Foraminifera] Biostratigraphy And Paleoecology Of The Cretaceous Oceanic Red Beds In Kangmar, Southern Tibet

Cretaceous oceanic red beds （CORBs） are widely exposed in the northernTethyan–Himalayan subbelt, especially in Gyangze-Kangma area. CORBs usuallycontain few macrofossils, but yield aboundant microfossils, especially foraminiferaand radiolarians are, therefore the study of microfossils is particularly important for usto determine the age and paleoecology of the CORBs. This paper carrys in thebenthic foraminiferal biostratigraphy and paleoecology of the CORBS exposed in theTianba section, Kangmar, southern Tibet, which aims to provide some constrain onthe age of the CORBS and explore the formation mechanism of the CORBs.Based on the foraminiferal biostratigraphy and paleoecology, combined with theanalysis of the sedimentary formation and other aspects of the CORBs in Kangmar,this paper initially draw the following conclusions:（1） By processing the samples from the CORBs of the Tianba section ofKangmar, more than1,500foraminifera were gained.27species belonging to21genera and5foraminiferal zones have been recognised from the CORBs: Spirotectaovata zone, Gyroidinoides globosus zone, Nautilus faba zone, Bulimina laevis zone,Guadrimorphina camerata umbilicata zone.（2） By studying on the foraminifera of Tianba, this paper has initially set up theforaminiferal biostratigraphic sequence of the CORBs of the Tianba, Kangmarian andit is referred that age the CORBs should be early Santonian to late Maastrichtian.（3） During the Campanian stage of late Cretaceous, the study area located in ashallowing environment, resulting in the breeding of foraminifera and a decline in thechemocline surface, Fe²⁺in water was oxidized into Fe³⁺, with North Asia with a setof red marine deposits rich in foraminiferal and radiolarian fossils red marine depositswere developed in the northern Tethyan Himalaya.（4） According to the analysis of sediment types and facies, it is suggested that that the Kamba area should be located in the continental slope.（5） By the study on the facies and bio-geographical features and comparison withthe neighbour area, it is revealed that the foraminiferal fauna of the Kangmar wasdistributed in a narrow deep-sea sedimentary rocks south to the Yarlung Zangbosuture which may be an east-west deep-sea trough, while Gamba area in southernHimalayan Tethayan subbelt should be in outer shelf.