Sedimentary characteristics of deep-lacustrine fans: a case study on the lower Jurassic Sangonghe formation of the Turpan Basin, NW China

Abstract

Ancient deep-lacustrine fans serve as prolific hydrocarbon reservoirs and provide records of climatic and tectonic activity. The deep-lacustrine fans of the Lower Jurassic Sangonghe Formation in Turpan Basin have become the most important exploration targets as stratigraphic traps. An integrated analysis of field profile investigation, core examination, well logging and seismic reflection profile interpretation, and grain size distribution patterns has enabled the identification of a series of deep-lacustrine fans. The deep-lacustrine fans of the Lower Jurassic Sangonghe Formation, deposited in the Turpan Basin consist of sandy debris flow, bottom current reworking and turbidite lithofacies. The deep-lacustrine fans are depicted by the following geological and geophysical features: (1) abundant soft-sediment deformation structures, and dish structures, normal graded beddings and inverse graded bedding structures developed in the strata, (2) the grain size distribution on the C–M diagram is parallel to the C = M baseline and cumulative probability curves display a bi-segment pattern with the suspension components to be the dominant parts, (3) gamma-ray logging curve are inverse-cycle features and seismic reflection profiles are characterized of poor continuity, high amplitudes, scattered and lenticular shapes. The deep-lacustrine fans are favorable target reservoirs, and have become the most important exploration targets in the Turpan Basin.