A Task of the Greater Platte River Basins and Northern Plains Geologic Framework Studies Project focusing on these study areas: (1) South Platte River Corridor, Eastern Colorado and (2) Niobrara National Scenic River, Nebraska
Background
The Greater Platte River Basins area spans a central part of the mid-continent and Great Plains from the Rocky Mountains on the west to the Missouri River on the east, and is defined to include drainage areas of the Platte, Niobrara, and Republican Rivers, the Rainwater Basin, and other adjoining areas overlying the northern High Plains aquifer.
The Greater Platte River Basins contains abundant surficial deposits that were sensitive to, or are reflective of, the climate under which they formed: deposits from multiple glaciations in the mountain headwaters of the North and South Platte Rivers and from continental ice sheets in eastern Nebraska; fluvial terraces along the rivers and streams; vast areas of eolian sand in the Nebraska Sand Hills and other dune fields; thick sequences of wind-blown silt (loess); and sediment deposited in numerous lakes and wetlands. In addition, the Greater Platte River Basins overlies and contributes surface water to the High Plains aquifer, a nationally important groundwater system that underlies parts of eight states and sustains one of the major agricultural areas of the United States.
The Greater Platte River Basins also provides critical nesting habitat for birds such as plovers and terns, and roosting habitat for cranes and other migratory birds that travel through the Central Flyway of North America. This broad area, containing fragile ecosystems that could be further threatened by changes in climate and land use, has been identified by the USGS and the University of Nebraska-Lincoln as a region where intensive collaborative research could lead to a better understanding of climate change and what might be done to adapt to or mitigate its adverse effects to ecosystems and to humans. (University of Nebraska-Lincoln Office of Research, 2008, Sustainability in a time of climate Change—Developing an intensive research framework for the Platte River Basin and the High Plains: Climate Change Workshop hosted by the University of Nebraska-Lincoln and U.S. Geological Survey, May 19-22, 2008, 92 p.)
Study Areas: (1) South Platte River Corridor, Eastern Colorado and (2) Niobrara National Scenic River, Nebraska
1. South Platte River Corridor, Eastern Colorado
The South Platte River flows across the semiarid, short-grass prairie of eastern Colorado, a region highly susceptible to drought. In this type of environment, geomorphic systems tend to be highly sensitive to climate change, and surficial deposits provide a past record of that change. Determining past system response can help predict potential future response to climate change that might have adverse effects on ecosystems and society.
Geologic Setting
Multiple topographic levels that define the tops of fluvial terraces have been recognized along the South Platte River. These terraces range from Pliocene to late Holocene in age. In addition, multiple generations of eolian silt and sand deposits, generated in part from fluvial sediments of the South Platte River, cover much of the terrain.
Project Objectives
Major objectives of this work are to produce digital maps, and develop a geochronology for surficial deposits along a portion of the South Platte River in eastern Colorado. This stretch of river has been affected by past alpine glaciations in the headwaters, and more locally, by past droughts severe enough to mobilize dune sand and produce significant deposits of wind-blown silt in the basin. Goals are to better understand how past changes in climate have affected the fluvial and eolian systems in hopes of better understanding potential effects of future climate change. Objectives of the work also include relating the record for the South Platte River to records for the North Platte River, central Platte River, and eolian deposits of the Greater Platte River Basins.
2. Niobrara National Scenic River, Nebraska
The Niobrara National Scenic River (NIOB), a 76-mile stretch of river at the northern edge of the Nebraska Sand Hills, is situated at the midcontinental crossroads of several ecosystems and is renowned for its biological diversity. Climate change has the potential of having significant effect in this ecoregion, where many plant and animal species are near their geographic range limits. Geomorphic systems also may be near threshold limits, and therefore particularly responsive to climate change. The Niobrara River map area will include the adjoining Middle Niobrara Preserve of The Nature Conservancy, and the Fort Niobrara Wildlife Refuge of the U.S. Fish and Wildlife Service.
Geologic Setting
Along the Niobrara River corridor, there are low and intermediate flood plains, multiple river terraces ranging from Holocene to Pleistocene in age, sand dunes, and lacustrine sediments that may have been deposited in dune-dammed lakes. A prominent terrace more than 50 m above the valley floor and considered late Pleistocene in age suggests that the Niobrara River system has experienced dramatic incision in the past.
Project Objectives
Major objectives of this work are to produce digital geologic maps of the Niobrara National Scenic River reach and develop a geochronology and stratigraphy for the surficial-geologic deposits. This work will satisfy NIOB park needs for a new geologic map and help us understand better the timing and causes of past river response. The unique setting of the NIOB makes it a prime area for detailed geologic mapping and stratigraphic studies focused on the geologic framework of ecosystems and effects of climate change on the fluvial system.
- Overview
A Task of the Greater Platte River Basins and Northern Plains Geologic Framework Studies Project focusing on these study areas: (1) South Platte River Corridor, Eastern Colorado and (2) Niobrara National Scenic River, Nebraska
Background
The Greater Platte River Basins area spans a central part of the mid-continent and Great Plains from the Rocky Mountains on the west to the Missouri River on the east, and is defined to include drainage areas of the Platte, Niobrara, and Republican Rivers, the Rainwater Basin, and other adjoining areas overlying the northern High Plains aquifer.
Map showing the GPRB, northern portion of the High Plains aquifer, and general areas targeted for study: (1) South Platte River corridor, (2) Niobrara National Scenic River and Eolian sediments, which cover much of the GPRB although only the Nebraska Sand Hills are shown here. (Base map taken from Thormodsgard, J.M., 2009, Greater Platte River Basins—Science to sustain ecosystems and communities: U.S. Geological Survey Fact Sheet 2009-3097, 6 p.) The Greater Platte River Basins contains abundant surficial deposits that were sensitive to, or are reflective of, the climate under which they formed: deposits from multiple glaciations in the mountain headwaters of the North and South Platte Rivers and from continental ice sheets in eastern Nebraska; fluvial terraces along the rivers and streams; vast areas of eolian sand in the Nebraska Sand Hills and other dune fields; thick sequences of wind-blown silt (loess); and sediment deposited in numerous lakes and wetlands. In addition, the Greater Platte River Basins overlies and contributes surface water to the High Plains aquifer, a nationally important groundwater system that underlies parts of eight states and sustains one of the major agricultural areas of the United States.
The Greater Platte River Basins also provides critical nesting habitat for birds such as plovers and terns, and roosting habitat for cranes and other migratory birds that travel through the Central Flyway of North America. This broad area, containing fragile ecosystems that could be further threatened by changes in climate and land use, has been identified by the USGS and the University of Nebraska-Lincoln as a region where intensive collaborative research could lead to a better understanding of climate change and what might be done to adapt to or mitigate its adverse effects to ecosystems and to humans. (University of Nebraska-Lincoln Office of Research, 2008, Sustainability in a time of climate Change—Developing an intensive research framework for the Platte River Basin and the High Plains: Climate Change Workshop hosted by the University of Nebraska-Lincoln and U.S. Geological Survey, May 19-22, 2008, 92 p.)
Sources/Usage: Public Domain.Ecosystems of the Greater Platte River Basins with general areas targeted for study: South Platte River area is classified as High Plains Ecoregion (mixed grass, short grass, and sandsage prairie), Niobrara River area is classified as Northwestern Great Plains Ecoregion (pine woodlands, eastern red cedar, deciduous woodlands, mixed grass and Sand Hills prairie). (Ecoregion boundries and descriptions are from the U.S. Environmental Protection Agency: "Level III and IV Ecoregions of the Continental United States" https://www.epa.gov/eco-research/level-iii-and-iv-ecoregions-continenta…; and "Level III and IV Ecoregions by State" https://www.epa.gov/eco-research/level-iii-and-iv-ecoregions-state) Study Areas: (1) South Platte River Corridor, Eastern Colorado and (2) Niobrara National Scenic River, Nebraska
1. South Platte River Corridor, Eastern Colorado
The South Platte River flows across the semiarid, short-grass prairie of eastern Colorado, a region highly susceptible to drought. In this type of environment, geomorphic systems tend to be highly sensitive to climate change, and surficial deposits provide a past record of that change. Determining past system response can help predict potential future response to climate change that might have adverse effects on ecosystems and society.
Geologic Setting
Multiple topographic levels that define the tops of fluvial terraces have been recognized along the South Platte River. These terraces range from Pliocene to late Holocene in age. In addition, multiple generations of eolian silt and sand deposits, generated in part from fluvial sediments of the South Platte River, cover much of the terrain.
South Platte River at the Highway 39 bridge, Orchard quadrangle, eastern Colorado. In this area, the late Pleistocene terrace of the South Platte River is partly buried by younger eolian dune sand.
Middle Pleistocene alluvium of the South Platte River. Whitish layer is the cemented calcium carbonate (K) horizon of the soil profile developed in the alluvium.
Early Pleistocene alluvium of the South Platte River. The iron-stained, gravel to boulder alluvium is well cemented, with well-rounded clasts and iron laminations along bedding planes.
Eolian sand deposits separated by a buried soil marking a period of landscape stability between two episodes of eolian activity. Project Objectives
Major objectives of this work are to produce digital maps, and develop a geochronology for surficial deposits along a portion of the South Platte River in eastern Colorado. This stretch of river has been affected by past alpine glaciations in the headwaters, and more locally, by past droughts severe enough to mobilize dune sand and produce significant deposits of wind-blown silt in the basin. Goals are to better understand how past changes in climate have affected the fluvial and eolian systems in hopes of better understanding potential effects of future climate change. Objectives of the work also include relating the record for the South Platte River to records for the North Platte River, central Platte River, and eolian deposits of the Greater Platte River Basins.
2. Niobrara National Scenic River, Nebraska
The Niobrara National Scenic River (NIOB), a 76-mile stretch of river at the northern edge of the Nebraska Sand Hills, is situated at the midcontinental crossroads of several ecosystems and is renowned for its biological diversity. Climate change has the potential of having significant effect in this ecoregion, where many plant and animal species are near their geographic range limits. Geomorphic systems also may be near threshold limits, and therefore particularly responsive to climate change. The Niobrara River map area will include the adjoining Middle Niobrara Preserve of The Nature Conservancy, and the Fort Niobrara Wildlife Refuge of the U.S. Fish and Wildlife Service.
Geologic Setting
Along the Niobrara River corridor, there are low and intermediate flood plains, multiple river terraces ranging from Holocene to Pleistocene in age, sand dunes, and lacustrine sediments that may have been deposited in dune-dammed lakes. A prominent terrace more than 50 m above the valley floor and considered late Pleistocene in age suggests that the Niobrara River system has experienced dramatic incision in the past.
Dark organic-rich beds at top of exposure in fine-grained Quaternary colluvium (?) probably are associated with grade of the fluvial system that was several meters higher than present. Most of the exposure is of underlying Tertiary sediments. Geologic mapping and geochronology of Quaternary terraces will provide constraints on the downcutting history of the Niobrara River to better understand relations such as those shown here.
Riffle at Fritz's Island, where the channel of the Niobrara River is eroded within Tertiary strata. Active channel sediment is locally sparse. Tertiary bedrock exposed on the bank is overlain by thin late Holocene sediment to form a low terrace that reflects a somewhat different and more sediment-rich channel system at the time the river was at the slightly higher grade.
The location of the Rocky Ford Rapids over a resistant zone in the bedrock channel illustrates the control geology has on river morphology and ecology that will be further investigated during geologic mapping.
Looking southward across the Niobrara River Valley near the town of Riverview, Nebraska (Highway 7 bridge), showing grade of inset high terrace on the south valley side. Project Objectives
Major objectives of this work are to produce digital geologic maps of the Niobrara National Scenic River reach and develop a geochronology and stratigraphy for the surficial-geologic deposits. This work will satisfy NIOB park needs for a new geologic map and help us understand better the timing and causes of past river response. The unique setting of the NIOB makes it a prime area for detailed geologic mapping and stratigraphic studies focused on the geologic framework of ecosystems and effects of climate change on the fluvial system.