolomite 
(TP/1 – the Trnovo nappe underthrust block). High 
below the northern edge of Trnovski gozd (not shown 
in Fig. 2), the Norian-Rhaetian dolomite of the Trno-
vo nappe is sliced by another thrust plane (Čar, 2010). 
Over it lies the Norian-Rhaetian dolomite with con-
tinuous transitions to Jurassic limestones of the next 
thrust unit (TP/2 – Trnovo nappe overthrust block, 
outside Fig. 2).
The Norian-Rhaetian dolomite has a normal po-
sition and practically identical dip and strike in the 
Čekovnik nappe slice as well as in the lower part of the 
Trnovo nappe (TP/1). The strata dip from 10 to 30° 
to the southwest. The dolomite is generally medium 
to thick-bedded (10 to 30 cm), with thinner (10 cm) 
or thicker strata (up to one metre) only as an excep-
tion. The dolomite is light to dark grey, here and there 
nearly white, and most often laminated or stromat-
olitic. In some places, thinly coated f lat pebble con-
glomerate can be observed on the top surface. In the 
Norian-Rhaetian dolomite sequence of the Čekovnik 
nappe slice, interbedded claystone intercalations and 
rare strata with fine oncoids occur in the lower part 
of the sequence in the Belca valley. Thin interbedded 
intercalations of shaly claystone and dolomitic marl-
stone occur only above Carnian clastic rocks in the 
Norian-Rhaetian dolomite in the Idrija area. This in-
dicates that the dolomite of the Čekovnik nappe slice 
is part of the lower Norian-Rhaetian dolomite se-
quence. Within the Trnovo nappe, there are no shaly 
1981). Na Idrijskem je na kamnine Hrušiškega 
pokrova narinjen spodnje in zgornjekredni apne-
nec Koševniške krovne luske (KKL) v normalni 
legi in debelini od 100 do 500 m (sl. 4). Glede 
na geološke razmere v Tektonskem oknu Strug 
in Idrijski Beli gradi Koševniško krovno lusko 
pod Zadloškim poljem predvsem zgornjekredni 
apnenec, v globljih delih pa že lahko zvezno pre-
haja v spodnjekredne apnence z redkimi vložki 
zgodnjediagenetskega dolomita. Ob narivnici so 
mehke f l išne kamnine pogosto izt isnjene tako, 
da na zgornjekrednih apnencih Hrušiškega po-
krova ležijo neposredno spodnje ali zgornje-
kredni apnenci Koševniške krovne luske (sl. 4). 
Koševniško krovno lusko prekriva norijsko-re-
t ijski dolomit Čekovniške krovne luske (ČKL) v 
normalni legi. Morfološko zelo izrazita narivni-
ca med krovnima enotama poteka po severnem 
obrobju Idrijskega Loga (Zagoda, 2004) (sl. 2), 
nato pa poteka čez Predgriško polje vzhodno od 
Črnega Vrha (Mlakar & Čar, 2009). Zgornjetr i-
asni dolomit Čekovniške krovne luske gradi se-
verno obrobje in severni del Zadloškega polja. 
Preostali del Zadloga in njegovo južno in za-
hodno obrobje je iz norijsko-retijskega dolomi-
ta Trnovskega pokrova (TP/1- spodnji narivni 
blok Trnovskega pokrova). Visoko pod severnim 
robom Trnovskega gozda (ni prikazano na karti 
sl. 2) reže norijsko-retijski dolomit Trnovskega 
pokrova še ena narivna ploskev (Čar, 2010). Nad 
njo leži norijsko-retijski dolomit z zveznimi pre-
hodi v jurske apnence naslednje narivne enote 
(TP/2 - zgornji narivni blok Trnovskega pokro-
va, izven okvir ja sl. 2).
Norijsko-retijski dolomit ima v Čekovniški 
krovni luski, kot tudi v spodnjem delu Trnovske-
ga pokrova (TP/1) normalno lego in praktično 
enak vpad. Plasti vpadajo od 10 do 30° proti jugo-
zahodu. Dolomit je v splošnem srednje do debelo 
(od 10 do 30 cm) plastnat, le izjemoma opazujemo 
tanjše plasti (10 cm) ali debele do enega metra. 
Dolomit je svetlo do temno siv, tu in tam skoraj 
bel, največkrat laminiran ali stromatoliten. Po-
nekod opazujemo na zgornji površini plasti tanke 
prevleke nadplimskega konglomerata. V zapored-
ju norijsko-retijskega dolomita Čekovniške krov-
ne luske se v spodnjem delu plasti v dolini Belce 
pojavljajo medplastni vložki glinavca in redke 
plasti z drobnimi onkoidi. Tanki medplastni vlož-
ki skrilavega glinavca in dolomitnega laporovca 
se v norijsko-retijskem dolomitu na Idrijskem 
pojavljajo le nad karnijskimi klastiti. To kaže, 
da je  dolomit Čekovniške krovne luske del spo-
dnjega zaporedja norijsko-retijskega dolomita. V 
okviru Trnovskega pokrova v norijsko-retijskem 
A B
Fig. 3. A – thrust-fault crushed zone in a quarry at Podtisov Vrh on the western perimeter of Zadloško polje. B – A thrust crushed zone in a 
sand quarry at Trebče near Črni Vrh, southeast of Zadloško polje. Photo: Jože Čar.
Sl. 3. A – Narivno-prelomna zdrobljena cona v peskokopu pri Podtisovem Vrhu na zahodnem obodu Zadloškega polja. B – Narivna zdroblje-
na cona v peskokopu v Trebčah pri Črnem vrhu, jugovzhodno od Zadloškega polja. Foto: Jože Čar.
258 Jože ČAR & Ela ŠEGINA
marlstone intercalations in the Norian-Rhaetian do-
lomite. The same dip of strata and strong lithologi-
cal similarity between the dolomites of both thrust 
units were an important reason why the thrust line 
between the Čekovnik nappe slice and the Trnovo 
nappe was previously delineated along the southern 
edges of Zadloško polje (Mlakar & Čar, 2009).
The thrust–shear deformations in the dolomites 
of both thrust units can be directly observed along 
the forest road Ipavšk–Podtisov Vrh on the slope 
of the Belca valley. The intensity and extent of the 
thrust–shear crushed zone varies, it is at least 10 to 
15 m thick and gradually transitions to a several me-
tres thick zone of less tectonically deformed dolomite. 
Within the crushed zone, the main thrust plane with 
a dip of 40 to 20° runs southwards. At Podtisov vrh 
(724 m), the thrust line veers to the western edges of 
Zadloško polje. An approximately 200 m wide zone 
of completely crushed dolomite has formed here as 
a result of a strong thrust–shear crushed zone inter-
secting the Podtis fault zone (Fig. 3A). A thrust-fault 
crushed zone with a tectonic (cataclastic) structure 
of ‘meal, grit and detritus’ is exposed in the larger 
sand quarry, where an intricate interplay of thrust 
and fault zones can be observed. Due to fault-in-
duced deformations, sections of the thrust plane 
dip 60° to the southwest (230/60°). The thrust zone 
continues beneath the anthropogenically levelled 
and ameliorated bedrock of Zadloško polje and can-
not be observed directly. Indirectly, the thrust line 
can be traced based on a distinctively levelled sur-
face with no bedrock outcrops. Thrust line crosses 
the complex zone of the Zadlog fault, intersects the 
less disturbed part of the polje between the Zadlog 
and the Plestenice fault, and continues to the Črni 
Vrh fault on the western edge of Zadlog. Its course 
dolomitu skrilavih laporastih vložkov ni. Prav 
enak vpad plasti in velika litološka podobnost med 
dolomitoma obeh narivnih enot je bil pomemben 
razlog, da je bila narivnica med Čekovniško krov-
no lusko in Trnovskim pokrovom doslej izrisana 
po južnem obrobju Zadloškega polja (Mlakar & 
Čar, 2009).
Obnarivne deformacije v dolomitih obeh na-
rivnih enot lahko neposredno opazujemo ob goz-
dni cesti Ipavšk – Podtisov Vrh na pobočju doline 
Belce. Intenzivnost in obseg obnarivne zdroblje-
ne cone se spreminja; debela je vsaj 10 do 15 m in 
postopno prehaja v več metrov debelo cono manj 
pretrtega dolomita. Znotraj zdrobljene cone po-
teka glavna narivna ploskev z vpadom 40 do 20° 
proti jugu. Pri Podtisovem Vrhu (724 m) se nariv-
nica previje na zahodno obrobje Zadloškega polja. 
Tu je nastalo okrog 200 m široko območje pov-
sem zdrobljenega dolomita, ki je rezultat močne 
obnarivne zdrobljene cone, ki jo seka cona Podti-
sovega preloma (sl. 3A). Narivno-prelomna zdro-
bljena cona s tektonsko (kataklastično) strukturo 
’moka, zdrob in drobir’ je odprta v večjem pesko-
kopu, kjer lahko opazujemo zapleteno prepletanje 
narivnih in prelomnih con. Zaradi obprelomnih 
deformacij vpadajo odseki narivne ploskve za 60° 
proti jugozahodu (230/60°). Narivna cona se na-
daljuje pod antropogeno izravnanim in meliori-
ranim dnom Zadloškega polja in jo neposredno 
ne moremo opazovati. Posredno lahko narivnici 
sledimo na podlagi izrazito uravnanega terena 
brez izdankov matične kamnine. Narivnica preč-
ka zapleteno cono Zadloškega preloma, seka manj 
pretrti del polja med Zadloškim in Plesteniškim 
prelomom in se nadaljuje do Črnovrškega pre-
loma na zahodnem obrobju Zadloga. Njen potek 
259Geologic structure and origin of the Zadlog karst polje
is also confirmed by the finding of pieces of cata-
clastic rocks in the field west of the Črni Vrh fault. 
The thrust line reappears about a kilometre further 
south in the sand quarry near the hamlet of Trebče 
at Črni Vrh, on the western side of the Črni Vrh fault, 
i.e. in the same structural block as in Zadloško pol-
je. Further towards Črni Vrh, the thrust zone runs 
parallel to the fault zone of the Črni Vrh fault. In the 
Trebče sand quarry, the thrust line dips 20° to the 
southwest (Fig. 3B) and has the same dip all the way 
to Črni Vrh (Fig. 2).
Structural and hydrological conditions 
The structural conditions and associated hydro-
logical features of Zadloško polje are evident from 
the attached cross-section (Fig. 4). In addition to 
the geological data directly from the line of the 
cross-section, the geological structure of the wider 
area of the Črni Vrh plateau has also been taken 
into account. The profile is a geologically typical 
cross-section of the Idrija overthrust structure.
The cross-section starts at the Strug tectonic win-
dow in the Idrijca valley, where the Idrijca riverbed 
already cuts into Upper Cretaceous limestone and 
the overlying Palaeocene-Eocene f lysch rocks of the 
Hrušica nappe. The cross-section then crosses the 
thrust contact between f lysch rocks and Cretaceous 
limestones of the Koševnik nappe slice. The thrust 
contact dips approx. 25° to the south and southwest. 
The Cretaceous limestone underneath Zadloško 
polje is, based on geological mapping at the Strug 
tectonic window in Idrijski Log and Predgriže, pre-
sumed to be slightly folded into synclinals and an-
ticlinals (Fig. 4). It is overthrust by Norian-Rhae-
tian dolomite of the Čekovnik nappe slice (Mlakar, 
1969; Zagoda, 2004; Mlakar & Čar, 2009; Čar, 2010) 
(Figs. 1 and 4) with the thrust plane dipping 10 to 
15° to the southwest or south. The dolomite con-
stitutes the higher northern edge of Zadlog and the 
northern part of the Zadloško polje plain, and then 
the section intersects the thrust line between the 
Čekovnik nappe slice and the Norian-Rhaetian do-
lomite of the Trnovo nappe underthrust block. The 
thrust contact between the two dolomites dips ap-
prox. 7° to 10° in general southwards. Southward of 
here, the geological cross-section continues in the 
slope of Špičasti vrh (1127 m) (Fig. 2). 
The cross-section shows that three strong hydro-
logical retention-def lection structures follow each 
other vertically below Zadloško polje (Čar, 2018), i.e. 
f lysch rocks, a lithological hydrological retention-de-
f lection zone (marked a in the profile), and two 
thrust–shear hydrological retention-def lection zones 
with several-metre-thick impermeable cataclastic 
dolomite rocks (marked b & c in the profile) (Fig. 4). 
potrjuje tudi najdba kosov kataklastičnih kamnin 
na njivi zahodno od Črnovrškega preloma. Nariv-
nica se ponovno pokaže kak kilometer južneje v 
peskokopu pri zaselku Trebče pri Črnem Vrhu, na 
zahodni strani Črnovrškega preloma, torej v is-
tem strukturnem bloku kot na Zadloškem polju. 
V nadaljevanju proti Črnemu Vrhu poteka nariv-
na cona vzporedno s prelomno cono Črnovrškega 
preloma. V peskokopu v Trebčah vpada narivnica 
za 20° proti jugozahodu (sl. 3B) in ima enak vpad 
vse do Črnega Vrha (sl. 2).
Strukturno-hidrološke razmere 
Strukturne razmere in nanje vezane hidrolo-
ške značilnosti Zadloškega polja so vidne iz pri-
loženega prereza (sl. 4). Poleg geoloških podatkov 
neposredno v liniji prereza je pri izrisu upošte-
vana tudi geološka zgradba širšega območja Čr-
novrške planote. Profil je v geološkem pogledu 
značilen presek idrijske narivne zgradbe.
Presek poteka iz Tektonskega okna Strug v do-
lini Idrijce, kjer je korito reke Idrijce že vrezano v 
zgornjekrednem apnencu in na njem ležečih pale-
ocensko-eocenskih f lišnih kamninah Hrušiškega 
pokrova. Prerez nato prečka narivni kontakt med 
f lišnimi kamninami in krednimi apnenci Košev-
niške krovne luske. Narivni stik vpada za okrog 
25° proti jugu in jugozahodu. Iz razmer, s kar-
tiranjem ugotovljenih v Tektonskem oknu Strug 
v Idrijskem Logu in Predgrižah sklepamo, da so 
kredni apnenci pod Zadloškim poljem rahlo sink-
linalno in nato antiklinalno upognjeni (sl. 4). Nanj 
je narinjen norijsko-retijski dolomit Čekovniške 
krovne luske (Mlakar, 1969; Zagoda, 2004; Mla-
kar & Čar, 2009; Čar, 2010) (sl. 1 in 4) z vpadom 
narivne ploskve od 10 do 15° proti jugozahodu ali 
jugu. Dolomit gradi višje severno obrobje Zadlo-
ga in severni del izravnave Zadloškega polja. V 
nadaljevanju prerez seka narivnico med Čekovni-
ško krovno lusko in norijsko-retijskim dolomitom 
spodnjega narivnega bloka Trnovskega pokrova. 
Narivni kontakt med dolomitoma vpada okrog 7 
do 10° v splošnem proti jugu. Južno od tod se ge-
ološki prerez nadaljuje v pobočju Špičastega vrha 
(1127 m) (sl. 2). 
Iz preseka v idimo, da si pod Zadloškim po-
ljem v vertikali sledijo tr i močne hidrološke za-
drževalno-zaporne strukture (Čar, 2018) in sicer 
f l išne kamnine kot l itološka hidrološka zadrže-
valno-zaporna cona (na prof i lu oznaka a) ter dve 
obnarivno hidrološki zadrževalno-zaporni coni 
z več-metrskimi neprepustnimi kataklastičnimi 
dolomitnimi kamninami (na prof i lu oznaki b  in 
c) (sl. 4). Flišne kamnine so ob narivnem stiku 
večkrat izt isnjene tako, da sta na več območjih 
260 Jože ČAR & Ela ŠEGINA
Several f lysch rocks are pushed out along the 
thrust contact in such a way that Upper Creta-
ceous limestone of the Hrušica nappe and Creta-
ceous limestone of the Koševnik nappe slice are in 
direct contact with each other. In such cases, wa-
ter f lows almost unimpeded from one thrust unit 
to the other. Such conditions can be observed in 
several places in the Strug tectonic window and 
are most likely also present beneath the Črni Vrh 
plateau. A smoothed out thrust plane in the lime-
stone in several places and an up to 20 m thick 
thrust–shear zone of completely crushed dolomite 
can be observed at the thrust contact between the 
limestone of the Koševnik nappe slice and the No-
rian-Rhaetian dolomite of the Čekovnik nappe slice 
in Strug and Bevk tectonic windows (Fig. 4, mark 
b, Fig. 3B). The thrust–shear cataclastic rocks at 
the thrust contact of the two dolomites between 
the Čekovnik nappe slice and Trnovo nappe (Fig. 
4, mark c) are from some metres up to 15 m thick, 
in some areas even thicker. Thrust–shear crushed 
zones may vary in thickness, but do not pinch out 
in the lateral direction. 
There is no direct data available on how deep 
underneath Zadloško polje the thrust contacts be-
tween f lysch and limestone, as well as between the 
dolomite of the Čekovnik nappe slice and the low-
er thrust block of Trnovo nappe, are located. The 
dip of the thrust plane between f lysch and Upper 
Cretaceous limestone of Čekovnik nappe slice, and 
its location underneath Zadloško polje may be in-
ferred from the conditions observed in the Strug 
tectonic window and from the findings of mapped 
f lysch outcrops in Dolenje Lome east of Črni Vrh 
(Mlakar & Čar, 2009; Čar, 2010). In the tectonic 
window, the thrust plane dips 15 to 25° roughly to 
the south, and then the contact gradually rises and 
surfaces in expansive outcrops in Dolenje Lome. 
The course and nature of the thrust line between 
Cretaceous limestones of the Koševnik nappe slice 
and Norian-Rhaetian dolomite of the Čekovnik 
nappe slice were observed on the plain of Idrijski 
Log and 1.5 to 2 km east of Zadlog between Idrijski 
Log and Predgriže (Zagoda, 2004; Čar & Zagoda, 
2005) (Fig. 2). The thrust line runs NW–SE and 
only drops by about 20 m over a distance of 3.5 km. 
The structural conditions beneath Zadloško polje 
are presumed to be similar. Taking into account the 
structural-geological data from the wider surround-
ings, the thrust contact between limestone and do-
lomite is only about 100–150 m below the surface 
of the polje. Based on the conditions in the vicinity 
of Črni Vrh and Predgriže, the thrust line gently de-
scends towards the Na Sredi site (sinking zones A, 
B & C) (Fig. 2), and lifts up at reverse faults. 
neposredno v st iku zgornjekredni apnenec Hru-
šiškega pokrova in kredni apnenec Koševniške 
krovne luske. Voda se v takih primerih skoraj 
nemoteno pretaka iz ene narivne enote v dru-
go. Take razmere lahko opazujemo na več mes-
t ih v Tektonskem oknu Strug in jih najver jetneje 
imamo tudi pod Črnovrško planoto. Na nariv-
nem stiku med apnencem Koševniške krovne 
luske in norijsko-retijskim dolomitom Čekov-
niške krovne luske (sl. 4,  oznaka b) opazujemo v 
tektonskih oknih Strug in Bevk zglajeno narivno 
ploskev v apnencu in do 20 m debelo obnarivno 
cono povsem zdrobljenega dolomita. Obnarivne 
kataklastične kamnine na narivnem stiku dveh 
dolomitov med Čekovniško krovno lusko in 
Trnovskim pokrovom (sl. 4,  oznaka c ,  sl. 3B) so 
debele od nekaj metrov do 15 m, ponekod lah-
ko tudi več. Po debelini se obnarivno zdrobljene 
cone lahko spreminjajo, v horizontalni smeri pa 
se ne izklinjajo. 
Neposrednih podatkov, kako globoko pod 
Zadloškim poljem se nahajajo nar ivni st ik i med 
f l išem in apnencem, dolomitom Čekovniške 
krovne luske in spodnjega nar ivnega bloka Tr-
novskega pokrova ter apnencem Koševniške in 
dolomitom Čekovniške  krovne luske, nimamo. 
Na vpad nar ivne ploskve med f l išem in zgor-
njekrednim apnencem Koševniške krovne lus-
ke in njeno lego pod Zadloškim poljem lahko 
sk lepamo na podlagi opazovanih razmer v Tek-
tonskem oknu Strug in ugotov itvah kart iranih 
izdankov f l iša v Dolenjih Lomeh vzhodno od 
Črnega Vrha (Mlakar & Čar, 2009; Čar, 2010). 
V tektonskem oknu vpada nar ivna ploskev od 
15 do 25° pr ibližno proti jugu, nato se st ik pos-
topno dviga in izdanja v obsežnih golicah v Do-
lenjih Lomeh. 
Potek in značaj nar ivnice med krednimi ap-
nenci Koševniške krovne luske in norijsko-re-
t ijskim dolomitom Čekovniške  krovne luske 
opazujemo na izravnavi Idr ijskega Loga ter od 
1,5 do 2  km vzhodno od Zadloga med Idr ijskim 
Logom in Predgrižami (Zagoda, 2004; Čar & 
Zagoda, 2005) (sl.  2). Narivnica poteka v smeri 
SZ-J V in se na dolžini 3,5  km spusti le za okrog 
20  m. Predpostavljamo, da imamo podobne 
strukturne razmere tudi pod Zadloškim poljem. 
Ob upoštevanju geološko-strukturnih podatkov 
iz širše okolice se nahaja nar ivni st ik med ap-
nenci in dolomitom le kakih 100 do 150  m pod 
površjem polja. Sodeč po razmerah v okolici Čr-
nega Vrha in Predgriž se nar ivnica proti lokaciji 
Na Sredi rahlo spušča (ponikalna območja A, B, 
in C) (sl.  2), ob reverznih prelomih pa je dv ig-
njena. 
261Geologic structure and origin of the Zadlog karst polje
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262 Jože ČAR & Ela ŠEGINA
More information is available on the thrust 
contact between the Norian-Rhaetian dolomites of 
the Čekovnik nappe slice and the lower part of the 
Trnovo nappe (TP/1). The thrust zone is visible in 
the slope above the Belca valley, in the sand quar-
ry at Podtisov vrh and in the Trebče sand quar-
ry (Fig. 3 B), and further towards Črni Vrh. From 
north to south the thrust line descends at a slight 
angle of 5 to 7° southward, then almost levels off 
or even rises slightly. The Norian-Rhaetian dolo-
mite of the Trnovo nappe north of Štef kova rupa 
is estimated to be only 20 to 30 m thick, depend-
ing on the dip of the thrust plane. Its thickness 
increases on the southwest side of the Zadlog fault.
Hydrological and geomorphological conditions 
 Weak and temporary springs with a small 
hydrological catchment area can be found on the 
southern slopes of Idrijski Log (Fig. 2) while Zad-
loško polje has no permanent running wa ter.
Morphological analysis of the surface of Zad-
loško polje showed that its bottom is relatively well 
levelled out, and lies between 714 and 716 m above 
sea level. The entire bottom is covered by dolomite 
eluvium. The perimeter of the basin is covered by 
colluvium, indicating that the recent maximal f lood 
range is smaller than in the past. The inf luence of 
sediment transport from the dolomitic catchment 
area is most clearly visible in the form of the collu-
vial fan at Plestenice on the southeastern edge of the 
basin (Fig. 8). A network of wide and shallow chan-
nels formed in the otherwise f lat bottom of Zadloško 
polje. Up to several metres deep erosion ditches 
formed in fractured zones along the faults (Zadlog, 
Kot, Plestenice, Klančar faults), while more shallow 
ones evenly drain the relatively f lat bottom. The 
whole western part that formed in the wider Zadlog 
fault zone from Podtisov Vrh to the southern edge of 
the polje, the entire western part (to Plestenice fault 
towards the east) and the southern and southeast-
ern part of the polje drain towards the ponor zones 
on the location Na Sredi, which confirms the ab-
sence of similar drainage structures in the western 
and eastern parts of the polje. The NW–SE oriented 
strike-slip faults and the N–S oriented reverse faults 
in the central part of the polje that cross the out-
er fault (crushed and fractured) zone of the Zadlog 
fault appear to be the key structures allowing water 
to drain from the major part of the polje to the un-
derground.
During heavy rainfall, the lower parts of the 
northern structural block of Zadlog quickly be-
come partially f looded from the northern edge of 
the polje to the thrust line between the Čekovnik 
nappe slice and the lower thrust block of Trnovsko 
O narivnem stiku med norijsko-retijskima do-
lomitoma Čekovniške krovne luske in spodnjim 
delom Trnovskega pokrova (TP/1) imamo več 
podatkov. Narivna cona je vidna v pobočju nad 
dolino Belce, peskokopu v Podtisovem Vrhu in 
peskokopu Trebče (sl. 3B) ter dalje proti Črnemu 
Vrhu. Od severa proti jugu se narivnica spušča 
pod blagim kotom od 5 do 7° proti jugu, nato 
skoraj izravna ali celo rahlo dviga. Debelina no-
rijsko-retijskega dolomita Trnovskega pokrova je 
severno od Štef kove rupe, glede na vpad narivne 
ploskve, po oceni le 20 do 30 m. Na jugozahodni 
strani Zadloškega preloma se poveča.
Hidrološke in geomorfološke razmere
Na južnih pobočjih Idrijskega Loga se ob pre-
lomnih conah pojavljajo večinoma občasni in šib-
ki izviri z majhnim hidrološkim zaledjem (sl. 2). 
Zadloško polje pa nima stalne tekoče vode. 
Morfološka analiza površja Zadloškega polja 
pokaže, da je njegovo dno relativno dobro urav-
nano, in sicer na v išini med 714 in 716  m nad 
morjem. Dno je med številnimi izdanki dolomita 
prekrito z dolomitno preperino, ki je nastajala v 
času ojezeritve. Obod kotline je prekrit s koluvi-
jem, kar kaže na recentno manjši obseg poplav 
kot v preteklosti. Najbolj jasno se vpliv premeš-
čanja sedimentov z dolomitnih pobočij kaže v ob-
liki vršaja v Plestenicah na jugovzhodnem robu 
kotline (sl. 8). V sicer ravnem dnu Zadloškega 
polja se je oblikovala mreža širokih in plitv ih 
kanalov. Do nekaj metrov globoki jarki so na-
stali v pretr t ih conah vzdolž prelomov (Zadlo-
ški, Kotenjski, Plesteniški, K lančarjev prelom), 
plitvejši enakomerno drenirajo relativno ravno 
površino dna. Zahodni del polja, ki je oblikovan 
v širši coni Zadloškega preloma od Podtisovega 
Vrha do južnega obrobja polja, ves osrednji del 
polja (do Plesteniškega preloma proti vzhodu) 
ter južni in jugovzhodni del polja drenirajo pro-
t i ponikvam na lokaciji Na Sredi, kar potr juje 
odsotnost podobnih odvodnih struktur v zahod-
nem in vzhodnem delu polja. Kaže, da so zmični 
prelomi z or ientacijo SZ-JV in reverzni prelo-
mi v smeri S-J osrednjega dela polja, ki sekajo 
zunanjo prelomno cono (porušena in razpoklin-
ska cona) Zadloškega preloma ključne struktu-
re, ki omogočajo podzemno odtekanje vode z ve-
likega dela polja.
Ob večjem deževju so nižji deli od severnega 
roba polja do narivnice med Čekovniško  krovno 
lusko in spodnjim narivnim blokom Trnovskega 
pokrova razmeroma hitro delno poplavljeni. Gle-
de na geološke podatke (sl. 2 in 4) imamo v tem 
delu Zadloškega polja nad hidrološko pregrado 
263Geologic structure and origin of the Zadlog karst polje
nappe. According to the geological data (Figs. 2 
and 4), there is permanently hanging aquifer in 
this part of Zadloško polje above the hydrological 
barrier b. Based on the observations, its level rap-
idly rises to the surface of the polje and f loods the 
lower parts and hollows on the polje (Fig. 1B). The 
conditions described also show that the dolomite 
of the Čekovnik nappe slice over the limestone of 
the Koševnik nappe slice is relatively thin, while 
the thrust–shear hydrological barrier b is largely 
impermeable and leaks only at the faults intersect-
ing it.
The hydrological conditions south of the thrust 
zone between the Čekovnik nappe slice and the 
Trnovo nappe (TP/1), are similar to the conditions 
to the north of it. We presume that the ground-
water here also needs to stay quite high above the 
hydrological retention-def lection thrust zone c 
at all times, as it starts to relatively rapidly over-
f low to the surface when it rains. Large amounts 
of groundwater f low onto Zadloško polje from the 
south during heavy rainfall (mostly along the lay-
ers) due to the extensive and rugged catchment 
area of Mrzli log with its highest peak Špičasti vrh 
(1127 m). 
Several morphologically distinct, intermittent 
sinking zones are observed in Zadlog, which are 
shown in capital letters A to F on the Fig. 2. The 
largest one – Štefkova rupa (mark A, Fig. 6A, B) 
– is up to 13 m deep, at the Na Sredi site in the 
central part of Zadlog. From the large sinkhole Šte-
f kova rupa (mark A), a narrow, some 200 m long 
valley or rather an erosion ditch in the fault zone 
runs southsoutheastward along the strike-slip 
fault. A relatively strong temporary spring f lows to 
the surface at its southern part. The water f lows 
northnortheastward down the erosion ditch to the 
central sinking area Štef kova rupa. At low inf lows, 
the water gradually sinks already in the strike-slip 
fault zone and does not f low to the central large 
sinkhole. An extensive larger sinkhole formed at 
the junction of one of the reverse faults of Kot with 
the connecting strike-slip fault, which intersect 
the area between the Zadlog and Plestenice faults. 
Štef kova rupa does not have an open swallow hole 
(Fig. 6A, B), but has slightly deepened, bare sur-
face in its NE part where substantial volumes of 
water sink through. The geological conditions sug-
gest that, due to the uplift along the reverse fault, 
there are karstified and therefore highly permea-
ble Upper Cretaceous limestones of the Koševnik 
nappe slice close to the surface. At high groundwa-
ter level, the water outf lows even sideway from the 
sinkhole in the crushed zone of Zadlog fault and 
Kot set of faults.
b  stalno ujeto ali v isečo podtalnico. Na podla-
gi opazovanj se njen nivo hitro dvigne in zalije 
nižje dele in kotanje na polju (sl. 1 B). Opisane 
razmere tudi kažejo, da je dolomit Čekovniške 
krovne luske nad apnencem Koševniške  krovne 
luske sorazmerno tanek, obnarivna hidrološka 
pregrada b  pa je v večini neprepustna in pušča 
le ob prelomih, ki jo sekajo.
Južno od poteka narivne cone med Čekov-
niško krovno lusko in Trnovskim pokrovom 
(TP/1) imamo podobne hidrogeološke razmere 
kot severno od nje. Domnevamo, da je podtal-
nica nad hidrološko zadrževalno zaporno nariv-
no cono c  stalno dokaj v isoko, saj ob deževju 
začne razmeroma hitro iztekati na površje. Za-
radi obsežnega in razgibanega zaledja Mrzlega 
loga z najv išjim Špičastim vrhom (1127  m) se 
ob izdatnejšem deževju z južne strani v glavnem 
medplastno stekajo na Zadloško polje velike ko-
l ičine podtalnice. 
V Zadlogu opazujemo več morfološko izsto-
pajočih, občasnih ponikalnih območij, k i so 
na sliki 2 označeni z velikimi črkami od A do 
F. Največje je do 13 m globoka Štef kova rupa 
(oznaka A, sl. 6A in B) na lokaciji Na Sredi v 
osrednjem delu Zadloškega polja. Iz ponikal-
ne globeli Štef kove rupa (oznaka A) poteka ob 
zmičnem prelomu proti JJV okrog 200 m dolga 
ozka dolina, ali bolje, razšir jen erozijski žleb v 
prelomni coni. Na njegovem južnem delu je rela-
t ivno močan občasni izv ir. Voda odteka po jarku 
proti SSZ k osrednjemu ponikalnemu območju 
Štef kove rupe. Ob nizkih pretokih voda posto-
pno ponikne že v coni zmičnega preloma in ne 
priteče do osrednje ponikalne globeli. Obsežna 
ponikalna globel je nastala na stičišču enega 
izmed Kotenjskih reverznih prelomov z veznim 
zmičnim prelomom, ki seka območje med Zadlo-
škim in Plesteniškim prelomom. V Štef kovi rupi 
ni odprtega požiralnika (sl. 6A in B), vendar je 
v njenem SV delu nekoliko poglobljeno golo ob-
močje, skozi katerega poniknejo izredno velike 
količine vode. Glede na geološke razmere skle-
pamo, da se zaradi dviga ob reverznem prelomu 
zakraseli in zato dobro prepustni zgornjekredni 
apnenci Koševniške krovne luske nahajajo blizu 
površja. Ob v išjih vodah se voda izteka iz globe-
l i  tudi bočno v pretr t i coni Zadloškega preloma 
in Kotovega prelomnega snopa.
V podobnih geoloških razmerah sta nasta-
l i  tudi ponikalni območji Ponikva  (oznaka B in 
sl. 5B)  in ponikalno območje pri kmet iji Cigale 
(oznaka C) severozahodno od Štef kove rupe v 
osrednjem delu polja. Ponikalno območje Po-
nikva je proti vzhodu povezano z erozijskim 
264 Jože ČAR & Ela ŠEGINA
The Ponikva sinking area (mark B and Fig. 5B) 
and the sinking area at the Cigale farm (mark C) 
northwest of Štefkova rupa in the central part of 
the polje formed under similar geological condi-
tions. The Ponikva sinking area is connected to the 
erosion ditch of Štefkova rupa to the east and on the 
other side to the inf low area below Tomažon (Fig. 
5B), and at high waters it connects to the springing/
sinking puddle Gregorcova lokev. This is an approx. 
400 m long water channel which runs in the NW–
SE direction and formed in the Zadlog fault zone. 
It ends in a large sinkhole where water also f lows 
into from the southeast from the Podgora farm. 
The extensive sinkhole (mark C) below the Cigale 
farm extends northward along the reverse fault and 
drains waters from the wide area under Podtisov 
Vrh north from the road Na Sredi – Figar and from 
the northern portion of the central part of the polje. 
Next is an approx. 15 m deep intermittent swallow 
hole (mark D) called Štirnska rupa. It lies between 
the two roads leading from the central part of Zad-
log towards Šoštar at the crossing towards Črni Vrh 
(Fig. 2). It formed in the Plestenice fault zone and 
extends along the Plestenice fault in the NW–SE 
direction of the fault. Štirnska rupa is approximate-
ly 200 m long and has a morphologically distinct 
swallow hole in its central part. Eastward lies an 
up to 6 m deep less pronounced sinking zone in the 
Klančar fault zone (mark E) with numerous sink-
holes that are interconnected with shallow lowered 
passes. The extensive and morphologically less vis-
ibly lowered sinking area in the wide broken zone of 
the Figar fault on the far western edge of Zadloško 
polje is also worth mentioning (mark F).
During heavy rainfall or rise of the groundwa-
ter level, Štefkova rupa fills up and water spills out 
into its wider surroundings. Gregorcova lokev fills 
up and water starts to f low along the distinctive 
and wide erosion ditch towards Ponikva, marked B. 
Strong temporary springs and water from several 
scattered interbedded inf lows from the wider area 
below Tomažon join together before the sinking area. 
Water f lows from the northwestern part of Zadloško 
polje into the wider fault zone of Zadlog and drains 
at Rovtar into the extensive sinkhole below Cigale. 
Excess water f lows on the southern side of the sink-
hole further towards Štefkova rupa. The sinking 
areas D and E also fill up (Fig. 2). As the ground-
water rises in the central and southern parts of the 
Zadloško polje, even weaker inf lows spring up along 
the permeable fault zones and along the stratifica-
tion. In the poorly permeable lower parts of dolomite 
in the Čekovnik nappe slice and the Trnovo nappe 
water starts to stagnate and the impoundments on 
Zadloško polje grow and merge. The entire Zadloško 
jarkom Štef kovih rup, na drugi strani pa z do-
točnim območjem pod Tomažonom (sl. 5B) in 
ob v išjih vodah z izv irno-ponikalno Gregorcovo 
lokvijo. To je okrog 400 m dolg jarek, ki pote-
ka v smeri SZ-JV in je nastal v coni Zadloškega 
preloma. Zaključuje se z večjo globeljo, v kate-
ro priteka voda tudi od jugovzhoda od kmetije 
Podgora. V obsežno ponikalno globel pod kme-
t ijo pri Cigaletu (oznaka C), ki je razpotegnjena 
proti severu ob reverznem prelomu, se stekajo 
vode z obsežnega območja izpod Podtisove-
ga Vrha severno od ceste Na Sredi – Figar in 
s severa osrednjega dela polja. Naslednji je ok-
rog 15 m globok občasni požiralnik imenovan 
Št irnska rupa (oznaka D).  Leži med obema ce-
stama, ki vodita iz osrednjega dela Zadloga proti 
Šoštar ju na prehodu proti Črnemu vrhu (sl. 2). 
Nastal je v prelomni coni Plesteniškega preloma 
in je ob njem podaljšan v prelomni smeri SZ-JV. 
Štirnska rupa je dolga okrog 200 m z morfolo-
ško izrazit im požiralnikom v osrednjem delu. 
Vzhodno od tod leži v prelomni coni K lančar-
jevega preloma manj izrazito, do 6 m globoko 
ponikalno območje (oznaka E) s štev ilnimi glo-
belmi, ki so povezane s plitv imi znižanimi pre-
hodi. Omenimo še obsežno in morfološko manj 
izrazito znižano ponikalno območje v široki po-
rušeni coni Figarjevega preloma na skrajnem 
zahodnem obrobju Zadloga (oznaka F).
Ob močnejših naliv ih in dv igu podtalnice se 
Štef kova rupa napolni in voda se razlije v šir-
šo okolico. Napolni se Gregorcova lokev in voda 
začne po izrazitem in širokem jarku odteka-
t i proti Ponikv i z oznako B. Pred ponikalnim 
območjem se iz širšega območja pod Tomažo-
nom prik ljučijo močnejši občasni izv ir i in voda 
iz štev i lnih razpršenih medplastnih dotokov. 
Iz severozahodnega dela Zadloškega polja se 
voda pretaka po širši coni Zadloškega prelo-
ma in se pr i Rov tar ju izteka v ponikalno glo-
bel pod Cigaletom. Višek vode odteka na južni 
strani ponikalne globeli naprej proti Štef kovi 
rupi. Napolnita se tudi ponikalni območji D in 
E (sl.  2). Z dv iganjem podtalnice se v osrednjem 
in južnem delu Zadloškega polja aktiv irajo še 
šibkejši dotoki ob prepustnih prelomnih conah 
in tudi vzdolž plastnatost i.  V slabo prepustnih 
znižanjih na dolomitu Čekovniške krovne luske 
in Trnovskega pokrova začne voda zastajat i,  za-
jezitve na Zadloškem polju se večajo in združu-
jejo. Postopno lahko poplav i celotno Zadloško 
polje tako, da nastane začasna ojezer itev (sl. 
5A) ali ,  kot prav ijo domačini, nastane ’zadloško 
morje’ (Bajec, 2007). Ob iz jemnih hidroloških 
razmerah začne voda odtekati čez nizek prehod 
265Geologic structure and origin of the Zadlog karst polje
polje can gradually become f looded, forming a tem-
porary impoundment (Fig. 5A) or the ‘sea of Zadlog’, 
as the locals call it (Bajec, 2007). Under exceptional 
hydrologic conditions, the water starts to f low over 
a low pass at Šoštar in the eastern part of Zadlog in 
the Črni Vrh fault zone towards Trebče at Črni Vrh. A 
particularly high lake impoundment formed in 1923, 
when the water f lowed for three hours over the pass 
at Šoštar towards Trebče (Bajec, 2007).
All sinking areas are formed in the dolomite of 
the Trnovo nappe, where the impermeable thrust–
shear def lector zone (thrust–shear and hydrolog-
ical collector & def lecting structure c) between 
the Čekovnik nappe slice and the Trnovo nappe 
is intersected by faults. The favourable conditions 
are apparently the result of relatively weak reverse 
faults pulling fractured and highly soluble Lower 
Cretaceous limestones of the Koševnik nappe slice 
closer to the surface. These are the positions of the 
sinking zones A, B & C. The prerequisite for the 
formation of swallets at the Plestenice and Klančar 
faults are wide fault zones with sufficiently exten-
sive broken and fissure zones.
Water f lows from Zadloško polje underground to-
wards the Divje jezero lake and Podroteja in the Id-
rijca valley through Cretaceous limestones in which 
extensive cave systems have already formed, as con-
firmed by cave diving surveys (Vrhovec, 1997).
The permanent groundwater level below Za-
dloško polje is now 336 m (Habe et al., 1955; 
Vrhovec, 1997), which is only 3 m above the stand-
ing water level at Divje jezero. In f lood conditions, 
the groundwater level in the catchment area of Div-
je jezero rises by 80 m, which was proven by the 
traces of stagnating water at the mentioned level in 
pr i Šoštar ju na vzhodnem delu Zadloškega polja 
v coni Črnovrškega preloma proti Trebčam pri 
Črnem Vrhu. Posebno v isoka ojezer itev je bi la 
leta 1923, ko je voda kar tr i ure tek la čez prelaz 
pr i Šoštar ju proti Trebčam (Bajec, 2007). 
Vsa ponikalna območja so oblikovana v do-
lomitu Trnovskega pokrova in sicer na mestih, 
kjer neprepustno obnarivno zaporno cono (ob-
narivno-hidrološka zadrževalno-zaporna struk-
tura c) med Čekovniško krovno lusko in Trnov-
skim pokrovom sekajo prelomi. Očitno so ugodni 
pogoji nastali ob sicer sorazmerno šibkih reverz-
nih prelomih, ki so potegnili pretrte in dobro top-
ne spodnje kredne apnence Koševniške krovne 
luske bliže površini. Tako lego imajo ponikalna 
območja A, B, in C. Pogoj za nastanek ponikev ob 
Plesteniškem in Klančarjevem prelomu sta široki 
prelomni coni z dovolj obsežnima porušenima in 
razpoklinskima conama.
Iz Zadloškega polja voda odteka podzemno 
proti Divjemu jezeru in Podroteji v dolini Idrijce 
po krednih apnencih, v katerih so že oblikovani 
obsežni jamski rovi, kar so potrdile potapljaške 
raziskave (Vrhovec, 1997).
Stalna gladina podzemne vode pod Zadlo-
škim poljem se danes nahaja na koti 336 m 
(Habe et a l.,  1955; Vrhovec, 1997), kar je le 
3 m nad nivojem stoječe vode v Div jem jezeru. 
V poplavnih razmerah se podtalnica v zaledju 
Divjega jezera dv igne za 80 m, kar je bi lo doka-
zano z znaki stagnacije vode na omenjeni v išini 
A B
Fig. 5. A – Zadloško polje during temporary lake-formation (‚Zadlog sea‘), view to the west (Figar). Photo: Francka Zagoda B – Inflow into 
the sinking zone B (Fig. 2). Photo: Jože Čar.
Sl. 5. A – Zadloško polje v času začasne ojezeritve (‚zadloško morje‘), pogled proti zahodu (Figar). Foto: Francka Zagoda B – Dotok v poni-
kalno območje B (sl. 2). Foto: Jože Čar.
266 Jože ČAR & Ela ŠEGINA
the Habečkovo brezno shaft (personal communica-
tion). Nowadays, the hanging groundwater in ČKL 
occasionally f loods Zadloško polje to the north of 
the thrust line while the groundwater within the 
Trnovo nappe (TP/1) f loods the polje to the south 
of the thrust line only during heavy rainfall. Nu-
merous dolomite outcrops that emerge from the 
sediment-covered bedrock have an average dip of 
230/20–30°, which is consistent with the stratifi-
cation of the underlying dolomites in the wider sur-
rounding. The equilibration of slopes at the thrust 
front and the emergence of parent rock outcrops in 
the sinking areas are indicative of the recent de-
creased capability of hydrologic retention of karst 
polje and intensive washing out of eluvium. The 
present hydrological conditions are therefore large-
ly the result of leaching fault zones and clayey eluvi-
um from the polje f loor, and the resulting increased 
drainage capacities. Instead of the accumulation 
and displacement of material, which took place dur-
ing the formation of Zadloško polje sediment plain, 
we now observe a gradual leaching into the subsur-
face as a result of the new hydrogeological condi-
tions, as well as of the increased karsification and 
associated f low capacity of the karst subsurface.
Conditions for the formation of Zadloško polje
The detailed structural-geological mapping of 
Zadloško polje and the analysis of its morphologi-
cal and hydrological conditions have provided some 
new insights and interesting benchmarks for fur-
ther ref lection on the origins of karst poljes in the 
Dinaric Karst. The authors define the karst polje as 
a large-scale depression of tectonic origin, formed 
by the selective karstification of regional tecton-
ic structures at the groundwater level, where the 
v Habečkovem breznu (ustni v ir). Danes v iseča 
podtalnica v ČKL občasno poplavlja Zadloško 
polje severno od nar ivnice, južno pa podtalni-
ca v okviru Trnovskega pokrova (TP/1) tako, da 
poplav i polje le ob močnejšem dežev ju. Štev i lni 
dolomitni izdanki, k i izdanjajo iz s sedimen-
t i  pokritega dna, imajo vpad plast i povprečno 
230/20-30°, kar je sk ladno s plastov itost jo do-
lomitov v širši okolici.  Pojav uravnovešanja po-
bočij polja in pojav izdankov matične kamnine 
na ponikalnih območjih nakazujeta na recent-
no zmanjšano vodno zadrževalno sposobnost 
izravnave in intenzivno izpiranje preper ine. 
Današnje hidrološke razmere so torej predvsem 
posledica izpiranja prelomnih con in glinene 
preper ine iz dna polja in zaradi tega povečanih 
odtočnih kapacitet. Namesto kopičenja in pre-
meščanja mater ia la, k i sta potekala v času na-
stajanja sedimentne uravnave Zadloškega polja, 
zdaj opazujemo postopno izpiranje v podzemlje, 
k i je posledica novih hidrogeoloških razmer, pa 
tudi povečane zakraselost i in s tem povezane 
pretočnosti kraškega podzemlja.
Razmere za nastanek Zadloškega polja
Podrobno strukturno-geološko kar t iranje 
Zadloškega polja in analiza njegovih morfo-
loških in hidroloških razmer so podali nekaj 
novih vpogledov in zanimiv ih izhodišč za na-
daljnje razmišljanje o nastanku kraških polj 
Dinarskega krasa. Av tor ja opredeljujeva kraško 
polje kot depresijo večjih dimenzij tektonskega 
nastanka, nastalo s selektivnim zakrasevan-
jem regionalnih tektonskih struktur na gladi-
ni podtalnice, pr i čemer se stopnja njene na-
daljnje ojezer itve pr i lagaja danim razmeram v 
A B
Fig. 6. A – The main larger sinkhole of Štefkova rupa. B – The inflow channel to Štefkova rupa formed along the connecting faults in the 
northeastern outer fault zone of Zadlog. Photo: Jože Čar.
Sl. 6. A – Glavna ponikalna globel Štefkove rupe. B – Dotočni kanal v Štefkovo rupo, nastal ob veznih prelomih v severovzhodni zunanji coni 
Zadloškega preloma. Foto: Jože Čar.
267Geologic structure and origin of the Zadlog karst polje
degree of its further capacity for surface water re-
tention is adapted to the given conditions in the 
dynamic karst hydrological system (Šegina, 2021, 
92), which also provides the basis for the formation 
of Zadloško polje and its evolution presented below. 
In accordance with the structural-geological 
conditions presented in the previous chapters, two 
types of thrusting were observed in the wider area 
of Zadloško polje, i.e. thrusts between different lith-
ological units (thrusts of dolomite of the Čekovnik 
nappe slice onto the limestone of the Koševnik nappe 
slice) and thrusts within the same lithological unit 
(thrusts of dolomite of the Trnovo nappe (TP/1) onto 
the dolomite of the Čekovnik nappe) (Fig. 2). All 
three thrust packages present a specific, intrinsical-
ly characteristicsurface morphology. The Koševnik 
nappe slice isdensely interspersed with small dolines 
with an average diameter of 30 m, the surface of the 
Čekovnik nappe slice is mostly the ref lection of de-
nuded and with occasional surface runoff deepened 
tectonic structures, while the surface of the Trnovo 
nappe is more strongly dissected, interspersed with 
few large dolines with an average diameter of 60 m 
and intermediate conical peaks (Fig. 8).
In the case of both the thrust within the dolo-
mite (TP/1–ČKL) and dolomite thrust over lime-
stone (ČKL–KKL) somewhat similar relief phenom-
ena were observed. Both shall be considered for a 
better understanding of the impact of thrust struc-
tures on the formation of the karst polje, albeit the 
interest of this research predominantly lies in the 
thrust within the dolomite in the area of Zadlog. 
At the thrust of the lower thrust block of the 
Trnovo nappe dolomite package onto the Čekovnik 
nappe slice, a thrust line formed with the corre-
sponding thrust–shear crushed zone in the dolo-
mite. Underneath the thrust front a thrust plain 
formed in the less permeable, thrust–shear crushed 
zone in the dolomite as a morphological basis for 
karst polje (Fig. 7A). This is where groundwater 
from the nappe block of the Trnovo nappe (TP/1) 
f lowed and stagnated on the surface due to the poor 
permeability of the crushed thrust–shear zone in 
the dolomite. During the lake-formation the bot-
tom of the karst polje was covered by the sediment 
(Fig. 7B). The karts polje expanded laterally along 
the fractured crushed zone. The main direction of 
expansion was towards the thrust front, where the 
dolomite slopes adapted to slope erosion. The pe-
rimeter of the hollow gradually cut into the dolomite 
of the Trnovo nappe southwest of the thrust zone 
and the Čekovnik nappe slice northeast of it (Fig. 
7C). During the formation of fault structures in the 
NW-SE direction, underground drainage formed 
in the Trnovo nappe dolomite and the Čekovnik 
dinamičnem kraškem hidrološkem sistemu (Še-
gina, 2021, 92), na čemer tudi temelji  v nadal-
jevanju predstavljen nastanek in razvoj Zadlo-
škega polja. 
Soglasno s predstavljenimi strukturno-geo-
loškimi razmerami v predhodnih poglav jih na 
širšem območju Zadloškega polja opazujemo 
dve vrst i nar ivov, in sicer nar iv med različnima 
l itološkima enotama (nar iv dolomita Čekovniš-
ke krovne luske na apnenec Koševniške krovne 
luske) in nar iv znotraj iste l itološke enote (nar iv 
dolomita Trnovskega pokrova (TP/1) na dolomit 
Čekovniške  krovne luske) (sl.  2). Vsi tr ije nar iv-
ni paketi kažejo specif ično, zase znači lno mor-
fologijo površja. Na Koševniški krovni luski so 
gosto posejane manjše vr tače premera povpreč-
no 30  m, površje Čekovniške  krovne luske je 
predvsem odraz denudiranih in z občasnim 
površinskim odtokom poglobljenih tektonskih 
struktur, medtem ko je površje na Trnovskem 
pokrovu močneje razčlenjeno, posejano z redki-
mi večjimi vr tačami povprečnega premera 60  m 
in vmesnimi kopastimi vrhovi (sl.  8).
Pri nar ivu tako znotraj dolomita (TP/1-
ČKL), kakor tudi pr i nar ivu dolomita na apne-
nec (ČKL-KKL) opazujemo do neke mere podob-
ne reliefne pojave. Za boljše razumevanje vpliva 
nar ivnih struktur na oblikovanje kraškega polja 
bomo obravnavali oba, čeravno je v ospredju te 
raziskave nar iv znotraj dolomita na območju 
Zadloga. 
Ob nar ivu spodnjega nar ivnega bloka dolo-
mitnega Trnovskega pokrova na dolomit Čekov-
niške krovne luske se je oblikovala nar ivnica s 
pripadajočo obnarivno zdrobljeno cono v do-
lomitu. V nar ivni coni se je v slabo prepustni, 
obnarivni zdrobljeni coni v dolomitu oblikova-
la nar ivna izravnava kot morfološka zasnova 
za kotanjo (sl.  7A). Tja je zatekala podzemna 
voda iz krovninskega bloka Trnovskega po-
krova (TP/1), kjer je zaradi slabe propustnosti 
zdrobljene obnarivne cone v dolomitu površin-
sko zastaja la. V času ojezer itve je nastalo sko-
raj povsem uravnano sedimentno dno (sl.  7B). 
Kotanja se je bočno šir i la po pretr t i zdrobljeni 
coni. Glavna smer šir jenja je bi la proti čelu na-
r iva, kjer so se dolomitna pobočja pr i lagajala 
spodjedanju pobočij.  Postopno je obod kotanje 
zarezal v dolomit Trnovskega pokrova jugoza-
hodno od nar ivne cone in Čekovniške  krovne 
luske severovzhodno od nje (sl.  7C). Ob nastan-
ku prelomnih struktur v smeri SZ-J V se je na 
mestih prelomov v dolomitu Trnovskega pokro-
va in Čekovniške  krovne luske vzpostav i l pod-
zemni odtok, nastali so ponori. Skozi oba paketa 
268 Jože ČAR & Ela ŠEGINA
nappe slice at the faults, and ponors emerged. Sur-
face water drainage and sediment transport to the 
underground developed through both rock packag-
es, which are now part of the basin f loor. This is 
why parent rock outcrops through the sediments 
covering the bottom of the karst polje. Similar con-
ditions to those in Zadlog are present in the wider 
surroundings of Črni Vrh. 
The conditions were somewhat different when 
the dolomite package of the Čekovnik nappe slice 
was thrust over the limestone of the Koševnik 
nappe slice. Underneath the thrust front, there 
was a slopeward displacement of dolomite eluvium 
from the thrust front and eluvium of the thrust–
shear crushed zone, with no water retention on 
the surface due to limestone contact. Water f lowed 
superficially over poorly permeable eluvium and 
percolated into well-karstified limestone. Due 
to erosion of the thrust–shear crushed zone, the 
slope of the thrust front gradually retreated and 
the slightly sloped surface covered with sediments 
spread towards the thrust front. Younger fault tec-
tonics established subsurface drainage and small 
areas of ponors. The weak springs in the thrust 
front (rather than in the f loor of the plain) suggest 
that the entire sedimentary plain did not expand 
beyond the thrust–shear zone, as its potential 
for lateral expansion is limited only to the level-
ling of the dolomite slope at the thrust front. Such 
conditions are present in the area of Idrijski Log 
and Predgriže. The karst which formed along the 
thrust belt of dolomite over limestone has its own 
features. This phenomenon has its specific char-
acteristics which has not yet been explored sys-
tematicall so far (Čar, 2001; Čar & Šebela, 2001; 
Zagoda, 2004; Čar & Zagoda, 2005).
kamnine, k i zdaj gradita dno kot line, se je vzpo-
stav i lo odtekanje površinskih voda in odnašan-
je sedimentov v podzemlje, zaradi česar so sko-
zi sediment, k i prekr iva kraško polje, pogledali 
izdanki matične kamnine. Podobne razmere kot 
v Zadlogu so tudi v širši okolici Črnega Vrha.
Ob narivu dolomitnega paketa Čekovniš-
ke krovne luske na apnenec Koševniške krovne 
luske so bile razmere nekoliko drugačne. Pod 
čelom nariva je potekalo pobočno premeščan-
je dolomitne preperine s čela nariva in preperi-
ne obnarivne zdrobljene cone, pri čemer zaradi 
kontakta z apnencem ni prišlo do površinskega 
zadrževanja vode. Voda se je po slabo propustni 
preperini pretakala površinsko in ponikala v dob-
ro zakraselem apnencu. Zaradi erozije obnarivne 
zdrobljene cone se je pobočje čela nariva posto-
poma umikalo in blago nagnjeno površje pokri-
to s sedimenti se je širilo v smeri proti čelu na-
riva. Mlajša prelomna tektonika je vzpostavila 
podzemni odtok in nastanek manjših ponornih 
območij. Šibki izviri v čelu nariva (in ne v dnu 
uravnave) kažejo na to, da se celotna sedimentna 
uravnava ni razširila izven obnarivne cone, saj je 
njen potencial za bočno širjenje povezan zgolj z 
uravnavanjem dolomitnega pobočja v čelu nariva. 
Takšne razmere so na območju Idrijskega Loga 
in Predgriž. Kras, ki je nastal ob narivnem pasu 
dolomita na apnenec, ima svoje značilnosti, ki pa 
zaenkrat še niso bile sistematično raziskane (Čar, 
2001; Čar & Šebela, 2001; Zagoda, 2004; Čar & 
Zagoda, 2005).
TP
ČKL
TP
ČKL ČKL
TP
VZPOSTAVITEV POGOJEV ZA 
NASTANEK KRAŠKEGA POLJA
ESTABLISHEMNT OF CONDITIONS
FOR THE FORMATION OF KARST POLJE
URAVNAVANJE IN ŠIRJENJE 
KRAŠKEGA POLJA
LEVELLING AND PROPAGATION
OF KARST POLJE 
DEGRADACIJA KRAŠKEGA POLJA
DEGRADATION OF KARST POLJE
A B C
Fig. 7. Formation of a karst polje along a dolomite thrust. A – Thrust tectonics. B – Peneplanation and lake-formation on the poorly perme-
able fault-induced crushed zones in the dolomite, and lateral expansion of the plain. C – Expansion of the plain into the dolomite, younger 
fault tectonics and the formation of subsurface drainage of surface water and sediments.
Sl. 7. Razvoj kraškega polja ob narivu v dolomitu. A – Narivna tektonika. B – Uravnavanje in ojezeritev slabo prepustne obprelomne zdroblje-
ne cone v dolomitu in bočno širjenje uravnave. C – Razširitev uravnave v dolomit, mlajša prelomna tektonika in vzpostavitev podzemnega 
odtoka površinske vode in sedimentov.
269Geologic structure and origin of the Zadlog karst polje
The Figure (Fig. 8) shows a typical profile of the 
dolomite-dolomite thrust and dolomite-limestone 
thrust, illustrating the characteristic and unique 
features of surface evolution along thrust struc-
tures (Fig. 8). Under the given conditions, steep 
slopes with an inclination of more than 30° formed 
at the thrust front between dolomite packages (Fig. 
8, mark a). High inclinations facilitated occasion-
al surface runoff along the fault structures where 
the removal of fractured dolomite on steep slopes 
led to the formation of mostly simple, rectilinear 
gullies. These have contributed additional deposits 
of dolomitic eluvium to the area of the thrust line. 
Slightly sloped sedimentary plains at the foot of the 
thrust block are nowadays made of dolomite eluvi-
um from the thrust front that partially filled in the 
f lattened sedimentary bed along the edges (Fig. 8, 
mark b). In the expanded thrust–shear zone (Fig. 4), 
Na sliki 8  je prikazan značilen prof i l čez na-
r iv dolomita na dolomit in dolomita na apnenec, 
ki ponazarja značilne in svojstvene značilnosti 
razvoja površja vzdolž narivnih struktur (sl. 8). 
V danih razmerah so se na čelu nariva med do-
lomitnima paketoma oblikovala strma pobočja z 
naklonom nad 30° (sl. 8, oznaka a). Zaradi v i-
sokih naklonov se je na njih občasno vzposta-
vil površinski odtok vzdolž prelomnih struktur, 
kjer so se zaradi odnašanja pretr tega dolomita 
po strmih pobočjih oblikovale večinoma eno-
stavne, premočrtne grape. Te so na območje 
narivnice prispevale dodaten vnos dolomitne 
preperine. Dolomitna preperina s čela nariva 
danes gradi rahlo nagnjene obode sedimentnih 
uravnav ob vznožju narivnega bloka, ki ob ro-
bovih deloma prekrivajo uravnano sedimentno 
dno (sl. 8, oznaka b). V razšir jeni obnarivni coni 
TP/1
ČKL
A
B
Črni vrh
a
a a
b c
Zadloško polje/Zadlog karst polje
obnarivna cona
dolomit-dolomit/
near-fault zone
dolomite-dolomite
obnarivna cona
dolomit-apnenec/
near-fault zone
dolomite-limestone
A
TP/1
ČKL
KKL
a
b a
c
d
Idrijski logb
B
d
a
Koluvialni vršaj
ČKL
TP/1
KKL
HP
d
Narivnica med pokrovi
Zadlog
Smer vpada narivne 
ploskve
Narivnica med krovnimi 
luskami
Prelom
b
Izravnava ob narivu dol.-apn. 
Izravnava ob narivu dol.-dol.
dolomit/
dolomite
KKL
Idr
ijs
ki 
log
b
fliš/
flisch
ČKL
KKL
P
redgriže
dolomit/
dolomite
dolomit/
dolomite
dolomit/
dolomite
dolomit/
dolomite
apnenec/
limestone
apnenec/
limestone
apnenec/limestone
apnenec/
limestone
Thrust border between nappes
Spring
Ponor
Strike of the thrust plane
Thrust border between nappe 
slices 
Fault
Colluvial fan
Planation at the thrust
dolomite-limestone 
Planation at the thrust
dolomite-dolomite 
Sediment-covered floor
Colluvial accumulation
from the dolomite thrust front
Outcrops of the dolomite 
baserock
Izvir
Ponor
S sedimenti prekrito dno
Koluvij z dolomitnega 
oboda
I
KKL
Fig. 8. Thrust–shear surface morphology.
Sl. 8. Obnarivna morfologija površja.
270 Jože ČAR & Ela ŠEGINA
a sediment-covered levelled surface can be observed 
today (Fig. 8, mark c). The absence of outcrops to-
wards the northern part of the polje marks the area 
of the thrust–shear zone and crushed rocks. There 
are springs and ponors along the younger faults in 
the extended bed of the karst polje, which extends 
beyond the thrust–shear zone.
A steep slope in the dolomite also formed at the 
thrust front between the dolomite and limestone 
packages (Fig. 8, mark a), where the dolomite eluvi-
um originates from, overlying the expanded area of 
the thrust–shear zone at a slight inclination (up to 
7°) (Fig. 8, mark b). It transitions into a classically 
dissected, morphologically distinct karstified karst 
surface of the Koševnik nappe slice (Fig. 8, mark d). 
Temporary springs are located in the slope of the 
thrust front over the dolomite crushed zone. Ponors 
and dolines formed along the younger faults.
Conclusion
With detailed geological mapping on a scale of 
1:5000, we found significantly different geologi-
cal conditions in Zadlog and the surrounding area 
than those previously drawn on geological maps. 
Three hydrological retention-def lection levels 
and numerous, different fault zones intersecting 
these levels have been identified. The established 
lithological-structural elements determine the 
inf low and outf low conditions in Zadloško polje 
and provide the basis for the formation of karst 
polje, while present geomorphological and hydro-
logical characteristics indicate recently reduced 
hydrologic-retention capability of the karst polje 
and intensive washing out of the eluvium. Denuda-
tion, karstification and sediment transport to the 
underground are the principal processes that, at 
present, shape the Zadlog karst polje.
Similar thrust and tectonic structures probably 
occur also in large karst poljes in the Notranjska 
region. What is the role of thrust tectonics in the 
formation of these karst poljes and what is the im-
pact on their recent morphological and hydrogeo-
logical characteristics will have to be verified with 
the detailed geological mapping in the future.
Acknowledgement
The research was funded by the Slovenian Research 
Agency through grants P1-0419 and project Mladi fo-
rum which is co-funded by the Slovenian Research and 
Innovation Agency within the framework of DFP (De-
velopmental funding pillar). 
(sl. 4) danes opazujemo s sedimentom prekri-
to, uravnano površje (sl. 8, oznaka c). Odsot-
nost izdankov proti severnemu delu polja naka-
zuje na območje obnarivne cone in zdrobjenih 
kamnin. Ob mlajših prelomih v razšir jenem dnu 
kraškega polja, ki sega izven obnarivne cone, so 
izv ir i in ponori.
Na čelu nariva med paketom dolomita in 
apnenca se je prav tako oblikovalo strmo pobo-
čje v dolomitu (sl. 8, oznaka a), od koder izv ira 
dolomitna preperina, ki v blagem naklonu (do 
7°) prekriva razšir jeno območje obnarivne cone 
(sl. 8, oznaka b). Ta prehaja v k lasično razčle-
njeno, morfološko izraziteje zakraselo kraško 
površje Koševniške krovne luske (sl. 8, oznaka 
d). Občasni izv ir i se nahajajo v pobočju čela na-
r iva nad dolomitno zdrobljeno cono. Ob mlajših 
prelomih so nastali ponori in vrtače.
Zaključek
S podrobnim geološkim kartiranjem v merilu 
1: 5000 smo v Zadlogu in širši okolici ugotovili 
bistveno drugačne geološke razmere, kot so bile 
na geoloških kartah izrisane doslej. Ugotovljeni 
so bili tr ije zaporno-zadrževalni nivoji in števil-
ne, različne prelomne cone, ki te nivoje sekajo. 
Ugotovljeni litološko-strukturni elementi dolo-
čajo dotočne in odtočne razmere na Zadloškem 
polju ter dajejo osnove za oblikovanje kraške-
ga polja, zatečene geomorfološke in hidrološke 
značilnosti pa kažejo recentno zmanjšano vodno 
zadrževalno sposobnost kraškega polja in inten-
zivno izpiranje preperine. Denudacija, zakrase-
vanje in odnašanje sedimenta v podzemlje so po-
glavitni procesi, ki trenutno delujejo na območju 
Zadloškega kraškega polja.
Podobne narivne in tektonske strukture se ver-
jetno pojavljajo tudi na velikih kraških poljih na 
Notranjskem. Kakšna je njihova vloga pri nastan-
ku, morfološkem oblikovanju in hidrogeoloških 
značilnostih  bo potrebno preveriti z natančnej-
šim geološkim kartiranjem.
Zahvale
Članek je bil sofinanciran s strani programske 
skupine P1-0419 in projekta Mladi forum, ki ga f inan-
cira Javna agencija za znanstvenoraziskovalno in ino-
vacijsko dejavnost Republike Slovenije v okviru razvoj-
nega stebra (RSF).
271Geologic structure and origin of the Zadlog karst polje
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