Impressions of algal mats from the Middle Proterozoic Belt Supergroup, northwestern Montana, U.S.A.

Irregular, low relief bedding-plane markings which probably represent impressions of thin, wrinkled algal mats have recently been detected in mudstones from the 1100 m.y. old Snowslip Formation, Belt Supergroup, Glacier National Park, Montana. Algal-mat impressions are rarely reported from ancient strata, yet algal mats are common in certain modern environments. Originating primarily in moist settings and in relatively quiescent shallow-water settings, such structures may be of some value in interpreting ancient depositional environments.