PALEOGEOGRAPHIC INTERPRETATION OF THE LATE CAMBRIAN GROVELAND MINE STRATIGRAPHY, DICKINSON COUNTY, MICHIGAN

In 2010, fossilized phosphatic lingulid brachiopods were discovered in quartz arenite and shaley sandstone outcrops near the Groveland Mine, which is located near Felch, MI in Dickinson County. The sandstones are often correlated with the Cambrian Munising Formation, because their proximity to the type locality, and position within the Michigan Basin, though no formal studies have yet been conducted to correlate them. The Munising Formation is also largely unfossiliferous except for the Prosaukia Zone within the Late Cambrian Miner’s Castle Member. The assemblage within the Prosaukia Zone is typically sparse, and composed of whole or fragmented brachiopods and rare fragments of trilobites. At the Felch outcrop, the abundance of brachiopds present in strata is abruptly dense and then absent. Core samples and outcrops from the Groveland Mine contain a few trilobite fragments and a couple different (as yet) unidentified (orthoconic cephalopod-like) fossils, as well as the brachiopods. The fossil assemblage, sedimentology and stratigraphy here appear to represent an equatorial shallow marine, nearshore to transitional (deltaic) tidal-influenced environment. Paleogeographic models place this area of Michigan on the southern coast of Laurentia during the Sauk I transgression. The moderate relief of the Proterozoic basement rock in this area most likely led to shallow embayments as the Sauk Sea transgressed onto the land, accentuated by tidal ebb and flow. We attempt to paint a clearer picture of the paleogeography of this portion of Laurentia during the Late Cambrian.