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)

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 finebedded 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 coarseto 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 mudstones and wackestones predominantly were analyzed in the so-called Sabotin-standardprofile 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 18. 09. 02, 20:37 71 Black doi: 10.5474/geologija.2002.006 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 interfingering with the general sedimentary textures intensively and resulting in larger „biogeniccemented“ 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.

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 interfingering with the general sedimentary textures intensively and resulting in larger "biogeniccemented" 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.

Introduction
Rudists, corals, and sponges (stromatoporoids, chaetetids) are the most important reef-forming elements of Cretaceous carbonate platforms (W i l s o n 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 (M a s s e & P h i l i p p 1981, K a u f f m a n & J o h n s o n 1988, M o u s s a v i a n 1992, H ö f l i n g 1997, S a nd e r s & H ö f l i n g 2000, H ö f l i n g & S c o t t 2002). Two essential basic reef-types are characteristic for the Cretaceous time interval. These are (1) mono-to paucispecific rudistbuildups and (2) coral-sponge-algae/coralalgae reefs. The rudist-population (mainly monopleurids, caprinids, radiolitids, hippuritids) commonly grows in bouquet-like buildups within a reduced commonly lagoonal environment with low diversity.
Coral or coral-sponge-dominated bioconstructions are best developed with highest diversity in a normal marine environment (open platform) of deeper water compared to the locations of the formation of rudistsbuildups (M o u s s a v i a n 1992, H ö f l i n g 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 & M a r i n 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 Lithocodium 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 Lithocodiumbuildups are valuable indicators for these specific environments in which only some very spezialized groups of organisms occur.
In the recent study a characteristic Lithocodium-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 (K o c  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 (B u s e r 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 (M l a k a r 1969, P l a c e r 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 (B u s e r 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).

Biostratigraphy
The whole assemblage of microfossils (appendix) indicate an Early Aptian (Bedoulian) age (S c h r o e d e r 1975, A r n a u d -V a n n e a u 1980, A r n a u d -V a n n e a u & C h i o c c i n i 1985, L u p e r t o S i n n i & M a s 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 Barremian to Early Aptian age. The most precise data given, are due to the occurrence of orbitolinids i.e. Palorbitolina lenticularis (B l um e n b a c h ) which indicate Early Aptian age.
Salpingoporella dinarica which has a general stratigraphic range from Valanginian to Albian (G r a n i e

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 profile-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.
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 Salpingoporella muehlbergi (L o r e n z ). The second one (unit-IT) in the upper part contains the  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. 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 monospecific 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 Lithocodium boundstones. Only in more massive beds of profile-B, rudists (up to 5 cm in size) are commonly in life position revealing biostromal growth forms and some small bundles (bouquets sensu H ö f l i n g 1997).
Benthic foraminifera are the main biogenic 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- 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.
2 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.
3 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.

4
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.

5
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.

6
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. 7

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). 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 requienids built biostrom-like thickets. The overlying unit-ST and unit-IT consists of a mixture of facies types (predominantly mudstones 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 finelaminated 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 Lithocodium reef-mound which has a thickness of 34 m and consists of succeccive Lithocodium 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 4 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 biogenic 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 intertidal (brackish ?) conditions are indicated by abundant birds-eyes and by vadose siltfillings (Pl. 2/6).

1-3 Palorbitolina lenticularis (Blumenbach
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 subtidal-intertidal). It is followed by unit-IT with more intertidal conditions as indicated by birds-eyes and microbial carbonates.

Characteristics of the Lithocodium
Lithocodium Lithocodium Lithocodium Lithocodium reef-mound As mentioned above, the "reef" was first noted due to it's marked and massive morphology in comparison to the bedded lagoonal 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 boundstones 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-tive amount of Lithocodium, forming boundstones 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) probabaly 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 Lithocodium Lithocodium Lithocodium 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 R a d o i~i } 1959, Pseudolithocodium M i s i k 1979, Bacinellacodium D r ag a s t a n 1985 and Radoicicinellopsis B a nn e r et al. 1990 which all seem to be synony-mous. Since E l l i o t t (1956) interpreted Lithocodium to be a green algae and R a d o i~i } (1959) regarded it as a microptroblematicum, such morphotypes were repeatedly attributed to different systematic groups, mainly of following systematic positions: Codiacean green algae (B a n n e r et al. 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 E l l i o t t 1956, M i s i k 1979, B a n 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 micritic Mg-calcite.
These characteristics resemble more to sponge than to any other organism. The new observations show that the systematic affinity of Lithocodium remains an open question inspite the frequent hypothesis as disccussed above.

Constructional type of Lithocodium Lithocodium Lithocodium Lithocodium 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" (M o u s s a v i a n 1995) within the "binder guild" (F a g e r s t r o m 1987, 1988).
Covering a facies of oolitic-bearing sands (unit-SO with superficial ooids), Lithocodium led to local fixing of fossil-rich wackestones 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 & R e i t n e r 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 environments.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 Lithocodiumencrustation sequences and associated rudist-lenses separated from each other by bioclastic 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 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 cyanobacteriamats, 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 Lithocodium. The marked morphology of the buildup is additonally forced by diffrential compaction of the neighboured lagoonal sediments which are more micritic and therefeore probably not so intensively lithified as the pack-and grainstones of the buildup.
Within the Triassic to Cretaceous Lithocodium is found more commonly in generally reduced internal platform settings than in external platform areas (E l l i o t t 1956, R a d o i~i } 1959, M i s i k 1979, F l ü g e l 1979, A l s h a r a n 1985, 1987, B a n n e r et al. 1990, N e u w e i l e r & R e i t n e r 1992, H ö f l i n g 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 (M o u s s a v i a n 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. Differential compaction will occur wherever a compactible unit changes laterally in thickness or compactibility (L a b u t e & G r e t e n e r 1969). It is generally accepted that finer-grained sediments (micrite, clay) have a higher water content than coarsergrained sediments. This effect triggers the compactional behaviour of fine-grained sediments (B a y e r & W e t z e l 1989). Consequently the geometry of pores will be altered by early compaction (W e t z e l 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 strcutures 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 (L i g h t y 1985). S h i n n & R o b b i n (1983) documented in experiments different the mode and degree of compaction can be in recent sediments. Similar experiments were carried out by F r u t h et al. (1966), documenting the varying degrees of compactibility 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 comparision 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 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.