CHARACTERIZATION OF THE K-PG BOUNDARY FOSSIL RECORD AT “AVALON” STARKVILLE, MISSISSIPPI THROUGH A COURSE-BASED RESEARCH PROJECT

Upper Cretaceous and Lower Paleocene marine sediments in the Gulf Coastal Plain, Mississippi, USA allow detailed examination of the effect of the K-Pg boundary extinction event on shallow marine invertebrate taxa. The “Avalon” locality in Starkville, the Prairie Bluff Chalk, is interpreted as a neritic shelf where chalk deposits accumulated with limited siliciclastic input. Previous lithological, biostratigraphic, and geochemical analyses demonstrate Milankovitch climate cycles through the Prairie Bluff Chalk which indicate a depositional duration of ~300ky of the latest Maastrichtian is preserved at the Avalon locality while an estimated ~80ky of the latest Maastrichtian is absent at this section. The silty marl of the Danian Clayton Formation followed a sea level regression to shallower shelf deposits. Planktonic foraminifera biozones indicate that deposition took place over a 2My interval of the earliest Danian. These deposits do not record the immediate aftermath of the KPg boundary but more likely the longer-term rebound of the benthic fauna during the re-establishment of export productivity.

Bulk samples (1L) were collected at 0.5m intervals from 2.5 m below the KPg boundary layer to 0.45 m above. Fossil samples were extracted from the matrix and identified by undergraduate students enrolled in paleontology at San Jose State as part of a course-based research project. Students documented sedimentary characteristics, taphonomy, body fossil diversity and abundance, and trace fossil size and morphology. In the Late Maastrichtian PBC, commonly recovered species included abundant ammonoids and occasional gastropods, oysters, and ostracods. Sporadic burrows in the PBC accumulated disarticulated fish remains. Sand-filled burrows in the chalk deposits are indicative of storm events or currents that transported coarser sediment out onto the shelf. In the early Danian, gastropods, oysters, and cucullaeid bivalves were abundant. The shift in facies prevents an exact comparison of the faunal changes observed at the Avalon site but when interpreted in the broader context of shallow marine invertebrate research ongoing in the Gulf Coastal Plain, the site contributes to interpreting taxonomic and functional ecological shifts in response to disruption of primary productivity above the shallow marine shelf.