Guwahati: A team of researchers from Nagaland University has uncovered fresh clues to Northeast India’s ancient geological past, revealing that parts of present-day Assam were once submerged beneath a warm, shallow tropical sea teeming with microscopic marine life around 50 million years ago.
The findings emerge from a detailed study of the Sylhet Limestone deposits at Dillai Parbat in Karbi Anglong district, offering new insights into how these rocks were formed during the Eocene Epoch and helping scientists reconstruct the region’s prehistoric environment.
Published in the peer-reviewed Journal of Geosciences Research, the study combines field investigations with laboratory analyses, including petrography and micropaleontology, to paint a more complete picture of the ancient depositional environment than previous studies, which relied largely on field observations.
The research team found evidence that the limestone was deposited in a shallow, warm marine setting, comparable to a lagoon or near-shore tropical sea with abundant oxygen and nutrients that supported diverse microscopic marine organisms.
By examining limestone, shale and sandstone layers, sedimentary structures and fossilised foraminifers preserved within the rocks, the researchers also identified repeated fluctuations in sea level and changing energy conditions in the basin. They found geological signatures indicating that ancient storms periodically disturbed the seafloor, leaving distinctive patterns in the sediment that were later preserved as rock.
The study further suggests that tectonic movements influenced the changing depositional conditions, providing valuable information for reconstructing the geological evolution of Northeast India and improving the understanding of carbonate sedimentation in the region.
The research was carried out by Prof. S.K. Srivastava and research scholar Tsenchumo Lotha of the Department of Geology, Nagaland University.
Congratulating the researchers, Nagaland University Vice-Chancellor Prof. Jagadish Kumar Patnaik said the work represents a significant scientific contribution to understanding the geological history of Northeast India and reflects the university’s commitment to high-quality research and interdisciplinary collaboration.
Explaining the findings, Prof. Srivastava said the team combined field observations with laboratory investigations to understand the conditions under which the limestone was deposited.
“The evidence indicates that the limestone was deposited in a shallow marine, warm-water environment with favourable ecological conditions for microfaunal growth,” he said.
Lotha said the laboratory analyses helped make sense of observations 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.
Beyond reconstructing the region’s ancient coastline, the study is expected to aid future geological correlation, basin analysis and paleoenvironmental research across Northeast India, while providing new insights into how the landscape and climate have evolved over millions of years.