Middle Jurassic stromatactis mud-mound in the Pieniny Klippen Belt (Western Carpathians)

Summary A stromatactis mud-mound has been found near Slavnické Podhorie in the Czorsztyn Unit of the Pieniny Klippen Belt (Western Carpathians, Slovakia). Its stratigraphic range is Bathonian to Callovian and it is one of the youngest known true stromatactis mud-mounds. The complete shape the mound is not visible since the klippe is a tectonic block encompassed by younger Cretaceous marls. The matrix is micritic to pelmicritic mudstone, wackestone to packstone with pelecypods, brachiopods, ammonites, and crinoids. An important component of the mound is stromatactis cavities that occur as low as the underlying Bajocian-Bathonian crinoidal limestones. The stromatactis cavities are filled by radiaxial fibrous calcite (RFC) as well as in some places by internal sediment and, finally, by clear blocky calcite. Some cavities remain open with empty voids in the centres. In some stromatactis cavities, tests of cavedwelling ostracodsPokornyopsis sp. were found, surrounded by the latest stages of the RFC. This indicates that stromatactis cavities formed an open network enabling migration of the ostracods and their larvae over a period of time. Except in the case of the stromatactis cavities, there are numerous examples of seeming recrystallizationsensu Black (1952) and Ross et al. (1975) and Bathurst (1977). The radiaxial fibrous calcite encloses patches of matrix and isolated allochems. The RFC crystals are oriented perpendicularly to the substrate whether it is a cavity wall or enclosed allochems. This means that the RFC crystals could not grow from the centre of the cavity outward as postulated by Ross et al. (1975). There are also numerous “floating” isolated allochems, which are much smaller than the surrounding RFC crystals. The explanation involving three-dimensional interconnection of allochems seems to be unlikely. In the discussed mud-mound there is a conflict between apparently empty cavities that had to exist in the sediment and seeming “recrystallization” related to the same RFC that forms the initial void filling. The authors favor an alternative explanation of the “recrystallization”. We presume that the allochems served as nucleation points on which the crystals started to grow. Obviously, the allochems and the micritic patches were different from the surrounding material. RFC crystals (either short-or long-bladed) of the “recrystallization” spar grew at the expense of decaying microbial mucillages. The mucus can enclose peloids, allochems, or whole micritic patches that “floated” in the cavity and served as nucleation sites for the RFC crystals. The entire mud-mound represents a microbially bound autochthonous micritic mass; the stromatactis and stromatactis-like cavities originated where purer mucillage patches occurred, giving rise to open spaces. Such features as the morphological variety of stromatactis fabrics, the pervasive penetration of the sparry calcite into matrix, and the enclosure of the “floated” allochems and mudstone patches by sparry calcite, seem to provide support for the presence of mucus aggregates within the mound body. The mucus might be related to protozoans rather than to sponges or other well organized metazoan organisms. Occurrence of the stromatactis cavities in the underlying Bajocian-Bathonian crinoidal limestones support the inference on biological origin of the stromatactis fabrics. The alternative inorganic models of stromatactis origin (e.g., internal erosion or water-escape) are hardly applicable to the sediment formed by crinoidal skeletal detritus.     

Microfacies and diagenesis of an upper oxfordian carbonate buildup in Mydlniki (Cracow Area,Southern Poland)

Summary A carbonate buildup near the top of the Upper Jurassic limestone sequence in the Cracow area with a rigid framework built ofTubiphytes and thrombolites, and some fragments of encrusted siliceous sponges and serpules is described. The limestones form a dome-like elevation at the eastern wall of a 15 m high quarry flanked on both sides by stratified limestones with cherts. Six microfacies have been distinguished within the buildup: (1)Tubiphytes/thrombolite boundstone and (2) bioclasticTubiphytes/thrombolite wackestone dominate in the central and bottom part of the buildup. They gradually replace the cyanobacterial crusts and siliceous sponges (3. sponge-algal boundstone), which are sporadically the rock-forming elements in the basal part of the buildup as well as the top. Serpules randomly distributed within the buildup also form small cm-sized structures with a rigid framework (4. serpula-peloid boundstone). (5) tuberoid-peloid wackestone/floatstone and (6) ooid intraclastic grainstone exhibit no significant distributional pattern. Bioclastic-peloidal packstone comprising material derived from the destruction of the buildup occurs in the highest part of the outcrop, overlying the buildup. The sediments of the buildup were subject to rapid lithification, evidence by borings and neptunian microdykes filled with internal sediments, as well as by fracturedTubiphytes. Numerous petrographic features indicate probable episodic emergence of the buildup during its growth; these include asymmetric dissolution textures, asymmetric cements, vadose crystal silt and calcite pseudomorphs after gypsum. Upper Oxfordian carbonate buildups in the Cracow area display various stages of evolution. The carbonate buildup in Mydlniki most closely resembles classical Upper Jurassic reefs.     

Platform-basin transect of a middle to late Jurassic large-scale carbonate platform system (Shotori mountains,Tabas area,east-central Iran)

Summary Following a phase of predominantly siliciclastic sedimentation in the Early and Middle Jurassic, a large-scale, low-latitude carbonate depositional system was established in the northern part of the Tabas Block, part of the central-east Iranian microplate, during the Callovian and persisted until the latest Oxfordian/Early Kimmeridgian. Running parallel to the present eastern block margin, a NNW/SSE-trending carbonate platform developed in an area characterized by reduced subsidence rates (Shotori Swell). The growth of this rimmed, flat-topped barrier platform strongly influenced the Upper Jurassic facies pattern and sedimentary history of the Tabas Block. The platform sediments, represented by the predominantly fine-grained carbonates of the Esfandiar Limestone Formation, pass eastward into slope to basin sediments of the Qal'eh Dokhtar Limestone Formation (platform-derived allochthonites, microbialites, and peri-platform muds). Towards the west, they interfinger with bedded limestones and marlstones (Kamar-e-Mehdi Formation), which were deposited in an extensive shelf lagoon. In a N−S direction, the Esfandiar Platform can be traced for about 170 km, in an E-W direction, the platform extended for at least 35–40 km. The width of the eastern slope of the platform is estimated at 10–15 km, the width of the western shelf lagoon varied considerably (>20–80 km). During the Late Callovian to Middle Oxfordian, the Esfandiar Platform flourished under arid climatic conditions and supplied the slope and basinal areas with large amounts of carbonates (suspended peri-platform muds and gravitational sediments). Export pulses of platform material, e.g. ooids and aggregate grains, into the slope and basinal system are interpreted as highstand shedding related to relative sealevel variations. The high-productivity phase was terminated in the Late Oxfordian when the eastern platform areas drowned and homogeneous deep water marls of the Upper Oxfordian to Kimmeridgian Korond Formation onlapped both the Qal'eh Dokhtar Limestone Formation and the drowned Esfandiar Limestone Formation. Tectonic instability, probably caused by faulting at the margins of the Tabas Block in connection with rotational movements of the east-central Iranian block assemblage, was responsible for the partial drowning of the eastern platform areas. In some areas, relicts of the platform persisted to produce shallow-water sediments into the Kimmeridgian.     

Possible origin of stromatactis-like cavities in Upper Jurassic sediments from the Wielkanoc quarry near Gołcza (Kraków–Częstochowa Upland,southern Poland)—experimental studies

Isolated stromatactis-like cavities were found in a microbial-sponge buildup exposed in the Wielkanoc quarry (eastern part of the Kraków-Częstochowa Upland). The cavities are filled with several generations of carbonate cements and with internal sediments. The top surfaces of internal sediments are flat or wavy, whereas the roofs of cavities are arcuate. The origin of cavities from the Kraków-Częstochowa Upland is difficult to constrain. It seems that the stromatactis-like cavities from the Wielkanoc quarry resulted, at least partly, from remodeling of open spaces left after dissolution of corals in incompletely lithified sediment. Dissolution of corals disturbed the primary stress field within the carbonate buildup and generated the secondary stress characterized by the appearance of compressional forces in the walls of cavities and tensional forces in their roofs. Thus, the lack of support of sediments over roofs of cavities after dissolution of corals resulted in their instability and collapse triggered by vibrations caused by various factors. One of such triggers might have been the rejuvenation of the Kraków-Lubliniec Fault Zone in the Late Jurassic or the collapse of reticular framework within the buildup. The material falling down from the roofs was deposited at the bottoms of cavities as an internal sediment. Results of experimental studies demonstrate that the arcuate shapes of the roof surfaces of cavities are related to compressional stress in the walls and tensional stress in their roofs.     

Middle Triassic basin evolution and stratigraphy in the Carnic Alps (Austria)

Summary A local intraplatform basin developed in the Gartnerkofel-Zielkofel area of the Carnic Alps (southern Carinthia, Austria) during the Middle Triassic (Ladinian). This basin was filled with a transgressive basinal sequence composed of the Uggowitz Formation and overlying Buchenstein Formation. At the northwestern slope of the Gartnerkofel, the platform carbonates of the Schlern Dolomite interfinger with the Buchenstein Formation, causing the formation of two depositional sequences. The Uggowitz Formation consists of the Uggowitz Breccia and the Kühweg Member. Sediments of the Uggowitz Breccia were formed by different types of gravity induced processes. The Kühweg Member is a thin sequence of silt-and fine-grained sandstones which were deposited in a slope to basin margin environment by turbidity currents. The overlying Buchenstein Formation consists of hemipelagic to pelagic limestones of Fassanian age with intercalated pyroclastic rocks (Pietra verde). Nodular limestones were deposited under slow rates of accumulation during a relative sea-level highstand. The uppermost Buchenstein Formation is composed of hemipelagic limestone beds with intercalated graded calcarenites and breccias of platform-derived debris, showing characteristics features of a fore-reef slope of the prograding Schlern Dolomite. Uggowitz Formation and basal Buchenstein Formation are interpreted as a transgressive systems tract, nodular limestones from the middle part of the Buchenstein Formation mark an early highstand systems tract, forereef slope sediments of the upper Buchenstein Formation formed during the beginning regression of a late highstand systems tract, the basal part of the overlying Schlern Dolomite probably reflects a lowstand systems tract. The intercalated bedded limestone facies within the Schlern Dolomite is characterized by large, platform derived blocks, slump structures, breccia beds, graded calcarenites and hemipelagic limestones indicating a forereef slope environent. This intercalated facies belongs to the Buchenstein Formation and interfingers with the Schlern Dolomite. Conodonts from this intercalated slope facies point to Late Fassanian age. Therefore, the two Middle Triassic depositional sequences of the Gartnerkofel area can be correlated with the depositional sequences ‘Ladinian 1’ and ‘Ladinian 2’ of the Dolomites, proposed byDe Zanche et al. (1993). A brief comparison with the basinal sequences of similar age of the karawanken Mountains and the Carnia is presented.     

Improving detection of foraminifera by cathodoluminescence

Cathodoluminescence (CL) studies of Lower–Middle Oxfordian marls and limestones, as well as clasts from the uppermost Turonian–?Early Coniacian conglomerates of the Cracow Upland (southern Poland), reveal that the CL view of foraminifers from some lithologies differs from that in transmitted light. In particular, the CL technique revealed abundant tests of planktonic species Globuligerina oxfordiana in the Middle Oxfordian glauconitic marls, which under transmitted light are either poorly visible or remain completely undetected. Bright red–orange luminescence characterizes originally hyaline aragonitic tests of G. oxfordiana, but also several calcitic benthic species, in spite of their different taxonomic position and original test structure and mineralogy. In sponge microbial boundstones, foraminifers generally do not show the CL emission, or show a weak luminescence. Similarly, Late Cretaceous foraminifera represented mostly by planktonic taxa were detected or their view was clearly improved under CL only in some clasts from the uppermost Turonian–?Early Coniacian conglomerates filling karstic cavities. In other clasts, foraminifera are clearly visible only under normal transmitted light, therefore the luminescence signature is highly spatially variable. These results indicate a strong influence of lithology and diagenesis and rather minor effects of shell structure on luminescence of microfossils. The CL technique can be a useful tool in the detection and documentation of abundance patterns of foraminifers that are poorly preserved under transmitted light.     

Birth and early evolution of a Jurassic escarpment: Monte Kumeta Western Sicily

Summary The accurate reconstruction of the facies architecture in the Jurassic succession of Monte Kumeta, coupled with a detailed biostratigraphy, allow to define dynamics and genetic factors controlling the conversion of a Bahamian-type carbonate platform to a pelagic escarpment. A change from tidalites to oolites i.e. from the restricted, interior lagoon to a more open-marine sandy depositional environment, records the establishment of a basin south of the Monte Kumeta sector in late Hettangian-Sinemurian times. The oolitic limestones are overlain by earliest Carixian bioclastic grainstones and packstones with micritized grains and by wackestones with radiolarians and sponge spicules, organized in thin sand prisms. The decrease of carbonate productivity indicated by these sediments records the dissection of the platform and the subsequent isolation of a submarine topographic high in the Monte Kumeta sector. Though based only on indirect evidence, it is suggested that a tectonically controlled scarp must have existed between the Monte Kumeta “high” and the basin. Progressive northward retreat of this scarp resulted in the conversion of a shallow platform sector into a gradually steepening slope, along which the distribution of sediments was controlled by repeated tectonic and gravity-induced modifications of the topography of the substrate. Vertical and lateral changes and geometrical relationships of the recognized lithofacies suggest that they were deposited on a stepped surface brought about mainly by, repeatedly reactivated basin ward dipping normal faults. This scenario is clearly reflected by the relationship of platform strata and the overlying encrinites of Carixian/Domerian age. The encrinite bodies show again a prismatic geometry, becoming thicker towards the south and filling the first generation of neptunian dykes. The top of the encrinites is marked by a peculiar jagged dissolution surface with dm-scale pinnacles capped by a thick ferromanganese crust. The formation of this peculiar surface could have been controlled by complex changes in water chemistry probably related to the Early Toarcian anoxic event. The crust itself is dissected by faults of decimetres to metres of throw, sometimes organized into small-scale positive flower structures. In the hollows/depressions of this highly articulated substrate pelagic sediments of Bajocian to Oxfordian age were deposited. They display a clearly onlapping relationship to the encrinites and to the carbonate platform beds. Their thickness rarely exceeds 4 to 5 meters and they are present also as neptunian dykes filling a dense network of fissures. During Late Callovian and Oxfordian times synsedimentary tectonics has intensified resulting in an increase of the inclination of the slope. This led to more and more abundant, gravitationally controlled deformations (slumping and sliding) of semi-lithified and unlithified sediments along the Monte Kumeta escarpment.     

Jurassic radiolarites in a Tethyan continental margin (Subbetic, southern Spain): palaeobathymetric and biostratigraphic considerations

A region of the pelagic Subbetic basin within the Southern Iberian Continental Margin is studied in lithostratigraphical and biostratigraphical detail. Jurassic radiolarites (Jarropa Radiolarite Formation, Bathonian–Oxfordian) interbedded with shallow-water marine limestones have been recognized. Underlying the radiolarites (Camarena Formation, Bajocian) are oolitic limestones showing shallowing-upward cycles with karstic surfaces on the top, corresponding to deposition on an isolated carbonate platform on volcanic edifices. The Milanos Formation (upper Kimmeridgian–Tithonian), overlying the radiolarites, contains calciclastic strata with hummocky cross-stratification, which indicate outer carbonate ramp deposition. In the Jarropa Radiolarite Formation some calcisiltite strata with hummocky cross-stratification have been found. The bathymetry of the Subbetic Jurassic pelagic sediments, including the radiolarites, is considered as moderate or shallow in depth. We suggest that the pelagic character of the Jurassic sediments in this margin and their equivalents in other Alpine domains is a consequence of distance from the continent (beyond the pericontinental platform) but not necessarily of depositional depth.     

Cyrtocrinids (Crinoidea) and associated stalked crinoids from the Lower/Middle Oxfordian (Upper Jurassic) shelfal deposits of southern Poland

Five cyrtocrinid crinoid taxa previously unknown from the epicratonic deposits of Poland, as well as associated millericrinids and isocrinids, are described. The studied materials were derived mainly from the Lower and Middle Oxfordian, but crinoids are also from uppermost Callovian and/or lowermost Oxfordian sediments of the Polish Jura Chain (southern Poland). The crinoids, preserved as more or less complete (e.g., basal circlets) cups, include Lonchocrinus dumortieri, Phyllocrinus belbekensis, Remisovicrinus polonicus, Remisovicrinus aff. polonicus, Tetracrinus moniliformis and Sclerocrinus sp. The occurrence of Remisovicrinus polonicus in the late Middle Oxfordian of the southern Poland is confirmed. Moreover, the present study extends the geographic range of all cyrtocrinid species studied and discusses their unusual environmental adaptations.     

An unusual brachiopod assemblage in a Late Jurassic (Kimmeridgian) stromatactis mud-mound of the Eastern Carpathians (Hăghimaş Mountains), Romania

An unusual fossil assemblage dominated by superabundant rhynchonellid brachiopods in a stromatactis mud-mound is recorded from the Hăghimaş Mountains (Eastern Carpathians), Romania. The mound mainly consists of bioclastic wackestones to packstones with a very rich macrofauna including crinoids, sponges, juvenile ammonites, and echinoids. The brachiopods represent a low-diversity but high-abundance association, dominated by the rhynchonellids Lacunosella and Septaliphoria. The taphonomical features of the fossil assemblage indicate an autochthonous fauna, with successive generations of brachiopods in life position and complete well-preserved individuals in different growth stage alongside an accessory population of crinoids and sponges. Brachiopod-brachiopod endosymbiotic life strategy is documented for the first time from a post-Paleozoic brachiopod assemblage. The mound reveals abundant stromatactis, filled by radiaxial fibrous or drusy calcite cement and internal polymud sediments. This is the first Late Jurassic (Kimmeridgian) stromatactis mud-mound identified in the Eastern Carpathians.     

Jurassic corals as emersion indicators

In Recent coral reefs, emersion has resulted in the development of special growth forms of colonial corals which have been named microatolls. These colonies grow almost exclusively in a horizontal direction. In the upper part of the colony, subaerial exposure leads to the decay of the living body. The growth then stops and the skeleton is later colonized by various boring and encrusting organisms. Here we show the first record of a massive Mesozoic coral colony displaying the main features of emersion. The colony has been collected in perireefal Oxfordian (Jurassic) limestones from the Jura Mountains (France). It is situated exactly at the expected place in a shallowing-upward sequence between infralittoral buildups and supralittoral limestones. We suggest that such growth structures could be more common than previously thought in ancient coralliferous sediments and add some new details to discriminate between these colonies.     

塔里木柯坪地层区中-上奥陶统萨尔干组碳酸盐岩微相和古地理

塔里木板块西北柯坪地层区中-上奥陶统萨尔干组的分布和相变受控于当时西浅东深的海底深度差异。萨尔干组的厚度10米左右,为富含有机物的黑色页岩并夹少量灰岩薄层或透镜体。位于研究区西南的伽师西克尔剖面缺失大部分奥陶纪地层,上奥陶统铁热克阿瓦提组碎屑岩不整合于下-中奥陶统鹰山组灰岩之上,中-晚奥陶世的大部分时段属于暴露海面的剥蚀区;北部乌什的亚科瑞克剖面无萨尔干组岩性单元,为红色居多且粒度偏粗的碎屑岩夹白云岩薄层,属于近岸带碎屑岩为主的沉积区。西克尔向东北延伸150km至柯坪羊吉坎亦无萨尔干组,与萨尔干组同期沉积的地层在此表现为大湾沟组上部浅海灰岩的相变,且与上奥陶统桑比阶坎岭组偏深水相的红色薄层含泥瘤状灰岩之间呈整合接触;由西向东出露于柯坪苏巴什沟、柯坪大湾沟、阿克苏四石厂3个剖面的萨尔干组黑色泥页岩指示典型的滞流盆地相,而夹含于萨尔干组下部和上部的薄层灰岩之微相特征差异甚为显著,表现为该组下部可见数层密集砂屑颗粒形成泥粒状灰岩或颗粒灰岩,可解释为西部相邻的浅海碳酸盐岩台地区灰岩经重力流搬运后的再沉积;而该组上部含生屑泥状灰岩则属滞流盆地相区类似于黑色页岩环境的正常沉积。从羊吉坎灰岩台地到苏巴什沟滞流盆地相之间距离仅20余千米,坡度偏大是导致重力流形成的主要原因。     

Early Triassic peritidal carbonate sedimentation on a Panthalassan seamount: the Jesmond succession,Cache Creek Terrane,British Columbia,Canada

The Jesmond succession of the Cache Creek Terrane in southern British Columbia records late Early Triassic peritidal carbonate sedimentation on a mudflat of a buildup resting upon a Panthalassan seamount. Conodont and foraminiferal biostratigraphy dates the succession as the uppermost Smithian to mid-Spathian. The study section (ca. 91 m thick) is dominated by fine-grained carbonates and organized into at least 12 shallowing-upwards cycles, each consisting of shallow subtidal facies and overlying intertidal facies. The former includes peloidal and skeletal limestones, flat-pebble conglomerates, stromatolitic bindstones, and oolitic grainstone, whereas the latter consists mainly of dolomicrite. The scarcity of skeletal debris, prevalence of microbialite, and intermittent intercalation of flat-pebble conglomerate facies imply environmentally harsh conditions in the mudflat. The study section also records a rapid sea-level fall near the Smithian-Spathian boundary followed by a gradual sea-level rise in the early to mid-Spathian.     

Taphonomic differentiation of Oxfordian ammonites from the Cracow Upland, Poland

Taphonomic analysis of Lower and Middle Oxfordian ammonites from the Cracow Upland, southern Poland (localities at Pod???e, Zalas, M?ynka) revealed differences in ammonite preservation. The studied ammonites, usually termed as external and internal moulds, show a more complex state of preservation. In the Middle Oxfordian glauconitic marls, ammonites are preserved as internal moulds with neomorphic calcite shells showing relics of the original internal structure. In the Middle Oxfordian platy peloidal limestones, ammonites are preserved mostly as external moulds, without septal suture, however under microscope might show relics of internal whorls and septa and/or subtle differences in sediment filling phragmocone chambers. In sponge–microbial bioherms and biostromes, ammonite internal moulds have shells, which in contrast to ammonites from glauconitic marls are not strictly neomorphic ones, but originated by shell dissolution and subsequent filling of moldic porosity by calcite cement. In sponge–microbial nodular limestones, the ammonites are strongly deformed and the outer wall is usually removed by dissolution under pressure. Other important taphonomic differences include the rate of compaction (highest in platy limestones), sedimentary infillings, microborings, encrustations and preservation of siphuncular tubes. The majority of the ammonites appear to be phragmocones; aptychi in all facies are rare. Siphuncular tubes are fossilized exclusively in oppeliids, only in specimens from glauconitic marls and platy limestones, although their other taphonomic attributes are different. Tubes seem to have fossilized due to microbially mediated phosphatization that could be favoured by a set of parameters which operated rather at the scale of ammonoid carcasses: closed, poorly oxygenated conditions, and reduced pH. Taphonomic processes were controlled by the sedimentary environment (fragmentation, sedimentary filling, phosphatization of siphuncular tubes), as well as by early and late diagenesis (neomorphic transformation, dissolution, cementation, compaction) influenced by lithology.     

Microbial boundstone dominated carbonate slope (Upper Carboniferous,N Spain): Microfacies,lithofacies distribution and stratal geometry

Summary The Carboniferous, particularly during the Serpukhovian and Bashkirian time, was a period of scarce shallow-water calcimicrobial-microbialite reef growth. Organic frameworks developed on high-rising platforms are, however, recorded in the Precaspian Basin subsurface, Kazakhstan, Russia, Japan and Spain and represent uncommon occurrences within the general trend of low accumulation rates and scarcity of shallow-water reefs. Sierra del Cuera (Cantabrian Mountains, N Spain) is a well-exposed high-rising carbonate platform of Late Carboniferous (Bashkirian-Moscovian) age with a microbial boundstone-dominated slope dipping from 20° up to 45°. Kilometer-scale continuous exposures allow the detailed documentation of slope geometry and lithofacies spatial distribution. This study aims to develop a depositional model of steep-margined Late Paleozoic platforms built by microbial carbonates and to contribute to the understanding of the controlling factors on lithofacies characteristics, stacking patterns, accumulation rates and evolution of the depositional architecture of systems, which differ from light-dependent coralgal platform margins. From the platform break to depths of nearly 300 m, the slope is dominated by massive cement-rich boundstone, which accumulated through the biologically induced precipitation of micrite. Boundstone facies (type A) with peloidal carbonate mud, fenestellid and fistuliporid bryozoans, sponge-like molds and primary cavities filled by radiaxial fibrous cement occurs all over the slope but dominates the deeper settings. Type B boundstone consists of globose centimeter-scale laminated accretionary structures, which commonly host botryoidal cement in growth cavities. The laminae nucleate around fenestellid bryozoans, sponges, Renalcis and Girvanella-like filaments. Type B boundstone typically occurs at depths between 20–150 m to locally more than 300 m and forms the bulk of the Bashkirian prograding slope. The uppermost slope boundstone (type C; between 0 and 20–100 m depth) includes peloidal micrite, radiaxial fibrous cement, bryozoans, sponge molds, Donezella, Renalcis, Girvanella, Ortonella, calcareous algae and calcitornellid foraminifers. From depths of 80–200 m to 450 m, 1–30 m thick lenses of crinoidal packstone, spiculitic wackestone, and bryozoan biocementstone with red-stained micrite matrix are episodically intercalated with boundstone and breccias. These layers increase in number from the uppermost Bashkirian to the Moscovian in parallel with the change from a rapidly prograding to an aggrading architecture. The red-stained strata share comparable features with Lower Carboniferous deeper-water mud-mound facies and were deposited during relative rises of sea level and pauses in boundstone production. Rapid relative sea-level rises might have been associated with changes in oceanographic conditions not favourable for thecalcimicrobial boundstone growth, such as upwelling of colder, nutrient-rich waters lifting the thermocline to depths of 80–200 m. Downslope of 150–300 m, boundstones interfinger with layers of matrix-free breccias, lenses of matrix-rich breccias, platform- and slope-derived grainstone and crinoidal packstone. Clast-supported breccias bound by radiaxial cement are produced by rock falls and avalanches coeval to boundstone growth. Matrix-rich breccias are debris flow deposits triggered by the accumulation of red-stained layers. Debris flows develop following the relative sea-level rises, which favour the deposition of micrite-rich lithofacies on the slope rather than being related to relative sea-level falls and subaerial exposures. The steep slope angles are the result of in situ growth and rapid stabilization by marine cement in the uppermost part, passing into a detrital talus, which rests at the angle of repose of noncohesive material. In the Moscovian, the aggradational architecture and steeper clinoforms are the result of increased accommodation space due to tectonic subsidence and due to a reduction of slope accumulation rates (from 240±45−605±35 m/My to 130±5 m/My). The increasing number of red-stained layers and the decrease of boundstone productivity are attributed to environmental changes in the adjacent basin, in particular during relative rises of sea level and to possible cooling due to icehouse conditions. The geometry of the depositional system appears to be controlled by boundstone growth rates. During the Bashkirian, the boundstone growth potential is at least 10 times greater than average values for ancient carbonate systems. The slope progradation rates (nearly 400–1000 m/My) are similar to the highest values deduced for the Holocene Bahamian prograding platform margin. The fundamental differences with modern systems are that progradation of the microbial-boundstone dominated steep slope is primarily controlled by boundstone growth rates rather than by highstand shedding from the platform top and that boundstone growth is largely independent from light and controlled by the physicochemical characteristics of seawater.     

Ultrastructures nouvelles et non identifiées dans les calcaires de l'oxfordien supérieur de la champagne berrichonne

A scanning microscope study of the upper Oxfordian foliated limestones of the western part of the Berry region of France has revealed new, but unidentified, well-conserved organisms, which are described and illustrated in this publication.     

Late Triassic sedimentary evolution of Slovenian Basin (eastern Southern Alps): description and correlation of the Slatnik Formation

Successions of the Slovenian Basin structurally belong to the easternmost Southern Alps. During the Late Triassic, they were part of the Adriatic continental margin. Norian–Rhaetian successions of the Slovenian Basin are characterized mainly by dolomite of the Bača Dolomite Formation. However, in the northern part of the basin, Late Triassic limestone is preserved above Bača Dolomite Formation and is formalized as the Slatnik Formation. It is composed of hemipelagic limestone alternating with resedimented limestones. The succession documents an upward progradation of the slope environment composed of three high-frequency cycles. Most prominent progradation is referred to the second, i.e., Early Rhaetian cycle. The Slatnik Formation ends with thin-bedded hemipelagic limestone that records the end-Triassic productivity crisis, or rapid sea-level fall. The overlying resedimented limestones of the Early Jurassic Krikov Formation, document the recovery of production and shedding from the adjacent carbonate platform.     

Origin and evolution of an Upper Jurassic complex of carbonate buildups from Zegarowe Rocks (Kraków–Wieluń Upland, Poland)

The Upper Jurassic complex of Zegarowe Rocks is situated on the Kraków–Wieluń Upland in southern Poland. The complex is dominated by massive limestones representing carbonate buildups. The successive stages of carbonate buildup development include: colonisation, aggradational growth and progradation phases. In the colonisation phase, on top of loose peloidal-ooid sands micritic peloidal thrombolites developed. Peloidal and agglutinated thrombolites and stromatolites proliferated during the aggradational growth phase, whereas the progradation phase was characterised by shallowing and related development of agglutinated stromatolites with coprolites. The latter were the effect of periodical stabilisation of detrital sediments by microbial mats. The Zegarowe Rocks complex developed upon an elevation of the Late Jurassic stable northern shelf of the Tethys. This elevation was formed due to local decrease in subsidence rate, induced by the presence of a Palaeozoic granitoid intrusion in the shelf substratum. The carbonate buildups of the Zegarowe Rocks complex, initially developing as sediment-starved mounds upon fault-controlled intraplatform highs under strongly restricted background sedimentation rate, were replaced by agglutinated microbial reefs.     

Pleistocene coral reefs associated with claystones, Southwestern Taiwan

 Scleractinian coral reefs, when coexistent with siliciclastic sediments, usually occur in association with deltaic or coastal sands. Nevertheless, Pleistocene reef limestones in southwestern Taiwan are developed in association with thick claystones that were deposited in a deeper-water environment. These reef limestones are characterized by: (1) rapid transition from underlying claystones upward to reefal limestones, (2) lateral interfingering with open-shelf claystones, (3) being overlain by terrestrial deposits or exposed with no covering strata, and (4) being located in close association with anticlines. The authors propose that these reef limestones developed on anticlinal ridges raised above the adjacent sea floor by thrust-front migration in a foreland setting. Accepted: 21 April 1998     

A microbial model for the Lower Devonian stromatactis mud mounds of the Montagne Noire (France)

Summary Lower Devonian mud mounds and stromatactis fabrics are exceptionally well exposed in quarry walls and industrially sawed blocks in the Montagne Noire in southern France. Interlayered red biomicrites and white to grey sparitic calcites form mounds up to 70 m high. The red biomicrites contain predominantly bryozoans, sponges and echinoderms. The sparitic layers show typical features of stromatactis fabrics, as outlined byBathurst (1982). We recognize two types of stromatactis fabrics: (1) Stromatactis type A: exentsive cavity systems filled by multiple cement generations, which are interpreted to be related to microbial mats, and (2) Stromatactis type B: smaller patches of blocky spar which are mainly diagenetic in origin, but show characteristic features of stromatactis. Type A is far more important in terms of rock volume. The cyclic interlayering of red biomicrites and sparitic layers is supposed to result from frequent changes in the composition of the mound biota. The bryozoan/sponge community was displaced by short term propagations of microbial mats during times of extremely low sedimentation. Sedimentation and thus the biotic community was probably determined by high frequency (6th order) sea level changes. Despite these changes, mound growth continued, because once established the ecological advantage over the surroundings was maintained by both communities alternating with each other. The microbial mats and the cavities they left after their decay were important for the stabilization of the mounds, the latter allowing for enormous quantities of dissolved carbonate to be transported and precipitated. We anticipate a close interrelation between mound formation and stromatactis formation, and we believe that it is not incidential that both, mud mounds and stromatactis, are mainly restricted to the same interval, namely the Paleozoic.