Figuring out whether the sedimentary provenance regions of the thick deep-water turbidite systems deposited during Middle–Upper Ordovician in South Quruqtagh are the intracontinental uplifts or the peripheral orogenic belts is of great significance for us to understand the tectono-sedimentary nature of the northeastern Tarim Basin and basin-range coupling processes in the middle Paleozoic.This paper reports the in situ LA-ICP-MS U–Pb ages and Hf isotope data on detrital zircons from two Middle–Upper Ordovician sandstone samples which were collected from the Charchag Formation and the Zatupo Formation in South Quruqtagh,respectively.The results show that the studied two samples have extremely similar U–Pb age patterns and Hf isotopic compositions,reflecting multiphase tectonothermal events with age groups of 527–694,713–870 Ma(peaking at 760 Ma),904–1,090,1,787–2,094 Ma(peaking at 1,975 Ma)and 2,419–2,517 Ma.Combining previous studies,the presence of age groups of 713–1,090 and1,787–2,094 Ma,respectively,demonstrates that Tarim had ever been a part of Rodinia and Columbia supercontinent.Moreover,98%of 713–870 Ma detrital zircons are characterized by negative e Hf(t)values ranging from-38.07 to-0.61,which are highly consistent with those of Neoproterozoic granites from the Quruqtagh area.No Early Paleozoic ages(*470–500 Ma)signifying subduction or collision events in Altyn Tagh were detected in the two samples,indicating that the Middle–Late Ordovician sediments in South Quruqtagh and northern Mangar depression were mainly derived from intracontinental uplifts,i.e.,the North Quruqtagh uplift or the Tabei paleo-uplift,rather than the Altyn Tagh.In conjunction with regional sedimentary-tectonic background and previous studies,we proposed preliminarily that the northeastern Tarim remained as a passive continental margin in Late Ordovician and changed into an active-continental margin in Silurian due to the southward subduction of the South-Tianshan Ocean.
The Upper Ordovician Lianglitag Formation carbonate rocks are important oil and gas reservoirs in the Tarim Basin,Northwest China,with obviously distinct reservoir properties among different oilfields.As a case area of the above carbonate reservoirs correlation,Tahe and Tazhong oilfields are chosen for the study through an integrated analysis of biostratigraphic isochronous framework,cores,thin sections,logs,and strontium isotopes.The research shows that the two areas were respectively attributed to different carbonate platforms during the Lianglitag Formation depositional phase.For the Lianglitag Formation,five fourth-order sequences may be divided in Tazhong,whereas only four fourth-order sequences are preserved in Tahe that correspond to the lower ones observed in Tazhong.The Lianglitag Formation carbonate platform in Tahe was characterized by ramp and/or weak rimmed types,with low depositional rates(37 μm/a),higher whole-rock clastic contents,and higher 87 Sr/86 Sr isotope ratios of carbonate matrix,showing relatively deep-water environment and evident terrigenous input for carbonate deposition.However,a strongly rimmed carbonate platform was developed in Tazhong,with high depositional rates of 250 m/a and less whole-rock clastic contents,indicating a high-energy depositional environment.Because of the sedimentary environment differences mentioned above,less high-energy facies but relatively intense syndepositional(early diagenetic) sea-water cementation of carbonates were developed in Tahe,and ubiquitous high-energy reef and shoal facies,with a frequent exposure to subaerial,and weak syndepositional sea-water cementation of carbonates in Tazhong.Therefore,fewer primary pores occurred in the Lianglitag Formation carbonate rocks of Tahe,whereas more primary pores were preserved in the same lithostratigraphic unit of the Tazhong(No.1 fault zone).Available high-energy reef-shoal facies and early diagenesis,with more primary pores preserved,provided a key material basis for the Lianglitag Formation carbonate res
