Palynostratigraphy and palaeoenvironmental significance of the Cretaceous palynomorphs in the Qattara Rim-1X well,North Western Desert,Egypt

Palynological and palynofacies analyses were carried out on some Cretaceous samples from the Qattara Rim-1X borehole, north Western Desert, Egypt. The recorded palynoflora enabled the recognition of two informal miospore biozones arranged from oldest to youngest as Elaterosporites klaszii-Afropollis jardinus Assemblage Zone (mid Albian) and Elaterocolpites castelainii–Afropollis kahramanensis Assemblage Zone (late Albian–mid Cenomanian). A poorly fossiliferous but however, datable interval (late Cenomanian–Turonian to ?Campanian–Maastrichtian) representing the uppermost part of the studied section was also recorded. The palynofacies and visual thermal maturation analyses indicate a mature terrestrially derived organic matter (kerogen III) dominates the sediments of the Kharita and Bahariya formations and thus these two formations comprise potential mature gas source rocks. The sediments of the Abu Roash Formation are mostly dominated by mature amorphous organic matter (kerogen II) and the formation is regarded as a potential mature oil source rock in the well. The palynomorphs and palynofacies analyses suggest deposition of the clastics of the Kharita and Bahariya formations (middle Albian and upper Albian–middle Cenomanian) in a marginal marine setting under dysoxic–anoxic conditions. By contrast, the mixed clastic-carbonate sediments of the Abu Roash Formation (upper Cenomanian–Turonian) and the carbonates of the Khoman Formation (?Campanian–Maastrichtian) were mainly deposited in an inner shallow marine setting under prevailing suboxic–anoxic conditions as a result of the late Cenomanian and the Campanian marine transgressions. This environmental change from marginal to open (inner shelf) basins reflects the vertical change in the type of the organic matter and its corresponding hydrocarbon-prone types. A regional warm and semi-arid climate but with a local humid condition developed near/at the site of the well is thought to have prevailed.     

Maastrichtian to Paleocene depositional environment of the Dakhla Formation, Western Desert, Egypt: sedimentology, mineralogy, and integrated micro- and macrofossil biostratigraphies

Integrated sedimentology, mineralogy, geochemistry, and microfossil and macrofossil biostratigraphies of the Maastrichtian–early Paleocene Dakhla Formation of the Western Desert, Egypt, provide improved age resolution, information on the cyclic nature of sediment deposition, and the reconstruction of depositional environments. Age control based on integrated biostratigraphies of planktic foraminifera, calcareous nannofossils and macrofossils yields the following ages for stratigraphic and lithologic sequences. The contact between the Duwi and Dakhla formations marks the Campanian/Maastrichtian boundary (zone CF8a/b boundary) and is dated at about 71 Ma. The age of the Dakhla Formation is estimated to span from 71 Ma at the base to about 63 Ma at the top (zones CF8a–Plc). The Cretaceous/Tertiary (K/T) boundary is within the upper unit of the Kharga Shale Member and marked by a hiatus that spans from 64.5 Ma in the lower Paleocene (base Plc) to at least 65.5 Ma (base CF2, base M. prinsii zones) in the upper Maastrichtian at Gebel Gifata, the type locality of the Dakhla Formation. As a result, the Bir Abu Minqar horizon, deposited between about 64.2 and 64.5 Ma (Plc(l) zone), directly overlies the K/T boundary hiatus. Major hiatuses also span the late Maastrichtian–early Paleocene in sections to the northwest (c. 61.2–65.5 Ma at North El Qasr, c. 61.2–69 Ma at Bir Abu Minqar and c. 61.2–65.5 Ma at Farafra), and reflect increased tectonic activity.During the Maastrichtian–early Paleocene a shallow sea covered the Western Desert of Egypt and the clastic sediment source was derived primarily from tectonic activity of the Gilf El Kebir spur to the southwest of Dakhla and the Bahariya arch. Uplift in the region resulted in major hiatuses in the late Maastrichtian–early Paleocene with increased erosion to the southwest. The area was located near the palaeoequator and experienced warm, wet, tropical to subtropical conditions characterized by low seasonality contrasts and predominantly chemical weathering (high kaolinite and smectite). A change towards perennially more humid conditions with enhanced runoff (increased kaolinite) occurred towards the end of the Maastrichtian and in the early Paleocene with shallow seas fringed by Nypa palm mangroves. Sediment deposition was predominantly cyclic, consisting of alternating sandstone/shale cycles with unfossiliferous shales deposited during sea-level highstands in inner neritic to lagoonal environments characterized by euryhaline, dysaerobic or low oxygen conditions. Fossiliferous calcareous sandstone layers were deposited in well-oxygenated shallow waters during sea-level lowstand periods.     

Stratigraphy of the upper cretaceous and lower tertiary strata in the Tethyan Himalayas of Tibet (Tingri area,China)

The 1500-m-thick marine strata of the Tethys Himalaya of the Zhepure Mountain (Tingri, Tibet) comprise the Upper Albian to Eocene and represent the sedimentary development of the passive northern continental margin of the Indian plate. Investigations of foraminifera have led to a detailed biozonation which is compared with the west Tethyan record. Five stratigraphic units can be distinguished: The Gamba group (Upper Albian - Lower Santonian) represents the development from a basin and slope to an outer-shelf environment. In the following Zhepure Shanbei formation (Lower Santonian - Middle Maastrichtian), outer-shelf deposits continue. Pebbles in the top layers point to beginning redeposition on a continental slope. Intensified redeposition continues within the Zhepure Shanpo formation (Middle Maastrichtian - Lower Paleocene). The series is capped by sandstones of the Jidula formation (Danian) deposited from a seaward prograding delta plain. The overall succession of these units represents a sea-level high at the Cenomanian/Turonian boundary followed, from the Turonian to Danian, by an overall shallowing-upward megasequence. This is followed by a final transgression — regression cycle during the Paleocene and Eocene, documented in the Zhepure Shan formation (?Upper Danian - Lutetian) and by Upper Eocene continental deposits. The section represents the narrowing and closure of the Tethys as a result of the convergence between northward-drifting India and Eurasia. The plate collision started in the Lower Maastrichtian and caused rapid changes in sedimentation patterns affected by tectonic subsidence and uplift. Stronger subsidence and deposition took place from the Middle Maastrichtian to the Lower Paleocene. The final closure of remnant Tethys in the Tingri area took place in the Lutetian.     

Syn-depositional continental rifting of the Southeastern Neo-Tethys margin during the Albian–Cenomanian: evidence from stratigraphic correlation

ABSTRACT

Albian–Cenomanian successions (Kazhdumi and Sarvak formations) represent remarkable variations in thickness, facies, fauna, and environments throughout the Zagros area. In the Coastal Fars (Charmu section), sedimentological and paleontological data evidence an intrashelf, with depths of 10s–100s m, surrounded by a shallow carbonate platform. Due to its depth, deposition of sequences in this setting has been controlled by eustatic sea-level changes rather than eurybathic changes, and several condensation episodes occurred related to marine transgressions. These observations are different from those in the adjacent sections in the Coastal Fars which recorded subaerial exposures instead. Combined with previous studies, this study denotes several intrashelf basins enclosed by a shallow carbonate platform on the southeastern margin of the Neo-Tethys during the Albian–Cenomanian. Development of intrashelf basins corresponds to basement faults in the Fars Salient. Likely, an extensional tectonic regime associated with a rifting event created horst–graben architecture by exerting extension along the basement faults and reactivating salt structures. Deposition on these troughs and highs led to the facies and thickness variations of the concomitant sequences. Development of several intrashelf basins on the southeastern margin of the Neo-Tethys indicates that syn-depositional continental rifting event could occur during the Albian–Cenomanian, prior to the tectonic inversion around the earliest Turonian.     

Palaeoecological significance of turritelline gastropod-dominated assemblages from the mid-Cretaceous (Albian-Cenomanian) of Texas and Oklahoma,USA

The faunas of three previously poorly known and highly fossiliferous limestones from the upper Lower Cretaceous of Texas are dominated by turritelline gastropods. These faunas consist of turritelline-dominated assemblages in the Whitestone Limestone Member of the Walnut Formation in Travis County (middle Albian), the Keys Valley Marl Member of the Walnut Formation in Coryell County (middle Albian), and the Fort Terrett Formation in Kimble County (middle Albian). A fourth high-spired gastropod assemblage in the Segovia Formation in Pecos County (upper Albian) is not dominated by turritellines. Two other turritelline-dominated assemblages in non-carbonate rocks from the Albian and Cenomanian of Texas and Oklahoma are also described. These turritelline-dominated assemblage occurrences add considerably to our knowledge of the facies occurrence of Cretaceous turritelline-dominated assemblages, and they are consistent with the global facies distribution of these assemblages: i.e., although they are widespread in siliciclastic facies from Cretaceous to Recent, turritelline-dominated assemblages in carbonate facies occur almost exclusively in the Cretaceous and Paleogene.     

Cretaceous,marine inundations of the San Marcos Platform,Texas

During most of the Cretaceous the San Marcos Platform, central Texas, was a low-lying, subaerial terrain. After the Middle Albian it was a low-lying, carbonate terrain, similar to modern Florida, receiving little sediment and yielding little sediment.The Platform was inundated eight times (late early Aptian into middle Aptian, late late Aptian to middle late Albian, earliest Cenomanian, late early Cenomanian, late Cenomanian, earliest Campanian, early middle Campanian, middle(?) Maastrichtian) during the Cretaceous, the last of which is based only on indirect evidence.There are some anomalies. During the latter part of the long normal, magnetostratigraphic interval (34) of the Cretaceous, the San Marco Platform was almost entirely subaerial. Many of the inundations agree neither with the Vail cycles nor with the Kauffman cycles. The conclusion is that transgressions onto the San Marcos Platform are probably associated with sediment-loading of the Gulf Coast Basin.     

New biostratigraphic data for the Chikkim Formation (Cretaceous, Tethyan Himalaya, India)

The Chikkim Formation as exposed in the Tethyan Himalaya (India) has been studied at its type locality, using planktonic foraminifera for a detailed biostratigraphic elaboration. Divided into two members, the Lower and Upper Chikkim members, this formation ranges in age from Albian to early Maastrichtian(?), and reaches a maximum thickness of 150 m. Examination of thin sections has yielded 34 species of foraminifera in five genus-level assemblages. The Lower Chikkim Member is about 55 m thick; its basal portion is of Albian age based on the presence of Biticinella breggiensis and Planomalina buxtorfi. At 26 m above the base, Whiteinella archaeocretacaea documents OAE 2 (Oceanic Anoxic Event 2), and thus the Cenomanian/Turonian boundary in this section. The carbonate sequence is capped by a Santonian-age hardground with iron oxide crusts and bioturbation. Macrofossils, including belemnites (at the base) and irregular echinoids (upper part), are present. The basal carbonaceous marls of the Upper Chikkim Member yield both large (benthic) rotaliid as well as planktonic foraminifera (Globotruncanita elevata, Gl. stuartiformis, Gl. stuarti, Gansserina gansseri and others), indicating a Campanian age. The co-occurrence of Gl. elevata and G. gansseri in a single thin section results either from condensation or reworking in the basal part of the Upper Chikkim Member. Late Cretaceous index foraminifera such as Gl. elevata document deposition within the Tethyan Realm. The original thickness of the Upper Chikkim Member is uncertain, but would have been around 100 m; the unit appears markedly reduced through weathering at a height of about 5000 m above sea level. Equivalent sediments are exposed in the Zanskar area to the northwest, and in Nepal and Tibet. Cretaceous Oceanic Red Beds (CORBs) are probably missing due to the proximality of these pelagic settings.     

Neptunian dykes along a drowned carbonate platform margin: an indication for recurrent extensional tectonic activity?

Three successive Mesozoic neptunian dyke generations and related unconformities suggest recurrent extensional fracturing and periods of relative sea-level rise along the NW Trento Plateau margin in the Southern Alps, Italy. The first neptunian dyke generation was induced by NNW–SSE directed extension of Early Jurassic skeletal oolitic periplatform deposits generating micritic early Middle Liassic neptunian dykes with orthogonal orientation. The second generation of neptunian dykes was possibly caused by marginal extension at the drowned platform edge penetrating Late Jurassic, red pelagic limestones with a pelagic matrix of Albian/Cenomanian age and nearly orthogonal fracture orientation. The third generation of neptunian dykes occurred after a prolonged period of submarine exposure and erosion (Aptian/Albian to Late Maastrichtian) during the rapid burial of the submarine Trento Plateau margin relief. The Late Maastrichtian neptunian dykes were caused by extension of Early to Middle Jurassic oolitic periplatform limestones along steep (inclination > 10°) submarine slopes. Generally successive neptunian dyke generations along drowned carbonate platform margins could be caused by repeated extensional brittle fracturing of lithified periplatform deposits and the filling of micritic matrix derived from overlying pelagic sediment sequences under substantial hydrostatic pressure. This would suggest that recurrent extensional fracturing is continuously recorded by neptunian dyke formation which could be used to indicate extensional tectonic activity at a foundering deep-marine carbonate platform edge.     

Reply to the Discussion by Rose of Phelps et al. (2014) ‘Oceanographic and eustatic control of carbonate platform evolution and sequence stratigraphy on the Cretaceous (Valanginian–Campanian) passive margin,northern Gulf of Mexico’, Sedimentology, 61, 461–496

Discussion points raised by Rose ( 2016 ) concentrate on late Albian stratigraphic relationships between formations of the East Texas Basin and the San Marcos Arch of the Comanche Platform in the northern Gulf of Mexico. Criticisms of Phelps et al. (2014) regarding stratigraphic nomenclature, palaeogeography and regional lithostratigraphic correlations generally focus on interpretive aspects of the study or do not account for the full scope of published information. Revisions to the top Aptian–Albian Supersequence boundary by Rose are incompatible with the relative location of a subaerial unconformity, as well as deepening lithofacies trends and retrogradational stratigraphic patterns below the interpreted boundary. Rose's placement of the top Aptian–Albian Supersequence boundary precisely at the Albian–Cenomanian stage boundary also implies ca 1·4 Ma of diachroneity in second order sea‐level patterns between the northern Gulf of Mexico and other documented global sedimentary basins.     

High‐resolution sequence stratigraphy of the Maastrichtian‐Ypresian succession along the eastern scarp face of Kharga Oasis,southern Western Desert,Egypt

A thick Maastrichtian‐Ypresian succession, dominated by marine siliciclastic and carbonate deposits of the regionally recognized Nile Valley and Garra El‐Arbain facies associations, is exposed along the eastern escarpment face of Kharga Oasis, located in the Western Desert of Egypt. The main objectives of the present study are: (i) to establish a detailed biostratigraphic framework; (ii) to interpret the depositional environments; and (iii) to propose a sequence stratigraphic framework in order to constrain the palaeogeographic evolution of the Kharga sub‐basin during the Maastrichtian‐Ypresian time interval. The biostratigraphic analysis suggests the occurrence of 10 planktonic zones; two in the Early Maastrichtian (CF8b and CF7), four in the Palaeocene (P2, P3, P4c and P5) and four in the Early Eocene (E1, E2, E3 and E4). Recorded zonal boundaries and biostratigraphic zones generally match with those proposed elsewhere in the region. The stratigraphic succession comprises seven third‐order depositional sequences which are bounded by unconformities and their correlative conformities which can be correlated within and outside Egypt. These depositional sequences are interpreted as the result of eustatic sea‐level changes coupled with local tectonic activities. Each sequence contains a lower retrogradational parasequence set bounded above by a marine‐flooding surface and an upper progradational parasequence set bounded above by a sequence boundary. Parasequences within parasequence sets are stacked in landward‐stepping and seaward‐stepping patterns indicative of transgressive and highstand systems tracts, respectively. Lowstand systems tracts were not developed in the studied sections, presumably due to the low‐relief ramp setting. The irregular palaeotopography of the Dakhla Basin, which was caused by north‐east to south‐west trending submerged palaeo‐highs and lows, together with the eustatic sea‐level fluctuations, controlled the development and location of the two facies associations in the Kharga Oasis, the Nile Valley (open marine) and Garra El‐Arbain (marginal marine).     

Cephalopod associations and palaeoecology of the Cretaceous (Barremian–Cenomanian) succession of the Alpstein,northeastern Switzerland

The Alpstein (cantons of Appenzell Ausserrhoden, Appenzell Innerrhoden and St. Gallen, northeastern Switzerland) has been of great interest for geologists over the last decades because of its excellent outcrops. However, there was no comprehensive overview over its Cretaceous fossil content. Here, we describe the cephalopod associations, which are moderately to highly diverse in some strata of the Alpstein. Furthermore, we document the regional palaeoecological changes that occurred during the radiation of heteromorph ammonites (ancyloceratids, scaphitids, turrilitids). To examine the palaeoecological changes, we quantitatively determined the macrofossil content of 11 associations of Barremian to early Cenomanian age. Here, we document 6 species (3 genera) of nautilids and 77 species (45 genera) of ammonoids (29 of the species are recorded from Switzerland for the first time). Our palaeoecological analyses revealed the disappearance of nektoplanktonic forms after the late Barremian to the middle early Aptian in the course of the development of a shallow carbonate platform. The upper lower Aptian to middle Albian strata were eroded due to successive emersion phases and condensation processes. In the late Albian, the number of nektoplanktonic species surged again with some benthos, followed by the Cenomanian fauna, which is dominated by nektoplanktonic elements including ammonites, belemnites and nautilids with only very little benthos. These results correlate well with the regional sea level fluctuations.     

High stress late Maastrichtian – early Danian palaeoenvironment in the Neuquén Basin, Argentina

During the late Maastrichtian to early Danian the Neuquén Basin of Argentina was adjacent to an active volcanic arc to the west and an extensive land area to the northeast. Mineralogical and geochemical studies of the Bajada del Jagüel in the Neuquén Basin indicate a generally warm climate with seasonal changes in humidity and an open seaway to the South Atlantic that maintained marine conditions. Biostratigraphic and quantitative foraminiferal and nannofossil analyses indicate that sediment deposition during the late Maastrichtian (zones CF4-CF2, N. frequens) occurred in relatively shallow middle neritic (100 m) depths with largely dysaerobic bottom waters (abundant low O₂ tolerant benthics) and fluctuating sea level. Calcareous nannofossils indicate a high stress marine environment dominated by Micula decussata. Planktic foraminifera mimic the post-K/T high stress environment with alternating blooms of the disaster opportunists Guembelitria and low oxygen tolerant Heterohelix groups, indicating nutrient-rich surface waters and an oxygen depleted water column. The high stress conditions were probably driven by high nutrient influx due to upwelling and terrestrial and volcanic influx. The K/T boundary is marked by an erosional surface that marks a hiatus at the base of a 15-25 cm thick volcaniclastic sandstone, which contains diverse planktic foraminiferal zone P1c assemblages and nannofossils of zone NP1b immediately above it. This indicates deposition of the sandstone occurred 500 ky after the K/T hiatus. No evidence of the Chicxulub impact or related tsunami deposition was detected.     

Evolution of Albian-Cenomanian floras of Northeast USSR and the association between their composition and facies conditions

We consider the evolution of Albian-Cenomanian floras of the Northeast USSR for both coal-bearing and "non-coal" deposits, taking the evolution of paleofloras in single-facies (coal-bearing) deposits as a base. In general, the taphofloras have been assigned to the sequence from which the plant remains were collected. During Albian-Cenomanian time the angiosperms migrated from higher to lower levels. The observed decrease in the role of angiosperms during Cenomanian (Arkagala) time after their "expansion" during Albian time (in the Toptan and Arman suites) is explained by their establishment at different topographic levels. We show parallel increase in the role of conifers and angiosperms in the floras from the coal-bearing deposits from the Albian to the Cenomanian. A temperature minimum occurred during Arkagala time. It is likely that old, pre-Albian angiosperms may be found in sediments of the intermontane basins. In analyzing the level of evolution of the floras on the Early - Late Cretaceous boundary, especially the angiosperms, one must take into account the facies in which they are present. —Authors.     

Sea-level change, carbon cycling and palaeoclimate during the Late Cenomanian of northwest Europe; an integrated palaeoenvironmental analysis

A new high resolution sea-level curve for the Late Cenomanian M. geslinianum Zone has been generated using sequence stratigraphic analysis on transects through the margins of the Anglo-Paris Basin in the UK and Saxony Basin in Germany. Transgressive sediments that bury a rocky shoreline in the Dresden area have proved particularly useful in determining both the absolute amount of sea-level change and the rate of rise. After a brief fall at the base of the M. geslinianum Zone, sea level rose rapidly through the higher part of the zone, resulting in an overall short term eustatic rise of 22–28 m. Biostratigraphy and carbon isotope stratigraphy have enabled detailed correlations to be made between marginal locations and thick, relatively complete, basinal successions. The basinal successions at Eastbourne, UK, and Gröbern, Germany, provide both geochemical proxies for palaeoenvironmental change, including oxygen and carbon isotope records, and an orbital timescale graduated in precession and eccentricity cycles. Integration of the sea-level history with palaeoclimate evolution, palaeoceanography and changes in carbon cycling allows a detailed reconstruction of events during the Late Cenomanian. Orbital forcing on long eccentricity maxima provides the underlying drive for these changes, but amplification by tectonic events and feedback mechanisms augmented the orbital effects and made the Cenomanian/Turonian Boundary Event distinctive. In particular, variations in atmospheric CO₂ caused by oceanic drawdown and a brief period of intense volcanic outgassing resulted respectively in short term cooling and warming events. The magnitude and high rates (up to 1 m/1 kyr) of sea-level rise are diagnostic of glacioeustasy, however improbable this may appear at the height of the Cretaceous greenhouse.     

Cretaceous stratigraphy of the Ionian Zone,Hellenides, western Greece

The Cretaceous sedimentary successions of the Ionian Zone, Hellenides, western Greece, are composed of pelagic limestones intercalated with cherty layers. The micritic and biomicritic beds with abundant chert nodules and cherty horizons, which were deposited during late Tithonian to early Santonian times, belong to the Vigla Limestone Formation, while the sediments deposited during the late Santonian to Maastrichtian, formed clastic limestone beds in which chert nodules also occur sparsely.In the Cretaceous beds calpionellids, planktonic and benthonic foraminifera characteristics of the Tethyan realm, and radiolaria have been recorded. The calpionellids, together with radiolaria, colonized the entire basin during the Berriasian to early Valanginian, the latter becoming dominant during the Hauterivian to early Albian as a result of anoxia. Planktonic foraminifera first appeared in the basin during the late Albian and persisted until the Maastrichtian. The numbers decreased, however, during the Cenomanian-early Turonian interval, when radiolaria increased owing to anoxic conditions, and during the Campanian-Maastrichtian interval because the basin became shallow. During this interval larger benthonic foraminifera colonized the basin. Zonal markers have been recognized in calpionellid and planktonic foraminiferal assemblages on the basis of which two calpionellid zones are distinguished, viz. the Calpionella alpina and Calpionellopsis Zones (Berriasian-early Valanginian) along with seven planktonic foraminiferal zones, viz. the Rotalipora ticinensis, Rotalipora appenninica (late Albian), Rotalipora brotzeni (early Cenomanian), Helvetoglobotruncana helvetica (early to middle Turonian), Marginotruncana sigali(late Turonian to early Coniacian), Dicarinella concavata (late Coniacian to early Santonian) and Dicarinella asymetrica (late early-late Santonian) Zones.The anoxic conditions that prevailed in the Ionian basin during the Barremian-early Albian, Cenomanian-early Turonian and Coniacian-Santonian intervals probably arose as a result of (a) the accumulation of large amounts of organic matter because the palaeotopography of the basin periodically hindered the circulation of water from the ocean and (b) the oxygen content of the intruding oceanic waters was low.     

西藏南部岗巴地区白垩纪化石碳酸盐岩微相与沉积环境研究

西藏南部岗巴地区发育着我国最完整的海相白垩纪地层,对该时期海相沉积演化特征的研究,能够较好地反映该地区在印度板块和欧亚板块碰撞前的演化信息。对白垩纪岗巴地区的化石碳酸盐岩微相进行了较为详细和系统的分析与研究。初步识别出12种微相和7种生物相类型,在此基础上对西藏特提斯白垩纪沉积环境的演变进行了初步的探讨。西藏特提斯在白垩纪的海水进退规程总体上表现为：Berriasian-Aptian期发生海侵,Albian早期发生海退,Albian晚期-Cenomanian期水体有进一步加深的趋势,Turonian期再次发生大规模海侵,Santonian-Coniacian期海侵持续进行,Maastrichtian期海水急剧变浅。     

Petreşti-Arini – An important but ephemeral Upper Cretaceous continental vertebrate site in the southwestern Transylvanian Basin,Romania

The Transylvanian region of Romania preserves some of the most unusual and iconic dinosaurs in the global fossil record, including dwarfed herbivores and aberrant carnivores that lived during the very latest Cretaceous (Maastrichtian) in an ancient island ecosystem (the Haţeg Island). A series of artificial outcrops recently exposed during a hydroelectric project, the Petreşti-Arini section near Sebeş in the Transylvanian Basin, records a 400+ meter sequence documenting the transition from fully marine to terrestrial environments during the Campanian–Maastrichtian. Calcareous nannofossil biostratigraphy indicates that the lower marine beds in this section, part of the uppermost Bozeş Formation, can be assigned to the CC22 biozone, corresponding to the lower–mid upper Campanian. These beds smoothly transition, via a brackish-water unit, into the fully continental Maastrichtian Sebeş Formation. Dinosaur and pterosaur fossils from the uppermost Bozeş Formation can be assigned a late Campanian age making them the oldest well-dated terrestrial fossils from the Haţeg Island, and indicating that the classic Haţeg dinosaur fauna was becoming established by this time, coincident with the first emergence of widespread land areas. Vertebrate fossils occur throughout the overlying Sebeş Formation at the site and are dominated by the small-bodied herbivorous dinosaur Zalmoxes. The dominance of Zalmoxes, and the absence of many taxa commonly seen elsewhere in Maastrichtian sites in Romania, suggests the possibility that either the Petreşti-Arini section preserves a somewhat unusual near-shore environment, or the earliest Haţeg Island dinosaur communities were structured differently from the more diverse communities later in the Maastrichtian. Alternatively, due to the limited sample size available from the studied succession, it is also conceivable that sampling biases give an incomplete portrayal of the Petreşti-Arini local fauna. Support for any one of these alternative hypotheses requires further data from Petreşti-Arini as well as from the larger Transylvania area.     

40Ar/39Ar ages and geochemical characterization of Cretaceous bentonites in the Nanushuk,Seabee, Tuluvak,and Schrader Bluff formations,North Slope,Alaska

Diagenetically altered volcanic ash deposits (bentonites) found in Cretaceous terrestrial and marine foreland basin sediments have the potential to be used for chronostratigraphy and subsurface correlation across Alaska's North Slope. Detailed age and geochemical studies of these volcanogenic deposits may also shed light on the tectonic evolution of the Arctic. Though these bentonites have been previously studied, there are few published results for regional bentonite ages and geochemistry due to challenges of dating weathered volcanic ash. We analyzed mineral separates from cored bentonites recovered from wells in the National Petroleum Reserve Alaska. The analyses confirm that an intense period of volcanic ash deposition on Alaska's North Slope began by the late Albian and persisted throughout the Cenomanian, an interval of rapid progradation and aggradation in the Colville basin. These results also add to a sparse record of radioisotopic ages from the Nanushuk Formation. A bentonite preserved in delta plain sediments in the upper Nanushuk Formation dates to 102.6 ± 1.5 Ma (late Albian), while a bentonite near the base of the overlying Seabee Formation was deposited at 98.2 ± 0.8 Ma, in the early Cenomanian. The two ages bracket a major flooding surface at the base of the Seabee Formation near Umiat, Alaska, placing it near the Albian-Cenomanian boundary (100.5 Ma). Several hundred feet up-section, the non-marine Tuluvak Formation contains bentonites with ⁴⁰Ar/³⁹Ar ages of 96.7 ± 0.7 to 94.2 ± 0.9 Ma (Cenomanian), several million years older than previously published K–Ar ages and biostratigraphic constraints suggest.Major and trace element geochemistry of a sub-sample of six bentonites from petroleum exploration wells at Umiat show a range in composition from andesite to rhyolite, with a continental arc source. The bentonites become more felsic from the late Albian (∼102 Ma) to late Cenomanian (∼94 Ma). A likely source for the bentonites is the Okhotsk-Chukotka Volcanic Belt (OCVB) of eastern Siberia, a continental arc which became active in the Albian and experienced episodes of effusivity throughout the Late Cretaceous. Chronostratigraphically anomalous ⁴⁰Ar/³⁹Ar ages coincide with peaks of magmatic activity in the OCVB, suggesting that these anomalously old ages may be due to magmatic contribution of xenocrysts or recycling of detrital minerals from older volcanic events. An alternative explanation for the chronostratigraphically anomalous ages is mixing of bentonites with detrital sediment derived from unroofing and erosion of metamorphic rocks in the Brooks Range, Herald Arch, and Chukotka throughout the mid to Late Cretaceous.     

Near-K/T age of clastic deposits from Texas to Brazil: impact,volcanism and/or sea-level lowstand?

Near-K/T boundary clastic deposits from Texas, Mexico, Haiti, Guatemala and Brazil, often described as impact-generated tsunami deposits, are stratigraphically below well-defined K/T boundary horizons and appear not to be causally related to the K/T boundary event. Stratigraphic evidence indicates that their deposition began during the last 170–200 kyr of the Maastrichtian, coincident with a major eustatic sea-level lowstand that lowered sea level by as much as 70–100 m. Clastic deposition ended a few tens of thousands of years before the K/T boundary during a rapidly rising sea level. The presence of glass in clastic deposits in Haiti, northeastern Mexico and Yucatan suggests that the sea-level lowstand coincided with a time of major volcanism or pre-K/T boundary bolide impact.     

Maastrichtian carbon cycle changes and planktonic foraminiferal bioevents at Gebel Matulla,west-central Sinai,Egypt

Comparison between the planktonic foraminiferal bioevents from different palaeolatitudes suggests that the biostratigraphic criteria used to identify the Maastrichtian stage boundaries are problematic. A new high-resolution calibration of planktonic foraminiferal biostratigraphic, carbon-isotope, and sequence-stratigraphic criteria has been recorded for the first time from the Maastrichtian Sudr Formation at Gebel Matulla, west-central Sinai. The sedimentary successions allow the identification of prominent long-term carbon isotope events in the Maastrichtian, namely the negative excursion of the Campanian–Maastrichtian Boundary Event (CMBE), the positive excursion of the mid-Maastrichtian Event (MME), and the decline towards the Cretaceous-Palaeogene transition (KPgE). Termination of these well known δ¹³C events is associated with unconformities, created by eustatic sea-level changes, although the long duration argues for superimposed local tectonic control.