Sr Chemostratigrphy, δ~(13)C, and δ~(18)O of Rocks in the Crimean Carbonate Platform (Late Jurassic, Northern Peri-Tethys)

摘要

The paper presents the results of study of the Sr, C, and O isotope compositions in Upper Jurassic carbonate rocks of the Baidar Valley and Demerdzhi Plateau in the Crimean Mountains represented by different facies of the carbonate platform at the northern active margin of the Tethys. The Sr-87/Sr-86 value in them varies from 0.70699 to 0.70728. Based on the Sr chemostratigraphic correlation, the age of massive and layered limestones in the western part of the Ai-Petri and Baidar yailas (pastures) is estimated as late Kimmeridgian-early Tithonian, whereas the age of flyschoids of the Baidar Valley are estimated as late Tithonian-early Berriasian. The nearly synchronous formation of carbonate breccias of the Baidar Valley and Demerdzhi Plateau in late Tithonian-early Berriasian is substantiated. A summary section of Upper Jurassic rocks is compiled based on the Sr chemostratigraphic data. It has been established that delta O-18 values in the studied carbonate sediments vary from -2.9 to 1.3 parts per thousand (V-PDB). At the same time, shallow-water sediments in the internal part and the edge of the Crimean carbonate platform are depleted in O-18 (-2.9 to +0.1 parts per thousand) relative to sediments on the slope and foothill (-0.5 to +1.3 parts per thousand). It is demonstrated that delta C-13 values do not depend on the facies properties and decrease in younger carbonate sediments from 3-3.5 parts per thousand to 1-1.5 parts per thousand in line with the Late Jurassic general trend. The delta C-13 values obtained for the Crimean carbonate platform turned out to be 0.5-1 parts per thousand higher than the values typical of the deep-water marine setting at the western margin of the Tethys. These discrepancies are likely related to peculiarities of water circulation and high bioproductivity in marine waters of the northern Peri-Tethys.