Abstract Dip-oriented profiles of the Yates-Capitan shelf margin were independently constructed from exceptional outcrops in McKittrick and Slaughter Canyons in the Guadalupe Mountains of west Texas and southern New Mexico. Comparison of the two profiles reveals significant similarities in the position and character of high-frequency sequence boundaries, the internal architecture of facies tracts and cycle-stacking patterns, and offlap angles of both the shelf and reef. The evolution of the Yates-Capitan shelf margin is recorded by systematic long-term trends in key depositional variables measured on individual high-frequency sequences in each canyon. This comparison of the two profiles, located along strike 25 km apart, provides a three-dimensional model of the extent and variability of genetic components of the Late Permian margin of the Northwest shelf of the Delaware basin. Comparison of the sequence stratigraphic models for the Yates Formation in McKittrick and Slaughter Canyons indicates that four complete high-frequency sequences can be confidently correlated along strike. Fundamental architectural characteristics of the Yates-Capitan shelf margin are evident in the comparative profiles from each canyon. (1) The Yates Formation in both canyons exhibits initial aggradational geometries followed by strong progradational patterns. The volume of the shelf-crest pisolite complex in the Yates progressively expands through time in concert with a reciprocal contraction of the outer-shelf facies tract. The time-equivalent Capitan reef in both canyons exhibits remarkably similar patterns of stepwise alternations of aggradational and progradational growth that relate to changes in high-frequency sequence architecture through time. (2) The thickness of the Yates varies considerably both across the dip of the shelf margin and along strike between the two canyons. The 240%—600% increases in downdip thickness primarily reflect the inherited depositional topography. The thickness variation along the 25-km strike distance may indicate significant lateral variability in subsidence and/or accumulation rate along the Yates-Capitan shelf margin. (3) Several individual siliciclastic beds can be correlated between each canyon, and the distribution of siliciclastics within individual high-frequency sequences exhibits similar patterns of retrogradation, aggradation, and progradation. Correlative facies-stacking patterns integrated with long-term variations in progradation:aggradation ratio and derived offlap angle act as sensitive indicators of relative changes in base level. Comparison of our integrated field observations with subsurface data from the northern Northwest shelf (65–90 km away), Central Basin platform (approximately 150 km away), and Eastern shelf (>300 km away) reveals a consistent, basin-wide pattern of the internal architecture of the high-frequency sequences that compose the Yates Formation. These widespread similarities provide compelling evidence for regional sea-level control on sequence development around the Permian 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

Abstract The interactive computer simulation, SEDPAK, can track the sedimentary geometries produced by the filling of a two-dimensional basin from both sides, with a combination of clastic sediment and in situ carbonate growth (Strobel et al., 1987, 1988; Heiland-Hansen et al., 1988; Scaturo et al., 1988). The simulation program is implemented in 'C' and has been executed on Apollo and Sun workstations using graphical plotting functions based on the 'X' windows system. Sediment geometries are plotted on the graphics terminal as they are computed, so the user can immediately view the results. Then, based on these observations, the parameters can be repeatedly changed and the program rerun till the user is satisfied with the resultant geometry. SEDPAK models geometries of clastic and carbonate sediments as they evolve through time and respond to depositional processes that include tectonic movement, eustasy, and sedimentation. Clastic modeling includes sedimentary bypass and erosion and sedimentation in alluvial and coastal plains, marine-shelf, basin-slope, and basin-floor settings. Carbonate modeling includes progradation, the development of hard grounds, downslope aprons, keep up, catch up, back step, and drowned reef facies, as well as lagoonal and epeiric facies. Also included is the capability to model extensional vertical faulting of the basin, sediment compaction, and isostatic response to sediment loading.

Abstract Shelf sandstone reservoirs are becoming a more and more common exploration target. What they are, how they may be characterized, and how they differ from shoreline and deep-water deposits in the subject of this publication. Shelf sands and sandstone reservoirs are among the more poorly understood types of sandstones. Continental, shoreline and deep water sandstones have all been studied in much more depth than have shelf sands and sandstones. However, during the last fifteen years significant progress has been made in understanding shelf sands and sandstones. Studies of modern sediments have allowed us to understand many of the depositional processes active on the shelf. This book is intended to be an up-to-date summary of shelf processes and products. The papers are intended for those new to shelf sands and sandstones as well as the shelf specialist.

Abstract A sequence of interbedded anhydrite, red siltstone, dolomite, and halite occurs in the Yates Formation on the Central Basin Platform 15 to 20 mi behind the Capitan shelf-margin. Anhydrite comprises approximately one-half of a 180 ft core from the Yates Formation. Textures within the anhydrite are extremely varied, and include crystallo-topic, nodular, nodular mosaic, mosaic, massive, and bedded massive. Much of the anhydrite and halite appear to have been deposited subaqueously. The depositional environment of the interbedded siltstone and dolomite is uncertain.

Abstract The Goat Seep Dolomite, which immediately underlies the Capitan Limestone, constitutes the lower third of the Guadalupian shelf-margin interval and formed the first large, high-angle, reef-like carbonate unit in the Permian Reef Complex of West Texas and New Mexico. The Goat Seep Dolomite and the Capitan Limestone are similar in that both consist predominantly of inclined strata deposited on a high-relief shelf margin with a steep edge of 25° to 30°, and both can be divided into three similar facies: a shelf-edge or reef facies, a high-angle foreslope, and a low-angle toe-of-slope facies. Shelf-to-basin relief ranged from about 250 m at the beginning of Goat Seep time to 600 m at the end of Capitan time (Fig. 1). The dominant fossils in both are sponges. However, the Goat Seep is not simply an older Capitan, but differs significantly in aspects of morphology, mineralogy, fossils, and cements. Compared to the Capitan, the Goat Seep (1) is largely dolomite; whereas, the Capitan is primarily limestone; (2) has a much thinner to absent shelf-edge or "massive" facies; (3) contains little or no skeletal boundstone, algae, or the problematic organism Tubiphytes , which are common in much of the Capitan (particularly the Upper Capitan); and (4) contains less coarse-fibrous and interparticle cement, interpreted to have an early marine origin. The major similarities and differences between the Goat Seep and the Capitan formations are discussed below and are summarized in Figure 2. Most of the information on the Capitan comes from the work of Babcock (1974, 1977) and Yurewicz (1976, 1977). Data on the Goat Seep are largely from Crawford (1981).

Abstract The Guadalupe Mountains provide dramatic exposures of the Capitan Limestone along the northwest margin of the Delaware Basin. These exposures provide unparalleled opportunities to examine lateral and vertical variations in the Capitan Limestone along a portion of the basin margin. Our work (Babcock, 1974, 1977; Yurewicz, 1976, 1977a) focused on outcrops of the massive facies of the Capitan Limestone in Slaughter, McKittrick, Walnut, and Dark canyons, and was supplemented by studies in Big, Rattlesnake, Bear, and Pine Springs canyons and Jurnigan Draw. These exposures show distinct, progressive changes in the Capitan as it prograded into the Delaware Basin. This paper summarizes those observations (Table 1). In order to document changes within the Capitan, we have divided it into three informal stratigraphic units: the lower, middle, and upper Capitan equivalent to the Seven Rivers, Yates, and Tansill formations on the shelf (Fig. 1). It is important to emphasize that our observations, although extensive, are not necessarily representative of the entire reef trend or even the entire exposed trend in the Guadalupe Mountains.

Abstract The Tansill Formation (Permian, Guadalupian) comprises the youngest back-reef platform facies of the Capitan Reef in the Guadalupe Mountains of New Mexico and Texas (Fig. 1). Here the Tansill is divided into "outer-shelf" and "shelf-crest" facies which pass landward into coeval bedded evaporites and sandstones (Pray, 1977; Mazzullo and Hedrick, 1985). The shelf-crest facies, consisting of peritidal dolomites with conspicuous pisolites, tepees, and some sandstones, is interpreted as a linear, low-lying island complex situated 1.6 km (1 mile) landward of the Capitan Reef (Pray, 1977; Mazzullo and Hedrick, 1985). It is therefore analogous to other island complexes of the Tansill in the subsurface (Ordonez, 1984) as well as to modern outer-shelf islands in Belize (Mazzullo and Reid, 1986). The outer-shelf facies consists mainly of biograins tones and, locally, patch-reefs deposited in shallow, high-energy environments (Mazzullo and Hedrick, 1985). Outcrops in an abandoned quarry near the mouth of Dark Canyon include spectacular exposures of stacked island deposits in the outer-shelf facies tract of the middle Tansill platform (Fig. 2A and B). These exposures lie within 0.8 km (0.5 miles) of the subsurface Capitan Reef shelf margin and are physically separated from contiguous shelf-crest facies (Fig. 2D). The occurrence of these islands is of particular significance in interpreting the depositional history of the Tansill platform, and their study provides critical information on sedimentation and diagenesis as they are related to relative sea-level fluctuations.

Abstract The Permian Basin Complex is characterized by a prograding and aggrading shelf-marginal megafacies which is flanked by a shelf megafacies and a basinal megafacies. Guadalupian units of the shelf-marginal megafacies are the Goat Seep Dolomite and the younger, overlying Capitan Limestone. Shelf strata equivalent to these shelf-marginal units comprise the Artesia Group. The subdivisions of the Artesia Group are the Grayburg, Queen, Seven Rivers, Yates, and Tansill formations. In the Grayburg, Seven Rivers, and Tansill, a broad band of shelf carbonates separates the shelf-margin megafacies from bedded evaporites and evaporite-bearing carbonates further shelfward (Fig. 1). Similar rocks and relationships occur in the Queen and Yates, but, in addition, the Queen and Yates contain several siliciclastic intervals which extend like sheets across the shelf and up to the shelf margin. The Shattuck is one of these siliciclastic intervals. The origin of the siliciclastic intervals is still controversial, some workers advocating predominantly subaqueous transport over a submerged shelf, while others argue for predominantly eolian transport during low sea stands.

Abstract This paper is a summary of a diagenetic study of calcite cements in the Capitan Limestone, McKittrick Canyon, West Texas (Mruk, 1985). This study deciphers the diagenetic history of the Capitan Limestone using basic field observations, detailed cathodoluminescence petrography, and carbon and oxygen isotopes.

Abstract This paper summarizes a detailed investigation of the sedimentology and stratigraphic setting of the lower Seven Rivers Formation in the Guadalupe Mountains, New Mexico (Hurley, 1978). Work is confined to superb exposures in North McKittrick Canyon of a lateral facies transition from bedded shelf carbonates and siliciclastic sediments to the massive facies of the lower Capitan Limestone. The major research questions addressed are: 1. What depositional processes and environments characterize the complex facies mosaic of the lower Seven Rivers Formation and the shelfward edge of the lower Capitan Limestone? 2. Did the shelf-to-basin profile in earliest Capitan time differ from later Capitan times (Yates and Tansill) where this transition has been more thoroughly studied? 3. What is the nature of the Seven Rivers to Capitan facies transition, and what does this transition imply as to growth rate of the early Capitan?

Abstract Lechuguilla Cave is located 3½ miles WNW of Carlsbad Cavern in the headwaters of Lechuguilla Canyon. The more shelfward position of this cave, combined with its great depth, allows the geologist a rare opportunity to study the very heart of the Permian-age Capitan Reef Complex.

Abstract Paleomagnetic methods have been used to obtain both qualitative and quantitative data concerning the depositional and diagenetic environments of rocks from the Capitan Reef Complex (Guadalupian, Upper Permian) in the Guadalupe Mountains of West Texas and New Mexico, southwestern U.S.A. The natural remanent magnetism (NRM) of rocks can be dated using paleomagnetic methods. This information on absolute ages can place constraints on the timing of depositional and diagenetic events. The study of magnetic minerals in rocks can also yield qualitative data concerning the nature of the system in which those minerals developed.

Abstract The youngest Guadalupian shelf deposits in the Permian Basin region of West Texas and southeastern New Mexico are exposed in the Tansill Formation in East Dark Canyon, Guadalupe Mountains, New Mexico (Figs. 1 and 2). Previous investigations of the Capitan Limestone have suggested that Ochoan deposition was foreshadowed by Delaware Basin shallowing conditions (Babcock, 1974; Toomey and Babcock, 1983) and increasing restriction of basinal and shelf waters (Given and Lohmann, 1985) at the end of the Guadalupian. The deposits of the middle and uppermost Tansill Formation (Tyrrell et al., 1978) in East Dark Canyon provided the opportunity to describe and interpret the latest pulses of Guadalupian back-reef sedimentation in the barrier-island complex of the shelf.