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Jurassic Time (jurassic + time)
Selected AbstractsExtensional 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] 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] Olivine-spinifex basalt from the Tamba Belt, southwest Japan: Evidence for Fe- and high field strength element-rich ultramafic volcanism in Permian OceanISLAND ARC, Issue 3 2007Yuji Ichiyama Abstract Permian basalt showing typical spinifex texture with >10 cm-long olivine pseudomorphs was discovered from the Jurassic Tamba accretionary complex in southwest Japan. The spinifex basalt occurs as a river boulder accompanied by many ferropicritic boulders in a Permian chert-greenstone unit. Groundmass of this rock is holocrystalline, suggesting a thick lava or sill for its provenance. Minor kaersutite in the groundmass indicates a hydrous magma. The spinifex basalt, in common with the associated ferropicritic rocks, is characterized by high high field strength element (HFSE) contents (e.g. Nb = 62 ppm and Zr = 254 ppm) and high-HFSE ratios (Al2O3/TiO2 = 3.9, Nb/Zr = 0.24 and Zr/Y = 6.4) unlike typical komatiites. The spinifex basalt and ferropicrite might represent the upper fractionated melt and the lower olivine-rich cumulate, respectively, of a single ultramafic sill (or lava) as reported from the early Proterozoic Pechenga Series in Kola Peninsula. Their parental magma might have been produced by hydrous melting of a mantle plume that was dosed with Fe- and HFSE-rich garnet pyroxenite. The spinifex basalt is an evidence for the Pechenga-type ferropicritic volcanism taken place in a Permian oceanic plateau, which accreted to the Asian continental margin as greenstone slices in Jurassic time. [source] Jurassic synorogenic basin filling in western Korea: sedimentary response to inception of the western Circum-Pacific orogenyBASIN RESEARCH, Issue 4 2009Kosuke Egawa ABSTRACT This is the first sedimentologic and stratigraphic attempt to demonstrate Jurassic subduction-induced basin-filling processes in the early stage of the western Circum-Pacific orogeny. The Chungnam Basin in western Korea was filled with a Lower to Middle Jurassic nonmarine succession, the Nampo Group, whose deposition postdated the Triassic final assembly of Chinese continental blocks. The Nampo Group consists of two repeated, fining- to coarsening-upward alluvio-lacustrine sequences, separated by an interval of thick breccia,gravel progradation deposits and its related strong proximal unconformities. No temporal variation in the degree of chemical weathering, along with the predominance of coals and a tropic to subtropic paleoflora, reveals little or no climate fluctuations during deposition of the Nampo Group. The observed relationships provide a record of sedimentation most likely controlled by temporal variations of tectonically driven sediment flux. Such syntectonic sedimentation of the Chungnam Basin occurred at a convergent margin of continental-arc setting during the Daebo orogeny, synchronous with the early subduction of the western paleo-Pacific ocean that resulted in formation of an accretionary complex along the East Asian continental margin during Jurassic time. Hence, synorogenic deposition in the Chungnam Basin is interpreted as sedimentary response to subduction,accretion of the western paleo-Pacific plate. [source] Palaeomagnetic evidence for the Gondwanian origin of the Taurides and rotation of the Isparta Angle, southern TurkeyGEOLOGICAL JOURNAL, Issue 4 2002John D. A. Piper Abstract The Taurides, the southernmost of the three major tectonic domains that constitute present-day Turkey, were emplaced following consumption of the Tethyan Ocean in Late Mesozoic to mid-Tertiary times. They are generally assigned an origin at the northern perimeter of Gondwana. To refine palaeogeographic control we have investigated the palaeomagnetism of a range of Jurassic rocks. Forty-nine samples of Upper Jurassic limestones preserve a dual polarity remanence (D/I=303/,9°, ,95=6°) interpreted as a primary magnetization acquired close to the equator and rotated during emplacement of the Taurides. Result from mid-Jurassic dolerites confirm a low palaeolatitude for the Tauride Platform during Jurassic times at the Afro,Arabian sector of Gondwana. Approximately 4000,km of Tethyan closure subsequently occurred between Late Jurassic and Eocene times. Although related Upper Jurassic limestones and Liassic redbeds preserve a sporadic record of similar remanence, the dominant signature in these latter rocks is an overprint of probable mid-Miocene age, probably acquired during a single polarity chron and imparted by migration of a fluid front during nappe loading. This is now rotated consistently anticlockwise by c. 30° and conforms to results of previous studies recording bulk Neogene rotation of the Isparta region following Lycian nappe emplacement. The regional distribution of this overprint implies that the Isparta Angle (IA) has been subject to only small additional closure (<10°) since Late Miocene time. A smaller amount (c. 6°) of clockwise rotation within the IA since Early Pliocene times is associated with an ongoing extensional regime and reflects an expanding curvature of the Tauride arc produced by southwestward extrusion of the Anatolian collage as a result of continuing northward motion of Afro,Arabia. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||