Late Devonian to Early Carboniferous sequence stratigraphy of the Tarim Basin, Xinjiang, NW China

Chen Zhong-Qiang

pp. 177-196, 1 plate, in English

Abstract:

In order to improve the basin analysis and petroleum exploration of the Tarim Basin, this paper concentrates on the Late Devonian to Early Carboniferous sequence stratigraphy of the Tarim Basin. The studied material of this paper was collected from 2 outcrop sections at Damusi and Xiaohaizi respectively, and 14 well logs from the Manxi, Hetianhe, Tazhong and Tabei areas of the Tarim Basin. The sliding window spectral analysis of Gamma ray logs with the spectrum/cyclicity band and sequences in applied to the analysis of logs under the deserts. Herein, four major sequences corresponding to the 3rd- order cycles are identified from the Late Devonian and Early Carboniferous outcrops and logs in the Tarim Basin. Among them, Sequences I and II form Supersequence I; Sequences III and IV consist of Supersequence II. In addition, sequences are divided internally into parasequence sets and Punctuated Aggradational Cycles (PACs) probably corresponding to the 4th-, 5th- or 6th- order cycles. Seventy-one Punctuated Aggradational Cycles (PACs) within Supersequence II are also recognised from the Damusi section by analysing microfacies and palaeoecology. The smaller scale unites commonly display an upward shallowing motif, at least 4 orders of cycles are preserved in the record of sediments. Sequences and depositional system tracts are correlative basinwide and synchronous within the resolution of bio- and event- stratigraphy. Several major drops in relative sea level are represented by sequence boundaries. The "Donghe Sandstones", the famous oil beds, can compare directly to the shallow grey quartz sandstones at the bottom of the Donghetang Formation in the Bachu area and the purple quartz sandstones at the upper portion of the Qizilafu Formation in the SW Tarim Basin, and they were likely deposited during the latest Famennian Stage (Late Devonian).

Keyword: Sequence stratigraphy, punctuated aggradational cycles, "Donghe Sandstones", Late Devonian to Early Carboniferous, Tarim Basin