Contributions to Geology 27.1

Presence of rounded boulders and large cobbles at base of White River Group (Oligocene) strata in southwest North Dakota and northwest South Dakota

E. N. CLAUSEN Division of Science, Minot State University, Minot, ND 58701

Pages
1-6

Keywords
White River Group, Dakota, conglomerates, channels

Abstract
Small rounded boulders and large cobbles of granite and quartzite are in talus below White River Group (Oligocene) conglomerates in southwest North Dakota and northwest South Dakota. These large clasts are present at White Butte-Chalky Buttes, the Rainy Buttes, and the Little Badlands in North Dakota and at Reva Gap (Slim Buttes) and the Short Pine Hills in South Dakota. Small rounded cobbles are common and are contained within the conglomerates. The Black Hills are ruled out as a source area because 1. the largest clasts are in North Dakota, 2. the greatest abundance of large clasts is in North Dakota, and 3. the North Dakota localities contain rock types which can be traced to the Yellowstone River valley and then upstream to the Beartooth Mountains. Localities containing the large clasts, plus the Killdeer Mountains in North Dakota, record six channels of a former river system. This river system originated in the headwaters region of the present-day Yellowstone River, closely followed the route of the modern Yellowstone River across Montana, and then flowed east and southeast into southwest North Dakota and northwest South Dakota. This river system transported boulders and large cobbles 400 kilometers, cut deep narrow valleys in the western Dakotas, and deposited the basal White River Group conglomerates.

Distribution of the Planomalinidae and the Schackoinidae in Upper Cretaceous strata of the Western Interior

WILLIAM E. FRERICHS Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071

Pages
7-14

Keywords
Western Interior, Cretaceous, planktic, foraminifera, Planomalinidae

Abstract
More than seventy species of planktic foraminifera have been identified from Upper Cretaceous strata of the Western Interior. Ten species of the Planomalinidae, with representatives found from the late Cenomanian to late Maastrichtian, and two species of the Schackoinidae, with a range from late Cenomanian to latest Campanian, have been reported from the Western Interior. Species of the Planomalinidae are very useful in Western Interior biostratigraphy, particularly in the Santonian and Campanian stages.

Stratigraphic occurrence of rodents and lagomorphs in the Orella Member, Brule Formation (Oligocene), northwestern Nebraska

WILLIAM W. KORTH Department of Geological Sciences, University of Rochester, Rochester, NY 14627

Pages
15-20

Keywords
Orella, Brule, Nebraska, rodents, lagomorphs, Chandronian, entoptychine, geomyoids

Abstract
Based on extensive collections of rodents and lagomorphs the Orella Member of the Brule Formation in Sioux County, Nebraska (the type area) can be divided into three distinct biostratigraphic units. The lowest (Palaeolagus hemirhizis zone) is distinguished by the first occurrence of many characteristic Orellan species and several species that are intermediate between the typical Orellan and Chadronian species. The middle (Eumys elegans zone) is characterized by the first occurrence of several, more typical, Orellan species such as Adjidaumo minutus, Eumys elegans and Palaeolagus haydeni. The upper (Diplolophus insolens zone) is marked by the first occurrence of at least nine new species, including the earliest occurrence of entoptychine and florentiamyid geomyoids.

Two previously described Orellan faunas, the Cedar Creek fauna from Colorado and the Cedar Ridge fauna from Wyoming, correlate with the Diplolophus insolens zone. Orellan faunas from the Slim Buttes area of South Dakota may correlate with both the middle and upper parts of the Orella Member in Nebraska.

Diagenetic pathways of sandstone and shale sequences

RONALD C. SURDAM                Department of Geology and Geophysics, University of Wyoming, P. O. Box 3006, Laramie, WY 82071
DONALD B. MacGOWAN and THOMAS L. DUNN Enhanced Oil Recovery Institute, University of Wyoming, Laramie, WY 82071

Pages
21-32

Keywords
diagenesis, sandstone, shale, reduction, alteration, elements

Abstract
Factors governing the evolutionary path that sandstone and shale sequences follow during burial diagenesis include: provenance and depositionally-controlled compositional and textural elements; near-surface redox reactions; organic-inorganic interactions within the zone of intense diagenesis; deep diagenetic reactions including abiotic, thermal sulfate reduction, carbonate mineral alteration and quartz cementation; and the potential for meteoric influx and renewal of near surface processes due to uplift, exposure, and/or base level fluctuation. These factors are presented as divides on a diagenetic pathway diagram (see Plate 1). This pathway diagram is useful in understanding the observed or anticipated diagenetic pathways of sandstone and shale sequences.

Stratigraphy, sedimentary structures, and petrology of the Middle Proterozoic Castner Marble, Franklin Mountains, far West Texas

WILLIAM F. THOMANN Department of Geosciences, Texas A&I University, Kingsville, TX 78363
ROBIN L. HOFFER Department of Geological Sciences, University of Texas at El Paso, El Paso, TX 79968

Pages
33-39

Keywords
Castner, Texas, Proterozoic, stromatolites, metamorphism, marine

Abstract
The Middle Proterozoic Castner Marble is the oldest stratigraphic unit in the Franklin Mountains, West Texas, and occurs as roof pendants in granite plutons of the Proterozoic Red Bluff Granite complex. Contact metamorphism due to the granite intrusions recrystallized the limestone and dolomite beds to marble, and other interbedded units to hornfels. The Castner Marble exhibits well preserved original layers, structures, and algal stromatolites despite contact metamorphism from the hornblende-hornfels to the pyroxene-hornfels facies. Prior to metamorphism, the formation is interpreted to have been a siliceous, dolomitic limestone with interbedded marl and/or shale. The Castner Marble is part of a regressive sequence of strata deposited in a shallow, subtidal to intertidal marine environment. The Castner Marble may be correlative to the Proterozoic Allamore Formation, Van Horn area, Texas. The tectonic setting was probably a back-arc marginal basin.