科研之友
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摘要
A group of varicolored marine deposits, including red colored beds, are widespread in the Kangmar area, southern Tibet. They are lithologically similar to the Upper Cretaceous Oceanic Red Beds (CORBs) (the Chuangde Formation) outcropping at other localities in southern Tibet. At Daba locality, they are mainly composed of intercalated pelagic red clays and reddish colored pelagic limestones. Micropaleontologic study of the strata led to the discovery of radiolarians in siliceous rocks and siliceous limestones. Radiolaria preservation is mostly satisfactory and fifty-four species from forty-nine genera were identified. These allow recognition of three main radiolarian assemblages: Cavaspongia califoniaensis - Xitus spicularius assemblage. Praeconoanyomma lipmanae - Clathropyrgus titthium assemblage, and Lithostrobus punctulatus - Lithocampe marinae assemblage.
Occurrence of these radiolarian assemblages indicate a Campanian age of the CORBs at Daba, corroborated by co-occurring planktic foraminifers. Radiolarian and foraminiferal microfossil evidence and lithology of the strata indicate that the sediments were deposited at the lower continental margin of the Indian continental plate and in an adjacent abyssal oceanic basin.
The discovery of radiolarians from the CORBs at Daba area contributes to the paleogeographic interpretation of Late Cretaceous strata in southern Tibet and the Tethyan Himalaya. Unanswered is the remaining question: Was it the difference in palaeoceanography, such as ocean circulation, or plate tectonics, which resulted in the CORBs in the Tethyan Himalaya being younger than similar deposits in the western Tethys, where the deposition of this lithofacies had already begun in the Turonian? To answer this question more detailed biostratigraphic studies in southern Tibet are needed.
- 出版日期2011-12-1
- 单位中国地质大学（北京）; 北京大学
