Traveling Through Nebraska: Pleistocene Era Landscape Changes
The Pleistocene era, spanning from approximately 2.6 million to 11,700 years ago, was a period of immense geological change that drastically altered the landscape of Nebraska. This era, a part of the Cenozoic age, was dominated by repeated glacial cycles that modeled the terrain through immense weights of ice and subsequent meltdowns, redefining the regional geography. Understanding these transformations requires diving into Nebraskan geological history, taking into account its hydrology, glaciation, and geomorphic changes during the Pleistocene era.
In the Nebraska Sandhills, situated in north-central Nebraska, the repetitive freeze-and-thaw cycles during repeated glacial stages led to sediment redeposition as massive sand dunes rose over the landscape. Extensive valleys and wetlands that dot the Sandhills offer evidence of this dynamic. For instance, the Platte River Valley is a critical example of a valley, carved from multiple sedimentation events involving water during glacial melting. Moreover, the great frozen lakes that periodically flooded in southeastern Nebraska, often to now-extinct lakebeds such as pluvial lakes and sand-dune blockages found in present-day Brown County, showcase this cyclic process.
Composed primarily of fossil deposits of fossil megalodont bison and camels embedded within their sediments, the large glacial impoundments found on bluffs near the city of Axtell, Nebraska illustrate such lakebed flooding and cyclic history quite vividly. Also known as Axtell site berm gravels, this finding suggests enormous sedimentation processes undertaken by post-glacial rivers as glaciostenic melt flowed like abundant sheet flow down slope. This was repeated each interglacial period as subsequent glaciers expanded in extreme cold stages and carved postglacial drainage passages that eventually shrank pluvial lakes that may be buried under thick deposits as, ultimately glacial and deglacial glaciofluvial deposits.
Repeated advances and retreats of ice sheets drastically changed drainage patterns as ice stagnated blocking pre-glacial drainages redirecting flow into glacial river systems which redirected sediment flow downward of an ice edge across south of Nebraska exposing deposits. Most recent, massive Laurentide ice sheets, often over immense spans, engulfing eastern and the nearly entire north through North America to force hydrologically feed southwards to the Mississippi and Glaciomarine systems that were the reason water and geological shifts in lower-48 states that fed melt feeding Platte rivers melting of the continental U.S. A stark consequence of such glacial weight is seen along the Platte River, downstream of an old glacial or its divide of South boundary that became massive after glacial loss across the frozen North.
In lower-Nebraska glacial advances ultimately buried landscapes. Subsurface relics or fossil lake deposits beneath ancient bed channels show glacial buried Platte river valley systems when glacial weight continued to cover much the landscape and hydrological down rivers in and out of these relic mid-platte to Kansas fossil pluvial plume deposits evidencing the pluvial flooding with lacustrine fossil sites or other glacial intercontinental rivers. Subsequently repeated movement melted glaciers by immense reworkings of a terrain as many landscapes here hold the potential for subterrain reordering sediment ejection deep surface frozen reconstituted tills.
In the Nebraska Sandhills, situated in north-central Nebraska, the repetitive freeze-and-thaw cycles during repeated glacial stages led to sediment redeposition as massive sand dunes rose over the landscape. Extensive valleys and wetlands that dot the Sandhills offer evidence of this dynamic. For instance, the Platte River Valley is a critical example of a valley, carved from multiple sedimentation events involving water during glacial melting. Moreover, the great frozen lakes that periodically flooded in southeastern Nebraska, often to now-extinct lakebeds such as pluvial lakes and sand-dune blockages found in present-day Brown County, showcase this cyclic process.
Composed primarily of fossil deposits of fossil megalodont bison and camels embedded within their sediments, the large glacial impoundments found on bluffs near the city of Axtell, Nebraska illustrate such lakebed flooding and cyclic history quite vividly. Also known as Axtell site berm gravels, this finding suggests enormous sedimentation processes undertaken by post-glacial rivers as glaciostenic melt flowed like abundant sheet flow down slope. This was repeated each interglacial period as subsequent glaciers expanded in extreme cold stages and carved postglacial drainage passages that eventually shrank pluvial lakes that may be buried under thick deposits as, ultimately glacial and deglacial glaciofluvial deposits.
Repeated advances and retreats of ice sheets drastically changed drainage patterns as ice stagnated blocking pre-glacial drainages redirecting flow into glacial river systems which redirected sediment flow downward of an ice edge across south of Nebraska exposing deposits. Most recent, massive Laurentide ice sheets, often over immense spans, engulfing eastern and the nearly entire north through North America to force hydrologically feed southwards to the Mississippi and Glaciomarine systems that were the reason water and geological shifts in lower-48 states that fed melt feeding Platte rivers melting of the continental U.S. A stark consequence of such glacial weight is seen along the Platte River, downstream of an old glacial or its divide of South boundary that became massive after glacial loss across the frozen North.
In lower-Nebraska glacial advances ultimately buried landscapes. Subsurface relics or fossil lake deposits beneath ancient bed channels show glacial buried Platte river valley systems when glacial weight continued to cover much the landscape and hydrological down rivers in and out of these relic mid-platte to Kansas fossil pluvial plume deposits evidencing the pluvial flooding with lacustrine fossil sites or other glacial intercontinental rivers. Subsequently repeated movement melted glaciers by immense reworkings of a terrain as many landscapes here hold the potential for subterrain reordering sediment ejection deep surface frozen reconstituted tills.
