Paper No. 26-31
Presentation Time: 1:30 PM-5:30 PM
VERTEBRATE MICROFOSSILS FROM THE SHIELD WOLF QUARRY, LANCE FORMATION (MAASTRICHTIAN), CARBON COUNTY, MT, USA
The Late Cretaceous (Maastrichtian) Lance Formation outcrops from central North Dakota to western Montana. Coarse siliciclastic and calcritic sandstone pebbles were surface collected by New Jersey State Museum (NJSM) staff from the Shield Wolf Quarry (SWQ) in Carbon County of south-central Montana in summer 2014. In spring 2016 Temple University was tasked to devise an extraction protocol to remove and prepare microfossils from the sandstone matrix in order to investigate SWQ fossil productivity and establish a standard to facilitate fossil extraction in future collections from the locality. Siliciclastic matrix was weighed in increments of 25 to 40 grams, placed into plastic beakers and dissolved with .15M acetic acid solution for seven days to remove calcritic cement. Sandstone pieces were then manually washed with water using sieves of sizes 5, 10, 35, 60, 120 and 230 mesh to further separate sediment from microfossils. Matrix and fossils were dried in a lab oven. Matrix in each dried sieve was handpicked under a binocular microscope. Temple University recovered 1.18% fossil material by weight out of 3053 grams of matrix collected. Vertebrate microfossils were identified to the most specific taxonomic level possible, usually to the family or genus level. To date 593 disarticulated vertebrate microfossils have been extracted of which 73.5% were identifiable. More material remains to be analyzed. 75% of recovered identifiable taxa were testudines, lepisosteiforms (gars) and crocodilians. Based on the matrix lithology, the high number of aquatic and semi-aquatic taxa identified, and the disarticulation of fossils, the depositional environment is interpreted as a meandering fluvial system. Conception of this extraction protocol and initial results found that SWQ is a highly productive microvertebrate locality suitable for future excavations by NJSM.