Problems Existing in the Division and Comparison of Late Cenozoic Strata in the Chengdu Basin

The Chengdu basin is a continental basin located between Longmenshan nappe orogenic belt and Longquanshan fold fault belt, which has deposited a thick layer of loose gravel in Late Cenozoic. In the past, the stratigraphic division and comparison of Late Cenozoic in Chengdu basin was mainly depended on the terrace sections around it. Through field investigation and indoor comprehensive research, it is considered that there are some defects about these terrace sections: (1) short length, poor stratigraphic continuity, similar in color, composition, structure of sediments and section sequence; (2) lack of chronostratigraphic and biostratigraphic data; (3) lack of standard sections and marker layers for stratigraphic division and comparison. As a result, the age attribution of lithostratigraphic units established according to terrace sections is uncertain, chronostratigraphy and lithostratigraphy are irreconcilable, and biostratigraphy has not played a supporting role in stratigraphic division and comparison. It is suggested to implement geological survey wells in the basin depression area, and establish the standard profile and auxiliary correlation section for stratigraphic division of Chengdu basin through systematic test of rock stratigraphic assemblage, filling sequence and chronological data, and systematic analysis of sporopollen assemblage. This can promote the stratigraphic division and comparison of Late Cenozoic in this area, which provides a basis for the three-dimensional geological structure modeling of underground space in Chengdu City.