Contributions to Geology 32.2   

Stratigraphic patterns and depositional environments in the Huesos Member (new lithostratigraphic unit) of the Palm Spring Formation of southern California              

MICHAEL L. CASSILIANO Department of Geology and Geophysics, The University of Wyoming, Laramie, Wyoming 82071-3006

Pages
133-157

Keywords
Stratigraphic patterns and depositional environments in the Huesos Member (new lithostratigraphic unit) of the Palm Spring Formation of southern California  

Abstract
The Huesos Member is proposed as a new lithostratigraphic unit for upper parts of the Palm Spring Formation in the Fish Creek-Vallecito Creek area of the Salton Trough, southern California. The Huesos Member is significant because it records the post-Colorado River history of this part of the Salton Trough, has produced the vast majority of vertebrate fossils in the Salton Trough, contains the Plio-Pleistocene boundary, and is a strong candidate for the Blancan-Irvingtonian bound-ary stratotype. Rocks of the Huesos Member are predominantly sandstone, silty sandstone, and siltstone. Texture, fabric, flu-vial architecture, and stratigraphic relationships suggest that the Huesos Member represents deposits of a shallow, braided, bedload stream system that formed as the basinward extension of a conglomeratic, basin-margin bajada. Deposition was mainly by unchannelized sheetflow, rather than by active channel migration and reworking of older deposits. The strati-graphic pattern of the Huesos Member consists of three packages of strata: (1) sequences of alternating beds of sandstone and siltstone that represent "normal" deposition; (2) sequences of very coarse-grained sandstone that grade upward to siltstone, representing geologically instantaneous depositional events; and (3) thick beds of siltstone or claystone that represent primarily alluvial overbank deposits. Evaluation of stratigraphic patterns within paleomagnetic subchrons shows that "normal" sedimentation events dominated Huesos deposition, that sediment accumulation rates decreased with time, and that sediment accumulation rates resulted in continuous deposition.

Soils and late Pleistocene-Holocene environments of the Sister Hill archeological site near Buffalo, Wyoming

RICHARD G. REIDER Department of Geography, The University of Wyoming, Laramie, Wyoming 82071-3371

Pages
117-127

Keywords
paleosol, Kaycee, Pleistocene, Holocene, Neoglacial

Abstract
Aquoll soil development at the Sister's Hill archeological site evidences high water table conditions in the late Pleistocene in association with Hell Gap Paleo-Indian occupation (c. 10,000 B.P.) of the Bull Creek arroyo. This was followed by well-drained, drier conditions in Altithermal time as marked by a strongly calcareous paleosol on gravelly late Pleistocene sediments which resembles a Calciustoll. Numerous weak, buried Fluvents in the Kaycee Formation characterize Neoglacial soil formation comprising the Kaycee terrace which indicate periodically brief floodplain stability between episodes of progressive overbank deposition. This Neoglacial sequence is capped by a strongly developed, clay-rich, calcareous soil (Argiustoll) at the surface of the Kaycee terrace. Weak development is also characteristic of Neoglacial soil formation in association with younger Moorcroft and Lightning terraces.

Faulting in Steamboat Butte and Pilot Butte anticlines, west-central Wyoming: a review

D. L. BLACKSTONE, JR. Department of Geology and Geophysics, The University of Wyoming, Laramie, Wyoming 82071-3006

Pages
159-180

Keywords
Faulting in Steamboat Butte and Pilot Butte anticlines, west-central Wyoming: a review

Abstract
Steamboat Butte and Pilot Butte anticlines are large, asymmetric folds bounded by east-dipping reverse faults that root in Precambrian basement. Displacement on the bounding faults is approximately 1,500 ft (457m). Reverse faults of lesser displacement parallel the major fault. An unusual out-of-the-syncline, east-dipping thrust fault exists on the northeast flank of Pilot Butte anticline. A major, down-to-the-west normal fault on the west flank of Steamboat Butte anticline postdates the Eocene Wind River Formation. No other major normal fault is known in this area. Production of hydrocarbons is limited to the hanging wall of the major reverse fault.

Neogene normal faulting superposed on a Laramide uplift: Medicine Bow Mountains, Sierra Madre, and intervening Saratoga Valley, Wyoming and Colorado

BRAINERD MEARS, JR. Department of Geology and Geophysics, The University of Wyoming, Laramie, Wyoming 82071-3006

Pages
181-185

Keywords
Neogene normal faulting superposed on a Laramide uplift: Medicine Bow Mountains, Sierra Madre, and intervening Saratoga Valley, Wyoming and Colorado

Abstract
The Medicine Bow Mountains, Sierra Madre, and intervening Saratoga Valley have been interpreted as structural fea-tures formed chiefly during the Laramide orogeny, but this concept needs revision. In this article, it is argued that Laramide regional contraction created a single Precambrian-cored range which was subsequently disrupted by Neogene normal faulting forming the present-day Saratoga Valley, Sierra Madre, and Medicine Bow Mountains.              

The originally broad Laramide range was bordered on the east by a thrust fault system directed toward the Laramie Basin and on the west by downwarped Paleozoic and Mesozoic strata which descend into the Washakie Basin. Erosion of the Laramide range during uplift exposed Precambrian basement rocks whose clastic debris were deposited in adjacent Paleocene basins. Following an episode of late Paleocene to early Eocene erosion, airborne pyroclastic ash from remote sources pro-gressively filled the broad Laramide basins during the middle Eocene, Oligocene, and early Miocene.

Ensuing Neogene epeirogenic uplift was accompanied by Miocene deposition, as the west flank of the Medicine Bow Mountains subsided along a normal fault thus creating the northeast-facing front of the Sierra Madre and associated half graben of Saratoga Valley. During this extensional event the North Platte River established its northward course from the floor of North Park Basin in Colorado through Saratoga Valley. The valley is interpreted as a northern manifestation of the Rio Grande rift which disrupted a broad Neogene uplift extending from New Mexico into southern Wyoming.

Koniaryctes, a new genus of apternodontid insectivore from Lower Eocene rocks of the Powder River Basin, Wyoming

PETE ROBINSON and DONALD G. KRON, Museum, Hunter Building, Campus Box 315, University of Colorado at Boulder, Boulder, Colorado 80309-0315

Pages
187-190

Keywords
Koniaryctes, a new genus of apternodontid insectivore from Lower Eocene rocks of the Powder River Basin, Wyoming

Abstract
Koniaryctes paulus is a very small apternodontid insectivore. It differs from Parapternodus in having: (1) lower molars with more rounded buccal sides of the protoconids; and (2) by having a wider talonid, with no heel cusp. Molar paraconids project forward, rather than upward as in Oligoryctes. The presence of two genera of apternodontids in the early Wasatchian indicates that significant evolution took place within that family prior to the Eocene. It is improbable that Koniaryctes was ancestral to the Chadronian genera Apternodus or Oligoryctes.