ABSTRACT

The lateral distribution of evaporite facies, thickness, and limestone/carbonate ratio can be used to reconstruct the paleogeography and mode of deposition of evaporite rocks. Distribution of the evaporite facies, developed theoretically for a hypothetical model basin from chemical data for the evaporation of seawater and for reflux equilibrium show that:

1.--The facies pattern is arcuate and convex about an inlet,

2.--The expected section is thickest where halite is deposited in the center of the basin near the edge of the influx tongue and thinnest where carbonate minerals are deposited around the edge of the basin,

3.--The limestone/carbonate ratio should be highest in the path of influx flow near the inlet where normal marine conditions project into the evaporite basin.

Facies analysis of the Upper Silurian Salina Formation in Michigan, Ontario, Ohio, and Pennsylvania indicate that

1.--The Michigan Basin and the Ohio-New York Basin were separate evaporite basins, connected across the Findley Arch through the Chatham Sag,

2.--The principal inlet to the salt basins was in the vicinity of Georgian Bay in Ontario, which connected the Michigan Basin with the Arctic seaway,

3.--A subsidiary channel flowed northward into the Michigan Basin through an inlet in the vicinity of Clinton, Michigan, connecting the basin with the southern Appalachian seaway principally during middle Salina time,

4.--A persistent river flowed eastward into the Michigan Basin in the vicinity of Ludington, Michigan.