LITTLE BIGHORN (TOURNASIAN) TO KEOKUK (VISEAN) SEDIMENTATION PATTERNS OF THE MCELHINNY MODEL (1961) OF NORTH AND SOUTH AMERICA

Sedimentation started in the seaway with a thin quartzose sand and deepened to silty limestone/mudstone cycles up to a meter thick and cherty. The inner seaway built up from cherty wackestones and packstones. Thin cherty units of mudstone, wackestone and packstone followed a thin basal fossiliferous unit on the platform.

After the Scalion member, Stanton (1958) shows in Manitoba sea level fell, exposing the platform to erosion. Four cycles starting with shale of a glacial period at the base and oolite lentile from the warm highstand on top. A ravinement surface on cycle 4 marks the withdrawal of the sea and start of siphonodellid extinction up to a thin glauconitic layer on a ravinement below the Northville member. The Osage begins with Gnathodus semiglauber conodonts Thompson (1969) of the Pierson member and continues with the Rosalea and Fern Glen. Three cycles with a silty base, very thin white ash and packstone are quite widespread, traceable from West Virginia to Alberta and Patagonia. Another marker bed occurs in the upper Fern Glen. The Dolbee Creek member has 3 cycles with crinoidal-oolitic caps. The White Ledge marker bed caps the member. The Haight Creek member base is glauconitic with "bone beds" and a "soft" cap. Above the lower Haight Creek has 3 coarse units with thin silty partings. A coarse Cap marker is 1 meter above. The upper Haight Creek also has 3 coarse bands with partings. The CF/HC marker is a coarse crinoidal bed between two silty dolomite beds.

The Cedar Fork member is the Sm-5 marker of bryo-oolitic grainstone at the base, a "BluBand" (glauconite) in the middle and 3 coarse units with 2 partings in the upper Cedar Fork. Partings and units are traceable from Alberta to Arizona, Arizona to Missouri, and St. Marys, KY to Pound Gap, KY. A ravinement marks the top. Visean conodonts Gnathodus texanus occurs in the Keokuk. The 3 Keokuk markers occur at Cadomin, Alberta, Pound Gap, KY and Patagonia, Argentina. The 3rd, and top marker, has cobbles and oolitic limestone,(Short Creek) deposited at the shelf margin by turbulent tide currents created by tilt of the Earth's axis. As time passed the outer seaway became more orogenic and structurally active.