--> Basin Evolution of the North Park – Middle Park basin, Colorado

2014 Rocky Mountain Section AAPG Annual Meeting

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Basin Evolution of the North Park – Middle Park basin, Colorado


The North Park- Middle Park basin, just ‘behind’ the Colorado Front Range, has been a target for oil and gas exploration since the early 1920s. As in the Denver Basin, recent drilling has mostly focused on the Niobrara Fm. Targets in the basin are not straightforward due to the area's structural complexity, and basin history is difficult to unravel due to absent marker beds. This study illustrates basin evolution based on field observations, paleobotany, well-logs, published seismic lines, vitrinite reflectance data and geochronology. Detailed study of the Tertiary basin fill reveals new insights in the Laramide and mid-Tertiary evolution of this basin and the neighboring Front Range. Late Cretaceous and early Paleocene time is marked by significant (>∼3000 ft) widespread erosion, and locally, as much as 7,000 ft of sediments were eroded down to the level of the Dakota Sandstone. The basin started to subside in middle Paleocene and accumulated coarse-grained, predominantly volcaniclastic deposits in the south after about 60.5 Ma. Rapid subsidence followed with sediment accumulation rates as great as ∼750 m/Ma. Ponding developed and lacustrine, paludal and fluvial sediments filled the basin. Deposition shifted northward during the later Paleocene and early Eocene time. Angular unconformities within the sediments indicate active deformation during deposition, but these unconformities appear to be local. Coarse-grained sediments are generally uncommon within the basin fill, suggesting that contemporaneous uplifted source areas were distant. Rise of basement rocks in the modern Park and Front Ranges is mostly younger than these Paleogene sediments.