Basin-wide Correlation Research Articles

Salt tectonics evolution in the Provençal Basin, Western Mediterranean Sea

The Messinian Salt Giant in the Provençal Basin represents a good example to study salt tectonics: salt deposition occurred throughout the basin well after basin opening, with a tectonic context stable since ∼16 Ma, in a closed system. Also, the youth of salt tectonics has led to less mature structures and an evolutionary history that is easier to decipher than in older salt-bearing margins. We conducted an analysis of the chronology of salt deformation, from its deposition to the present-day, thanks to the basin-wide correlation of the Late Miocene and Pliocene-Pleistocene stratigraphic markers. The large seismic dataset provided detailed analysis of the causes and timing of salt deformation at a regional level. The salt tectonics started relatively early, during the Messinian Upper Unit (UU) deposition (phase 1) in the deepest part of the basin. From the Pliocene to the present-day, salt movement is divided into two more main phases (phases 2 and 3), the first of small intensity, occurred during the Pliocene and the second, more intense, during the Pleistocene. The geometric relationship between salt tectonics and crustal nature domains has revealed, regardless of the timing deformation phases, a more rapid and intense salt deformation above the proto-oceanic crust domain than in the continental or transitional crust domain. This observation, remaining unexplained, emphasizes the role of the influence of crustal nature, associated thermal regime and fluid circulation system on salt tectonics.

Spatial heterogeneity in benthic foraminiferal assemblages tracks regional impacts of paleoenvironmental change across Cretaceous OAE2

AbstractThe impact of global climate events on local ecosystems can vary spatially. Understanding this potential heterogeneity can illuminate which environments will be most impacted and the proximal drivers of ecosystem responses. Cenomanian–Turonian marine deposits of the Western Interior Seaway (WIS) record paleoceanographic changes associated with the Greenhorn transgression and the onset of Oceanic Anoxic Event 2 (OAE2). They provide an ideal setting to study basin-wide paleoecological responses during a global perturbation. Here, we integrate benthic foraminiferal assemblages from before, during, and after OAE2 via multivariate ordination analysis to examine spatial patterns in faunal responses across the western United States on a common scale and to interrogate a previously defined faunal marker commonly used for basin-wide correlation, the Benthonic Zone (BZ). We identify oxygenation and organic matter quality as primary and secondary controls of faunal variation across the 10 stratigraphic records and use this variation to infer paleoenvironmental changes. Stratigraphic trends reveal, in contrast to previous studies, deoxygenation at the onset of OAE2. They also reveal temporal patterns in oxygenation and productivity consistent with the gradual northward migration of a southern water mass into the WIS. This spatial heterogeneity hinders the use of the BZ as a temporal marker, because assemblages change in response to diachronous environmental change, and thus timing of the BZ with respect to OAE2 is not consistent across the basin. Our study demonstrates that regional processes can overshadow ecosystem responses to global events and underscores the importance of considering how changes in the position of water masses impact the expression of global biogeochemical perturbations.

Calibrating the zenith of dinosaur diversity in the Campanian of the Western Interior Basin by CA-ID-TIMS U-Pb geochronology.

The spectacular fossil fauna and flora preserved in the Upper Cretaceous terrestrial strata of North America’s Western Interior Basin record an exceptional peak in the diversification of fossil vertebrates in the Campanian, which has been termed the ‘zenith of dinosaur diversity’. The wide latitudinal distribution of rocks and fossils that represent this episode, spanning from northern Mexico to the northern slopes of Alaska, provides a unique opportunity to gain insights into dinosaur paleoecology and to address outstanding questions regarding faunal provinciality in connection to paleogeography and climate. Whereas reliable basin-wide correlations are fundamental to investigations of this sort, three decades of radioisotope geochronology of various vintages and limited compatibility has complicated correlation of distant fossil-bearing successions and given rise to contradictory paleobiogeographic and evolutionary hypotheses. Here we present new U–Pb geochronology by the CA-ID-TIMS method for 16 stratigraphically well constrained bentonite beds, ranging in age from 82.419 ± 0.074 Ma to 73.496 ± 0.039 Ma (2σ internal uncertainties), and the resulting Bayesian age models for six key fossil-bearing formations over a 1600 km latitudinal distance from northwest New Mexico, USA to southern Alberta, Canada. Our high-resolution chronostratigraphic framework for the upper Campanian of the Western Interior Basin reveals that despite their contrasting depositional settings and basin evolution histories, significant age overlap exists between the main fossil-bearing intervals of the Kaiparowits Formation (southern Utah), Judith River Formation (central Montana), Two Medicine Formation (western Montana) and Dinosaur Park Formation (southern Alberta). Pending more extensive paleontologic collecting that would allow more rigorous faunal analyses, our results support a first-order connection between paleoecologic and fossil diversities and help overcome the chronostratigraphic ambiguities that have impeded the testing of proposed models of latitudinal provinciality of dinosaur taxa during the Campanian.

Stratigraphy and Paleoenvironment(s) of the Late Cretaceous deposits in Ohafia area, Afikpo Basin, Southeastern Nigeria

Lithofacies and biofacies data extracted from three outcropping sections of Nkporo and Mamu Formations’ sediments in Ohafia area were used for paleoenvironmental and sequence stratigraphic interpretations. The five (5) lithofacies distinguished from the sections were Dark-Grey to Black Shale Facies (A), Oolitic Limestone Facies (B), Calcareous Siltstone Facies (C), Sandstone Facies (D) and Heterolithic Facies (E). The attributes of these lithofacies, including lithotype, rootlets, bioturbation, reducing conditions and microfossil contents, were used to discriminate the units into various environments of deposition and paleodepths. The oolithic limestone facies for instance was interpreted as deposits in shallow coastal areas with high turbulence, especially, in warm shallow marine environments. Paleobathymetry of the lithofacies ranged from non-marine through coastal deltaic, shallow inner neritic, inner neritic to middle neritic paleodepths. Micropalaeontological analysis of the sediments revealed a complete absence of planktonic foraminifera while agglutinated benthic assemblages (dominated by Haplophragmoides spp., Textularia spp. and Anomalinoides spp.), calcareous benthic foraminifera (Gavelinella guineana and Planulina nacatochensis), Gastropods, Ostracods, and Arenaceous indeterminate were recovered. The recognition of Bolivina afra-Haplophragmoides talokaense assemblage zone in the Mamu Formation conferred Maastrichtian age to the deposits. The presence of palynological assemblages like the Adallussiella polymorpha were used to assign Late Campanian age for the Nkporo Formation. Sequence stratigraphic analysis using the integration of foraminiferal, paleontological and lithofacies data identified two incomplete depositional sequences. The first sequence identified in the Nkporo Formation, comprised a Highstand systems tract (HST) bounded at the top by a sequence boundary (SB) dated 75 Ma. The SB also marked the beginning of the second depositional sequence that occurred in the successions of the Mamu Formation and comprised of Transgressive systems tract (TST), bounded at the top by a maximum flooding surface (MFS) dated 69.8 Ma. The results of this study have indicated the presence marker beds and constrained stratigraphic surfaces which can be used to map the identified play elements (source, reservoirs, traps and seals) in the study area. The surfaces are thus essential ingredients in basin-wide correlations for improved hydrocarbon exploration and development in the Afikpo and other adjoining inland basins of Nigeria.

Synchronous onset of the Messinian salinity crisis and diachronous evaporite deposition: New evidences from the deep Eastern Mediterranean basin

We present a basin-wide correlation of the pre-evaporitic succession across the deep Levant basin, based on integrated bio- and cyclostratigraphy. The onset of Messinian salinity crisis (MSC) can be placed in all studied wells where foraminifers suddenly disappear and normal marine calcareous nannofossils are replaced by opportunistic assemblages. These changes mark the base of the Foraminifers Barren Interval (FBI), a 10s-of-m-thick (below seismic resolution), evaporite-free, shale unit that records the entire duration of the first stage. Moving towards the basin margin the FBI is progressively truncated on top by the Messinian erosional surface (MES), a regional-scale discontinuity sealed by a thin clastic evaporite units overlain by thick halite deposits. Our results confirm previous hypothesis suggesting that the crisis started in deep- as well as in shallow-water settings at 5.97 Ma and pointing to a synchronous onset of the MSC but diachronous deposition of evaporites. During stage 1 of the crisis, coeval with gypsum deposition in marginal basins, the salinity in deep basins progressively increased (with possible oxygen reduction) hindering the life of marine organisms. Then, at 5.60 Ma, when salinity in deep basins exceeded halite saturation, massive halite precipitation started, and a nearly 2-km-thick salt sequence accumulated in deep basins within a short period of 60 kyr. At that time (stage 2), sedimentation rate jumped by an order of magnitude reaching a few cm/yr. Similar sedimentation rates are inferred for the Realmonte salt mine (Sicily) and observed in the modern Dead Sea and artificial salinas.

Impact of the late Cenomanian sea-level rise on the south Tethyan coastal ecosystem in the Middle East (Jordan, Egypt, and Tunisia): A quantitative eco-biostratigraphy approach

Sea-level rise can cause changes in coastal ecosystems. To understand the link between sea-level rise and the coastal ecosystems during the late Cenomanian of the southern Tethys, five exposed sections from three Middle East countries were quantitatively analyzed. The Unitary Association (UA) method allowed a two-fold increase in the resolution of zones compared to the Oppel method. Five UAs were obtained from analyses of both ammonite and benthic fauna. However, they were grouped into 3 UA Zones (UAZ) to enable basin-wide correlation. These zones were linked to one and half 3rd-order depositional cycles. During the Neolobites vibrayeanus/ Calycoceras guerangeri ammonite zone (95.5–94.4 Ma), high-energy shallow subtidal environments were formed by the transgression that followed the global sequence boundary ‘KCe 4’. They were dominated by stationary epifauna and suspension-feeders (mainly oyster bivalves). During highstand, a restricted lagoonal environment prevailed, where oyster bivalves, which have well-known adaptive strategies, were still dominant. No ammonites were recorded in this zone. Upward, the fauna has underwent a major shift, which documents the beginning of a new depositional sequence above a regional sequence boundary ‘KCe 5’ with a gradual increase of hemipelagic organic-rich sediments and planktic/nektic fauna in addition to infaunal deposit-feeders and mobile benthos, which have lived in a deeper subtidal environment (Vascoceras cauvini/Pseudospidoceras pseudonodosides ammonite zone; 94.4–93.8 Ma). This dramatic change in the character of the macrofauna at the Cenomanian/Turonian boundary (maximum flooding of KCe 5) can be attributed to the hydrodynamic changes associated with the eustatic sea-level rise. Therefore, the sea-level-based faunal changes can be integrated in sequence stratigraphic analyses. The geographic reproducibility of the UA mirrors the delay of the transgressive onlap in proximal sections, and thus, can be used to define transgressive and maximum flooding surfaces. This eco-biostratigraphic scheme can be implemented in reliable large-scale correlations.

Resolving lithostratigraphic complexities in the Crayfish Group, Otway Basin using chemostratigraphy

The Otway Basin comprises a significant part of the eastern Australian Southern Rift System, a divergent passive continental margin formed during the Cretaceous separation of the Australian and Antarctic continents. Early rifting activity resulted in the development of many half grabens within the Otway Basin, which are largely infilled by sediments of the Casterton Formation and Crayfish Group. Despite over 20 years of exploration and hydrocarbon production from these units however, their lithostratigraphic characterisation and nomenclature remain ambiguous, with structural complexity and prevalent lateral facies changes leading to confusion in their basin-wide correlation. Deposited in a largely non-marine, fluvial/lacustrine environment, repeating cycles of sandstones and shales of the Crayfish Group can be difficult to resolve using petrology, palynology and wireline log data. The use of chemostratigraphy is favoured as an investigative tool in this situation since changes in provenance, lithic composition, facies, weathering and diagenesis are reflected in the mineralogy of the sediments, resulting in variations in their inorganic geochemistry. Uniform sedimentary successions can thus potentially be differentiated into unique sequences and packages based on their characteristic geochemistry, aiding in the resolution of complex structural relationships and facies changes. In this study, we present new inorganic geochemistry data for four key wells in the South Australian (SA) Penola Trough and interpret the geochemistry data consistent with, and building on, the chemostratigraphic schema of Forbes et al. to demonstrate its utility and robustness. We then undertake inter-well wireline log correlations across the SA Penola Trough using the wells with chemostratigraphic data as controls.

Palynological evidence supporting widespread synchronicity of Early Jurassic silicic volcanism throughout the Transantarctic Basin

Throughout the Transantarctic Mountains, Early Jurassic silicic magmatism preceding the emplacement of the Ferrar flood-basalt province (Heimann et al. 1994) is documented by the increasing input of silicic ash into otherwise epiclastic, fluviolacustrine deposits of the Beacon Supergroup (see Elliot et al. 2017). Vertebrate biostratigraphy and radiometric analyses indicate a Sinemurian to Pliensbachian age span for silicic volcaniclastic deposits in the central Transantarctic Mountains (CTMs) (Elliot et al. 2017). For northern Victoria Land (NVL), radiometric geochronology and palynostratigraphy revealed that explosive silicic volcanism began with minor pulses during the early Sinemurian (c. 195 Ma) and reached a peak phase beginning in the middle Pliensbachian (c. 187 Ma) (Bomfleur et al. 2014). A basin-wide correlation of these widely separated age frameworks has so far been hampered by the scarcity of data on coeval deposits in southern Victoria Land (SVL). Here, we present new palynostratigraphic data from mixed epiclastic–volcaniclastic deposits in the Prince Albert Mountains that provide supporting evidence for the widespread synchronicity of silicic volcanic episodes preceding Ferrar magmatism.

Tectonic, Oceanographic, and Climatic Controls on the Cretaceous‐Cenozoic Sedimentary Record of the Australian‐Antarctic Basin

AbstractUnderstanding the patterns and characteristics of sedimentary deposits on the conjugate Australian‐Antarctic margins is critical to reveal the Cretaceous‐Cenozoic tectonic, oceanographic, and climatic conditions in the basin. However, unraveling its evolution has remained difficult due to the different seismic stratigraphic interpretations on each margin and sparse drill sites. Here, for the first time, we collate all available seismic reflection profiles on both margins and use newly available offshore drilling data to develop a consistent seismic stratigraphic framework across the Australian‐Antarctic basins. We find sedimentation patterns similar in structure and thickness, prior to the onset of Antarctic glaciation, enabling the basinwide correlation of four major sedimentary units and their depositional history. We interpret that during the warm and humid Late Cretaceous (~83–65 Ma), large onshore river systems on both Australia and Antarctica resulted in deltaic sediment deposition offshore. We interpret that the onset of clockwise bottom currents during the early Paleogene (~58–48 Ma) formed prominent sediment drift deposits along both continental rises. We suggest that these currents strengthened and progressed farther east through the Eocene. Coevally, global cooling (<48 Ma) and progressive aridification led to a large‐scale decrease in sediment input from both continents. Two major Eocene hiatuses recovered by the Integrated Ocean Discovery Program site U1356A at the Antarctic continental slope likely formed during this preglacial phase of low sedimentation and strong bottom currents. Our results can be used to constrain future paleo‐oceanographic modeling of this region and aid the understanding of the oceanographic changes accompanying the transition from a greenhouse to icehouse world.

Sequence Stratigraphic Interpretation of Late Cretaceous-Early Paleogene Sediments in the Central Part of Southern Anambra Basin, Nigeria

ABSTRACT The identification of additional hydrocarbon reserves to buffer pressure from increasing energy demands in Nigeria necessitated the application of sequence stratigraphic framework in the analysis of sedimentary successions in the central portion of southern Anambra basin. Wireline logs and biofacies data from three exploratory wells (S-1, S-2 and S-3) were used for the study. The stratigraphy of the study area observed from the three wells showed an overall regressive succession with short-lived transgressions. Lithofacies associations deduced from well log signatures defined four lithostratigraphic units: The Mamu and Ajali formations of kate Maastrichtian age; the Nsukka Formation of kate Maastrichtian - Danian age and Imo Formation of Paleocene age. The study further used the depositional sequence model to identify sequences and accompanying systems tracts that are bounded at the top and bottom by unconformities. Dating of identified key stratigraphic surfaces was achieved by correlating chronostratigraphic biofacies data to third order cycle charts. Correlation across the three wells highlighted spatial distributions of reservoirs and some useful stratigraphic and structural discontinuities that could form hydrocarbon traps. It also showed profitable stratigraphic surfaces that would aid basin-wide correlation for improved horizon(s) mapping and hydrocarbon prospectivity in the Anambra basin. Erosional unconformities identified in the wells that correlated with major drops in global sea level, fingerprinted the influence of eustacy on sedimentation and sequence development. Other factors such as subsidence and sediment supply have direct relationships to the identified structures (faults) which also initiated the accommodation created for sedimentation in the study area.

High-frequency depositional cycles in the Muschelkalk (Middle Triassic) of southern Poland: Origin and implications for Germanic Basin astrochronological scales

High-frequency depositional cycles are often used for long-distance correlations within sedimentary basins and constructing high-resolution chronostratigraphic scales calibrated to the orbital clock. Such an approach has been used for the tropical, epicontinental Muschelkalk Sea covering most of Europe in the Middle Triassic. This paper aims at establishing the spatial extent and internal architecture of shallow-marine Muschelkalk cycles within a small (120 by 50 km) area of the Germanic Basin, to identify their local vs. regional distribution and cycle-forming mechanisms. Three groups of cycles are distinguished: 1) peritidal cycles representing a tidal flat-lagoon system which experienced longer periods of emersion; 2) shallow subtidal cycles formed around the fair-weather wave base; and 3) deep subtidal cycles developed around the storm wave base. The three cycle types differ markedly in the composition, facies homogeneity, sedimentary trends, hierarchical organization, continuity, and degree of lateral changeability and complexity, which collectively translates into the ease of cycle recognition. Despite the differences, the defined cycles do not extend laterally beyond the studied area and have laterally variable facies heterogeneities, sedimentary trends, and thicknesses. This variability resulted from more or less mosaic infilling of accommodation space, reflecting local bathymetry, physicochemical conditions, and carbonate production and accumulation rates on the platform. Accommodation space evolved by the interplay of eustatic sea-level fluctuations regional subsidence, and synsedimentary tectonic-block movements, but the contribution of these factors changed over time and was to varying degrees masked for each of the three cycle types by intrinsic sedimentary processes. The study shows that Middle Triassic cycles of the Germanic Basin have a local to sub-regional distribution and thereby are inappropriate for basin-wide correlations and chronostratigraphic inferences. It also strengthens the opinion of several workers that correlation of idealized cycles is unrealistic without checking the horizontal continuity of facies and key surfaces directly in the field.

HYDROCARBON POTENTIAL AND PALAEO‐DEPOSITIONAL ENVIRONMENT OF LACUSTRINE SOURCE ROCKS: MIDDLE JURASSIC SHIMENGOU FORMATION, NORTHERN QAIDAM BASIN, NW CHINA

The Middle Jurassic Shimengou Formation in the Qaidam Basin, NW China, includes coals and lacustrine source rocks which locally reach oil shale quality (i.e. yielding >3.5 % oil on low‐temperature distillation). In the present study, the palaeo‐depositional environment and hydrocarbon potential of the 84.5 m thick Shale Member of the Shimengou Formation are investigated based on bulk geochemical parameters, organic petrographic data, biomarker analysis, and stable isotope geochemistry of 88 core samples.The Shale Member was deposited in an anoxic freshwater lake which formed following the drowning of a precursor low‐lying mire. Variations in bulk geochemical parameters allow four informal units to be identified, referred to (from the base up) as Units 1 to 4. These contain intervals of oil shale of varying thicknesses. In Unit 1, mudstones in the interval referred to as oil shale Layer 1 (true thickness [TD]: 2.06 m) are OM‐rich as a result of algal blooms and photic zone anoxia, and correspond to an initial flooding event. Subsequently, productivity of aquatic organisms decreased, resulting in the deposition of organic‐lean mudstones in Unit 2. Oil shale Layers 2 (TD: 2.03 m) and 3 (TD: 8.03 m) near the base of Unit 3 were deposited during maximum water depths. As with Layer 1, high productivity by algal blooms resulted in photic zone anoxia in a stratified water column. The shales in the upper part of Unit 3 are characterized by high TOC contents and a gradual increased input of terrigenous OM, and were deposited in a stable semi‐deep lake. Finally, organic‐lean mudstones in Unit 4 were deposited in shallow lacustrine conditions. The reconstruction of depositional environments in thick, non‐marine shale‐rich successions by mineralogical, petrographic and inorganic geochemical methods may be challenging as a result of the homogenous composition of component mudstones. The results of this study indicate, however, that sub‐division and basin‐wide correlation of such intervals can be achieved by organic geochemical analyses.Oil shales and organic‐rich mudstones in Units 1 and 3 of the Shimengou Formation Shale Member are excellent oil‐prone source‐rocks with a Source Potential Index of 3.2 t HC/m2. Considering the large area covered by the Shimengou Formation in the northern Qaidam Basin (∼34,000 km2), the results of this study highlight the regional significance for future petroleum exploration. They indicate that variations in organic productivity and dilution by minerals are key factors controlling the abundance and type of organic matter in the formation. An understanding of these factors will assist with the identification of exploration targets.

Recognition of stratigraphic sequence in the northeast Asian continent: a critical essay

This paper discusses the equivocal nature of the refined definition of stratigraphic sequence for universal recognition. The current definition requires a couple of inferences to be drawn: diagnosis of “a full cycle of base-level change” and, in turn, evaluation of stratal lapout “systems tract”. In the initial depositional models, the inferences were made in vertically exaggerated seismic profiles of passive continental margins with condensed clinoform geometry and bounding surfaces. In ancient outcrop sections, which are devoid of the clinoforms, the inferences are practically implausible. On the other hand, the cycle change is not always in phase with the unconformity, especially with the upper unconformity affected by tectonic movements. For these reasons, a sequence is limited for universal recognition. Intercontinental correlation of stratigraphic sequence is implausible. An alternative sequence can be defined by “a basin-wide correlation of recurrent facies succession bounded at the base by distinctive lithologic discontinuity or erosion surface”. A sequence in alluvial deposits can be identified on the basis of its bounding discontinuities. The evolving definition of stratigraphic sequence signals the demise of the initial concept of sequence stratigraphy and leads to a new avenue for the recognition of stratigraphic sequence. A distinctive sequence can be recognized based on the descriptive characteristics and scale of the succession.

High Resolution Trilobite Biostratigraphy for the Early Late Tremadocian (Tr2) Interval (Early Ordovician) Santa Rosita Formation, Argentine Cordillera Oriental

The early late Tremadocian (Tr2) interval is exceptionally well-represented in eastern areas of the Argentine Cordillera Oriental. New field collections and detailed taxonomic reassessments, as well as a reevaluation of regional data, permit the development of a highly resolved trilobite-based biostratigraphic framework. The concept of the traditional Bienvillia tetragonalis biozone is emended and the new Asaphellus nazarenensis biozone is proposed. Hence, the Tr2 interval encompasses a succession of four trilobite biozones including in ascending order the Kainella teiichii, the Bienvillia tetragonalis, the Asaphellus nazarenensis, and the Notopeltis orthometopa biozones. This resolution is notably higher than that provided by biostratigraphically significant groups such as graptolites and conodonts, and allows a detailed basinwide correlation. New taxonomic information on A. nazarenensis Tortello and Esteban and N. orthometopa (Harrington), is provided and the new species Asaphellus albae sp. nov. is defined. Detailed correlation of the trilobite fauna from the Tr2 interval with that of other paleocontinents is difficult. Taxa are mostly endemic or display wide geographic distributions but with long stratigraphic ranges. Overall, both trilobite-based and indirect international correlations highlight that this interval is hardly recognized, incompletely preserved, or the trilobite fauna is poorly known in most areas of Gondwana. Consequently, due to the completeness of the stratigraphic and fossil records of the Tr2 in the Cordillera Oriental, this region represents a global reference site for the study of this interval.

Sea-level changes vs. organic productivity as controls on Early and Middle Devonian bioevents: Facies- and gamma-ray based sequence-stratigraphic correlation of the Prague Basin, Czech Republic

Abstract The Devonian marine stratigraphic record is characterized by a number of bioevents – overturns in pelagic and benthic faunal assemblages, which are associated with distinct changes in lithology. The coincidence of lithologic and biotic changes can be explained by the causal link between biotic evolution, carbonate production and relative sea-level changes. To gain insight into the sea-level history of Early and Middle Devonian bioevents (the Lochkovian/Pragian Event, Basal Zlichovian E., Daleje E., and Chotec E.) we carried out a sequence-stratigraphic analysis of carbonate-dominated successions in the Prague Basin (peri-Gondwana), a classic area of Devonian bioevents. The study is based on a basin-wide correlation of facies and field gamma-ray spectrometry (GRS) logs from 18 sections (Lochkovian to Eifelian), supported by element geochemistry and published biostratigraphic and carbon isotope data. Devonian carbonate deposition in the Prague Basin alternated between two end-member modes: an oligotrophic, homoclinal ramp (Praha and Daleje-Třebotov Formations) and a mesotrophic, distally steepened ramp (Lochkov, Zlichov, and Chotec Formations). They show contrasting facies, particularly the absence/presence of gravity-flow deposits, allochem composition, U/Th ratios, and geochemical composition (productivity proxies such as P/Al, Si/Al, Zn/Al, TOC and stable carbon isotopes). The mesotrophic systems reflect an increased availability of nutrients on the shelf during the late Lochkovian, early Emsian (Zlichovian), and Eifelian periods when sea surface temperature, pCO2, and silicate weathering rates were higher. The oligotrophic systems deposited during the Pragian–to-earliest Emsian and late Emsian (Dalejan) periods reflect reversed palaeoclimatic trends. We identified three depositional sequences (DS), DS1 (base of Pragian to early Emsian); DS2 (early Emsian to mid Emsian); and DS3 (mid Emsian to mid Eifelian). These sequences were integrated into a peri-Gondwana relative sea-level curve, which was then compared with the Euramerican sea-level curve of Johnson et al. (1985). The bioevents coincided with several sequence stratigraphic surfaces, representing variable limbs of the relative sea-level curve. On the other hand, their conspicuous coincidence with the switching intervals between the colder oligotrophic and warmer mesotrophic modes suggests that organic production linked to global climate was the primary control on biotic overturns, while sea-level fluctuations may have only amplified its effects.

The significance of Upper Cretaceous hardgrounds and other discontinuity surfaces for basin-wide correlations, based on drillcore data from boreholes in northern Poland

The paper presents the hardgrounds and some other correlative discontinuity surfaces found in Upper Cretaceous (Cenomanian–Maastrichtian) borehole sections of northern Poland. They were briefly described, and depositional environment was identified for both the underlying deposit (UD) and the overlying deposit (OD). The significance of these features for both basin-wide correlations and broadly understood sequence stratigraphic techniques is highlighted. They were correlated with other major discontinuity surfaces identified in boreholes of northern Poland in both drill cores and well logs if such identification was reliable based on geophysical borehole data. All these discontinuity surfaces were referred to the boundaries of the individual depositional cycles determined within the Upper Cretaceous succession: K3-II/K3-III, K3-III/K3-IV, K3-IV/K4-I, K3-IV/K4-II, K4-I/K4-II (or II or IV or V), K4-III/K4-IV (or V), K4-IVa/K4-IVb, probably K4-IVb/K4-V, and K4-V/Pc-I. The discontinuity surfaces can be related to both sea level fluctuations and tectonic activity during the Subhercynian phases. Most of them developed in relatively calm sedimentary conditions, outside the central part of the Mid-Polish Trough. The exceptions are three hardgrounds from the Czlopa–Szamotuly Zone, which seem to be associated mainly with the Late Cretaceous tectonic (including salt tectonics) activity of this zone. The most common UD/OD configuration of sedimentary environments is the open-marine carbonate shelf both beneath and above the discontinuity surface. The second most common situation is the open-marine carbonate shelf beneath and the open-marine shelf with carbonate-siliceous sedimentation above. The gaps at the surfaces span variously long intervals, ranging from short periods (spanning a fraction of a depositional cycle) to long periods (comprising one or more depositional cycles). The position of the discontinuity surfaces facilitates searching for any possible hiatuses in the sections of other boreholes, and paying attention to local changes in sediment distribution patterns, and local tectonic activity.

Time Slicing the Cooper Basin

An efficient and practical method of generating composite time slices using all available, non-confidential 3D seismic data recorded in the South Australian sector of the Cooper Basin has been developed. Twenty georeferenced tiff images of time slices between 1000 ms and 2900 ms at 100 ms intervals have been prepared and are intended to be made publicly available through the Department of State Development SARIG website. 2D seismic data has also been used in this project in an attempt to ‘fill in’ some of the gaps between 3D datasets. Forty eight 3D and 5076 2D seg-y data files were utilised in this project. All 3D and 2D segy files were scaled to normalise amplitude levels for gridding and imaging. The ability to time slice 3D volumes of seismic seg-y data is a basic method employed in seismic interpretation. This method is usually applied to a single survey as commonly used software packages are not designed to view and analyse multiple 3D surveys at the same time or such functionality is not yet well implemented. For large scale regional interpretation, such constraint limits interpreting potential, especially in terms of basin wide correlation of main structural features. Whilst the methodology developed in this project retains the quality and resolution inherent in the variety of surveys used, it provides a cost effective method of generating basin wide time slice images, compared to costly reprocessing required in merging of 3D data sets into one 3D volume. The time slice data suite prepared complements other value-added regional datasets prepared by the Department of State Development to stimulate petroleum exploration in South Australia.

Stratigraphy and palaeoecology of the Upper Marine Molasse (OMM) of the central Swiss Plateau

The lithostratigraphic framework of the Upper Marine Molasse (OMM) in Switzerland is represented by two concepts. One was established in the central-northern Molasse Basin largely based on informal lithostratigraphic units without biostratigraphic control. The other concept was developed in the southern basin part and resulted in the distinction of the Lucerne Formation and the St. Gallen Formation based on detailed lithofacies analysis. This study aims at linking both concepts at map scale 1:25,000 for a potentially basin-wide correlation of the existing lithostratigraphic units. Based on lithostratigraphic analyses, mammal biostratigraphy and on the palaeoecological reconstruction of marine selachian faunas throughout the OMM of the central Swiss Plateau, we were able to allocate this part of the OMM into the well-established Lucerne Formation and St. Gallen Formation (Middle–Late Burdigalian, mammal units MN3a to MN4b). We further define two new lithostratigraphic units: The member Safenwil-Muschelsandstein (Lucerne Formation), and the bed Staffelbach-Grobsandstein (St. Gallen Formation). The Safenwil-Muschelsandstein denominates the well-known marker horizon of shell sandstone deposits, rich in fragments of irregular echinoids (scutella sp.), near the top of the Lucerne Formation. The Staffelbach-Grobsandstein represents a coarse-grained, often pebbly sandstone or even a fine-grained conglomerate at the base of the St. Gallen Formation. In the study area, the distinction between the Lucerne Formation and the St. Gallen Formation is best documented in the composition of the remnant marine fauna (especially teeth of selachii). Throughout the Lucerne Formation, the marine fauna is dominated by shallow marine faunal elements. In contrast, the Staffelbach-Grobsandstein reveals for the first time a large number of faunal elements of the open sea, which is interpreted as an indication of the marine transgression of the St. Gallen Formation. Furthermore, we present a unique palaeoecological study on marine faunas (mostly sharks) throughout the entire OMM sequence of the central Swiss Plateau.

The Dinantian (Mississippian) succession of southern Belgium and surrounding areas: stratigraphy improvement and inferred climate reconstruction

1. IntroductionAfter fundamental works such as those of de Dorlodot (1910) and Delepine (1911), the stratigraphy and the sedimentology of the Belgian Dinantian – a term better describing the Lower Carboniferous carbonate strata in western and central Europe than ‘Mississippian’ – were the subject of numerous papers during the 1960th and 1980th by various authors (Pirlet, Groessens, Bless, Bouckaert and others), mainly under the leadership of Raphael Conil. Especially the litho- and biostratigraphic work was summarized in two important synopses: Paproth et al. (1983) and Conil et al. (1991). In the first decade of this century, the older stratigraphic framework has been significantly revised and new basin-wide correlation schemes have been developed using bio-, chrono-, litho- and sequence stratigraphy – mainly in Hance et al. (2001, 2002, 2006), Poty et al. (2002a, 2006) and Devuyst (2006, for the Tournaisian – Visean boundary). These works led to a relatively coherent bio-, litho- and sequence stratigraphic model, which can be efficiently used in the Eurasia realm in shallow-water (e.g. Hance et al., 2011; Poty et al., 2007, 2014) and deeper water facies (e.g. Aretz, 2016, this volume; Herbig, 2016, this volume). This model also enabled the redefinition of the Belgian substages. Their boundaries can be correlated globally, which shows their high potential for further chronostratigraphic subdivision of the Carboniferous (Poty et al., 2014). Consequently, the Dinantian success

Radiometric dating of marine-influenced coal using Re–Os geochronology

Coal deposits are integral to understanding the structural evolution and thermal history of sedimentary basins and correlating contemporeous estuarine and fluvial delatic strata with marine sections. While marine shales may readily lend themselves to Re–Os dating due to the dominance of hydrogenous Re and Os, the lack of a chronometer for near-shore sedimentary environments hampers basinwide correlations in absolute time. Here, we employ the Re–Os geochronometer, along with total organic carbon (TOC) and Rock–Eval data, to determine the timing and conditions of a marine incursion at the top of the Matewan coal bed, Kanawha Formation, Pottsville Group, West Virginia, USA. The observed range for hydrogen index (HI: 267–290 mg hydrocarbon/gram total organic carbon) for these coal samples suggests dominance of aliphatic hydrocarbons with low carbon (<C19) chain length. Average Re (107.6±16.4 ng/g) and Os (0.52±0.09 ng/g) concentrations of the marine-influenced Matewan coal are higher by few orders of magnitude than published data for terrestrial coal. A Re–Os isochron for the Matewan coal provides an age of 325±14 Ma (Model 3; MSWD = 12; n=19; 2σ). This is the first Re–Os age derived from coal samples; the age overlaps a new composite Re–Os age of 317±2 Ma for the immediately overlying Betsie Shale Member.External precision for replicate Os analyses carried out for several Matewan coal samples shows a positive correlation with their HI. The HI, which is low in terrestrial organic matter, reflects the degree of marine influence. Thus, samples with the most profound marine influence also have the best analytical reproducibility. Equilibration of Os isotopes with seawater under marine conditions overwhelms variability inherited from terrestrial plant debris, decreasing scatter on the isochron. The 187Re/188Os ratios of the Matewan coal (∼3300–5135) are higher than most of those previously published for Phanerozoic black shale (mostly <2000). Mass balance calculations based on Re/TOC and Os/TOC ratios for the Matewan coal indicate that both Re and Os are primarily marine in origin, and their high 187Re/188Os ratios confirm efficient removal of both elements from a sulfidic water column into the coal. We show that Re–Os geochronology of marine-influenced coal can be a viable tool for constraining depositional ages.