Stratigraphic distribution and structural characteristics of the Meso?Neoproterozoic in southern Ordos Basin, China

Xiaoke Li; Gang Chen; Faqian ZhangZihao DangAojie Liu

摘要

With the successive discovery of large-scale Proterozoic gas reservoirs worldwide, ultra-deep Proterozoic strata have graduallybecome a new field of interest with great potential for gas reservoir exploration. The Ordos Basin in China has richProterozoic stratigraphic deposits and high gas reservoir exploration potential, but it has not been sufficiently explored.The lack of geological data has become a key shortcoming limiting its in-depth study. This study aimed to clarify the divisionand evidence of Meso-Neoproterozoic strata in the southern part the Ordos Basin, and clarify the stratum distributionand tectonic evolution process, which need to be prioritized before exploration. To this end, the multi-data joint researchmethod of lithology-drilling-field outcrop-seismic data was used. The results showed that Sinian tillite, Jixianian dolomite,and Changchengian quartz sandstone developed in the Meso-Neoproterozoic strata from top to bottom. Seismic reflectionsfrom the bottoms of the Sinian and Jixianian showed weak-amplitude and medium-strong amplitude, respectively. TheChangchengian strata can be divided into depression and rift layers. The rift layer presents a high-angle medium-strongamplitude reflection, and the depression layer presents a continuous medium-weak amplitude reflection. In the study area,during the early basin rift of the Changchengian, the NE-trending fault trough was filled with deposits, and the late riftingactivities stopped, forming widespread depression deposits, with an angular unconformity contact between them. During theJixian Period, the southwest continued to be depressed, and during the Sinian, the main body of the basin was uplifted, andthe southwest margin was partially depressed. The strata were widely absent in the study area, and showed an “L”-shapeddistribution only in the southwest margin of the study area. The depositional range is the largest in the Changchengian,followed by the Jixian, and the smallest in the Sinian. The thickness of the strata gradually thinned to the northeast. TheProterozoic strata in the Qyang paleo-uplift are covered by multiple sets of high-quality Paleozoic source rocks, and thegenerated oil and gas accumulate along the strata to the paleo-uplift, corresponding to an accumulation model of “multiplesources converge, and paleo-uplifts form reservoirs”. This study compensates for the lack of basic research on the Meso-Neoproterozoic strata division in the Ordos Basin, and more accurately determines the distribution pattern of the strata inthe basin, which are highly relevant for the Ordos Basin and other Meso-Neoproterozoic gas reservoirs. The exploration hasimportant reference significance.

Stratigraphic distribution and structural characteristics of the Meso?Neoproterozoic in southern Ordos Basin, China

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