Chapter 12 - Chemostratigraphy of the Dhosa Oolite Member (Oxfordian), Kachchh Basin, Western India: Implications for Completeness of the Stratigraphic Record and Correlation with Global Oolite Peak

Abstract

Based on bio and lithofacies characteristics and occurrences of hardground surfaces, iron-rich ooids, iron crusts, and shell lags, the Dhosa Oolite member deposited during Oxfordian in the Kachchh Basin of western India is traditionally considered to be equivalent of Fe-oolitic deposits formed as a result of eustatic sea-level maximum during Callovian-Oxfordian in southern Poland, Madagascar, France, and England. The regionally extensive and unique lithological characteristics of the Dhosa Oolite member made this member a regional marker interval. This member is also in use for correlation as marker interval in adjacent basins too. Yet, correlation of this member with regional and global equivalents is often mired with skepticism due to its condensed nature, occurrences of omission and hardground surfaces, mixed fauna typical of many biozones, and resedimented nature of sediments. In order to address this issue, this paper documents chemostratigraphic characteristics of this member to identify synchronicity of chemical signatures with regional and global signals. The geochemical profiles constructed with the present study recognized a major sea-level cycle spanning from upper part of the Dhosa Sandstone member that reached its zenith near the top of the Dhosa Oolite member. Individual short-term fluctuations represented by positive excursions of P and negative excursion of Ba were recognized within the studied sections. These excursions are regionally recognizable, and sedimentation pattern in the basin was found to be coupled with climate-sea-level fluctuations (as indicated by corresponding variations in source area weathering and detrital influx). However, correlating the Oxfordian oolite deposit of the Kachchh Basin with coinciding Fe-oolite deposits elsewhere requires adequate precautions.