Biota, palaeoenvironments and biostratigraphy of continental Oligocene deposits of the South German Molasse Basin (Penzberg Syncline)

Six charophyte, 13 mollusc, four ostracod and nine fish otolith taxa are taxonomically described, and one fruit, one seed and two foraminiferal taxa are briefly noted from the Lower Cyrena Beds and the Lower Coloured Molasse of the Sindelsdorf section near Penzberg (approximately 50 km south of Munich). Our palaeoecological and lithological data from the Lower Cyrena Beds suggest a delta plain with lagoons, estuaries, slowly flowing rivers, lakes and swamps. Faunal and floral elements of the Lower Coloured Molasse indicate lacustrine environments. The gastropod Tympanotonos and the tropical to subtropical fish fauna (Eleotridae, Ambassidae and Cyprinodontidae) suggest a warm, at least subtropical climate. Furthermore, Tympanotonos suggests comparisons with Recent molluscan faunas of the mangrove swamps of the West African coast, and thus hints at mangrove vegetation bordering the coasts of the Upper Bavarian Molasse Sea. A biostratigraphical classification for the Oligocene Molasse deposits of the Penzberg Syncline is established for the first time based on otoliths and charophytes. The Lower Cyrena Beds are attributed to the newly defined otolith zone OT-O1/2 and probably correspond to the oldest part of the Chara microcera Zone. The lowermost part of the Lower Coloured Molasse can be correlated both with otolith zone OT-O2 and the Chara microcera Zone. The Sindelsdorf section lies within the Rupelian–Chattian transition zone and thus the chronostratigraphic age is approximately 29–28 Ma.     

Facies analysis and depositional environments of the Taulanne Limestone Formation in the South Alpine Foreland Basin (Oligocene, southeastern of France)

The Taulanne Limestone Formation of the Castellane region (South Alpine Foreland Basin of France) represents an Oligocene lake depositional system developed above the marine Nummulitic succession. A sedimentological analysis of the Taulanne limestone allows the identification of nine marine, lacustrine, and palustrine facies. The spatial and temporal distribution of these facies records five depositional sequences that are correlated between the Sant Peire section (edge of the lake) and the Prés section (central lake). Water-level variations highlight the high-frequency balance between drying and wetting periods under fluctuating climatic conditions. Lacustrine facies developed during more humid periods while palustrine facies correspond to more arid conditions and longer lake shoreline exposure. At the basin scale, the lateral changes in accommodation space are attributed to differential subsidence between the Prés and the Sant Peire sections, which permitted the deposition of a thicker succession in the central part of the lake (Prés section). The Taulanne limestone records a marine to continental transition. The progressive filling of the basin is related to the regional tectonic activity, namely the emplacement of the Embrun-Ubaye nappes to the northeast of the study area at about 30–32 Ma. This final regressive trend represents the transition between the underfilled flysch stage (marine Nummulitic succession) of a foreland-basin cycle to the overfilled stage (alluvial Red Molasse deposits) during the primary exhumation of the Internal Alps.     

Upper Ladinian to Lower Carnian sedimentary evolution in the Idrija-Cerkno Region,Western Sovenia

Summary An Upper Ladinian to Lower Carnian succession in the Idrija-Cerkno region (W Slovenia) is described and correlated with similar successions in the Dolomites. Structurally, the area belongs to the Rodne unit (Trnovo nappe, NW Dinarides). The succession was reconstructed from three stratigraphically superimposed sections. The Orehovska Grapa section is characterised by finegrained turbidites composed of sandy mudstones with intercalations of lenses and beds of trachy-andesite tuff and resedimented tuffs. Beds of hemipelagic light grey wackestone are rarely interstratified. These rocks are correlative with the Upper Ladinian Wengen Group. The Police1 section is composed of black shaly marls and mudstones, hemipelagic wackestone, tuffaceous sand-stones, and in the upper part, of calciturbidites overlain by black laminated shales. The section is correlated with the lower part of the San Cassiano Formation. The Police 2 section consists mainly of wavy bedded peloidal and bioclastic limestone, alternating with thin interbeds of shaly mudstones and marls. The limestone and mudstones are interpreted as tempestites and gradually pass into bedded and massive dolomite of Early Carnian age. This succession is similar to the transition from the San Cassiano Formation to the Cassian Dolomite. The studied succession represents a shallowing upward basinal sequence capped by carbonate platform deposits. Palaeogeographically it is a Late Ladinian transition from the carbonate platform in the south to the typical basinal area in the north.     

Middle Ottnangian (late Burdigalian) mollusks from the Rott Valley (SE Germany): the ultimate marine fauna of the Western Paratethys

The Bivalvia and Gastropoda from the Upper Marine Molasse deposits of the lower Rott Valley (North Alpine Foreland Basin, Lower Bavaria, SE Germany) comprise the first mollusk fauna of middle Ottnangian age (ca 17.5 Ma) to be documented in detail. Altogether, the assemblages from Brombach, Kainerding and Anzenkirchen yielded 27 species of Bivalvia and 9 species of Gastropoda. The bivalve species Spisula brombachensis n. sp. is described as new to science, and Aequipecten camaretensis is first reported from the Ottnangian of the North Alpine Foreland Basin. Furthermore, the well-preserved material allowed for the taxonomic revision of the Ottnangian index fossil Pecten herrmannseni. The bivalve community is dominated by suspension feeders, mostly shallow, soft bottom dwellers (Glycymeris, Anadara) and cementing epifauna (Ostrea). Gastropods almost exclusively comprise carnivorous browsers and predators. The parautochthonous assemblages are indicative of normal marine, well-oxygenized sandy-silty shoals at a water depth of presumably less than 20 m. Except for the presence of a single estuarine Crassostrea, the middle Ottnangian fauna is not indicative of reduced salinities. Consequently, the paleoenvironmental turnover to the brackish-water fauna of the directly overlying upper Ottnangian deposits of the Rzehakia Lake was abrupt. Glycymeris–Anadara–Ostrea communities similar to the one recorded from the Rott Valley are widespread in European seas and beyond during the Neogene and Quaternary.     

Upper Ordovician sequences of western Estonia

The Upper Ordovician (uppermost Caradoc-Ashgill) section of western Estonia consists of a series of seven open-shelf carbonate sequences. Depositional facies grade laterally through a series of shelf-to-basin facies belts: grain-supported facies (shallow shelf), mixed facies (middle shelf), mud-supported facies (deep shelf and slope) and black shale facies (basin). Locally, a stromatactis mud mound occurs in a middle-to-deep shelf position. Shallow-to-deep shelf facies occur widely across the Estonian Shelf and grade laterally through a transitional (slope) belt into the basinal deposits of the Livonian Basin.

Each sequence consists of a shallowing-upward, prograding facies succession. Sequences 1 (Upper Nabala Stage) and 2 (Vormsi Stage) record step-wise drowning of underlying shelf units (lower Nabala) that culminated in the deposition of the most basinal facies (Fjäcka Shale) in the Livonian Basin. Sequences 3–6 comprise the overlying Pirgu Stage and record the gradual expansion of shallow and middle-shelf facies across the Estonian Shelf. The Porkuni Stage (sequence 7) is bracketed by erosional surfaces and contains the shallowest-water facies of the preserved strata. The uppermost part of the section (Normalograptus persculptus biozone) is restricted to the Livonian Basin, and includes redeposited carbonate and siliciclastic grains; it is the lowstand systems tract of the lowest Silurian sequence 8. Sequence 7 and the overlying basinal redeposited material (i.e., the lowstand of sequence 8) correspond to the latest Ordovician (Hirnantian) glacial interval, and the bracketing unconformities are interpreted as the widely recognized early and late Hirnantian glacial maximums.

The sequences appear correlative to Upper Ordovician sequences in Laurentia. Graptolite biozones indicated that the Estonian sequences are equivalent to carbonate ramp sequences in the western United States (Great Basin) and mixed carbonate-siliciclastic sequences in the eastern United States (Appalachian Basin–Cincinnati Arch region). These correlations indicate a strong eustatic control over sequence development despite the contrasting tectonic settings of these basins.     

Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean

A substantial body of evidence suggests that subsurface water masses in mid‐Proterozoic marine basins were commonly anoxic, either euxinic (sulfidic) or ferruginous (free ferrous iron). To further document redox variations during this interval, a multiproxy geochemical and paleobiological investigation was conducted on the approximately 1000‐m‐thick Mesoproterozoic (Lower Riphean) Arlan Member of the Kaltasy Formation, central Russia. Iron speciation geochemistry, supported by organic geochemistry, redox‐sensitive trace element abundances, and pyrite sulfur isotope values, indicates that basinal calcareous shales of the Arlan Member were deposited beneath an oxygenated water column, and consistent with this interpretation, eukaryotic microfossils are abundant in basinal facies. The Rhenium–Osmium (Re–Os) systematics of the Arlan shales yield depositional ages of 1414 ± 40 and 1427 ± 43 Ma for two horizons near the base of the succession, consistent with previously proposed correlations. The presence of free oxygen in a basinal environment adds an important end member to Proterozoic redox heterogeneity, requiring an explanation in light of previous data from time‐equivalent basins. Very low total organic carbon contents in the Arlan Member are perhaps the key—oxic deep waters are more likely (under any level of atmospheric O₂) in oligotrophic systems with low export production. Documentation of a full range of redox heterogeneity in subsurface waters and the existence of local redox controls indicate that no single stratigraphic section or basin can adequately capture both the mean redox profile of Proterozoic oceans and its variance at any given point in time.     

Ichnological and Sedimentological Characteristics of Submarine Fan-Delta Deposits in a Half-Graben,Lower Cretaceous Palnatokes Bjerg Formation,NE Greenland

Fault-scarp related fan deltas developed in tilted half grabens in NE Greenland during late Jurassic—early Cretaceous rifting. This study documents ichnological and sedimentological characteristics of the Lower Cretaceous interval of a submarine fan-delta succession (Palnatokes Bjerg Formation, Wollaston Forland), which represents a time of waning rift activity and transgression. For this purpose, two variably exposed ca. 150 m-thick sections were studied ～10 km from the coeval fault scarp, near the axis of the most proximal fault block. Moreover, an additional ～20 m thick coeval succession was studied in the next fault block ～20 km from the coastline defining fault. The results indicate deposition on the basin floor, in the distal fan and in a mid-fan channel-overbank/splay complex of a subaqueous fan delta. The deposits are characterized mainly by various facies of high and low density turbidity currents, hybrid event beds, and transitional flow facies that grade upward into sediment starved basinal mudstones. The ichnological pattern recorded in these strata is strongly mixed, frequently containing elements of the impoverished Skolithos, Cruziana, Zoophycos ichnofacies, and more rarely of the Nereites ichnofacies. Characteristic features also include suites dominated by infaunal locomotion and feeding trails (including the “Curvolithus suite”) and the common occurrence of crustacean burrows. The results are indicative of a depositional system resembling a fjord-side delta that differs sedimentologically and ichnologically from many other gravity-flow systems of similar grain-size caliber. The ichnological pattern recorded in these strata is potentially a characteristic feature of the subaqueous fan-deltas in comparable settings, reflecting the distinct basin physiography with an abrupt change in bathymetry, a narrow basin geometry, and environmental stress resulting from unstable physical conditions. The counter slope of the rotated fault block may explain the common signs of flow concentration and abrupt fan termination.     

A Late Triassic lake system in East Greenland: facies, depositional cycles and palaeoclimate

The Upper Triassic Fleming Fjord Formation of the Jameson Land Basin in East Greenland contains a well-exposed succession, 200–300 m thick, of lake deposits. The Malmros Klint Member, 100–130 m thick, is composed of cyclically bedded intraformational conglomerates, red siltstones and fine-grained sandstones and disrupted dolomitic sediments (paleosols). The cyclicity is composite with cycles having mean thicknesses of (25), 5.9 and 1.6 m. The overlying Carlsberg Fjord beds of the Ørsted Dal Member, 80–115 m thick, are composed of structureless red mudstones rhythmically broken by thin greyish siltstones. This unit also has a composite cyclicity with cycles having mean thicknesses of 5.0 and 1.0 m. The uppermost Tait Bjerg Beds of the Ørsted Dal Member, 50–65 m thick, can be divided into two units. A lower unit is composed of cyclically bedded intraformational conglomerates or thin sandstones, red mudstones, greenish mudstones and yellowish marlstones. An upper unit is composed of relatively simple cycles of grey mudstones and yellowish marlstones. Recognized cycles have mean thicknesses of 5.6 and 1.6 m. The lake deposits contain evidence of seasonal, orbital and long-term climatic change. Seasonal change is documented by numerous desiccation surfaces especially in the Malmros Klint Member and Carlsberg Fjord beds, orbital change is suggested by the composite cyclicity, and long-term climatic change is indicated by the systematic upwards change in sedimentary characteristics of the lake deposits. The sedimentary features of the Malmros Klint Member suggest lacustrine deposition in a dry climate that fluctuated between desert and steppe conditions, the Carlsberg Fjord beds probably record lacustrine lake deposition in a rather constant dry (steppe) climate, while the Tait Bjerg Beds record lake sedimentation in a climate that fluctuated between dry (steppe) and warm moist temperate. In the Tait Bjerg Beds the upward change in cycle characteristics indicates a shift towards more humid conditions. Climatic deductions from sedimentary facies are in good agreement with climate maps of Laurasia, as simulated by numerical climate models. Palaeomagnetic data indicate a northward drift of East Greenland of about 10° from ca. 25°N to ca. 35°N in the Middle to Late Triassic. The Fleming Fjord Formation which represents ca. 5 m.y. of the Late Triassic interval was deposited during latitudinal drift of 1–2°. It is possible that the observed long-term upward shift in climatic indicators within the formation can be ascribed to plate drift, but southward shift of climatic belts could also have been of importance.     

Palynofacies and sedimentology-based high-resolution sequence stratigraphy of the lignite-bearing muddy coastal deposits (early Eocene) in the Vastan Lignite Mine, Gulf of Cambay, India

Geological records of early Paleogene warming are rare in low latitudinal regions. The Indian subcontinent preserves records of this global event on western and eastern margins. We attempt to decipher paleoenvironmental setup and facies architecture of the paleo-equatorial early Eocene succession at the Vastan Lignite Mine, Gulf of Cambay, western India. The Vastan lignite succession was deposited in a low-energy coastal marsh-bay complex receiving only fine-grained muddy sediments from the weathered Deccan Traps. The lower part of the Vastan lignite deposit, designated as “Vastan Succession A”, comprises four depositional facies representing distinct environments (open bay, restricted bay, creek and channel, and coastal marsh) and one diagenetic facies. Palynofacies analysis, backed by precise sedimentological framework, records changes in terrestrial supply and fluctuating marine characters of bay and marshes. Eleven Palyno-Units are identified in distinct lithofacies sequences stacked in shallowing-upward cycles representing five parasequences that constitute a Transgressive Systems Tract (TST) deposit. Each parasequence starts with a transgressive sheet deposit, followed by shallowing-upward bay fill-marsh deposits. In the vertical succession, each parasequence acquires increasing marine character, culminating in a maximum flooding surface (shell carbonate) that represents large-scale coastal onlap during early Ypresian time. The TST is followed by a Highstand Systems Tract deposit, which shows an erosional surface at the top of the upper lignite indicating Lowstand Systems Tract and a sequence boundary at ~52 Ma. The Vastan Succession A represents TST (3rd-order cycle) deposits with parasequences and hemicycles representing 4th- and 5th-order cycles. The study demonstrates sea level rise along the Indian western coastal margin in response to early Eocene warming between ~55 and ~52 Ma with maximum transgression at 53.7 Ma.     

Hydrodynamic control of sedimentation in the Ordovician (Arenig–Caradoc) Baltic Basin

Changes in mineralogy, geochemistry and grain size in a deep shelf succession from the Ordovician Baltic Basin are used to determine shifts in marine current direction and sea-level fluctuations. The analyses show a long-term, relatively stable interval in the Arenig–Llanvirn followed by shorter periods of perturbations and rearrangements in the early Caradoc. The Arenig deposits of the Aizpute-41 core have a high 2–10 µm terrigenous component. During the Llanvirn the proportion of this size fraction diminished. The grain size change was accompanied by mineralogical changes. In the early Caradoc the kaolinite disappeared, the muscovite content decreased, and quartz and albite increased. This and several geochemical indicators point to an input of considerable part of sediment from different sources than in the Arenig–Llanvirn. Two currents, a southwesterly for the Arenig and a westerly for the early Caradoc, are proposed. A red facies belt in the deep shelf marks the pathway of the Arenig–Llanvirn current. Smaller shifts in SiO₂/Al₂O₃ ratio in the Aizpute-41 section are interpreted as reflecting transgressions and regressions corresponding to regional stage boundaries.     

Cyclic sedimentation across a Middle Ordovician carbonate ramp (Duwibong Formation), Korea

Summary The Middle Ordovician Duwibong Formation (about 100 m thick), Korea, comprises various lithotypes deposited across a carbonate ramp. Their stacking patterns constitute several kinds of meter-scale, shallowing-upward carbonate cycles. Lithofacies associations are grouped into four depositional facies: deep- to mid-ramp, shoal-complex, lagoonal, and tidal-flat facies. These facies are composed of distinctive depositional cycles: deep subtidal, shallow subtidal, restricted marine, and peritidal cycles, respectively. The subtidal cycles are capped by subtidal lithofacies and indicate incomplete shallowing to the peritidal zone. The restricted marine and peritidal cycles are capped by tidal flat lithofacies and show evidence of subaerial exposure. These cycles were formed by higher frequency sea-level fluctuations with durations of 120 ky (fifth order), which were superimposed on the longer term sea-level events, and by sediment redistribution by storm-induced currents and waves. The stratigraphic succession of the Duwibong Formation represents a general regressive trend. The vertical facies change records the transition from a deep- to mid-ramp to shoal, to lagoon, into a peritidal zone. The depositional system of the Duwibong Formation was influenced by frequent storms, especially on the deep ramp to mid-ramp seaward of ooid shoals. The storm deposits comprise about 20% of the Duwibong sequence.     

Upper Cambrian-Ordovician successions overlying Timanian complexes: new evidence of acritarchs and brachiopods from Kolguev Island, Arctic Russia

Drillholes to several kilometres depth on Kolguev Island in the southern Barents Sea have sampled early Palaeozoic successions, known elsewhere in the Pechora Basin to overlie Neoproterozoic basement complexes. New studies on acritarch microfossils from the lowermost part of the Palaeozoic succession (c. 4500 m depth), reached by the Bugrino 1 and North-Western 202 boreholes, revealed diverse and biostratigraphically significant assemblages, which indicate the position of the Cambrian-Ordovician boundary in a sedimentologically continuous offshore marine succession. Upper Cambrian strata equivalent to the Peltura and Acerocare zones are distinguished on the basis of common taxa known from the neighbouring East European Platform and other areas in Baltica, Avalonia, and Gondwana. Invertebrate faunas, including brachiopods, problematic mollusc and phyllocarid arthropods, are revised taxonomically; they are indicative for the Tremadocian and Arenigian stages in the upper part of the succession. The Cambrian strata are insofar documented by fossil record only on the Kolguev Island, although their extension (of various series) in other areas of the Pechora Basin is claimed on the grounds of geophysical data and/or is inferred from geological successions. This new biostratigraphic evidence and facies development suggest that the Upper Cambrian-Tremadocian platformal deposits were likely widely distributed over the northeastern Baltica, as they were in the East European Platform and Baltoscandia. They were accumulated on a stable and passive margin of the craton with steady subsidence and a high rate of sedimentation.     

A sequence stratigraphic approach to a Middle Triassic shelf-slope complex of the Ligurian Alps (Ligurian Briançonnais,Monte Carmo-Rialto unit,Italy)

The Mesozoic sedimentary cover belonging to the Monte Carmo-Rialto unit of the Ligurian Briançonnais domain is composed of Scythian clastics and Anisian to Carnian carbonate rocks over 300 m thick. This paper focuses on the stratigraphy of this carbonate complex, its environmental significance, and its evolution in light of dynamic stratigraphy. Our facies analysis of limestones and dolomites of the Triassic complex allowed us to reconstruct an environmental model. Data support a distally steepened carbonate ramp of Anisian age evolving to a more diversified Ladinian platform with an oolitic sand-bar belt separating the lagoon from the slope. The Monte Carmo-Rialto slope facies are the only witnesses of deep sedimentation in the Triassic terrains of the Ligurian Briançonnais domain, otherwise represented by shallow-water carbonate deposits. On the basis of facies succession, we have identified nine medium-scale cycles (third-order sequences) in the study area, comparable to those evidenced in the Briançonnais s.s. domain by the French authors. Small-scale cycles analysis evidenced mainly shallowing-upward trends in the examined sequences; although a few evidences of transgression-related deposits (deepening upward cycles) have been found at the base three sequences, they have been mostly obliterated by dolomitization and masked by local tectonics. For this reason, we can undoubtedly distinguish only the part of each sequence belonging to HST, while the TST, though present, still remains a partition that cannot be precisely characterized. In the same way, LSTs are not present in the Monte Carmo-Rialto unit, due to the original relative landward position of the examined area. Sequence stratigraphy analysis indicates different long-term dynamics for the two evolutionary stages of the Triassic Ligurian platform: a general landward backstepping to moderate progradation during the Early Anisian and true progradation during the latest Anisian and Ladinian. In addition, a good fit with the sequences proposed by the SEPM chart has been found, indicating a correspondence for the third-order sequences of the Middle Triassic.     

Middle Miocene warm-temperate carbonates of Central Paratethys (Mt. Zrinska Gora, Croatia): paleoenvironmental reconstruction based on bryozoans, coralline red algae, foraminifera, and calcareous nannoplankton

Carbonate deposits from Zrin in the Mt. Zrinska Gora were deposited in the SW part of the Central Paratethys Sea during the Middle Badenian (Middle Miocene). The studied section contains a rich fossil community of non-geniculate coralline red algae (Subfamily Melobesioideae), bryozoans, benthic and planktonic foraminifera, echinoderms, ostracods, molluscs, and calcareous nannoplankton. Based on lithological variations and changes in the biogenic components, four facies associations (FA) are distinguished. Their distribution points to skeletal production and sedimentation on a middle to proximal outer carbonate ramp. The main lithological feature of the section is an alternation of two lithofacies: fully lithified grainstone–rudstone and packstone, and semi-lithified rudstone–floatstone with a carbonate sandy matrix. Depositional environments on the ramp were periodically influenced by minor high-frequency sea-level changes and/or changes of hydrodynamic conditions, which are suggested as the driving mechanisms causing the alternation of the two lithofacies. Vertically in the succession, the two lithofacies alternate to give three thinning- and fining-upward units. The lower part of each unit is formed of a rhodolith and coralline algal FA, which passes upwards into a bryozoan-coralline algal FA and/or FA of bioclastic packstone-grainstone. Based on the vertical upward change in FAs, each unit can be interpreted as a deepening-upward sequence. Patterns in the relative abundance of bryozoan colony growth form (vinculariiform, cellariiform, adeoniform, membraniporiform, celleporiform, and reteporiform), size and abundance of rhodoliths and coralline branches, and benthic foraminifera are interpreted by comparison with data from modern and fossil environments. Based on these data, a water depth range for each FA is interpreted, providing evidence of low-frequency relative sea-level changes. It is hypothesized that relative sea-level fluctuated in the water depth range from 30 to 80 m, and in the uppermost part of the section, rich in planktonic foraminifera and calcareous nannoplankton, possibly deeper. Causes of the low-frequency relative sea-level fluctuations and the general deepening trend observed within the succession cannot be interpreted based on one section; however, they may be related to the subsidence of the depositional basin. The benthic biotic communities are a vertical alternation of rhodalgal and bryorhodalgal associations, and this is attributed to relative sea-level fluctuations. These biotic associations gave rise to warm-temperate carbonates of the Middle Badenian N9 planktonic Zone (Orbulina suturalis, O. universa) and NN4–NN5 nannoplankton Zones (Sphenolithus heteromorphus).     

Paleoecology of some molluscan assemblages from the badenian (Miocene) marine sandy facies of Poland

Three molluscan assemblages from the Badenian (Miocene) marine sandy facies of Poland are described in terms of their taxonomic composition, diversity, and trophic structure. The structural variation between the molluscan assemblages seems to be largely controlled by a gradient in water energy which in turn results in gradients in substrate mobility and organic content of bottom sediments. Together with a subordinate factor of local sedimentation rate, these gradients control the distribution of lucinoid mucus tube feeders vs. deep burrowing siphonate suspension feeders, of browsers, and of deposit feeders vs. suspension feeders. Some structural features of the molluscan assemblages are regarded as related to biotic factors. The graphs of cumulative species frequencies vs. the logarithm of cumulative individual frequencies are used as a measure of community organization. These graphs indicate distinct differences in ecological maturity between the molluscan assemblages. On this basis, two different stages of ecological succession in an offshore sandy bottom environment are recognized. The evidence from the comparison of the Miocene molluscan assemblages with their recent counterparts may support the view that the evolutionary stability of species populations of a given community, and long-term stability of the community structure are independent. High environmental variability and stress seem to be correlated with evolutionary stability of species populations rather than with long-term permanence of community structure.     

Stratigraphy, age and environments of the late Miocene Mpesida Beds, Tugen Hills, Kenya.

Interpretations of faunal assemblages from the late Miocene Mpesida Beds in the Tugen Hills of the Central Kenyan Rift Valley have figured prominently in discussions of faunal turnover and establishment of the modern East African communities. These faunal changes have important implications for the divergence of the human lineage from the African apes ca. 8-5 Ma. While fossil material recovered from the Mpesida Beds has traditionally been analyzed collectively, accumulating evidence indicates that Mpesida facies span the 7-6 Ma interval and are scattered more than 25 km along the eastern flanks of the Tugen Hills. Stratigraphic distinctions between Mpesida facies and younger sediments in the sequence, such as the Lukeino Formation, are not yet fully resolved, further complicating temporal assessments and stratigraphic context of Mpesida facies. These issues are discussed with specific reference to exposures of Mpesida facies at Rurmoch, where large fossil tree fragments were swept up in an ancient ash flow. Preserved anatomical features of the fossil wood as well as estimated tree heights suggest a wet, lowland rainforest in this portion of the rift valley. Stable isotopic analyses of fossil enamel and paleosol components indicate the presence of more open habitats locally. Overlying air-fall tuffs and epiclastic debris, possibly associated with the ash flow, have yielded an assemblage of vertebrate fossils including two teeth belonging to one of the earliest colombines of typical body size known from Africa, after the rather small Microcolobus. Single-crystal, laser-fusion,(40)Ar/(39)Ar dates from a capping trachyte flow as well as tuffs just below the lava contact indicate an age of greater than 6.37 Ma for the fossil material.     

Upper Devonian shoal-water delta integrated with cyclic back-reef facies off the Mowanbini Archipelago (Canning Basin), Western Australia

The Oscar Range in Western Australia’s Canning Basin exhibits folded Proterozoic, quartzite, quartzite conglomerate, phyllite, and metavolcanic rocks that survive with positive relief. Facies of the Pillara Limestone were deposited around this relief during Late Devonian (Frasnian) time. A segment of the Great Devonian Barrier Reef with a linear reef margin strikes parallel to the outer paleoislands in the Mowanbini Archipelago. A more sheltered strait separates inner islands from the cratonic Devonian mainland on the Kimberley Block. Large fan-deltas emanated from the craton, but locally small shoal-water deltas prograded from a drainage basin on one of the larger paleoislands in the Oscar Range. That island is expressed today by local topography exhumed from beneath a cover of former Devonian, Carboniferous, and Permian strata. The Devonian shoal-water delta rests unconformably on tilted Proterozoic phyllite and incorporates abundant phyllitic debris accumulated under fluvial to shoreface conditions. Some quartzite pebbles and hydrothermal quartz were derived from a source more than a kilometer away. Rare gastropods and stromatoporoid fragments in the deltaic sediments were abraded from the adjacent reef margin. The clast-supported conglomerate in the exposed shoal-water delta is mapped over a distance of 130 m to within 15 m of the inner reef margin, exposed nearby on steeply dipping phyllite. A cyclic succession of mixed clastic and carbonate parasequences, 31.5 m in thickness, follows above a disconformity surface on the delta-top facies. The overall succession represents a minor fall in relative sea level associated with erosion of delta facies and a major transgression characterized by a retrograde parasequence stacking pattern. The succession shifts through siliciclastic-rich shoreface to intertidal distal back-reef facies, ending with a subtidal, siliciclastic-poor proximal back-reef facies. The study demonstrates how variability in sedimentary cycles is influenced by local paleogeographic constraints in an island system dominated by quartzite highlands and phyllite lowlands.     

Salinity reduction of the end-Triassic sea from the Alpine region into northwestern Europe

A palaeoecological analysis of the Penarth Group (='Rhaetic') of southern England and Wales is undertaken in terms of a species-richness comparison with the Zlambach and Kössen Beds of the Austrian Alps. The three groups studied, bivalves, foraminifers and ostracodes, comprise the most important invertebrate faunas occurring in the deposits cited. All show significant diversity from the Alps into northwest Europe. Coupled with the disappearance of stenohaline elements including ammonites, and taking into account other facies information, the evidence suggests a transgression of a shallow epicontinental sea in northwest Europe at the end of the Triassic. The salinity of this sea (˜25–30%□) was appreciably below that of the Tethyan ocean.     

Ammonite succession at the Bajocian/Bathonian boundary in the Cabo Mondego region (Portugal)

The Cabo Mondego outcrops exposed along the cliffs, on the western margin of the Iberian Plate, show an expanded stratigraphic section of Lower Bathonian deposits containing abundant ammonoids. Upper Bajocian deposits correspond to similar facies, of muddy limestones alternating with marlstones, although ammonoids are scarce. A detailed succession of ammonites across the Bajocian/Bathonian boundary has been recognized at Cabo Mondego, which can form a useful bio‐ and chronostratigraphic standard for the Lusitanian Basin. The revision of previous collections from the classical section and new field samplings of two other separate sections allow the recognition through up to twenty metres of thickness, the highest zone of Bajocian (Parkinsoni Zone) and the lowest zone of Bathonian (Zigzag Zone). The Parkinsoni and the Zigzag zones established for NW European areas and belonging to the Northwest European Province, can be identified in the Lusitanian Basin, although the ammonite fossil assemblages are composed of Submediterranean taxa. However, a subdivision of the Parkinsoni Zone is not possible, due to the scarcity of well preserved ammonoids. The Zigzag Zone can be recognized and characterized as composed of two subunits (Parvum and Macrescens subzones) as represented in diverse European basins of the Submediterranean Province. Ammonite fossil assemblages of the Parvum Subzone may be grouped into two successive horizons, which are biochronostratigraphically equivalent to the subdivisions of the Convergens Subzone distinguished in the Digne‐Barrême area (SE France). New biochronostratigraphic data on the Bigotitinae, youngest members of Leptosphinctinae and oldest members of Zigzagiceratinae are relevant in understanding the evolution and faunal turnover of the West Tethyan Perisphinctidae during earliest Bathonian. The ammonite succession at the Bajocian/Bathonian boundary in the Cabo Mondego region (Portugal) represents one of the most complete biostratigraphic records so far recognized on the Iberian Plate.     

Microbial carbonates and corals on the marginal French Jura platform (Late Oxfordian,Molinges section)

Molinges was located on an Upper Jurassic ramp system of low-energy regime that developed at the southern margin of the French Jura platform. The sedimentary succession is characterized by the transition from a mixed siliciclastic-carbonate to a carbonate depositional setting that occurred during a long-term shallowing-upward trend. The disappearance of siliciclastics is explained by a climatic change, from humid and cold to drier and warmer conditions, previously identified in Late Oxfordian adjacent basins. The base of the section shows marl-limestone alternations of outer ramp. In its middle part, the section displays oncolitic marls, coral-microbialite beds and oncolitic limestones that deposited in a mid ramp position. Finally, the upper section part is made of oolitic limestones of inner ramp. In outer- to mid-ramp settings submitted to terrigenous inputs, the stacking pattern of deposits and facies evolution allow the identification of elementary, small-, medium-, and large-scale sequences. Small amplitudes of sea-level variations probably controlled rapid shifts of facies belts and reef window occurrences. In small-scale sequences, the coral beds developed during periods of sea-level rise. The decreasing rate of sea-level rise is marked by the downramp shift of the oncolitic limestone belt that led to the demise of coral-microbialite beds. These bioconstructions are mainly represented by thin biostromes in which corals never reach great sizes. The coral assemblages mainly include the genera Enallhelia, Dimorpharaea, Thamnasteria, and some solitary forms (Montlivaltia and Epistreptophyllum). They suggest relatively low-mesotrophic conditions in marine waters during the edification of the primary framework. Relatively cold water temperatures and periods of more elevated nutrient contents are probably responsible of the reduced coral development and the formation of a large amount of microbialites.