Soft Tissue Diagenesis Project
Diane Burns, Ph.D.
During the Late Maastrichtian, a back-barrier bay or lagoon on the Dakota Isthmus was the site of an extensive intertidal, muddy sand flat occupied by a population of the deep-burrowing pelecypod, Panopea occidentalis (Meek and Hayden). This population was covered by a storm-generated overwash fan trapping these large, poorly mobile, clams in their burrows by a sheet of impenetrable sand. The population dynamics of these in situ clams have been studied by Palmateer (1996) and the taphonomy was reported by Erickson and Palmateer (1996). More than 60 individuals were collected in living position, most encased in cylindrical, iron-rich concretions representing the deep burrows maintained by each clam into which storm-generated sands had infiltrated.
Implications of the burial scenario include recognition that tissues of these large bivalves, once expired, gravitated to the bottom half of each vertically oriented specimen and were infiltrated by the entombing sediments. Over twenty years since being collected, a pattern of museum weathering has been recognized in several specimens and suggests localized early mineralization within confines of the valves. In particular, it appears that reducing conditions were created during decay of the tissue creating diagenesis of pyrite or marcasite that subsequently became unstable reacting with and damaging the shell from the inside out in stereotypical locations on the valves. Encasing sandstone is grain supported fine and medium quartz sand, whereas the sand filling the interior is matrix supported often with angular quartz grains floating in a clay(?) matrix which includes the cement.
This project is an on-going effort collaborative effort between myself and Dr. J. Mark Erickson (St. Lawrence University) to understand the diagenetic process that has occurred since burial to present-day. Questions that are being investigated are:
1. What chemical signatures are preserved throughout the fabric of a cross-section of the specimens?
2. What is the composition of the sediments currently encasing the specimens?
3. How might minerals/elements have migrated throughout the specimen during the diagenetic process?
4. What are the implications for changing influences between fresh and saline water infiltrations?
For more information about this project, please contact Diane Burns at email@example.com.