The evolution history of the early Eocene transient transgression in the Kuqa Depression:Evidence from strontium isotopes
Five major transgression-regression cycles during the period from Late Cretaceous to Paleogene have been identified in the Tarim Basin.The Late Paleocene-Early Eocene transgression event is the largest one among them.At present,the research on the evolution history of the early Eocene transgression in the Kuqa Depression is still relatively limited,especially has not been undertaken by means of strontium isotope of carbonate rocks.In this paper,the lithofacies characteristics and strontium isotopic compositions of carbonate rocks within the Lower Eocene evaporate section of the Xiaokuzibai profile in the western Kuqa Depression have been studied in order to explore the evolution history of the early Eocene transgression in this area.Based on the petrographic characteristics and the sedimentary sequence of evaporites,it is believed that the early Eocene climate was hot and dry,and the barrier lagoon facies were mainly developed in the Kuqa Depression.The study shows that the strontium isotopic compositions of the Lower Eocene limestone samples in the Xiaokuzibai profile vary from 0.708 627 to 0.708 909,which are slightly higher than the strontium isotopic values(0.7077-0.7078)of seawaters in the same period,but are far lower than those of terrestrial materials in the same period.Combined with the microscopic and strontium isotopic characteristics of micrite,that seawater deposits were mainly deposited in this period with a small amount of terrigenous materials,it is suggested that there was mainly seawater deposition in the area,with accompanied input of a small amount of terrestrial materials.Comparing the evolution curves of strontium and sulfur isotopic compositions of limestones in the Xiaokuzibai Formation and carbonate rocks in the Gamba area of Tibet,it is speculated that a short transgression event occurred in the Kuqa Depression in the early Eocene,and the reason for sea level change in the area may be responded to the global sea level change.
strontium isotopeKuqa depressionsea level changecarbonate rock
万方数据
维普
