Valentine Formation

The Valentine Formation is a geologic formation or member within the Ogallala unit with outcrops in South Dakota, Nebraska, and Kansas. It preserves fossils dating to the Neogene period and is particularly noted for Canid fossils.[1][2]

At the beginning of the Ogallala deposits washing out from the rising Rocky Mountains into the central plains states, the members of the Pierre Shale[3] and Niobrara Formation outcrop had been largely exposed in their present range. The Niobrara had been incised by the present river systems, but to only a fraction of the present depths. Therefore, the earliest Ogallala deposits, the Valentine, filled in these shallower valleys; but there was no continuous exposure over the range of the eastern outcrop of the Ogallala.[4][5] Isolated exposures of the Valentine phase have been located along the Niobrara outcrop and quarried along the Smoky Hill River, Solomon River, Republican River, and Niobrara River where these watersheds have cut deeply down through the Niobrara Chalk into the Carlile Shale.

The Valentine Formation presents gray to gray-green, unconsolidated, fine-to-coarse grained, fluvial siltstone, channel sandstone, and gravel eroded from uplift of the Rocky Mountains as well as locally eroded materials,[6] particularly Niobrara chalk cobbles and chalk sand.[7] The specific index stone for the Valentine is the lenticular beds of grey-green opaline sandstone. The silicate cementation makes the opaline sandstone denser and harder than any other local stone, and it has been quarried as ballast, road gravel, and dam outflow rip-rap (e.g., Cedar Bluff Reservoir, Sherman Dam[8]). The opaline sandstone sandstone has had limited use in construction, and example being the structures in the city park of Hill City, Kansas. Beds of flint or chert can be found higher in the Valentine and the weathered Niobrara Chalk is also silicified where there is contact with these beds in the Valentine.