The mid-Cretaceous Tres Hermanos Sandstone of Herrick (1900), later changed to the Tres Hermanos Sandstone Member of the Mancos Shale by Lee (1912), is raised in stratigraphic rank to the Tres Hermanos Formation.The Tres Hermanos Formation is a northeastwarddirected elastic wedge of nearshore marine and nonmarine rocks that was deposited in westcentral New Mexico during early and late Turonian time.This wedge, which ranges in thickness from 200 to 300 ft (61-91 m), except near its seaward extent where it grades into the Mancos Shale, conformably overlies the Rio Salado Tongue (new name) of the Mancos Shale and is conformably to disconformably overlain by the D-Cross or Pescado Tongue of the Mancos Shale.The Tres Hermanos Formation is subdivided into three members: the lower, regressive marine Atarque Sandstone Member (revised to member rank in west-central New Mexico); the medial, generally nonmarine Carthage Member (new name); and the upper, transgressive marine Fite Ranch Sandstone Member (new name).The outcrop belt of the Tres Hermanos Formation along the Rio Salado in Tps. 2 and 3 N., Rs. 5 and 6 W., Socorro County, is designated as the type area for the formation.A principal reference section for the Tres Hermanos is established in this report at Carthage in southeast Socorro County; other refer ence sections for it are established in the type area in northwest Socorro County and along Pescado Creek in southern McKinley County.The D-Cross and Pescado Tongues of the Mancos Shale represent a significant transgressive episode that separates the Tres Hermanos from the younger Gallup Sandstone.Consequently, the Tres Hermanos Formation, previously referred to as the Atarque Member of the Gallup Sandstone or as the lower Gallup, is removed from the Gallup.The Rio Salado Tongue of the Mancos Shale is defined as that part of the Mancos Shale separating the underlying Twowells Tongue of the Dakota Sandstone from the overlying Tres Hermanos Formation (or Atarque Sandstone to the southwest where the Tres Hermanos terminology is not used).In west-central New Mexico, the Rio Salado Tongue ranges in thickness from about 200 to 300 ft (6191 m) and consists of a lower calcareous shale and limestone unit and an upper noncalcareous clay-shale unit that intertongues with or grades into the overlying Tres Hermanos Formation.Within the lower unit, the Bridge Creek Limestone has been identified and given the stratigraphic rank of beds.The contacts of the Rio Salado Tongue with both the overlying and underlying rock units are conformable.

10.58799/c-185

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Stratigraphic framework of the Paleocene coal beds in the Broadus 30' x 60' Quadrangle, Powder River basin, Montana-Wyoming

M.W. McLellan Laura Biewick

A network comprised of 156 stratigraphic sections on 10 interlocking cross sections and an accompanying text show thickness, lateral extent, splitting, convergence, and regional correlations for the 16 principal coal beds, and the sandstone beds. Stratigraphic sections were prepared from field measurements and mapping supplemented by study and interpretation of geophysical logs and aerial photographs. The Sawyer coal bed, and its equivalent the Broadus coal bed, is now recognized as extending from northwest of Ashland 60 miles eastward to Broadus, Montana. Locally, just north and west of the Broadus 30' by 60' Quadrangle, it has converged with the Knobloch and Flowers-Goodale coal beds to form a 73-ft-thick coal bed.

Quadrangle

10.3133/coal119a

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