Lithogeochemical characteristics and sedimentary environments of the Uk Formation limestones (upper Riphean, Southern Urals)

Abstract

The lithogeochemical characteristics of the Uk Formation limestones (Uppermost Unit of the Riphean stratotype section in the Southern Urals) are considered. Data points of limestones (40 samples) accumulated in the middle and inner ramp environments have a quite contrasting distribution on diagrams with parameters (La/Sm)sh, (La/Yb)sh and (Sm/Yb)sh, proposed based on the systematization of a significant amount of analytical data on carbonate sequences formed in various platetectonic (in the broad sense of the word, paleogeographic) environments (according to [Zhang et al., 2017]) was established. The data points of the limestones of the Medved Member of the Uk Formation, which was formed, according to a detailed lithological-facies analysis, in the middle ramp environment, in the indicated diagrams located towards the field of limestones of the open ocean, while the limestones of the Manaysu Member (inner ramp deposits) in their geochemical characteristics are more consistent with the limestones of the near-coastal environments. Thus, the geochemical characteristics of the Uk Formation limestones seem to confirm the conclusions of the previous reconstructions. It has been suggested that in the example we described, the distribution of trace elements in the inner ramp limestones was apparently controlled by fine-grained siliciclastic material coming from the continent, while in the geochemical features of deeper-sea middle ramp limestones the influence of the open ocean environment is already perceptible.