Lithostratigraphic Subdivision Research Articles

Detailed Late Pliocene-Quaternary sedimentation history and diagenesis processes in the eastern part of the Norwegian-Greenland Basin based on mathematical statistical methods

As a result of univariate regression analysis, quantitative parameters on the distribution of Mn/Al and Mn/Fe ratios in the sections of the studied holes of ODP Leg 151 were obtained. On the basis of correlation analysis data with Pearson matrix construction and classical factor analysis with varimax rotation, a division of rather homogeneous Upper Pliocene-Quaternary sediments was carried out with the allocation of 3 main factors that characterize the history of sedimentation and diagenesis in the Norwegian-Greenland Basin. The boundaries between lithostratigraphic subdivisions are drawn on a strict mathematical basis. It is established that the nature and degree of intensity of diagenesis processes in this region were influenced by the following main factors: sedimentation environments in the Norwegian-Greenland Basin in the Late Pliocene-Quaternary time; grain-size and chemical composition of the studied sediments; total organic carbon content in the sediments; sedimentation rates.

Nigerian Case Study Explores Drilling Through Shales Below Depleted Sands

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 217195, “Drilling Through Shales Below Depleted Sands: Case Study of a Niger Delta HP/HT Gas Development Well,” by Stella Ogbodu, SPE, Bart Tichelaar, and Chibueze Amadi, SPE, Shell, et al. The paper has not been peer reviewed. _ Choosing the right casing depth is a key step in executing high-pressure/high-temperature (HP/HT) wells in the geologically complex Niger Delta. In the wells of Astra East Field, a casing shoe was set in a homogeneous shale of approximately 200 ft vertical thickness located between overlying heavily depleted sand and underlying overpressured sand. The question remained, however, as to what depth the casing shoe should be set to minimize the risk of kicks or wellbore instability and losses. To address this issue, wireline log data and drilling observations from other wells in the same field were analyzed and evaluated. Introduction The Astra East field was planned to provide feedstock gas. The field is in the Central Swamp depobelt of the Niger Delta and is 90 km west of Port Harcourt. More than 40 wells have been drilled in the field to date. A regional shale layer at approximately 11,400 ft subsea caps the regional top of overpressure in this field. This approximately 200-ft-thick shale layer vertically segments the field into two pressure regimes: a near-hydrostatic regime above it and an overpressured regime below. In other words, this shale layer acts as a regional pressure seal. Historically, oil and gas production has focused on the reservoirs above this regional seal, resulting in pressure depletion to pore-pressure values below hydrostatic in some of the reservoirs. Of the wells drilled in the field, only a handful penetrate the deeper overpressured section below the regional pressure seal and have faced various drilling challenges. Location and Geology of the Study Area The Astra East study interval is part of the Agbada formation, a paralic sequence of sands and shales up to 4 km thick in the central parts of the basin. Three lithostratigraphic subdivisions exist in the delta: the prodelta Akata shale formation, the paralic deltaic Agbada formation, and the continental Benin formation. These units represent an overall regressive, progradational stratigraphy. Depletion History and Drilling Performance The produced reservoir that sits immediately above the regional pressure seal is the C reservoir. Because hydrocarbon production from the C reservoir began more than 50 years ago, reservoir pressure gradient has depleted from approximately 5,150 psi before production to subhydrostatic. During the last 20 years, this depletion has remained relatively constant at approximately 1,660 psi below hydrostatic. The underlying, unproduced D reservoir is not depleted and is, in fact, at its virgin pressure, which is overpressured at approximately 3,035 psi above the hydrostatic pressure. This implies that the approximately 200-ft-thick intrareservoir shale between C and D reservoirs holds a large differential pore pressure of approximately 4,700 psi for the last 20 years. In fact, because the aquifer of the C reservoir was hydrostatic at virgin conditions, a large pressure differential was in place across this intrareservoir shale (between C and D reservoirs) even before production started.

Diagenetic signatures in the deltaic and fluvial-estuarine Messinian sandstone reservoirs in the Nile Delta as a tool for high-resolution stratigraphic correlations

The current study utilizes a range of diagenetic fingerprints to differentiate between sandstone facies deposited in the Nile Delta before and during the Messinian salinity crisis (MSC), which is normally a challenging task considering the complex bio- and lithostratigraphic subdivisions of Messinian rock units. Subaerial exposure of the pre-MSC (Qawasim deltaic sandstone), during drawdown of the Mediterranean Sea at the time of the MSC, triggered pervasive dissolution of unstable rock fragments, kaolinization of feldspar, and meteoric dolomitization of carbonate. This was followed by mesogenetic calcite cementation and kaolinite transformation into dickite in deeply buried Qawasim sandstone. Comparatively, the Abu Madi estuarine facies, deposited during transgression after drawdown related to the MSC, is characterized by eogenetic iron (Fe)-calcite, glauconite, and pyrite (averages of 14.5%, 6%, and 2%, respectively). This facies transition is marked by abundance of mature glauconite (with potassium oxide (K2O) at about 8%) whose content abates upward from the transgression surface. Moreover, the compositional variability of the Abu Madi sandstone gave rise to multiple diagenetic trajectories that resulted in chlorite formation presumably following smectite and kaolinite. Listed diagenetic variations in the studied Messinian sandstone resulted from a complex interplay between rocks’ compositional, depositional, and burial attributes, ultimately serving as a basis for high-resolution stratigraphic correlation in continental and marginal marine settings with poor biostratigraphic controls.

Revised planktic foraminiferal biostratigraphy of the early late Albian of northern Tunisia (southern Tethys)

The upper Albian exposed near the Imbrication Zone of northern Tunisia is composed of a pelagic sequence that includes organic-rich beds. High-resolution biostratigraphy based on planktic foraminiferal bioevents across marker beds (i.e., organic-rich beds), allows revision of the lithostratigraphic subdivision and zonal scheme in comparison with late Albian time equivalents recorded in the northern Tethyan margins. In the present study, we proposed a new subdivision of the upper Albian lithostratigraphic section that now includes the Mellegue horizon as an equivalent of theAmadeus Segment rhythmic marl/limestone interval (central Italy). Three studied sections are subdivided into five biozones with the abundance and morphological trends of planktic foraminifera and inferred paleoenvironments: 1) The Biticinella breggiensis Total Range Zone is characterized by the appearance of ticinellids with pinched chambers (i,e., Ticinella praeticinensis) and is recorded a few meters above the first occurrence of Biticinella breggiensis. Agradual increase of trochospiral thick-walled (B. breggiensis, T. roberti, T. raynaudi) and Globigerinelloides taxa, reflecting mesotrophic conditions. 2) The Pseudothalmanninella subticinensis Interval Zone includes the first appearance of keeled forms (Ps.subticinensis), associated with abundant ticinellids with flattened chambers (B.breggiensis, T. roberti) below the base of the organic-rich Mellegue horizon, indicating an oligotrophic environment. 3) The Pseudothalmanninella ticinensis Interval Zone. The continuous occurrence of T. primula and the scarcity of Globigerinelloides throughout the lower part of this zone indicates an oligotrophic to weakly mesotrophic environment. The occurrences of radiolarian-rich horizons and abundant forms with elongated chambers (T. raynaudi) in the lower part of this zone indicate an abrupt shift to enhanced eutrophic and dysaerobic conditions. 4) The Thalmanninella appenninica Zone, which shows a decrease in abundance preceding the extinction of ticinellids, and a gradually increasing number of specialized keeled forms (i.e., Th. appenninica), indicates oligotrophic conditions. 5) The Planomalina buxtorfi Total Range Zone is characterized in its lower part by an increasing abundance of clavate forms with radially elongated chambers (i.e., Clavihedbergella) above the organic-rich bed of the Mouelha Member, indicating low-oxygen, oligotrophic to mesotrophic conditions.

Stratigraphy, Lithology, and Geochemistry of Coastal and Shallow-Sea Sections of the Uppermost Middle Jurassic–the Lowermost Cretaceous Section in the Anabar River Region (Arctic Siberia)

Abstract —Concepts of the stratigraphy of the coastal and shallow-sea sections of the uppermost Middle Jurassic and Lower Cretaceous, exposed on the right bank of the Anabar River, have radically changed many times. The performed study and analysis of the published data are aimed at refining the bio- and lithostratigraphic subdivision of the section, substantiating its stratigraphic completeness, and describing the identified stratigraphic units in detail. Comprehensive biostratigraphic studies of the uppermost Bathonian — the lowermost Boreal Berriasian reveal a sequence of nine biostratigraphic units with dinocysts and palynoflora in the ranks of zones and local zones. Some of the palynological biostratigraphic units have been identified for the first time. Foraminiferal assemblages of the boreal standard zones are recorded in the sections under study. The obtained biostratigraphic data and analysis of all known ammonite occurrences make it possible to demonstrate the stratigraphic continuity of the section in the Anabar River region, despite the reduced thickness of the stratigraphic units. The stratigraphic position of the boundary between the Sodiemykha and Buolkalakh formations is accurately defined. According to the interpretation proposed, the basal horizon of the Buolkalakh Formation is associated with a beginning of a new major sedimentation stage in the late Oxfordian–early Kimmeridgian, identified as the lower boundary of lithostratigraphic units of different ranks throughout the entire Arctic Region and partially in the Boreal Region. The lithogeochemical parameters of the studied formations are obtained for the first time. The content of Corg in the studied samples does not exceed its Clarke values, and the pyrolytic parameter Tmax indicates that the organic matter is immature and the petroleum potential is low. The considered organic matter of the rocks is characterized by a heavy isotope composition of carbon, suggesting its mostly terrigenous genesis.

The Triassic of New Siberian Islands Archipelago and Its Position in the Structure of Sedimentary Cover of the Laptev Sea Shelf

AbstractThe geological study of the Mesozoic sections of the New Siberian Islands archipelago and Asian coastal sections of the Arctic Ocean plays a key role in tying the results of comprehensive studies with seismic data on the Laptev Sea shelf and the western part of the East Siberian Sea. Therefore, it is extremely important to improve the subdivision of the Triassic system of the New Siberian archipelago and to define the position of the system in the structure of the Laptev Sea shelf sedimentary basin. The results of our study were used to improve and refine the lithostratigraphic subdivision of the Triassic in the study area and to recognize a distinct interregional stratigraphic marker, i.e., the Czekanowski Formation (lower Olenekian). In terms of genetic, structural, and sedimentological features, the Triassic strata were grouped into two Groups: the Reshetnikov Group (Induan–upper Ladinian) and the Svetlaya Group (Ladinian–Rhaetian), reflecting major stages of sedimentation. For the Triassic of the eastern Laptev Sea shelf and adjacent onshore areas, the facies zonation scheme has been developed and refined on a unified basis. Based on their structure, the Phanerozoic sections of the study area can be considered as a part of the intermediate structural stage of the Laptev Sea plate at the margins of the Siberian craton.

Lithostratigraphic definition of the Upper Jurassic – lowermost Cretaceous (upper Volgian–Ryazanian) organic-rich and oil-prone Mandal Formation in the Danish Central Graben, North Sea

The Volgian–Ryazanian shale interval in the Norwegian Central Graben, North Sea, is assigned to the Mandal Formation. Despite shales with similar lithological and log characteristics are being present in the Danish Central Graben, the formation is not defined for this part of the Central Graben. This paper presents a new lithostratigraphic subdivision of the Upper Volgian–Upper Ryazanian interval in the Danish Central Graben, where the Mandal Formation is defined and replaces the uppermost part of the Farsund Formation in the ‘old’ lithostratigraphy. The Mandal Formation is recognized from its log character and is correlatable across the Danish Central Graben. The formation typically has high gamma-ray (GR) and resistivity readings accompanied by low velocity and density values. In basin centres it normally consists of a lower part showing an upward increase in GR readings (‘warming-up’ interval), an overlying interval with conspicuous high GR readings (Bo Member), and an upper heterogeneous shale interval. The base of the Mandal Formation can be seismically mapped in most of the Danish Central Graben. The upper boundary of the formation, corresponding to the Base Cretaceous Unconformity (BCU) at the transition to the Lower Cretaceous, can likewise be seismically mapped throughout the basin. The Mandal Formation is developed with thick successions in basin depocentres, while it is thin or absent along inversion structures and on structural highs. The organic-rich shales of the Mandal Formation were deposited in a restricted, low-energy, oxygen-deficient/anoxic marine environment distal from any significant terrestrial influence. Along the eastern Coffee Soil Fault in the Danish Central Graben, siliciclastic deposits constituting the gravity-flow sandstones of the Poul Member interfinger with the Mandal Formation. Gravity-flow deposits formed by turbidite currents are also common throughout the Mandal Formation in basin centres. The Mandal Formation and particularly the Bo Member are highly oil-prone and contain the best source rock quality of the entire Upper Jurassic – lowermost Cretaceous shale succession in the Danish Central Graben. Interbedded potential reservoir sandstones suggest the Mandal Formation may in places be considered as an interval with hydrocarbon prospectivity, especially along the Coffee Soil Fault.

The Neogene Siwalik Succession of the Arunachal Himalaya: A Revised Lithostratigrphic Classification and its Implications for the Regional Paleogeography

Abstract Marine deposits in the Neogene Siwalik succession have been documented from the Tista valley, Bhutan and Kameng river sections of the Eastern Himalaya. This study was designed to investigate possible marine influence further east. During this investigation, it was revealed that the current classification and description of the stratigraphic units were inadequate to describe the variations present in this succession fully. In place of the existing three-fold classification, a four-fold lithostratigraphic classification of the Siwalik Group in the Arunachal Himalaya has been proposed by adding a new Siji Formation. This newly proposed formation is completely different from the underlying sand-dominated Subansiri or overlying conglomerate-dominated Kimin formations. Nearly 1000 m thick succession of the Siji Formation is characterised by of alternating tabular sheet like beds of grey mudstone, siltstone and sandstone with uncommon thin conglomerate beds. On the basis of the four-fold classification, the Siwalik rocks of the Arunachal Himalaya have been mapped over a strike length of ~230 km, demonstrating the lateral continuity of the individual formations and the large-scale deformational features affecting the rocks. Three lithologs prepared show the distinctive lithological characters and overall paleocurrent pattern of these formations. The lithological, sedimentological and ichnological features of the Dafla and Siji formations provide evidence for marine influence in the study area. The proposed new lithostratigraphic subdivisions are expected to facilitate regional correlation and evidence of marine sedimentation which will throw new light on the basin analysis of the Siwalik Group in the Eastern Himalayan.

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.

Bashkirian meganticlinorium: Late Riphean-Vendian hiatuses and possible transformations of basin provenances

The object of research. At the top of the Upper Riphean-Vendian sedimentary sequence of the Bashkirian meganticlinorium (western and central parts of the named structure, corresponding to the stratotypical locality of Riphean) there is a series of fairly well-established hiatuses – the pre-Uk and pre-Bakeevo. One can also assume the existence of the pre-Uruk and pre-Basa hiatuses. During each of them, the thin-grained aluminosiliciclastic’s distribution systems could be subjected to one or another transformations. However, whether this is actually the case is still not entirely clear. To solve this problem, the lithogeochemical features of clayey rocks of the Inzer, Minyar, Uk, Bakeevo and Basa formations are analyzed. If we assume that the hiatuses are accompanied by restructuring of the provenances, then this can/should lead to the appearance of more fresh, previously not subject to weathering, rock complexes at the paleo-watersheds. This circumstance should cause a change in the lithochemical characteristics of the thin-grained aluminosiliciclastics entering to the sedimentation area. Methods. The analysis of the lithogeochemical features of clayey rocks is based on data on the content of the main rock-forming oxides (about 40 analyzes) and rare and trace elements (total of 70 analyzes). These data make it impossible to investigate the change in different lithogeochemical parameters of clayey rocks (for example, CIA, GM, K2O/Al2O3, or others) from the bottom upwards through the section of each of the formations listed above, therefore we operate with the averages for the formation values of such parameters taking into account the values their standard deviations. Results and conclusions. On the majority of the discriminant diagrams used by us, the figurative data points of the Basa Fm. mudstones occupy a position that to some extent differs from the position of the clayey rocks of other formations. The only lithostratigraphic subdivision in the part of the Upper Precambrian sedimentary sequence of the Bashkirian meganticlinorium under consideration, whose clayey rocks demonstrate a chemically noticeably less mature, compared to the underlying formations, is the Uk Fm. It may be thought that this is the result of the appearance of more fresh (less transformed by weathering) rock complexes at the provenances. The scales of the pre-Bakeevo and pre-Basa breaks, if they existed, were, most likely, noticeably less significant.

Revised definition/outline of the Kheis Terrane along the western margin of the Kaapvaal Craton and lithostratigraphy of the newly proposed Keis Supergroup

AbstractThe Kheis Province is situated between the Namaqua-Natal Province and the western margin of the Kaapvaal Craton in the Northern Cape Province of South Africa. It has been described as a thin-skinned fold and thrust belt formed between 1800 and 1700 Ma. The lithostratigraphic subdivision of the rock units comprising the Kheis Province has been a source of much controversy. From detailed study of aerial photography and satellite imagery, as well as field-based studies, the outcrop patterns in the Kheis Province and Kaaien Terrane were reinterpreted and a new stratigraphic subdivision is outlined here. It is proposed that the structural Kaaien Terrane and Kheis Province should be combined into the Kheis Terrane and that the rocks occurring in the Kheis Terrane should be grouped together to form the new Keis supergroup, with the basal metaconglomerate of the Mapedi/Gamagara Formation recognised as the regional unconformity between the Keis supergroup and the underlying rocks of the Transvaal Supergroup in the Griqualand West area. The Keis supergroup is subdivided from the base upwards into the Elim-, Olifantshoek-, Groblershoop- and Wilgenhoutsdrif groups. The basal Elim group is composed of the Mapedi/Gamagara- and Lucknow formations. It is overlain with a regional erosional unconformity by the Olifantshoek group, which is made up of the Neylan-, Hartley-, Volop- and Top Dog formations. The Olifantshoek group is conformably overlain by the Groblershoop group which is comprised of three upward coarsening successions:the Faanshoek- and Faansgeluk formations,the Maraisdraai- and Vuilnek formations andthe Opwag- and Skurweberg formations.The Groblershoop group is in turn erosively overlain by the rocks of the Wilgenhoutsdrif Group, which include the basal erosive Groot Drink formation which is overlain by the Zonderhuis- and Leerkrans formations. The lithologies of the Keis supergroup are in faulted contact with the rocks of the younger Areachap Group of the ~1200 Ma Namaqua-Natal Metamorphic Province.

Glaciers, flows, and fans: Origins of a Neoproterozoic diamictite in the Saratoga Hills, Death Valley, California

The Kingston Peak Formation of Death Valley, California, provides an exceptional archive of Cryogenian glaciation and concomitant rifting of Rodinia. In the Saratoga Hills, an 800 m thick succession of diamictite-dominated strata is exposed, allowing lithofacies and clast compositions to be studied in detail, and for the relative influence of glacial versus slope processes on sedimentation to be critically assessed for the first time. Two detailed sections, 400 m apart, allow four facies associations to be established: (1) Thinly Laminated Argillaceous Sandstone (interpreted as low density turbidites), (2) Laminated, Deformed, and Brecciated Limestone (interpreted as carbonate-sourced turbidites), (3) Bedded Massive Diamictite (interpreted as glacially-fed debrite), and (4) Interbedded Mudstone, Sandstone, and Diamictite (interpreted as stratified diamictite deposited via ice rafted debris and passing gradually into turbidites separated by intensely deformed intervals). Bedded massive diamictite is dominant in the succession and shows a gradual up section transition into interbedded mudstone, sandstone, and diamictite. This succession is interpreted to record a waning glacial influence: from glacially sourced debris flows to stratified diamictite strongly influenced by ice rafted debris. Clasts in the diamictite include carbonate, siliciclastic intraclasts, granite, diabase, gneiss, and quartzite. Clast presence profiles suggest that in spite of the comparable along-strike facies profiles between the two logs, clast content is significantly different within the same stratigraphic unit. This finding suggests that clast content is of little use in aiding correlation and lithostratigraphic subdivision of the Kingston Peak Formation. The differences in clast compositions is envisaged to be due to complex drainage network. Examinations of the sedimentary structures and stacking pattern of the lithofacies, complex drainage network, and localized deformation features of FA4 all support deposition as part of a trough mouth fan system.

An updated and revised stratigraphic framework for the Miocene and earliest Pliocene strata of the Roer Valley Graben and adjacent blocks

AbstractIn the Netherlands, the bulk of the Miocene to lowest Pliocene sedimentary succession is currently assigned to a single lithostratigraphical unit, the Breda Formation. Although the formation was introduced over 40 years ago, the definition of its lower and upper boundaries is still problematic. Well-log correlations show that the improved lecto-stratotype for the Breda Formation in well Groote Heide partly overlaps with the additional reference section of the older Veldhoven Formation in the nearby well Broekhuizenvorst. The distinction between the Breda and the overlying Oosterhout Formation, which was mainly based on quantitative differences in glauconite and molluscs, gives rise to ongoing discussion, in particular due to the varying concentrations of glauconitic content that occur within both formations. In addition, the Breda Formation lacks a regional-scale stratigraphic framework which relates its various regionally to locally defined shallow marine to continental members.In order to resolve these issues, we performed renewed analyses of material from several archived cores. The results of archived and new dinocyst analyses were combined with lithological descriptions and wire-line log correlations of multiple wells, including the wells Groote Heide and Broekhuizenvorst. In this process, the updated dinocyst zonation of Munsterman & Brinkhuis (2004), recalibrated to the Geological Time Scale of Ogg et al. (2016), was used. To establish regionally consistent lithostratigraphic boundaries, additional data was used along a transect across the Roer Valley Graben running from its central part (well St-Michielsgestel-1) towards the southern rift shoulders (well Goirle-1). Along this transect, chronostratigraphic and lithostratigraphic analyses were integrated with well-log correlation and the analyses of seismic reflection data to constrain geometrical/structural relationships as well.The results led to the differentiation of two distinct seismic sequences distinguished by three recognisable unconformities: the Early Miocene Unconformity (EMU), the Mid-Miocene Unconformity (MMU) and the Late Miocene Unconformity (LMU). The major regional hiatus, referred to as the Mid-Miocene Unconformity, occurs intercalated within the present Breda Formation and compels subdivision of this unit into two formations, viz. the here newly established Groote Heide and the younger Diessen formations. Pending further studies, the former Breda Formation will be temporally raised in rank to the newly established Hilvarenbeek subgroup, which comprises both the Groote Heide and Diessen formations. Whereas these two sequences were already locally defined, a third sequence overlying the LMU represents two newly defined lithostratigraphical units, named the Goirle and the Tilburg members, positioned in this study at the base of the Oosterhout Formation. Besides their unique lithological characteristics, in seismic reflection profiles the Goirle and the Tilburg members stand out because of their distinct seismic facies.Use of an integrated, multidisciplinary and regional approach, an improved southern North Sea framework and more comprehensive lithostratigraphic subdivision of Neogene successions is proposed for the Netherlands, to make (cross-border) correlations more straightforward in the future.

Lithostratigraphic subdivisions of the Mesoproterozoic Copper Harbor Formation (Oronto Group) in Michigan and Wisconsin, USA

Lithostratigraphic subdivisions of the Mesoproterozoic Copper Harbor Formation (Oronto Group) in Michigan and Wisconsin, USA

Jurassic and Cretaceous biostratigraphy and organic matter geochemistry of the New Siberian Islands (Russian Arctic)

The Jurassic-Cretaceous terrigenous complex of the Laptev and East Siberian Seas is of considerable interest as a potential exploration target. However, the key Jurassic and Cretaceous sections of the New Siberian Islands have been poorly studied. The results of this study were used to provide a detailed micropaleontological description of these sections and substantiation of the previous lithostratigraphic subdivision. We first identified a series of Boreal standard zones in the Jurassic and Cretaceous sections, based on the foraminifers, ostracods, dinocysts, and terrestrial palynomorphs. Our results, along with the published data on ammonites, bivalves, and terrestrial palynomorphs and the results of radiometric dating, provide more precise constraints on the stratigraphic position of the identified lithostratigraphic units. The results of this study can be corroborated by seismic data to explore offshore areas of the Laptev and East Siberian Seas. We also present detailed data on the geochemistry of organic matter from the Pestsovaya Formation (Hettangian-lowermost Upper Pliensbachian).

U-Pb detrital zircon dates and provenance data from the Beaufort Group (Karoo Supergroup) reflect sedimentary recycling and air-fall tuff deposition in the Permo-Triassic Karoo foreland basin

Detrital zircon U-Pb age dating was used for provenance determination and maximum age of deposition for the Upper Permian (upper Teekloof and Balfour formations) and Lower Triassic (Katberg Formation) lithostratigraphic subdivisions of the Beaufort Group of South Africa's Karoo Basin. Ten samples were analysed using laser ablation - single collector - magnetic sectorfield - inductively coupled plasma - mass spectrometry (LA-SF-ICP-MS). The results reveal a dominant Late Carboniferous-Late Permian population (250 ± 5 Ma – 339 ± 5 Ma), a secondary Cambrian-Neoproterozoic (489 ± 5 Ma to 878 ± 24 Ma) population, a minor Mesoproterozoic (908 ± 24 Ma to 1308 ± 23) population, and minor occurrences of Devonian, Ordovician, Proterozoic and Archean zircon grains. Multiple lines of evidence (e.g. roundness and fragmentary nature of zircons, palaeo-current directions, and previous work), suggest the older zircon populations are related to sedimentary recycling in the Gondwanide Orogeny. The youngest and dominant population contain elongate euhedral grains interpreted to be directly derived from their protolith. Since zircons form in felsic igneous rocks, and no igneous rocks of Late Permian age occur in the Karoo Basin, these findings suggest significant input of volcanic material by ash falls. These results support sedimentological and palaeontological data for a Lopingian (Late Permian) age for the upper Beaufort Group, but contradict previous workers who retrieved Early Triassic dates from zircons in ashes for the Beaufort and Ecca Groups. Pb-loss not revealed by resolvable discordance on the concordia diagram, and metamictization of natural zircons are not factored into the conclusions of earlier workers.

Stratigraphy of the marine Lower Triassic succession at Kap Stosch, Hold with Hope, North-East Greenland

The classical marine uppermost Permian – Lower Triassic succession exposed on the north-east coast of Hold with Hope in East Greenland, south-east of Kap Stosch, is placed in the Wordie Creek Group. A new lithostratigraphic subdivision of the group is proposed here. The group comprises the revised Kap Stosch Formation overlain by the new Godthåb Golf Formation. The Kap Stosch Formation is dominated by alternating fine- and coarse-grained, cliff-forming units that constitute the basis for the erection of eight new members. They are (from below): 1. The Nebalopok Member, uppermost Permian, Hypophiceras triviale ammonoid zone, and lowermost Triassic, lower Griesbachian, Hypophiceras triviale – H. martini ammonoid zones, composed of basinal and base-of-slope siltstones and turbiditic sandstones. 2. The conglomeratic Immaqa Member (H. martini ammonoid zone), consisting of a thick clinoform-bedded unit commonly overlain by horizontally bedded deposits, representing the foreset and topset, respectively, of a Gilbert-type delta. 3. The fine-grained Fiskeplateau Member (H. martini ammonoid zone), composed of siltstones and fine-grained sandstones, representing basinal and delta front deposits. 4. The conglomerate-dominated Knolden Member (H. martini ammonoid zone), comprising a clinoform-bedded unit overlain by horizontally-bedded deposits, representing foreset and topset, respectively, of a Gilbert-type delta. 5. The fine-grained Pyramiden Member, (lower–upper Griesbachian Metophiceras subdemissum, Ophiceras commune and Wordieoceras decipiens ammonoid zones), composed of variegated siltstones and sandstones deposited in proximal basin and slope environments. 6. The Naasut Member (top Griesbachian, probably Wordieoceras decipiens ammonoid zone), dominated by thick structureless coarse-grained sandstones commonly showing clinoform bedding, deposited in slope, base-of-slope and proximal basin environments. 7. The Falkeryg Member (lowermost Dienerian, Bukkenites rosenkrantzi ammonoid zone), comprising thick, commonly pebbly sandstones deposited in shelf, slope and base-of-slope environments. 8. The Vestplateau Member (lower Dienerian, Bukkenites rosenkrantzi ammonoid zone) composed of siltstones and fine-grained sandstones deposited in basinal environments. The overlying Godthåb Golf Formation (Dienerian, Anodontophora breviformis – A. fassaensis bivalve zones) is dominated by shallow marine sandstones with several coarser grained levels. The rich ammonoid faunas of the Wordie Creek Group allow a biostratigraphic zonation which can be correlated with schemes from other parts of the Arctic region. This zonation is complemented with information on palyno, conodont, fish and isotope stratigraphy.

Litho- and biostratigraphy of the Opalinus Clay and bounding formations in the Mont Terri rock laboratory (Switzerland)

A 250 m-deep inclined well, the Mont Terri BDB-1, was drilled through the Jurassic Opalinus Clay and its bounding formations at the Mont Terri rock laboratory (NW Switzerland). For the first time, a continuous section from (oldest to youngest) the topmost members of the Staffelegg Formation to the basal layers of the Hauptrogenstein Formation is now available in the Mont Terri area. We extensively studied the drillcore for lithostratigraphy and biostratigraphy, drawing upon three sections from the Mont Terri area. The macropaleontological, micropaleontological, and palynostratigraphical data are complementary, not only spatially but they also cover almost all biozones from the Late Toarcian to the Early Bajocian. We ran a suite of geophysical logs to determine formational and intraformational boundaries based on clay content in the BDB-1 well. In the framework of an interdisciplinary study, analysis of the above-mentioned formations permitted us to process and derive new and substantial data for the Mont Terri area in a straightforward way. Some parts of the lithologic inventory, stratigraphic architecture, thickness variations, and biostratigraphic classification of the studied formations deviate considerably from occurrences in northern Switzerland that crop out further to the east. For instance, with the exception of the Sissach Member, no further lithostratigraphic subdivision in members is proposed for the Passwang Formation. Also noteworthy is that the ca. 130 m-thick Opalinus Clay in the BDB-1 core is 20 m thinner than that equivalent section found in the Mont Terri tunnel. The lowermost 38 m of the Opalinus Clay can be attributed chronostratigraphically solely to the Aalensis Zone (Late Toarcian). Deposition of the Opalinus Clay began at the same time farther east in northern Switzerland (Aalensis Subzone, Aalensis Zone), but in the Mont Terri area the sedimentation rate was two or three orders of magnitude higher.

Tectonostratigraphic framework and depositional history of the Cretaceous–Danian succession of the Danish Central Graben (North Sea) – new light on a mature area

Abstract An integrated tectonic and sequence stratigraphic analysis of the Cretaceous and Danian of the Danish Central Graben has led to significant new insights critical for our understanding of the chalk facies as a unique cool-water carbonate system, as well as for the evaluation of its potential remaining economic significance. A major regional unconformity in the middle of the Upper Cretaceous chalk has been dated as being of early Campanian age. It separates two distinctly different basin types: a thermal contraction early post-rift basin (Valanginian–Santonian), which was succeeded by an inversion tectonics-affected basin (Campanian–Danian). The infill patterns for these two basin types are dramatically different as a result of the changing influence of the tectonic, palaeoceanographic and eustatic controlling factors. Several new insights are reported for the Lower Cretaceous: a new depositional model for chalk deposition along the basin margins on shallow shelves, which impacts reservoir quality trends; recognition of a late Aptian long-lasting sea-level lowstand (which hosts lowstand sandstone reservoirs in other parts of the North Sea Basin); and, finally, the observation that Barremian–Aptian sequences can be correlated from the Boreal to the Tethyan domain. In contrast, the Late Cretaceous sedimentation patterns have a strong synsedimentary local tectonic overprint (inversion) that influenced palaeoceanography through the intensification of bottom currents and, as a result, the depositional facies. In this context, four different chalk depositional systems are distinguished in the Chalk Group, with specific palaeogeography, depositional features and sediment composition. The first formalization of the lithostratigraphic subdivision of the Chalk Group in the Danish Central Graben is proposed, as well as an addition to the Cromer Knoll Group.

Update of the Devonian lithostratigraphic subdivision in the subsurface of the Campine Basin (northern Belgium)

1. Introduction During the systematic lithostratigraphic description of the Palaeozoic deposits from the subsurface of the Campine Basin in northern Belgium (Lagrou, 2012), it appeared that certain stratigraphic intervals in deep boreholes, already identified and investigated as separated units by different authors (Langenaeker, 2000; Laenen, 2003), were not yet formally named. As one of the goals of the detailed stratigraphic study of Lagrou (2012) was to put all data in the Flemish web-based ‘Databank Ondergrond Vlaanderen’ (DOV), codes for the different lithostratigraphic units were needed. To be in accordance with DOV as well as with the Belgian official stratigraphy, the newly proposed lithostratigraphic units were submitted to the Belgian National Commission on Stratigraphy. This was the case for the Devonian Booischot Formation which is defined at the base of the Booischot borehole, above the Caledonian basement of the Brabant Massif. The Booischot borehole (Fig. 1A) has been drilled in 1963 for the Geological Survey of Belgium where the collection of cores is still stored and easily available. More generally, we present in this paper a complete stratigraphic overview of the Devonian from the Campine Basin, which has also been intersected by the Heibaart borehole (Fig. 1A). The study of the Heibaart borehole is mainly based on the unpublished report of Cornet (1976) illustrated by two photographic volumes of discontinuous cores with comments, which are stored in the Ar