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Cretaceous
Kinds of Cretaceous Terms modified by Cretaceous Selected AbstractsCRETACEOUS CARBONATES IN THE ADIYAMAN REGION, SE TURKEY: AN ASSESSMENT OF BURIAL HISTORY AND SOURCE-ROCK POTENTIALJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2000I. H. Demirel The burial history and source-rock potential of Cretaceous carbonates in the Adiyaman region of SE Turkey have been investigated. The carbonates belong to the Aptian-Campanian Mardin Group and the overlying Karabogaz Formation. The stratigraphy of these carbonates at four well locations was recorded. At each well, the carbonate succession was found to be incomplete, and important unconformities were present indicating periods of non-deposition and/or erosion. These unconformities are of variable extent. When combined with the effects of rapid subsidence and sedimentation which took place in the SW of the Adiyaman region during end-Cretaceous foredeep development, they have resulted in variations in the carbonates' present-day burial depths, thereby influencing the regional pattern of source-rock maturation and the timing of oil generation. Burial history curves indicate that the carbonates' maturity increases from SW to NE, towards the Late Cretaceous thrust belt. Predicted levels of maturity for the Mardin Group are consistent with measured geochemical data from three of the wells in the study area (the exception being well Karadag-1). Three potential source-rock intervals of Cretaceous age have been identified. Two of these units , the Derdere and Karababa Formations of the Mardin Group , are composed of shallow-water carbonates which were deposited on the northern margin of the Arabian Platform. The third source-rock unit, the overlying Karabogaz Formation, is composed of pelagic carbonates which were deposited during a regional transgression. These potential source-rock intervals contain marine organic matter dominated by Type II kerogen. Total organic carbon contents range from 0.5 to 2.9 %. Time-temperature analyses indicate that the Mardin Group carbonates are immature to marginally mature at well locations in the SW of the study area, and are mature at western and NE well locations. The onset of oil generation in these Cretaceous source rocks took place between the middle Eocene (48 million yrs ago) and the Oligocene (28 million yrs ago). [source] UNIQUE MANIRAPTORAN EGG CLUTCH FROM THE UPPER CRETACEOUS TWO MEDICINE FORMATION OF MONTANA REVEALS THEROPOD NESTING BEHAVIOURPALAEONTOLOGY, Issue 6 2008DARLA K. ZELENITSKY Abstract:, Egg clutches of non-avian maniraptoran theropods (Dinosauria) are rare, particularly in North America where those of Troodon formosus are the only maniraptoran clutches known. Here we describe a new partial maniraptoran clutch and nesting trace referred to Montanoolithus strongorum oogen. et oosp. nov. (Montanoolithidae oofam. nov.), from the Upper Cretaceous Two Medicine Formation of Montana. Based on a cladistic analysis of reproductive traits, we infer that this clutch belonged either to a caenagnathid or to a dromaeosaurid, which makes it the first clutch known of either taxon. This specimen preserves impressions and eggshell fragments of at least five eggs on a nest structure. The eggs are asymmetrical, paired, and lay radially in a ring configuration on the sloped sides of a bioturbated, flat-topped sandstone mound. Geology of the locality indicates the female nested in a poorly-vegetated area of freshly deposited sand, possibly near an active river channel. This clutch reveals that the egg-layer of Montanoolithus strongorum had a unique suite of reproductive characteristics and nesting behaviours among maniraptorans. [source] A NEW SPINICAUDATAN GENUS (CRUSTACEA: ,CONCHOSTRACA') FROM THE LATE CRETACEOUS OF MADAGASCARPALAEONTOLOGY, Issue 5 2008ALYCIA L. STIGALL Abstract:, A new spinicaudatan genus and species, Ethmosestheria mahajangaensis gen. et sp. nov., is described from the Anembalemba Member (Upper Cretaceous, Maastrichtian) of the Maevarano Formation, Mahajanga Basin, Madagascar. This is the first spinicaudatan reported from the post-Triassic Mesozoic of Madagascar. The new species is assigned to the family Antronestheriidae based on the cavernous or sievelike ornamentation on the carapace. Of well-documented Mesozoic spinicaudatan genera, Ethmosestheria mahajangaensis is most closely related to Antronestheria Chen and Hudson from the Great Estuarine Group (Jurassic) of Scotland. However, relatively poor documentation of the ornamentation of most Gondwanan Mesozoic spinicaudatan species precludes detailed comparison among taxa. Ethmosestheria mahajangaensis exhibits ontogenetic trends in carapace growth: a change in carapace outline from subcircular/subelliptical to elliptical, and from very wide juvenile growth bands to narrow adult growth bands. Ornamentation style, however, does not vary with ontogeny. Ethmosestheria mahajangaensis individuals lived in temporary pools in a broad channel-belt system within a semiarid environment; preserved desiccation structures on carapaces indicate seasonal drying out of pools within the river system. Specimens of Ethmosestheria mahajangaensis are preserved with exquisite detail in debris flow deposits; these are the first spinicaudatans reported from debris flow deposits. These deposits also contain a varied vertebrate fauna, including dinosaurs, crocodyliforms, turtles, and frogs. Rapid entombment of the spinicaudatan carapaces likely promoted early fossil diagenesis leading to highly detailed preservation. [source] AN EARLY HERBIVOROUS LIZARD FROM THE LOWER CRETACEOUS OF JAPANPALAEONTOLOGY, Issue 2 2008SUSAN E. EVANS Abstract:, The Lower Cretaceous Tetori Group of Japan has yielded diverse freshwater and terrestrial vertebrate assemblages. The most productive small vertebrate locality is the ,Kaseki-Kabe' or ,fossil-bluff' at Kuwajima, Hakusan City, Ishikawa Prefecture. These deposits have produced at least six distinct lizard taxa of which one, described and named here as Kuwajimalla kagaensis, has lanceolate denticulate teeth convergent on those of the living Iguana. This type of dentition is rare among living lizards and is usually considered indicative of herbivory and, more specifically, folivory. Kuwajimalla kagaensis provides the earliest unambiguous record of squamate herbivory. Comparisons with modern and fossil lizards suggest that Kuwajimalla may be an early relative of the macrocephalosaurines, a group of large herbivores well represented in the Upper Cretaceous of Mongolia. [source] ANACORACID SHARKS FROM THE ALBIAN (LOWER CRETACEOUS) PAWPAW SHALE OF TEXASPALAEONTOLOGY, Issue 4 2007MIKAEL SIVERSON Abstract:, Recent collecting from the Pawpaw Shale in north-east Texas has yielded several hundred teeth of anacoracid sharks. The material allows for a much-needed revision of the Late Albian anacoracids from North America. The previously recognized Squalicorax sp., also referred to as S. volgensis in more recent publications, is a mix of two different species: S. priscoserratus sp. nov. and S. pawpawensis sp. nov. In addition to these two new species, a single tooth is assigned to S. aff. S. baharijensis. Our data indicate that anacoracids were a considerably more diverse group in the North American Cretaceous than previously thought. We attribute much of the underestimation of diversity to vague species concepts, poor preparation techniques and the associated lack of attention to certain dental features, in particular neck morphology, root surface porosity and the root's vascularization. [source] HIGHER SYSTEMATICS OF SCORPIONS FROM THE CRATO FORMATION, LOWER CRETACEOUS OF BRAZILPALAEONTOLOGY, Issue 1 2007FEDERICA MENON Abstract:, Several new specimens of Protoischnurus axelrodorum Carvalho and Lourenço and Araripescorpius ligabuei Campos from the Crato Formation, Brazil, are described. The preservation and recognition of new morphological features allows a re-diagnosis of both species and a modification of their familial placement. Protoischnurus axelrodorum is the oldest species belonging to the scorpionoid family Hemiscorpiidae Pocock (= Ischnuridae Simon; =,Liochelidae Fet and Bechly) and the first Cretaceous record. It was originally placed in the extinct family Protoischnuridae Carvalho and Lourenço, which is here synonymized with Hemiscorpiidae. Araripescorpius ligabuei, now assigned to Chactidae Pocock, is the first chactoid recorded for the Cretaceous of Brazil. These findings confirm that the lineages of two modern families date back at least to the Early Cretaceous and, considering their current distribution, were probably present before the break-up of the supercontinent Gondwana. Palaeoecological inferences indicate the presence of tropical habitats in the vicinity of the Crato lake/lagoon. [source] A NEW ELASMOBRANCH ASSEMBLAGE FROM THE LOWER CRETACEOUS OF THAILANDPALAEONTOLOGY, Issue 3 2006HENRI CAPPETTA Abstract:, The discovery of a new elasmobranch assemblage from the Lower Cretaceous of Thailand allows expansion of the faunal list and refinement of our knowledge of the dental morphological features of some previously described taxa. The root morphology of Thaiodus is now known and a more complete description of the dentition of the genus Heteroptychodus, known formerly by a single tooth from Japan, is given. A new genus and species, Acrorhizodus khoratensis, characterized by teeth of very special morphology is described. Besides these taxa, some teeth of a genus probably close to Hybodus, but with more bulbous teeth, are present. Owing to the sedimentological characters of the deposits and the associated fauna (dinosaurs), it is probable that this elasmobranch fauna lived in a freshwater or brackish environment. The simultaneous occurrence of teeth of Heteroptychodus in Thailand and Japan favours the existence of a large continental area in south-east Asia during the Early Cretaceous. [source] AN EXCEPTIONALLY PRESERVED ANTLION (INSECTA, NEUROPTERA) WITH COLOUR PATTERN PRESERVATION FROM THE CRETACEOUS OF BRAZILPALAEONTOLOGY, Issue 6 2005SAM W. HEADS Abstract:, A new species of palaeoleontid neuropteran Baisopardus cryptohymen sp. nov. is described. The holotype is remarkable for the preservation of fine body structures and colour patterning on all of its four wings. The specimen is nearly complete, lacking only the abdomen and the right mesothoracic leg, and is preserved as a black-brown compression in laminated limestone of the Nova Olinda Member, Crato Formation (late Aptian, Early Cretaceous), Ceará, Brazil. The colour pattern of the forewings comprises a series of dark brown bands that overlap with colourless bands of the hindwings; it produced a cryptic colour pattern when the wings were folded. [source] Sources of sulphur in gypsiferous sediments and crusts and pathways of gypsum redistribution in southern TunisiaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2004Nick A. Drake Abstract Southern Tunisia contains one of the most extensive gypsum accumulations in Africa comprising Triassic, Cretaceous, Eocene and Mio-Pliocene marine evaporites, spring deposits, playa sediments, aeolian sands and gypsum crusts. Sulphur isotope analysis (,34S) of bedrock samples, groundwater, playa brines, playa sediments, and gypsiferous crusts provides insight into the sources of gypsum in the region and sheds light on the processes that lead to gypsum crust formation. Results suggest that recycling of marine gypsum is the most likely source of the sulphate in the groundwater, playa sediments and crusts. The low ,34S values found in Eocene and Mio-Pliocene samples suggest that this recycling has been going on for millions of years. Though bedrock appears to be the ultimate source of the gypsum in the crusts, transport of this sulphate to playas, concentration therein, and subsequent dispersal across the landscape by aeolian processes provides the most likely pathway for sur,cial gypsum crust formation. Comparison of these results with those from Australia, Chile and Namibia suggests that, although the source of the sulphur varies from region to region, the processes of sur,cial crust formation appear to be similar. Copyright © 2004 John Wiley & Sons, Ltd. [source] Tooth row counts, vicariance, and the distribution of the sand tiger shark Carcharias taurusECOGRAPHY, Issue 5 2003Luis O. Lucifora Geographic variation in tooth row counts among sand tiger sharks Carcharias taurus (Chondrichthyes), from the SW Atlantic, NW Atlantic and the East China Sea is analyzed in this paper. We found significant differences between sand tigers from the SW Atlantic (Southern Hemisphere population) and each of the other two (Northern Hemisphere) regions in the number of upper lateral tooth rows, and between individuals from the SW Atlantic and the East China Sea in the total number of upper tooth rows. Sand tiger sharks from the two Northern Hemisphere populations did not differ in any of the studied variables. Our results agree with comparisons of vertebral counts between sand tiger sharks from Southern and Northern Hemispheres. Both lines of evidence suggest that Southern and Northern Hemisphere populations of C. taurus were isolated to a larger extent than populations of the Northern Hemisphere. The fossil record of the genus Carcharias begins in the Early Cretaceous and C. taurus is certainly known since the Late Miocene. During the Miocene, the Tethys Sea separating northern and southern land masses was still present and it provided a continuous temperate shallow sea that could allow dispersal of sand tiger sharks along Northern Hemisphere seas. Independent observations on the distribution and evolutionary history of the genera Myripristis, Neoniphon, Sargocentron and Aphanius, and genetic studies on the temperate shark genus Mustelus that indicate a close relationship between the Indo-Pacific M. manazo and the Mediterranean M. asterias suggest that this hypothesis is plausible and deserves to be tested. [source] Appraising the roles of nutrient availability, global change, and functional traits during the angiosperm rise to dominanceECOLOGY LETTERS, Issue 5 2010Kevin E. Mueller Ecology Letters (2010) 13: E1,E6 Abstract To explain the rise of angiosperms during the Cretaceous, Berendse & Scheffer (Ecol. Lett., 12, 2009, 865) invoke feedbacks between leaf litter, soil nutrients, and growth, overlooking other factors affecting resource acquisition by Cretaceous plants. We evaluate their hypothesis, highlight alternative explanations, and emphasize use of a broader framework for understanding the angiosperm radiation. [source] The angiosperm radiation revisited, an ecological explanation for Darwin's ,abominable mystery'ECOLOGY LETTERS, Issue 9 2009Frank Berendse Abstract One of the greatest terrestrial radiations is the diversification of the flowering plants (Angiospermae) in the Cretaceous period. Early angiosperms appear to have been limited to disturbed, aquatic or extremely dry sites, suggesting that they were suppressed in most other places by the gymnosperms that still dominated the plant world. However, fossil evidence suggests that by the end of the Cretaceous the angiosperms had spectacularly taken over the dominant position from the gymnosperms around the globe. Here, we suggest an ecological explanation for their escape from their subordinate position relative to gymnosperms and ferns. We propose that angiosperms due to their higher growth rates profit more rapidly from increased nutrient supply than gymnosperms, whereas at the same time angiosperms promote soil nutrient release by producing litter that is more easily decomposed. This positive feedback may have resulted in a runaway process once angiosperms had reached a certain abundance. Evidence for the possibility of such a critical transition to angiosperm dominance comes from recent work on large scale vegetation shifts, linking long-term field observations, large scale experiments and the use of simulation models. [source] Foraging energetics of arctic cormorants and the evolution of diving birdsECOLOGY LETTERS, Issue 3 2001David Grémillet Efficient body insulation is assumed to have enabled birds and mammals to colonize polar aquatic ecosystems. We challenge this concept by comparing the bioenergetics of cormorants (Phalacrocorax carbo) living in temperate and arctic conditions. We show that although these birds have limited insulation, they maintain high body temperature (42.3 °C) when diving in cold water (1,10 °C). Their energy demand at these times is extremely high (up to 60 W kg,1). Free-living cormorants wintering in Greenland (water temperature ,1 °C) profoundly alter their foraging activity, thus minimizing time spent in water and the associated high thermoregulatory costs. They then meet their daily food demand within a single intense dive bout (lasting 9 min on average). Their substantial energy requirements are balanced by the highest predatory efficiency so far recorded for aquatic predators. We postulate that similar behavioural patterns allowed early diving birds (Cretaceous) to colonize cold coastal areas before they evolved efficient insulation. [source] RESISTANCE OF SPIDERS TO CRETACEOUS-TERTIARY EXTINCTION EVENTSEVOLUTION, Issue 11 2003David Penney Abstract Throughout Earth history a small number of global catastrophic events leading to biotic crises have caused mass extinctions. Here, using a technique that combines taxonomic and numerical data, we consider the effects of the Cenomanian,Turonian and Cretaceous,Tertiary mass extinctions on the terrestrial spider fauna in the light of new fossil data. We provide the first evidence that spiders suffered no decline at the family level during these mass extinction events. On the contrary, we show that they increased in relative numbers through the Cretaceous and beyond the Cretaceous,Tertiary extinction event. [source] The Tendaguru Formation (Late Jurassic to Early Cretaceous, southern Tanzania): definition, palaeoenvironments, and sequence stratigraphyFOSSIL RECORD-MITTEILUNGEN AUS DEM MUSEUM FUER NATURKUNDE, Issue 2 2009Robert Bussert Abstract The well-known Late Jurassic to Early Cretaceous Tendaguru Beds of southern Tanzania have yielded fossil plant remains, invertebrates and vertebrates, notably dinosaurs, of exceptional scientific importance. Based on data of the German-Tanzanian Tendaguru Expedition 2000 and previous studies, and in accordance with the international stratigraphic guide, we raise the Tendaguru Beds to formational rank and recognise six members (from bottom to top): Lower Dinosaur Member, Nerinella Member, Middle Dinosaur Member, Indotrigonia africana Member, Upper Dinosaur Member, and Rutitrigonia bornhardti-schwarzi Member. We characterise and discuss each member in detail in terms of derivation of name, definition of a type section, distribution, thickness, lithofacies, boundaries, palaeontology, and age. The age of the whole formation apparently ranges at least from the middle Oxfordian to the Valanginian through Hauterivian or possibly Aptian. The Tendaguru Formation constitutes a cyclic sedimentary succession, consisting of three marginal marine, sandstone-dominated depositional units and three predominantly coastal to tidal plain, fine-grained depositional units with dinosaur remains. It represents four third-order sequences, which are composed of transgressive and highstand systems tracts. Sequence boundaries are represented by transgressive ravinement surfaces and maximum flooding surfaces. In a more simple way, the depositional sequences can be subdivided into transgressive and regressive sequences/systems tracts. Whereas the transgressive systems tracts are mainly represented by shallow marine shoreface, tidal channel and sand bar sandstones, the regressive systems tracts predominantly consist of shallow tidal channel, tidal flat, and marginal lagoonal to supratidal deposits. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A new Cenomanian (Late Cretaceous) coleoid (Cephalopoda) from Hâdjoula, LebanonFOSSIL RECORD-MITTEILUNGEN AUS DEM MUSEUM FUER NATURKUNDE, Issue 2 2009Dirk Fuchs Abstract A new vampyropod coleoid from the late Cenomanian limestones of Hâdjoula (north-west Lebanon) is described. Glyphiteuthis abisaadiorum n. sp. is classified as a representative of the Trachyteuthididae, mainly on the basis of its general gladius morphology. It represents the fourth species of its genus and the second species of its genus recorded from Hâdjoula. Glyphiteuthis abisaadiorum n. sp. differs from Glyphiteuthis libanotica in having a more slender gladius. Additionally, the arms are considerably longer in Glyphiteuthis abisaadiorum n. sp. than in Glyphiteuthis libanotica. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Palaeoecology and depositional environments of the Tendaguru Beds (Late Jurassic to Early Cretaceous, Tanzania)FOSSIL RECORD-MITTEILUNGEN AUS DEM MUSEUM FUER NATURKUNDE, Issue 1 2002Martin Aberhan Abstract The Late Jurassic to Early Cretaceous Tendaguru Beds (Tanzania, East Africa) have been well known for nearly a century for their diverse dinosaur assemblages. Here, we present sedimentological and palaeontological data collected by the German-Tanzanian Tendaguru Expedition 2000 in an attempt to reconstruct the palaeo-ecosystems of the Tendaguru Beds at their type locality. Our reconstructions are based on sedimentological data and on a palaeoecological analysis of macroinvertebrates, microvertebrates, plant fossils and microfossils (ostracods, foraminifera, charophytes, palynomorphs). In addition, we included data from previous expeditions, particularly those on the dinosaur assemblages. The environmental model of the Tendaguru Beds presented herein comprises three broad palaeoenvironmental units in a marginal marine setting: (1) Lagoon-like, shallow marine environments above fair weather wave base and with evidence of tides and storms. These formed behind barriers such as ooid bar and siliciclastic sand bar complexes and were generally subject to minor salinity fluctuations. (2) Extended tidal flats and low-relief coastal plains. These include low-energy, brackish coastal lakes and ponds as well as pools and small fluvial channels of coastal plains in which the large dinosaurs were buried. Since these environments apparently were, at best, poorly vegetated, the main feeding grounds of giant sauropods must have been elsewhere. Presumably, tidal flats and coastal plains were visited by dinosaurs primarily during periods of drought. (3) Vegetated hinterland. Vegetation of this environment can only be inferred indirectly from plant material transported into the other depositional environments. Vegetation was dominated by a diverse conifer flora, which apparently formed part of the food source of large herbivorous sauropods. Evidence from various sources suggests a subtropical to tropical palaeoclimate, characterised by seasonal rainfall alternating with a pronounced dry season during the Late Jurassic. In Early Cretaceous times, sedimentological and palaeontological proxies suggest a climatic shift towards more humid conditions. Die Tendaguru-Schichten von Tansania in Ostafrika (Oberjura bis Unterkreide) sind als Lagerstätte oberjurassischer Dinosaurier seit nahezu einem Jahrhundert weltweit bekannt. Anhand von sedimentologischen und paläontologischen Daten, die während der Deutsch-Tansanischen Tendaguru Expedition 2000 im Typus-Gebiet der Tendaguru-Schichten gewonnen wurden, werden Paläo-Ökosysteme rekonstruiert. Grundlage der Rekonstruktionen sind die Auswertung sedimentologischer Daten sowie die paläo-ökologische Analyse von Makroinvertebraten, Mikrovertebraten, pflanzlichen Fossilien und Mikrofossilien (Ostrakoden, Foraminiferen, Charophyten, Palynomorphen). Darüber hinaus werden Informationen über Dinosaurier berücksichtigt, die bei früheren Expeditionen gewonnen wurden. Das hier vorgestellte Ablagerungsmodell der Tendaguru-Schichten umfaßt drei Teilbereiche eines randlich marinen Sedimentationsraumes, die wie folgt gekennzeichnet werden können: (1) Lagunen-artige, marine Flachwasserbereiche, die oberhalb der Schönwetter-Wellenbasis lagen und unter deutlichem Einfluß von Gezeiten und Stürmen standen. Sie waren vom offenen Meer durch Barrieren, wie Ooidbarren und siliziklastischen Sandbarrenkomplexen, getrennt und wiesen einen leicht schwankenden Salzgehalt auf. (2) Ausgedehnte Wattgebiete und flache Küstenebenen. Dort befanden sich niedrig-energetische, brackische Strandseen und Teiche sowie Tümpel und kleinere Flußrinnen, in denen die großen Dinosaurier eingebettet wurden. Da diese Lebensräume bestenfalls dürftig bewachsen waren, müssen die Nahrungsquellen und der eigentliche Lebensraum der riesigen Sauropoden anderswo gelegen haben. Vermutlich wurden die Wattgebiete und Flachküsten von Dinosauriern vorrangig in den Trockenzeiten aufgesucht. (3 ) Bewachsenes Hinterland. Die Vegetation dieses Lebensraumes kann nur indirekt aus Pflanzenresten erschlossen werden, die in die anderen Ablagerungsraume transportiert wurden. Die Vegetation wurde von einer diversen Koniferenflora dominiert, die zumindest teilweise die Nahrungsgrundlage der großen, herbivoren Sauropoden bildete. Sedimentologische und paläontologische Indikatoren sprechen für ein subtropisches bis tropisches Klima wahrend der späten Jurazeit mit einem jahreszeitlichen Wechsel von Regenfällen und ausgeprägten Trockenzeiten. In der frühen Kreidezeit deutet sich ein Wechsel zu starker humiden Bedingungen an. [source] The rock-hewn churches of Tigrai, Northern Ethiopia: A geological perspectiveGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 7 2002Asfawossen Asrat Ethiopia is endowed with many rock-hewn churches, with the largest group in central and eastern Tigrai. These churches can be divided into four zones: the Atsbi, Hawzen-Ger'alta, Sinkata-Adigrat, and Tembien, with more than 100 rock-hewn churches of different ages, sizes, and histories. However, they have one thing in common: All are carved into sandstone. The Enticho, Adigrat, and Ambaradam sandstones (Permo-Carboniferous, Triassic,Middle Jurassic, and Early Cretaceous, respectively) are extensively exposed in these areas and are characterized by thick and massive beds of coarse- to fine-grained and well-sorted successions. These sandstones are easily carved, yet compact enough to withstand pressure. Although limestone, basalt, and crystalline rocks are exposed in the same area, few rock-hewn churches have been carved into them. The rock type is, therefore, the most important factor in the location of these rock-hewn churches. © 2002 Wiley Periodicals, Inc. [source] Diagenesis of the Amposta offshore oil reservoir (Amposta Marino C2 well, Lower Cretaceous, Valencia Trough, Spain)GEOFLUIDS (ELECTRONIC), Issue 3 2010E. PLAYÀ Abstract Samples from the Amposta Marino C2 well (Amposta oil field) have been investigated in order to understand the origin of fractures and porosity and to reconstruct the fluid flow history of the basin prior, during and after oil migration. Three main types of fracture systems and four types of calcite cements have been identified. Fracture types A and B are totally filled by calcite cement 1 (CC1) and 2 (CC2), respectively; fracture type A corresponds to pre-Alpine structures, while type B is attributed to fractures developed during the Alpine compression (late Eocene-early Oligocene). The oxygen, carbon and strontium isotope compositions of CC2 are close to those of the host-rock, suggesting a high degree of fluid-rock interaction, and therefore a relatively closed palaeohydrogeological system. Fracture type C, developed during the Neogene extension and enlarged by subaerial exposure, tend to be filled with reddish (CS3r) and greenish (CS3g) microspar calcite sediment and blocky calcite cement type 4 (CC4), and postdated by kaolinite, pyrite, barite and oil. The CS3 generation records lower oxygen and carbon isotopic compositions and higher 87Sr/86Sr ratios than the host-limestones. These CS3 karstic infillings recrystallized early within evolved-meteoric waters having very little interaction with the host-rock. Blocky calcite cement type 4 (CC4 generation) has the lowest oxygen isotope ratio and the most radiogenic 87Sr/86Sr values, indicating low fluid-rock interaction. The increasingly open palaeohydrogeological system was dominated by migration of hot brines with elevated oxygen isotope ratios into the buried karstic system. The main oil emplacement in the Amposta reservoir occurred after the CC4 event, closely related to the Neogene extensional fractures. Corrosion of CC4 (blocky calcite cement type 4) occurred prior to (or during) petroleum charge, possibly related to kaolinite precipitation from relatively acidic fluids. Barite and pyrite precipitation occurred after this corrosion. The sulphur source associated with the late precipitation of pyrite was likely related to isotopically light sulphur expelled, e.g. as sulphide, from the petroleum source rock (Ascla Fm). Geofluids (2010) 10, 314,333 [source] Syntectonic infiltration by meteoric waters along the Sevier thrust front, southwest MontanaGEOFLUIDS (ELECTRONIC), Issue 4 2006A. C. RYGEL Abstract Structural, petrographic, and isotopic data for calcite veins and carbonate host-rocks from the Sevier thrust front of SW Montana record syntectonic infiltration by H2O-rich fluids with meteoric oxygen isotope compositions. Multiple generations of calcite veins record protracted fluid flow associated with regional Cretaceous contraction and subsequent Eocene extension. Vein mineralization occurred during single and multiple mineralization events, at times under elevated fluid pressures. Low salinity (Tm = ,0.6°C to +3.6°C, as NaCl equivalent salinities) and low temperature (estimated 50,80°C for Cretaceous veins, 60,80°C for Eocene veins) fluids interacted with wall-rock carbonates at shallow depths (3,4 km in the Cretaceous, 2,3 km in the Eocene) during deformation. Shear and extensional veins of all ages show significant intra- and inter-vein variation in ,18O and ,13C. Carbonate host-rocks have a mean ,18OV-SMOW value of +22.2 ± 3, (1,), and both the Cretaceous veins and Eocene veins have ,18O ranging from values similar to those of the host-rocks to as low as +5 to +6,. The variation in vein ,13CV-PDB of ,1 to approximately +6, is attributed to original stratigraphic variation and C isotope exchange with hydrocarbons. Using the estimated temperature ranges for vein formation, fluid (as H2O) ,18O calculated from Cretaceous vein compositions for the Tendoy and Four Eyes Canyon thrust sheets are ,18.5 to ,12.5,. For the Eocene veins within the Four Eyes Canyon thrust sheet, calculated H2O ,18O values are ,16.3 to ,13.5,. Fluid,rock exchange was localized along fractures and was likely coincident with hydrocarbon migration. Paleotemperature determinations and stable isotope data for veins are consistent with the infiltration of the foreland thrust sheets by meteoric waters, throughout both Sevier orogenesis and subsequent orogenic collapse. The cessation of the Sevier orogeny was coincident with an evolving paleogeographic landscape associated with the retreat of the Western Interior Seaway and the emergence of the thrust front and foreland basin. Meteoric waters penetrated the foreland carbonate thrust sheets of the Sevier orogeny utilizing an evolving mesoscopic fracture network, which was kinematically related to regional thrust structures. The uncertainty in the temperature estimates for the Cretaceous and Eocene vein formation prevents a more detailed assessment of the temporal evolution in meteoric water ,18O related to changing paleogeography. Meteoric water-influenced ,18O values calculated here for Cretaceous to Eocene vein-forming fluids are similar to those previously proposed for surface waters in the Eocene, and those observed for modern-day precipitation, in this part of the Idaho-Montana thrust belt. [source] A large collection of Presbyornis (Aves, Anseriformes, Presbyornithidae) from the late Paleocene and early Eocene of MongoliaGEOLOGICAL JOURNAL, Issue 4 2010Evgeny N. Kurochkin Abstract We describe a large collection of fossil ,waterfowl' bones that are referable to the extinct clade Presbyornithidae (Anseriformes). All of these fossils were collected between 1971 and 1994 from Upper Paleocene and Lower Eocene sediments at the Tsagaan Khushuu site in the Gobi Desert of southern Mongolia. The collection includes specimens referred to a new small species within the genus Presbyornis Wetmore, 1926 as well as large numbers of bones that we place in the genus Presbyornis. On this basis of the Tsagaan Khushuu collection we suggest that several species of Presbyornis likely coexisted in this region; indeed, the presence of large numbers of middle-sized, morphologically consistent but probably ecologically disparate species at the Tsagaan Khushuu site is consistent with the range of variation seen, for example, in taxa of extant dabbling ducks (Anatini). Although the anatomy and phylogenetic position of Presbyornithidae (in particular Presbyornis) are well known, this material from Mongolia further demonstrates the prevalence of these birds in aquatic and semi-aquatic habitats by the earliest Paleogene. Because presbyornithids are also well documented from the late Cretaceous, their palaeoecology and morphological diversity provides a clue to selective avian survivorship across the Cretaceous-Paleogene (K-Pg) boundary. Copyright © 2009 John Wiley & Sons, Ltd. [source] Stratigraphic and structural evolution of the Blue Nile Basin, Northwestern Ethiopian PlateauGEOLOGICAL JOURNAL, Issue 1 2009N. DS. Abstract The Blue Nile Basin, situated in the Northwestern Ethiopian Plateau, contains ,1400,m thick Mesozoic sedimentary section underlain by Neoproterozoic basement rocks and overlain by Early,Late Oligocene and Quaternary volcanic rocks. This study outlines the stratigraphic and structural evolution of the Blue Nile Basin based on field and remote sensing studies along the Gorge of the Nile. The Blue Nile Basin has evolved in three main phases: (1) pre-sedimentation phase, include pre-rift peneplanation of the Neoproterozoic basement rocks, possibly during Palaeozoic time; (2) sedimentation phase from Triassic to Early Cretaceous, including: (a) Triassic,Early Jurassic fluvial sedimentation (Lower Sandstone, ,300,m thick); (b) Early Jurassic marine transgression (glauconitic sandy mudstone, ,30,m thick); (c) Early,Middle Jurassic deepening of the basin (Lower Limestone, ,450,m thick); (d) desiccation of the basin and deposition of Early,Middle Jurassic gypsum; (e) Middle,Late Jurassic marine transgression (Upper Limestone, ,400,m thick); (f) Late Jurassic,Early Cretaceous basin-uplift and marine regression (alluvial/fluvial Upper Sandstone, ,280,m thick); (3) the post-sedimentation phase, including Early,Late Oligocene eruption of 500,2000,m thick Lower volcanic rocks, related to the Afar Mantle Plume and emplacement of ,300,m thick Quaternary Upper volcanic rocks. The Mesozoic to Cenozoic units were deposited during extension attributed to Triassic,Cretaceous NE,SW-directed extension related to the Mesozoic rifting of Gondwana. The Blue Nile Basin was formed as a NW-trending rift, within which much of the Mesozoic clastic and marine sediments were deposited. This was followed by Late Miocene NW,SE-directed extension related to the Main Ethiopian Rift that formed NE-trending faults, affecting Lower volcanic rocks and the upper part of the Mesozoic section. The region was subsequently affected by Quaternary E,W and NNE,SSW-directed extensions related to oblique opening of the Main Ethiopian Rift and development of E-trending transverse faults, as well as NE,SW-directed extension in southern Afar (related to northeastward separation of the Arabian Plate from the African Plate) and E,W-directed extensions in western Afar (related to the stepping of the Red Sea axis into Afar). These Quaternary stress regimes resulted in the development of N-, ESE- and NW-trending extensional structures within the Blue Nile Basin. Copyright © 2008 John Wiley & Sons, Ltd. [source] Amphibolite and blueschist,greenschist facies metamorphism, Blue Mountain inlier, eastern JamaicaGEOLOGICAL JOURNAL, Issue 5 2008Richard N. Abbott Jr Abstract Cretaceous (possibly older) metamorphic rock occurs mainly in the Blue Mountain inlier in eastern Jamaica. Fault-bounded blocks reveal two styles of metamorphism, Westphalia Schist (upper amphibolite facies) and Mt. Hibernia Schist (blueschist (BS),greenschist (GS) facies). Both Westphalia Schist and Mt. Hibernia Schist preserve detailed records of retrograde P,T paths. The paths are independent, but consistent with different parts of the type-Sanbagawa metamorphic facies series in Japan. For each path, phase relationships and estimated P,T conditions support a two-stage P,T history involving residence at depth, followed by rapid uplift and cooling. Conditions of residence vary depending on the level in a tectonic block. For the critical mineral reaction (isograd) in Westphalia Schist, conditions were P ,7.5,kbars, T ,600°C (upper amphibolite facies). Retrograde conditions in Hibernia Schist were P,=,2.6,3.0,kbars, T,=,219,237°C for a(H2O),=,0.8,1.0 (GS facies). Mt. Hibernia Schist may represent a volume of rock that was separated and uplifted at an early time from an otherwise protracted P,T path of the sort that produced the Westphalia Schist. Reset K,Ar ages for hornblende and biotite indicate only that retrograde metamorphism of Westphalia Schist took place prior to 76.5,Ma (pre-Campanian). Uplift may have commenced with an Albian,Aptian (,112,Ma) orogenic event. Copyright © 2008 John Wiley & Sons, Ltd. [source] Transition from arc- to post-collision extensional setting revealed by K,Ar dating and petrology: an example from the granitoids of the Eastern Pontide Igneous Terrane, Arakl,-Trabzon, NE TurkeyGEOLOGICAL JOURNAL, Issue 4 2005Sabah Yilmaz- Abstract The Eastern Pontide Igneous Terrane (EPIT) includes several Cretaceous to Neogene intrusive rocks, ranging in composition from low-K tholeiitic gabbros through calc-alkaline and high-K calc-alkaline metaluminous granitoids or peraluminous leucogranites to alkaline syenites. Such high diversity in age and composition is also accompanied by a broad spectrum in terms of geodynamics,i.e. from arc through syn-collisional thickening to post-collisional extensional regimes. Shallow-seated porphyritic acidic to intermediate rocks are from oldest to youngest, on the basis of field relations, the Gündo,du altered microgranite, the Bo,al, K-feldspar-megacrystic monzogranite and the Uzuntarla porphyritic granodiorite. These rocks, exposed in the southern part of the Arakl, region, east of Trabzon, Turkey, were studied in terms of their mineralogy and petrography, whole-rock geochemistry and hornblende K,Ar dating. The mineralogical and geochemical data reveal an apparent diversity in incompatible-element enrichment and depletion, for the Bo,al, unit and Uzuntarla unit, respectively. The Bo,al, and Uzuntarla units yield hornblende K,Ar ages ranging from 75.7,±,1.55 to 61.4,±,1.47,Ma and from 42.4,±,0.87 to 41.2,±,0.89,Ma, respectively. The diversity in both mineralogy,geochemistry and hornblende K,Ar ages suggests that the Bo,al, and Uzuntarla units are parts of the Cretaceous arc and Eocene post-collision extensional-related igneous activity, respectively, in the EPIT of northern Turkey. Copyright © 2005 John Wiley & Sons, Ltd. [source] Fish and ostracod remains from the Santos Basin (Cretaceous to Recent), BrazilGEOLOGICAL JOURNAL, Issue 4 2002C. Giles Miller Abstract For the first time, ichthyoliths are described from the Santos sedimentary basin, offshore southern Brazil. Isolated teeth, dermal scales and the first documented otoliths from Cretaceous (Albian) to Recent cuttings from five wells are described. The following groups are represented: Chondrichthyans: Triakidae, Carcharhinidae; Ginglymostomatidae: ?Ginglymostoma sp., Lamnidae indet., Scyliorhinidae; Osteichthyans: Teleostei; Myctophiidae: Diaphus aff. splendidus sp. complex, Diaphus spp., Diaphus cf. garmani, Ceratoscopelus aff. warmingii; Sternoptychidae: Valenciennellus tripunctulatus, teeth of indeterminate Teleostei. The majority of these ichthyofossils represent extant forms, known to occur in the Atlantic Ocean, and are of potential value for stratigraphical correlations between oil-yielding basins in the region. Ostracods are not well preserved but can be identified to generic level indicating marine environments. The ostracod faunas offer potential for intrabasinal correlation in the Eocene and Oligocene. Copyright © 2002 John Wiley & Sons, Ltd. [source] Carbon and oxygen isotopes: a tool for Jurassic and early Cretaceous pelagic correlation (southern Spain)GEOLOGICAL JOURNAL, Issue 4 2002J. Rey Abstract The isotopic evolution of ,13C and ,18O is reported for the Jurassic and early Cretaceous in two pelagic sections of the External Zones in the Betic Cordilleras (SE Spain). Stable isotope curves from pelagic trough and swell sections display similar patterns. Variations in ,18O and ,13C values from strata at equivalent age probably reflect both early diagenetic cementation and later temperature-related burial diagenesis. Comparison of global isotope curves with those presented in this work allows the differentiation of global from local events. Thus, the anoxic event during the early Toarcian (falciferum Zone) is characterized by elevated ,13C and depressed ,18O values. The isotopic record also allows the detection of the middle Oxfordian transgression. There are other peaks for the late Toarcian, early Bajocian, Callovian and early Berriasian that can also be used as tools for correlation purposes. Copyright © 2002 John Wiley & Sons, Ltd. [source] The Cretaceous volcanic succession around the Songliao Basin, NE China: relationship between volcanism and sedimentationGEOLOGICAL JOURNAL, Issue 2 2002Pujun Wang Abstract With volume ratio of 8:1:1.5 amongst acidic, intermediate and basaltic rocks, the Cretaceous volcanics around the Songliao Basin are a series of high-K or medium-K, peraluminous or metaluminous, calc-alkaline rocks, lacking typical basalts and peralkaline members of typical rift-related types. Their eruption ages range between 133 and 127,Ma, 124 and 122,Ma and 117 and 113,Ma respectively. They are high in total (Rare earth element) REE contents (96.1,326,ppm), enriched in LREE and depleted in HREE (LREE/HREE,=,4.6,13.8), with negative Eu and Ce anomalies (Eu/Eu*,=,0.04,0.88; Ce/Ce*,=,0.60,0.97). They have enriched large-ion lithophile elements (e.g. K, Ba, Th) and depleted high field strength elements (e.g. Nb, Ti and Y), suggesting a subduction-related tectonic setting. The volcanic activities migrated from south to north, forming a successively northward-stepping volcanic series and showing a feature significantly different from the overlying sedimentary sequence striking northeast. Thus, an overlap basin model was proposed. Accompanied by opening of the basin, the volcanogenic succession was formed at the block-faulting stage (131,113,Ma) owing to the closure of the Mongolia,Okhotsk ocean in the Jurassic and early Cretaceous, while the overlying sedimentary sequence was unconformably deposited at the spreading stage (Albian,Maastrichtian) owing to the oblique subduction of the Pacific plate under the Eurasian plate. The volcanic succession constitutes the lower unit of basin filling and is the forerunner of further basin spreading. Copyright © 2002 John Wiley & Sons, Ltd. [source] Palaeomagnetic and rock-magnetic studies of Cretaceous rocks in the Gongju Basin, Korea: implication of clockwise rotationGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2002Seong-Jae Doh Summary Palaeomagnetic and rock-magnetic studies have been carried out for Cretaceous non-marine sedimentary rocks (Gongju Group) and volcanic rocks in the Gongju Basin, located along the northern boundary of the Ogcheon Belt, Korea. K,Ar age dating for the volcanic rocks was also performed. It is found that the Gongju Group was remagnetised during the tilting of the strata with the characteristic remanent magnetisation (ChRM) direction of at 30 per cent untilting of the strata with a maximum value of precision parameter (k), while the volcanic rocks are revealed to acquire primary remanence with the direction of after the tilt-correction. The K,Ar ages of the volcanic rocks range from 81.8 ± 2.4 to 73.5 ± 2.2 Ma, corresponding to the Campanian stage of the Late Cretaceous. Electron microscope observations of samples from the Gongju Group show authigenic iron-oxide minerals of various sizes distributed along the cleavage of chlorite and in the pore spaces, indicating that the strata acquired the chemical remanent magnetisation due to the formation of secondary magnetic minerals under the influence of fluids. The palaeomagnetic pole positions are at Lat./Long. = 69.6°N/224.3°E (dp= 3.5°, dm= 5.2°) calculated for the 30 per cent tilt-corrected direction of the Gongju Group and at for the volcanic rocks. Based on the results of this study, it is interpreted that the volcanic rocks acquired the primary magnetisation almost at the same time as the remagnetisation of the Gongju Group in the Late Cretaceous. Comparisons of Cretaceous palaeomagnetic poles from the Korean Peninsula with those from Eurasia implies that the Korean Peninsula underwent clockwise rotation of 21.2°± 5.3° for the middle Early Cretaceous, 12.6°± 5.4° for the late Early Cretaceous, and 7.1°± 9.8° for the Late Cretaceous with respect to Eurasia, due to the sinistral motion of the Tan-Lu Fault. [source] Cretaceous,Tertiary geodynamics: a North Atlantic exerciseGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Trond H. Torsvik Summary New reconstructions are presented for the Cretaceous,Early Tertiary North Atlantic using a combination of palaeomagnetic, hotspot and magnetic anomaly data. We utilize these reconstructions in an analysis of previously described misfits between the North Atlantic Plate elements at successive intervals during this time period. We are able to achieve reasonable overlap between the hotspot and palaeomagnetic reconstructions between 40 and 95 Ma and thus are able to support the idea that the Indo,Atlantic hotspots are relatively stationary. Small, but systematic discrepancies for this time interval can readily be modelled with a long-term, octopole non-dipole field contribution (G3 = g30/g10 = 0.08). However, hotspot and palaeomagnetic reconstructions for the Early Cretaceous North Atlantic show substantial differences that cannot be explained by constant, non-dipole fields and we favour an explanation for these discrepancies in terms of true polar wander (TPW) triggered by mantle instabilities between 125 and 95 Ma; this constitutes the only identifiable event of significant TPW since the Early Cretaceous. Taken in the context of available geochronological and geological data and seismic tomography from the region, the 95,40 Ma reconstructions and their time-consequent geological products are interpreted in terms of specific conditions of mantle-crust coupling and global plate motions/tectonic activity. Highlights from these reconstructions show uniform NE movement of the coupled North American, Greenland and Eurasian plates from 95 to 80 Ma; a marked cusp in the paths for all three elements at 80 Ma where the three plates simultaneously change direction and follow a uniform NW-directed motion until c. 20 Ma when Eurasia diverges NE, away from the still-NW-moving Greenland and North American elements. Positioning of the Iceland plume beneath the spreading-ridge at 20 Ma may have increased upwelling below the ridge, increased the ridge-push, and caused a NE shift in the absolute direction of Eurasia. [source] The influence of hydroelectrical development on the flow regime of the karstic river CetinaHYDROLOGICAL PROCESSES, Issue 1 2003Ognjen Bonacci Abstract The Cetina River is a typical karst watercourse in the deep and well-developed Dinaric karst. The total length of the Cetina River open streamflow from its spring to the mouth is about 105 km. Estimated mean annual rainfall is 1380 mm. The Cetina catchment is built of Triassic, Jurassic, and Cretaceous carbonate strata. The western part of the catchment by the Cetina River is referred to as the ,direct' or topographic catchment. It was defined based on surface morphologic forms, by connection between mountain chain peaks. This part of the catchment is almost entirely situated in the Republic of Croatia. The eastern part of the catchment is referred to as the ,indirect' catchment, and is mainly situated in Bosnia-Herzegovina. Water from the ,indirect' catchment emerges from the western ,direct' catchment in numerous permanent and temporary karst springs. Since 1960, numerous hydrotechnical works have been carried out on the Cetina River and within its catchment. Five hydroelectric power plants (HEPPs), five reservoirs, and three long tunnels and pipelines have been built. Their operation has significantly altered the natural hydrological regime. The Cetina River is divided into two hydrological reaches. In the 65 km upstream, the hydrological regime was redistributed within the year: low flows had increased and high flows had decreased, although the mean annual discharge remained the same. Part of the Cetina watercourse downstream from the Pran,evi,i Reservoir lost the majority of its flow. The mean annual discharges dropped from 100 m3 s,1 to less than 10 m3 s,1 because of the Zaku,ac HEPP development. Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||