Lithofacies, Depositional Systems,and Reservoir Elements in the Burro Canyon-Dakota Interval, Southwest Piceance Basin, Colorado
Rex Cole and George Moore
A surface and subsurface investigation of the Burro Canyon-Dakota interval (Aptian-Albian to earliest Cenomanian) was conducted along a 60 mile transect from the Utah-Colorado border to near Delta, CO. Detailed measured sections (with gamma-ray data) were defined at 10 locations along the Colorado and Gunnison Rivers, supplemented by wireline logs from nearby wells (N = 55). Emphasis was on lithofacies variations, interpretation of depositional settings and trends, and characterization of sandstone bodies from a reservoir perspective. In the study area, the Burro Canyon Formation ranges in thickness from 0 to 130 ft and consists of three main lithofacies: (1) fine- to coarse-grained sandstone and conglomeratic sandstone; (2) sandy, granule-pebble conglomerate; and (3) green, calcareous mudrock, which occasionally contains carbonate nodules. Sandstone and conglomerate facies are concentrated in the lower half of the Burro Canyon, whereas mudrock facies dominate the upper half. Sand and gravel deposition was by low-sinuosity braided-river systems that flowed within northeast-oriented (?) incised valleys. The upper mudrock-dominated interval was deposited in a flood-plain setting with local lacustrine influences. The Dakota Sandstone ranges in thickness from 50 to 150 ft in the study area, and has five major lithofacies: (1) fine- to coarse-grained, cross-stratified, channel-form sandstone and conglomeratic sandstone; (2) very fine to medium-grained, cross-stratified to ripple stratified, partially bioturbated, channel-form sandstone; (3) very fine to fine-grained, well-sorted, partially bioturbated, tabular sandstone, with horizontal lamination and hummocky cross-stratification; (4) burrowed to bioturbated fissile mudrock; and (5) bioturbated, fissile, carbonaceous mudrock with thin coal interbeds. The lower third of the Dakota was deposited in a lower coastal-plain setting, the middle third in a deltaic-estuarine setting, and the upper third in a shallow-marine setting. Reservoir-analog sandstone bodies in the lower Dakota were deposited by high-sinuosity, fluvial-estuarine channel systems flowing to the north-northeast. Sandstone-body heterogeneity in the Dakota is much greater than in the Burro Canyon.
AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012