Late Cretaceous Sequence Research Articles

High-resolution calcareous nannofossil biostratigraphy and facies of Nimar Sandstone Formation (Bagh Group), central India and its bearing on Oceanic Anoxic Event 2

It is proposed to consider Narmada Valley Late Cretaceous sequences in three sectors with proper selection of stratotype in each sector: Eastern Sector: comprising of Lameta group of rocks with type area in Jabalpur area, essentially laid down in lacustrine-paedogenic milieu and containing a variety of fossils including dinosaur remains of Late Maastrichtian age. No evidence of sea incursion is available in the Eastern Sector either via the Narmada lineament or the K-G Basin. Central Sector: comprising of the Bagh Group in ascending order of: Nimar Sandstone Formation–Nodular Limestone Formation–Coralline-Bryozoan Limestone Formation, laid down in estuarine complex entirely within Turonian without any evidence of Cenomanian and Coniacian age calcareous nannofossils or other fossils being present. In the western part of Central Sector: Siliciclastic rocks and limestones referred to as Nimar Sandstone Formation curiously lack Late Cenomanian marker species, hence could be of Early Turonian age. Western Sector: comprises of Lacustrine sediments associated with Deccan Flood Basalt. The absence of the Cenomanian/Turonian Boundary and Black shales negates the presence of global OAE2 events in the Narmada lineament, but several OAE events are recognised in the Cauvery Basin, southeastern India. Uranium- and Thorium-rich Lower and Upper Nimar Sandstone Formation overlying crystalline basement are interpreted to have been essentially laid down in a fully marine estuarine milieu with reworked plant, and palynofossils including dinosaur remains. Calcareous nannofossils recovered from Upper Nimar Sandstone Formation over four decades ago and assigned Late Turonian age is revised based on modern data incorporating calcareous nannofossil and planktonic foraminifera datum and now suggest an older age of Early Turonian matching a zone with FAD of Quadrum gartneri at the base and FAD of H. helvetica at the top. It must be emphasised that except for the solitary and unique incursion of Early Turonian (ca. 93.9 Ma) sea along the Narmada lineament reaching eastward (>300 km) up to the present town of Indore, no other marine intrusion ever took place on Indian shield except along collision facing Subathu–Dogadda lineament during Late Maastrichtian. It would be erroneous to suggest that the global eustatic rise of sea level caused the entry of the Turonian sea along the Narmada lineament; instead, it was earlier speculated by me that Large Igneous Province activity of Mahajanga Flood Basalt of Madagascar (ca. 93.9 Ma) could have most probably caused a short-lived Turonian sea to enter Narmada lineament from the west around C/T boundary.

Late Cretaceous stratigraphic division in the northwestern Songliao Basin, Northeast China: Evidence from palaeontology and palaeomagnetism

This paper combines new palaeomagnetic studies, palaeontological dating, and sedimentary analyses to propose a modified stratigraphic classification scheme in the northwestern Songliao Basin, which is of great significance for stratigraphic correlation, sedimentation analysis, basinal subsidence, and oil and gas exploration. New palaeontological and palaeomagnetic evidence redefined a group of semi‐consolidated lacustrine strata, buried beneath the Quaternary Yaluhe Formation on the Western Slope of the Songliao Basin, as Late Cretaceous, not the Middle Pleistocene. The chronostratigraphic framework re‐evaluates its stratigraphic age as late Coniacian to early Campanian (Late Cretaceous), between 83 and 85 Ma. Sedimentation research from 17 boreholes on the Western Slope of the Songliao Basin displays that the semi‐consolidated strata successively experienced lacustrine and delta facies deposits. Comparison of this new stratigraphy with the Late Cretaceous sequences on the adjacent Central Depression of the Songliao Basin reveals significant variations in lithology and palynological assemblages. Three new palynological assemblages are also reported from the Late Cretaceous sequences of the Songliao Basin.

Late Cretaceous (Turonian-Coniacian) sequence stratigraphy, sea level, and deltaic facies, Magothy Formation, U. S. Middle Atlantic Coastal Plain

ABSTRACT: The peak "hothouse" interval of the Turonian-Coniacian (93-87 Ma) is represented on the U.S. middle Atlantic Coastal Plain by sequences of the Raritan/Bass River, Magothy, and Cheesequake Formations deposited on a passive continental margin as mixed wave-, tide-, and river dominated deltas. We apply sequence stratigraphy integrated with biostratigraphy to identify and map two major sequence boundaries separating the Raritan/Bass River, Magothy, and Cheesequake Formations and four to five (Mg1, Mg2, Mg3, ?Mg4, Mg5) Magothy sequences using continuous cores, outcrops, and geophysical logs in New Jersey. We extend correlations into New York and Delaware using well logs. The Magothy sequences disconformably overlie the well-dated (>93 Ma) lower Turonian to Cenomanian marine Raritan/Bass River sequences and are disconformably overlain by the marine Cheesequake Formation, which straddles the Coniacian/Santonian boundary. A "mid-Turonian" hiatus (ca. 93-90 Ma) associated with this major disconformity is a global sequence boundary (K-Tu4) reflecting a ~ 25 m sea-level lowering based on published NJ and Russian Platform backstripping records that indicate this was a major lowering of Global Mean Sea Level (GMSL).Higher-order (~1 Myr scale) sequence boundaries bracketing Mg1-Mg5 apparently correlate with global sequences but are only associated with low-amplitude (<25 m) sea-level falls.Mapping of sequences within the Magothy Formation shows the influence of 2 to 3 moderate-sized river sources, with thickening northeastward toward Long Island, New York, and thinning southwestward toward Delaware. Thick northern depocenters contrast with the preceding Potomac Formation (Barremian-early Cenomanian) with thick southern depocenters. This seesawing of basins on the 100-300 km and 2-10+ Myr scales is due to tectonism likely from changes inmantle dynamic topography. The remarkably widespread distribution of Magothy sequences and facies indicates stability of this deltaic depositional system over ~ 4Myr despite low-amplitude (less than 25m) sea-level variations.Widespread facies correlation provides a predictable distribution of aquifer sands and confining-unit clays tied to sea-level changes on complex deltaic facies.

Dolomite cements in Cenomanian continental sand deposits: Time evolution and significance (Zoovch Ovoo U-deposit, East Gobi Basin, Mongolia)

Shallow buried unconsolidated sands generally provide very little information about diagenesis as most detrital minerals remain unchanged. However, in rare cases carbonate cemented nodules or sandstone layers may occur inside unconsolidated series. These cements could help to reconstruct the chronology of events from early to late phase stages of diagenesis. The Late Cretaceous sequence of the Zoovch Ovoo depocenter in East Gobi Basin is represented by 600 m of clastic deposits. The 60–80 m of Cenomanian unconsolidated sands and clays, deposited in alluvial-deltaic to lacustrine settings, compose the upper part of the post-riftmedium-grained siliciclastic reservoir, the Sainshand Formation which hosts uranium roll-front systems. Dolomite cemented sandstone layers with 10–20 cm thickness occur among the unconsolidated rock facies. Calcite is absent from this formation, but is present only in the overlying, also outcropping, Bayanshiree Formation. Samples from the dolomite cemented sandstone layers were investigated in detail to uncover their origin and diagenetic history. Four dolomite cement types were recognized that indicate recrystallization episodes and were classified based on the size and shape of the crystals, namely: (i)microcrystalline dolomite frequently associated with siderite, (ii) euhedral dolomite also associated with siderite, (iii) subhedral dolomite and (iv) finally anhedral dolomite. Their REE content varies significantly from dolomite I to IV, in particular by a strong depletion in LREE about 30 times. The contrasted precipitation of calcite in Bayanshiree and dolomite cements in Sainshand formations could be attributed to different Mg/Ca ratio of the circulation fluids in the two aquifers. Both carbonates display however rather homogenous oxygen and carbon isotopic compositions for δ18O (−10 ± 1‰ V-PDB) and δ13C (−7 ± 1‰ V-PDB). The δ18O values are interpreted as inherited from typical meteoric waters quite close to present day waters. The δ13C values indicate a mixed source of both organic and mineral carbon. All data taken into account, a full paragenetic succession was constructed. It includes the evolution of dolomite during burial diagenesis and the effects of the oxidizing roll-front uranium rich waters in the system. The latter induces partial dissolution followed by precipitation of a dolomite phase typical of roll-front zones. Carbonate cements can be thus considered as the best and rather unique geochemical indicators for the recognition of a burial history framework to paleofluid circulations and fluid-rock interactions in these intracontinental series of unconsolidated sands.

Geochemistry, detrital zircon geochronology and Hf isotope of the clastic rocks in southern Tibet: Implications for the Jurassic-Cretaceous tectonic evolution of the Lhasa terrane

In order to reconstruct tectonic evolution history of the southern margin of Asia (i.e., Lhasa terrane) before the India-Asia collision, here we present a comprehensive study on the clastic rocks in the southern Lhasa terrane with new perspectives from sedimentary geochemistry, detrital zircon geochronology and Hf isotope. Clasts from the Jurassic-Early Cretaceous sedimentary sequences (i.e., Yeba and Chumulong Formations) display high compositional maturity and experienced moderate to high degree of chemical weathering, whereas those from the late Early-Late Cretaceous sequences (Ngamring and Shexing Formations) are characterized by low compositional maturity with insignificant chemical weathering. Our results lead to a coherent scenario for the evolution history of the Lhasa terrane. During the Early-Middle Jurassic (∼192-168Ma), the Lhasa terrane was speculated to be an isolated geological block. The Yeba Formation is best understood as being deposited in a back-arc basin induced by northward subduction of the Neo-Tethys ocean with sediments coming from the interiors of the Lhasa terrane. The Middle Jurassic-Early Cretaceous Lhasa-Qiangtang collision resulted in the formation of a composite foreland basin with southward-flowing rivers carrying clastic materials from the uplifted northern Lhasa and/or Qiangtang terranes. During the late Early-Late Cretaceous (∼104-72Ma), the Gangdese magmatic arc was uplifted rapidly above the sea level, forming turbidites (Ngamring Formation) in the Xigaze forearc basin and fluvial red beds (Shexing Formation) on the retro-arc side. At the end of Late Cretaceous, the Lhasa terrane was likely to have been uplifted to high elevation forming an Andean-type margin resembling the modern South America before the India-Asia collision.

Tectono-stratigraphic evolution of Late Cretaceous basins into Veslemøy High, SW Barents Sea

The Veslemoy High is located in the southwestern sector of the Barents Sea and its geological evolution is strictly linked to the geodynamic development of the Norwegian region. The tectonic evolution of the Veslemoy High and several other structural elements of the Barents Sea remains poorly understood mostly because of a general lack of stratigraphic control, high-quality data and the complexinterplay of geodynamic episodes, which has prevented the structures and ages of several stratigraphic units to be correctly constrained. This study used 3-D and 2-D seismic reflection data, integrated with well data to reconstruct the geological history of the Veslemoy High area. The methods here used include seismic interpretation of several horizons and faults, seismic-well data calibration (well 7219/8-1S) and well data (7216/11-1S; 7218/11-1; 7218/8-1; 7219/8-1S). Such an investigation led to the definition of several compressional and extensional tectonic phases, which affected the area most especially in pre-Cenozoic time. The oldest compressional phase here documented is Late Cretaceous and is marked by large-scale anticlines and synclines (about 10 km wavelength). Following this tectonic phase, the study area was affected by a system of mainly west dipping normalfaults, creating several half graben structures. In some cases, these grabens display evidences of slight positive inversion. Analysis of the Late Cretaceous sequence provides interesting markers of sediments infilling patterns, erosional surfaces, uplift, tilting, faulting, extensional and contractional structures. All these structures point to a complex interplay of Pre-, Syn- and Post-Late Cretaceous tectonicactivities. Importantly, the Lower Regional Unconformity (LRU), Upper Regional Unconformity (URU), stratigraphic terminations, and faults are significant tectonic markers in the Veslemoy High area and in surrounding basins. Tectonic structures documented here are characteristics of the Mesozoic and Cenozoic geological framework of the NE Atlantic margin.

کانه زایی مس- نقره سولفید توده ای آتشفشان زاد نوع بشی در توالی آتشفشانی- رسوبی کرتاسه پسین: مثال موردی کانسار گرماب پایین، جنوب شرق شاهرود

کانسار مس- نقره گرماب پایین در توالی آتشفشانی- رسوبی کرتاسه پسین زیر پهنه سبزوار واقع ‌شده است. کانه زایی به شکل هندسی چینه‌سان و چینه‌کران در افق چینه‌ای خاص به همراه نهشته‌های برون‌دمی رخ‌داده است. سنگ میزبان کانه زایی را سنگ‌های آتشفشانی آندزیتی- داسیتی و آذرآواری‌های وابسته تشکیل می‌دهند. کانه زایی از کمرپایین به سمت کمربالا در چهار رخساره رگه- رگه‌چه ای، توده‌ای- نیمه توده‌ای، لایه‌ای و رسوبات برون‌دمی رخ‌داده است. کانی‌شناسی ماده معدنی شامل کانی‌های اولیه نظیر پیریت، مگنتیت و کالکوپیریت و کانی‌های ثانویه نظیر مس طبیعی، مالاکیت، کوپریت، کولیت و اکسیدهای آهن- منگنز است. دگرسانی سنگ دیواره، به‌طور عمده از نوع کلریتی و به مقدار کمتر شامل سیلیسی، آرژیلیتی و زئولیتی است. حداکثر عیار طلا و نقره در کانسار به ترتیب 1 و 19 گرم در تن است. به نظر می‌رسد که بروز فعالیت آتشفشانی زیردریایی در یک حوضه پشت‌کمانی در کرتاسه پسین، به تشکیل این کانسار سولفید توده‌ای نوع بشی منجر شده است.

The Ikom-Mamfe basin, Nigeria: A study of fracture and mineral vein lineament trends and Cretaceous deformations

The Ikom-Mamfe basin is approximately a 130km long, east–west abutment onto the eastern flank of the lower Benue trough of Nigeria and extends westwards into Cameroon. Two hundred and six fracture lineaments were analyzed in the Nigerian sector of this basin. They vary in length from 0.5 to 23.75km, with the most frequently occurring fracture length being about 2.25km. The most prominent fracture sets have NE-SW and NW-SE orientations, while less prominent patterns are in the NNE-SSW and ESE-WNW directions. NW-SE and NNE-SSW fracture sets are interpreted as “ac” extension fractures from two different deformation episodes, while NE-SW and ESE-WNW sets are “bc” tensile fractures parallel to the axes of F1 and F2 folds, respectively. This implies two deformation episodes in this basin, with the earlier one producing the NE-SW (F1) fold axes, exactly as in the Benue trough. Two prominent mineral vein trends in the basin are the NW-SE and NNE-SSW sets, in which minerals are loaded in “ac” extension fractures. The orientations, lengths and frequency of these lineaments should help in differentiating their ages. The less prominent veins are in the NE-SW and ESE-WNW directions, which are in the “bc” tensile fractures. Early Cretaceous sediments are characterized by NW-SE major and NE-SW minor sets of veins, while the late Cretaceous sequence is characterized by NNE-SSW major and ESE-WNW minor, mainly barite, veins. More than 70% of the barite samples tested gave specific gravity values of 4.2 and above, which is the range specified by the American Petroleum Institution (API) as drilling mud additive or weighting agent. Other vein-filling minerals in this basin are lead ore (galena), zinc ore (sphalerite), pyrite and amethyst, which are altogether subsidiary to barite mineralization.

The Eastern Black Sea-type volcanogenic massive sulfide deposits: Geochemistry, zircon U–Pb geochronology and an overview of the geodynamics of ore genesis

The Meso-Cenozoic geodynamic evolution of the eastern Pontides orogenic belt provides a key to evaluate the volcanogenic massive sulfide (VMS) deposits associated with convergent margin tectonics in a Cordilleran-type orogenic belt. Here we present new geological, geochemical and zircon U–Pb geochronological data, and attempt to characterize the metallogeny through a comprehensive overview of the important VMS mineralizations in the belt. The VMS deposits in the northern part of the eastern Pontides orogenic belt occur in two different stratigraphic horizons consisting mainly of felsic volcanic rocks within the late Cretaceous sequence. SHRIMP zircon U–Pb analyses from ore-bearing dacites yield weighted mean 206Pb/238U ages ranging between 91.1±1.3 and 82.6±1Ma. The felsic rocks of first and second horizons reveal geochemical characteristics of subduction-related calc-alkaline and shoshonitic magmas, respectively, in continental arcs and represent the immature and mature stages of a late Cretaceous magmatic arc. The nature of the late Cretaceous magmatism in the northern part of the eastern Pontides orogenic belt and the various lithological associations including volcaniclastics, mudstones and sedimentary facies indicate a rift-related environment where dacitic volcanism was predominant. The eastern Pontides VMS deposits are located within the caldera-like depressions and are closely associated with dome-like structures of felsic magmas, with their distribution controlled by fracture systems. Based on a detailed analyses of the geological, geophysical and geodynamic information, we propose that the VMS deposits were generated either in intra arc or near arc region of the eastern Pontides orogenic belt during the southward subduction of the Tethys oceanic lithosphere.

Structure of the sedimentary cover of the Pugachevo mud volcano area in Sakhalin: Evidence from geophysical modeling

The geological-geophysical data on the Pugachevo mud volcano group located in the zone of the submeridional Central Sakhalin Fault (CSF) are analyzed. The results of the density and geothermal modeling along two orthogonal profiles passing through the central part of the Pugachevo area are examined. It is found that the Late Cretaceous sequence of this fault-related area contains a subvertical narrow anomalous deconsolidation cone-shaped zone widening from 1 km on the surface to 4 km at its base (at the depths more than 6 km). The density of the deconsolidation blocks is 2.20–2.22 g/cm3, whereas that of the adjacent blocks reaches around 2.4–2.5 g/cm3. The largest deconsolidation block is located in the Lower Cretaceous Ai Formation, where a vast reservoir zone with mainly hydrocarbon gas (HC) is inferred at depths of more than 4400 m with temperatures of more than 140°C. The modeling results showed that the main reservoir of gases periodically ejected from the Pugachevo mud volcano is localized in the Ai Formation sequence in the tectonically weakened zone of the CSF at depths of 4.5–5.6 km. The overlying sequences contain smaller intermediate reservoirs. The Pugachevo area is promising for economic hydrocarbon reservoirs.

Geology, Geotechnical Engineering, and Natural Hazards of Memphis, Tennessee, USA

The generally flat landscape of the Memphis, TN, area hides a fascinating geologic history. Cambrian rifting resulted in the concealed faults of the Reelfoot rift, currently the active component of the New Madrid Seismic Zone, lying immediately northwest of the city. Memphis also sits within the Mississippi Embayment. Subsidence of the embayment brought about deposition of the thick Late Cretaceous and Cenozoic sedimentary sequence underlying the city. This sequence provides one of the finest groundwater aquifers in the world, the Memphis Sand. Pliocene ancestral Ohio River alluvium (Upland Complex) is an excellent source of sand and gravel for the region. Plio-Pleistocene fluvial degradation by the Mississippi River and its tributaries, in addition to deposition of Pleistocene loess sheets, have produced the subtle topography of Memphis and Shelby County. Memphis geology makes geotechnical engineering design challenging because loess is highly sensitive to disturbance. Exploratory sampling techniques tend to cause disturbance to loess during sampling and sample extraction. Thus, conventional sampling techniques yield variable engineering property test results (e.g., strength and compressibility). The city of Memphis and Shelby County have together become a major commodities distribution center for the United States, North America, and the global economy. The principal natural hazards are the frequent severe weather and the prospect of a repeat of the >7M 1811–1812 New Madrid earthquakes. These unavoidable exposures to severe weather, urban and riverine flooding, and earthquakes combined with social conditions tend to amplify the consequences of hazard events.

Brittle tectonic evolution along the western margin of South Africa: More than 500 Myr of continued reactivation

The brittle structural history of western South Africa has been investigated by remote sensing and field studies to build a conceptual scheme for its > 500 Ma long evolution. Paleostress tensors were computed from a significant fault-slip dataset and a relative geochronological succession of brittle deformation events was established. This was aided by separating in time faulting events through the usage of Cretaceous weathering horizons, silicified fluvial deposits, paleosols and 77–54 Ma olivine melilitite plugs as time markers. The oldest features recognized formed during four compressional episodes assigned to the Neoproterozoic Pan African evolution. This history is expressed by sub-vertical conjugate fracture sets and fits well the inferences derived from remote sensing. The greatest compressive direction rotated from NW-SE to NNE-SSW and finally to almost E–W. A subsequent ENE-WSW-oriented extensional episode is associated with the local effects of the opening of the Atlantic Ocean and was followed by a second, ca. E–W extensional episode, linked to the well-acknowledged Mid-Cretaceous (115–90 Ma) event of margin uplift. A late Santonian (85–83 Ma) NW-SE compressive paleostress deformed the Late Cretaceous sequences and was in turn followed firstly by a renewed episode of NE-SW extension and later by ca. NNE-SSW Late Maastrichtian (69–65 Ma) shortening. The latter is broadly coeval with the emplacement of the Gamoep magmatic suite. A phase of WNW-ESE Cenozoic extension is assigned to the extensional phase recorded in the Okawango delta, interpreted as reflecting propagation of the East African Rift System into southern Africa. No stress tensor was computed for the present day “Wegener anomaly” stress field, oriented NW-SE. However, in situ stress measurements were used to perform slip tendency analysis, which indicates that, under the currently existing stress conditions, WNW-ESE- and NNW-SSE-striking faults are critically stressed and are the most likely reactivated, in agreement with the present seismicity.

Stable isotope and mineralogical investigations on clays from the Late Cretaceous sequences, Haţeg Basin, Romania

In the Haţeg basin, South Carpathians, a thick continental sequence accumulated during the Maastrichtian. The alluvial sequences are characterized by the formation of paleosol horizons developed on the alluvial plain. In order to investigate the environmental signal stable isotope and mineralogical investigations have been carried out on smectites from paleosol. The RX as well as the FTIR spectra of the fraction < 2 µm indicate that the main clay mineral is smectite. Based on XRF analysis, the smectite is a montmorillonite with the formula {Na 0.67 Ca 0.1}[Al 1.19 Mg 0.62 Fe 3+ 0.19] (Si 3.78 Al 0.22 O 10) (OH) 2. FTIR data show that interlayer water from smectite is liberated after ~ 24 h heating at 200 °C. Stable isotopic composition of precipitations have been monitored in the Hateg basin and in a neighbored area situated in the Apuseni mountains. The results show the same meteoric water line (LMWL) with the equation δD = 7.9 ⁎ δ 18O + 8.14 for both sites. Stable isotope data on clay fraction less than 2 µm show that the structural water from smectites formed under different environmental conditions during the Maastrichtian have re-equilibrated isotopically with the present meteoric water.

Mineralogical control on mudstone compaction: a study of Late Cretaceous to Early Tertiary mudstones of the Vøring and Møre basins, Norwegian Sea

The Late Cretaceous to Early Tertiary sediments of the Vøring and Møre basins are predominantly composed of fine-grained mudstones. Variations in the mineralogy and chemistry of these mudstones provide information regarding facies, provenance and burial history, and may also be used to predict rock properties. Over 300 cuttings’ samples from five wells were analysed by XRD. The results show significant changes in mineralogy as a function of burial depth, as well as important lateral variations throughout the basins. Eocene mudstones with up to 55% smectite probably represent a northern equivalent of the Balder Formation (North Sea). The underlying Late Cretaceous sequence probably had less primary smectite derived from volcanic ash, as indicated by the lower iron content. The distribution of smectite is also limited by its thermal stability, thus providing important constraints on the temperature history. These mudstone sequences may appear to be relatively homogeneous based on gamma-ray and shale volume calculations from wireline logs, but mineralogical and geochemical analyses from cuttings show that they vary significantly in composition. The smectite content is greatest in the south ( c . 55%) and decreases significantly northward ( c . 20%), indicating a marked regional control on velocity/porosity–depth curves. Mudstones containing high smectite content are characterized by lower velocities, lower densities and higher porosities when compared with published burial curves. Stratigraphic and regional variations in velocity and density are important for seismic interpretation and are significant for basin modelling.

Source Rock Characteristics and Hydrocarbon Potential of the Late Cretaceous Deposits in the Eastern Black Sea Region, NE Turkey

In this article, source rock characteristics and hydrocarbon potential of the late Cretaceous turbidite sequences in the eastern Black Sea region were investigated. The total average organic carbon (TOC) contents of sequences in Trabzon, Gümüshane, Giresun, and Erzurum are 0.06, 0.18, 0.12, and 0.30 wt%, respectively. In addition, low potential yield (PY), low hydrogen index (HI), and very high oxygen index (OI) values were calculated for these sequences. On the basis of Tmax values, most of sequences are thermally immature, and only some parts are mature and over-mature. Sequences generally contain residual organic matter and lesser amounts of type III kerogen. CPI values higher than 1, n-alkane distributions with high carbon numbers, and type III kerogen content indicate that organic matter has a terrestrial origin. The Pr/Ph ratios calculated as 1.10 and 2.15 for the Mescitli section of the Gümüshane region and the Tortum section of the Erzurum region reveal that the Mescitli section was deposited in a suboxic environment, while the Tortum section was in an oxic environment. According to these data, late Cretaceous sequences show weak source rock characteristics.

Middle Cretaceous to Eopleistocene Sequences on the New Siberian Islands: an approach to interpret offshore seismic

The New Siberian Islands divide the Laptev Sea from the East Siberian Sea. The Archipelago comprises three island groups: De Long Islands, Anjou Islands, and Lyakhov Islands. The regional structural ensemble comprises De Long, Kotel'nyi, Faddeya and Lyakhov tectonic Domains. Aptian–Albian, Late Cretaceous, Palaeocene–Eocene, Oligocene–Miocene, and Pliocene–Eopleistocene tectono-stratigraphic and igneous sequences have been identified on the Islands. The succession of these sequences and their structural and compositional characters provide to distinguish specific stages in the tectonic history of the region showing alteration of regional tectonic environment through the middle Cretaceous and the Tertiary correlative to major North-East Eurasia, Arctic, and Global events. LS1, LS2, and LS3 major regional unconformities have been identified offshore by German geoscientists based on MCS data in the New Siberian Islands area. It is hypothesized in this paper that three offshore sedimentary cover units bounded by the unconformities correlate to the onshore sequences the following way: Unit I comprises Aptian–Albian and late Cretaceous Sequences, Unit II, Palaeocene–Eocene and Oligocene–Miocene Sequences, and Unit III comprises Pliocene–Eopleistocene Sequence and overlying Quaternary sediments.

EXPLORING THE POTENTIAL FOR OIL GENERATION, MIGRATION AND ACCUMULATION IN CAPE SORELL–1, SORELL BASIN, OFFSHORE WEST TASMANIA

Given the underexplored nature of the Sorell Basin, offshore Tasmania, the reported presence of oil stains and shows in the Late Cretaceous sequence below 3,000 m in Cape Sorell–1 is seen as encouraging evidence of an effective petroleum system. To investigate the significance of these shows, an integrated palynological, geochemical and burial history analysis of Cape Sorell–1 has been undertaken. New data have been collected on palynology, potential source rocks (biomarker and chemical kinetics), oil migration indicators (quantitative grain fluorescence—QGF, and grains–with–oil– inclusions—GOI) and thermal history parameters (vitrinite reflectance—VR, vitrinite–inertinite reflectance and fluorescence—VRF® and apatite fission track analysis—AFTA®). A synthesis of these analyses has resulted in a model that suggests that the terrestrial organic–rich potential source rocks in Cape Sorell–1 are very labile for hydrocarbon generation and are presently at the initial phase of oil generation. The model also indicates that increasing hydrocarbon generation with time reflects a progressive increase in temperature reaching maximum temperatures at the present–day. According to the model, accelerated rate of oil generation from the Maastrichtian potential source rock interval at ~3,200 m in the lower Sherbrook Group Equivalent occurred at ~48 Ma and is in response to the maximum burial heating rate in the Early Eocene, during rapid deposition of the thick Wangerrip Group Equivalent. This heating event may have been related to gateway opening along the Otway coast and west Tasmanian margin. Although there was a declining heating rate since the Early Eocene, gas and oil may continue to be generated to the present–day at Cape Sorell–1.The low content of mobile oil below sealing facies higher in the section negates a pervasive oil migration phase sourced down–dip from the basin centre, or from older sedimentary sequences below TD in Cape Sorell–1. However, the possibility that Cape Sorell–1 is in a migration shadow cannot be excluded. The restricted areal extent of the depocentre associated with Cape Sorell–1, together with thin, isolated potential source beds at the well site, would indicate the major risk for hydrocarbon occurrences in the local region is limited source rock volume. However, seismic evidence suggests the possible presence of similar facies within the deeper syn–rift succession below TD at Cape Sorell–1. The labile nature of the organic matter would support oil generation and migration at maturities lower and depths shallower than traditionally viewed. This work provides evidence to support a possible oil play from terrestrial source rocks in the Sorell Basin, and may also provide useful insights into recent large offshore gas discoveries to the north in the adjacent Otway Basin.

Tectonique synsedimentaire d'age cretace superieur en Tunisie nord orientale; blocs bascules et reorganisation des aires de subsidence

Abstract Structural analysis of late Cretaceous sequences from the northeastern Tunisian Atlas, led to conclude on an active basin floor instability. Regional tectonics resulted in tilted blocks with a subsidence reorganization, since the Campanian time. These structural movements are controlled both by N140 and N100-120 trending faults. The Turonian-Coniacian and Santonian sequences display lateral thickness and facies variation, due to tectonic activity at that time. During Campanian-Maastrichtian, a reorganization of the main subsidence areas occurred, the early Senonian basins, have been sealed and closed and new half graben basins developed on area which constituted previously palaeohigh structures. These syndepositional deformations are characterized by frequent slumps, synsedimentary tilting materials, sealed normal faults and progressive low angle unconformities. These tilted blocks combined to a subsidence axis migration were induced by a NE-SW trending extensional regime. This extension which affects the Tunisian margin during the Upper Cretaceous, is related to the Tethyan and Mesogean rifting phase which resulted from the combined movements of the African and European plates.

Stratigraphy and Magnetostratigraphic/Faunal Constraints for the Age of Sauropod Embryo-Bearing Rocks in the Neuquén Group (Late Cretaceous, Neuquén Province, Argentina)

The stratigraphy and age of a sauropod nesting ground containing the first definitive embryonic remains of sauropods preserved inside their eggs is analyzed. The fossil locality, called Auca Mahuevo, occurs in the Anacleto Member of the Río Colorado Formation in Neuquén Province, Argentina. The 5 m thick interval of overbank mudstones containing the fossilized eggs and embryos occurs near the middle of a 35 m sequence of thin, fluvial, concretionary sandstones and thicker units of silty sandstone. Flooding of shallow stream channels deposited overbank silt and mud on the eggs, killing the embryos and initiating the process of fossilization. Egg fragments containing patches of fossilized integument were found as float weathering out of the mudstone on local flats. Complete eggs containing embryonic bones and teeth were quarried from a steep ridge where the mudstone was exposed.Twelve paleomagnetic samples collected throughout the lower 30 m of the section establish the presence of a Reverse geomagnetic polarity interval. This constitutes the first magneto-stratigraphic characterization for this part of the Río Colorado Formation and for the late Cretaceous sequence of formations that comprise the Neuquén Group. Biochronologic age estimates for the Río Colorado fauna combined with the Reverse polarity determinations for the fossiliferous sediments in the Anacleto Member argue for an age younger than the long Cretaceous C34 Normal, which ends at the upper boundary of the Sartonian and older than the late Campanian. The Reverse interval containing the fossils at Auca Mahuevo is therefore considered to be early or middle Campanian in age, most likely correlative with C33R between 83.5 and 79.5 Ma.

Signature of hydrodynamic activity caused by rapid sea level changes in pelagic organic-rich sediments, Tarfaya basin (southern Morocco)

Abundant beds with calcareous tempestites, hummocky cross-stratifications ‘HCS’, bioclastic limestones ‘BL’ and limestone channels ‘LCh’ occur in the Late Cretaceous sequence (Middle-Late Cenomanian / Early Turonian) of the Tarfaya basin (SW Morocco) with a strongly erosive base. Results of the study have significant implications for sea level fluctuations in fine-grained basinal facies. According to the palaeoenvironmental reconstructions, the strata were deposited in the offshore area dominated by an upwelling system. The regular distribution of the ‘BL’, ‘HCS’ and ‘LCh’ throughout the section provides a constraint on palaeobathymetry. The water depth during deposition fluctuated frequently and ranged from below, but near, storm wave base.