Paleo-plateau/-seamount Limestone of the Cambrian Accretionary Complex in the Gorny Altai Mountains, Southern Siberia

Abstract

Vendian-Cambrian Baratal limestone occurs as large allochthonous blocks in the Cambrian accretionary complex of the Gorny Altai Mountains, southern Russia. We analyzed the primary stratigraphy and depositional environments of Baratal limestone in the Kurai and Akkaya areas in the eastern part of the Gorny Altai Mountains.In the Kurai and the Akkaya areas, Baratal limestone conformably overlies basaltic greenstone. Geochemistry of this greenstone is similar to that found in modern oceanic plateau basalt or oceanic island basalt. The limestone lacks terrigeneous elastic influx. These suggest that the Baratal limestone was originally deposited on and around a plateau or seamount far from the continents in a mid-oceanic environment.Baratal limestone in the study area is lithologically divided into four types; 1) massive lime mudstone, 2) massive limestone conglomerate 3) bedded lime mudstone with slump structures, and 4) laminated lime mudstone. Massive lime mudstone contains stromatolites and ooids. This evidence suggests that the massive lime mudstone was formed in a shallowmarine environment. The massive limestone conglomerate contains angular clasts of lime mudstone, greenstone and chert. Its poorly graded and poorly sorted characteristics suggest that the limestone conglomerate was formed as debris flow deposits. Some parts of bedded lime mudstone have slump structures, and are interpreted as sliding deposits. In addition, laminated lime mudstone that shares an affinity with limestone turbidite, is associated with the massive limestone conglomerate.Sedimentary environments of these four types of limestone are inferred, respectively as follows ; massive lime mudstone may have been diposited on the top of a paleo-plateau/ -seamount, while massive limestone conglomerate, bedded lime mudstone with slump structures, and laminated lime mudstone on the slope of a paleo-plateau/-seamount.