Abstract: The trace element characteristics of Cambian-Ordovician carbonates in Bachu area of Tarim basin are studied, and their enrichment mechanisms are discussed. The results show that the enrichment of trace elements is closely related to the original sedimentary settings. The contents of trace elements as K, Na, Al and Fe are relatively low in open platform and platform marginal shoal in comparison with relatively high contents in the slope zone. Trace elements as Mn, Cr, Ni and V trend towards increases from shallow to deep water sedimentary settings, thus could be used to indicate relatively changes of paleo-water depth. The w(Ca)/w(Mg) ratio of major elements is relatively low in dolomite-domi-nated evaporate platform and restricted platform facies, while relatively high in open platform and platform marginal shoal deposits where dolomite is not developed. The w(Sr)/ w(Ba) ratio of open platform facies is relatively high, while relatively low in dolomite-dominated evaporate platform and restricted platform facies. Hence, the trace elements together with major elements of carbonates could be used as effective mark for identification of the sedimentary settings in this area.

Key words: Tarim basin, Buchu, Cambrian, Ordovician, carbonate, trace element, setting, environment