Geology of the Capitan Shelf Margin - Subsurface Data from the Northern Delaware Basin

Abstract

Facies relations determined from outcrop studies have been used in conjunction with subsurface data to better understand the geologic evolution, depositional facies, and diagenesis of the Capitan shelf margin. These studies have centered on a 2400 ft (731 m) portion of a 4800 ft (1463 m) continuous core from the Gulf PDB-04 research well that is located in Eddy County, New Mexico, at the northern end of the Delaware Basin. The evolution of the Capitan shelf and margin was examined after (a) the establishment of time lines for shelf-to-basin correlations in the Late Guadalupian and (b) the confirmation of the stratigraphic units penetrated in the PDB-04 well. Subsurface and outcrop data revealed that the evolution of the 2.5 m.y. duration Capitan shelf margin occurred in two major growth phases: a 1.5 m.y. duration phase during Seven Rivers time when over 80% of the total progradation, over half of the total aggradation, deposition of thick carbonate debris units on the slope and basin margin, and influx of over 60% of the total siliciclastics of the Bell Canyon Formation occurred. A subsequent, 1.0 m.y. growth phase during Yates and Tansill time is dominated by aggradation, steepening of the margin, and corresponds with abundant clastic deposition on the shelf. Maximum progradation of up to 12 miles (19 km) occurred along the northern rim of the basin, where progradation rates in excess of 7500 µm/year are measured. Detailed shelf-to-basin correlations have revealed that three major processes were responsible for the profound progradation and differentiation of Capitan growth into two major phases: (a) fluctuations of sea level, (b) maximum emplacement of allochthonous carbonate debris along the basin margin during Seven Rivers time, and (c) that abundant siliciclastics bypassed the actively prograding shelf margin and were an important foundation for the progradation. Because the Capitan was a deeply submerged reef during most of its growth, progradation occurred during both

Extensive, uplift-related and non-fault-controlled spar precipitation in the Permian Capitan Formation

“…These temperatures overlap in places but broadly disagree with the purported burial progression of the Capitan shown in Fig. 7 (after Scholle et al, 1992), which is an adaptation from multiple sources (King, 1948;Hills, 1984;Barker and Halley, 1986;Crysdale, 1987) and pinned to a maximum burial depth based on the thickness of Capitan strata in core PDB-04 (Garber et al, 1989). The high temperatures may be indicative of warm fluid migration (UlmerScholle et al, 1993; Budd et al, 2013), rather than absolute burial depth as proposed in scenario 2 above.…”

“…In outcrop and at shallow core depths (b1 km), various amounts of authigenic mineral phases occur including fibrous, formerly aragonitic precipitates (Mazzullo, 1980), multiple generations of relatively thin, isopachous fringe cements and locally abundant, pore/ vug-filling blocky calcite spars (Mruk, 1985). In deeper core (N1 km), however, gypsum and/or anhydrite represent the dominant vug-filling phase (Garber et al, 1989). The relative relationships among these phases support the following cement chronologic sequence succession: 1) fibrous aragonite 'marine cements', 2) isopachous fringes, 3) evaporite precipitation, and 4) calcite spar replacement of evaporites.…”

“…As detailed above, spars exhibit characteristics consistent with pseudomorphic replacement of the evaporites (Murray, 1960;Clark and Shearman, 1980;Scholle et al, 1992). Of particular importance is the limited occurrence of late calcite in core PDB-04 (Garber et al, 1989) which contains calcite spar only at depths of b1 km, below which evaporites become the pore-occluding phase. Similarly, outcrop exposures of Capitan reef and fore-reef facies are conspicuously devoid of evaporite (Scholle et al, 1992).…”

“…The associated units experienced burial relatively soon after deposition and remained at a more or less constant depth until~175 million years later when Basin and Range tectonic activity fostered abrupt exhumation (Scholle et al, 1992). Dominant rock types of the Capitan Formation and its equivalents include carbonate boundstones, grainstones, wackestones, packstones and mudstones; the distribution of which are strongly associated with the particular depositional environments listed above (Garber et al, 1989). In outcrop and at shallow core depths (b1 km), various amounts of authigenic mineral phases occur including fibrous, formerly aragonitic precipitates (Mazzullo, 1980), multiple generations of relatively thin, isopachous fringe cements and locally abundant, pore/ vug-filling blocky calcite spars (Mruk, 1985).…”

Characterization of bedded salt for storage caverns -- A case study from the Midland Basin, Texas

“…This relationship is apparent in the continuity of strata across structural positive areas with only minor changes in thickness or composition (Adams, 1968;Feldman, 1962;Matchus and Jones, 1984;Fracasso and Hovorka, 1986). The classic and extensively studied Capitan Reef is a strongly aggradational Guadalupian carbonate accumulation that rims the Delaware Basin (King, 1942;Garber and others, 1989;Bebout and Kerans, 1993, Kerans and Kernpter, in press) During Limestone at the top of the Bell Canyon Formation is the basinal equivalent to the Tansill (Garber andothers, 1989, Bebout andKerans, 1993, Kerans andKempter, in press). …”