Subsurface Bell Canyon Fm (Guadalupian, Permian) toe-of-slope carbonate-siliclastic transition: correlation and implications for stratigraphic trapping, SE New Mexico
Wireline log cross sections along the northwestern margin of the Delaware basin from the base of the Manzanita Limestone (upper Cherry Canyon Fm.) to the top of the Bell Canyon Fm. show the transition from Capitan slope to Bell Canyon basin. Lithology was interpreted from density, neutron, and Pe curves. The Manzanita and Hegler limestone mbrs. have relatively abrupt transition from slope to basin. Their distinctive log patterns could be traced from the base of slope to the basin center. The subsurface interval approximately equivalent to the Pinery Mbr. contains a sandstone traceable from slope to basin. Carbonates below this sandstone (lower Pinery) pinchout close to the slope, whereas the upper Pinery contain basinward- thinning siliciclastics near the base of slope and basinward thickening siliciclastics farther toward the basin. The total Pinery equivalent thins significantly basinward as carbonates thin. The carbonate unit roughly equivalent to the Rader Mbr. abruptly interfingers with siliciclastics near the base of slope, and the predominantly siliciclastic Rader equivalent thins rapidly basinward. Rader-equivalent strata can be traced to the basin center. The Hegler through Rader interval comprises about the lower third of Bell Canyon Fm. near the basin center. The McCombs Mbr. correlates to a siltstone with bentonites in the basin. Bell Canyon siliciclastics between the Rader and McCombs equivalents comprise about a third of the basinal Bell Canyon thickness and thin systematically towards the slope. Siliciclastics above the McCombs equivalent also comprise about a third of the basin Bell Canyon, but these strata thicken at the toe of slope before pinching out against the slope carbonates. The Ford Shale correlates to the McKittrick Limestone. The Lamar Limestone thins rapidly away from the slope. Most of the Delaware Lime is equivalent to the Reef Trail Mbr. with a thin Lamar Ls. at its base. Bell Canyon basin-center deposition was episodic. Lower Bell Canyon siliciclastics appear to be predominantly slope fed, with sandstones on the slope and siltstones in the basin. Post-Rader basin siliciclastics are predominantly strike-fed sandstones and siltstones with slope-fed sandstones near the slope. Toe-of-slope carbonates have low porosity that typically increases towards the slope. High-porosity sandstones pinch out against carbonates high on the toe-of-slope; however, porosity typically decreases before the sandstones pinch out. Both of these configurations are unfavorable for stratigraphic trapping.
AAPG Datapages/Search and Discovery Article #90343 ©2019 AAPG Southwest Section Annual Convention, Dallas, Texas, April 6-9, 2019