Abstract
The older and deeper hydrocarbon accumulations receive increasing attention across the world, providing more technical and commercial challenges to hydrocarbon exploration. We present a study of an asymmetrical, N-S striking intracratonic sag which developed across the Sichuan basin, south China, from Late Ediacaran to Early Cambrian times. The Mianyang-Changning intracratonic sag is ~50 km wide, with its steepest part in the basin center. In particular the eastern margin shows its greatest steepness. Five episodes in the evolutions of the sag can be recognized. It begins in the Late Ediacaran with an uplift and erosion correlated to Tongwan movement. Initial extension occurred during the Early Cambrian Maidiping period, when more strata of the Maidiping Formation were deposited across the sag. Subsequently, maximum extension occurred during the Early Cambrian Qiongzhusi period that resulted in 450–1700 m thick Maidiping-Canglangpu Formations being deposited in the sag. Then, the sag disappeared at the Longwangmiao period, as it was infilled by the sediments. The intracratonic sag has significant influence on the development of high-quality reservoirs in the Dengying and Longwangmiao Formations and source-rock of the Niutitang Formation. It thus indicates that a high probability for oil/gas accumulation exists along the intracratonic sag, across the central Sichuan basin.
Highlights
Continental rift basins are widespread extensional structures on the Earth’s surface and are known from the Archean up to the present
The paleouplift of Leshan-Longnvshi formed during Late Carboniferous-Early Permian period and is roughly prior to the period of peak hydrocarbon-generation [48, 49]; we argue that the paleohigh along the margins of the intracratonic sag has the highest probability to be charged by hydrocarbons, as maturity of the source-rocks was increasing with increased burial
Our study shows an asymmetrical, S-N striking intracratonic sag, that is, the Mianyang-Changning intracratonic sag, which developed across the Sichuan basin from the Late Ediacaran to Early Cambrian time
Summary
Continental rift basins are widespread extensional structures on the Earth’s surface and are known from the Archean up to the present They account for ∼30% of global hydrocarbon discoveries [1]. Deposits of evaporites and black shale are widespread in rift-related basins, providing effective seal and source-rock across from Oman, Pakistan, and India to South China [3, 11]. This generated an interest in exploring for the Infra-Cambrian plays along the Peri-Gondwanan Margin.
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