--> --> Fluvial architecture and sequence stratigraphy of the Burro Canyon Formation using UAVbased outcrop models, southwestern Piceance Basin, Colorado

AAPG Rocky Mountain Section Meeting

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Fluvial architecture and sequence stratigraphy of the Burro Canyon Formation using UAVbased outcrop models, southwestern Piceance Basin, Colorado

Abstract

Well-exposed outcrops of the Lower Cretaceous Burro Canyon Formation in the southwestern Piceance Basin, Colorado, are evaluated along a 48-mi (77 km) transect for identification of depositional environments, fluvial architectures, and sequence stratigraphy. The Burro Canyon Formation in the area represents a sequence deposited unconformably over the Jurassic Morrison Formation and truncated by a regional unconformity that defines the base of the Dakota Formation. The architecture of these fluvial deposits is described using seven composed measured sections combined with eight UAV-based outcrop models, core, and well-log data. Analysis of facies, architectural elements and bounding surfaces allows for determination and mapping of the resulting depositional environments that are placed in a sequence-stratigraphic context. The Burro Canyon Formation in the area represents local incised-valley fills comprised of sandstone-rich amalgamated channel complexes overlain by non-amalgamated channel complexes. Deposits within the amalgamatedchannel complex interval include multiple upward-fining, conglomerate- tosandstone deposits recognized as unit bars and bar sets. These deposits are interpreted to result from lateral and down-stream accretion, which is characteristic of low-sinuosity braided-fluvial environments. Channel-fill architectural elements exhibit cross-bedding and numerous truncated contacts and are interpreted to have formed during periods when the geomorphic base 65 Wyoming Geological Association – September 15-18, 2019 level was relatively low (lower to moderate accommodation). Vertically and laterally stacked channel-fill elements (N= 131) exhibit an apparent-width range of 137-1300 ft (40-420 m) and a thickness range of 5-60 ft (1.5-18 m). The sequence transitions upward into non-amalgamated channel-complex deposits that contain inclined-heterolithic strata interbedded with mudstonedrape successions deposited by low net-to-gross, high-sinuosity braided to meandering-fluvial environments. Mudstone-prone intervals of the nonamalgamated channel complex contain isolated channel-fill elements interbedded with floodplain mudstones and represent a period of relatively high base level. Associated channel-fill elements range in apparent width from 200-1000 ft (60-300 m) and thickness from 20-30 ft (6-18 m). These fluvial deposits serve as outcrop analogs for subsurface interpretations and development of hydrocarbons in similar reservoirs.