THE SECOND EXTINCTION OF THE LATE CRETACEOUS COLERAINE FORMATION (CENOMANIAN) AT THE HILL-ANNEX MINE, CALUMET, MINNESOTA

The Hill-Annex Mine in the Mesabi Iron Range District of Northern Minnesota located in Calumet, Minnesota is a source of abundant marine vertebrate and invertebrate fossils from the Coleraine Formation (Late Cretaceous; Cenomanian) that were collected in-situ in its early history and since 1916 from spoil dumps in and near the mine. These fossils include abundant shark and ray teeth, plesiosaur teeth and vertebrae, crocodilian post-cranial elements, turtles, pycnodont and other fishes and dinosaurian material. Early geological surveys and investigations provide stratigraphic records and details of the Cretaceous marine deposits in and around the Hill-Annex Mine ranging in thickness from 10-22 meters. Ore production ceased in 1978 and the water table began to rise in the 400 foot deep mine pit. This locality is one of the last remaining sites where the Coleraine Formation can be studied and documented in-situ, as nearly all other Cretaceous localities along the Mesabi District are mined out or are underwater. Several areas of the Hill-Annex Mine previously accessible for study to the authors since 2009 are also now underwater negating further investigation.

In 2014 the Hill-Annex Paleontology Project (HAPP) began to document the stratigraphy of the Coleraine Formation in the mine and collect specimens for further research ahead of the rising water levels. By late spring of 2019 the last available exposure of the Cretaceous deposits in Northern Minnesota will be underwater and lost to science. The current water level as of September 2018 has covered the Cretaceous sediments to within 0.5 meters of the uppermost surface just below the glacial drift and will cause a catastrophic collapse of the mine walls and the available road access. Many important specimens and records are located in the Hill-Annex Mine Clubhouse museum which is now 29 meters from the current edge of the mine, previously 100 meters from the mine edge in 2010 and are now at risk as well. Efforts need to be made to preserve these significant historical collections currently housed in this museum before they too are lost to science.