THE 2013 GREAT PLAINS DISTINGUISHED BOOK PRIZE

After long deliberations by members of three subcommittees and the chairs of those committees, the Great Plains Distinguished Book Prize was awarded to Blackfoot Redemption: A Blood Indian\u27s Story of Murder, Confinement, and Imperfect Justice, by William E. Farr, published by the University of Oklahoma Press. As the chair of the prize committee, I am pleased to state that many fine books were submitted for the competition, and that each of them was meritorious in some way. Nevertheless, Blackfoot Redemption is unique among the submissions-and indeed among the vast majority of accounts of Plains Native American lives in the shadows of the post-Custer and pre-American Indian Movement era-in its well researched and skillful narrative of what is a singularly incredible story

A Delicate Balance: Rainfall and Groundwater in Nebraska During the 2000-2005 Drought

Recent decreases in rainfall and the accompanying decreases in groundwater levels since 1999 indicate heightened vulnerability to drought in Nebraska and the surrounding Great Plains. Precipitation across Nebraska during 2000-2005 ranged from 72% to 108% of the 30-year normal value, with fully 90% of 150 stations reporting below-normal precipitation. Simultaneously, groundwater levels declined more than 9 m in the most heavily impacted areas, most of which were already experiencing declines due to extensive irrigation development and low recharge rates. Thus, recovery from the drought and long-term intensive land use will be particularly challenging in densely irrigated areas of Nebraska. In contrast, contemporaneous groundwater-level changes in areas with little groundwater irrigation were comparatively modest. These observations demonstrate that drought mitigation efforts in the central and northern Great Plains must consider the combined effects of area-specific reduced recharge, local geohydrology (especially as it affects recharge), and increased groundwater withdrawals

New Insights into Carboniferous Cyclothems. The Fourth Biennial Field Conference of the American Association of Petroleum Geologists (AAPG) Midcontinent Section Fourth Biennial Field Conference Abstracts and Guidebook

The term “cyclothem” was coined by Wanless & Weller (1932) to describe repetitive stratigraphic successions of Carboniferous age in Illinois. Nonetheless, comparable rhythmicity had been identified in Carboniferous rocks both in the central and eastern USA, and in Europe during the preceding century. Cyclothems were found to comprise repetitive vertical successions of sandstones, heterolithic (thinly interbedded) sandstones and mudrocks, mudrocks, limestones, and coals, in many cases with pedogenic overprinting of these lithologies. As usage of the term “cyclothem” increased, so did the diversity of successions to which the term was applied, to the point where many geologists advocated abandonment of the expression. An example of this misuse was the modified term “continental cyclothem”, used to describe alternations of coarse- and fine-grained alluvial and other strata. Using the term “cyclothem” to describe essentially non-cyclic, binary arrays of lithologies is here considered a retrograde step, as it introduces confusion as to what a cyclothem is and represents geologically. The original definition of “cyclothem” as an alternation of marine and nonmarine lithologies, however, is a robust and useful concept, and by this definition cyclothems are largely confined to Carboniferous and Permian systems in the paleotropics of North America and Europe. Their stratigraphic range broadly coincides with the timing of the late Paleozoic Ice Age, and many researchers have postulated that they are a record of eustatically-controlled rises and falls in sea-level associated with waxing and waning of Gondwanan ice centers. We propose a restricted definition of “cyclothems” that is limited to successions that were deposited (1) on low-gradient pericontinental shelves in paleotropical regions, (2) as far-field products of Gondwanan glacial growth and decay at various timescales, and (3) under conditions of low sediment supply in most cases (Fig. 1). As such, they are important archives of late Paleozoic paleoenvironmental change, and the concept can be used in a number of ways. For example, the onset of a cyclothemic motif in stratigraphic successions of late Visean age across Euramerica has been used to infer the onset of the main phase of glaciation in Gondwana. Cyclothems are also important as hosts for economic mineral resources, including oil and gas, coal, lime, water, and base and precious metals. This symposium introduces Field Conference participants to the nature and variety of cyclothems, and their geology. Papers concern aspects of cyclothems in numerous states of the USA from Illinois in the east to Utah in the west, and from Montana in the north to Texas in the south. Papers describe the stratigraphy, sedimentology, and resource geology of Carboniferous cyclothemic successions, including numerous petroleum-prospective regions and plays. The Field Excursion will allow participants to view well-exposed examples of classical Midcontinent cyclothems in SE Nebraska (the Virgilian--or uppermost Pennsylvanian--Indian Cave Sandstone). The Core Workshop will feature examples of cyclothemic Carboniferous successions from Illinois, Iowa, Nebraska, Kansas, and Montana, some of which are in active petroleum-producing areas

Geomorphic and Environmental Change Around a Large, Aging Reservoir: Lake C. W. McConaughy, Western Nebraska, USA

Lake C. W. McConaughy, a 63-year-old manmade reservoir in the North Platte Valley of western Nebraska, is the largest standing body of water in the state. From the time that Kingsley Dam was completed in 1941 until the present day (2004), many geomorphic and environmental changes have occurred along the shores and within the North Platte Valley. Erosion on the southeastern shoreline of the lake had been perceived as a problem for landowners and managers for at least three decades, but the full scale of erosion was revealed only after a cumulative 18-m drawdown in lake level: bedrock platforms, extending from cliffs on headlands, as well as minor caves, alcoves, potholes, and beach erosion scarps were revealed. Actual headland retreat since 1941 has probably been on a scale of magnitude of tens of meters. Erosional platforms, however, are as much as 266 m in length, indicating that they are, collectively, the results of a combination of pre-reservoir geomorphic conditions, erosion during reservoir filling, and wave erosion after filling. Serial observations of the shoreline made in the period 1999-2002 demonstrated that shoreline erosion continues. Depositional features such as pocket beaches and beach ridges have formed de novo in bays between headlands. Also, a delta that prograded at least 4 km from the North Platte River into the lake between 1952 and 1993 continues to grow, and major morphometric changes have occurred on the North Platte River immediately upstream since 1941 in response to the elevation of the local base level by the lake; most of the change in channel patterns in the river upstream from the delta took place in a mere 8 years from 1952 to 1960. Since 1999, some emergent beaches and areas of exposed lake floor have developed sand dunes; eolian erosion and re-deposition is widespread elsewhere in these areas during periods of high winds, which are frequent in western Nebraska. The water table beneath lands adjacent to the reservoir generally rose until 1953 as the lake was filling. The far-flung irrigation system of which Lake McConaughy is the key element has elevated water tables as far as 250 km from the lake. Since at least 2000, soil salinization (episodic thenardite accumulation) has developed in exposed lake sediments at the western end of the lake. On a smaller scale, groundwater has been discharging lakeward along shoreline beach scarps through springs and seeps while lake levels have been low. Slightly lowering the operating level of Lake McConaughy could slow some of the more dramatic effects of shoreline erosion when the lake returns to its predrought volume, but erosion will continue, particularly at the ends of headlands on the southeastern shore, which are exposed to strong waves driven by northerly to northwesterly winds. Eolian erosion and re-deposition will, on the other hand, continue as long as lake level remains particularly low as a result of drought and the removal of irrigation waters. Salinization can be considered an ephemeral phenomenon, dependent on future management of the lake, but it indirectly represents the potential for larger-scale changes in hydrogeologic systems. The longer-term effects of lake-related water-table changes, both near the lake and downstream in irrigated lands, as well as the ability of the lake to supply irrigation water if drought conditions continue, remain to be seen

Post-Mississippian tectonic evolution of the Nemaha Tectonic Zone and Midcontinent Rift System, SE Nebraska and N Kansas

The geologic structures of the central Midcontinent of the USA are largely buried and known only from geophysical datasets, coupled with sparse well control and limited outcrop. Such unconstrained geophysical models preclude a deeper assessment of possible continental interior seismic hazards, which have the potential to cause appreciable damage. Within the study area in southeastern Nebraska and northeastern Kansas is an area of elevated seismic risk, with a spatial relationship to the Nemaha Tectonic Zone and the Midcontinent Rift System. Using sequential restorations of three published cross sections within Nebraska and Kansas this study demonstrates that the Nemaha Tectonic Zone and Midcontinent Rift System have each been reactivated several times since the end of the Mississippian (the details of deformation prior to the Mississippian are not considered). Our reconstructions indicate that in addition to major Pennsylvanian-Early Permian fault reactivation during the Ancestral Rocky Mountain orogeny there was also deformation both prior to the post-Mississippian unconformity associated with uplift on the Nemaha Tectonic Zone and after the deposition of late Early-early Late Cretaceous sediments in the study area, potentially due to the Laramide orogeny. Results also indicate that the magnitude of the far-field stresses is sufficient to cause seismogenic reactivation on favorably oriented pre-existing faults. This history of reactivation of geologic structures in the central Midcontinent suggests that seismic hazards in the region in the present cannot be ruled out. Though dangerous large earthquakes are uncommon in the continental interior, seismic activity along the structures in the study area would threaten several large population centers and the potential for this activity should not be ignored

Post-Mississippian tectonic evolution of the Nemaha Tectonic Zone and Midcontinent Rift System, SE Nebraska and N Kansas

The geologic structures of the central Midcontinent of the USA are largely buried and known only from geophysical datasets, coupled with sparse well control and limited outcrop. Such unconstrained geophysical models preclude a deeper assessment of possible continental interior seismic hazards, which have the potential to cause appreciable damage. Within the study area in southeastern Nebraska and northeastern Kansas is an area of elevated seismic risk, with a spatial relationship to the Nemaha Tectonic Zone and the Midcontinent Rift System. Using sequential restorations of three published cross sections within Nebraska and Kansas this study demonstrates that the Nemaha Tectonic Zone and Midcontinent Rift System have each been reactivated several times since the end of the Mississippian (the details of deformation prior to the Mississippian are not considered). Our reconstructions indicate that in addition to major Pennsylvanian-Early Permian fault reactivation during the Ancestral Rocky Mountain orogeny there was also deformation both prior to the post-Mississippian unconformity associated with uplift on the Nemaha Tectonic Zone and after the deposition of late Early-early Late Cretaceous sediments in the study area, potentially due to the Laramide orogeny. Results also indicate that the magnitude of the far-field stresses is sufficient to cause seismogenic reactivation on favorably oriented pre-existing faults. This history of reactivation of geologic structures in the central Midcontinent suggests that seismic hazards in the region in the present cannot be ruled out. Though dangerous large earthquakes are uncommon in the continental interior, seismic activity along the structures in the study area would threaten several large population centers and the potential for this activity should not be ignored