Florida drowned sites

Why this is extraordinary

Page-Ladson is a sinkhole in the bed of the Aucilla River, about 11.5 kilometres inland from the Gulf of Mexico, under about 9 metres of water. The sink is about 60 metres across, cut into limestone, and it was not always a river. Around 14,550 calendar years ago it was a pond in the open air. A 2016 study in Science Advances, led by Jessi Halligan and Michael Waters, reports six stone artefacts of local coastal-plain chert in undisturbed sediments there, including a biface, a reworked knife, found in place. Seven radiocarbon samples from immediately beside that biface date to about 14,550 calendar years ago. The piece sat under 1.1 metres of later sediment and under a shell-rich bed dated to about 14,400. A vertical series of 24 radiocarbon samples, from above the biface to below it, falls in order. Seventy-one radiocarbon ages underpin the paper. The sea, rising at the end of the ice age, eventually pushed water and about 4 metres of sediment over the pond and left the site submerged.

A mastodon was already there. In 1993 a tusk came out of the same unit, with multiple parallel grooves across the end that had sat in the skull. The 2016 team looked again and agreed the grooves were made by people, most likely while the tusk was being pulled from its socket. They did not find cut marks on the other bones. Their sentence is that people butchered or scavenged a mastodon beside the pond. Sporormiella, a fungus that grows on dung, and the other proxies in the mud, are their case that hunters and megafauna shared this coast for about 2,000 years, until the animals drop out of the record around 12,600 calendar years ago. A university account of the project places Clovis, the fluted-point horizon long treated as the first widespread culture south of the ice, nearer 13,000 years ago. Page-Ladson is older than that placement on the 2016 clock. The site carries the name of Buddy Page, the diver who brought the sinkhole to archaeologists, and of the Ladson family, who owned the land, which is the University of Michigan’s account of how the place entered the literature.

The shelf is the other half, and it is why the pin sits in the Gulf rather than on the bridge at Lamont. At the last glacial maximum the western Florida shelf reached 185 kilometres or more beyond the modern Aucilla, at depths somewhere between 60 and 100 metres, in Michael Faught’s 2004 report. The Aucilla of that time, the PaleoAucilla, ran across a forested plain that is now Apalachee Bay. Faught’s own work followed one drowned reach of that river. Nine prehistoric sites lie 6 to 9 kilometres off the modern coast, in 4 to 6 metres of seawater, with bifaces and unifaces of late Paleoindian and early Archaic age, and later Middle Archaic material, plus terrestrial animal bone and tree stumps still in place. J&J Hunt is the most dug of them. The tools include a Suwannee point and Bolen points, types of the late Paleoindian and the early Holocene. The edges are sharp. A black stain helps a diver see them. This is not the 14,550-year pond. It is the next country out, drowned later, and it is already yielding camps.

Two other American clocks sit on land that did not drown. Paisley Caves has dated human coprolites. Meadowcroft has early hearths. Far to the north, Bluefish Caves is the Yukon argument. Page-Ladson does not borrow their dates. It has seventy-one of its own. The catch is the size of the toolkit and the size of the shelf. Six artefacts and one grooved tusk are a real association, and they are a small one. The outer shelf, 60 to 100 metres down and 185 kilometres out, is where a glacial coastline would be, and Faught’s nine sites are still in the shallows.