The age of the Chuangde Formation in Kangmar, southern Tibet of China: Implications for the origin of Cretaceous oceanic red beds (CORBs) in the northern Tethyan Himalaya

The Chuangde Formation in the northern Tethyan Himalaya consists of the Upper Cretaceous oceanic red beds (CORBs). Due to the structural complexity and poor fossil preservation, the age of this unit remains an issue. In one interpretation, the age of the Chuangde Formation in the eastern Tethyan Himalaya is significantly older than in the western Tethyan Himalaya, suggesting that the formation of CORBs in the Late Cretaceous Tethys ocean may have been triggered by the ocean circulation pattern change in response to the changes associated with the collision between Indian and Asian plates. New foraminiferal biostratigraphic data from a well-preserved and fossil-rich section in Kangmar, southern Tibet, China, reveal that the Chuangde Formation in the eastern Tethyan Himalaya has an age from Early Campanian to Maastrichtian. Fossil assemblages from this section allow its correlation with other CORE-bearing sections and argue against the age discrepancy of CORBs between the eastern and western parts of the northern Tethyan Himalaya. Biostratigraphic correlation and paleogeographic reconstruction indicates that the CORBs in the Tethyan Himalaya are restricted to the slope and basinal environments but they are entirely missing in the shelf environments including the shelf margin. The similar thicknesses (and therefore potentially similar sedimentation rates) of time-equivalent units between shelf and slope/basinal sections argues against the formation of CORBs in the Tethyan Himalaya by transportation of terrigenous iron into a sediment-starved ocean. The lack of CORBs in shelf environments and the widespread occurrence CORBs in slope/basinal environments suggest that the CORBs were likely formed by oxidation of reduced iron in the upper ocean water column close to the chemocline rather than in oxic bottom waters. (C) 2010 Elsevier BM. All rights reserved.