Researchers from Nagaland University have carried out a comprehensive geological investigation of the Sylhet Limestone deposits in the Dillai Parbat area of Karbi Anglong district, Assam, shedding new light on how these rocks were formed during the Eocene epoch, around 34–56 million years ago. The findings provide important insights into the geological evolution, ancient marine environments and sedimentation history of Northeast India.
The research, conducted by Prof SK Srivastava and research scholar, Tsenchumo Lotha from the Department of Geology, adopts an integrated scientific approach that combines detailed field observations, petrographic studies and micropaleontological investigations to reconstruct the depositional history of the limestone formations.
The study has been published in the peer-reviewed Journal of Geosciences Research, which publishes original research in geology, geophysics, geochemistry, paleontology, hydrogeology, remote sensing and environmental geology.
According to the researchers, previous studies on the Sylhet Limestone were largely based on limited datasets and field observations. The latest research bridges this gap by combining field-based geological mapping with microscopic examination of rocks and fossil remains, enabling a much more comprehensive understanding of the ancient depositional environment.
During the investigation, the researchers examined different sedimentary rock formations, including limestone, shale and sandstone, along with various physical and biological sedimentary structures preserved in the field. They also analysed microscopic marine fossils known as foraminifers and studied the mineral composition of the rocks through detailed petrographic analysis.
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The findings indicate that the Dillai Parbat region was once covered by a shallow, warm tropical sea, rich in oxygen and nutrients that supported abundant marine life. Scientists believe the environment resembled a lagoon or near-shore shallow marine setting under tropical to subtropical climatic conditions.
The study further reveals that the region experienced repeated fluctuations in sea level, resulting in changing depositional environments and varying energy conditions. Geological evidence also points to the occurrence of ancient storms that left distinctive sedimentary structures preserved within the rock layers.
Besides reconstructing the ancient marine environment, the study contributes significantly to understanding carbonate sedimentation, microfossil assemblages and basin evolution in Northeast India. The findings are expected to support future geological correlation studies and basin analysis in similar geological settings across the region.
The researchers also concluded that many of the observed geological changes were influenced by tectonic movements, providing valuable evidence of how Earth’s dynamic processes shaped the region millions of years ago.
Congratulating the research team, Nagaland University Vice-Chancellor, Prof Jagadish Kumar Patnaik described the work as an important scientific contribution to understanding the geological history of Northeast India.
“I congratulate our researchers on this significant scientific contribution that enhances our understanding of the geological history of Northeast India. Such high-quality research reflects Nagaland University’s commitment to advancing knowledge through rigorous scientific inquiry and interdisciplinary collaboration. I hope this achievement will inspire our faculty and students to pursue impactful research that addresses fundamental scientific questions while contributing to national and global scholarship,” he said.
Explaining the significance of the research, Prof SK Srivastava said the team sought to understand the depositional conditions by integrating field observations with laboratory analysis.
“We attempted to understand the depositional conditions by combining field observations and laboratory analysis. The evidence indicates that the limestone was deposited in a shallow marine, warm-water environment with favourable ecological conditions for microfaunal growth,” he said.
Sharing his experience during the study, research scholar Tsenchumo Lotha said the laboratory analysis played a crucial role in interpreting the geological evidence collected during fieldwork.
“Things are not always clear when we are in the midst of fieldwork. But when we connected the same with lab results, the overall picture started becoming clearer. That process was really important for understanding the environment of deposition,” he said.
This research helped scientists to understand how these rocks were formed; learn about the ancient environment of Northeast India; and study how the Earth changed over time.
