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Early Jurassic (early + jurassic)
Selected AbstractsTHE AFFINITIES OF THE ENIGMATIC DINOSAUR ESHANOSAURUS DEGUCHIIANUS FROM THE EARLY JURASSIC OF YUNNAN PROVINCE, PEOPLE'S REPUBLIC OF CHINAPALAEONTOLOGY, Issue 4 2009PAUL M. BARRETT Abstract:,Eshanosaurus deguchiianus is based on a single left dentary from the Lower Lufeng Formation (Lower Jurassic) of Yunnan Province, China. It was originally identified as the earliest known member of Therizinosauroidea (Theropoda: Coelurosauria), a conclusion that results in a significant downward range extension for this clade (>65 million years) and for many other major lineages within Coelurosauria. However, this interpretation has been questioned and several authors have proposed that the anatomical features used to refer Eshanosaurus to Therizinosauroidea are more consistent with attribution to a basal sauropodomorph dinosaur. Detailed consideration of the holotype specimen suggests that several features of the dentary and dentition exclude Eshanosaurus from Sauropodomorpha and support its inclusion within Therizinosauroidea. If accepted as an Early Jurassic coelurosaur, Eshanosaurus has important implications for understanding the timing and tempo of early theropod diversification. Moreover, its provenance also suggests that substantial portions of the coelurosaur fossil record may be missing or unsampled. However, the Early Jurassic age of Eshanosaurus requires confirmation if this taxon is to be fully incorporated into broader evolutionary studies. [source] An eastern Tethyan (Tibetan) record of the Early Jurassic (Toarcian) mass extinction eventGEOBIOLOGY, Issue 3 2006P. B. WIGNALL ABSTRACT A record of the Early Jurassic mass extinction event is reported from eastern Tethyan (Tibetan) locations for the first time. In the Mount Everest region a thick Lower Jurassic carbonate formation, here named the Yungjia Formation, is developed within the predominantly clastic Triassic,Jurassic succession. Within the formation a sharp transition from peloidal packstones/grainstones to thin-bedded, pyritic micrite-shales interbeds records a sharp pulse of deepening and development of dysoxic bottom waters. Both the lithiotid bivalves and the lituolid foraminifera are important constituents of the lower Yungjia Formation but they disappear at this flooding surface or a short distance below it. This extinction event is comparable to that seen at the base of the Pliensbachian/Toarcian boundary in western Tethyan platform carbonates but the Tibetan events occurred late in the Toarcian Stage as indicated by nannofossil biostratigraphy and C isotope chemostratigraphy. The Early Jurassic extinction event (and the associated spread of oxygen-poor waters) was therefore not synchronous throughout the Tethyan region. [source] Contribution of different kinematic models and a complex Jurassic stratigraphy in the construction of a forward model for the Montagna dei Fiori fault-related fold (Central Apennines, Italy)GEOLOGICAL JOURNAL, Issue 5-6 2010L. Di Francesco Abstract The Montagna dei Fiori has received attention from geologists over the past decades because of both its Jurassic stratigraphy and its complex present-day structure. The latter is the result of multiple phases of deformation, from the Early Jurassic, during the opening of the Tethyan Ocean, to Neogene evolution of the Apennines fold-and-thrust belt. In this paper, we present a new stratigraphic interpretation of the Jurassic palaeogeography, based on a new geological mapping project in the area. Using this new stratigraphy, we constructed two forward models, using a combination of different fault/fold interactions, in order to unravel the kinematic evolution of the Montagna dei Fiori fault-related fold. The first model was constructed manually using the fault-bend and fault-propagation theories from an initial configuration which included previous extensional features, whereas the second model was constructed using the software 2DMove (Midland Valley) using the fault-bend and trishear fault-propagation folding theories and starting from a layer-cake stratigraphy. Both forward models involved the same main steps and provided a reasonable geological simulation of the geometry of the Montagna dei Fiori structure. Copyright © 2010 John Wiley & Sons, Ltd. [source] Tectonic deformation of the Indochina Peninsula recorded in the Mesozoic palaeomagnetic resultsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2009Kazuhiro Takemoto SUMMARY In order to describe features of tectonic deformation in the Indochina Peninsula, Early Jurassic to Early Cretaceous red sandstones were sampled at three localities in the Shan-Thai and Indochina blocks. Stepwise thermal treatment of most samples revealed the presence of characteristic remanent magnetization, which is generally unblocked by 680 °C. This component from Phong Saly (21.6°N, 101.9°E) and Borikhanxay (18.5°N, 103.8°E) localities yield positive fold tests with Late Jurassic,Early Cretaceous directions of Dec/Inc = 28.8°/32.1° (ks= 15.4, ,95= 8.8°, N= 22) and Dec/Inc = 42.1°/46.9° (ks= 20.1, ,95= 7.9°, N= 18), respectively. Additionally, a syn-folding mid-Cretaceous characteristic magnetization is observed in the samples of Muang Phin locality (16.5°N, 106.1°E), which gave a mean direction of Dec/Inc = 30.8°/39.9°, k= 102.6, ,95= 3.0°, N= 23. This reliable Late Jurassic to Mid-Cretaceous palaeomagnetic directions from three different localities are incorporated into a palaeomagnetic database for Shan-Thai and Indochina blocks. Based on these compilations, tectonic deformation of the Shan-Thai and Indochina blocks is summarized as follows: (1) the Shan-Thai and Indochina blocks experienced a clockwise rotation of about 10° as a composite unit in the early stage of India,Asia collision and (2) following this, the Shan-Thai Block underwent an internal tectonic deformation, whereas the Indochina Block behaved as a rigid tectonic unit during the same period. Comparison of our palaeomagnetic results with seismic tomographic images suggests that the strength of continental lithosphere beneath these blocks played an important role in the process of deformation rather than any other tectonic regime. In contrast to the Shan-Thai Block, an existence of continental roots beneath the Indochina Block prevented its internal deformation. [source] THE HYDROCARBON POTENTIAL OF LEBANON: NEW INSIGHTS FROM REGIONAL CORRELATIONS AND STUDIES OF JURASSIC DOLOMITIZATIONJOURNAL OF PETROLEUM GEOLOGY, Issue 3 2004F. H. Nader This paper presents an updated review of the petroleum prospects of Lebanon. We briefly describe the known hydrocarbon shows in Lebanon and compare them with adjacent countries, leading to the construction of a model for hydrocarbon migration which takes into account regional facies and reservoir correlations. The oldest exposed rocks in Lebanon are the Jurassic carbonates of the Kesrouane Formation (over 1,000m thick). This formation can be divided into a basal unit dominated by seepage-reflux stratabound dolostones (the Chouane Member,) and an overlying limestone-prone unit (the Nahr Ibrahim Member). A two-stage dolomitisation model for the Jurassic carbonates in Lebanon has recently been proposed by the authors. According to this model, second-stage Late Jurassic hydrothermal dolomitisation is believed to have occurred as a result of the circulation of mixed dolomitising fluids along faults. Hence, the resulting dolostones are fault-controlled and strata-discordant, and may occur at any level within the Kesrouane Formation, locally redolomitising the Chouane Member dolostones and replacing the Nahr Ibrahim Member limestones. In this paper, we discuss the implications of diagenesis (especially dolomitisation) on the petroleum prospects of the Kesrouane Formation in Lebanon. The hydrothermal fault-related dolostones possess porosities of up to 20%, which result from intercrystalline and mouldic porosity enhancement. Porosities in the stratabound reflux dolostones (Early Jurassic) and limestones are much lower. The fact that most of the Jurassic system in onshore Lebanon was affected by meteoric diagenesis during the Late Jurassic - Early Cretaceous and the Cenozoic may downgrade hydrocarbon prospectivity. However, offshore areas far from the meteoric realm may have been less (or not at all) affected by meteoric invasion. If effective seals are present there, these areas may host promising Jurassic reservoir units. We also review the prospectivity of unexposed Triassic potential reservoir units in onshore Lebanon (e. g. the "Qartaba" structure). By analogy with the Syrian portion of the Palmyride Basin, Triassic strata here may include both reservoir units and evaporite seals. [source] POTENTIAL STRUCTURAL TRAPS ASSOCIATED WITH LOWER CARBONIFEROUS SALT IN THE NORTHERN TARIM BASIN, NW CHINAJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2004Jiangyu Zhou In the Aixieke-Santamu area of the northern Tarim Basin (NW China), 45 relatively low amplitude structures related to the plastic flow of Lower Carboniferous salt have been discovered in the Lower Carboniferous Kalashayi Formation and the Middle-Upper Triassic Akekule and Halahatan Formations. Three small hydrocarbon accumulations have so far been located at the margins of a Lower Carboniferous salt body (measuring about 55km x 75km and 115,225m thick, controlled by wells and 2D and 3D seismic sections). In this paper, we consider the development of this salt body and discuss possible reasons why vertical diapirs are absent from the study area. We attempt to develop a model of salt flow and we investigate the relationship between salt flow and the occurrence of oil and gas traps. Using recently-acquired high-resolution 2D and 3D seismic profiles, we show that the Lower Carboniferous salt has undergone three separate phases of plastic flow. At the end of the Early Permian, the salt flowed southwards by 2.0,2.8 km; then, during the Late Triassic,Early Jurassic, it flowed in the same direction by 1.0,1.8 km; and finally at the end of the Tertiary, it flowed northwards by 0.6,1.5 km. These movements resulted in the formation of various types of structural trap in the Kalashayi, Akekule and Halahatan Formations including salt ridge anticlines, domes and marginal troughs. Salt ridge and salt edge low-amplitude anticlines are probably the most important targets for future hydrocarbon exploration. [source] UPPER TRIASSIC-MIDDLE JURASSIC STRATIGRAPHY AND SEDIMENTOLOGY IN THE NE QAIDAM BASIN, NW CHINA: PETROLEUM GEOLOGICAL SIGNIFICANCE OF NEW OUTCROP AND SUBSURFACE DATAJOURNAL OF PETROLEUM GEOLOGY, Issue 4 2003Yang Yongtai Although Mesozoic source and reservoir rocks are known to occur at oilfields in the northern Qaidam Basin (NW China), the precise identification and distribution of Mesozoic rocks in the subsurface are outstanding problems. The Dameigou locality has in the past been considered as the type section for Lower-Middle Jurassic strata in northern Qaidam. Previous studies have concluded that the onset of non-marine sedimentation here took place in the Early Jurassic; and that Mesozoic strata penetrated by wells in the Lenghu structural zone are Middle Jurassic. In this paper, we present new data from the Lengke-1 well, drilled in the Lenghu structural zone in 1997. This data indicates the existence of a more extensive pre-Middle Jurassic stratigraphy than has previously been recognized. Biostratigraphic data together with regional seismic mapping suggest that the pre-Middle Jurassic succession at Lengke-1 includes both Late Triassic and Early Jurassic deposits. The Late Triassic sedimentary rocks appear to have been deposited in local half graben, some of which were later inverted during Jurassic, Cretaceous and Cenozoic tectonism. Lower and Middle Jurassic strata (lacustrine and fluvial deposits) are present in the SW and NE parts of the Lenghu structural zone, respectively. Extensive organic-rich intervals are present in both successions. Lower Jurassic lacustrine mudstones may represent a previously under-appreciated, and potentially large, source rock sequence. [source] Schmeissneria: An angiosperm from the Early JurassicJOURNAL OF SYSTEMATICS EVOLUTION, Issue 5 2010Xin WANG Abstract, The origin of angiosperms has been a focus of intensive research for a long time. The so-called pre-Cretaceous angiosperms, including Schmeissneria, are usually clouded with doubt. To expel the cloud around the enigmatic Schmeissneria, the syntype and new materials of Schmeissneria collected previously in Germany and recently in China are studied. These materials include female inflorescences and infructescences. The latter are old materials but were under-studied previously. Light microscopy and scanning electron microscope observations indicate that the fruits in these infructescences have in situ seeds enclosed, and that the ovaries are closed before pollination. Thus the plants meet two strict criteria for angiosperms: angiospermy plus angio-ovuly. Placing Schmeissneria in angiosperms will extend the record of angiosperms up to the Early Jurassic, more compatible with many molecular dating conclusions on the age of angiosperms, and demanding a reassessment of the current doctrines on the origin of angiosperms. Although the phylogenetic relationship of Schmeissneria to other angiosperms apparently is still an open question, this study adds to research concerning the origin of angiosperms. [source] The two Early Toarcian (Early Jurassic) extinction events in ammonoidsLETHAIA, Issue 1 2004FABRIZIO CECCA The Early Toarcian (Early Jurassic) biological crisis was one of the ,minor' mass extinctions. It is linked with an oceanic anoxic event. Fossil data from sections located in northwestern European (epicontinental platforms and basins) and Tethyan (distal, epioceanic) areas indicate that Late Pliensbachian,Early Toarcian ammonoids experienced two extinction events during the Early Toarcian. The older one is linked with disruption of the Tethyan,Boreal provinciality, whereas the younger event correlates with the onset of anoxia and corresponds with the Early Toarcian mass-extinction event. These two extinctions cannot be interpreted as episodes of a single, stepwise, event. Values of the net diversification, more than the number of extinctions, allow the two extinction events to be clearly recognized and distinguished. Values of regional net diversification for northwestern European and Tethyan faunas point to greater evolutionary dynamics in the epioceanic areas. The inclusion of Mediterranean faunas in the database proves that the ammonite turnover at the Early Toarcian mass-extinction event was more important than previously thought. Progenitor (evolute Neolioceratoides), survivor (Dactylioceras, Polyplectus pluricostatus) and Lazarus (Procliviceras) taxa have been recognized. Different selectivity patterns are shown for the two events. The first one, linked to the disruption of the Tethyan,Boreal provinciality, has mainly affected ammonites adapted to epicontinental platforms. In the mass-extinction event, no selectivity is recognized, because also Phylloceratina and Lytoceratina were deeply affected at species level, although their wide biogeographical distribution at clade level was a significant buffer against extinction. In contrast to Palaeozoic mass extinctions, ammonoid survivors and Lazarus taxa are characterized by complex sutures: Phylloceratina (long-ranging ammonoids) and Polyplectus (relatively long-ranging compared to other Ammonitina). [source] Lower Jurassic Foraminifera and Calcified Microflora from Gibraltar, Western MediterraneanPALAEONTOLOGY, Issue 4 2001M. K. Boudagher-Fadel Benthic foraminifera are described for the first time from the Gibraltar Limestone Formation of the Rock of Gibraltar. The new species Siphovalvulina colomiS. gibraltarensisRiyadhella praeregularis occur with Duotaxis metula Kristan, Everticyclammina praevirguliana Fugagnoli, Siphovalvulina sp.,an atypically early example of Textulariopsis sp., and Nodosaria sp. Microflora are present as the probable cyanobacterium Cayeuxia ?piae Frollo, the alga Palaeodasycladus ?mediterraneus (Pia), and the disputed alga Thaumatoporella ?parvovesiculifera (Raineri). The foraminifera compare most closely with poorly-known taxa from Italy, Spain and Morocco, and are consistent with an Early Jurassic (Sinemurian) age for the upper part of the &62;460-m-thick Gibraltar Limestone. Most are textulariids and more primitive than species well known from the later Early Jurassic (Pliensbachian) of the Mediterranean region, especially Morocco and Italy. The biota as a whole is characteristic of inner carbonate platform environments widespread along the rifted western margins of the Early Jurassic Tethys, notably those recorded from Morocco, Italy and Greece as well as southern Spain. [source] The structural evolution of the Halten Terrace, offshore Mid-Norway: extensional fault growth and strain localisation in a multi-layer brittle,ductile systemBASIN RESEARCH, Issue 2 2010N. Marsh ABSTRACT Tectonic subsidence in rift basins is often characterised by an initial period of slow subsidence (,rift initiation') followed by a period of more rapid subsidence (,rift climax'). Previous work shows that the transition from rift initiation to rift climax can be explained by interactions between the stress fields of growing faults. Despite the prevalence of evaporites throughout the geological record, and the likelihood that the presence of a regionally extensive evaporite layer will introduce an important, sub-horizontal rheological heterogeneity into the upper crust, there have been few studies that document the impact of salt on the localisation of extensional strain in rift basins. Here, we use well-calibrated three-dimensional seismic reflection data to constrain the distribution and timing of fault activity during Early Jurassic,Earliest Cretaceous rifting in the Åsgard area, Halten Terrace, offshore Mid-Norway. Permo-Triassic basement rocks are overlain by a thick sequence of interbedded halite, anhydrite and mudstone. Our results show that rift initiation during the Early Jurassic was characterised by distributed deformation along blind faults within the basement, and by localised deformation along the major Smørbukk and Trestakk faults within the cover. Rift climax and the end of rifting showed continued deformation along the Smørbukk and Trestakk faults, together with initiation of new extensional faults oblique to the main basement trends. We propose that these new faults developed in response to salt movement and/or gravity sliding on the evaporite layer above the tilted basement fault blocks. Rapid strain localisation within the post-salt cover sequence at the onset of rifting is consistent with previous experimental studies that show strain localisation is favoured by the presence of a weak viscous substrate beneath a brittle overburden. [source] Stratigraphic evolution of the Triassic,Jurassic succession in the Western Southern Alps (Italy): the record of the two-stage rifting on the distal passive margin of AdriaBASIN RESEARCH, Issue 3 2009Fabrizio Berra ABSTRACT The Triassic,Lower Jurassic succession of the Southern Alps is characterized by rapid thickness changes, from an average of about 5000 m east of Lago Maggiore to about 500 m in the Western Southern Alps. The stratigraphy reflects the Triassic evolution of the Tethyan Gulf and the Early Jurassic rifting responsible for the Middle Jurassic break-up of Adria from Europe. The succession of the Western Southern Alps starts with Lower Permian volcanics directly covered by Anisian sandstones. The top of the overlying Ladinian dolostones (300 m) records subaerial exposure and karstification. Locally (Gozzano), Upper Sinemurian sediments cover the Permian volcanics, documenting pre-Sinemurian erosion. New biostratigraphic data indicate a latest Pliensbachian,Toarcian age for the Jurassic synrift deposits that unconformably cover Ladinian or Sinemurian sediments. Therefore, in the Western Southern Alps, the major rifting stage that directly evolved into the opening of the Penninic Ocean began in the latest Pliensbachian,Toarcian. New data allowed us to refine the evolution of the two previously recognized Jurassic extensional events in the Southern Alps. The youngest extensional event (Western Southern Alps) occurred as tectonic activity decreased in the Lombardy Basin. During the Sinemurian the Gozzano high represents the western shoulder of a rift basin located to the east (Lombardy). This evolution documents a transition from diffuse early rifting (Late Hettangian,Sinemurian), controlled by older discontinuities, to rifting focused along a rift valley close to the Pliensbachian,Toarcian boundary. This younger rift bridges the gap between the Hettangian,Sinemurian diffuse rifting and the Callovian,Bathonian break-up. The late Pliensbachian,Toarcian rift, which eventually lead to continental break-up, is interpreted as the major extensional episode in the evolution of the passive margin of Adria. The transition from diffuse to focused extension in the Southern Alps is comparable to the evolution of the Central Austroalpine during the Early Jurassic and of the Central and Northern Atlantic margins. [source] The origin and early evolution of dinosaursBIOLOGICAL REVIEWS, Issue 1 2010Max C. Langer The oldest unequivocal records of Dinosauria were unearthed from Late Triassic rocks (approximately 230 Ma) accumulated over extensional rift basins in southwestern Pangea. The better known of these are Herrerasaurus ischigualastensis, Pisanosaurus mertii, Eoraptor lunensis, and Panphagia protos from the Ischigualasto Formation, Argentina, and Staurikosaurus pricei and Saturnalia tupiniquim from the Santa Maria Formation, Brazil. No uncontroversial dinosaur body fossils are known from older strata, but the Middle Triassic origin of the lineage may be inferred from both the footprint record and its sister-group relation to Ladinian basal dinosauromorphs. These include the typical Marasuchus lilloensis, more basal forms such as Lagerpeton and Dromomeron, as well as silesaurids: a possibly monophyletic group composed of Mid-Late Triassic forms that may represent immediate sister taxa to dinosaurs. The first phylogenetic definition to fit the current understanding of Dinosauria as a node-based taxon solely composed of mutually exclusive Saurischia and Ornithischia was given as "all descendants of the most recent common ancestor of birds and Triceratops". Recent cladistic analyses of early dinosaurs agree that Pisanosaurus mertii is a basal ornithischian; that Herrerasaurus ischigualastensis and Staurikosaurus pricei belong in a monophyletic Herrerasauridae; that herrerasaurids, Eoraptor lunensis, and Guaibasaurus candelariensis are saurischians; that Saurischia includes two main groups, Sauropodomorpha and Theropoda; and that Saturnalia tupiniquim is a basal member of the sauropodomorph lineage. On the contrary, several aspects of basal dinosaur phylogeny remain controversial, including the position of herrerasaurids, E. lunensis, and G. candelariensis as basal theropods or basal saurischians, and the affinity and/or validity of more fragmentary taxa such as Agnosphitys cromhallensis, Alwalkeria maleriensis, Chindesaurus bryansmalli, Saltopus elginensis, and Spondylosoma absconditum. The identification of dinosaur apomorphies is jeopardized by the incompleteness of skeletal remains attributed to most basal dinosauromorphs, the skulls and forelimbs of which are particularly poorly known. Nonetheless, Dinosauria can be diagnosed by a suite of derived traits, most of which are related to the anatomy of the pelvic girdle and limb. Some of these are connected to the acquisition of a fully erect bipedal gait, which has been traditionally suggested to represent a key adaptation that allowed, or even promoted, dinosaur radiation during Late Triassic times. Yet, contrary to the classical "competitive" models, dinosaurs did not gradually replace other terrestrial tetrapods over the Late Triassic. In fact, the radiation of the group comprises at least three landmark moments, separated by controversial (Carnian-Norian, Triassic-Jurassic) extinction events. These are mainly characterized by early diversification in Carnian times, a Norian increase in diversity and (especially) abundance, and the occupation of new niches from the Early Jurassic onwards. Dinosaurs arose from fully bipedal ancestors, the diet of which may have been carnivorous or omnivorous. Whereas the oldest dinosaurs were geographically restricted to south Pangea, including rare ornithischians and more abundant basal members of the saurischian lineage, the group achieved a nearly global distribution by the latest Triassic, especially with the radiation of saurischian groups such as "prosauropods" and coelophysoids. [source] Continental basalts in the accretionary complexes of the South-west Japan Arc: Constraints from geochemical and Sr and Nd isotopic data of metadiabaseISLAND ARC, Issue 1 2000Hiroo Kagami Abstract The Ryoke Belt is one of the important terranes in the South-west Japan Arc (SJA). It consists mainly of late Cretaceous granitoid rocks, meta-sedimentary rocks (Jurassic accretionary complexes) and mafic rocks (gabbros, metadiabases; late Permian,early Jurassic). Initial ,Sr (+ 25, + 59) and ,Nd (, 2.1,,5.9) values of the metadiabases cannot be explained by crustal contamination but reflect the values of the source material. These values coincide with those of island arc basalt (IAB), active continental margin basalt (ACMB) and continental flood basalt (CFB). Spiderdiagrams and trace element chemistries of the metadiabases have CFB-signature, rather than those of either IAB or ACMB. The Sr,Nd isotope data, trace element and rare earth element chemistries of the metadiabases indicate that they result from partial melting of continental-type lithospheric mantle. Mafic granulite xenoliths in middle Miocene volcanic rocks distributed throughout the Ryoke Belt were probably derived from relatively deep crust. Their geochemical and Sr,Nd isotopic characteristics are similar to the metadiabases. This suggests that rocks, equivalent geochemically to the metadiabases, must be widely distributed at relatively deep crustal levels beneath a part of the Ryoke Belt. The geochemical and isotopic features of the metadiabases and mafic granulites from the Ryoke Belt are quite different from those of mafic rocks from other terranes in the SJA. These results imply that the Ryoke mafic rocks (metadiabase, mafic granulite) were not transported from other terranes by crustal movement but formed in situ. Sr,Nd isotopic features of late Cretaceous granitoid rocks occurring in the western part of the Japanese Islands are coincident with those of the Ryoke mafic rocks. Such an isotopic relation between these two rocks suggests that a continental-type lithosphere is widely represented beneath the western part of the Japanese Islands. [source] | ||||||||||||||||||||||