Abstract:

In order to investigate the distribution of trace elements of mudstone and its geological significance in the Yacheng Formation
in Yanan sag, the trace elements of 13 mudstone samples that were collected from Y1 well were analyzed by ICP-MS. The results show
that (1) A majority of continental elements and a minority of thalassophile elements are enriched, indicating a transitional environment.
The periodic development of coal accumulation is recorded the trace elements such as U, Ba, Th, Sr showing cyclic changes with depth
marked by distinct cycle boundaries. These boundaries indicate the transgression surface and the exposed surface of unconformity; (2)
The climate was warm and humid during the deposition period in the Yacheng Formation in the study region as indicated by Sr/Cu, V/(V+
Ni) and Ni/Co ratios indicating poor oxygen condition during this period. In addition, high S content suggests the existence of theYacheng transgression events in the Oligocene when Qiongdongnan Basin was transformed from a faulted depression to a sag basin while
the regional sea-level rose.

Key words: Coalsourcerock;traceelement;distributioncharacteristics;geologicalimplications;YachengFormation;QiongdongnanBasin