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Data Release of OSL, 14C, and U-series age data supporting geologic mapping along the South Platte River corridor in northeastern Colorado

February 1, 2018

In conjunction with geologic mapping of four 7.5′ quadrangles along the South Platte River corridor in northeastern Colorado (Masters, Orchard, Weldona, and Fort Morgan), geochronology samples were collected and analyzed using optically stimulated luminescence (OSL), radiocarbon (14C), or U-series methods to provide age control for mapping units. This section of river corridor is largely covered by surficial deposits that formed from alluvial, eolian, and hillslope processes operating in concert with environmental changes from the Pleistocene to the present. The South Platte River originates high in the Colorado Rocky Mountains and recurrent glaciation of basin headwaters has affected river discharge and sediment supply far downstream, influencing aggradation and incision along this part of the river corridor. Unglaciated tributaries originating in the Colorado Piedmont east of the Front Range have periodically deposited large volumes of sediment at their confluences during major flood events. Eolian sand deposits cover much of the area and record past episodes of sand mobilization during times of prolonged drought. Sediment samples dated using OSL provide ages for alluvial and eolian sand deposits; organic samples dated using 14C methods constrain ages of alluvial deposits; and bone and river gravels with calcium carbonate rinds dated using U-series methods provide minimum ages for alluvial deposits.