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Triassic
Kinds of Triassic Selected AbstractsGUODUNITES, A LOW-PALAEOLATITUDE AND TRANS-PANTHALASSIC SMITHIAN (EARLY TRIASSIC) AMMONOID GENUSPALAEONTOLOGY, Issue 2 2009ARNAUD BRAYARD Abstract:, Based on new, bed-rock controlled material from Oman and Utah, USA, the Early Triassic genus Guodunites, which was recently erected on the basis of scarce specimens from northwestern Guangxi, South China, is now shown to be a representative of Proptychitidae. This solves the question of the previously unknown phylogenetic affinity of this genus. The genus is restricted to the late middle Smithian, and to date, its biogeographical distribution comprises Oman, South China and Utah, thus indicating an essentially low palaeolatitudinal distribution during the Early Triassic. Its palaeobiogeographical distribution further strengthens the existence of significant equatorial faunal exchanges between both sides of the Panthalassa at that time. It also suggests that, in addition to the potential stepping stones represented by Panthalassic terranes, vigorous equatorial oceanic currents must have contributed largely to the dispersal of ammonoids during such time intervals. [source] PERMIAN OSTRACODS FROM THE LERCARA FORMATION (MIDDLE TRIASSIC,CARNIAN?), SICILY, ITALYPALAEONTOLOGY, Issue 3 2008SYLVIE CRASQUIN Abstract:, A rich, diverse Permian ostracod fauna has been recovered from the red and grey, laminated shales and quartz-rich shales of the Triassic Lercara Formation. Forty-seven species have been identified, 13 of which are newly described here; they belong to 26 genera of which three are new: Anahuacia lercaraensis sp. nov., Aurigerites siciliaensis sp. nov., Bairdia portellaensis sp. nov., Cristanaria? katyae sp. nov., Fabalicypris gruendeli sp. nov., Lethiersa salomonensis gen. et sp. nov., Lethiersia sinusoventralis gen. et sp. nov., Portella trapezoida gen. et sp. nov., Siciliella elongata gen. et sp. nov., Siciliella infernespinosa gen. et sp. nov., Siciliella prima gen. et sp. nov., Siciliella quadrata gen. et sp. nov., and Siciliella spinorobusta gen. et sp. nov. The assemblages contain or are composed of palaeopsychrospheric forms, which are regarded as index fossils for deep environments. The bathymetry of the different associations in life is evaluated. [source] HORSETAILS AND SEED FERNS FROM THE MIDDLE TRIASSIC (ANISIAN) LOCALITY KÜHWIESENKOPF (MONTE PRÀ DELLA VACCA), DOLOMITES, NORTHERN ITALYPALAEONTOLOGY, Issue 5 2007EVELYN KUSTATSCHER Abstract:, Well-preserved floras from the Alpine Early,Middle Triassic are rare, and thus our understanding of the vegetation in this area during this period of time continues to be incomplete. As a result, every new find represents a significant piece of information that deserves thoughtful consideration. Anisian (Middle Triassic) sphenophytes and pteridosperms have recently been recovered from the Kühwiesenkopf locality (Monte Prà della Vacca) in northern Italy. The sphenophytes are represented by stem fragments, strobili and isolated sporangiophore heads of Equisetites, as well as by a few specimens of Neocalamites sp. and Echinostachys sp. The pteridosperms include abundant remains of the peltasperm foliage type Scytophyllum bergeri. A second Scytophyllum species in this flora, S. apoldense, is regarded as conspecific with S. bergeri based on epidermal anatomy; the two morphotypes are interpreted as sun and shade leaves of a single biological species. The seed-bearing disc Peltaspermum bornemannii sp. nov. probably represents the female reproductive structure of S. bergeri. Additional pteridosperm remains include foliage assignable to Sagenopteris sp. and Ptilozamites sp., in both cases perhaps the earliest records of these genera. [source] A NEW SPECIES OF CLEVOSAURUS (LEPIDOSAURIA: RHYNCHOCEPHALIA) FROM THE UPPER TRIASSIC OF RIO GRANDE DO SUL, BRAZILPALAEONTOLOGY, Issue 4 2006JOSÉ F. BONAPARTE Abstract:, Well-preserved cranial remains of a small sphenodontian lepidosaur from the Upper Triassic Caturrita Formation of Rio Grande do Sul, Brazil, are the first record of the genus Clevosaurus Swinton, 1939 from South America. They represent a new species, Clevosaurus brasiliensis, which is distinguished by a very short antorbital region of the skull (corresponding to about 20 per cent of skull length) and the presence of teeth in addition to two longitudinal rows on the pterygoid. C. brasiliensis most closely resembles C. bairdi from the Lower Jurassic of Nova Scotia (Canada) and C. mcgilli from the Lower Jurassic of Yunnan (China). The discovery of Clevosaurus in the Upper Triassic of southern Brazil provides a significant range extension of this widely distributed sphenodontian genus. Along with other recent finds, it also suggests that there may have been less biotic provincialism among terrestrial vertebrates during the Late Triassic than has previously been assumed. [source] A TERRESTRIAL STEREOSPONDYL FROM THE LOWER TRIASSIC OF SOUTH AFRICA: THE POSTCRANIAL SKELETON OF LYDEKKERINA HUXLEYI (AMPHIBIA: TEMNOSPONDYLI)PALAEONTOLOGY, Issue 2 2005K. PAWLEY Abstract:, Description of the postcranial skeleton of the basal stereospondyl amphibian Lydekkerina huxleyi from new material shows it to be heavily ossified with large processes for muscle attachment and well-developed articulation surfaces. The structure of the postcranial skeleton implies a substantial capability for terrestrial locomotion, rather than a primarily aquatic existence as has been suggested for most other stereospondyls. The postcranial skeleton is most similar to that of Uranocentrodon and the Archegosauroidea, and is unlike that of the poorly ossified, more derived stereospondyls and Dvinosauria. The postcranial skeleton does not display any of the particular apomorphies of the fully ossified Permian terrestrial temnospondyls. Cladistic analysis using the postcranial data obtained in this study indicates that within the Stereospondyli Lydekkerina huxleyi is neither a member of the Rhinesuchidae nor the Mastodonsauroidea, rather the Lydekkerinidae are a separate taxon. [source] The cranial morphology of Kayentachelys, an Early Jurassic cryptodire, and the early history of turtlesACTA ZOOLOGICA, Issue 3 2010Eugene S. Gaffney Abstract Gaffney, E.S. and Jenkins, F.A., Jr. 2010. The cranial morphology of Kayentachelys, an Early Jurassic cryptodire, and the early history of turtles. , Acta Zoologica (Stockholm) 91: 335,368 The skull morphology of Kayentachelys aprixGaffney et al., 1987, a turtle from the Early Jurassic Kayenta Fm of northern Arizona, demonstrates the presence of cryptodiran synapomorphies in agreement with Gaffney et al. (1987, 1991, 2007), and contrary to the conclusions of Sterli and Joyce (2007), Joyce (2007), Sterli (2008), and Anquetin et al. (2008). Specific characters found in Kayentachelys and diagnostic of cryptodires include the processus trochlearis oticum, the curved processus pterygoideus externus with a vertical plate, and the prefrontal,vomer contact, which are confirmed as absent in the outgroups, specifically the Late Triassic Proganochelys. The Joyce (2007) analysis suffers from the reduction of the signal from skull characters, with a consequently greater reliance on shell characters, resulting in pleurodires being resolved at various positions within the cryptodires. Kayentachelys reveals what a primitive cryptodire would be expected to look like: a combination of primitive and derived characters, with the fewer derived characters providing the best test of its relationships to other turtles. Although incompletely known, the Mid-Late Jurassic Condorchelys, Heckeremys, and Eileanchelys may be early cryptodires close to Kayentachelys. We confirm the Late Triassic Proterochersis as a pleurodire, dating the pleurodire,cryptodire split as Late Triassic or earlier. [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] 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] 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] Extensional development of the Fundy rift basin, southeastern CanadaGEOLOGICAL JOURNAL, Issue 6 2009Martha O. Withjack Abstract The Fundy rift basin of Nova Scotia and New Brunswick, Canada, is part of the Eastern North American rift system that formed during the breakup of Pangaea. Integrated seismic-reflection, field, digital-elevation and aeromagnetic data indicate that the Fundy rift basin underwent two phases of deformation: syn-rift extension followed by post-rift basin inversion. Inversion significantly modified the geometries of the basin and its rift-related structures. In this paper, we remove the effects of inversion to examine the basin's extensional development. The basin consists of three structural subbasins: the Fundy and Chignecto subbasins are bounded by low-angle, NE-striking faults; the Minas subbasin is bounded by E- to ENE-striking faults that are steeply dipping at the surface and gently dipping at depth. Together, these linked faults form the border,fault system of the Fundy rift basin. Most major faults within the border,fault system originated as Palaeozoic contractional structures. All syn-rift units imaged on seismic profiles thicken towards the border,fault system, reflecting extensional movement from Middle Triassic (and possibly Permian) through Early Jurassic time. Intra-rift unconformities, observed on seismic profiles and in the field, indicate that uplift and erosion occurred, at least locally, during rifting. Based on seismic data alone, the displacement direction of the hanging wall of the border,fault system of the Fundy rift basin ranged from SW to SE during rifting. Field data (i.e. NE-striking igneous dykes, sediment-filled fissures and normal faults) indicate NW,SE extension during Early Jurassic time, supporting a SE-displacement direction. With a SE-displacement direction, the NE-striking border,fault zones of the Fundy and Chignecto subbasins had predominantly normal dip slip during rifting, whereas the E-striking border,fault zone of the Minas subbasin had oblique slip with left-lateral and normal components. Sequential restorations of seismic-reflection profiles (coupled with projections from onshore geology) show that the Fundy rift basin underwent 10,20,km of extension, most of which was accommodated by the border,fault system, and was considerably wider and deeper prior to basin inversion. Post-rift deformation tilted the eastern side of the basin to the northwest/north, producing significant uplift and erosion. 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] Triassic metasedimentary successions across the boundary between the southern Apennines and the Calabrian Arc (northern Calabria, Italy)GEOLOGICAL JOURNAL, Issue 2 2005A. Iannace Abstract The boundary area between the Apenninic fold-and-thrust belt and the crystalline Calabrian Arc, located around Sangineto in northern Calabria, has been investigated. New geological mapping in the Sant'Agata area has been performed on the Triassic successions traditionally attributed to the metasedimentary San Donato Unit. This, coupled with a reappraisal of the stratigraphy and tectonics of coeval successions present more to the south in the Cetraro Unit, results in a new reconstruction of the Triassic evolution of all the metasedimentary successions found in the region. Four informal stratigraphic units have been distinguished in the S. Agata area. The lowest one (Unit A) consists of well-bedded metalimestones and bioturbated marly limestones that correlate with Ladinian,Carnian carbonates in nearby areas. A second unit (Unit B), never recognized before, contains a complex alternation of dolomites, phyllites and some meta-arenites containing several beds of Cavernoso facies, attributed to the Carnian. They grade upward to platform and platform-margin dolomites of Norian,Rhaetian age (Unit C) that in turn are replaced upward and laterally by a fourth unit (Unit D) consisting of well-bedded, dark dolomites and metalimestones with marly interlayers locally found as resedimented large blocks in slope conglomerates. Unit D correlates with Rhaetian,Liassic beds in nearby areas. Several pieces of evidence of post-metamorphic contractional tectonics, with 140°N and 30°N trends, are found together with evidence of SW-directed extension. The siliciclastic Carnian beds of Unit B are correlated with the phyllites of Cetraro, formerly believed to be Middle Triassic; moreover, it is suggested that in the Cetraro area Unit C is almost totally replaced by Unit D. This demonstrates that the former distinction between the two tectonic units in the whole area has to be discarded. We have made a general palaeoenvironmental reconstruction which progresses laterally, during Ladinian,Carnian times, from (i) a coastal, mixed siliciclastic,carbonate,evaporitic area at Cetraro to (ii) a transitional carbonate shelf where siliciclastic input was only episodic, and finally to (iii) a bioconstructed margin which was later replaced by a steepened margin created by tectonic instability. Starting from the Norian, subsidence shifted toward the former coastal area where an intraplatform, restricted basin developed. The proposed stratigraphy corresponds closely to the Alpujarride units of the Betic Cordillera, Spain. Moreover, it is shown that strong affinities also exist, in terms of the structural framework, with the metamorphic units of Tuscany and Liguria. Copyright © 2005 John Wiley & Sons, Ltd. [source] Mesozoic,Paleogene sedimentary facies and paleogeography of Tibet, western China: tectonic implicationsGEOLOGICAL JOURNAL, Issue 3 2002Kai-Jun Zhang Abstract In Early,Middle Triassic time, an abyssal sea covered most of the Songpan,Ganzi area, whereas a Central Tibetan Landmass, up to 400,km wide, may have stretched across the Lhasa and Western Qiangtang terrains. In Late Triassic time, the Songpan,Ganzi sea closed, the Central Tibetan Landmass receded westwards away from southern Western Qiangtang, a littoral environment dominated Eastern Qiangtang, middle Western Qiangtang, and southeastern Lhasa, a shelf environment existed only in northern and southeastern Western Qiangtang and northwestern Eastern Qiangtang, and abyssal flysch was spread along the eastern Bangonghu,Nüjiang zone. In Early,Middle Jurassic time, Songpan,Ganzi had become part of the Eurasian continent, abyssal flysch sediments stretched throughout the Bangonghu,Nüjiang zone, the Central Tibetan Landmass was only locally present in southwestern Lhasa, and the Tethyan epicontinental sea nearly covered all Tibet southwest of the Jinsajiang suture. In Late Jurassic time, oceanic flysch deposition existed only along the westernmost Bangonghu,Nüjiang zone, nearly all of Tibet was covered by coastal deposits, and shelf deposits existed only in northern Western Qiangtang and westernmost Lhasa. In the early stage of Early Cretaceous time, the majority of Qiangtang had become dry land, and a supralittoral environment dominated across the entire Lhasa terrain. However, during the late stage of the Early Cretaceous time, platform,shelf carbonates prevailed on southern Western Qiangtang and northern Lhasa. In Late Cretaceous time, the majority of Qiangtang had become emergent land, and a supratidal environment dominated Lhasa, the western rim of Western Qiangtang, and Tarim. In Paleogene time, the majority of Tibet became emergent land, and a supratidal environment existed only on the southern and western rims. The dominance of Upper Triassic,Jurassic shelf carbonates on the northwestern Eastern Qiangtang corner and the northern Western Qiangtang rim suggests a diachronous closing of the Jinsajiang paleo-Tethys ocean, first during latest Triassic time when the Eastern Qiangtang terrain collided with Asia and finally in Jurassic time when the Western Qiangtang terrain was amalgamated to Asia. Rich picotites in Upper Triassic sandstones of middle Qiangtang suggest that the Shuanghu suture could have extended along the middle of Qiangtang, and stable shelf sedimentation during Late Triassic,Middle Jurassic time in the Western Qiangtang terrain shows that the suture probably could not have formed until Middle Jurassic time. The opening time of the Bangonghu,Nüjiang mid-Tethys ocean could be Late Triassic time due to the existence of the Central Tibetan Landmass across Western Qiangtang and Lhasa during Early,Middle Triassic time. However, its opening was diachronous, at Late Triassic time in the east and at Early,Middle Jurassic time in the west. Furthermore, its closing was also diachronous, first in the east at the beginning of Late Jurassic time and later in the west in latest Jurassic to earliest Cretaceous time. Widespread upper Lower Cretaceous limestone up to 5,km thick over the northern half of Lhasa indicates that southern Tibet could have undergone an extensive backarc subsidence during late Early Cretaceous time. Continuous shallow marine sedimentation through the entire Cretaceous time over much of southern Tibet indicates that southern Tibet was intensely elevated only after the end of Paleogene time, its high topography being the product of the Indo-Asian collision. Copyright © 2002 John Wiley & Sons, Ltd. [source] Fabrics, facies control and diagenesis of lacustrine ooids and associated grains from the Upper Triassic, southwest EnglandGEOLOGICAL JOURNAL, Issue 1 2002P. G. Milroy Abstract Petrographic analysis of ooids from the Upper Triassic (Mercia Mudstone Group) of southwest England provides an opportunity to assess in detail the origins, transport pathways and diagenesis of an ancient oolite. The Clevedon Oolite is dolomitized and contains a variety of dissolved ooids (oomoulds) and associated grains. The oomoulds occur in well-sorted, planar and cross-stratified grainstones, packstones, sandstones and conglomerates associated with shoreface, intershoal, foreshore, beachrock and littoral strandplain deposits. The ooids grew in suspension in the shoreface zone and developed a radial aragonite microstructure. The ooids grew to 0.80 mm in diameter, after which they fractured or ceased growing. Broken grains deposited on or near mobile shoals were rapidly recoated, while other grains, deposited in less agitated, intershoal and lower foreshore areas, were micritized or microbially bound into grapestone aggregates. Locally peloids, intraclasts, quartz grains and micritized grains from intershoal areas supplied nuclei for ooids on nearby shoals. Grains deposited in foreshore areas were rapidly cemented into beachrock and reworked into conglomerates. Soon after deposition, the ooids were subjected to widespread aragonite dissolution followed by dolomitization. The lack of pre-dolomitization calcite, together with the abundance of early (pre-compaction) dolospar cements and fabric-selective dolomitization of micritic fabrics, suggest aragonite dissolution by dolomitizing fluids. Copyright © 2002 John Wiley & Sons, Ltd. [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] 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] Structure of Sumatra and its implications for the tectonic assembly of Southeast Asia and the destruction of PaleotethysISLAND ARC, Issue 1 2009Anthony J. Barber Abstract It is now generally accepted that Southeast Asia is composed of continental blocks which separated from Gondwana with the formation of oceanic crust during the Paleozoic, and were accreted to Asia in the Late Paleozoic or Early Mesozoic, with the subduction of the intervening oceanic crust. From east to west the Malay peninsula and Sumatra are composed of three continental blocks: East Malaya with a Cathaysian Permian flora and fauna; Sibumasu, including the western part of the Malay peninsula and East Sumatra, with Late Carboniferous,Early Permian ,pebbly mudstones' interpreted as glaciogenic diamictites; and West Sumatra, again with Cathaysian fauna and flora. A further unit, the Woyla nappe, is interpreted as an intraoceanic arc thrust over the West Sumatra block in the mid Cretaceous. There are varied opinions concerning the age of collision of Sibumasu with East Malaya and the destruction of Paleotethys. In Thailand, radiolarites have been used as evidence that Paleotethys survived until after the Middle Triassic. In the Malay peninsula, structural evidence and the ages of granitic intrusions are used to support a Middle Permian to Early Triassic age for the destruction of Paleotethys. It is suggested that the West Sumatra block was derived from Cathaysia and emplaced against the western margin of Sibumasu by dextral transcurrent faulting along a zone of high deformation, the Medial Sumatra Tectonic Zone. These structural units can be traced northwards in Southeast Asia. The East Malaya block is considered to be part of the Indochina block, Sibumasu can be traced through Thailand into southern China, the Medial Sumatra Tectonic Zone is correlated with the Mogok Belt of Myanmar, the West Burma block is the extension of the West Sumatra block, from which it was separated by the formation of the Andaman Sea in the Miocene, and the Woyla nappe is correlated with the Mawgyi nappe of Myanmar. [source] SHRIMP zircon and EPMA monazite dating of granitic rocks from the Maizuru terrane, southwest Japan: Correlation with East Asian Paleozoic terranes and geological implicationsISLAND ARC, Issue 3 2008Masahiro Fujii Abstract The Maizuru terrane, distributed in the Inner Zone of southwest Japan, is divided into three subzones (Northern, Central and Southern), each with distinct lithological associations. In clear contrast with the Southern zone consisting of the Yakuno ophiolite, the Northern zone is subdivided into the western and eastern bodies by a high-angle fault, recognized mainly by the presence of deformed granitic rocks and pelitic gneiss. This association suggests an affinity with a mature continental block; this is supported by the mode of occurrence, and petrological and isotopic data. Newly obtained sensitive high mass-resolution ion microprobe (SHRIMP) zircon U,Pb ages reveal the intrusion ages of 424 ± 16 and 405 ± 18 Ma (Siluro,Devonian) for the granites from the western body, and 249 ± 10 and 243 ± 19 Ma (Permo,Triassic) for the granodiorites from the eastern body. The granites in the western body also show inherited zircon ages of around 580 and 765 Ma. In addition, electron probe microanalysis (EPMA) monazite U,Th,total Pb dating gives around 475,460 Ma. The age of intrusion, inherited ages, mode of occurrence, and geological setting of the Siluro,Devonian granites of the Northern zone all show similarities with those of the Khanka Massif, southern Primoye, Russia, and the Hikami granitic rocks of the South Kitakami terrane, Northeast Japan. We propose that both the Siluro,Devonian and Permo,Triassic granitic rocks of the Northern zone are likely to have been juxtaposed through the Triassic,Late Jurassic dextral strike-slip movement, and to have originated from the Khanka Massif and the Hida terrane, respectively. This study strongly supports the importance of the strike-slip movement as a mechanism causing the structural rearrangement of the Paleozoic,Mesozoic terranes in the Japanese Islands, as well as in East Asia. [source] Zircon U,Pb ages and tectonic implications of ,Early Paleozoic' granitoids at Yanbian, Jilin Province, northeast ChinaISLAND ARC, Issue 4 2004Yanbin Zhang Abstract The Yanbian area is located in the eastern part of the Central Asian Orogenic Belt (CAOB) of China and is characterized by widespread Phanerozoic granitic intrusions. It was previously thought that the Yanbian granitoids were mainly emplaced in the Early Paleozoic (so-called ,Caledonian' granitoids), extending east,west along the northern margin of the North China craton. However, few of them have been precisely dated; therefore, five typical ,Caledonian' granitic intrusions (the Huangniling, Dakai, Mengshan, Gaoling and Bailiping batholiths) were selected for U,Pb zircon isotopic study. New-age data show that emplacement of these granitoids extended from the Late Paleozoic to Late Mesozoic (285,116 Ma). This indicates that no ,Caledonian' granitic belt exists along the northern margin of the North China craton. The granitoids can be subdivided into four episodes based on our new data: Early Permian (285 ± 9 Ma), Early Triassic (249,245 Ma), Jurassic (192,168 Ma) and Cretaceous (119,116 Ma). The 285 ± 9 Ma tonalite was most likely related to subduction of the Paleo-Asian Oceanic Plate beneath the North China craton, followed by Triassic (249,245 Ma) syn-collisional monzogranites, representing the collision of the CAOB orogenic collage with the North China craton and final closure of the Paleo-Asian Ocean. The Jurassic granitoids resulted from subduction of the Paleo-Pacific plate and subsequent collision of the Jiamusi,Khanka Massif with the existing continent, assembled in the Triassic. The Early Cretaceous granitoids formed in an extensional setting along the eastern Asian continental margin. [source] Jurassic depositional records and sandstone provenances in Hefei Basin, central China: Implication for Dabie orogenesisISLAND ARC, Issue 2 2004Zhong Li Abstract Detrital composition and major element geochemistry of Jurassic sandstones in the south Hefei Basin, central China, show their provenance to be the Dabie Mountains, whose tectonic attributes are closely related to continent,island arc complexes. It was found that a provenance change, from recycled orogen signatures and mixed orogenic sandstones to arc orogen, occurs from the lower Middle Jurassic to the Upper Jurassic (the Zhougongshan Formation). Dissected magmatic arc sources were gradually exposed in the Dabie Mountains due to intensive exhumation during the Late Jurassic, particularly after the Fenghuangtai depositional phase. Furthermore, it can be infered that the magmatic arc was initially present in both the Early Paleozoic and the Triassic, according to isotopic dating studies in previously published reports. ,13C,,18O tracing between existing marbles of different strata in the Dabie block and marble gravels of the Fenghuangtai Formation in the Hefei Basin indicate that partial lithostratigraphic units for the Jurassic provenances have entirely disappeared from the Dabie block; therefore, it is impossible to reconstruct integral orogenic processes from studies on the remaining Dabie block alone. These findings, together with basin-fill sequences, also suggest that the Hefei Basin was mainly subjected to compressive mechanical regimes rather than extensional regimes in the Jurassic, which resulted in reverse-grading clastic depositional sequences, and is probably related to the northward intracontinental deep subduction of the Yangtze Plate. Regional exhumation properties and a tectonic model of the Late Mesozoic Dabie orogenesis are discussed in this paper. [source] Biosynthesis of ascorbic acid by extant actinopterygiansJOURNAL OF FISH BIOLOGY, Issue 3 2000R. Moreau Polypterus senegalus, the longnose gar Lepisosteus osseus and the bowfin Amia calva had gulonolactone oxidase activity in the kidney and thus can synthesize ascorbic acid de novo. The enzyme activity was associated with the microsomal fraction. The common carp Cyprinus carpio and the goldfish Carassius auratus had no gulonolactone oxidase activity. Antibodies directed against white sturgeon gulonolactone oxidase showed cross-reactivity with lake sturgeon, bowfin and longnose gar kidney enzymes, but not with enzymes from Polypterus, sea lamprey, and tadpole kidney or pig liver. Given cross-reactivity, gulonolactone oxidase relatedness matched actinopterygian phylogeny, and suggested homology of the character throughout fishes. Modern teleosts may have lost the ability to synthesize ascorbic acid since the late Triassic as a result of a single reversal in the founding population. Wild bowfin and longnose gar exhibited high ascorbate concentrations in liver and spleen when compared with the teleosts rainbow trout Oncorhynchus mykiss and common carp fed vitamin C-supplemented diets. [source] Ultrahigh-pressure eclogite transformed from mafic granulite in the Dabie orogen, east-central ChinaJOURNAL OF METAMORPHIC GEOLOGY, Issue 9 2007Y.-C. LIU Abstract Although ultrahigh-pressure (UHP) metamorphic rocks are present in many collisional orogenic belts, almost all exposed UHP metamorphic rocks are subducted upper or felsic lower continental crust with minor mafic boudins. Eclogites formed by subduction of mafic lower continental crust have not been identified yet. Here an eclogite occurrence that formed during subduction of the mafic lower continental crust in the Dabie orogen, east-central China is reported. At least four generations of metamorphic mineral assemblages can be discerned: (i) hypersthene + plagioclase ± garnet; (ii) omphacite + garnet + rutile + quartz; (iii) symplectite stage of garnet + diopside + hypersthene + ilmenite + plagioclase; (iv) amphibole + plagioclase + magnetite, which correspond to four metamorphic stages: (a) an early granulite facies, (b) eclogite facies, (c) retrograde metamorphism of high-pressure granulite facies and (d) retrograde metamorphism of amphibolite facies. Mineral inclusion assemblages and cathodoluminescence images show that zircon is characterized by distinctive domains of core and a thin overgrowth rim. The zircon core domains are classified into two types: the first is igneous with clear oscillatory zonation ± apatite and quartz inclusions; and the second is metamorphic containing a granulite facies mineral assemblage of garnet, hypersthene and plagioclase (andesine). The zircon rims contain garnet, omphacite and rutile inclusions, indicating a metamorphic overgrowth at eclogite facies. The almost identical ages of the two types of core domains (magmatic = 791 ± 9 Ma and granulite facies metamorphic zircon = 794 ± 10 Ma), and the Triassic age (212 ± 10 Ma) of eclogitic facies metamorphic overgrowth zircon rim are interpreted as indicating that the protolith of the eclogite is mafic granulite that originated from underplating of mantle-derived magma onto the base of continental crust during the Neoproterozoic (c. 800 Ma) and then subducted during the Triassic, experiencing UHP eclogite facies metamorphism at mantle depths. The new finding has two-fold significance: (i) voluminous mafic lower continental crust can increase the average density of subducted continental lithosphere, thus promoting its deep subduction; (ii) because of the current absence of mafic lower continental crust in the Dabie orogen, delamination or recycling of subducted mafic lower continental crust can be inferred as the geochemical cause for the mantle heterogeneity and the unusually evolved crustal composition. [source] Fluid flow during exhumation of deeply subducted continental crust: zircon U-Pb age and O-isotope studies of a quartz vein within ultrahigh-pressure eclogiteJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2007Y.-F. ZHENG Abstract Quartz veins in high-pressure to ultrahigh-pressure metamorphic rocks witness channelized fluid flow that transports both mass and heat during collisional orogenesis. This flow can occur in the direction of changing temperature/pressure during subduction or exhumation. SHRIMP U-Pb dating of zircon from a kyanite-quartz vein within ultrahigh-pressure eclogite in the Dabie continental collision orogen yields two age groups at 212 ± 7 and 181 ± 13 Ma, which are similar to two groups of LA-ICPMS age at 210 ± 4 and 180 ± 5 Ma for the same sample. These ages are significantly younger than zircon U-Pb ages of 224 ± 2 Ma from the host eclogite. Thus the two age groups from the vein date two episodes of fluid flow involving zircon growth: the first due to decompression dehydration during exhumation, and the second due to heating dehydration in response to a cryptic thermal event after continental collision. Laser fluorination O-isotope analyses gave similar ,18O values for minerals from both vein and eclogite, indicating that the vein-forming fluid was internally derived. Synchronous cooling between the vein and eclogite is suggested by almost the same quartz,mineral fractionation values, with regularly decreasing temperatures that are in concordance with rates of O diffusion in the minerals. While the quartz veining was caused by decompression dehydration at 700,650 °C in a transition from ultrahigh-pressure to high-pressure eclogite-facies retrogression, the postcollisional fluid flow was retriggered by heating dehydration at ,500 °C without corresponding metamorphism. In either case, the kyanite,quartz vein formed later than the peak ultrahigh-pressure metamorphic event at the Middle Triassic, pointing to focused fluid flow during exhumation rather than subduction. The growth of metamorphic zircon in the eclogite appears to have depended on fluid availability, so that their occurrence is a type of geohygrometer besides geochronological applicability to dating of metamorphic events in orogenic cycles. [source] SHRIMP U-Pb zircon dating from Sulu-Dabie dolomitic marble, eastern China: constraints on prograde, ultrahigh-pressure and retrograde metamorphic agesJOURNAL OF METAMORPHIC GEOLOGY, Issue 7 2006F. L. LIU Abstract Laser Raman spectroscopy and cathodoluminescence (CL) images show that zircon from Sulu-Dabie dolomitic marbles is characterized by distinctive domains of inherited (detrital), prograde, ultrahigh-pressure (UHP) and retrograde metamorphic growths. The inherited zircon domains are dark-luminescent in CL images and contain mineral inclusions of Qtz + Cal + Ap. The prograde metamorphic domains are white-luminescent in CL images and preserve a quartz eclogite facies assemblage of Qtz + Dol + Grt + Omp + Phe + Ap, formed at 542,693 °C and 1.8,2.1 GPa. In contrast, the UHP metamorphic domains are grey-luminescent in CL images, retain the UHP assemblage of Coe + Grt + Omp + Arg + Mgs + Ap, and record UHP conditions of 739,866 °C and >5.5 GPa. The outermost retrograde rims have dark-luminescent CL images, and contain low- P minerals such as calcite, related to the regional amphibolite facies retrogression. Laser ablation ICP-MS trace-element data show striking difference between the inherited cores of mostly magmatic origin and zircon domains grown in response to prograde, UHP and retrograde metamorphism. SHRIMP U-Pb dating on these zoned zircon identified four discrete 206Pb/238U age groups: 1823,503 Ma is recorded in the inherited (detrital) zircon derived from various Proterozoic protoliths, the prograde domains record the quartz eclogite facies metamorphism at 254,239 Ma, the UHP growth domains occurred at 238,230 Ma, and the late amphibolite facies retrogressive overprint in the outermost rims was restricted to 218,206 Ma. Thus, Proterozoic continental materials of the Yangtze craton were subducted to 55,60 km depth during the Early Triassic and recrystallized at quartz eclogite facies conditions. Then these metamorphic rocks were further subducted to depths of 165,175 km in the Middle Triassic and experienced UHP metamorphism, and finally these UHP metamorphic rocks were exhumed to mid-crustal levels (about 30 km) in the Late Triassic and overprinted by regional amphibolite facies metamorphism. The subduction and exhumation rates deduced from the SHRIMP data and metamorphic P,T conditions are 9,10 km Myr,1 and 6.4 km Myr,1, respectively, and these rapid subduction,exhumation rates may explain the obtained P,T,t path. Such a fast exhumation suggests that Sulu-Dabie UHP rocks that returned towards crustal depths were driven by buoyant forces, caused as a consequence of slab breakoff at mantle depth. [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] THE NATURE AND ORIGIN OF PETROLEUM IN THE CHAIWOPU SUB-BASIN (JUNGGAR BASIN), NW CHINAJOURNAL OF PETROLEUM GEOLOGY, Issue 2 2000H. P. Huang The Chaiwopu Sub-basin is a minor extension of the Junggar Basin, hW China, and covers an area of about 2,500 sq. km. It is bounded to the east and north by the Bogda Shan and to the south by the Tian Shan ("Shan" meaning "mountains" in Chinese). Four wells have been drilled in the sub-basin; condensate and gas have been produced in noncommercial quantities at one of the wells (Well C), but the other three wells were dry. In this paper, I investigate the nature and origin of the petroleum at Well C. Three of the four wells in the Chaiwopu Sub-basin penetrated the Upper Permian Lucaogou Formation. Previous studies in the Junggar Basin have established that laminated lacustrine mudstones assigned to this formation comprise a very thick high quality source rock. However, the analysis of cores from wells in the sub-basin shows that the Lucaogou Formation is composed here of shallow lacustrine, fluvial and alluvial deposits which have very low petroleum generation potential. Overlying sediments (Upper Permian, Triassic and younger strata) likewise have little source potential. Around 1,000 m of Upper Permian laminated oil shales crop out at Dalongkou and Tianchi on the northern side of the Bogda Shan. On the southern side of the Bogda Shan, however, only 30 m of Upper Permian oil shales occur at Guodikong. Shales and oil seeps from these locations were analysed using standard organic-geochemical techniques. The physical properties of the petroleum present at Well C, and its carbon isotope and biomarker characteristics, suggest that it has migrated over long distances from its source rock, although an alternative explanation for its origin is not precluded. Burial history modelling indicates that hydrocarbon generation and migration may have occurred before the uplift of the Bogda Shan in the Late Jurassic,Early Cretaceous, the orogenic episode which resulted in the diflerentiation of the Chaiwopu Sub-basinfrom the Junggar Basin. [source] Bone histology of Silesaurus opolensisDzik, 2003 from the Late Triassic of PolandLETHAIA, Issue 2 2010UCJA FOSTOWICZ-FRELIK Fostowicz-Frelik, ,. & Sulej, T. 2009: Bone histology of Silesaurus opolensisDzik, 2003 from the Late Triassic of Poland. Lethaia, Vol. 43, pp. 137,148. The phylogenetic relationships of Silesaurus opolensis have been the subject of intense debate since its discovery. Silesaurus possesses some features characteristic of ornithischian dinosaurs, such as the presence of a beak at the front of the lower jaw, yet it lacks a number of important femoral and dental synapomorphies of Dinosauria. The microstructure of the long bones (femur, tibia and metatarsal) and ribs of this species reveals a relatively intensive rate of growth, comparable with that seen in small dinosaurs and the gracile crocodylomorph Terrestrisuchus. Cortical bone formed mainly by periosteal tissue with fibro-lamellar matrix (in older specimens parallel fibred) shows very little secondary remodelling and only in one specimen (large tibia ZPAL Ab III/1885) few lines of arrested growth are present in the outermost cortex. The vascularization is relatively dense, mainly longitudinal and ceases towards the periphery, forming almost avascular parallel fibred bone at the bone surface. This indicates maturation and significant decrease in the growth ratio in mature specimens of S. opolensis. The delicate trabeculae exhibit cores formed by the primary cancellous tissue lined with lamellar endosteal bone. The rather intense growth of S. opolensis implies a relatively high metabolic rate. Moreover, evidence from the fibro-lamellar tissue, predominant in the cortex, suggests that this kind of rapid bone deposition could be more typical of Archosauria than previously assumed, a prerequisite for the evolution of the very fast growth rates observed in large ornithischians, sauropods and large theropods. ,Archosauria, Bone histology, Dinosauriformes, Late Triassic, Silesaurus opolensis. [source] Lystrosaurus species composition across the Permo,Triassic boundary in the Karoo Basin of South AfricaLETHAIA, Issue 2 2007JENNIFER BOTHA Lystrosaurus is one of the few therapsid genera that survived the end-Permian mass extinction, and the only genus to have done so in abundance. This study identifies which species of Lystrosaurus have been recovered from Permian and Triassic strata to determine changes in the species composition across the Permo,Triassic (P,T) boundary in the Karoo Basin of South Africa. Data generated from museum collections and recent fieldwork were used to stratigraphically arrange a total of 189 Lystrosaurus specimens to determine which species survived the extinction event. Results reveal that L. curvatus and L. maccaigi lived together on the Karoo floodplains immediately before the extinction event. L. maccaigi did not survive into the Triassic in South Africa. L. curvatus survived, but did not flourish and soon became extinct. Two new species of Lystrosaurus, L. murrayi and L. declivis, appeared in the Early Triassic. It is possible that L. murrayi and L. declivis occupied different niches to L. maccaigi and L. curvatus, and had special adaptations that were advantageous in an Early Triassic environment. We suggest that L. maccaigi may be used as a biostratigraphic marker to indicate latest Permian strata in South Africa and that, in support of previous proposals, the genus Lystrosaurus should not be used as a sole indicator of Triassic-aged strata. Our field data also show that L. curvatus may be regarded as a biostratigraphic indicator of the P,T boundary interval. [source] High diversity dinoflagellate cyst assemblages from the Late Triassic of southern England: new information on early dinoflagellate evolution and palaeogeographyLETHAIA, Issue 4 2006Raffaella Bucefalo Palliani Abundant and diverse dinoflagellate cyst assemblages from the Rhaetian of southern England are characterized by the occurrence of a new species of Rhaetogonyaulax, some undescribed taxa and numerous forms with Arctic and Australasian affinities. The dinoflagellate cyst assemblages permit a discussion of the palaeogeographic distribution of dinoflagellate cysts in the Late Triassic. The hypothesis on a Late Triassic migration event of organic walled microplankton from higher latitudes to the Boreal domain is presented. [source] | |||||||||||||||||||||||||||||||