نتایج جستجو برای: late neoproterozoic
تعداد نتایج: 196368 فیلتر نتایج به سال:
It has recently been found that Neoproterozoic glaciogenic sediments were deposited mainly at low paleolatitudes, in marked qualitative contrast to their Pleistocene counterparts. Several competing models vie for explanation of this unusual paleoclimatic record, most notably the high-obliquity hypothesis and varying degrees of the snowball Earth scenario. The present study quantitatively compil...
The Chuar Group (approximately 1600 m thick) preserves a record of extensional tectonism, ocean-chemistry fluctuations, and biological diversification during the late Neoproterozoic Era. An ash layer from the top of the section has a U-Pb zircon age of 742 +/- 6 Ma. The Chuar Group was deposited at low latitudes during extension on the north-trending Butte fault system and is inferred to record...
The cycles of carbon and oxygen at the Earth surface are intimately linked, where the burial of organic carbon into sediments represents a source of oxygen to the surface environment. This coupling is typically quantified through the isotope records of organic and inorganic carbon. Yet, the late Neoproterozoic Eon, the time when animals first evolved, experienced wild isotope fluctuations which...
The Band-e-Hezarchah granitoids mainly include alkali granite and granite. that intruded in Late Neoproterozoic metamorphic rocks. Orthoclase, microcline, plagioclase, quartz and biotite are the main rock-forming minerals. Plagioclase is mostly albite and oligoclase with Si = 2.57-2.7 a.p.f.u. and An0.4–12.6. Biotite is mostly siderophyllite, with Si = 4.30-6.22 a.p.f.u. and XMg= 0.025 - 0.859....
Neoproterozoic gneisses at Meatiq and Hafafit in the Eastern Desert of Egypt give Rb–Sr and U–Pb zircon ages of 600–750 Ma. These gneisses are interpreted by different workers to represent deeper levels of juvenile Neoproterozoic crust or Archaean/Palaeoproterozoic crust that was remobilized during Neoproterozoic time. Geochemical and Sr–Nd isotope compositions for these gneisses reported here ...
New stratigraphic, geochronological and palaeomagnetic constraints allow updates to be made to a synthesis of Neoproterozoic glacial palaeolatitudes, including modifications to some reliability estimates. The overall pattern of a Neoproterozoic climatic paradox persists: there is an abundance of tropical palaeolatitudes and near to complete absence of glaciogenic deposits demonstrably laid down...
, 65, 85–87.Prasad, N. and Roscoe, S.M., 1996. Evi-dence for anoxic to oxic atmosphericchange during 2.45–2.22 Ga from lowerand upper sub-Huronian paleosols.Catena, 27, 105–121.Prave, A.R., 1999a. Two diamictites, twocap carbonates, two dC excursions,two rifts: the Neoproterozoic KingstonPeak Formation, Death Valley, Califor-nia. Geology, 27, 339–342....
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