Offshore Facies Research Articles

Facies analysis and depositional environment of the Carboniferous Singa Formation: Case study

Due to limited information, this paper aims to present a detailed facies analysis and depositional environment of the Carboniferous age, Singa Formation at Pulau Ular, Langkawi, Kedah. One exposed outcrop at Hill C was examined in detail, and one sedimentary log was created. The log is categorized bed by bed into several facies according to lithology and sedimentary structures. The focus was to identify the facies succession and to analyze the depositional environment as Singa Formation. This study is vital to reconstructing the pattern of past glacial as it will provide the crucial link between glacial processes and history, ice masses, and a more comprehensive Earth system. The Singa Formation is concluded into coarsening upward facies successions based on the facies succession grades upward from offshore facies. The depositional environment of Pulau Ular is interpreted as a coastal and a glacier depositional environment. Eight facies have been recognized; shale (FC1), shale with burrows (FC2), siltstone (FC3), shale with burrows, clay to silt (FC4), laminated shale with dropstone (FC5), sandstone that consists of dropstone (FC6), shale consists of dropstone (FC7) and sandstone with diamictite rock (FC8). Facies shale, sandstone, and siltstone proved that the study area is a coastal depositional environment, while facies consisting of dropstones and diamictite show that the study area is a glacier depositional environment.

Sedimentary, climatic, and provenance controls of mineral and chemical composition of the Ediacaran and Cambrian mudstones from the East European Craton

Mineralogical and geochemical compositions of mudstones were used for untangling provenance and climatic signals preserved in the upper Ediacaran - lower Cambrian strata from the western part of the East European Craton (ECC). Quantitative mineralogy and geochemistry data were obtained for 735 argillaceous rock samples from 71 wells and outcrops and compared with the analyses of Proterozoic palaeosols from the same area. Additionally, sedimentological analyses of well-preserved cores were performed to reconstruct predominant Ediacaran and early Cambrian environments. Seven major facies associations were distinguished and interpreted as both continental and basinal in nature. Terrestrial environments include weathering crust, alluvial fans, and associated interlobe areas, fluvial channels, floodplains, and lakes. Transitional environments are represented by tidal lithofacies, whereas central bay and upper offshore facies associations are typical of distal deposits. The central basin area is interpreted as an estuary opening toward the east, while a separate basin developed in Podillya. Provenance heavily influenced the mineralogical and geochemical characteristics of the sediments and affected derived weathering indices. The change from mafic to felsic sources in the western ECC is evident towards the Cambrian. All geochemical and newly introduced mineralogical weathering indices show advanced kaolinite-type weathering, evidence of a hot and humid climate during this interval. Based on these indices, mudstones are weathered to a greater extent than palaeosols. This observation is interpreted as resulting from the redeposition of highly weathered topsoils, combined with additional weathering on-route to the basin. Mineral authigenesis (berthierine, pyrite, goethite, fluorapatite, and carbonates) was particularly intensive in the terrestrial interlobe areas. Berthierine is common in most environments, which reflects the reaction of kaolinite with iron oxides, mediated by microorganisms, in shallow dysoxic tropical waters, with high lateritic sediment input. Marine, more oxic conditions in the Cambrian are indicated by a pervasive appearance of glauconite.

Multiple glacio-eustatic cycles and associated environmental changes through the Hirnantian (Late Ordovician) in South China

The Hirnantian glaciation, which was the first in the Phanerozoic to occur with elevated CO 2 levels, caused severe mass extinctions and disrupted biogeochemical cycling in the latest Ordovician. Previous research that aimed at exploring the triggers and consequences (both abiotic and biotic) of this glacial event have largely been based on condensed or incomplete sections. However, there is much debate over the detailed glacio-eustatic processes, and especially over the possible existence and characterization of multiple glacial cycles. Herein we conduct high-resolution geochemical analyses (via XRF core scanning and ICP-OES/MS) and a sedimentological study of three continuous upper Katian – lower Rhuddanian drill cores (Well Huangge-1, Well Shuanghe-1 and Well Yiwan-1), which represent a combination of nearshore and offshore facies in South China. The geochemical and sedimentological evidences reveal for the first time three glacio-eustatic cycles encompassed within a major sea level cycle through the upper Katian and Hirnantian. Each glacio-eustatic cycle comprises a combination of regressive and transgressive systems tracts, with the third one denoting the largest sea level fall and the glacial maximum. This pattern of sea level changes can be correlated with both the glacial sedimentary records and geochemical signals in North Gondwana, Laurentia and Baltica. These glacio-eustatic changes likely led to perturbations in regional marine nutrient cycling and formed a redox landscape that is depicted herein as somewhat different from previous models. We also present the glacio-eustatic effects at a basin scale, and a refined constraint for the tempo of polar ice sheet advances and retreats. It also calls for a re-evaluation of the mechanisms whereby a multi-cycle glaciation led to the Hirnantian biotic crisis, a relationship that may be much more complicated than the simplified cause-and-effect relationship proposed before. • Core scanning data revealed three glacio-eustatic cycles for the Hirnantian glaciation. • New pattern of glacial cycles correlates well with other records among different blocks. • Glacio-eustatic changes formed the redox landscape both temporally and spatially.

Sedimentological evolution and diagenesis of lower Eocene limestones, the Sinn El-Kaddab Plateau, the southern extent of the Tethys Sea in Egypt

This article describes a 135-m-thick sequence collection from the lower Eocene limestones of the Dungul Formation that caps the Sinn El-Kaddab Plateau in the Kurkur area. A sedimentological evolution model of these limestones has been constructed for the first time primarily based totally on lithology, microfacies analysis, SEM microscopy, and EDAX microchemical analyses. This carbonate sequence has been subdivided into three shallowing-upward facies. The hemipelagic facies at the base is dominated by foraminiferal wackestone, unconformably overlain by shallow offshore facies dominated by larger benthic foraminiferal grainstone and packstone, and capped by middle ramp facies dominated by bioclastic grainstone and packstone. These facies are analog of the Eocene facies of the Tethys Sea that had been formerly defined from Libya, Tunisia, Spain, and Kirkuk oil field in Iraq. Results suggest deposition in a basin characterized by oscillation in relief, in response to tectonic uplifting coupled with eustatic sea fluctuations associated with and the Syrian arching system. The limestones exhibit four successive diagenetic stages. The first stage is early marine diagenesis with the formation of micrite rim cement and preferential micritization of some skeletal grains. The second stage is shallow burial diagenesis, compaction, drusy calcite cement, and silicification. The third stage is meteoric diagenesis, the formation of isopachous calcite rim cement, dissolution and formation of blocky cement. The fourth stage is vadose diagenesis which includes karstification and ferrugination with iron oxy-hydroxides impregnation.

The Turonian-Coniacian stage boundary in an expanded siliciclastic succession: Integrated stratigraphy in deltaic through offshore facies, Bohemian Cretaceous Basin

During the latest Turonian – early Coniacian time, a succession of sand-rich, Gilbert-type deltas was deposited along the faulted margin of the Bohemian Cretaceous Basin (BCB, Central Europe), fining along depositional dip into prodeltaic heterolithic facies and offshore mudstones to marlstones. The active tectonic setting with accelerated subsidence and supply rates contributed to deposition and preservation of an expanded record showing otherwise insufficiently known parts of the Turonian-Coniacian (T–C) boundary interval. In this study a combination of detailed biostratigraphy, genetic sequence stratigraphy, and carbon isotope chemostratigraphy is employed to characterize the T–C boundary in the northern part of the BCB, in both nearshore and offshore facies. The basis of the biostratigraphic framework was the establishment of the same succession of inoceramid bivalves and other molluscan marker taxa and bioevents as that in Salzgitter-Salder (Germany) and Słupia Nadbrzeżna (Poland). All the faunal markers from the Mytiloides scupini through Cremnoceramus crassus crassus inoceramid zones were found both in the nearshore and offshore facies. The linkage of biostratigraphic and carbon isotope-stratigraphic data to a regional stratigraphic picture, as well as to individual outcrop and core sections, provides an important new database for further study of the boundary interval, with a direct link to the transgressive-regressive history of the nearshore depositional systems. Therefore it is proposed here that the T–C interval in the BCB complements the Salzgitter-Salder and Słupia Nadbrzeżna sections and together with them constitutes a broader type region for definition of the T–C boundary.

The Devonian–Carboniferous boundary in the stratotype area (SE Montagne Noire, France)

Sections with continuous sedimentation across the Devonian–Carboniferous (D-C) boundary in the Montagne Noire allow to build a virtual transect from shoreline to deep basin. Nearshore facies characterise the D-C boundary stratotype and neighbouring sections at La Serre in the Cabrieres klippen domain, and offshore facies are present at the Col de Tribes and Puech de la Suque sections in the Mont Peyroux nappe domain. Both domains exhibit equivalents of the Hangenberg Black Shale (HBS). At La Serre, an initial regressive trend is indicated by the presence of oculated trilobites in the topmost pre-HBS Wocklumeria Limestones. Above the HBS level, regressive depositional conditions characterise oolitic deposits that comprise lithic erosional flows with an admixture of transported shallow-water biotas. Maximum regression is recognised with the deposition of coarse breccias and local features of emergence prior to the first appearance of Protognathodus kockeli. The oolites are superseded by the transgression of outer shelf deposits. In the nappe domain, the HBS is intercalated in outer ramp nodular limestones, and it exhibits detrital elements pointing to its regressive nature. The regressive trend culminates than reverses when post-HBS carbonate sedimentation resumes. Protognathodus kockeli appears in the post-HBS carbonates. Associated oculated trilobites indicate shallower bathymetric conditions then those of the pre-HBS Wocklumeria Limestones. Thereafter, replacement of sighted trilobites by blind ones and the protognathodid biofacies by facies dominated by siphonodellids indicate a deepening trend. The near- and offshore sites of the D-C transition permit correlation of short-term bathymetric fluctuations with faunal turnovers and entries of biostratigraphic markers.

Facies analysis and depositional setting of the upper pliocene Akchagyl Formation in southeastern Caspian Basin, NE Iran

Pliocene deposits of the Cheleken and Akchagyl Formations constitute the most important hydrocarbon reservoirs in the Caspian Basin of Iran and other adjacent countries. In this study, facies characteristics and depositional setting of these sequences were examined using detailed field observations, petrographical studies, wireline-log and 2D seismic interpretations. Three outcrop sections were measured as the oldest and thickest Paleogene–Neogene units in the southeastern part of the Caspian Sea. Based on macroscopic and microscopic investigations, eleven sedimentary facies were identified in the studied sequence. These facies indicate deposition in alluvial fan, mud-flat, foreshore, shoreface and offshore of a wave-dominated lacustrine environment. The Akchagyl Formation is mainly composed of foreshore and shoreface facies with low gamma-ray values, which grades into offshore facies towards southwestern parts of the basin. The presence of marine biota such as Globigerinoides fistulosus, Ammonia becccarii, Pullenia praecursor, Cardium dombra and nanoplanktons (Discoaster brouweri and Discoaster pentaradiatus) demonstrate that this lacustrine setting was periodically connected to the global oceans, particularly in the Late Pliocene–Pleistocene. The stratigraphic correlation of the studied sections shows significant changes in lithology, facies and thickness of the Pliocene deposits. These changes were controlled by tectonic subsidence and clastic sediment supply during the Early-to-Middle Pliocene along with sea-level fluctuation as a consequence of the Akchagylian transgression episode in the Late Pliocene. Lateral changes in the geological parameters of the Akchagyl deposits indicate a more stable condition within the most part of the study area, especially towards the South Caspian Basin.

Late Devonian carbon isotope chemostratigraphy: A new record from the offshore facies of South China

We present a new biostratigraphically constrained carbon isotope record from the Lali section (South China) to document perturbations in the Late Devonian carbon cycle. Positive carbon isotope excursions (CIEs) are most important components of the Late Devonian long-term carbon isotope cycle: Frasnes (+2‰), Middlesex (+1‰), Lower Kellwasser (+3‰), Upper Kellwasser (+3‰) and Upper annulata (+1‰) events, as well as a small positive CIE (+1‰) in the Famennian expansa-aculeatus zones were recorded. It is noteworthy that no significant carbon isotope shifts are found for the Rhinestreet, Nehden, Condroz and Enkeberg events. The Late Devonian long-term carbon isotope curve from South China is in agreement with contemporaneous world-wide trends in Euramerica (Europe and North America) and Gondwana. Global data suggests a higher Famennian δ13Ccarb baseline (about +2.5 ‰) than that of the Frasnian (about +1‰). Previous studies have related the positive CIE to ocean anoxia, but its ultimate driver remains unclear. Other interpretations include the spread of land plants or increased tectonic activity, but these explanations are questionable due to the relative short durations of the CIEs compared to long-term processes of plant evolution and plant cover extension as well as tectonic movements.

Sandstone Reservoir Distribution Mapping of Bekasap Formation Using Seismic Attributes and Identification of Stratigraphic Trap in ‘X’ Field, Central Sumatera Basin

The ‘X’ field is an oil-producing field in the Central Sumatra Basin. Central Sumatra Basin is the largest oil-producing sedimentary basin in Indonesia. The field is an area in the form of onlaping Bekasap Formation to the Basement High. The onlapping feature has potential for stratigraphic traps. This study aims to identify the potential stratigraphic traps for hydrocarbon accumulation, the distribution of sandstone reservoirs, facies types and the depositional environments. The data used in the study are 3D seismic data, well log, and core data. The research methods used including the analysis of electrofacies based on well log, seismic attributes, and conceptual geology model. The research shows that there is a stratigraphic trap in the form of intra-formation and regional traps. Intra-formation traps were formed vertically by the intersection of sandstone and shale lithologies and lateral facies changes, whereas the regional traps are formed by the shale layer of Telisa Formation and Bekasap Formation with onlapping on the Basement High. Based on AI inversion and RMS amplitude show the distribution of Top A sandstone reservoir is Northeast - Southwest on onlaping zone to the Basement High. The reservoir was deposited in depositional environment as wave dominated delta which is four facies associations: distributary channel, upper shoreface, lower shoreface, and offshore facies.

The lower Upper Cretaceous of the south-eastern Münsterland Cretaceous Basin, Germany: facies, integrated stratigraphy and inter-basinal correlation

Integrated stratigraphic (litho-, bio-, event, chemo-, gamma ray, and sequence stratigraphy) and sedimentologic analyses of two new core sections greatly improved the understanding of facies development, sea-level changes and correlation of the lower Upper Cretaceous in the south-eastern Munsterland Cretaceous Basin, Germany. A large-scale second-order sea-level cycle is mirrored by the increasing importance of offshore facies and thicknesses of depositional sequences, reflecting the rise of accommodation during the Cenomanian to Early Turonian. In the Middle Turonian, this trend started to become reversed and the cycle ends with a major unconformity at the base of the Soest Grunsand Member in the mid-Upper Turonian. Condensation of the mid- and uppermost Turonian reflects the lack of accommodation during a phase of second-order lowstand, followed by a retrogradational trend during the Early Coniacian that marks the transgressive part of a new second-order cycle. Sedimentary unconformities in the Cenomanian–Turonian successions provide evidence for third-order sea-level changes superimposed onto the first early Late Cretaceous second-order cycle. They correspond to sequence boundaries SB Ce 1–5 and SB Tu 1–4 that have been identified in Central European basins and elsewhere, supporting their eustatic origin. The sea-level fall expressed by Upper Turonian unconformity SB Tu 4 is of major magnitude. The overlying Soest Grunsand Member is the only level of greensands in the Upper Turonian of the south-eastern Munsterland: the Alme Grunsand, introduced for another, allegedly uppermost Turonian greensand level, does not exist. Carbon stable isotopes from the mid-Upper Cenomanian to Lower Coniacian allowed calibrating the successions on intra- and interbasinal scales. A conspicuous mid-Middle Turonian positive isotope event has been newly named, i.e., the Niederntudorf Event. Sequence boundaries, marker beds (marl layers) and bentonites turned out to be isochronous within the chemostratigraphic framework. The identification of Turonian bentonites greatly improved the understanding of the stratigraphic relationships, especially in the Upper Turonian while natural gamma radiation logs turned out as a valuable method for intrabasinal correlation. In conclusion, the new sections provide a high-quality standard succession for the lower Upper Cretaceous in the south-eastern Munsterland Cretaceous Basin.

ONSHORE-OFFSHORE FACIES CHANGE OF NGRAYONG SANDSTONE IN MADURA AREAINDONESIA

Ngrayong sandstone composes a siliciclastic reservoir that produces oil for more than a century in North East Java Basin of Indonesia. Clean sand facies makes the best reservoir in western part of the basin, onshore East Java Island. Meanwhile, sand quality decreases eastward to Madura Island. In Madura, rock gradually changes to be more calcareous and shaly, due to the change of depositional environment. In offshore of Madura, the depositional environment is still questionable. This study is aimed to reveal differences between onshore and offshore facies of Ngrayong sandstone in Madura as their distribution is not well known and oil potential of Madura Strait is not well identified. Study methods consisted of geological field work, well correlation, and petrophysical analysis from several well data. The results show that Ngrayong sandstone was deposited during Middle Miocene, composed by interbedding of thickly bedded sandstone and alternating thinly bedded sandstoneshale. The succession is commonly intercalated by mudstone and thinly bedded limestone. At Madura Island, Ngrayong sandstone overlies the Early-Middle Miocene Tawun Formation, which both represent the Megasequence (MS) 3 interval. Due to regional subsidence and transgression during Late Miocene, Ngrayong sandstone and other equivalent rocks were overlain by monotonous mudstone and calcareous sandstone of Wonocolo Formation. The Ngrayong sandstone is evenly distributed in whole surface area of Madura Island and it spreads further 25-50 Km to the south and 100-125 Km to eastern part of offshore Madura Strait. Sandstone distribution is roughly depleted from the gross thickness hundreds of meters in northern part to only few centimeters in southeast part of study area. The facies changes to be more calcareous to the east, while the southward facies is shaly due to a deeper depositional environment. Despite of facies changing into shales or carbonate facies, Ngrayong sandstone potential in offshore Madura Strait needs to be considered as upside potential due to its distribution is wider than initial estimation, and its petrology and petrophysic data support it as a clastic reservoir.

Sedimentary facies analysis of the Upper Bahariya sandstone reservoir in East Bahariya C area, North Western Desert, Egypt

The present work aims to deduce the depositional processes of the Lower Cenomanian Bahariya Formation, that is one of the main hydrocarbon siliciclastic reservoirs in the Northern Western Desert of Egypt. This has been achieved through the analyses of the core photographs, micro-resistivity image logs, mud logs and conventional wireline logs. The Bahariya Formation comprises a complex of depositional lithofacies such as interbedded siltstone, shale, sandstones and pebbly sandstones. The current work highlights the effectiveness of the integrative approach. A variety of datasets including core photographs, micro-resistivity image logs, mud logs and conventional wireline logs are integrated to define the conceptual depositional model in the study area.Different recorded sedimentary features point to various depositional processes. Hummocky cross stratification (HCS) is the common sedimentary structure indicating the storm action. Wave ripples are recorded providing evidence for fair-weather action on shoreface. Rhythmic heterolithics, tidalites indicate the tidal processes. The upper part of the Bahariya Formation has been influenced by wave and storm processes more than the lower parts. The core and image facies are designated, being dominated by Sandstone (S), Siltstone (Z), Mudstone (M), Heterolithic (H) and Limestone (L.s). The studied core and image facies with wireline logs facies are grouped into five major facies associations (FA). They are Tidal Channel and Tidal Creeks, Tidal Flat, Storm, Shoreface, Offshore Transition to Offshore Facies Associations. The integrative approach indicates that the Upper Bahariya Member has been deposited in a storm influenced tidal coastal realm.

Facies and Sequence Stratigraphy Analyses of Klasaman Formation in the “X Well”, Northern Salawati Basin, Papua, Indonesia

The “X Well” is located in the Salawati Basin which is part of Western Papua. The interval of study is the Klasaman Formation that is characterized by thick sediment intercalated sandstones and shales. The movement of Sorong Fault strongly controlled the sedimentation of this formation. This study is very important to give a contribution for developing exploration prospect by predicting reservoir distribution since localized facies change may mark the distribution of sandstones. The current study aims: 1) to define the age of Klasaman Formation; 2) to define the vertical facies; 3) to define the sequence stratigraphy; and 4) to predict the lateral change of facies. Five nannofossil datum planes are found throughout the interval and cover the age Late Miocene to Early Pliocene. LO Sphenolithus abies points the age 3.65 Ma, LO Reticulofenestra pseudoumbilicus points the age 3.79 Ma, FO Pseudoemiliania lacunosa points the age 4 Ma, LO Discoaster quinqueramus and LO Discoaster berrgrenii point the age 5.59 Ma and Top of small Reticulofenestra Interval points the age 7.167 Ma. They define the NN11 up to NN16 Martini’s zonation. The age of Klasaman Formation is known as the uppermost Late Miocene to the Early Pliocene. Four facies can be identified, namely Upper Shoreface, Lower Shoreface, Offshore Transition and Offshore. The upper shoreface facies is characterized by thick and clean sandstones, about 2.41 - 20.64 meters thick, while the lower shoreface facies consists of predominantly very fine to fine-grained sandstones intercalated by siltstones and claystones. The offshore transition facies is marked by thick claystones and siltstones intercalated with thin sandstones, whilst the offshore facies is marked by thick laminated claystones. Nine Parasequences 4th order can be identified within study interval, namely Progradational Parasequence-1 to 2, Retrogradational Parasequence-3, Progradational Parasequence-4 to 6, Retrogradational Parasequence-7 to 9. They are bounded by Sequence Boundary-1 to 8. The upper shoreface sandstones of Parasequence-4 to 9 can be potential reservoir rocks in the Klasaman Formation since the sandstones are very thick and clean. The sediments of Klasaman Formation have been sourced from elevated highland in the northeast area, so the upper shoreface sandstones have changed become the offshore claystones from northeast to southwest. High sedimentation rate and rapid subsidence of the basin mark the deposition of Klasaman Formation especially during the deposition of Parasequence-6 to 9 as a result of Sorong Fault tectonics.

Palynology, microfacies and biostratigraphy across the Daleje Event (Lower Devonian, lower to upper Emsian): new insights from the offshore facies of the Prague Basin, Czech Republic

The Zlichovian/Dalejan boundary interval (Emsian, Lower Devonian) of the Pekarek Mill section was studied employing biostratigraphy (dacryoconarid tentaculites, conodonts) and palynology (chitinozoans, prasinophytes, scolecodonts) and microfacies analysis in order to shed more light on the timing and characteristics of the Daleje Event. The results of our study stress the great importance of the base of the Nowakia elegans Zone for the substage level division of the Emsian. Onset of the Daleje transgression is linked with higher terrigenous input, and coinciding changes in the chitinozoan assemblages were recorded at this level. The transgression at the base of the N. elegans Zone preceded the main transgression taking place in the N. cancellata Zone; it can be correlated with the Upper Zlichov Event. For the first time, Emsian chitinozoans and a jawed polychaete fauna are described in detail from the Prague Basin and can be correlated with other northern Gondwanan regions. The family-level composition of scolecodont assemblage confirms the dominance of paulinitids in the peri-Gondwanan realm.

Faunal response to sea‐level and climate change in a short‐lived seaway: Jurassic of the Western Interior, USA

Understanding how regional ecosystems respond to sea‐level and environmental perturbations is a main challenge in palaeoecology. Here we use quantitative abundance estimates, integrated within a sequence stratigraphic and environmental framework, to reconstruct benthic community changes through the 13 myr history of the Jurassic Sundance Seaway in the western United States. Sundance Seaway communities are notable for their low richness and high dominance relative to most areas globally in the Jurassic, and this probably reflects steep temperature and salinity gradients along the 2000 km length of the Seaway that hindered colonization of species from the open ocean. Ordination of samples shows a main turnover event at the Middle–Upper Jurassic transition, which coincided with a shift from carbonate to siliciclastic depositional systems in the Seaway, probably initiated by northward drift from subtropical latitudes to more humid temperate latitudes, and possibly global cooling. Turnover was not uniform across the onshore–offshore gradient, but was higher in offshore environments. The higher resilience of onshore communities to third‐order sea‐level fluctuations and to the change from a carbonate to a siliciclastic system was driven by a few abundant eurytopic species that persisted from the opening to the closing of the Seaway. Lower stability in offshore facies was instead controlled by the presence of more volatile stenotopic species. Such increased onshore stability in community composition contrasts with the well‐documented onshore increase in taxonomic turnover rates, and this study underscores how ecological analyses of relative abundance may contrast with taxonomically based analyses. We also demonstrate the importance of a stratigraphic palaeobiological approach to reconstructing the links between environmental and faunal gradients, and how their evolution through time produces local stratigraphic changes in community composition.

Paleoenvironmental evolution of the southern Neuquèn basin (Argentina) during the Tithonian-Berriasian (Vaca Muerta and Picún Leufú Formations): a multi-proxy approach

The Tithonian-Berriasian interval in the southern part of the Neuquén Basin is represented by the Vaca Muerta and the Picún Leufú Formations. Facies analysis and correlation of the Vaca Muerta Formation and the lower part of the Picún Leufú Formation in the Picún Leufú Anticline allow us to characterize the evolution of successive facies belts representing siliciclastic shelf and mixed ramp environments. Shoreface and offshore facies are developed on the siliciclastic shelf in the western and southern parts of the Picún Leufú Anticline. The offshore transition domain is characterized by storm beds and slump features, whereas the offshore domain corresponds to black to grey shales and turbidites. The mixed siliciclastic-carbonate ramp is characterized by the development of a lagoon and high-energy shoal in the proximal part of the inner ramp, whereas the distal part comprises a tidal complex. The mid-ramp zone is characterized by storm influence and the outer ramp by fine-grained deposits. Two major transgressive-regressive sequences and five high-frequency transgressive-regressive sequences are recognized. The high-frequency transgressive-regressive sequences make up three progradational sequences, an aggradational-progradational sequence and an aggradational sequence. The geochemical characteristics and clay mineralogy of the Tithonian-Berriasian interval in the southern Neuquén Basin indicate that (1) climate played a key role in the evolution of the sedimentary environment, (2) a “normal marine” depositional environment with oxic sea water and sediment pore waters, rapidly changing to suboxic conditions at shallow depth below the seabed and (3) the occurrence of episodically restricted water-mass circulation at the onset of deposition of the Vaca Muerta Formation.

A specimen-based approach to reconstructing the late Neogene seabird communities of California

California has experienced major climate change from the early Miocene (~23Ma) to the present. Fossil seabirds are useful for studying marine faunal responses to these changes because they are numerous in museum collections and easily identified to the family-level from fragmentary remains. Because extant seabirds respond quickly to environmental changes, we hypothesize that the fossil record of crown-group Miocene seabirds will reflect past environments. Previous studies of fossil seabird diversity through the Cenozoic of the North Pacific relied mainly on literature records to describe the appearance and disappearance of seabird species and correlated these patterns to geologic and climatic events. Our study uses an empirical, specimen-based approach to describe the seabird response to climate and tectonic change during ~12 million years of coastal California's geologic history (middle Miocene to early Pliocene). The foundation of our dataset is 242 fossil seabird specimens from Orange County. The strata from Orange County form the basis for delineating chronostratigraphic bins used for studying 285 additional seabird fossils from other parts of California, for a total of 527 seabird fossils examined. Our results show a relationship between pelagic seabirds and offshore facies as well as a clear increase of pan-alcid abundance and decline of sulid abundance through time. This pattern may be the result of taphonomic bias combined with the effect of shallower facies preserved through time. The increase in pan-alcid abundance is also coincident with global climatic and tectonic changes and with enhanced and stable nutrient upwelling. Upwelling through this time also helps to explain morphological changes in salmon and speciation rates in marine mammals. The specimen-based methodology used here can be applied to contemporaneous taxa, such as marine mammals, to quantitatively analyze diversity during the late Neogene and further explore the relationship between physical drivers and faunal change.

Wenlock–Ludlow boundary interval revisited: new insights from the offshore facies of the Prague Synform, Czech Republic

Wenlock–Ludlow boundary beds exposed near Nesvačily in the Prague Synform are documented in terms of their lithology, faunal content, high-resolution record of 19 graptolite species, graptolite biostratigraphy, and conodont record. This is the first time in Bohemia and peri-Gondwanan Europe that a continuous graptolite-bearing section through upper ludensis – middle nilssoni biozones is described in detail to refine high-resolution biostratigraphy and correlation of the Wenlock–Ludlow boundary. Organic-rich shale, relatively rare nongraptolite fauna, and absence of bioturbation indicate a stable deep-water offshore setting with sporadic, low-level bottom oxygenation. The uninterrupted succession revealed a series of origination events of principal graptolite taxa employed in determination of the Wenlock–Ludlow boundary strata worldwide. Bohemograptus represented by B. praecox appeared as early as in the uppermost Wenlock ludensis Biozone. Bohemograptus praecox is later accompanied and replaced by B. bohemicus, associated with Uncinatograptus uncinatus. The lowest Neodiversograptus nilssoni marked the base of the Ludlow nilssoni Biozone. Speciation within Bohemograptus continued in the middle nilssoni Biozone when the robust B. butovicensis evolved from B. bohemicus. Colonograptus colonus shows its lowest occurrence in the middle part of the nilssoni Biozone together with the latest C. gerhardi. The monograptids are associated with abundant and diverse plectograptids that are at present mostly known from Baltica. Bohemograptus praecox sp. nov. and B. butovicensis ( Bouček, 1936 ) are described in the systematic part. The conodont Kockelella ortus absidata, found in the lower–middle part of the nilssoni Biozone, is consistent with a stratigraphic interval within Oz. bohemica and K. crassa conodont biozones.

Influence of relative sea-level variations on the genesis of palaeoplacers, the examples of Sarrabus (Sardinia, Italy) and the Armorican Massif (western France)

The aim of this work is to analyse the role of allocyclic processes in the genesis of marine Ordovician palaeoplacers laid down on a terrigenous shelf dominated by storm waves. Sedimentological (facies, sequence stratigraphy) and petrographic analyses combined with natural radioactivity measurement (gamma ray) are carried out. Two facies containing heavy minerals are identified: a shoreface facies and a proximal upper offshore facies. Heavy minerals (mainly titaniferous minerals, zircon and monazite) are concentrated in laminae that can amalgamate to form placers that are several decimetres thick. Their occurrence is highlighted by an increase in the total radioactivity (up to 140,000cpm) and in the U and Th contents (up to 130ppm and 800ppm, respectively). The palaeoplacers are the result of a combination of autocyclic and allocyclic factors. In the stratigraphic record, the palaeoplacers are located in the retrogradation phases and express condensation processes in the nearshore environments.

Orbital-scale glacio-eustasy in the Middle Devonian detected using oxygen isotopes of conodont apatite: Implications for long-term greenhouse–icehouse climatic transitions

Results from previous paleoclimate studies indicate Gondwanan glaciation, marking the onset of middle Paleozoic icehouse climate conditions, began by the Latest Devonian (Famennian). More recently, δ18O trends from conodont apatite suggest cooling Middle Devonian subtropical seasurface temperatures >20My prior to Famennian glaciation and high-latitude temperatures cool enough to permit the growth of continental glaciers which controlled longer term (My-scale) glacio-eustasy. This study evaluates the details and patterns of Middle Devonian high-frequency (<100ky) climate variability that are superimposed upon these longer term cooling trends and evaluates the origins of common and globally widespread carbonate cycles (or parasequences).Thirteen complete Middle Devonian (Givetian) subtidal cycles (0.5–3m thick) in the Little Cedar Formation of southeastern Iowa are characterized by oxygenated offshore facies (transgression), poorly oxygenated offshore facies (maximum flooding), a return to oxygenated facies, and are capped by bioturbated lower shoreface facies (regression/lowstand) which lack evidence of subaerial exposure. Across-shelf cyclostratigraphic facies relationships suggest relatively subdued water-depth changes were responsible for cycle development. Measured δ18O values from conodont apatite range from 15.9‰ to 18.4‰ and repeated, systematic intracycle trends are dominated by lower isotopic values in offshore facies and higher isotopic values in cycle-capping lower shoreface facies, which is consistent with glacio-eustasy driving the water-depth changes. The average ~0.6‰ magnitude of intracycle isotopic shift (0.2‰ to 1.0‰=total range) suggests ~15–23m glacio-eustatic oscillations were responsible for observed water-depth changes. The higher range of intracycle isotopic magnitudes may be the result of increased subtropical evaporation rates during glacial stages which locally enriched surface seawater δ18O values.Orbital-scale (<100ky) glacio-eustasy superimposed on Middle Devonian cooling trends ~20My prior to Late Devonian glaciation highlights the difficulties in attempting to pinpoint the specific timing of the middle Paleozoic greenhouse-to-icehouse climate transition and calls in to question the traditional delineations of greenhouse versus icehouse conditions.