Rock Magnetism Research Of The Shahezi Formation Of The Songke 2 Well Eastern Drilling Core

A series of major geological events such as extreme greenhouse climate,ultra-static magnetism,large-scale igneous province eruption,and dinosaur extinction occurred in the Cretaceous.Studying the causes and connections of events is important in exploring the history of Earth's evolution,understanding today's global environmental patterns,and predicting future climate change.So far,the geological data of the Cretaceous stratigraphic research mostly come from the marine phase,and the continental stratigraphic research is relatively lacking.In May 2018,the Songke 2 well was successfully completed,becoming the first scientific drilling drilled through the Cretaceous,providing an opportunity for the Cretaceous continental sedimentary study.In this study,from the perspective of rock magnetism,the magnetic parameters of 1119core samples?resolution 1m?taken from the lower half of the Shahezi Formation in the Songliao Basin were tested to determine the magnetic properties including magnetic mineral content,type and particle size.Mineral combination characteristics.In order to reflect the Cretaceous continental paleoenvironment and paleoclimate information through magnetic characteristics.In this study,from the perspective of rock magnetism,the magnetic parameters of1119 core samples?resolution 1m?taken from the lower half of the Shahezi Formation in the Songliao Basin were tested to determine the magnetic properties including magnetic mineral content,type and particle size.Mineral combination characteristics.The purpose of this research is to reflect the Cretaceous continental paleoenvironment and paleoclimate information by magnetic characteristics.The rock magnetic test items carried out during the experiment include:magnetic susceptibility?,anhysteresis remanent magnetization magnetic ARM,saturated isothermal remanent magnetization SIRM,reverse demagnetization 100 mT isothermal remanent magnetization ITM_-100,?-T curve,IRM acquisition curve and the reverse field demagnetization curve.The strata of the Shahezi Formation in the Songliao Basin were formed in the early Cretaceous,with an absolute age of 125-113 Ma.The lower section of 4542m-5690m selected in this paper develops gray-black mud shale,silty mudstone,argillaceous siltstone,siltstone,fine sandstone,medium sandstone,coarse sandstone,pebbly sandstone,conglomerate,and coal seams in individual layers.According to the variation trend of mass magnetic susceptibility in the depth domain,the curve is divided into four sections A,B,C and D,section A is 4542m-4850m,section B is 4850m-4950m,section C is 4950m-5375m,and section D is 5375m-5690m.From the test data,the following conclusions are drawn:?1?The magnetic minerals in the samples in sections A and C are magnetite,but the content is small.The magnetic minerals of the core samples of sections B and D contain magnetite and iron sulfide.The presence of iron sulfide may be related to the reducing environment during the high lake level.?2?The lithological change of the D section of the Shahezi Formation is conglomerate-mudstone-conglomerate,indicating the shallow-deep-shallow variation of the high lake plane,consistent with the fluctuation of the magnetic parameters.The change of magnetic parameters from C to A may be related to the rise of the lake level in the Songliao Basin.?3?The entire research section may represent the depositions in the gradual warming phase of the Early Cretaceous climate cool period.