Abstract:

Based on field survey and thin section analysis of tempestites in the Xiaweidian section, western Beijing, 59 sets of storm deposits are characterized. The storm sedimentary sequences are determined, and an epicontinental sea deposition model is established. There are four sedimentary facies types in the Cambrian, Xiaweidian section: micritic limestone, pebbled micritic limestone, wackstone and packston, where in-situ, proximal and distal tempestites are developed in sequences of oolitic-gravel limestone, mudstone/siltstone-gravel limestone and micritic-gravel limestone, respectively. In-situ tempestites develop erosion surfaces and have high grain content and large axial ratio; proximal tempestites contain flat peebles with good orientation and show graded bedding; and distal tempestites have high matrix content. The three tempestites types are deposited in the subtidal zone under epicontinental sea environment, with the in-situ, proximal and distal types deposited from top to bottom and separated by normal- and storm-wave bases, respectively, in the order of increasing distance from the storm center and thus increasing transport distance. Results of this study not only complement the storm deposition records of the Cambrian in Xiaweidian, but also provide evidence for the study of palaeoenvironment in this period.

Key words: Xiaweidian, storm deposition, tempestites, Cambrian, carbonate rocks