Open Marine Conditions Research Articles

Progressive opening of a shallow-marine bay (Oliete Subbasin, Spain) and the record of possible eustatic fall events near the Barremian-Aptian boundary

In this paper, we analyse the upper Barremian-lowermost Aptian Alacón Formation (Oliete subbasin, Maestrazgo Basin) of Spain to understand the progressive opening of a shallow-marine bay found on the northeastern margin of Iberia. The succession consists of four transgressive-regressive sequences (S1S4) bounded by widespread unconformities caused by rapid base-level fall. The transgressive interval of each sequence is characterized by relatively high detrital input and fresh-water inflow that caused the demise of shallow-marine benthic communities. The regressive interval of each sequence triggered progressive regeneration of the benthic carbonate producers. Sequences 1 and 2 consist of lacustrine to restricted shallow-marine facies, followed by accumulations of the gryphaeid oyster Ceratostreon , with progressive colonization of the bay by marine benthic communities subjected to frequent salinity oscillations. Sequences 3 and 4 represent the stabilization of open-marine conditions in the bay with widespread development of high-energy bioclastic tidal dunes. The long-term transgression around the Barremian-Aptian boundary, which gave rise to the progressive flooding of the Oliete bay, was episodically interrupted by shorter-term episodes of abrupt base-level fall, with the eventual subaerial exposure of the entire bay at the end of the deposition of the Alacón Formation. Our data suggest that the observed sequence architecture was mostly controlled by climatic and eustatic sea-level oscillations, with local synsedimentary tectonics having a minor impact. Two major sea-level fall events responsible for the discontinuities found on top of sequences 3 and 4 are possibly correlated to the cooling episodes close to the Barremian-Aptian boundary and during the earliest Aptian (predating the OAE 1a) described in many other worldwide basins. • The progressive opening of a shallow marine bay in Iberia (W Tethys) is documented. • Four sequences register progressive paleogeographical and paleoecological changes. • Sequence boundaries are tentatively linked to major cooling events KBa5 and KAp1.

Low-accommodation foreland basin response to long-term transgression: A record of change from continental-fluvial and marginal-marine to open-marine sequences over 60,000 km2 in the western Canada foreland basin

Low-accommodation foreland basins have been of recent interest because their stratigraphic architectures provide insight into the interaction of tectonic subsidence and eustasy. Aptian-aged strata in Alberta, Canada (McMurray Formation and Wabiskaw Member) were deposited under the influence of a continental-scale river that longitudinally transported and debouched sediment into the southward-transgressing Boreal Sea in the distal, low-accommodation Western Canada Foreland Basin (WCFB). In this study, we present a high-resolution stratigraphic framework for the McMurray-Wabiskaw interval, which was deposited during a long-term transgression. Using wireline logs from >20,000 wells and more than 500 cores, regional mapping focused on resolving stratigraphic relationships and the distribution of depositional environments across approximately 60,000 km2 in the Athabasca Oil Sands Region of northeastern Alberta. The studied stratigraphic interval is part of a third-order sequence: the McMurray Formation developed during a period of relative sea-level fall, lowstand, and early transgression, while the overlying Wabiskaw Member was deposited during late transgression. Within the McMurray Formation, superimposed fourth-order sea-level fluctuations in this low accommodation setting created a complex amalgam of deltaic strata vertically and laterally juxtaposed with valley-fill deposits. Relative sea-level rises resulted in rapid transgressions in which the shorelines migrated >400 km landward. Thin (5–15 m thick), widespread deltaic parasequence sets were deposited during subsequent sea-level highstands. During relative sea-level falls, fluvial meandering channel belts developed in downcutting valleys, with associated shorelines dramatically prograding basinward. In the Wabiskaw Member, continued sea-level rise coupled with potentially decreasing sediment supply resulted in the development of tide-influenced/dominated channels and bars in estuaries. The final phase of the third-order transgression was marked by a regional transgressive ravinement event and several southwestward backstepping wave-dominated shorefaces/strandplains. This low-accommodation foreland basin succession demonstrates a transition from deposition in continental fluvial and marginal-marine settings subject to high-frequency eustatic changes, to open-marine conditions over a long-term transgression.

Reconciling persistent sub-zero temperatures in the McMurdo Dry Valleys, Antarctica, with Neogene dynamic marine ice-sheet fluctuations

Abstract In the Ross Sea sector of Antarctica, periodic large-scale marine ice-sheet fluctuations since the mid-Miocene are recorded by drill core and seismic data, revealing a dynamic ice-sheet response to past increases in temperature and atmospheric CO2. In the adjacent, predominantly ice-free McMurdo Dry Valleys (MDVs), preserved terrestrial landscapes reflect persistent cold conditions and have been interpreted as indicators of a stable polar ice sheet, implying that the Antarctic Ice Sheet was largely insensitive during past warm periods. These disparate data-based perspectives highlight a long-standing debate around the past stability of the Antarctic Ice Sheet, with direct implications for the future ice-sheet response to ongoing climate warming. We reconcile marine records of dynamic ice-sheet behavior and episodic open-marine conditions with nearby ancient terrestrial landscapes recording consistent cold-polar conditions. Coupled ice-sheet and regional climate models nested at a high resolution are used to investigate surface temperatures in the MDVs during past warm periods. We find that high-elevation regions of the MDVs remain below freezing even when ice-free conditions prevail in the nearby Ross Sea. We compare observed landscapes with the spatial extent of modeled persistent cold conditions required for preservation of these ancient features, demonstrating that frozen MDVs landscapes could have coexisted with receded or collapsed ice sheets during past warm periods.

Biostratigraphic ages and depositional environments of the upper Oligocene to lower Miocene Veldhoven Formation in the central Roer Valley Rift System (SE Netherlands-NE Belgium)

Abstract Discussions on the age and the depositional environments of the Veldhoven Formation and its members are persistent in Belgium and the Netherlands. Uncertainties on stratigraphy and the constructive process of sediment accumulation continue today as a result of lack of data on this succession within the Roer Valley Rift System. The present study provides new information on the bio- and lithostratigraphy and facies from two boreholes based on dinoflagellate cyst taxa. The results were correlated by gamma-ray logs towards other key boreholes in the region and show a good consistency for stratigraphy and depositional environments for the members of the Veldhoven Formation. After marginal to restricted marine conditions in the latest Rupelian (early Oligocene), the start of deposition of the Veldhoven Formation marked the transition towards a higher sea level, expressed by increased glauconite contents and gamma-ray values. The Voort Member in the lower part of the Veldhoven Formation has an early to late Chattian (Late Oligocene) age and comprises predominantly shallow marine (fluctuating restricted to open marine) conditions. The lithology in the lower part of this unit is often very clayey but is coarsening upward into sands. The superjacent Wintelre Member has a latest Chattian to early Aquitanian (early Miocene) age. This member is distinct by its clayey nature which is expressed by relatively high gamma-ray values. Earlier studies suggest a deeper marine facies for the Wintelre Member compared to the Someren and Voort members. However, the dinoflagellate cyst assemblages in this unit are mostly dominated by a single genus indicating a restricted marine setting, including salinities that deviate from normal marine conditions, most probably due to minor ventilation by narrow or lack of connection to the Atlantic Ocean. A glacio-eustatic sea-level fall around the Oligocene/Miocene boundary limited the sea coverage to the strongest subsiding areas, where deposition of the Wintelre Member is recorded, while non-deposition or erosion occurred in the surrounding highs, hence creating an isolated (sub)basin. The superjacent Someren Member was deposited during the late Aquitanian to middle Burdigalian and consists of shallow to open marine clayey fine sands. Increasing clay contents indicate a gradual development towards a higher sea level, which coincide with upward increasing gamma-ray values. The biostratigraphic results of this study suggest that no major hiatuses are present in the differentially subsiding blocks of the Roer Valley Rift System during the late Oligocene to early Miocene.

Oceanographic and climatic influences on Trooz Glacier, Antarctica during the Holocene

To evaluate the significance of recent widespread glacial recession in the Antarctic Peninsula, it is imperative to extend the limited instrumented record of glacier change with long sedimentary archives of the Holocene. Reconstructing glacial histories that capture the variability of environments in the Antarctic Peninsula will enable better constraint of ocean and climate forcings on regional glacial stability. Two sediment cores are analyzed from the 2007 RV/IB N.B. Palmer cruise to Collins Bay, the embayment immediately offshore Trooz Glacier on the Graham Land coast, and provide an archive to test controls on long-term stability of outlet glaciers in an open bay setting. Radiocarbon and Lead-210 (a short-lived radioisotope) age-depth models provide a timeline for Trooz Glacier behavior and associated oceanographic changes over the last 10,000 years.Magnetic susceptibility, grain size, diatom assemblage, total organic carbon, nitrogen, and stable isotopes of organic carbon are utilized as proxies for changing glacial and ocean conditions. Outer Collins Bay deglaciated by ∼10000 cal yr B.P. Diatom abundance and organic content signal productivity increase during further glacial recession from ∼8900 to 6100 cal yr B.P., which coincided with upwelling of relatively warm Circumpolar Deep Water into the bay. High productivity, characterized by Thalassiosira antarctica-dominated diatom assemblages with prominence of Fragilariopsis kerguelensis, indicate open marine conditions with incursion of offshore currents into the bay from ∼6100 to 760 cal yr B.P. A sharp decrease in organic content, diatom abundance, and grain size indicate more sea ice and ice-tongue/ice-canopy advance from ∼760 to 240 cal yr B.P., when the floating ice canopy in outer Collins Bay retreated to near its present-day position and productivity increased. During the period of the 1950's to 1990's, Trooz Glacier was one of only two Antarctic Peninsula glaciers that advanced slightly. Over the Holocene, oceanographic forcing dominated the long-term stability of Trooz Glacier due to its open aspect, and it is unknown how Trooz Glacier will respond to continued influence of Circumpolar Deep Water in the future. Understanding ocean forcings on glacial stability, together with other local controls like drainage basin configuration and bay geometry, should help contextualize the modern retreat and improve prediction of glacial response to prevalent Circumpolar Deep Water circulation in this dynamic region.

Changing depositional environments in the semi-restricted Late Jurassic Leme\u0161 Basin (Outer Dinarides; Croatia)

The up to 450 m-thick Upper Jurassic Lemeš Formation includes organic-rich deep-water (max. ~ 300 m) sedimentary rocks deposited in the Lemeš Basin within the Adriatic Carbonate Platform (AdCP). The Lemeš Formation was investigated regarding (1) bio- and chemostratigraphy, (2) depositional environment, and (3) source rock potential. A multi-proxy approach—microfacies, Rock–Eval pyrolysis, maceral analysis, biomarkers, and stable isotope ratios—was used. Based on the results, the Lemeš Formation is subdivided from base to top into Lemeš Units 1–3. Deposition of deep-water sediments was related to a late Oxfordian deepening event causing open-marine conditions and accumulation of radiolarian-rich wackestones (Unit 1). Unit 2, which is about 50 m thick and Lower early Kimmeridgian (E. bimammatum to S. platynota, ammonite zones) in age, was deposited in a restricted, strongly oxygen-depleted basin. It consists of radiolarian pack- and grainstones with high amounts of kerogen type II-S organic matter (avg. TOC 3.57 wt.%). Although the biomass is predominantly marine algal and bacterial in origin, minor terrestrial organic matter that was transported from nearby land areas is also present. The overlying Unit 3 records a shallowing of the basin and a return to oxygenated conditions. The evolution of the Lemeš Basin is explained by buckling of the AdCP due to ophiolite obduction and compressional tectonics in the Inner Dinarides. Lemeš Unit 2 contains prolific oil-prone source rocks. Though thermally immature at the study location, these rocks could generate about 1.3 t of hydrocarbon per m2 surface area when mature.

Biostratigraphy, Depositional and Diagenetic Processes in Carbonate Rocks from Southern Lebanon: Impact on Porosity and Permeability

AbstractCarbonate rocks contain prolific hydrocarbon reserves all over the world, particularly in the Middle East. For exploration and production strategies, it is essential to understand carbonate reservoirs in terms of their internal characteristics, depositional environment, relative age, diagenetic processes and impact on petrophysical properties. This study has been performed on exposed Cretaceous, Paleocene and Miocene marine carbonate sedimentary sequences in two localities (Maghdoucheh and Qennarit) near the city of Sidon (Southern Lebanon). It represents the first comprehensive study that takes into consideration the carbonate reservoir facies, diagenetic history and reservoir quality in the area. Rocks at Maghdoucheh are mainly dominated by limestone beds showing sedimentary structures and erosive bases alternating with microfossil‐rich silty marls, related to a shallowing upward sequence in a restricted marine platform environment. Shells of benthic foraminifera and mollusks dominate the fossil assemblage extracted from the studied rocks. The microfossil and nannofossil assemblage detected in the Maghdoucheh sections indicates a middle Miocene age. Rocks at Qennarit are composed of mudstone/wackestone limestone beds rich in planktonic foraminifera and nannofossils related to open marine conditions. Based on the nannofossil content, rocks from Qennarit 1 and 2 are Paleocene and Cretaceous in age, respectively. Four main types of microfacies have been identified, i.e. (1) microbioclastic peloidal calcisiltite, (2) pelagic lime mudstone and wackestone with planktonic microfossils, (3) grainstone/packstone with abundant foraminifera and (4) fenestral bindstones, mudstones and packstones with porostromate microstructures. The porosity‐permeability (poroperm) analysis of representative samples reveals moderate to good porosity but very low permeability. This is mainly due to the presence of large moldic pores that are isolated in nature. The diagenetic features are dominated by micritization and dissolution (both fabric selective and non‐fabric selective). Among all diagenetic features, dissolution in both localities contributes to porosity enhancement, while micritization, cementation, compaction and the filled fractures have negative impacts on permeability; hence the overall reservoir quality.

Two turtles with soft tissue preservation from the platy limestones of Germany provide evidence for marine flipper adaptations in Late Jurassic thalassochelydians.

Late Jurassic deposits across Europe have yielded a rich fauna of extinct turtles. Although many of these turtles are recovered from marine deposits, it is unclear which of these taxa are habitually marine and which may be riverine species washed into nearby basins, as adaptations to open marine conditions are yet to be found. Two new fossils from the Late Jurassic of Germany provide unusually strong evidence for open marine adaptations. The first specimen is a partial shell and articulated hind limb from the Late Jurassic (early Tithonian) platy limestones of Schernfeld near Eichstätt, which preserves the integument of the hind limb as an imprint. The skin is fully covered by flat, polygonal scales, which stiffen the pes into a paddle. Although taxonomic attribution is not possible, similarities are apparent with Thalassemys. The second specimen is a large, articulated skeleton with hypertrophied limbs referable to Thalassemys bruntrutana from the Late Jurassic (early Late Kimmeridgian) platy limestone of Wattendorf, near Bamberg. Even though the skin is preserved as a phosphatic film, the scales are not preserved. This specimen can nevertheless be inferred to have had paddles stiffened by scales based on the pose in which they are preserved, the presence of epibionts between the digits, and by full morphological correspondence to the specimen from Schernfeld. An analysis of scalation in extant turtles demonstrated that elongate flippers stiffed by scales are a marine adaptation, in contrast to the elongate but flexible flippers of riverine turtles. Phylogenetic analysis suggests that Thalassemys bruntrutana is referable to the mostly Late Jurassic turtle clade Thalassochelydia. The marine adapted flippers of this taxon therefore evolved convergently with those of later clades of marine turtles. Although thalassochelydian fossils are restricted to Europe, with one notable exception from Argentina, their open marine adaptations combined with the interconnectivity of Jurassic oceans predict that the clade must have been even more wide-spread during that time.

The Sedimentology of the Late Campanian–Maastrichtian Sequence, Southwestern Iraq

Petrography, diagenesis, and facies analyses as well as the depositional environments of the late Campanian-Maastrichtian sequence in southwestern Iraq are studied in five keyholes. The sequence incorporates parts of the Hartha, Shiranish and Tayarat Formations. The Hartha Formation comprises creamy and organodetrital dolomite, grey dolomitic marl, and evaporites. The Shiranish Formation is composed of grey marl and claystone, whereas the Tayarat Formation is composed of grey ash, along with tough and fossiliferous dolomitic limestone inter-bedded with grey mudstone layers and/or wisps. Several diagenetic processes affected the sequence, such as neomorphic replacement, dissolution, dolomitization, and sulphate development. Some of these processes obliterated the primary textures.
 The late Campanian-Maastrichtian sequence consists of three microfacies (Dolomitic Intraclastic Limestone, Dolomitized Biomicrite, and Biomicrosparite Microfacies) and two lithofacies (Mudrock and Sulphates-Rock Lithofacies), in addition to Fine- to Medium-Crystalline Dolomite Lithotype.
 The Hartha Formation is evaporitic, possibly with supratidal sabkha deposits. The overlying Tayarat and Shiranish Formations reflect deposition in a warm tropical to subtropical reefal and open marine conditions, as deduced from faunal assemblages. Some effects of deep marine condition are evident by the presence of Shiranish facies. The sequence represents deposition in the central reef- fore reef area. The absence of isolated back-reef lagoon facies suggests that the reef was patchy without isolation of water in the middle shelf region. However, at the top of the sequence, i.e. at the end of the Cretaceous Period, restricted lagoons seem to have dominated the studied succession.

Depositional environments and sequence stratigraphy of post-last glacial maximum incised valley-fill, Malay Basin, northern Sunda Shelf

The alternating submergence and subaerial exposure of the low-gradient, shallow Sunda Shelf of southeast Asia during Quaternary interglacial-glacial cycles played an important role in ocean circulation and monsoonal climate through the interchange of Indian Ocean and Pacific Ocean waters. The Quaternary stratigraphic development of this margin is, however, poorly understood. This study uses a multi-proxy approach (AMS radiocarbon, bulk sediment magnetic susceptibility, X-ray fluorescence spectrometry, and foraminiferal assemblage data) to characterize environmental change and late Pleistocene to Holocene sequence stratigraphic architecture in 16 cores from the northern Sunda Shelf off the east coast of Peninsular Malaysia.Five chronostratigraphic units are recognized. Unit 1 is an inner shelf deposit dating from a late Pleistocene sea-level highstand (the highstand systems tract of the pre-LGM base-level cycle). Units 2–4 represent different paleoenvironmenal components of the transgressive systems tract (TST) of the most recent base-level cycle. Unit 2 is a late Pleistocene shallow open embayment deposit that formed during the post-LGM inundation of the paleo-Chao Phraya River valley as sea level rose. Unit 3 is composed of late Pleistocene to early Holocene paralic peat and organic-rich mud and is capped by a transgressive ravinement surface. Unit 4 is a shallow shelf unit deposited during the early Holocene transgression on the Sunda Shelf prior to ca. 6500 cal yr BP (the onset of the regional Holocene sea-level highstand). Unit 5 represents the mid-Holocene to recent highstand systems tract (HST) deposited from ca. 6500 cal yr BP to present.The incised paleovalleys of the paleo-Chao Phraya River and its tributaries provide more accommodation space for sediment accumulation than the surrounding shelf. However, the thinness of the Holocene sedimentary record, 2–3 m in the incised valleys compared to <1 m over the adjacent shelf, indicates that the LGM incised valleys were almost filled by fluvial and coastal plain sediments before open marine conditions returned near the beginning of the Holocene. The multi-proxy approach of this study elucidates the geologic response of this shelf to sea-level rise and the sequence stratigraphic development of tropical, siliciclastic-dominated shallow shelf depositional sequences.

Provenance and Sedimentary Context of Clay Mineralogy in an Evolving Forearc Basin, Upper Cretaceous-Paleogene and Eocene Mudstones, San Joaquin Valley, California

Mudstone samples from the Moreno (Upper Cretaceous-Paleocene) and Kreyenhagen (Eocene) formations are analysed using X-ray diffraction (XRD) and X-ray fluorescence (XRF) to determine their mineralogy. Smectite (Reichweite R0) is the predominant phyllosilicate present, 48% to 71.7% bulk rock mineralogy (excluding carbonate cemented and highly bio siliceous samples) and 70% to 98% of the &lt;2 μm clay fraction. Opal CT and less so cristobalite concentrations cause the main deviations from smectite dominance. Opal A is common only in the Upper Kreyenhagen. In the &lt;2 μm fraction, the Moreno Fm is significantly more smectite-rich than the Kreyenhagen Fm. Smectite in the Moreno Fm was derived from the alteration of volcaniclastic debris from contemporaneous rhyolitic-dacitic magmatic arc volcanism. No tuff is preserved. Smectite in the Kreyenhagen Fm was derived from intense sub-tropical weathering of granitoid-dioritic terrane during the hypothermal period in the early to mid-Eocene; the derivation from local volcanism is unlikely. All samples had chemical indices of alteration (CIA) indicative of intense weathering of source terrane. Ferriferous enrichment and the occurrence of locally common kaolinite are contributory evidence for the intensity of weathering. Low concentration (max. 7.5%) of clinoptilolite in the Lower Kreyenhagen is possibly indicative of more open marine conditions than in the Upper Kreyenhagen. There is no evidence of volumetrically significant silicate diagenesis. The main diagenetic mineralisation is restricted to low-temperature silica phase transitions.

Petrological, geochemical, and microfacies analysis of the Sylhet limestone, Bengal Basin, Bangladesh: implication for depositional environment and diagenesis

The fossiliferous Sylhet limestone formation of the Eocene age in the Bengal Basin is important for scientific and geoheritage study. This formation is exposed in the two locations of Bengal Basin; however, it is least studied. In this study, petrological, geochemical, and microfacies analysis of the Sylhet limestone was carried out by analyzing twenty-eight (28) samples from the two exposed sections and two underground (boreholes) in the Bengal Basin. The microscopic and XRD analysis shows that the calcite is the most dominant mineral in the studied samples along with some amount of dolomite, siderite, ankerite, pyrite, and quartz. The presence of the crystal structure of calcite, dolomite, quartz, and pyrite was confirmed through SEM-EDX. Geochemical results show that the samples are composed of high CaO (14.296 to 53.326%) with a significant amount of Fe2O3 (0.095 to 18.482%), Al2O3 (0.664 to 7.357%), K20 (0.83 to 2.274%), MgO (0.157 to 8.109%), and SiO2 (0.08 to 0.451%). Beside the major oxides, some minor and trace elements including Sr, Mn, Zr, Zn, Sc, Co, V, Ba, Ni, and Cu were also measured. Among these, Sr, V, Mn, and Cu concentration within the Sylhet limestone directly indicates its depositional environment at a shallow continental shelf in open marine condition and its diagenetic change to convert as dolomitic limestone. Geochemical characteristics indicate that the Sylhet limestone is highly dolomitized with high Ca/Mg ratio and was deposited in a low-energy shallow continental shelf marine depositional environment. Higher values of the Ca/Mg ratio of the studied samples also confirm lower salinity during its deposition. The presence of silica in the limestone was observed with a positive/negative correlation with Ca which implies that the silica is derived either from a terrestrial source due to increases of sediment supply during the Middle Eocene for the consequences of the Indo-Asian plate Himalayan Collision or dissolution from the siliceous shells of fossils that replace the calcite. Eight (08) microfacies (MFT) types were identified based on abundance of foraminifera or calcareous algae (e.g., Nummulites sp., Discocyclina sp., Alveolina sp., Quinqueloculina sp., Cibicides sp., Lenticulina sp., Ovulites sp.) which are similar to grainstone/packstone carbonate of 18 standard microfacies types (SMF 18). The observed SMF was deposited under restricted to open marine carbonate platform of shallow water depth at different hydrodynamic conditions.

The Kimmeridgian of the south-western margin of the Holy Cross Mts., central Poland: stratigraphy and facies development. Part I. From deep-neritic sponge megafacies to shallow water carbonates

The stratigraphical interval of the Kimmeridgian between the Bimammatum and the Hypselocylum zones in the SW margin of the Holy Cross Mts. shows a transition from the open shelf deep-neritic sponge megafacies to the shallow-water carbonate platform, including its development and decline. The uniform progradation of the shallow-water carbonate platform occurred at the end of the Planula Chron. Development of the shallow-water carbonate platform was controlled by climatic and tectonic factors. The former induced by orbital cyclicity resulted in changes of sea-level, revealed i.a. by the incoming of open-marine ammonite faunas, the latter were related to the synsedimentary activity of faults which resulted in contrasted facies changes. The episodically occurring strong influx of siliciclastic material was at least partly controlled by the tectonic activity. The newly elaborated formal lithostratigraphic subdivision takes into account the facies development of the succession in relation to climatically and tectonically induced changes. Such is e.g. the Małogoszcz Oolite Formation, corresponding to a single 100-kyr eccentricity cycle from the late Platynota Chron to the earliest Hypselocyclum Chron, bordered from the base and top by two transgressive climatically-controlled levels. The final stage of the shallow-water platform development at the end of the Hypselocyclum Chron was marked by the successive limitation of restricted environments, and the appearance of more open-marine conditions related to tectonic subsidence of the area of study. Comparison between the carbonate platform development of the Holy Cross Mts. in central Poland, and the coeval shallow-water carbonates of the Jura Mts. in northern Switzerland and south-eastern France provides an opportunity to consider similarities in the successions which can be attributed to the climatically-controlled sedimentary cyclicity and/or the wide-ranged tectonic phenomena. The palaeontological part of the study gives comments on the classification and phylogeny of ammonites of the families Ataxioceratidae and Aulacostephanidae.

Biostratigraphy and depositional environments of the Palaeocene–Eocene succession at Um El Huwaitat area, Eastern Desert, Egypt

The Palaeocene–Eocene succession in southwest Safaga, Eastern Desert, Egypt has been studied to determine its lithostratigraphic units, biostratigraphic zonation, microfacies association, and depositional environments. The variation in lithofacies allows the subdivision of the Danian–Ypresian interval into four lithostratigraphic units that are arranged, from base to top, as the Dakhla Shale (only its upper part), Tarawan Chalk, Esna Shale, and Thebes Formation (only its lower part). Moreover, the Esna Shale is further subdivided into four members, arranged from base to top, as El Hanadi, Dababiya Quarry, El Mahmiya, and Abu Had. The depositional setting is interpreted to primarily reflect the relative sea‐level changes. The planktonic/benthic (P/B) foraminiferal ratio is indicative of oscillations of depositional settings in normal open marine conditions, ranging from shallow inner to outer neritic environments. Biostratigraphically, the Palaeocene–Eocene succession in the studied area is subdivided into 12 biozones and subbiozones. These are correlated with the standard biozonation of the Palaeocene–Eocene. Deposition of the Palaeocene–Eocene succession in the studied area took place on a relatively stable shelf. Three lithofacies were recognized: shale, marl, and limestone. The shale lithofacies is differentiated into two sub‐lithofacies; pure shale and calcareous foraminiferal shale, whereas marl lithofacies contains abundant planktonic foraminifera. The encountered carbonate rocks comprise eight microfacies types. In addition, the studied interval is correlated with the Global Standard Stratotype Section and Point in the Dababiya section, south of Luxor, Egypt.

New species of the dinoflagellate cyst genus &amp;lt;i&amp;gt;Svalbardella&amp;lt;/i&amp;gt; Manum, 1960, emend. from the Paleogene and Neogene of the northern high to middle latitudes

Abstract. Species of the fusiform peridiniacean dinoflagellate cyst genera Svalbardella Manum, 1960, emend. (Eocene–Oligocene) and Palaeocystodinium Alberti, 1961 (Late Cretaceous–Miocene), have been examined from the high to middle latitudes of the Northern Hemisphere: Spitsbergen, Norwegian-Greenland Sea, Labrador Sea, western North Atlantic, and the North Sea basin. The genus Svalbardella is emended to comprise species with smooth or finely ornamented surfaces and for which one or both horns are bluntly rounded. Svalbardella clausii sp. nov. has a narrow range restricted to the lowermost Chattian (close to the NP24–NP25 boundary and within Chron C9n), and it therefore appears a useful stratigraphical marker. This species has a wide distribution across the North Atlantic, having been reported from the North Sea basin, western North Atlantic, and the Labrador Sea. Svalbardella clausii sp. nov. overlaps stratigraphically with the reoccurrence interval of Svalbardella cooksoniae Manum, 1960, and spans the Oi-2b cooling maximum. Its presence may therefore be related to the establishment of cooler surface waters at this time. Svalbardella kareniae sp. nov. has a discordant occurrence: Lower Oligocene and Lower Miocene of the Norwegian Sea at Deep Sea Drilling Project Site 338 and Ocean Drilling Program Site 643, respectively, and mid-Oligocene of the North Sea. Its distribution suggests that Svalbardella kareniae sp. nov. favours more open marine conditions. Palaeocystodinium obesum Fensome et al., 2009, described from offshore eastern Canada where it has a highest occurrence in the Lower Oligocene, is emended to include specimens with a finely ornamented periphragm and traces of tabulation in addition to the archeopyle.

Classification of the Paleoproterozoic Gulcheru Formation: Implications on Early Paleogeographic and Tectonic Evolution of the Cuddapah Basin, India

Abstract The Papaghni sub-basin of the Cuddapah basin is an arcuate NW-SE trending intracratonic basin, stretching from Kurnool in the NW to Guvvalacheruvu in the SE, in southern peninsular India. Despite of large number of researches, an understanding of the evolution of the basin is still elusive. The sub-basin preserves records of repeated opening and closing of Paleoproterozoic rifts along the zone of NW-SE trending axis in the East Dharwar craton. Present study was carried out along the southwestern margin of the Papaghni sub-basin, in and around Tadpatri-Gooty-Dhone area, where the successive litho-units are represented by two major unconformity-bound sequences. Each of these sequences are characterized by a distinctive set of litho-assemblage, deposited under diverse tectonic environments with highly variable modes and tempos of sedimentation in an extensional basin. The basin initiated at about 2 Ga and shortly evolved into a shallow sea, with development of wide siliciclastic shelf in an open marine condition, the Gulcheru Formation. Gradually, with time the siliciclastic shelf was replaced by an extensive stromatolitic carbonate platform, the Vempalle Formation. Dedicated fieldwork exemplifies that the initial basin-fill is characterized largely by several cycles of simple, but amalgamated and stacked fanglomerates (alluvial fan to fan-delta) systems developed from several single stream breaches onto the proximal setting of the basin, in a syn-rift setting. These fanglomerates display a fining upward sequence, which progressively passes up to high-energy coastal, tide-storm dominated shelf environments of post-rift setting. This study justifies the subdivision of the Gulcheru Formation into two formal lithostratigraphic members, the Daditota Member and the Karvipalle Member. The Daditota Member directly overlies the granitoid basement and grades upward to Karvipalle Member. Karvipalle Member, comprising predominantly of medium to fine-grained, reddish brown and white quartz arenites of stable shelf deposits, distinctly differs from the conglomerate and very coarse-grained mass-flow dominated deposits of the Daditota Member. The Vempalle Formation overlies the Gulcheru Formation with a gradational contact and consists of stromatolitic dolomite, oolite and shale, developed in a ramp type carbonate platform setting. Gradual transition from siliciclastic to carbonate sequence points to passive margin setting developed during the breakup of the supercontinent Kenorland. Disposition of proximal to distal sequences and northeastern, eastern and southeastern paleocurrent of the sequences advocate a NW-SE shoreline and eastern paleo-slope of the basin.

Tracing bottom-water redox conditions during deposition of Lower and Upper Jurassic organic-rich sedimentary rocks in the Lusitanian Basin (Portugal): Insights from inorganic geochemistry

The Lower Jurassic Água de Madeiros (AM Fm) and Vale das Fontes (VF Fm) Formations, and the Upper Jurassic Cabaços Formation (Cab Fm) are considered the most important units with petroleum source-rock potential in the Lusitanian Basin, and the likely sources for its widespread hydrocarbon occurrences. Nonetheless, the bottom-water redox conditions during their deposition remain debatable. To resolve this controversy, we investigated whole-rock inorganic geochemical data of the most significant organic-rich levels of the AM, VF and Cab Fms cropping out at basin scale. Significant variations in TOC, TS and redox-sensitive elements contents and their ratios are evident within and between the organic-rich levels of the studied units. A positive covariation between primary productivity proxies, TOC enrichment and paleo-redox proxies for the Lower Jurassic units clearly suggest an interdependence between enhanced primary productivity, organic matter accumulation and bottom-water redox conditions. For the AM Fm, the paleo-redox proxies indicate that the black shales deposition took place beneath bottom-waters that ranged from suboxic to strongly euxinic conditions, with a clear predominance of the latter. A TOC threshold of ~6–7 wt% clearly separates samples deposited under suboxic to anoxic conditions from those deposited under true euxinic conditions, and is interpreted as the minimum amount of organic matter (OM) accumulation within sediments required to sustain H2S production at rates that outpaced its consumption through precipitation of sulphides and/or OM sulphurization, allowing the diffusion of H2S to the bottom-waters. For the Vale das Fontes Fm, the paleo-redox proxies suggest a prevalence of suboxic to anoxic bottom-waters, despite all black shales displaying TOC contents greater than the above threshold. The less reducing conditions relative to the AM Fm euxinic black shales are attributed to: i) a larger proportion of continental OM; ii) lower reactivity of the OM reaching the sediment-water interface (decreasing oxygen consumption); and iii) higher availability of reactive iron (increasing the buffer effect to H2S produced through OM remineralization by sulphate-reducing bacteria). Both units display Mo-EF vs U-EF covariation patterns that deviate from the field of sediments deposited under unrestricted open-marine conditions, towards higher Mo enrichment relative to that of U, indicating an accelerated transport of aqueous Mo to the sediments, consistent with the operation of a metal-oxyhydroxide particulate shuttle linked to Mn and Fe redox cycling within the water column in a weakly-restricted basin. The Mo-COT regression-line slope indicates a moderate degree of bottom-water mass restriction, with [Mo]aq concentration of ~60–70% of the present-day seawater value and bottom-water renewal times of ~10–20 years, akin to the present-day Cariaco Basin. The redox conditions of the Cab Fm organic-rich levels are dependent on the location of the depositional environment in the basin, with deposition taking place beneath oxygenated bottom-waters at Cabo Mondego, and under suboxic conditions at Vale de Ventos and Pedrógão, the latter denoting a larger degree of oxygen depletion than the former. In this context, the overall potential for OM preservation should increase from Cabo Mondego to Vale de Ventos and Pedrógão.

Microbial Diversity Responding to Changes in Depositional Conditions during the Last Glacial and Interglacial Period: NE Ulleung Basin, East Sea (Sea of Japan)

Microbial interaction with minerals are significantly linked with depositional conditions during glacial and interglacial periods, providing a unique redox condition in the sedimentary process. Abiotic geophysical and geochemical properties, including sedimentary facies, magnetic susceptibility, grain size, clay mineralogy, and distribution of elemental compositions in the sediments, have been widely used to understand paleo-depositional environments. In this study, microbial abundance and diversity in the core sediments (6.7 m long) from the northeastern slope of Dokdo Island were adapted to characterize the conventionally defined sedimentary depositional units and conditions in light of microbial habitats. The units of interglacial (Unit 1, &lt;11.5 ka) and late glacial (Unit 2, 11.5–14.5 ka) periods in contrast to the glacial period (Unit 3, &gt;14.5 ka) were distinctively identified in the core, showing a sharp boundary marked by the laminated Mn-carbonate (CaM) mud between bioturbated (Unit 1 and 2) and laminated mud (Unit 3). Based on the marker beds and the occurrence of sedimentary facies, core sediments were divided into three units, Unit 1 (&lt;11.5 ka, interglacial), Unit 2 (11.5–14.5 ka, late glacial), and Unit 3 (&gt;14.5 ka, glacial), in descending order. The sedimentation rate (0.073 cm/year), which was three times higher than the average value for the East Sea (Sea of Japan) was measured in the late glacial period (Unit 2), indicating the settlement of suspended sediments from volcanic clay in the East Sea (Sea of Japan), including Doldo Island. The Fe and Mg-rich smectite groups in Unit 2 can be transported from volcanic sediments, such as from the volcanic island in the East Sea or the east side of Korea, while the significant appearance of the Al-rich smectite group in Unit 1 was likely transported from East China by the Tsushima Warm Current (TWC). The appearance of CaM indicates a redox condition in the sedimentary process because the formation of CaM is associated with an oxidation of Mn2+ forming Mn-oxide in the ocean, and a subsequent reduction of Mn-oxide occurred, likely due to Mn-reducing bacteria resulting in the local supersaturation of Mn2+ and the precipitation of CaM. The low sea level (−120 m) in the glacial period (Unit 3) may restrict water circulation, causing anoxic conditions compared to the late glacial period (Unit 2), inducing favorable redox conditions for the formation of CaM in the boundary of the two units. Indeed, Planctomycetaceae, including anaerobic ammonium oxidation (ANAMMOX) bacteria capable of oxidizing ammonium coupled with Mn-reduction, was identified in the CaM layer by Next Generation Sequencing (NGS). Furthermore, the appearance of aerobic bacteria, such as Alphaproteobacteria, Gammaproteobacteria, and Methylophaga, tightly coupled with the abundance of phytoplankton was significantly identified in Unit 1, suggesting open marine condition in the interglacial period. Bacterial species for each unit displayed a unique grouping in the phylogenetic tree, indicating the different paleo-depositional environments favorable for the microbial habitats during the glacial and interglacial periods.

Middle Eocene dinoflagellate cysts from the Tsoul section, eastern External Rif, Morocco: biostratigraphy and paleoenvironmental interpretations

This palynological study is carried out on the Eocene sediments in the Tsoul section, which is located in the Taza region, Tsoul Unit, eastern External Rif, northeastern Morocco. It aims their age assessment and paleoenvironmental interpretations, based on palynological data. The palynological content is diverse, well preserved and rich in organic-walled dinoflagellate cysts (dinocysts), whereas spores and pollen are rare. We identified 117 dinocyst species (including some reworked species), among which 6 species and 1 acme are good biostratigraphic markers of the Bartonian (middle Eocene). The main dinocyst bioevents that are used to assign the studied section to the Bartonian include the lowest occurrences (LOs) of Glaphyrocysta semitecta, Impagidinium dispertitum, Lentinia serrata, Membranophoridium aspinatum and Operculodinium divergens, the highest occurrence (HO) of Castellodinium compactum and the acme of Polysphaeridium spp. Regarding the paleoenvironment, the studied section was deposited in a marine environment, characterized by a low productivity inferred from the scarcity of peridinioid cysts and by important environmental changes ranging from restricted inner neritic (lagoon) conditions, inferred from the dominance of Homotryblium and Polysphaeridium, to outer neritic open marine conditions inferred from the dominance of Spiniferites.

Late Eocene to Early Oligocene palynostratigraphy of the Western Black Sea, Eastern Paratethys

The Eastern Thrace and Western Black Sea basins provide unique perspectives on the palaeogeographic reconstructions of the Paratethys. Although very thick and extensive Oligocene outcrops and well sections exist in the Thrace Basin, only a few comparable sections are available in the Black Sea onshore areas. In this study, five measured stratigraphic sections of Eocene to Oligocene age from the margins of the Western Black Sea were studied and palynomorph assemblages were identified quantitatively. Index dinoflagellate cyst events and a palynological biozonation as established in the Mediterranean were applied successfully. Priabonian units contain the Aal biozone, whereas Rupelian successions were represented by the Adi, Rac, Cin, and Hpu zones. Palynological analyses suggest that the youngest interval of the studied sections, the highest sample of Karaburun (2) and the upper part of Servez Beach, sit just above the Wetzeliella gochtii interval and are early-middle Rupelian in age (Cin and Hpu zones). The Karaburun (1) and the lower part of the Servez Beach sections represent W. gochtii-bearing intervals and are interpreted as early Rupelian in age (Rac, Cin, and Hpu zones). The Servez Road Dam section occurs below the W. gochtii interval. It is characterized by common occurrences of Glaphyrocysta semitecta and interpreted as earliest Rupelian in age (Adi and Rac zones). Finally, the Sazlıbosna section lies below the Glaphyrocysta semitecta zone and represents the oldest stratigraphic unit of the studied intervals. It yielded Eocene dinoflagellates such as Areoligera taulomasentosa, Areosphaeridium michoudii, Rhombodinium perforatum, Homotryblium pallidum, and Stoveracysta ornata and is interpreted as late Priabonian in age (Aal zone). Both palynomorph assemblages and organic matter constituents reflect shallow to open marine and nutrient-rich depositional conditions that occurred during Late Eocene?Early Oligocene time. The dominance of marine palynomorphs, without any indication of fresh water influx, might suggest that deposition took place before the isolation of the Paratethys, when the Western Black Sea region was still part of the Western Tethys during the earliest Oligocene (NP21-23).