GEOLOGIJA 45/1, 71–90, Ljubljana 2002 Development of a Lithocodium (syn. Bacinella irregularis)-reef-mound-A patch reef within Middle Aptian lagoonal limestone sequence near Nova Gorica (Sabotin Mountain, W-Slovenia) Alga Lithocodium (syn. Bacinella irregularis)-graditelj krpastih grebenov znotraj srednjeaptijskega lagunskega apnenca, Sabotin pri Novi Gorici Roman KOCH1, Esmail MOUSSAVIAN2, Bojan OGORELEC3, Dragomir SKABERNE3 & Ioan I. BUCUR4 1 Institut für Paläontologie, Loewenichstr. 28, D-91054 Erlangen; e-mail: rkoch@pal.uni-erlangen.de; 2 Institut für Paläontologie u. hist. Geologie der Universität München, Richard-Wagner-Straße 10, D- 8000 München; 3 Geolo{ki zavod Slovenije, Dimi~eva 14, SLO-1000 Ljubljana, e-mail: bojan.ogorelec@geo-zs.si, dragomir.skaberne@geo-zs.si, 4 Babes-Bolyai University, Department of Geology-Paleontology, M. Kogalniceanu str. 1, RO-3400 Cluj-Napoca, Romania, ibucur@biogeo.ubbcluj.ro Key words: Reef, Lithocodium, Aptian, Sabotin Mt., Slovenia Abstract A Middle-Aptian (zone of Palorbitolina lenticularis) „patch reef“ of about 40 m maximum thickness with marked morphology was analyzed at the Sabotin Mountain near Nova Gorica. It is developed above an basal unit of superficial oolites within lagoonal sediments and is overlain by shallow subtidal to intertidal sediments which reveal short time periodically subaerial exposure and early diagenetic freshwater influxes (birds eyes, vadose silt, characeans). Above these sediments within the zone of Salpingoporella dinarica fine-bedded to platy, laminated bituminous limestones occur. The central part of the reef structure reveals an alternation of individual lenses of Lithocodium-boundstones and of rudist-beds (up to 4 m thickness) which are separated by coarse- to medium-grained, moderately to poorly sorted bioclastic sands. These facies types show also lateral interfingering and are concentrated in the central part of the buildup where the greatest thickness can be observed and where packstones, grainstones and boundstones prevail. The neighbouring lagoonal sediments which consist of mud-stones and wackestones predominantly were analyzed in the so-called Sabotin-standard-profile which is located north of the patch reef at a lateral distance of about 300 m. Three vertical profiles (A = 90 m, B = 100 m, C = 64 m thickness) were analyzed. The middle profile B of greatest thickness is taken as reference profile and documents best the vertical facies development within the patch reef directly overlying a basal unit of peloidal packstones with superficial ooids. The patch reef itself is characterized by the faunal associations within the unit rich in Lithocodium and rudists. It is overlain by a subtidal unit of peloidal mudstones with very minor biogenic allochems. An intertidal unit above rich in birds-eyes and vadose silt is followed by fine-laminated black shales which are covering the general seqeunce of interfingering patch-reef – lagoonal sediments. Using different time lines (marker horizons) for correlation it can be shown that already very early differential compaction of fine-grained uncemented sediments in comparison to the core area of the patch reef is of great importance. The greater thickness of the patch reef itself is caused by an intensive early diagenetic marine phreatic cementation within the core zone and by the early fixing of sediment by Lithocodium aggregatum (syn. Bacinella irregularis) resulting in a greater resistivity 07-71-90.p65 71 18. 09. 02, 20:37 Black 72 Roman Koch, Esmail Moussavian, Bojan Ogorelec, Dragomir Skaberne & Ioan I. Bucur against compaction. Furthermore a lagoonal side and an more open marine side of the patch reef can be determined. Lithocodium aggregatum is the main constructing organism within the buildup investigated, beginning with the incrustation of varying substrates and biogenic particles. Finally, a dense network of encrustation-sequences is formed interfin-gering with the general sedimentary textures intensively and resulting in larger „biogenic-cemented“ patches within the sediment. The correlation of the three profiles A, B, and C allows to reveal the history of differential compaction of the associated lagoonal sediments in comparison to the more massive patch reef limestones. It becomes obvious that the main compaction must have occurred within the time span of about 50 m sediment-deposition overlying the patch reef. Differential compaction resulted in differences in thickness of about 10 m from the patch reef (profile B) to the more lagoonal influenced sediments (profile A) within a lateral distance of about 50 m. Kratka vsebina V vzhodnem pobo~ju Sabotina pri Novi Gorici smo raziskali do okoli 40 m debel, morfolo{ko lepo izra`en srednjeaptijski (cona Palorbitolina lenticularis) krpasti greben (patch reef). Razvit je med lagunskimi apnenci nad bazalno enoto, sestavljeno iz nepopolno razvitih oolitov (supeficial oolites). Prekrivajo ga sedimenti nastali v plitvem morju in v medplimski coni, ki razkrivajo kratkotrajne periodi~ne okopnitve in zgodnje diagenatski dotok sladke vode (teksture pti~jega o~esa, vadozni melj, haraceje). Nad temi sedimenti, znotraj cone Salpingoporella dinarica, so razviti tanko plastnati do plo{~asti laminirani bituminozni apnenci. V osrednjem delu grebena se menjavajo le~e apnenca z algami Lithocodium in strukturo boundstone z do 4 m debelimi plastmi z rudistnimi {koljkami, ki jih lo~ujejo pasti debelo do srednjezrnatega, srednje do slabo sortiranega biokasti~nega apnenca. Ti faciesi se tudi lateralno prepletajo in so koncentrirani v osrednjem delu grebena. V tem delu je greben najdebelej{i. V njem prevladujejo apnenci s strukturo packstones, grainstones in bound-stones. Obdajajo~e lagunske sedimente, ki jih sestavljajo apnenci s prevladujo~o strukturo mudstone in wackstone, smo raziskali v tako imenovanem standardnem profilu Sabotin, ki je 300 m severno od obravnavanega grebena. Raziskali smo tri vertikalne profile, ki zajemajo debelino 64 do 100 m (A = 90 m, B = 100 m, C = 64 m). Srednji profil B, ki obsega najve~jo debelino in najbolje prikazuje vertikalni facialni razvoj znotraj krpastega grebena, smo dolo~ili kot referen~ni profil. Ta zajema tudi neposredno bazalno enoto iz peloidnih apnencev s packstone strukturo, ki vsebujejo tudi ne popolnoma razvite ooide. Za sam krpasti greben je zna~ilna favnisti~na zdru`ba enot bogatih z algami Lithocodium in rudistnimi {koljkami. Prekriva ga enota plitvomorskih peloidnih apnencev s strukturo packstone in z zelo malo biogenih alo-kemi~nih komponet. Nad njimi je enota bogata s teksturami pti~jega o~esa in vadoznim meljem, nastala v medplimski coni. Sledijo tanko laminirani ~rni muljevci, ki prekrivajo splo{no zaporedje prepletanja grebenskih in lagunskih sedimentov. Pri korelaciji z uporabo razli~nih ~asovnih ~rt (vodilnih horizontov), se poka`e velik vpliv in pomembnost, `e zelo zgodnje diferencialne kompakcije ne cementiranih drobno-zrnatih sedimentov v primerjavi z jedrom krpastega grebena. Ve~ja debelina samega krpastega grebena, je posledica zgodnje diagentske morske freatske cementacije osrednjega dela grebena in zgodnje vezave sedimenta z algami Lithocodium aggregatum (syn. Bacinella irregularis), kar je povzro~ilo manj{o stopnjo kompakcije. Nadalje smo lahko, glede na polo`aj krpastega grebena, dolo~ili smer raztezanja lagune in odprtega morja. Alge Lithocodium aggregatum so glavni sestavni organizem raziskovanega krpastega grebena, ki se pri~enja z inkrustacijami razli~ne podlage in biogenih drobcev. Kon~no se je izoblikovala gosta mre`a zaporedja inkrustacij, ki se intenzivno prepletajo s splo{nimi sedimentnimi teksturami in grade znotraj sedimentov velik »biogeno-cementiran« krpasti greben. Korelacija treh profilov A, B in C nam dovoljuje razkritje zgodovine diferencialne kompakcije sosednjih lagunskih sedimentov v primerjavi z bolj masivnim apnencem krpa-stega grebena. Izka`e se, da je glavnina kompacije potekala v ~asu odlaganja okoli 50 m sedimentov krovnine krpastega grebena. Diferencialna kompakcije je povzro~ila razliko v debelini od krpastega grebena (profil B) proti sedimentom z ve~jim lagunskim vplivom (profil A) za okoli 10 m na lateralni razdalji pribli`no 50 m. Introduction Rudists, corals, and sponges (stromatopo-roids, chaetetids) are the most important reef-forming elements of Cretaceous carbonate platforms (Wilson 1975). Within the photic zones of carbonates platforms numerous mono- to multispecific types of bio- constructions are formed by these potential (classic) constructional organisms including local individual occurrences as biostroms, mounds, patchreefs and even extended barrier-like reef-systems (Masse & Philipp 1981, Kauffman & Johnson 1988, Mous savian 1992, Höfling 1997, S an -ders & Höfling 2000, Höfling & Scott 07-71-90.p65 18. 09. 02, 20:37 72 Black Development of a Lithocodium (syn. Bacinella irregularis)-reef-mound- … 73 2002). Two essential basic reef-types are characteristic for the Cretaceous time interval. These are (1) mono- to paucispecific rudist-buildups and (2) coral-sponge-algae/coral-algae reefs. The rudist-population (mainly monopleurids, caprinids, radiolitids, hippu-ritids) commonly grows in bouquet-like buildups within a reduced commonly lago-onal environment with low diversity. Coral or coral-sponge-dominated biocon-structions are best developed with highest diversity in a normal marine environment (open platform) of deeper water compared to the locations of the formation of rudists-buildups (Moussavian 1992, Höfling 1997, V o i g t et al. 1999, K a u f f m a n et al. 2000, H ö f l i n g & S c o t t 2002). But generally they can be found in a lagoonal environment too. The worldwide expansion of these main reef types was developed during the Lower Cretaceous (pre-Barremian), subsequently to a time of reorganisation of carbonate platforms and reef communities. Lithocodium (syn. Bacinella; S e g o n z a c & Marin 1972) is an incrusting organism living generally in reef facies. Already during the Upper Triassic and Jurassic it plays an important role within reef communities. During the Berriassian to Aptian Lithoco-dium reached its greatest expansion worldwide resulting in the formation of reef-like buildups. It is obvious that a higher reduced energy environment is most favourable for the growth of Lithocodium as also valid for the occurrence of rudists. Therefore Lithocodium-buildups are valuable indicators for these specific environments in which only some very spezialized groups of organisms occur. In the recent study a characteristic Litho-codium-mound in W-Slovenia is analyzed (Pl. 1/1-3). It has a thickness of about 40 m, a lateral extension of about 200 m and is characterized by a marked morphology in comparison to the adjacent lagoonal bedded sediments (Plate 1/1). Furthermore characteristic are thin platy, laminated black shales (Pl. 1/4) which cover the structure (Koch 1988, Koch & Zimmerle 1996). Comparative analyses dealing with the facial and diagenetic development of Cretaceous beds in neighboured areas (Nanos and Trnovo) were carried out by K o c h (1978), K o c h et al. (1989), Koch & Ogorelec (1990) and by Koch et al. (1998). Cretaceous beds of 07-71-90.p65 73 Black the Trieste – Komen Plateau were investigated by Jurkov{ek et al. (1996) and L. Šribar (1995). The methods used for the recent study are (1) field analysis by taking three vertical profils over the vertical walls of the structure (A – 90 m, B – 100 m, C – 64 m) and (2) microscopic thin section analysis including semiquantitative estimation of the most important groups of organisms. The results of analysis are representatively documented by the analysis of the middel profile B (Fig. 2) in the description of thin sections, in the microfossil list and in photoplate 2-4 documenting the most important microfossil elements (foraminifera and algae), microfacies-types as well-as textural and diagenetic characteristics. Geological setting The Cretaceous strata studies are situated in the high Karst area of the Outer Dinarides in W-Slovenia and belong to the Dinaric Carbonate Platform (Buser 1976, 1987). In NW- and W-Slovenia where the northern part of the platform occurs, small tectonic units form overthrusts with a lateral movement of 30 km or less (Mlakar 1969, Placer 1981, 1999). The Cretaceous sequence at the Sabotin (thickness about 800 m) which is situated north of Nova Gorica just at the Slovenian-Italian border belongs to the overthrust anticline of Sabotin Mountain, which passes towards the east to the Trnovo overthurst (Buser 1973). A standard section of about 600 m thickness (Hauterivian – Turonian) was analyzed in comparison to the neighboured profiles (Trnovo, Nanos, Fig. 1). An obvious sequence of more massive limestones (Pl. 1/1-3) with a total thickness of about 40 m and of indivudual beds of 2-4 m in the middle part is of Aptian age. Due to the marked morphology it was interpreted as patch-reef in general terms already during field work. Following the W-Flank of the Sabontin it becomes obvious that the patch reef is unique in this part of the Sabotin Mountain. Laterally the thick-bedded part is developed as normal-bedded limestones (bed thickness predominantly 5 – 15 cm) of lagoonal facies which are analyzed in the so-called Sabotin standard profile positioned about 300 m north of the patch reef (Pl. 1/1). 18. 09. 02, 20:37 74 Roman Koch, Esmail Moussavian, Bojan Ogorelec, Dragomir Skaberne & Ioan I. Bucur Fig.1: Detail of the geological map of W-Slovenia with location of the Sabotin profile (S). Other profiles analyzed in this area are the Trnovo profile (T: Koch et al. 1989, Koch & Ogorelec 1990) and the Nanos profile (N: Koch 1978, Koch et al. 1998). The Trnovo overthrust is characterized by the Sabotin and Trnovo sections and the Hru{ica overthrust by the Nanos section. Modified from „Geological map of Slovenia“. T = Triassic, J = Jurassic, K1 = Lower Cretaceous, K11 = Berriasian/Valanginian, K12 = Hauterivian, K13,4 = Barremian/Aptian, K15 = Albian, K1,2 = Lower-Upper Cretaceous, K21 = Cenomanian, K21,2 = Cenomanian-Turonian, K22 = Turonian, K22,3 = Turonian-Senonian, K23 = Senonian (Koch 1988; modified from Buser 1986). Biostratigraphy The whole assemblage of microfossils (appendix) indicate an Early Aptian (Bedou-lian) age (Schroeder 1975, Arnaud-Vanneau 1980, Arnaud-Vanneau & Chioccini 1985, Luperto Sinni & M as s e 1993). Macrofauna was recently not used for age determination. Most elements of the foraminiferal fauna are characteristic for urgon facies and indicate a Late Barre-mian to Early Aptian age. The most precise data given, are due to the occurrence of orbi-tolinids i.e. Palorbitolina lenticularis (B l u -m e n b a c h ) which indicate Early Aptian age. Salpingoporella dinarica which has a general stratigraphic range from Valanginian to Albian (Granier & Deloffre 1993, Bucur 1999) is known in this region as beeing indicative for Aptian time interval (upper part of the Lower Aptian and lower part of the Upper Aptian (Farinacci & Radoi~i} 1994, Veli} 1977, Soka~ et al. 1978, Lj. Šribar 1979, Turn{ek & Buser 1966, K o c h et al., 1989, K o c h et al. 1998, Jurkov{ek et al.1996, L. Šribar 1995). Facies development, distribution pattern of biota Three profiles were analyzed in order to characterize the patch-reef which is best developed in profile-B, as indicated by the most thick-bedded limestones (up to 4 m bed thickness). About 300 m north of pro-file-A, fine-bedded lagoonal sediments are found and samples in the Sabotin standard section (Pl. 1/1). Five characteristic litho- and microfacial units can be distinguished in the profiles (Fig. 2). These are well-bedded limestones (unit-SO) at the base which contain superficial ooids (Pl. 2/1), the central unit-LBR which is rich in Lithocodium (Pl 2/2-4), forming the core of the patch-reef, an overlying unit-ST of peloidal mud- wackestones with very minor biogenic allochems, and a unit-IT rich in mudstones and wackestones with birds-eyes and vadose silt (Pl. 2/6) reflecting predominantly an intertidal depositional environment. The structure is covered by thin-bedded to platy, laminated black shales rich in Sal- 07-71-90.p65 18. 09. 02, 20:37 74 Black Development of a Lithocodium (syn. Bacinella irregularis)-reef-mound- … 75 pingoporella dinarica (Pl. 2/7) and ostracod mudstones (Pl. 2/8) which grade upwards in normal lagoonal well-bedded sediments (Fig. 2 and 3). Besides the correlation in the field which was carried out be tracing single beds through all four profiles, the semiquantitative estimation of fauna elements is another base for the correlation of the profiles (Fig. 3). The bioigenic constitutents are nearly exclusively composed of foraminifera, Lithocodium, molluscs (predominantly rudists), echinoid fragments and green algae. Dasycladaceans occur in two horizons. The first one (unit-SO) in the lower part of the sequence contains predominantly Salpingo-porella muehlbergi (Lorenz). The second one (unit-IT) in the upper part contains the Fig. 2: The middle profile B of the Sabotin patch reef is taken as example for the vertical distribution of varying faunal elements. In the lithologic column rudist fragments, lithoclasts, peloids and ooids are indicated as well as the measured thickness of individual beds. Textures comprise algal laminations, birds-eyes and vadose silt as well as geopetal fillings. Lithocodium means occurrence of undifferentiated Lithocodium-Bacinella. Furthermore dasycladaceans (dasy; S.m. = Salpingoporella muehlbergi; S.d. = Salpingoporella dinarica) general amounts of biogenic allochems (bio), rudists, echinoids (echin), foraminefera (foram), orbitolinids (orbito; Palorbitolina lenticularis), miliolids (mil), cyanobacteria mats (cyano) and ostracods (ostra) are indicated in relative abundance. 07-71-90.p65 18. 09. 02, 20:37 75 Black 76 Roman Koch, Esmail Moussavian, Bojan Ogorelec, Dragomir Skaberne & Ioan I. Bucur Fig. 3: Correlation of the profiles A, B and C from North to South, i.d. from the lagoonal influenced part of the patch reef in direction to the more open marine side rich in biogenic debris. Note thickness variations of different beds due to early cementation, organigenic reef growth and differential compaction. For explanation see text. Plate 1 1 The Sabotin profile; view from the S-side with position of the Aptian patch reef with marked morphology within the Cretaceous sequence. 2,3 Detail of the Aptian patch reef with position of the three profiles (A, B, and C) studied. Marked facial boundaries (1, 2, and 3) are separating the base of pack- to grainstones with superficial ooids (unit-SO), the zone rich in Lithocodium (unit-LBR), the zone with intertidal sediments (unit- ST and unit-IT), and the overlying limestones containing fine-bedded black shales with Salpingoporella (unit-BS) from eachother. 4 Detail of the overlying fine-bedded, laminated black shales show deformation structure at a small fault. Thickness of individual beds is some mm to 10 cm. 07-71-90.p65 18. 09. 02, 20:37 76 Black Development of a Lithocodium (syn. Bacinella irregularis)-reef-mound- … 77 07-71-90.p65 18. 09. 02, 20:37 77 Black 78 Roman Koch, Esmail Moussavian, Bojan Ogorelec, Dragomir Skaberne & Ioan I. Bucur single species Salpingoporella dinarica. As indicated by the slightly reduced fauna of the unit-IT dasycladaceans lived in a more restricted environment compared to the underlying beds, rich in Lithocodium. Red algae are represented only by one species (Polystrata alba) too, which occur very rarely within the Lithocodium boundstones (profile C). Lithocodium aggregatum is found in unit-LBR exclusively forming the monospe-cific reef mound. Corals, stromatoporoidsd and chaetetids are quantitatively not significant and only occur in some horizons with lowered diversity. Predominantly fragments of rudists are abundant in unit-LBR, within the Litho-codium boundstones. Only in more massive beds of profile-B, rudists (up to 5 cm in size) are commonly in life position revealing bio-stromal growth forms and some small bundles (bouquets sensu Höfling 1997). Benthic foraminifera are the main bio-genic components in thin sections analyzed. Agglutinated and porcellaneous families are predominant. The first group mentioned consist of Ataxiophragmiids, Textulariids and Lituolids mainly. More complex agglutinated groups (as Cuneolinids and Charentiids) generally occur in minor amounts throughout the sequence and are enriched only in some horizons. Orbitolinids show similar distribution patterns and are represented by Palorbitolina. Miliolids and other porcellaneous foraminifera show a relatively homogeneous composition when occurring abundantly. For the description of the profile only the most characteristic fossil elements are documented in profile B (Fig. 2) and in plates 3 and 4. Profile-A has a thickness of about 90 m and consists of intercalations of thin-bed- Plate 2 Unit-SO: Sample C – 12 Oobiopelsparite predominantly rich in superficial ooids besides ooids with thicker cortices (arrow). Besides common small benthic foraminifera also some dasycladaceans occur (right). The grains are surrounded by marine phreatic cements. Unit-LBR: Sample C – 5 In this Lithocodium-biolithite from the centre of the patch reef fragments of rudists and some orbitolinids are bound together by Lithocodium/Bacinella. The chamber walls of Lithocodium are lined by interior isopacheous rims of bladed crystals indicating an early marine phreatic cementation by high Mg-calcite. Unit-LBR: Sample C – 2 Lithocodium-orbitolina biosparit-boundstone with tight, inclusion-rich cements. This limestone type is characteristic for the central part of a thick bed rich in rudist fragements. Unit-LBR: Sample C – 17 Peloidal sediments are stabilized by a combination of Lithocodium type with vertical perforations (arrows) and also by a Lithocodium type which reveals more microbial growth forms. Unit-ST: Sample A – 13 A bed of foraminiferal biopelsparite is intercalated in the fine-bedded limestones of unit-ST which are generally nearly barren of fossils. Besides abundant small foraminifera also some larger foraminifera as e.g. ?Praecrysalidina sp. can be found. The sediment is lithified by fine granular cements. Unit-IT: Sample B – 30 The intertidal sediments of unit-IT are characterized by birds-eyes which commonly show geopetal filling by peloidal, slightly recrystallized internal sediments (1). The upper part of the pores is often filled by granular calcite (2). Late fractures are cutting through cements and fillings. Unit-BS: Sample A – 22 In thin layers within the fine-bedded to platy black shales of unit-BS which is covering the complete structure, Salpingoporella dinarica commonly occurs (1). Furthermore some rudist fragments can be found (2). Unit-IT: Sample B – 32 The Upper part of the intertidal unit-IT in profile-B reveals completely preserved ostacods which are floating in the micritic matrix together with miliolids and other small fossil fragments. 07-71-90.p65 18. 09. 02, 20:37 1 Z i 4 5 6 7 8 78 Black Development of a Lithocodium (syn. Bacinella irregularis)-reef-mound- … 79 07-71-90.p65 18. 09. 02, 20:37 79 Black 80 Roman Koch, Esmail Moussavian, Bojan Ogorelec, Dragomir Skaberne & Ioan I. Bucur ded limestones in the lower and middle part, indicating lateral interfingering of the more massive patch-reef sediments (profile B) with the normal-bedded (5 – 10 cm) lagoonal sediments which occur northwards in the standard section. Intercalated are beds of up to 2m thickness which are rich in molluscs occur representing interfingering with the reefal sediments. The microfacial development reveals the Lithocodium-rich unit-LBR with abundant orbitolinids at the base. Marine conditions are indicated also by the presence of locally abundant echinoid fragments and by isopacheous cements surrounding the allochems in packstones and grainstones. Fragments of requienid rudists occur commonly. At the top of unit-I re-quienids built biostrom-like thickets. The overlying unit-ST and unit-IT consists of a mixture of facies types (predominantly mud-stones and wackestones) indicating close alternation of shallow subtidal to intertidal conditions. Chracateristic sedimentary features are birds-eyes, internal sediments and microbial laminations. Echinoids occur in traces. The strongly reduced diversity of the foraminiferal fauna, dominated by a few agglutinated forms, indicate reduced, probably more brackish conditions. The overlying unit-BS starts with fine-laminated to platy, bituminous limestones very rich in Salpingoporella dinarica. The restricted marine conditions change periodically into episodic short time freswater influxes. Predominantly mudstones with small ostracods and charcophytes (oogonia) were deposited. Profile-B (thickness about 100 m) cuts through the central part of the reef mound investigated. The basal unit-SO is characterized by beds rich in small superficial ooids (Pl. 2/1) overlying foraminiferal packstones and grainstones with subordinate ooids. This unit shows well-bedded limestones (Fig. 2) with beds of about 10 – 20 cm thickness. It is overlain by unit-LBR, the core of the Lit-hocodium reef-mound which has a thickness of 34 m and consists of succeccive Litho-codium boundstones with a thickness of individual beds up to 4m. Besides Lithocodium, echinoid fragments, foraminifera (mainly orbitolinids) and rudists (in life position) occur. Between samples B-13 and B-25 (32 m thickness) the section is characterized by several rudist banks composed of requienid forms of up to 5 cm size. The amount of rudists in most layers is up to 20% of total rock volume. The shells of Plate 3 1, 2 Salpingoporella muehlbergii (Lorenz). Obliques sections. 1-sample B14, x 50; 2-sample B20-44276, x 25. 3 Cylindroporella ivanovici (Soka~). Oblique section through the lower part of the thallus. Sample A30-44265, x 25. 4 Cylindroporella sp. Oblique section. Sample B14, x 50 5, 9 Salpingoporella dinarica Radoi~i}. 5-Longitudinal-oblique section. Sample A22-44262, x 25 ; 9-Specimens in longitudinal, oblique and transverse sections. Sample C28-44270, x 12. 6, 7 Carpathocodium anae (Dragastan). Longitudinal-tangential (6) and transverse-oblique (7) sections. Sample A28-44233, x 50. 8 Bacinella irregularis Radoi~i} growing on a bivalve shell. Note the perforations of Bacinella threads (films) inside the bivalve shell. Sample B5-44289, x 12. 10 Bacinella threads (films) binding diferent grain types (bioclasts, peloids). Sample B20-44276, x 25. 11 Polystrata alba (Pfender). Sample A28-44233, x 50. 12 Lithocodium aggregatum Elliott-Bacinella irregularis Radoi~i} assemblage growing around a bivalve shell fragment. Sample C5-44290, x 12. 07-71-90.p65 18. 09. 02, 20:37 80 Black Development of a Lithocodium (syn. Bacinella irregularis)-reef-mound- … 81 07-71-90.p65 18. 09. 02, 20:37 81 Black 82 Roman Koch, Esmail Moussavian, Bojan Ogorelec, Dragomir Skaberne & Ioan I. Bucur the rudists are mostly black coloured. Brown micritic beds are commonly found intercalated between beds rich in rudists. The overlying unit-ST consists of peloidal mud- to wackestones with very minor bio-genic allochems. It is overlain by the unit-IT which reveals intertidal sediments and a reduced faunal composition in comparison to the standard-profile-A. Increasing inter-tidal (brackish ?) conditions are indicated by abundant birds-eyes and by vadose silt-fillings (Pl. 2/6). In the overlying unit-BS renewed normal marine conditions are indicated by the frequency of Salpingoporella dinarica and minor amounts of echinoid fragments, found in the fine-laminated bituminouis marker beds. Thin micritic beds with octracods (Pl. 2/8) are intercalated in the bituminous beds. Profile-C (thickness about 64 m) begins with the basal grainstone layer rich in superficial ooids (Pl. 2/1), forming the top of unit-SO. In the Lithocodium zone (unit-LBR) less massive limestones with a maximum bed-thickness up to 2 m occur. They are rich in rudists, commonly in life position. The top of the unit is characterized by the scattered occurrence of solitary corals and a single species of peryssonneliacean red algae. Similar to the neighbouring sections the overlying unit-ST indicates more marine conditions (dasycladaceans; shallow subti-dal-intertidal). It is followed by unit-IT with more intertidal conditions as indicated by birds-eyes and microbial carbonates. Characteristics of the Lithocodium reef-mound As mentioned above, the „reef“ was first noted due to it’s marked and massive morphology in comparison to the bedded la-goonal facies of adjoining areas (Plate 1). In the central part it attains a thickness of up to 40 m. The massive central part laterally changes in increasing thin-bedded facies, although the boundaries at the top and the base are constantly developed. Sampling the vertical walls of the outcrop it can observed that within the bound-stones rudists in life position occur at different levels. Orbitolinid foraminifera, which are characteristic for this interval too, occur also in varying amounts within the unit-LBR (Fig. 2). All other small biogenic components show a relative homogeneous distribution pattern. Opposite to this, the rela- Plate 4 1-3 Palorbitolina lenticularis (Blumenbach). 1-Vertical section through a specimen showing the embrionar apparatus. Sample A4-44257, x 25; 2, 3-Sections through the embrionar apparatus, 2: sample C10-44297, x 50, 3: sample C5-44290, x 50. 4 Vercorsella laurentii (Sartoni & Crescenti). Longitudinal-oblique section. Sample B30-44260, x 25. 5 Pseudolituonella conica Luperto Sinni & Masse. Subaxial section. Sample C20-44282, x 50. 6 Debarina hahounerensis Fourcade, Raoult & Vila. Subaxial section. Sample A13-44271, x 50. 7 Vercorsella arenata Arnaud-Vanneau. Longitudinal section. Sample B32-44271, x 50. 8-9 Sabaudia minuta Hofker. 8-axial section. Sample A30-44265, x 60; 9-transverse section. Sample A28-44233, x 50. 10 Spiroloculina cretacea (Reuss). Subaxial section. Sample B24-44298, x 50. 11 Pseudolituonella gavonensis Foury. Axial section. Sample B21-44255, x 50. 12-13 Voloshinoides murgensis Luperto Sinni & Masse. 12-transverse-oblique section; 13-Longitudinal-oblique section. Sample C28-44270, x 50. 07-71-90.p65 18. 09. 02, 20:37 82 Black Development of a Lithocodium (syn. Bacinella irregularis)-reef-mound- … 83 07-71-90.p65 18. 09. 02, 20:38 83 Black 84 Roman Koch, Esmail Moussavian, Bojan Ogorelec, Dragomir Skaberne & Ioan I. Bucur tive amount of Lithocodium, forming bound-stones predominantly, can be correlated within the profiles in a well-defined level (Fig. 3). Therefore, it is interpreted that the accumulation of biogenic debris composed of varying amounts of different organisms is one important parameter for the formation of a Lithocodium reef mound. The small benthic organisms, especially foraminifera, probably did not live in this environment. Most of them and their fragments were transported by weak bottom currents. These piles of bioclastic debris (rich in pellets) pro-babaly formed shallow marine, subtidal sand bars which subsequently to their deposition were fixed at the top by cyanobacterial layers during periods of lower or even nonsedimentation. In contrast, Lithocodium (Bacinella) bound these particles together in the sand piles forming Lithocodium- (Bacinella) boundstones, marking periods of lowered or non-sedimentation too. The lithification of the carbonate constituents occurred very early, probably before the sedimentation of the next overlying sediment of varying composition took place. Thus Lithocodium togther with an early diagenetic cementation in inter- and intraparticle pores is responsible for the greater stability of the sediments in the central part of the positive structure, forming a shelter against later campaction. This together with differential compaction being more intensive in the neighboured lagoonal sediments, results in the marked positive morphology of the central part of the buildup revaling also laterally decreasing degrees of primary porosity and cementation. Remarks on systematic affinity of Lithocodium The systematic position of Lithocodium (Bacinella) is still uncertain and was often discussed in literature. Several species and five genera were established from the time-span Triassic – Upper Cretaceous: Lithocodium E l l i o t t 1956, Bacinella Radoi~i} 1959, Pseudolithoco-dium Misik 1979, Bacinellacodium Dra-gastan 1985 and Radoicicinellopsis Bann e r et al. 1990 which all seem to be synony- 07-71-90.p65 84 Black mous. Since Elliott (1956) interpreted Lit-hocodium to be a green algae and Ra doi~i} (1959) regarded it as a microptroblematicum, such morphotypes were repeatedly attributed to different systematic groups, mainly of following systematic positions: Codiacean green algae (Banner et al. 1990), cyanobacteria/microbes/porostromata (Ma s se 1979, Maurin et al. 1985, Ca-moin & Maurin 1988), and multispecific cyanobacteria/algae/foraminifera associations (J o h n s o n 1969, L e i n f e l d e r et al. 1993). S c h m i d & L e i n f e l d e r (1996) interprete it as a foraminifer. Based on systematic and paloecological studies on Triassic to Cretaceous specimens by E. Moussavian it is interpreted to be a complex, encrusting organism of sheet-like basic growth form primarily, which is able to penetrate deeply in e given substrate. In association with other organisms it forms a dense network of incrustation-sequences living in an environment with general common microbial activity. Due to the dense, micritic preservation of the cell-walls, it was probably originally formed by tiny Mg-calcite crystals of < 1 ?m size which are slightly recrystallized to micrite (< 4 ?m). The skeleton of a juvenil Lithocodium aggregatum was built of a network-like mat which shows a structural differentiation from the surface (cortical zone) to the basal zone. Fine and branched channels are changing to somewhat larger canals from the periphery of the cortical zone towards the inner part of the tuissue. The larger channels alter to basin-like cavities (chambers) of different shape and size (see illustrations at Elliott 1956, Misik 1979, B an n e r et al. 1990). Canals beginnign in the chambers and ending at the base occur only in very minor amounts. During the autogenetic growth stages an increasing number of canals and chambers is formed. In the late stages neighbouring chambers can be fused to a system of chambers which are separated from each other only by lamellar-like walls. In mature forms the internal structure under the cortex likes a loose network, whereas the canals and chambers in the oldest parts of the iorganism became „impregnated“ by micri-tic Mg-calcite. These characteristics resemble more to sponge than to any other organism. The new 18. 09. 02, 20:38 Development of a Lithocodium (syn. Bacinella irregularis)-reef-mound- … 85 observations show that the systematic affinity of Lithocodium remains an open question inspite the frequent hypothesis as disccussed above. Constructional type of Lithocodium buildup The primary mode of life of Lithocodium is encrusting various substrates and sedimentary particles, due to genetic and ecological controls. Therefore Lithocodium can be defined as typical „plano-occupant“ (Mous savian 1995) within the „binder guild“ (Fagerstrom 1987, 1988). Covering a facies of oolitic-bearing sands (unit-SO with superficial ooids), Lithoco-dium led to local fixing of fossil-rich wacke-stones and packstones. Micritic rims around biogenic particles generally indicate a high microbial acivity in this environment which was favourable for the initiation of the massive growth of Lithocodium aggregatum by encrusting and binding various substrates and particles (compare also N e u w e i l e r & Reitner 1992). Thus a growth-sequence was formed which interfingers intesively with sedimentary textures. Also important in this environment, but generally subordinate, other encrusters as microbial/cyanobacterial associations, agglutinating foraminifera and probably non-skeletal organisms occured too. The intensive encrustation took place periodically and diachronous, interrupted by short-term higher energy bioclastic environ-ments.Thus a vertical alternation and lateral interfingering of bioclastic sediments and massive encrusted carbonate-sands with rudist-biostroms are formed which all together make up the complete buildup. Therefore the obvious patchreef is interpreted as a vertical pile of Lithocodium-encrustation sequences and associated ru-dist-lenses separated from each other by bio-clastic sands. All sediments are lithified by early diagenetic marine phreatic cements. Depositional environment The central part of the buildup analyzed, rich in Lithocodium, has a thickness od about 40 m occurring within a complete positive 07-71-90.p65 85 Black structure of total thickness of about 100 m. The general sahallow subtidal depositional environment in which this structures has been formed is characterized by the predominance of agglutinating and porcellaneous foraminifera throughout. Above a basal oolitic unit, bioclastic sand bars were deposited periodically. In periods of reduced or interrupted sedimentation they were fixed at their top by cyanobacteria-mats, whereas Lithocodium was responsible for the internal stabilization of these sand bodies at the same time. Additonally early marine phreatic cements were formed in open pores of the packstones and grainstones. Lenses of small rudist-biostroms formed which are sepatered laterally by bioclastic sands. Thus the complete buildup is constructed by a vertical and lateral alternation of bioclastic sands, fixed by Lithocodium, by small rudist biostroms (up to 4 m thickness) and by bioclastic sands without Litho-codium. The marked morphology of the buildup is additonally forced by diffrential compaction of the neighboured lagoonal sediments which are more micritic and the-refeore probably not so intensively lithified as the pack- and grainstones of the buildup. Within the Triassic to Cretaceous Litho-codium is found more commonly in generally reduced internal platform settings than in external platform areas (E lliott 1956, Radoi~i} 1959, Misik 1979, Flügel 1979, Alsharan 1985, 1987, Banner et al. 1990, Neuweiler & Reitner 1992, Höfling 1997). The massive „reef-like“ constructions of Lithocodium are characteristic for restricted, internal platform areas with reduced diversity. During the Cretaceous these were also the best locations for requieniid rudists (Moussavian 1992). But due to adaptive strategy and constructional morphology requienids could not form „reefs“. Therefore Lithocodium was the only successful organism, in the formation of buildups within these environments. Differential Compaction The correlation of the three profiles A, B, and C allows to reveal the history of differential compaction of the associated lagoonal sediments in comparison to the more massive patch reef limestones. 18. 09. 02, 20:38 86 Roman Koch, Esmail Moussavian, Bojan Ogorelec, Dragomir Skaberne & Ioan I. Bucur Differential compaction will occur wherever a compactible unit changes laterally in thickness or compactibility (Labute & Gretener 1969). It is generally accepted that finer-grained sediments (micrite, clay) have a higher water content than coarser-grained sediments. This effect triggers the compactional behaviour of fine-grained sediments (Bayer & Wetzel 1989). Consequently the geometry of pores will be altered by early compaction (Wetzel 1984). Therefore the pore water in micritic sediments shows only very minor flow rates due to decrease of permeability with decreasing grains size, decreasing pore-throat diameters with increasing time of overburden. Thus coarse grained sediments and also reefal str-cutures with high fluid rates of pore water commonly reveal a much more intensive eraly diagenetic cementation than associated finer-grained sediments where even nearly no cementation can occur at the same time (Lighty 1985). S hinn & Robbin (1983) documented in experiments different the mode and degree of compaction can be in recent sediments. Similar experiments were carried out by Fruth et al. (1966), documenting the varying degrees of compacti-bility of wackestones, packstones and oolitic grainstones. These help to establish the following genetic model of differential compaction of the lateral deposited sediments in comparison to the more massive Sabotin patch reef limestone in different. The top of the basal unit-SO, which is characterized by a marked bed surface, is taken as horizontal time line upon which the patch reef dveloped by accumulation of organisms, growth franmework and cementation. The key for this model is documented best by the decreasing dip of correlation lines between profile B and A from bottom to top. It is obvious that the sediments of the unit-LBR have been most intensively compacted in profile A (25 m; more micritic) in com-parision to the massive limestones in profile B (34 m). Therein intensive cementation additionally to early binding and probabaly also in-situ carbonate production caused a more rigid structure. The overlying unit-ST reveals reversal compaction in comparison of 20 m in profile A to 15 m in profile B due to deposition of more granular sediments in the area profile 07-71-90.p65 86 Black A. The same can be concluded for the overlying unit-IT. It can be assumed that the base of the unit-BS has been a nearly horizontalline immediately after deposition of the micritic, fine-layered sediments. Consequently it becomes obvious that the main compaction must have occurred within the time span of about 50 m sediment-deposition overlying the patch reef. Furthermore a decrease in the degree of compaction from unit-LBR to unit-BS can be assumed which was caused by relief-egalisation due to sedimentation and early machanical compaction. Compaction went on after the depostion of sediments overlying the limestones studied. This resulted in a further deformation process also of micritic fine-bedded sediments which were primary sedimented horizontal. Thus differential compaction resulted in differences in thickness of about 10 m from the patch reef (profile B) to the more lagoonal influenced sediments (profile A) within a lateral distance of about 50 m. 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W i l s o n , J.L. 1975: Carboante facies in geologic history.- 471 pp., Springer – Berlin, Heidelberg, New York. 07-71-90.p65 88 Black APPENDIX List of microfossils: Profile A A2-44259 Palorbitolina lenticularis (Blumenbach) Arenobulimina sp. Verneuilina sp. A4-44257 Palorbitolina lenticularis (Blumenbach) A6-44272 Orbitolinidae Everticyclammina sp. A7-44263 Glomospira sp. Nezzazatinella sp. A8-44295 Salpingoporella dinarica Radoi~i} Vercorsella sp. Nezzazatinella sp. A13-44271 Debarina hahounerensis Fourcade, Raoult & Vila Earlandia conradi Arnaud-Vanneau Arenobulimina sp. Dobrogelina sp. Nezzazatinella sp. Vercorsella sp. A16-44291 Sabaudia minuta (Hofker) Vercorsella laurentii (Sartoni & Crescenti) Bolivinopsis sp. A18-44277 Salpingoporella dinarica Radoi~i} Dobrogelina sp. A19-44282 Praechrysalidina infracretacea Luperto Sinni Vercorsella cf. scarsellai (De Castro) Novalesia sp. Dobrogelina sp. A21-44293 (?) Salpingoporella dinarica Radoi~i} A22-44262 Salpingoporella dinarica Radoi~i} Glomospira urgoniana Arnaud-Vanneau Nezzazatinella sp. A24-44301 Salpingoporella dinarica Radoi~i} A26-44287 (?) Charopytes A28-44233 Halimedaceae Orbitolinidae Sabaudia minuta (Hofker) Glomospira urgoniana Arnaud-Vanneau Vercorsella laurentii (Sartoni & Crescenti) Debarina sp. 18. 09. 02, 20:38 Development of a Lithocodium (syn. Bacinella irregularis)-reef-mound- … 89 A29-44258 Sabaudia minuta (Hofker) Nezzazatinella sp. Glomospira sp. A30-44265 Cylindoporella ivanovici (Sokaè) Giraliarella? prismatica Arnaud-Vanneau Earlandia? conradi Arnaud-Vanneau Sabaudia minuta (Hofker) Nezzazatinella sp. Vercorsella sp. (?)Pseudocyclammina sp. Profile B B3-4428(?) Orbitolinidae – (?)Palorbitolina Earlandia? conradi Arnaud-Vanneau Nezzazatinella sp. Meandrospira sp. B5-44289 Orbitolinidae Glomospira sp. Andersenolina sp. B6-44267 Orbitolinidae – (?)Palorbitolina Verneuilina sp. B17-44283 Glomospira urgoniana Arnaud-Vanneau Vercorsella sp. Novalesia sp. Belorusiella sp. Nezzazatinella sp. B18/19 (?) Salpingoporella muehlbergii (Lorenz) (?) Cylindroporella sp. Vercorsella camposaurii Sartoni & Crescenti Pseudolituonella gavonensis Foury Sabaudia minuta (Hofker) Verneuilina sp. Nezzazatinella sp. Arenobulimina sp. Andersenolina sp. B20-44276 Salpingoporella muehlbergii (Lorenz) Vercorsella laurentii (Sartoni & Crescenti) Nezzazatinella sp. B21-44255 Salpingoporella muehlbergii (Lorenz) Pseudolituonella gavonensis Foury Nezzazatinella sp. B24-44298 Orbitolinidae Spiroloculina cretacea Reuss B25-44278 Polystrata alba (Pfender) Orbitolinidae B30-44260 Verneuilina polonica Cushman & Galzewki Vercorsella laurentii (Sartoni & Crescenti) Andersenolina sp. 07-71-90.p65 89 Black B32-44300 Vercorsella arenata Arnaud-Vanneau Nezzazatinella sp. B33-44275 Salpingoporella dinarica Radoi~i} Praechrysalidina infracretacea Luperto Sinni Sabaudia minuta (Hofker) Nezzazatinella sp. Vercorsella sp. B35-44286 Salpingoporella dinarica Radoi~i} B37-44285 Salpingoporella dinarica Radoi~i} Spiroloculina cretacea Reuss Vercorsella sp. Nezzazatinella sp. Bolivinopsis sp. Debarina sp. Earlandia? sp. Profile C C2-44299 Palorbitolina lenticularis (Blumenbach) C5-44290 Polystrata alba (Pfender) Palorbitolina lenticularis (Blumenbach) C8-44266 Earlandia? sp. Gaudryina sp. C10-44297 Vermiporella sp. Palorbitolina lenticularis (Blumenbach) C12-44402 Salpingoporella muehlbergii (Lorenz) Cylindroporella sp. Nautiloculina broennimanni Arnaud-Vanneau & Peybernes Sabaudia minuta (Hofker) Involutina sp. Vercorsella sp. Dobrogelina sp. C15-44294 Earlandia? sp. Vercorsella sp. C17-44296 Polystrata alba (Pfender) Vercorsella sp. C19-44296 Polystrata alba (Pfender) Orbitolinidae Charentia sp. Gaudryina sp. C20-44284 Orbitolinidae Sabaudia minuta (Hofker) Charentia cuvillieri Neumann Pseudolituonella conica Luperto Sinni & Masse Earlandia? conradi Arnaud-Vanneau 18. 09. 02, 20:38 90 Roman Koch, Esmail Moussavian, Bojan Ogorelec, Dragomir Skaberne & Ioan I. Bucur C22-44254 Salpingoporella dinarica Radoièic Pseudochrysalidina infracretacea Luperto Sinni Vercorsella sp. Nubecularia sp. Spiroloculina sp. Nezzazatinella sp. C28-44270 Salpingoporella dinarica Radoièic Praechrysalidina infracretacea Luperto Sinni Voloshinoides murgensis Luperto Sinni & Masse Arenobulimina sp. Dobrogelina sp. C35-44269 Praechysalidina infracretacea Luperto Sinni Arenobulimina cf. corniculum Arnaud-Vanneau C38-44288 Salpingoporella dinarica Radoièic (?) Cretacicladus menervini Luperto Sinni Praechrysalidina infracretacea Luperto Sinni Glomospira urgoniana Arnaud-Vanneau Dobrogelina sp. Arenobulimina sp. C40-44279 Salpingoporella dinarica Radoièic General list CALCAREOUS ALGAE Cylindoporella ivanovici (Soka~) Cylindroporella sp. (?) Cylindroporella sp. Salpingoporella muehlbergii (Lorenz) Salpingoporella dinarica Radoi~i} Halimedaceae Polystrata alba (Pfender) Vermiporella sp. (?) Cretacicladus menervini Luperto Sinni (?) Charophytes FORAMINIFERA Arenobulimina cf. corniculum Arnaud-Vanneau Charentia cuvillieri Neumann Debarina hahounerensis Fourcade, Raoult & Vila Earlandia? conradi Arnaud-Vanneau Giraliarella? prismatica Arnaud-Vanneau Glomospira urgoniana Arnaud-Vanneau Nautiloculina broennimanni Arnaud-Vanneau & Peybernes Palorbitolina lenticularis (Blumenbach) Praechrysalidina infracretacea Luperto Sinni Pseudolituonella conica Luperto Sinni & Masse Pseudolituonella gavonensis Foury Sabaudia minuta (Hofker) Spiroloculina cretacea Reuss Vercorsella arenata Arnaud-Vanneau Vercorsella camposaurii Sartoni & Crescenti Vercorsella laurentii (Sartoni & Crescenti) Vercorsella cf. scarsellai (De Castro) Verneuilina polonica Cushman & Galzewki Voloshinoides murgensis Luperto Sinni & Masse Andersenolina sp. Arenobulimina sp. Belorusiella sp. Bolivinopsis sp. Charentia sp. Debarina sp. Dobrogelina sp. Earlandia? sp. Everticyclammina sp. Gaudryina sp. Glomospira sp. Involutina sp. Meandrospira sp. Novalesia sp. Nezzazatinella sp. Nubecularia sp. (?)Pseudocyclammina sp. Spiroloculina sp. Vercorsella sp. Verneuilina sp. 07-71-90.p65 18. 09. 02, 20:38 90 Black