Complex characteristics of suevites at the B. Vanuyta river (Kara astrobleme, Russia)

Abstract

Research subject. Suevites from the eastern sector of the Kara astrobleme, located in the basin of the Bolshaya Vanuyta river. Aim. To identify the suevitic type and to clarify the facial features of the suevites from the B. Vanuyta River. Materials. Hand-size samples of suevites collecteed in the basins of B. Vanuyta, Anaroga, Kara, and Sopchayu rivers, as well as samples of siltstones collected outside the Kara crater (rivers Halmeryu, Sayakha, Putyu, Anaroga and the creek Lavovyi). The samples were used for preparing polished thin sections and powder specimens for analytical works. Methods. Field observations, optical and electron scanning microscopy, and silicate analysis by the wet chemical method. Results and conclusions. The structural-textural and petrochemical features of the matrix, fragments of impact glasses, and lithoclasts of suevites from the B. Vanuyta river were characterized. The suevite matrix was found to exhibit an intensely sintered character and to be presented by feldspar, quartz, calcite, chlorite, muscovite, glauconite, and titanite. Lithoclasts include siltstones, sandstones, limestones, mudstones, and shales. Vitroclasts are characterized by angular and irregular morphology with different border patterns, and spotted, fluid, and porous textures. The similarity of the chemical composition of siltstone clusters and similar target rocks confirms the genetic relationship and the leading role of this type of target rocks in the formation of the studied suevites. The proximity in the composition of the impact glasses of the studied suevites and the glasses of type I and II suevites indicates the formation of suevite vitroclasts in the river B. Vanuyta by a similar protolith – siltstones and a clay component of the limestones. The matrix lithification character, morphology and nature of the vitroclast outlines indicate that the suevites from the B. Vanuyta river are the rocks of an aerodynamic facies formed under relatively high-temperature conditions, which structurally lie at the lower part of the detrital impactites sequence of the aerodynamic facies. The studied rocks are close to the type I suevites by the composition of the protolith and differ in the conditions of their formation. With the type II suevites, they have similar facies characteristics, but differ in the composition of the target rocks fragments. It is determined that the leading factor in the typification of suevites from the Kara astrobleme is the chemical composition, at the same time, the types can be subdivided more fractionally based on the specifics of the facies environments of their formation.