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Surficial Geologic Mapping in the Greater Platte River Basins

Completed
By Geosciences and Environmental Change Science Center July 14, 2017

Egelhoff Rapids

Niobrara River, northern Nebraska

After wildfire

Niobrara River, northern Nebraska

Holocene and late Pleistocene alluvial deposits

South Platte River corridor

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

Link to main project.

 

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.

Greater Platte River Basins map showing project location
Sources/Usage: Some content may have restrictions. View Media Details
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.)

 

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.

 

An active channel along the South Platte River
Sources/Usage: Some content may have restrictions. View Media Details
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.

 

 

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.

 

Quaternary and Tertiary sediments seen in exposure along Niobrara River
Sources/Usage: Some content may have restrictions. View Media Details
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.
Photo of holocene terrace along Niobrara River
Sources/Usage: Some content may have restrictions. View Media Details
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.

 

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.

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

Link to main project.

 

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.

Greater Platte River Basins map showing project location
Sources/Usage: Some content may have restrictions. View Media Details
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.)

 

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.

 

An active channel along the South Platte River
Sources/Usage: Some content may have restrictions. View Media Details
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.

 

 

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.

 

Quaternary and Tertiary sediments seen in exposure along Niobrara River
Sources/Usage: Some content may have restrictions. View Media Details
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.
Photo of holocene terrace along Niobrara River
Sources/Usage: Some content may have restrictions. View Media Details
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.

 

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.

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