Chirananda De

Crabs on the Sundarban sand

The work began on the beaches of the western Sundarban, as a research fellow at Jadavpur University under Professor S. K. Bakshi. The question was simple and turned out to be a career: what do the burrows of living crabs tell you about the ground they dig in? His first paper, in 1980, described the workings of beach crabs on the Bengal delta. The habit of watching living animals make traces, and then looking for the same traces in old rock, never left him.

Ladakh, Gujarat, and the coalfields

He joined the Geological Survey of India in 1980 and was sent first to the Ladakh Project in Kashmir, mapping in the Zanskar Himalaya. There he found the hydrozoan Burgundia and used trace fossils to place the boundary between the Precambrian and the Cambrian in the Liddar valley. Six years in Gujarat followed, working the Quaternary deposits of the Banas river basin, where he developed a paraffin-wax method for casting burrows in loose sediment and began to use burrow orientation to find buried channels.

In the Gondwana coalfields of Orissa and Bihar he read marine signatures where none had been expected: stromatolites with trapped cyanophytes in the Talchir limestones, Skolithos burrows in the Barakar, and the oldest charophytes then known from India.

The Vindhyan years

From the late 1990s his field seasons went to the Bhander Group of the Vindhyan Supergroup in eastern Madhya Pradesh, rocks laid down before there were animals with hard parts. On bedding planes there he recorded impressions he interpreted as Ediacaran organisms, the first such assemblage reported from the Vindhyans, published in the Journal of Asian Earth Sciences in 2003 and 2006 and taken up in an international review of Ediacaran biogeography.

In the same rocks he found something rarer still: a surface pitted with the craters of raindrops, preserved from a tidal coast more than a billion years old. The finding, published in Current Science in 2001, was picked up by the journal Science, drew a live BBC interview, and entered the 2005 Guinness World Records as the oldest known rain imprints.

Burrows put to work

Alongside deep time, he kept returning to the Bay of Bengal coast, and there he made ichnology useful. The tubes of the worm Diopatra, built differently above and below the sand, gave a way to measure a year's erosion or deposition on a beach in an afternoon. The mud volcanoes of the fiddler crab Uca marked the segments of shore that were least stable. Crab burrows at Digha explained why a resort beach was eroding. In drought-hit Banaskantha, oriented crustacean burrows pointed to buried aquifers.

He gathered this work into a biophysical model of beach-crab burrowing and, after retirement, into a Springer monograph on the ichnology of the Sundarban mangroves. His last posting was as Director of the Palaeontology Division in Jaipur, where with colleagues he reported Ediacaran and early Cambrian fossils from the Marwar Supergroup of Rajasthan.