Lithogeochemical Characteristics and Sedimentary Environments of the Uk Formation Limestones (Upper Riphean, Southern Urals)

Abstract

Lithogeochemical characteristics of limestones of the Uk Formation (uppermost unit of the Riphean stratotype section in the Southern Urals) are considered. Data points of limestones (40 samples), accumulated on the middle and inner ramps have a quite contrasting distribution on the (La/Sm)_sh, (La/Yb)_sh, and (Sm/Yb)_sh diagrams based on the systematization of numerous analytical data on carbonate sequences in various plate-tectonic (paleogeographic in the broad sense) environments, according to (Zhang et al., 2017). The data points of limestones of the Medved Member of the Uk Formation deposited on the middle ramp, according to a detailed lithofacies analysis, are shifted in these diagrams toward the field of limestones of open ocean, whereas limestones of the Manaysu Member (inner ramp) correspond to the near-coastal deposits in terms of their geochemical characteristics. Thus, the geochemical characteristics of the Uk limestones generally confirm the conclusions based previous reconstructions. In the described example, the distribution of trace elements in the inner ramp limestones was controlled apparently by the fine-grained aluminosiliciclastic material transported from the continent, whereas influence of the open ocean environment is already perceptible in geochemical features of the middle ramp limestones deposited in the deeper sea.