Tectonic evolution of Caledonian Palaeohigh in the Sichuan Basin and its relationship with hydrocarbon accumulation

Abstract

The Caledonian Palaeohigh is an important gas exploration domain of Sinian and Lower Paleozoic in western Central Sichuan Basin where gas discoveries have been made successively in recent years. In order to sort out the relationship between the tectonic evolution of this Palaeohigh and hydrocarbon accumulation there, we carried out a new round of research based on previous study results. The evolution history of this Palaeohigh can be divided into seven episodes: the Late Sinian overall tilting and the youth form development of this Palaeohigh, the Cambrian-Ordovician syndepositional uplifting, the Silurian joint uplifting, the Devonian-Carboniferous uplifting and erosion, the Permian overall subsidence and deposition of regional caprock, the Triassic-Jurassic migration of structural high of the eastern segment of this Palaeohigh, and Cretaceous-Neogene strong deformation of the western segment of this Palaeohigh. The hydrocarbon accumulation in the SinianLower Paleozoic experienced three evolution stages, namely the formation of ancient oil reservoirs in the Silurian-Triassic period, the development of the paleo-gas reservoirs in the Jurassic-Oligocene period, and differential evolution of gas reservoirs since the Miocene era. The Sinian-Lower Paleozoic paleo-reservoirs mainly occur in the Leshan-Ziyang-Gaoshiti-Longnǚsi zone and in the area to its north. The tectonic movement of the western segment of the Palaeohigh was strong, while its eastern segment was relatively stable since the later Himalayan epoch, which is favorable for gas accumulation and preservation. It is believed that the Gaoshiti-Moxi-Longnǚsi structural belt and its northern flank are not only favorable for the development of structural gas reservoirs in the Lower Paleozoic but also for gas reservoirs of karstic-lithologic type on the top of the Cambrian and Ordovician. The later type will be the major exploration target of this area in the future.

Structural Characteristics and their Significance for Hydrocarbon Accumulation in the Northern Slope of the Central Sichuan Paleo‐uplift

“…The Caledonian unconformity referred to in this study was caused by the late Caledonian (also known as the Guangxi) movement and the early Hercynian Yunnan movement following deposition of the Silurian (Wang et al, 2002). The period of formation of the unconformity was the most intense uplift stage of the Central Sichuan paleo-uplift (Song, 1996;Li W et al, 2014).…”

“…Similarly, a series of denudation apatites can be identified from the seismic profiles at the lower boundary of the lower Cambrian Qiongzhusi Formation, which shows that the sedimentary discontinuities occurred prior to the Cambrian deposition, forming a regional parallel unconformity between the lower Cambrian strata and the Sinian strata. These were the results of differential uplift of the crust in the Sichuan Basin and its peripheral areas during the Tongwan stage II tectonic movement at the end of the Dengying Formation's deposition (Li W et al, 2014;Wang et al, 2014).…”

“…1a), reflecting that the formation of the Sichuan Basin and its internal structural development were controlled by the evolutionary process of the deep and large faults which extended in a rhombic style in the Yangtze plate. The Central Sichuan Paleo-uplift is an irregular giant nose-shaped uplift, controlled by rigid basement in the central and western part of the basin (Yuan et al, 2013;Li W et al, 2014). It is the largest foremost tectonic unit in the basin, having undergone multiple synsedimentary uplifts and denudation events (Li W et al, 2014;Mei et al, 2014;Su et al, 2020).…”

Factors Affecting Shale Gas Chemistry and Stable Isotope and Noble Gas Isotope Composition and Distribution: A Case Study of Lower Silurian Longmaxi Shale Gas, Sichuan Basin

“…Repeated uplift and erosion and numerous faults destroyed the preservation conditions of Longmaxi shale gas in the WY and CN areas [36,70] and consequently caused shale gas loss. The formation of the Leshan-Longnvsi paleo uplift involved several periods of tectonic movements, from the Tongwan movement to Yanshanian movement [35]; its tectonic evolution has had a greater influence on the formation and distribution of the WY shale gas reservoirs than that of the CN shale gas reservoirs [72][73][74].…”

Difference Analysis of Organic Matter Enrichment Mechanisms in Upper Ordovician-Lower Silurian Shale from the Yangtze Region of Southern China and Its Geological Significance in Shale Gas Exploration

“…Under the influence of the Caledonian movement, large-scale tectonic uplift occurred at the end of the Silurian period, which formed a large paleouplift in the middle and upper Yangtze regions. This uplift caused the Sichuan Basin to be entirely eroded, contributing to the widespread absence of the Devonian and Carboniferous systems in the Sichuan Basin [26]. During the early Permian, the large-scale invasion of Tethyan sea water from the southwest resulted in the formation of a vast epicontinental sea.…”