Abstract:

The Lower Triassic deposited in deep-water environment in Chaohu area, in which nodular limestone was widely developed.
Some previous genetic analysis of Lower Triassic nodular limestone had not come to consensus. Based on the method of field
observation, indoor macro, micro observation and the consideration of the relationship between sedimentation and diagenesis within nodular limestone genesis, we made a comprehensive analysis of the nodular limestone genesis. The research results indicated that nodular limestone was a product of both sedimentation and diagenesis. The periodic fluctuation of carbonate compensation depth (CCD) interface is the basis of the nodular limestone necking phenomenon occured in the sedimentary period, while the periodic fluctuation of CCD interface was related to periodic change of climate and dissolution of bottom current in the Early Triassic. The dissolution of acid pore water was an important reason which causes the break of nodular limestone necking phenomenon. The disorder distribution of nodular limestone was mainly caused by the local stress field resulting from pressolution. Three kinds of nodular limestone summarized before, namely, banded nodular limestone, discontinuous nodular limestone and random nodular limestone, were formed by gradually enhancement of sedimentation and diagenesis.

Key words: Nodular limestone, characteristic, genesis, Lower Triassic, Chaohu Region