Type sections and stratigraphy of the members of the Blackleaf and Marias River formations (Cretaceous) of the Sweetgrass arch, Montana

Integrating 40Ar/39Ar, U-Pb, and astronomical clocks in the Cretaceous Niobrara Formation, Western Interior Basin, USA

“…(1-4, 6-9) where most ash beds analyzed in this study were sampled (ashes from two biozones were sampled elsewhere, at sites 5, 10, and 11); (2) Montana measured sections of the Kevin and Ferdig Members of the Marias River Shale (squares), based on Cobban et al (1976); (3) Libsack and Aristocrat Angus boreholes in Colorado (circle with cross-hairs, representing location of both cores, drilled within 5 km of each other); and (4) measured section of the Niobrara Formation (square) near Pueblo, Colorado, based on Scott and Cobban (1964). The locality numbering scheme begins with the uppermost biozone and increases with age and stratigraphic depth; numbered ash layers were sampled within corresponding ammonite biozones, originally by Bill Cobban and colleagues (including Al Merewether and Neil Landman).…”

Chapter 1: Integrated, High-Resolution Allostratigraphic, Biostratigraphic and Carbon-Isotope Correlation of Coniacian Strata (Upper Cretaceous), Western Alberta and Northern Montana

“…A change of lithostratigraphic terminology occurs at the Canada-U.S. border: rocks of the Cardium and Wapiabi formations in Alberta being broadly correlative with the Ferdig and Kevin members of the Marias River Formation in Montana (Cobban et al, 1976;Nielsen et al, 2003;figs. 2, 3; figs.…”

“…This bed lies at, or just above, the boundary between middle and upper Coniacian strata. A second bed of green-stained phosphate nodules, some of which are bivalve steinkerns, is located 3.5 m above the MacGowan Bed at the Type Section of the Kevin Member (Bed 108 of Cobban et al, 1976). Cobban et al (2005) speculated that the MacGowan Bed in Montana might be correlative with the erosion surface documented beneath the Bad Heart Formation in Alberta, 850 km to the NW Donaldson et al, 1998Donaldson et al, , 1999.…”

“…In Montana, Cobban et al (1976) Cobban et al, 1976) that, because it was so distinctive and widespread, was named by Cobban et al (1959) the MacGowan Concretionary Bed. The bed contains small, wellrounded chert pebbles as well as reworked phosphate nodules and molluscan fossils.…”

Rocks and mineral resources of the Wolf Creek area, Lewis and Clark and Cascade counties, Montana

“…It is divided into a lower unit, the Blackleaf Formation, composed of three members, and an upper unit, the Marias River Shale, composed of four members. These units correspond to subdivisions of the Colorado Group on the Sweetgrass arch in western Montana (Cobban and others, 1959;1976). BLACKLEAF FORMATION From the base upward, the Blackleaf Formation is composed of the Flood, Taft Hill, and Vaughn Members.…”