Field Trip Summary -
Location: Front Range, Rock Canyon Section
Leaders: B. Sageman, M. Leckie, M. Arthur
Objectives - Examine the Greenhorn and Niobrara third-order, tectonic-eustatic marine cycles in the Rock Canyon anticline along the Arkansas River, west of Pueblo, Colorado. The sections are located in and around the Pueblo Reservoir, south of Colorado Springs and Pikes Peak, and north of the Wet Mountains and Greenhorn Peak. They are located at the mouth of the Canon City Embayment, which opens up to the Great Plains to the east.
Lithostratigraphic units -
Units of the Greenhorn Cycle include the Dakota Sandstone, Graneros Shale, Greenhorn Formation (Lincoln Shale, Hartland Shale, and Bridge Creek Limestone Members), and Carlile Shale (Fairport Chalky, Blue Hill Shale, and Codell Sandstone Members).
The Niobrara Cycle is represented by the Niobrara Formation (Ft. Hays Limestone and Smoky Hill Shale Members).
Outcrops will feature -
- the symmetrical transgressive-regressive depositional sequence of the middle Cenomanian-middle Turonian Greenhorn cycle and the asymmetrical uppermost Turonian-lower Campanian Niobrara cycle
- lithofacies and biofacies expression of shifting water mass characteristics (Boreal and Tethyan) with the rise and fall of global sea level
- major global sea level fall event and unconformity at the middle/upper Turonian boundary
- peak transgressive carbonates (late Cenomanian-early Turonian and latest Turonian-early Coniacian) that express documented Milankovitch cyclicity
- Cenomanian/Turonian boundary interval (biotic turnover and Oceanic Anoxic Event II)
A detailed stratigraphic log of these units is published in SEPM Field Trip Guidebook No. 4: Fine-grained Deposits and Biofacies of the Cretaceous Western Interior Seaway: Evidence of Cyclic Sedimentary Processes, edited by Lisa Pratt, Erle Kauffman, and Fred Zelt (1985).
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