The first week of excavations and coring are finished at Bayou Grand Caillou and we’ve had quite a week! Although the heat and mosquitoes are difficult to manage, the site itself is in trees (and poison ivy), and working in the shade isn’t too bad. Our work is directed at understanding how the Mississippi River builds land and after that land forms, when do people come and live (and build villages and mounds) on these deltaic landscapes.
The big mound at Bayou Grand Caillou, its about 6 meters tall and in really excellent condition. Unlike many of the other mounds around coastal Louisiana, this one is really well preserved, many thanks to Westerfeldt Properties and the United Houma Nation!
This first week, we have opened up two excavation units on the big mound and made six bore holes (manually of course!) into the surrounding landscape (and one into the big mound). Many thanks for volunteers from Tulane and Macalester for helping with this research and work!
Our units are located on the mound summit and the mound flank and they are designed to help us understand more about mound construction and the relationship between the mound and the prehistoric land surface on which the mound was built. As of right now, the unit on top of the mound has helped us to define how the last mound stage was built and the kinds of soil present on top of the penultimate mound stage – unfortunately for us, the penultimate mound stage is about a meter of clay, which we absolutely won’t be excavating into (because clay is hard to dig)! The picture below shows (from right to left) a brown silty clay loam that is part of the very last mound building stage, and the soils to the left (the dark, smeared soil) is pretty much just clay. The Oakfield coring device is a great tool for taking a quick look at the underlying sediments in our summit unit – we also found the clay soils all over the mound summit through shovel testing, and decided that the clay stage must underlie the whole mound and really is a stage, rather than a thin cap.
CLAY. And lots of it.
So we also started excavating on the flank of the mound, and I’ll post up some pictures later this week, but we went through final stage construction (mostly just slope wash), and found what might comprise the final mound stage, based on the clays present. The soils on the slope below the surface are not nearly as clayey as on the summit, but perhaps they used different soils around the slopes. We did find the remains of an ancient midden – I don’t have too many pictures of it right now, but we did find some cool Plaquemine pottery, including a L’Eau Noir Incised rim sherd (picture forthcoming), which generally dates to around AD 1200 to 1350 in the Natchez Bluffs area but might be a later component this far south.
Haley Holt Mehta taking a break from writing her dissertation to excavate, thank you!
The picture below shows Liz Chamberlain, co-principal investigator and doctoral student in Earth and Environment Sciences at Tulane University, and John Bridgeman, MA student at Tulane in the same department, auguring a 4 cm diameter core into part of the mound. This is a minimally intrusive way to study mound construction and the relationship between the mound and the natural surface (and environment) on which the mound was built. Liz’ specialty in in deltaic environments and OSL and she’ll be working to identify the geomorphology of the specific landform and how we might date the landform/mound to get a better handle on the chronology of the site. While we are still working up results , we think that the big mound may have been constructed on an area that was forest (not marsh) and that was a relatively sheltered basin when Bayou Lafourche became active and sub-aerial prior to mound construction.
Liz and John rocking the Dutch coring device – so many times better than an Oakfield.
Seriously, the best soils ever! Liz and John found this on the last day – it shows a clear break between mound fill (brown), preserved organic material from the forest floor before the mound was built, and then natural crevasse sediments underneath it. The organic material likely preserved because the clays on top, which created an anoxic environment below the water line.
Liz explaining coring and soils to visitors from Tulane and the Center for the Study of the Gulf South
So we’ll keep at it this week, looking for pottery and deposits that will help us understand the people that lived at Bayou Grand Caillou and what the natural environment was life before and during settlement at the mound and in the region.
More to come !! And many many thanks to Rebecca Snedeker for coming to visit, and Arielle Pentes for taking such wonderful pictures! Thanks also to Rebecca and the Center for the Study of the Gulf at Tulane University for funding this project! And many thanks also to the landowners for supporting our work and letting us dig at the site.