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Sedimentary Geology Of Cretaceous In Southern Tibet, And The Upper Cretaceous Oceanic Redbeds

Posted on:2003-10-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:X M HuFull Text:PDF
GTID:1100360062486598Subject:Paleontology and stratigraphy
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Studies of the evolution and changes in the Tethys Ocean occurring during past 200 Ma may provide a model for future oceanic evolution and a key to the knowledge of our planet's global behavior (Cadet, 1996).Particularly the Cretaceous time period is a time of major changes in the Earth Systems demonstrated by major plate tectonic processes, as is the dispersal of Pangea supercontinent, plaeoclimate and paleoceanography changes. Such changes are revealed for example by worldwide distribution of organic-rich black shales, occurrence of oceanic anoxic events, periods of carbonate platforms drowning, high oceanic production, and brief periods of an extreme hot climate. Causes of many such changes are poorly understood. Therefore studies of the Cretaceous strata in southern Tibet contribute to the understanding of above processes and particularly to the global carbon cycling.We may ask: what happened during Cretaceous in eastern Tethys? This question can only be answered from the stratigraphical records in Tethys Himalaya. That is the reason why 1 select the Cretaceous in Tibetan Tethys Himalayas as my thesis topic.Based on field studies by the author and research by previous workers the Cretaceous stratigraphy in southern Tibet is refined. The Cretaceous in the southern subzone of Tibetan Himalaya consists upward of Gucuo Formation (? early Berriasian ~?Aptian), Gangbadongshan Fm. (? -Aptian), Chaquiela Fm. (Albian), Lengqingre Fm. (Cenomanian -early Turanian), Gangbachunkou Fm. (Turanian -Santonian), Zongshan Fm. (Campanian -Maastrichtian), and Zhepure Shanpo Fm. (middle-late Maastrichtian ~Danian). In the northern subzone of Tibetan Himalaya, the Gyabula Fm. can be extended from pre-Valanginian to Coniacian. The Chuangde Fm. is of Santonian ~ Campanian according to studies of planktonic foraminifera and nannofossils, while the overlying Zongzhuo Fm. is of latest Cretaceous through Paleocene age.Study of sediment composition and sedimentary microfacies of Cretaceous sedimentary sequences in Tibetan Himalayas allow to separate six stages in their development: 1) latestJurassic to earliest Cretaceous (Tithonian ~Berriasian) widespread deposition of quartz arenitic sandstone; 2) Early Cretaceous (Berriasian ~Aptian) occurrence of volcanic sandstones; 3) Middle Cretaceous (Albian ~ Coniacian) black shales deposition; 4) early Late Cretaceous deposition of oceanic red beds (Santonian ~ Campanian) on a continental slope, while shale was deposited on a shelf; 5) late Late Cretaceous (late Campanian -Maastrichtian) carbonate-rich sediments were deposited on a shelf and olistoliths on the slope; 6) latest Cretaceous to earliest Tertiary (late Maastrichtian ~ early Danian) deposition of mixed carbonate and elastics on the shelf and olistoliths on continental slope.The sedimentary geology study of the Cretaceous in the southern Tibet allows correlation with the Cretaceous strata both in Nepal Himalaya and Lhadkh Himalaya. Results show that the Spiti shale in Zanskar terminated 15Ma later than that in southern Tibet, while the lowermost Cretaceous quartz sandstone in Zanskar appeared 18Ma later than that in southern Tibet. The age of volcanic sandstone in southern Tibet is very poorly time constraint and their deposition occurred somewhere within Berriasian -early Albian. In Thakkhola, the Chukh Group volcanic sandstone are of late Hauterivian -early Albian age (duration about 20Ma), while in Zanskar, the volcanic sandstones facies only appeared in Albian (duration of less than lOMa). Therefore, it can be concluded that the onsets of both quartz sandstone and volcanic sandstone occurred earlier in eastern Tethys Himalayas (southern Tibet) than in western Tethys Himalayas (Lhadkh). It implies that during early Cretaceous major geotectonic activity occurred earlier on the eastern side of the India continental plate than at its western part, perhaps 15~20 Ma earlier in east This is interpreted to be the result of separation of Australia from Greater India.The continental doming preceding the break-up of Gond...
Keywords/Search Tags:Cretaceous, Upper Cretaceous/ Late Cretaceous, Sedimentary Geology, Sedimentary Facies, Sedimentology, Sedimentary Petrology, Sedimentary Microfacies, Sedimentary History, Tethys, Tethys Himalaya, Tibet/Southern Tibet/Qinghai-Tibet Plateau
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