Chemostratigraphy as a Tool for Determining Depositional Ages of Metamorphosed Carbonate Rocks Prior to Supercontinent Formation

Abstract

Chemostratigraphy or chemical stratigraphy deals with the correlation of sedimentary strata based on systematic variation of a particular chemical composition with time in the history of the Earth. In particular, this method is widely used in decoding the temporal variations seen in marine sediments that are deposited uninterruptedly in deep sea or in shallow marine carbonate depositional environments. In this review, the application of strontium and carbon isotope based chemostratigraphy in marine carbonate sediments is discussed. Irrespective of post depositional geological events such as metamorphism or tectonic displacements to form Mountain chains during continental collision, chemostratigraphy helps in determining the apparent depositional ages of sedimentary rocks in the Precambrian time, where biostratigraphy is not applicable. Although carbonate rocks are vulnerable to post depositional alterations, a systematic geochemical screening can guide in identifying the best chemically preserved carbonate rocks. A novel method of using Mn/Sr ratios for determining the best estimate of strontium initial ratio for carbonate rocks is presented, on the basis of a worked example of metamorphosed carbonate rocks from the Sør Rondane Mountains in the Dronning Maud Land, East Antarctica. The future potential of chemostratigraphy in decoding the early history of the Earth is also discussed.