New Mexico Geological Society Annual Spring Meeting — Abstracts

Fossil corals are extremely rare in the Upper Cretaceous deposits of the Western Interior epicontinental seaway, with less than 10 documented reports in the published literature. We add to this record an occurrence of the ahermatypic coral Archohelia dartoni Wells from Mescal Canyon in the northern Caballo Mountains of Sierra County, New Mexico. The coral fossils occur at a single horizon over about one km of strike east of the creek in the W1I2, sec. 36, T13S, R3W. The fossiliferous horizon is in the Rio Salado Tongue of the Mancos Shale 30 m below the base of the Atarque Sandstone and thus is of middle Turonian age. The corals display features characteristic of Archohelia dartoni, including circular individual branches with persistent axial corallites and small, circular corallites that branch at right angles from the axial corallite and ascend the branch in spirals. The coral fossils are Isolated and broken branches that occur in lenticular masses of sedimentary breccia up to 100 cm long and as much as 25 cm thick. Coral branches are concentrated near the top of each breccia mass and show no preferred orientation. Clearly, these corals are not an in situ thicket but represent reworked and redeposited debris, probably reflecting a Turonian storm event.