Paleomagnetic And Rock Magnetic Study Of The Lower Jurassic Marine Succession Of Wolong Section Tingri,Southern Tibet

Paleomagnetism is one of the most effective method to restore the paleogeographic location of plate,previous paleomagnetic studies of Tethyan Himalaya mainly focused on its early Cretaceous-Paleogene rocks,little attention has been paid to its early to middle Mesozoic history.Meanwhile,there was a global paleoceanographic event,Toarcian Oceanic Anoxic Event(TOAE),in the early Jurassic period.Although much has been learned about TOAE from the western Tethys realm,little is known about its responses in the eastern Tethys realm.To address these two aspects of questions,a paleomagnetic and rock magnetic study was carried out on the Lower Jurassic Pupuga-Nieniexiongla Group in the Wolong section,Tingri,southern Tibet.Paleomagnetic results show that the mean low temperature/coercivity component of the lower Jurassic strata in Wolong section is:Dg=358.1°,Ig=41.40(n=132,?=13.4,?95=3.5°),Ds=220.90,Is=48.80(n=132,?=1 1.6 ?95=3.80);and the mean ChRM is:Dg=227.6°,Ig=27.5°,(n=170,a95=2.1°),Ds=328.5°,Is=-54.0°,(n=170,a95=2.3°).The ChRMs show a single polarity,suggesting that the rocks may be affected by remagnetizaiton.According to former studies,there is no separation between Tethyan Himalaya and India during Cretaceous.Comparison of the new results with the APWP and paleolatitude of India craton indicates that the remagnetization probably occurred-90-102 Ma,which is within the Cretaceous normal polarity Superchron.In order to characterize the type,content,and particle size of magnetic minerals,high-resolution rock magnetic measurements were carried out for the 20-m thick interval including x?S-ratio?HIRM?SIRM??ARM/??nd ?fd According to the phase characteristics of above tests,further experiments were carry out on selected representative samples in order to show more details,including isothermal remanent magnetization curves(IRM)?3-axis thermal demagnetization curves and ?-T curves.The TOAE interval was tentatively delineated in the Wolong section.High-resolution rock magnetic data from the 20-m thick section containing the TOAE interval show four stages of environmental evolution,i.e.,Stages I,II,III,and IV.Variations in rock magnetic data in Stages I and IV document the deposition processes before and after the TOAE event,respectively.Stage II is characterized by a decrease in the abundance of fine-grained magnetic mineral and the subsequent occurrence of iron sulfides.These features likely represent responses to the vertical and lateral expansion of the Oxygen Minimum zone(OMZ)caused by the transgression during the early and middle TOAE.Stage III saw a pronounced increase in the abundance of high-coercivity minerals(hematite)and corresponded to the recovery stage C3 of the TOAE.This feature may indicate that a rapid change in the marine depositional environment from a reducing to an oxidizing state.Overall,changes in rock magnetic parameters could provide important insight and new methods into understanding the evolution of TOAE in Eastern Tethys.