Sequence architecture and depositional evolution of theOrdovician carbonate platform margins in theTarimBasin and its response to tectonism and sea‐level change

Abstract

The sequence architecture and depositional evolution of the Ordovician carbonate platform margins in the Tarim Basin, China, were formed in response to the interplay of tectonism and sea‐level change, their history being documented by the integrated analysis of many seismic lines, drilling and outcrop data. The Ordovician carbonate system in the basin is divided into four composite sequences defined by major unconformities. Each sequence consists of a regional depositional cycle from transgression with an onlapping transgressive systems tract (TST) to regression with a prograding highstand systems tract (HST), and can be further subdivided into 10 third‐order sequences based on subordinate discontinuous boundaries at the carbonate platform marginal zones. Constrained by the marginal slope of the early‐rifted Manjiaer aulacogen, the carbonate platform margins of the Lower and Middle Ordovician that prograded eastward in an arcuate belt extending generally north‐south across the northern part of the basin. The development of the Tazhong uplift due to compression resulted in an extensive paleokarst hiatus between the Middle and the Upper Ordovician in the south‐central basin, and subsequently constrained the formation of a peninsula‐shaped carbonate platform whose margins were controlled by marginal thrust‐fault belts of the paleo‐uplift during the Late Ordovician. In the northern basin, the Late Ordovician carbonate platform margin developed around the marginal slope of the Tabei paleouplift. The transgressive–regressive cycles of the carbonate system are comparable and seem to have occurred simultaneously across the entire basin, suggesting that the cyclic sequence architecture was fundamentally controlled by eustatic fluctuations. Stacking patterns of the composite sequences varied due to the interplay between the accommodation produced by tectonism and sea‐level change, and the carbonate production rate. The reef–shoal facies complexes that developed along the platform margins, with paleokarst development at unconformities, constitute the major reservoir of large petroleum reserves in the basin.

Tectonically driven dolomitization of Cambrian to Lower Ordovician carbonates of the Quruqtagh area, north‐eastern flank of Tarim Basin, north‐west China

“…The Quruqtagh area, located to the north‐east of Tarim Basin, suffered multiphase tectonic deformations (Lin et al ., ,b). Due to missed/eroded strata, the burial history cannot be reconstructed precisely in the Quruqtagh area.…”

“…At that time, the north‐eastern margin of the Tarim block experienced extensive uplift and intense tectonic deformation due to the oblique collision and accretion of these terranes. The widespread angular unconformity at the top of Permian strata in the northern and north‐eastern flanks of the Tarim Basin, as disclosed by seismic reflectors (Lin et al ., ,b), is probably a response to this widespread tectonic uplift. Accordingly, subsequent post‐collision overthrusting and strike‐slip faulting may also have taken place (Shu et al ., , ; Cunningham et al ., ).…”

Paleokarst of the Lianglitage Formation related to tectonic unconformity at the top of the Ordovician in the eastern Tazhong Uplift, Tarim Basin, NW China

“…1 Fault (TZF1) to the north and the Tazhong South Fault Belt (TZSFB) to the south, having an area of approximately 27,000 km 2 . The depositional background in this area was dominated by a carbonate platform during the Ordovician (Lin, Yang, Liu, Rui, Cai, & Li, ), and the Ordovician system in the Tazhong area contains four distinct formations (Figure ): (1) The Lower Ordovician Penglaiba Formation, this formation is predominantly composed of silt‐sized crystalline dolomites and dolomudstones with abundant microbial binding and birds‐eye structures, interbedded with minor calcareous dolomites; these lithofacies associations indicate a restricted‐marine carbonate platform environment (Cai, Qian, Chen, & You, ; Chen et al, ). (2) The Middle‐Lower Ordovician Yingshan Formation, the main lithofacies are dolomitic limestones, calcareous dolomites, and micritic limestone in the lower part and various types of limestones such as grainstones, packstones, wackestones, and mudstones in the upper part.…”

Depositional facies and stratal cyclicity of dolomites in the Lower Qiulitag Group (Upper Cambrian) in northwestern Tarim Basin, NW China

“…The Tarim Basin is the largest petroliferous basin in China where a number of oil and gas fields have been discovered in the last two decades, with production taking place from Lower Paleozoic strata, particularly Ordovician carbonates (Li et al 1996;Zheng et al 2007;Lin et al 2011). More recently, there has been an increasing interest in more deeply buried (generally >5 km) Cambrian dolomites.…”