TRACE FOSSILS IN THE LATE CRETACEOUS COLERAINE FORMATION; HILL ANNEX MINE STATE PARK, CALUMET, MINNESOTA

Hill Annex Mine State Park in Calumet, Minnesota has produced a large collection of trace fossils from the Coleraine Formation that has not been well reported yet. The Coleraine Formation is made up of conglomerates, shales, and sandstones that are considered Cenomanian to Turonian (100 – 90 Ma) in age. The paleo environment for the Coleraine Formation is characterized as a sequence of transgressions and regressions of the Western Interior Sea. The initial reports of trace fossils in the Coleraine Formation were made by Stauffer and Thiel in their 1933 paper on Limestones and Marls of Minnesota which mentioned Ophiomorpha burrows. Bergquist reported traces of a marine annelid worm known as Serpula sp. on bivalve steinkerns and oyster shells and Teredolites sp. in 1944. The primary trace fossils found at Hill Annex Mine State Park are from Ophiomorpha, Thalassinoides tracemakers, and small unidentified burrows infills. Borings in fossilized wood also show evidence of Teredolites longissimus and Teredolites clavatus. Additional trace fossils that have been collected at the site include shark coprolite and a possible tetrapod burrow.