125 / 2022-02-24 09:37:09

The Paleoclimate Characteristics of late Jurassic in Hongqi depression of the Hailar Basin

海拉尔盆地，塔木兰沟组，孢粉组合，锆石U-Pb年代学，晚侏罗世，古气候

It is the first time that several oil-bearing layers have been discovered in siltstones intercalated by basalts in Hong 6 Well of the Hailar Basin. This makes a great progress in oil and gas exploration for the Jurassic deposit in the Hailar Basin, showing a bright future in the new exploration layers deep in the Basin. The strata characterized by volcanic rocks and interlayered sedimentary rocks with oil can be correlated to the Tamulangou Formation outcropped in the Chaoer area of Hulunbuir City, Inner Mongolia, China. In order to ascertain the horizon of the strata, 20 samples were collected systematically for palynological analysis, and finally 4 samples were productive in pollen and spores which enable to establish sporopollen assemblage named as Podocarpidites-Cedripites-Perinopollenites-Pseudowalchia. Therefore, the age of the assemblage is convinced lithologically to the Middle- Late Jurassic. This is coincident with the latest U-Pb isotopic dating of zircons (LA-ICP-MS) from the volcanic beds of Hong 6 Well, i.e., 149.8±3.6Ma-151.6±2.6Ma. Thus, the volcanic rocks with sedimentary interlayers bearing oil, pollen and spore fossils can be assigned to the Tamulangou Formation. Based on the sporopollen assemblage and isotopic age data, we can confirm that the age of Tamulangou Formation in Hong 6 Well can be correlated to the Middle-Late Jurassic, but the Late Jurassic is more likely. The palynological assemblage has obvious characteristics and can be used as a marker for biostratigraphic correlation of Tamulangou Formation in Hailar Basin. This is consistent with the palynological data. Furthermore, the vegetation reconstructed on the palynological data of the Tamulangou Formation is conifer forest, belonging to the semi-humid to temperate climate.