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Late Cretaceous (late + cretaceous)
Selected AbstractsA 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] 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] 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] Role of southeastern Sanandaj,Sirjan Zone in the tectonic evolution of Zagros Orogenic Belt, IranISLAND ARC, Issue 4 2009Ramin Arfania Abstract Geological studies indicate that the southeastern Sanandaj,Sirjan Zone, located in the southeastern Zagros Orogenic Belt, is subdivided transversally into the Esfahan,Sirjan Block with typical Central Iranian stratigraphic features and the Shahrekord,Dehsard Terrane consisting of Paleozoic and Lower Mesozoic metamorphic rocks. The Main Deep Fault (Abadeh Fault) is a major lithospheric fault separating the two parts. The purpose of this paper is to clarify the role of the southeastern Sanandaj,Sirjan Zone in the tectonic evolution of the southeastern Zagros Orogenic Belt on the basis of geological evidence. The new model implies that Neo-Tethys 1 came into being when the Central Iran Microcontinent split from the northeastern margin of Gondwana during the Late Carboniferous to Early Permian. During the Late Triassic a new spreading ridge, Neo-Tethys 2, was created to separate the Shahrekord,Dehsard Terrane from Afro,Arabian Plate. The Zagros sedimentary basin was formed on a continental passive margin, southwest of Neo-Tethys 2. The two ophiolitic belts of Naien,Shahrebabak,Baft and Neyriz were developed to the northeast of Neo-Tethys 1 and southwest of Neo-Tethys 2 respectively, related to the sinking of the lithosphere of the Neo-Tethys 1 in the Late Cretaceous. It can be concluded that deposition of the Paleocene conglomerate on the Central Iran Microcontinent and Pliocene conglomerate in the Zagros Sedimentary Basin is directly linked to the uplift generated by collision. [source] Molecular clocks keep dispersal hypotheses afloat: evidence for trans-Atlantic rafting by rodentsJOURNAL OF BIOGEOGRAPHY, Issue 2 2010Diane L. Rowe Abstract Aim, In order to resolve disputed biogeographical histories of biota with Gondwanan continental distributions, and to assess the null hypothesis of vicariance, it is imperative that a robust geological time-frame be established. As an example, the sudden and coincident appearance of hystricognath rodents (Rodentia: Hystricognathi) on both the African and South American continents has been an irreconcilable controversy for evolutionary biologists, presenting enigmas for both Gondwanan vicariance and Late Eocene dispersal hypotheses. In an attempt to resolve this discordance, we aim to provide a more robust phylogenetic hypothesis and improve divergence-date estimates, which are essential to assessing the null hypothesis of vicariance biogeography. Location, The primary centres of distribution are in Africa and South America. Methods, We implemented parsimony, maximum-likelihood and Bayesian methods to generate a phylogeny of 37 hystricognath taxa, the most comprehensive taxonomic sampling of this group to date, on the basis of two nuclear gene regions. To increase phylogenetic resolution at the basal nodes, these data were combined with previously published data for six additional nuclear gene regions. Divergence dates were estimated using two relaxed-molecular-clock methods, Bayesian multidivtime and nonparametric rate smoothing. Results, Our data do not support reciprocal monophyly of African and South American lineages. Indeed, Old World porcupines (i.e. Hystricomorpha) appear to be more closely related to New World lineages (i.e. Caviomorpha) than to other Old World families (i.e. Bathyergidae, Petromuridae and Thryonomyidae). The divergence between the monophyletic assemblage of South American lineages and its Old World ancestor was estimated to have occurred c. 50 Ma. Main conclusions, Our phylogenetic hypothesis and divergence-date estimates are strongly at odds with Gondwanan-vicariance isolating mechanisms. In contrast, our data suggest that transoceanic dispersal has played a significant role in governing the contemporary distribution of hystricognath rodents. Molecular-clock analyses imply a trans-Tethys dispersal event, broadly confined to the Late Cretaceous, and trans-Atlantic dispersal within the Early Eocene. Our analyses also imply that the use of the oldest known South American rodent fossil as a calibration point has biased molecular-clock inferences. [source] Australian biogeographical connections and the phylogeny of large genera in the plant family MyrtaceaeJOURNAL OF BIOGEOGRAPHY, Issue 7 2003Pauline Y. Ladiges Abstract Aim To compare the phylogeny of the eucalypt and melaleuca groups with geological events and ages of fossils to discover the time frame of clade divergences. Location Australia, New Caledonia, New Guinea, Indonesian Archipelago. Methods We compare published molecular phylogenies of the eucalypt and melaleuca groups of the plant family Myrtaceae with geological history and known fossil records from the Cretaceous and Cenozoic. Results The Australasian eucalypt group includes seven genera, of which some are relictual rain forest taxa of restricted distribution and others are species-rich and widespread in drier environments. Based on molecular and morphological data, phylogenetic analyses of the eucalypt group have identified two major clades. The monotypic Arillastrum endemic to New Caledonia is related in one clade to the more species-rich Angophora, Corymbia and Eucalyptus that dominate the sclerophyll vegetation of Australia. Based on the time of rifting of New Caledonia from eastern Gondwana and the age of fossil eucalypt pollen, we argue that this clade extends back to the Late Cretaceous. The second clade includes three relictual rain forest taxa, with Allosyncarpia from Arnhem Land the sister taxon to Eucalyptopsis of New Guinea and the eastern Indonesian archipelago, and Stockwellia from the Atherton Tableland in north-east Queensland. As monsoonal, drier conditions evolved in northern Australia, Arnhem Land was isolated from the wet tropics to the east and north during the Oligocene, segregating ancestral rain forest biota. It is argued also that the distribution of species in Eucalyptopsis and Eucalyptus subgenus Symphyomyrtus endemic in areas north of the stable edge of the Australian continent, as far as Sulawesi and the southern Philippines, is related to the geological history of south-east Asia-Australasia. Colonization (dispersal) may have been aided by rafting on micro-continental fragments, by accretion of arc terranes onto New Guinea and by land brought into closer proximity during periods of low sea-level, from the Late Miocene and Pliocene. The phylogenetic position of the few northern, non-Australian species of Eucalyptus subgenus Symphyomyrtus suggests rapid radiation in the large Australian sister group(s) during this time frame. A similar pattern, connecting Australia and New Caledonia, is emerging from phylogenetic analysis of the Melaleuca group (Beaufortia suballiance) within Myrtaceae, with Melaleuca being polyphyletic. Main conclusion The eucalypt group is an old lineage extending back to the Late Cretaceous. Differentiation of clades is related to major geological and climatic events, including rifting of New Caledonia from eastern Gondwana, development of monsoonal and drier climates, collision of the northern edge of the Australian craton with island arcs and periods of low sea level. Vicariance events involve dispersal of biota. [source] Sub-ophiolite metamorphic rocks from NW Anatolia, TurkeyJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2000Önen The metamorphic rocks from near Kütahya in north-west Anatolia record different stages in the history of closure of the Neo-Tethyan ,zmir,Ankara,Erzincan ocean. Sub-ophiolite metamorphic rocks within the Tav,anl, zone are a tectonically composite sequence of quartz,mica schists, amphibole schists, amphibolites and garnet amphibolites. They show increasing metamorphic grade towards the base of the ophiolite. A first metamorphic event, typical of sub-ophiolite metamorphic sole rocks, was characterized by high-grade assemblages, and followed by retrograde metamorphism. A second event was marked by a medium-to high-pressure overprint of the first-stage metamorphic assemblages with assemblages indicating a transition between the blueschist and greenschist facies. The chemistry of the sub-ophiolite metamorphic rocks indicates an ocean island basalt origin, and Ar,Ar dating indicates a high temperature metamorphic event at 93±2 Ma. Counter-clockwise P,T,t paths recorded by the sub-ophiolite metamorphic rocks are interpreted to result from intra-oceanic thrusting during the closure of the ,zmir, Ankara,Erzincan ocean, initiating subduction, which formed the high-temperature assemblages. Further subduction then produced the widespread blueschists of the Tav,anl, zone during the Late Cretaceous. Later cold thrusting obducted the ophiolite (with the metamorphic sole welded to its base), ophiolitic melanges and blueschists onto the Anatolide passive margin in the latest Cretaceous. All these events pre-date the final Anatolide,Pontide continent,continent collision. [source] THE STRUCTURAL STYLE OF SEDIMENTARY BASINS ON THE SHELVES OF THE LAPTEV SEA AND WESTERN EAST SIBERIAN SEA, SIBERIAN ARCTICJOURNAL OF PETROLEUM GEOLOGY, Issue 3 2005D. Franke A total of 11,700 km of multichannel seismic reflection data were acquired during three recent reconnaissance surveys of the wide, shallow shelves of the Laptev and western East Siberian Seas in the Siberian Arctic Ocean. Three seismic marker horizons were defined and mapped in both shelf areas. Their nature and age were predicted on the basis of regional tectonic and palaeoenvironmental events and corroborated using onshore geology. To the north of the Laptev Sea, the Gakkel Ridge, an active mid-ocean ridge which separates the North American and Eurasian Plates, abruptly meets the steep slope of the continental shelf which is curvilinear in plan view. Extension has affected the Laptev Shelf since at least the Early Tertiary and has resulted in the formation of three major, generally north-south trending rift basins: the Ust'Lena Rift, the Anisin Basin and the New Siberian Basin. The Ust'Lena Rift has a minimum east-west width of 300km at latitude 75°N and a Cenozoic infill up to 6 s (twt) in thickness. Further to the NW of the Laptev Shelf, the downthrown and faulted basement is overlain by a sub-parallel layered sedimentary succession with a thickness of 4 s (twt) that thins towards the west. Although this area was affected by extension as shown by the presence of numerous faults, it is not clear whether this depression on the NW Laptev Shelf is continuous with the Ust'Lena Rift. The Anisin Basin is located in the northern part of the Laptev Shelf and has a Cenozoic sedimentary fill up to 5 s (twt) thick. The deepest part of the basin trends north-south. To the west is a secondary, NW-SE trending depression which is slightly shallower than the main depocentre. The overall structure of the basin is a half-graben with the major bounding fault in the east. The New Siberian Basin is up to 70 km wide and has a minimum NW-SE extent of 300 km. The sedimentary fill is up to 4.5 s (twt) thick. Structurally, the basin is a half-graben with the bounding fault in the east. Our data indicate that the rift basins on the Laptev Shelf are not continuous with those on the East Siberian Shelf. The latter shelf can best be described as an epicontinental platform which has undergone continuous subsidence since the Late Cretaceous. The greatest subsidence occurred in the NE, as manifested by a major depocentre filled with inferred (?)Late Cretaceous to Tertiary sediments up to 5 s (twt) thick. [source] HYDROCARBON SEEPAGE AND CARBONATE MOUND FORMATION: A BASIN MODELLING STUDY FROM THE PORCUPINE BASIN (OFFSHORE IRELAND)JOURNAL OF PETROLEUM GEOLOGY, Issue 2 2005J. Naeth This study assesses whether the growth of deep water carbonate mounds on the continental slope of the north Atlantic may be associated with active hydrocarbon leakage. The carbonate mounds studied occur in two distinct areas of the Porcupine Basin, 200 km offshore Ireland, known as the Hovland-Magellan and the Belgica areas. To evaluate the possible link between hydrocarbon leakage and mound growth, we used two dimensional cross-section and map-based basin modelling. Geological information was derived from interpretation of five seismic lines across the province as well as the Connemara oilfield. Calibration data was available from the northern part of the study area and included vitrinite reflectance, temperature and apatite fission track data. Modelling results indicate that the main Jurassic source rocks are mature to overmature for hydrocarbon generation throughout the basin. Hydrocarbon generation and migration started in the Late Cretaceous. Based on our stratigraphic and lithologic model definitions, hydrocarbon migration is modelled to be mainly vertical, with only Aptian and Tertiary deltaic strata directing hydrocarbon flow laterally out of the basin. Gas chimneys observed in the Connemara field were reproduced using flow modelling and are related to leakage at the apices of rotated Jurassic fault blocks. The model predicts significant focussing of gas migration towards the Belgica mounds, where Cretaceous and Tertiary carrier layers pinch out. In the Hovland-Magellan area, no obvious focus of hydrocarbon flow was modelled from the 2D section, but drainage area analysis of Tertiary maps indicates a link between mound position and shallow Tertiary closures which may focus hydrocarbon flow towards the mounds. [source] POST-DRILLING ANALYSIS OF THE NORTH FALKLAND BASIN, PART 1: TECTONO-STRATIGRAPHIC FRAMEWORKJOURNAL OF PETROLEUM GEOLOGY, Issue 3 2000P. C. Richards Six wells were drilled in the extensional North Falkland Basin in 1998. The wells encountered a Devonian to Cenozoic stratigraphy dominated by thick Mesozoic syn- and post-rift successions. Although most previously published models predicted that the succession would most likely be of marine origin, it is in fact predominantly terrestrial; marine conditions did not become established in the basin until the Late Cretaceous. The oldest rocks recorded are Devonian and these were penetrated in only one well. The overlying succession comprises: a fluvio-lacustrine, early syn-rft interval of ?mid-Jurassic to Tithonian age; a late syn-rift fluvio-lacustrine interval of Tithonian to Berriasian age; a rift-sag transitional unit of Berriasian to Valanginian age; an early post-rift lacustrine unit of Valanginian to early Aptian age; a middle post-rift, transgressive unit of Aptian to Albian age; a late post-rift, terrestrial to marine unit of Albian to early Palaeocene age; and a post-up lift thermal subsidence unit of Palaeocene to Recent age. Much of the sediment appears to have been derived from volcanic and/or metamorphic terranes, probably located to the north or NW of the basin. As well as the volcanic material which occurs in the ground mass and as lithoclasts in many of the units, some volcaniclastic rocks and minor amounts of ashfall tufls are observed, particularly within the late syn-rift succession. [source] Mammalian tooth marks on the bones of dinosaurs and other Late Cretaceous vertebratesPALAEONTOLOGY, Issue 4 2010NICHOLAS R. LONGRICH Abstract:, We describe bones from the Late Cretaceous of Alberta , including bones of large dinosaurs, a femur from the aquatic reptile Champsosaurus, and a dentary from the marsupial Eodelphis, that bear tooth marks made by animals with opposing pairs of teeth. Of the animals known from the Late Cretaceous of North America, only mammals are capable of making such tooth marks. In particular, multituberculates, which have paired upper and lower incisors, are the most likely candidates for the makers of these traces. The traces described here represent the oldest known mammalian tooth marks. Although it is possible that some of these tooth marks represent feeding traces, the tooth marks often penetrate deep into the dense cortices of the bone. This raises the possibility that, much as extant mammals gnaw bone and antler, some Cretaceous mammals may have consumed the bones of dinosaurs and other vertebrates as a source of minerals. However, none of the tooth marks described here resemble the extensive gnaw traces produced by Cenozoic multituberculates or rodents. This suggests that specialized gnawing forms may have been rare or absent in the Late Cretaceous of North America. [source] Chondrichthyans from a Cenomanian (Late Cretaceous) bonebed, Saskatchewan, CanadaPALAEONTOLOGY, Issue 4 2010CHARLIE J. UNDERWOOD Abstract:, Acid preparation of samples of a bonebed from the Cenomanian of central Canada yielded several thousand well-preserved chondrichthyan teeth, in addition to numerous other vertebrate remains. Teeth and other remains of one species of chimaeroid, one species of hybodont shark, three species of Ptychodus, 10 species of neoselachian sharks and two species of batoid were recorded. The family Archaeolamnidae fam. nov., genera Meristodonoides gen. nov. and Telodontaspis gen. nov. and species Ptychodus rhombodus sp. nov., Telodontaspis agassizensis gen et sp. nov., Eostriatolamia paucicorrugata sp. nov., Roulletia canadensis sp. nov., Cretorectolobus robustus sp. nov. and Orectoloboides angulatus sp. nov. are described. Status of the genus Palaeoanacorax and the species Cretoxyrhina denticulata, Squalicorax curvatus and ,Rhinobatos'incertus are discussed, and reconstructed dentitions of Archaeolamna and Roulletia presented. The fauna is of low diversity and dominated by active hunters, with many species apparently endemic to the northern Western Interior Seaway. [source] A LONG-SNOUTED DYROSAURID (CROCODYLIFORMES, MESOEUCROCODYLIA) FROM THE PALEOCENE OF MOROCCO: PHYLOGENETIC AND PALAEOBIOGEOGRAPHIC IMPLICATIONSPALAEONTOLOGY, Issue 2 2008STEPHANE JOUVE Abstract:, New material of a long-snouted dyrosaurid has been discovered in the Paleocene of Morocco. It consists of a well-preserved skull with embedded mandible and four dorsal vertebrae. The particularly elongate snout, proportionally the longest of all known dyrosaurids, allows precise identification of this material as Atlantosuchus coupateziBuffetaut, 1979a, and presentation of an emended diagnosis for this species previously known only from a mandibular symphysis. A phylogenetic analysis of the dyrosaurids indicates a close relationship between A. coupatezi and Rhabdognathus. It also confirms a previous hypothesis that Congosaurus is distinct from Hyposaurus. It is more closely related to Atlantosuchus than Hyposaurus. The analysis also allows palaeobiogeographic interpretations to be made. Dyrosaurids ranged from North Africa to other areas. They were rare during the Maastrichtian and endemic to each continent at this time. Competition with large marine reptiles, such as mosasaurs, limited their dispersal during the Late Cretaceous. The disappearance of these rivals during the ,K-T crisis' enabled their diversification and widespread dispersal during the Paleocene, with the same genera present on several continents. [source] Fossil Woods From Williams Point Beds, Livingston Island, Antarctica: A Late Cretaceous Southern High Latitude FloraPALAEONTOLOGY, Issue 6 2001Imogen Poole The wood flora from Williams Point, Livingston Island, contains 12 wood types of gymnosperm and angiosperm origin. Recent collections of material have increased the biodiversity of a postulated species-rich vegetation. The gymnosperm wood can be readily assigned to four form-genera: Araucarioxylon Kraus, Araucariopitys Jeffrey, Podocarpoxylon Gothan and Sahnioxylon Bose and Sah. This indicates a diversity of coniferous araucarian and podocarp trees alongside woods of uncertain affinity (Sahnioxylon; Bennettitales). Two angiosperm morphotypes are assigned to the organ genera Hedycaryoxylon Su¨ss (Monimiaceae) and Weinmannioxylon Petriella (Cunoniaceae). The remaining four taxa of angiosperm wood cannot be confidently placed in extant families as they exhibit features that suggest relationships with the Magnoliidae, Hamamelidae and Rosidae. This paper presents the first comprehensive taxonomic revision of the wood flora from Livingston Island and discusses the palaeoecology that prevailed at a latitude of about 60 degrees south during the Late Cretaceous. Newly described taxa are Araucarioxylon chapmanae sp. nov., Araucariopitys antarcticus sp. nov., Podocarpoxylon chapmanae sp. nov., P. verticalis sp. nov., P. communis sp. nov., Weinmannioxylon ackamoides sp. nov., Antarctoxylon livingstonensis gen. et sp. nov., A. multiseriatum gen. et sp. nov., A. heteroporosum gen. et sp. nov. and A. uniperforatum gen et sp. nov. [source] Presence Of Nemathecia In Parachaetetes Asvapatii Pia, 1936 (Rhodophyta, Gigartinales?): Reproduction In ,Solenoporaceans' RevisitedPALAEONTOLOGY, Issue 6 2001J. Aguirre Parachaetetes asvapatii is a very common algal species in the Palaeogene deposits of the Tethyan realm and has been considered as a member of the heterogeneous family Solenoporaceae. This attribution is exclusively based on features of the vegetative tissue, since no reproductive structures have ever been recovered. However, detailed analysis of Late Cretaceous,Eocene material from Turkey has revealed nemathecia-like structures in one specimen attributable to P. asvapatii. These nemathecia are small wart-like structures protruding on the thallus surface that formed by enlargement of the most peripheral cells of the plant. Nemathecia only occur in three families of the order Gigartinales (Rhodophyta): Rhizophyllidaceae, Peyssonneliaceae and Polyideaceae. Since reproductive structures are stable characters, the presence of nemathecia leads us to tentatively refer P. asvapatii and related species (probably Elianella elegans) to the Gigartinales. [source] Orogenic Gold Mineralization in the Qolqoleh Deposit, Northwestern IranRESOURCE GEOLOGY, Issue 3 2007Farhang Aliyari Abstract The Qolqoleh gold deposit is located in the northwestern part of the Sanandai-Sirjan Zone, northwest of Iran. Gold mineralization in the Qolqoleh deposit is almost entirely confined to a series of steeply dipping ductile,brittle shear zones generated during Late Cretaceous,Tertiary continental collision between the Afro-Arabian and the Iranian microcontinent. The host rocks are Mesozoic volcano-sedimentary sequences consisting of felsic to mafic metavolcanics, which are metamorphosed to greenschist facies, sericite and chlorite schists. The gold orebodies were found within strong ductile deformation to late brittle deformation. Ore-controlling structure is NE,SW-trending oblique thrust with vergence toward south ductile,brittle shear zone. The highly strained host rocks show a combination of mylonitic and cataclastic microstructures, including crystal,plastic deformation and grain size reduction by recrystalization of quartz and mica. The gold orebodies are composed of Au-bearing highly deformed and altered mylonitic host rocks and cross-cutting Au- and sulfide-bearing quartz veins. Approximately half of the mineralization is in the form of dissemination in the mylonite and the remainder was clearly emplaced as a result of brittle deformation in quartz,sulfide microfractures, microveins and veins. Only low volumes of gold concentration was introduced during ductile deformation, whereas, during the evident brittle deformation phase, competence contrasts allowed fracturing to focus on the quartz,sericite domain boundaries of the mylonitic foliation, thus permitting the introduction of auriferous fluid to create disseminated and cross-cutting Au-quartz veins. According to mineral assemblages and alteration intensity, hydrothermal alteration could be divided into three zones: silicification and sulfidation zone (major ore body); sericite and carbonate alteration zone; and sericite,chlorite alteration zone that may be taken to imply wall-rock interaction with near neutral fluids (pH 5,6). Silicified and sulfide alteration zone is observed in the inner parts of alteration zones. High gold grades belong to silicified highly deformed mylonitic and ultramylonitic domains and silicified sulfide-bearing microveins. Based on paragenetic relationships, three main stages of mineralization are recognized in the Qolqoleh gold deposit. Stage I encompasses deposition of large volumes of milky quartz and pyrite. Stage II includes gray and buck quartz, pyrite and minor calcite, sphalerite, subordinate chalcopyrite and gold ores. Stage III consists of comb quartz and calcite, magnetite, sphalerite, chalcopyrite, arsenopyrite, pyrrhotite and gold ores. Studies on regional geology, ore geology and ore-forming stages have proved that the Qolqoleh deposit was formed in the compression,extension stage during the Late Cretaceous,Tertiary continental collision in a ductile,brittle shear zone, and is characterized by orogenic gold deposits. [source] Mid,Cretaceous Episodic Magmatism and Tin Mineralization in Khingan-Okhotsk Volcano,Plutonic Belt, Far East RussiaRESOURCE GEOLOGY, Issue 1 2002Kohei SATO Abstract: Age of magmatism and tin mineralization in the Khingan-Okhotsk volcano,plutonic belt, including the Khingan, Badzhal and Komsomolsk tin fields, were reviewed in terms of tectonic history of the continental margin of East Asia. This belt consists mainly of felsic volcanic rocks and granitoids of the reduced type, being free of remarkable geomagnetic anomaly, in contrast with the northern Sikhote-Alin volcano,plutonic belt dominated by oxidized-type rocks and gold mineralization. The northern end of the Khingan-Okhotsk belt near the Sea of Okhotsk, accompanied by positive geomagnetic anomalies, may have been overprinted by magmatism of the Sikhote-Alin belt. Tin,associated magmatism in the Khingan-Okhotsk belt extending over 400 km occurred episodically in a short period (9510 Ma) in the middle Cretaceous time, which is coeval with the accretion of the Kiselevka-Manoma complex, the youngest accretionary wedge in the eastern margin of the Khingan-Okhotsk accretionary terranes. The episodic magmatism is in contrast with the Cretaceous-Paleogene long,lasted magmatism in Sikhote,Alin, indicating the two belts are essentially different arcs, rather than juxtaposed arcs derived from a single arc. The tin-associated magmatism may have been caused by the subduction of a young and hot back-arc basin, which is inferred from oceanic plate stratigraphy of the coeval accre-tionary complex and its heavy mineral assemblage of immature volcanic arc provenance. The subduction of the young basin may have resulted in dominance of the reduced-type felsic magmas due to incorporation of carbonaceous sediments within the accretionary complex near the trench. Subsequently, the back-arc basin may have been closed by the oblique collision of the accretionary terranes in Sikhote,Alin, which was subjected to the Late Cretaceous to Paleogene magmatism related to another younger subduction system. These processes could have proceeded under transpressional tectonic regime due to oblique subduction of the paleo-Pacific plates under Eurasian continent. [source] Unearthing the Anatomy of Dinosaurs: New Insights Into Their Functional Morphology and PaleobiologyTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 9 2009Peter Dodson Guest Editor The meek shall inherit the earth. Triceratops horridus encounters Tyrannosaurus rex. Late Cretaceous of Montana, 65 million years before present. The encounter did not come out the way many thought it would. This young Tyrannosaurus had insufficient respect for a powerful and dangerous adversary. In this special issue we explore recent advances in understanding the anatomy and paleobiology of dinosaurs, including Tyrannosaurus, using powerful modern anatomical techniques. Painting by Wayne D. Barlowe from The Horned Dinosaurs by Peter Dodson (1996), Princeton University Press. Reproduced with permission of the artist. [source] The Facial Integument of Centrosaurine Ceratopsids: Morphological and Histological Correlates of Novel Skin StructuresTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 9 2009Tobin L. Hieronymus Abstract The horned dinosaur Pachyhinosaurus possesses rugose bony bosses across the skull roof in lieu of the projecting bony horn cores seen in most ceratopsians. This elaboration of typical ceratopsian ornaments provides an opportunity to test hypotheses of ceratopsian facial skin morphology and function. We analyze bone morphology and histology associated with several classes of skin features in extant amniotes using a classification tree analysis. We isolate key osteological and histological correlates for unpreserved skin structures, including both a pattern of pitting and resorption characteristic of muskox (Ovibos) frontal horn boss, and a pattern of metaplastic ossification characteristic of rhinoceros nasal horn boss. We also describe correlates for other skin features, such as epidermal scales and horn sheaths. Dermatocranial elements from centrosaurine ceratopsians are then examined for the same osteological and histological correlates. From this comparison we propose that the rugose bosses that replace horn cores in many centrosaurine dinosaurs, most notably Achelousaurus and Pachyrhinosaurus, were covered by a thick pad of cornified skin derived from the caudodorsal side of the primitive horn sheath comparable to the horny boss of extant muskoxen (Ovibos). We examine extant taxa with skin morphologies similar to Pachyrhinosaurus for consistent adaptive relationships between structure and behavior. We determine that high-energy headbutting is consistently associated with the acquisition of thick cornified pads, seen in muskoxen as well as helmeted hornbills [Buceros (=Rhinoplax) vigil] and African buffalo (Syncerus). The association of the bony ornaments of Pachyrhinosaurus with risky agonistic behaviors casts doubt on the role of species recognition as a primary selection pressure driving the diversity of all ceratopsian horns. We conclude that social selection (a broad form of intraspecific competition) is a more appropriate explanation for the diversity of centrosaurine ceratopsian ornaments in the Late Cretaceous. Anat Rec, 292:1370,1396, 2009. © 2009 Wiley-Liss, Inc. [source] Alluvial fan development and morpho-tectonic evolution in response to contractional fault reactivation (Late Cretaceous,Palaeocene), Provence, FranceBASIN RESEARCH, Issue 2 2009S. Leleu ABSTRACT Along-strike variability within a Late Cretaceous to early Palaeocene contractional growth structure and associated alluvial fan deposits is documented at the northern margin of the Arc Basin (Provence, SE France). This contribution shows that alluvial fans can be used as high-resolution proxies to reconstruct structural segmentation and palaeo-geomorphological evolution of a source/basin margin system. Facies-based reconstruction allows the spatial and temporal distribution of alluvial fan bodies to be mapped. Relationships between fan area and catchment size from modern alluvial fan systems were used to estimate palaeo-catchment size. Combining alluvial fan morphologies with catchment area, pebble provenance analysis and growth structure reconstruction, we show that: (1) fan distribution and related depositional processes were strongly influenced by intrinsic parameters such as drainage basin evolution, local structural inheritance and lateral facies changes in source area lithologies; (2) Inherited structures trending N100 effectively controlled the first-order location of the fold and thrust structures (Montagne Sainte-Victoire Range) and adjacent depositional areas (Arc Basin); (3) Syn-sedimentary faults trending N010-030 influenced the source/basin margin development and interacted with developing growth structures; (4) Facies changes in Jurassic carbonates controlled fold development and consequently the structural evolution of the source area; and (5) the N010-030 faults and along-strike variability of the source/basin margin system were ultimately controlled by basement structures that controlled where Late C etaceous deformation nucleated. The overall architecture of the source/basin margin system reflects segmentation and strain partitioning along strike, as demonstrated by diachronous alluvial fan distribution. [source] Detrital zircon geochronology of Carboniferous,Cretaceous strata in the Lhasa terrane, Southern TibetBASIN RESEARCH, Issue 3 2007Andrew L. Leier ABSTRACT Sedimentary strata in the Lhasa terrane of southern Tibet record a long but poorly constrained history of basin formation and inversion. To investigate these events, we sampled Palaeozoic and Mesozoic sedimentary rocks in the Lhasa terrane for detrital zircon uranium,lead (U,Pb) analysis. The >700 detrital zircon U,Pb ages reported in this paper provide the first significant detrital zircon data set from the Lhasa terrane and shed new light on the tectonic and depositional history of the region. Collectively, the dominant detrital zircon age populations within these rocks are 100,150, 500,600 and 1000,1400 Ma. Sedimentary strata near Nam Co in central Lhasa are mapped as Lower Cretaceous but detrital zircons with ages younger than 400 Ma are conspicuously absent. The detrital zircon age distribution and other sedimentological evidence suggest that these strata are likely Carboniferous in age, which requires the existence of a previously unrecognized fault or unconformity. Lower Jurassic strata exposed within the Bangong suture between the Lhasa and Qiangtang terranes contain populations of detrital zircons with ages between 200 and 500 Ma and 1700 and 2000 Ma. These populations differ from the detrital zircon ages of samples collected in the Lhasa terrane and suggest a unique source area. The Upper Cretaceous Takena Formation contains zircon populations with ages between 100 and 160 Ma, 500 and 600 Ma and 1000 and 1400 Ma. Detrital zircon ages from these strata suggest that several distinct fluvial systems occupied the southern portion of the Lhasa terrane during the Late Cretaceous and that deposition in the basin ceased before 70 Ma. Carboniferous strata exposed within the Lhasa terrane likely served as source rocks for sediments deposited during Cretaceous time. Similarities between the lithologies and detrital zircon age-probability plots of Carboniferous rocks in the Lhasa and Qiangtang terranes and Tethyan strata in the Himalaya suggest that these areas were located proximal to one another within Gondwanaland. U,Pb ages of detrital zircons from our samples and differences between the geographic distribution of igneous rocks within the Tibetan plateau suggest that it is possible to discriminate a southern vs. northern provenance signature using detrital zircon age populations. [source] Late Cretaceous and Cenozoic sea-level estimates: backstripping analysis of borehole data, onshore New JerseyBASIN RESEARCH, Issue 4 2004William A. Van Sickel Backstripping analysis of the Bass River and Ancora boreholes from the New Jersey coastal plain (Ocean Drilling Project Leg 174AX) provides new Late Cretaceous sea-level estimates and corroborates previously published Cenozoic sea-level estimates. Compaction histories of all coastal plain boreholes were updated using porosity,depth relationships estimated from New Jersey coastal plain electric logs. The new porosity estimates are considerably lower than those previously calculated at the offshore Cost B-2 well. Amplitudes and durations of sea-level variations are comparable in sequences that are represented at multiple boreholes, suggesting that the resultant curves are an approximation of regional sea level. Both the amplitudes and durations of third-order (0.5,5 Myr) cycles tend to decrease from the Late Cretaceous to the late Miocene. Third-order sea-level amplitudes in excess of 60 m are not observed. Long-term (108,107 years) sea level was approximately constant at 30,80 m in the Late Cretaceous, rose to a maximum early Eocene value of approximately 100,140 m, and then fell through the Eocene and Oligocene. [source] Multiphase cooling and exhumation of the southern Adelaide Fold Belt: constraints from apatite fission track dataBASIN RESEARCH, Issue 1 2000H. J. Gibson Data from apatite fission track analysis are presented for 20 outcrop samples collected in the southern Adelaide Fold Belt, South Australia. Interpretation of these data, with the aid of numerical models which allow inference of multiphase cooling histories, indicate three discrete cooling events that are likely to correlate with sedimentation events in surrounding depositional settings. An event beginning some time after 85 Ma (Late Cretaceous) was characterized by cooling throughout the study area from temperatures of roughly 50 to 70 °C. An event beginning at 300,270 Ma (Late Palaeozoic) was characterized by cooling from temperatures >120 °C in all areas except for the Mount Lofty Ranges and Murray Bridge region, where peak temperatures were only 95,115 °C prior to Palaeozoic cooling. Some samples from these subregions of relatively cool Late Palaeozoic temperatures also retain evidence for even earlier cooling from temperatures >120 °C, beginning prior to 350 Ma. We interpret the post 85-Ma event as the consequence of regional exhumation from a depth of 1.0,1.6 km. The Late Palaeozoic event (300,270 Ma) is interpreted as cooling associated with the termination of the Alice Springs Orogeny, while cooling prior to 350 Ma probably represents the final stages of Early Middle Palaeozoic unroofing of the southern Adelaide Fold Belt. The results highlight the importance of regional, episodic postorogenic exhumation of Palaeozoic fold belts, where , in some cases , conventional methods have erroneously suggested relatively long-term stability. [source] Discovery of Radiolaria from the Zongzhuo Formation in Tianba, Kangmar, Tibet and its Age ImplicationACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2009Guobiao LI Abstract: There is a group of variegated marine deposits, including the red beds widespread in the area of Tianba, Kangmar, southern Tibet, which previous works have contributed to Cretaceous Zongzhuo Formation by lithologic associations only, but with poor fossil evidence. Due to the absence of age dating fossils, the red bed age is obscure. Abundant Cretaceous radiolaria were discovered from the Zongzhuo Formation in the present study. In spite of the poor general preservation of some radiolarian specimens as recrystallized quartz infillings, 58 species from 46 genera of radiolaria, extracted from chert and silicous limestone of the Zongzhuo Formation in Kangmar, were identified on the basis of their shape and ornamentation. Based on the radiolaria, the age of the Zongzhuo Formation of this area has been referred to as Late Cretaceous. The new radiolarian data from the Zongzhuo Formation of Tianba area provide a local basis to correlate these deposits with other regions of the Tethyan Himalaya. [source] A New Basal Neoceratopsian Dinosaur from the Middle Cretaceous of Jilin Province, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009Liyong JIN Abstract: A new basal neoceratopsian dinosaur, Helioceratops brachygnathus gen. et sp. nov., is described from the Quantou Formation (late Early Cretaceous or early Late Cretaceous) in the Liufangzi locality (Jilin province, China). Helioceratops differs from other basal neoceratopsians with its deep dentary ramus, its steeply-inclined ventral predentary facet, its heterogeneous dentary crowns, and by the denticles and secondary ridges asymmetrically distributed on either side of the primary ridge on its dentary teeth. Along with Auroraceratops and Yamaceratops, Helioceratops represents one of the most derived non-coronosaurian neoceratopsians. The palaeogeographical distribution of basal neoceratopsians appears limited to northern China and southern Mongolia in the current state of our knowledge. It is therefore probable that this region constituted the birthplace for more advanced, Late Cretaceous Coronosauria. [source] A Titanosaurian Sauropod Dinosaur with Opisthocoelous Caudal Vertebrae from the Early Late Cretaceous of Liaoning Province, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2004YOU Hailu Abstract, We describe a new titanosaurian sauropod dinosaur, Borealosaurus wimani gen. et sp. nov., based on a distinctive mid-distal caudal vertebra from the early Late Cretaceous Sunjiawan Formation exposed in the Shuangmiao village of Beipiao in Liaoning, China. We provisionally refer an isolated tooth crown, a middle caudal vertebra, and a right humerus from the same locality and horizon to this taxon. Borealosaurus is distinguished from other sauropods in its possession of opisthocoelous mid-distal caudal vertebrae. The occurrence of opisthocoelous caudals in Borealosaurus and the Mongolian sauropod Opisthocoelicaudia raises the possibility that these taxa pertain to an as-yet unrecognized titanosaurian subclade endemic to the Cretaceous Asia. [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] Late Cretaceous-Cenozoic exhumation of the Yanji area, northeast China: Constraints from fission-track thermochronologyISLAND ARC, Issue 1 2010Xiaoming Li Abstract The Yanji area, located at the border of China, Russia, and Korea, where the Phanerozoic granitoids have been widely exposed, was considered part of the orogenic collage between the North China Block in the south and the Jiamusi,Khanka Massifs in the northeast. In this study, the cooling and inferred uplift and denudation history since the late Mesozoic are intensively studied by carrying out apatite and zircon fission-track analyses, together with electron microprobe analyses (EMPA) of chemical compositions of apatite from the granitoid samples in the Yanji area. The results show that: (i) zircon and apatite fission-track ages range 91.7,99.6 Ma and 76.5,85.4 Ma, respectively; (ii) all apatite fission-track length distributions are unimodal and yield mean lengths of 12,13.2 µm, and the apatites are attributed to chlorine-bearing fluorapatite as revealed by EMPA results; and (iii) the thermal history modeling results based on apatite fission-track grain ages and length distributions indicate that the time,temperature paths display similar patterns and the cooling has been accelerated for each sample since ca 15 Ma. Thus, we conclude that sequential cooling, involving two rapid (95,80 Ma and ca 15,0 Ma) and one slow (80,15 Ma) cooling, has taken place through the exhumation of the Yanji area since the late Cretaceous. The maximum exhumation is more than 5 km under a steady-state geothermal gradient of 35°C/km. Combined with the tectonic setting, this exhumation is possibly related to the subduction of the Pacific Plate beneath the Eurasian Plate since the late Cretaceous. [source] Geological and Geochemical Characteristics of the Hydrothermal Clay Alteration in South KoreaRESOURCE GEOLOGY, Issue 4 2000Sang-Mo KOH Abstract: Hydrothermally altered areas forming pyrophyllite-kaolin-sericite-alunite deposits are distributed in Chonnam and Kyongsang areas, Cretaceous volcanic field of the Yuchon Group. The Chonnam alteration area is located within depression zone which is composed of volcanic and granitic rocks of late Cretaceous age. The clay deposits of this area show the genetic relationship with silicic lava domes. The Kyongsang alteration area is mainly distributed within Kyongsang Basin comprising volcanic, sedimentary and granitic rocks of Cretaceous and Tertiary age. Most of the clay deposits of this area are closely related to cauldrons. Paleozoic clay deposit occurs in the contact zone between Precambrian Hongjesa granite gneiss and Paleozoic Jangsan quartzite of Choson Supergroup. Cretaceous igneous rocks of the both alteration areas belong to high K calc-alkaline series formed in the volcanic arc of continental margin by subduction-related magmatism. Chonnam igneous rocks show more enrichment of crustal components such as K, La, Ce, Sm, Nd and Ba, higher (La/Yb)cn ratio, and higher initial 87Sr/86Sr ratio (0. 708 to 0. 712) than those of Kyongsang igneous rocks. This might be due to the difference of degree of crustal contamination during Cretaceous magmatism. The most characteristic alteration minerals of Chonnam clay deposits are alunite, kaolin, quartz, pyrophyllite and diaspore which were formed by acidic solution. Those of Kyongsang clay deposits are sericite, quartz and pyrophyllite which were formed by weak acid and neutral solution. The formation ages of the clay deposits of two alteration areas range from 70. 1 to 81. 4 Ma and 39. 7 to 79. 4 Ma, respectively. The Daehyun clay deposit in Ponghwa area of Kyongsang province shows the alteration age range from 290 to 336 Ma. This result shows the different alteration episode from the hydrothermal alteration of Cretaceous to early Tertiary in the Kyongsang and Chonnam alteration areas. These data indicate, at least, three hydrothermal activities of Tertiary (middle to late Eocene), late Cretaceous (Santonian to Maastrichtian) and Paleozoic Carboniferous Periods in South Korea. [source] Insights in the exhumation history of the NW Zagros from bedrock and detrital apatite fission-track analysis: evidence for a long-lived orogenyBASIN RESEARCH, Issue 5 2010Stéphane Homke ABSTRACT We present the first fission-track (FT) thermochronology results for the NW Zagros Belt (SW Iran) in order to identify denudation episodes that occurred during the protracted Zagros orogeny. Samples were collected from the two main detrital successions of the NW Zagros foreland basin: the Palaeocene,early Eocene Amiran,Kashkan succession and the Miocene Agha Jari and Bakhtyari Formations. In situ bedrock samples were furthermore collected in the Sanandaj-Sirjan Zone. Only apatite fission-track (AFT) data have been successfully obtained, including 26 ages and 11 track-length distributions. Five families of AFT ages have been documented from analyses of in situ bedrock and detrital samples: pre-middle Jurassic at ,171 and ,225 Ma, early,late Cretaceous at ,91 Ma, Maastrichtian at ,66 Ma, middle,late Eocene at ,38 Ma and Oligocene,early Miocene at ,22 Ma. The most widespread middle,late Eocene cooling phase, around ,38 Ma, is documented by a predominant grain-age population in Agha Jari sediments and by cooling ages of a granitic boulder sample. AFT ages document at least three cooling/denudation periods linked to major geodynamic events related to the Zagros orogeny, during the late Cretaceous oceanic obduction event, during the middle and late Eocene and during the early Miocene. Both late Cretaceous and early Miocene orogenic processes produced bending of the Arabian plate and concomitant foreland deposition. Between the two major flexural foreland episodes, the middle,late Eocene phase mostly produced a long-lasting slow- or nondepositional episode in the inner part of the foreland basin, whereas deposition and tectonics migrated to the NE along the Sanandaj-Sirjan domain and its Gaveh Rud fore-arc basin. As evidenced in this study, the Zagros orogeny was long-lived and multi-episodic, implying that the timing of accretion of the different tectonic domains that form the Zagros Mountains requires cautious interpretation. [source] | |||||||||||||||||||||||||