Paleozoic evolution of southern margin of Permian basin

CHARLES A. ROSS Chevron U.S.A., Inc., P.O. Box 1635, Houston, Texas 77251

ABSTRACT a relatively stable tectonic area. The Glass those of the Marathon basin (Wilson, 1954b). Mountains expose a series of north- and Faulted and folded sandstone turbidite beds Prior to Late Pennsylvania!! time, the northwest-dipping cuestas of Permian car- identified as the Tesnus Formation (Mississip- Permian basin o f West Texas was a part of bonate shelf and shelf-edge deposits that pian) are also exposed. The stratigraphi; units the southern margin of the North American accumulated on a platform constructed from are the same as those known from the Marathon craton and was the site of shallow, warm- these two allochthonous accretionary basin, and so the Solitario exposes a south- water carbonate deposition. As the South wedges. These Permian deposits prograded south westward continuation of the Marathon American margin of Gondwana gradually north and northwestward into the narrow fold belt. Small patches of Cambrian, Ordovi- moved northwestward during late Paleozoic Hovey Channel, which connected the Marfa cian, and/or Tesnus beds are also exposed be- time, the oceanic floor deposits and overlying basin with the southern end of the Delaware neath Lower Cretaceous beds at the Olc. Jones turbidite fan deposits between North America basin. Carbonate-reef growth finally re- Ranch, southeast of the Marathon basin, and at and South America became parts of large ac- stricted the inflow of marine water into the Persimmon Gap, near the entrance to Big Bend cretionary wedges of semiconsolidated sedi- Delaware basin near the end of late Guadalu- National Park (Fig. 1). ments. In a series of steps, these wedges were pian time. Until the late 1960s and early 1970s, the re- folded and thiust toward the northwest gion west of these erosional windows was against, then fuuilly onto, the southern margin INTRODUCTION poorly understood, and, even at present, only a of North America. These compressive steps general outline seems possible. This region of caused the repeated piling up of the accre- This paper reviews the Paleozoic strata along >8,000 mi2 (25,000 km2) includes the Marfa tionary wedges to form rapidly eroding high- the southern margin of the Permian basin and basin, Hovey Channel, and the southern end of lands on the cratonic margins. Repeated their depositional histories and the tectonic the Diablo Platform (Fig. 3) and is covered by loading on the North American margin events that formed and then closed the southern extensive deposits of Cretaceous and Cenozoic formed a series of elongate, deep-water, dep- end of the Permian basin. The southern margin age. Most of our present understanding of the ositional troughs (fore-deeps) immediately of the Permian basin is almost completely cov- Paleozoic history of this region is based on data north and west of the accretionary wedges, ered by Mesozoic and Cenozoic rocks, except from ~20 deep drill holes and on several small and these received thick accumulations of for two large erosional windows and several exposures of late Paleozoic rocks in the Chinati turbidites. The youngest of these deep basins smaller ones that give us incomplete views (Fig. Mountains (Fig. 1), —50 mi (80 km) west of the include the northwestern part of the Val 1). The largest window is made up of two dis- Marathon basin. These Paleozoic outcrops in- Verde basin to the north and the Marfa basin tinct parts, the Marathon basin and, adjacent to clude thick successions of basinal shale, siltstone, to the west which received basinal deposits it on the north, the Glass Mountains. The other and sandstone turbidites and only minor shal- from within Desmoinesian into early Late large window is the Solitario, a dome ~50 mi low-water units. Permian time. (80 km) to the south-southwest. North of the Glass Mountains, considerably Loading of the cratonic margin also re- The Marathon basin exposes complexly more deep drill-hole data are available. The sulted in renewed faulting along generally folded and faulted strata, most of which were Permian shelf carbonates in the Glass Mountains northwest- to north-trending older zones of deposited in deep-water environments (Fig. 2). were deposited on imbricated thrust sheets, the weakness. These zones are apparently of These strata were deformed and thrust north- youngest of which is middle Wolfcarr.pian in Precambrian a^e. On the craton, the late Pa- westward as allochthonic masses in front of an age, and are composed of basinal turbidites and leozoic faults mainly had high-angle to verti- advancing cratonic mass that came from the clastics. These have been thrust on top of Late cal fault planes and commonly had large southeast (King, 1930b, 1937). In contrast, the Pennsylvanian-early Wolfcampian basinal de- components of horizontal displacement. This Glass Mountains are composed of a succession posits that overlie a cratonic succession made up fault system outlines the major uplifts and of chiefly carbonate strata that form northwest- of carbonate-shelf facies of Middle Pennsylva- basins in the Pe rmian basin region. dipping cuestas (Fig. 2). In comparison to the nian and older beds. The northern limit of these The joining together of Gondwana and Marathon basin, strata in the Glass Mountains thrusts formed the southern edge of the Permian Euramerica across the Marathon salient of are relatively undisturbed and, for the most part, basin, which approximately corresponds to the the orogenic bel t was essentially completed by were deposited as shallow-water shelf or shelf- northern exposures of Permian rocks, in the mid-Wolfcampian time. After that time, the edge beds. Glass Mountains (Moore and others. 1981). southern margiin of the Permian basin, rep- The Solitario (Fig. 1) exposes a much smaller Northwest of the Glass Mountains, the Hovey resented by the Dugout and Marathon area. There, lower Paleozoic strata are com- Channel (Fig. 3) lay between rocks of i;he mid- allochthons and the Diablo Platform, became plexly folded and faulted in the same manner as dle Wolfcampian allochthon and the cratonic

Geological Society of America Bulletin, v. 97, p. 536-554, 10 figs., May 1986.

536

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• FT. \VAN HORN MTNS STOCKTON SIERRA SOUTHERN SHELF O FACIES MADERA

DIABLO SHELF FACIES

I;-': \| MARFA BASIN FACIES MARFA • P^j DUGOUT ALLOCHTHON DUGOUT CREEK FAU LT

t N3 MARATHON \ J ALLOCHTHON HOUSE TOP MTN

JÄ^PINTO CA

RUIDOSA CIBOL8 O CREEK \ (h OLD JONES CHINATI MTNS \ RANCH 1 "àj^MSHAFTER CHa, vy HELLS HALF ACRE - ~<^Df>a,a ^0/ DEVILS BACKBONE FAU LT Figure 1. Location of Paleo- f^^i^^y /0/1" GAP / zoic outcrops in Marathon ba- sin, Glass Mountains, Chinati Mountains, and Van Horn Mountains areas in West Texas.

Diablo Platform. Northeast of the Glass Moun- tain, another channel, the Sheffield Channel, separated the cratonic Central basin Platform from the middle Wolfcampian allochthon.

PREVIOUS INVESTIGATIONS

Many geologists have contributed signifi- cantly to a better understanding of different as- pects of the complex geology of the region. major diastrophism in the Marathon orogenic the region were made. Thomson and Thomas- Many interpretations have been diametrically belt, a problem that continued to hold his inter- son (1964) interpreted the Pennsylvanian Dim- opposed, and these have stimulated lively de- est after retirement, because he wrote me in the ple Limestone as including both shelf and bate. A broad, general understanding of the mid-1960s pleased to have read evidence that turbidite carbonates. McBride (1964, 1966) Glass Mountains-Marathon basin region, how- pieced together at least two major diastrophisms studied the flysch sedimentology of the Pennsyl- ever, does exist and forms the basis for this (Ross, 1963a). Among the most valuable studies vanian Haymond Formation. Ross (1959, discussion. of this era were those of King (1930b, 1937), 1963a) restudied the Permian Wolfcampian Se- Early studies of the geology of the Glass who carefully mapped the Glass Mountains and ries and showed that the last major thrusting Mountains-Marathon basin area and adjacent most of the Marathon basin on a scale of event was within the middle of that epoch. Ross areas started at about the beginning of this cen- 1:62,500 and placed this succession of complex (1967) showed that the shelf facies of the Penn- tury with Hill's (1901) Physical geology of the strata into a stratigraphic and structural frame- sylvanian Gaptank Formation in the northern Texas region. Udden (1907, 1917), Baker and work that others could use. part of the Marathon basin was deposited on a Bowman (1917), and Bôse (1917) made impor- Faunal studies on ammonoids by Smith thrust sheet that included strata as young as late tant early contributions. In the late 1920s, a (1929) and Miller and Furnish (1940), on Desmoinesian. Extensive brachiopod studies by number of geologists looked at various parts of brachiopods and other faunas by R. E. King Cooper and Grant (1972-1977) made the the Marathon basin, the Glass Mountains, and (1932), and on fusulinids by Dunbar and famous Permian silicified faunas of the Glass the Marfa basin and recognized both the impor- Skinner (1937) did much to establish the Glass Mountains much better known. tance and the difficulties of interpreting the re- Mountains as a stratigraphic reference section More recently, interest in the Glass Moun- gion. Schuchert (1927) tried to place the area for the Lower and lower Upper Permian, not tains-Marathon basin and other southern areas into a regional perspective, and King (1930a; only in southwestern North America but world- of Paleozoic exposures has centered on two im- King and King, 1928, 1929) summarized their wide (Adams and others, 1939). portant aspects. First, these outcrops represent early findings in the Glass Mountains. Baker During the 1950s to 1970s, many refinements orogenic-belt sediments and structures asso- (1928) tried to establish a single date for the in our understanding of the geological history of ciated with the late Paleozoic collision of two

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Sandstone, shale, and limestone turbidites, HAYMOND FORMATION DESMOINESIAN 2000 - 4000' (600 • 1200m) upper beds, may include shallow water deposits locally MIDDL E AN D ATOKAN DIMPLE LIMESTONE 300 - 1000' (90 • 300m) Limestone turbidites from northern source PENNSYLVANIA N LOWE R MORROWAN

UPPER TESNUS FORMATION 300 - 6200' (90 • 2000m) Massive sandstone and shale turbidites MISSISSIPPIAN

LOWER MISSISSIPPIAN ? DEVONIAN CABALLOS NOVACULITE Deep oceanic chert and novaculite 250 • 500' (75 • 150m) SILURIAN ?

PERSIMMON GAP SHALE 0 • 60' (0 • 18m) Deep water shale UPPER

MARAVILLAS CHERT Limestone, shale, and chert turbidites 100 - 500' (30 - 150m)

Burrowed shale with thin, graded beds of WOODS HOLLOW SHALE 180 • 500' (55 • 150m) sandstone and calcarenite and boulder MIDDLE beds.

FT. PENA Chert, limestone, and sandstone pebble FORMATION ORDOVICIA N 125 • 600' (35 • 180m) turbidites and boulder beds

ALSATE SHALE Deep water shale 0 • 100' (0 • 30m)

MARATHON LIMESTONE Limestone clastic turbidites and shale; LOWER 350 - 1000' (106 - 300m) boulder-beds

DAGGER FLAT SANDSTONE UPPER Siliciclastic turbidites of sandstone and shale CAMBRIAN 300 • 940' (100 • 310m)

Figure 2. Paleozoic stratigraphie units and their rock types in the Marathon basin-Glass Mountains area. See text for references for each unit.

great landmasses, F.uramerica and Gondwana, considerable distances from their place of origin. posed structures have never been deeply bu ried which formed Pangea (Ross, 1979). Other seg- There is a strong hint of this translocation in the and we see the upper part of the deformed l>elt. ments of the belt have been encountered in drill- Ordovician graptolite faunas, which Berry The second aspect that has continued to at- ing (Flawn and others, 1961). In a very real (1960) found to be closely similar to those of tract interest is the possibility that the Marathon sense, some of the;;e strata, particularly pre- Victoria, Australia. The style of deformation, thrust belt, by overriding both cratonic shelf Mississippian strata, were probably transported furthermore, is relatively unique, in that the ex- deposits and some of its own synorogenic trough

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TRIASSIC ? BISSETT CONGLOMERATE

TESSEY LIMESTONE OCHOAN ? 1000' (300m) Calcitized anhydrite and associated beds

CAPITAN LIMESTONE Reef (Vidrio Member), back-reef (Gilliam Mbr), 1800' (540m) and upper-slope (Altura Mbr.) facies

GUADALUPIAN

WORD LIMESTONE Reef, back-reef, fore-reef, and upper-slope 500 • 800' (150 • 240m) facies

ROAD CANYON FORMATION Reef, back-reef, fore-reef, and upper-slope Z < 150 • 200' (45 • 60m) facies S OC CATHEDRAL MOUNTAIN / / LU FORMATION 4 4 Fore-reef and upper-slope limestone and LEONARDIAN sandstone facies

SKINNER RANCH ^ FORMATION HESS Reef, back-reef, fore-reef, and upper-slope 650 - 1400' ? pM. (200 • 420m) 7 1850' (560m) facies

LENOX HILLS Reef and biohermal limestone; back-reef FORMATION limestone, shale, sandstone; fore-reef 0 - 650' (0 • 200m) clastic facies; conglomerate WOLFCAM PIAN NEAL RANCH Biohermal limestone, FORMATION shale, sandstone, 0 - 270' (0 • 81m) and conglomerate -o . Limestone and "5 ® sandstone akz VIRGILIAN Shelf-edge limestone ìu «/) < GAPTANK FORMATION §)iS turbidites «LZ 5 ^ CQ 0. z < 1900' (570m) Shelf sandstone = MISSOURIAN Fluvial conglomerate ?o

Figure 2. (Continued).

deposits, has formed significant petroleum traps Ammon (1981), Luff (1981), and Moore and not found in association, these rocks are inter- in strata of the same age as those of known others (1981). preted as having been deposited as turbidite fans producing reservoirs in areas to the north. Re- and open deep-ocean sediments in a passive area cent publications that examine one or both of DEPOSITIONAL HISTORY: of an ancient ocean crust and subsequently these aspects include several field conferences MARATHON BASIN AND stripped off well above the oceanic crust. and symposia of the Permian Basin Section of GLASS MOUNTAINS The oldest beds exposed in the Marathon SEPM (Mazzullo, 1978; Jons and others, 1981). basin belong to the Late Cambrian Dagger Flat Subsurface data from the southern shelf are Pre-Mississippian Sandstone (King, 1937; Wilson, 1954a). Most relatively scattered and commonly difficult to of the Dagger Flat is made up of turbidite clastic interpret. Much of the Glass Mountains-Mara- The lower Paleozoic succession is composed beds (Anan, 1965; McBride, 1969a) that grade thon basin well data was summarized by Hall of turbidites and novaculites (Fig. 2). Although upward with no apparent break in deposition (1956) and more recently by King (1978,1980), basic volcanic rocks typical of oceanic crusts are into the overlying Marathon Formation.

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Thomson, 1964). Sandstones in the upper part of the Tesnus have markedly coarser grain sizes and also include significantly more metimor- phic and granitic rock fragments, suggesting that new sources of clastics became available abrupt- ly as a result of tectonic displacements or ex- tremely rapid erosion. Both paleocurrent direc- tions (Johnson, 1962) and the direction of thickening and coarsening indicate a rapidly eroding source area to the southeast. The Tesnus Formation is of considerable significance, be- cause it represents the beginning of the filling stage of a deep oceanic basin that had been far EXPOSED PALEOZOIC ROCKS distant from clastic sediment sources for nearly

T77\ NORTHERN SHELF & 120 m.y., that is, for Silurian, Devonian, and XZA BASIN FACIES perhaps much of Mississippian time. [Vj MARFA BASIN FACIES The age of the Tesnus is not well delimited. ] SOUTHERN SHELF FACIES The lower part of the Tesnus has Mississippian conodonts, and beds near the top of the underly- | | DUGOUT A LLOCHTHON ing Caballos have Late Devonian conodonts MARATHON ALLOCHTHON (Ellison, 1962). Either or both of these conodont faunas could be reworked in these turbidites. A Figure 3. Late Paleozoic tectonic features of West Texas (modified from Flawn and others, Pennsylvanian age assignment for the highest 1961, and other sources). part of the Tesnus may be possible, because Sanderson and King (1964) found Moi rowan The Marathon Formation, the lowest of the formably above the Maravillas in the southern assemblages of fusulinids only locally in the Ordovician units, includes sandstones, siltstones, part of the region. lower part of the overlying Dimple Limestone. shales, calcarenites, limestone-pebble conglom- The Caballos Novaculite overlies the Maravil- This suggests that the upper beds of the Tesnus erates, and boulder olistostromes (Young, las and Persimmon Gap Formations with ap- may intertongue with the lower part of the 1969). The dark shales contain a typical oceanic parent conformity (McBride and Thomson, Dimple, and therefore the Tesnus may be partly assemblage of graptolites, sponge spicules, and 1969). The Caballos is apparently Silurian and Pennsylvanian in age. conodonts; the sandstones and siltstones have Devonian in age, although only the upper fragments from typical shallow-shelf assem- member is firmly dated as Late Devonian on the Lower and Middle Pennsylvanian blage of mollusca, brachiopods, trilobites, and basis of conodonts (Graves, 1952; Berry and algae. The olistoitromes include many types of Nielsen, 1958; Ellison, 1962). In view of the Dimple Limestone. The Dimple Limestone limestones, dolostones, sandstones, cherts, and basinal depositional history of the Late Cam- (Fig. 2) is a succession of Lower anc. lower rare volcanic rocks. The Alsate Shale was re- brian and Ordovician rocks below and also of Middle Pennsylvanian cherty limestones with corded by Young (1969) as the upper member the Mississippian and Lower and Middle Penn- some shales, conglomerates, and bedded chert. It of the Marathon Formation. sylvanian rocks above the Caballos, and of the represents a range of shelf, slope, and basinal Middle Ordovician rocks include the Fort lack of evidence of major diastrophic events environments of deposition, as interpreted by Pefia Formation and Woods Hollow Shale within this part of the succession, a deep-basinal Thomson and Thomasson (1964). They showed (King, 1937; Berry, 1960; McBride, 1969b, origin for the Caballos away from sources of that a carbonate-shelf facies is exposed along the 1969c). Boulder beds in the Woods Hollow shelf debris seems likely, notwithstanding the northern part of the Marathon Basin, where the Shale were interpreted by Wilson (1954b) as objections raised by Folk (in Folk and McBride, Dimple consists of 250-300 ft (75-90 m) of being turbidite flows. Thomson (1964) and 1978). This is also suggested by the very low oolitic and fossil fragmental grainstones and McBride (1969c) presented additional evidence depositional rates for these siliceous sediments conglomerates. The Dimple slope facies forms a supporting a basinal turbidite environment for (Thomson, 1964). four-mile band to the south of the shelf carbon- the deposition of both the Fort Pena and Woods ate facies. These two facies grade and inter- Hollow Formations. Mississippian tongue, indicating a gradual topographic: change The Upper Ordovician Maravillas Formation from shelf to slope. Individual slope linestone represents a rapid change from a mainly shale Tesnus Formation. The Tesnus Formation beds are mainly nongraded in their uppsr parts. depositional regime to a mainly calcarenite re- (Fig. 2) lies conformably and, in places, grada- They are chiefly packstones. Boulders are locally gime (Berry, I960; McBride, 1969c). Bryozoan- tionally above the upper chert and shale common, as are lime mudstones. rich limestones are common, but all have been member of the Caballos Novaculite. Cotera The Dimple basinal facies attains >900 ft derived from shallower environments and rede- (1969) showed that in the northwestern part of (270 m) thick and is widespread in most of the posited as turbid ite beds. The interpretation that the Marathon Basin the Tesnus consists of 300 ft Marathon basin. The lithologies of this facies the Maravillas also was deposited in a deep- (90 m) of mostly shale with some sandstone. To pass gradationally from those of the slope facies. water, turbidite basin seems to have been well the southeast, the Tesnus thickens to >6,200 ft The basinal limestones are characteristically documented by McBride (1969d). The thin Per- (1,880 m) of massive sandstone and shale tur- graded with internal convolutions and £.re lami- simmon Gap Shale (Wilson, 1954b) lies con- bidites in about equal proportions (McBride and nated in their upper part. Spicules are common,

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and shales form the interbedded rock. Siliceous up in the Dugout Creek thrust and Tertiary (Ross, 1963a, 1967) that are three or four zones bands may replace considerable portions of the faults. (These beds are shown as Gaptank For- younger than those of the Chaetetes-bearing limestone turbidites. mation on maps by King, 1930b, 1937.) limestone near Gap Tank. King probably was In contrast to the underlying Tesnus siliciclas- Haymond Formation. The Haymond For- not able to study this locality except cursorily, tic turbidites, the Dimple Limestone turbidites mation (McBride, 1966) (Fig. 2) overlies the because he mapped this area as Tesnus and originated on the northern and northwestern Dimple conformably, and the two formations Dimple Formations on both his 1930b and sides of the Early Pennsylvanian depositional are transitional through as much as 300 ft (90 1937 maps. This fauna indicates that much trough and were transported southeastward to m) of gradational and alternating changes in more Desmoinesian strata are present in the form a thick wedge on the northern side of the lithologies. In the eastern part of the Marathon Haymond turbidite facies than indicated by ex- trough. This wedge thinned southeastward into Basin, the Haymond consists of 4,000 ft (1,200 posures near Gap Tank and that Haymond dep- more distal turbidite facies (Thomson and m) of repetitively interbedded sandstone and osition extended almost to the end of Des- Thomasson, 1964). shale of distal turbidite origin. In comparison to moinesian time. The Dimple carbonate shelf area is within the Tesnus proximal turbidites, the Haymond One, and possibly several, intervals of chaotic one of the allochthonous thrust sheets, and so it turbidites typically are thinner (0.5-2 ft thick) bedding with large olistostromes occur in the obviously was not part of the cratonic shelf area (0.15-0.6 m) and more evenly bedded. The upper part of the Haymond in the eastern part of that must have been still farther to the northwest sandstone and shale couplets are of about equal the basin. The most famous are the Haymond at that time. Ross (1979) suggested an uplifted thickness. The lower part of the Haymond inter- boulder beds, -650 ft (200 m) thick, near welt of ocean-floor sediments as a local shelf tongues with the upper part of Dimple, and so it Housetop Mountain (King, 1937, 1980). The on which shallow-water Dimple carbonates is at least as old as late Atokan. The youngest origin of these has been extensively studied formed. Other shelf and slope carbonates also fossils in the Haymond are on the lower slopes (King and others, 1931; Sellards, 1931; King, occurred in the northern part of the Marathon of the southern flank of Leonard Mountain, 1932, 1937, 1958, 1978, 1980; Baker, 1932; Basin in the Haymond Formation. where folded and faulted, orange-brown-weath- Carney, 1934; Hall, 1957; McBride, 1964, Sanderson and King (1964) studied fusulinids ering, dark gray limestone, and sandstone 1966). When first studied in the early 1930s, from the Dimple and were able to establish that turbidites contain late Desmoinesian fusulinids these boulder-bearing beds were confused with three zones were present. The lowest, the Zone of Millerella, is not widely distributed but does indicate that the lower part of the Dimple was Vacuum Elsinore, No. 1 locally Morrowan in age. The Zone of Profusu- linella of Atokan age is widely distributed in the shelf and slope facies of the Dimple. The Zone of Fusulinella of late Atokan age also occurs in the Dimple in the western part of the Marathon Basin. At Black Peak in the western part of the Marathon Basin, the Zone of Profusulinella in- cludes a section, possibly overturned, of shelf carbonates that may be a cratonic facies caught

Figure 4. Generalized geo- logic map of the Glass Moun- tains and northern part of the Marathon Basin, showing lo- cations of measured sections used in Figures 5 and 6. In- cludes sections from King (1930b) and Ross (1960, 1962, 1963a, 1963b, 1965, 1967).

Measured section Capitan Limestone and Tessey Limestone Upper Wolfcampian 3 through Word Fm. Upper Pennsylvanian and Lower Wolfcampian (shelf facies) Dugout Allochthon m (basin facies) Marathon Allochton 15 Miles

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many other types of coarse conglomeratic de- tailed measured section, in which he used a dark thon, Ross (1967) revised the base of the Gap- posits, including glacial deposits having erratics. gray, lower Desmoinesian (Middle Pennsylva- tank Formation so as to include the Chaetetes- It was not until a much more complete under- nian), CTwete/es-bearing limestone, the lowest bearing limestone in the Haymond Formation. standing of continental-slope and ocean-floor easily datable bed in the Gap Tank area, as the King (1980) did not accept this change. deposits became available during the 1950s and base of the Gaptank Formation and placed the 1960s that it became possible to find convincing underlying 1,800 ft (500 m) of sandstone, shale, Middle Pennsylvanian Orogeny and the: similarities in these Haymond deposits to prox- and conglomerate beds in the Haymond. King Marathon Allochton imal turbidites, or wildflysche. The boulders fall (1930b, 1937) was able to locate the Chaetetes- into two main groups: larger ones that are de- bearing limestone in several outcrops to the In the later part of the Desmoinesian into rived from sedimentary rocks that can be recog- southeast in a series of open and tight folds. The early Missourian time (—6 m.y.), major com- nized from exposures within the Marathon Basin fossils in this bed are not in growth position, and pressional faulting, folding, and thrusting de- area and mainly smaller ones that are exotic and it is possible that this bed, like similar beds of formed the sediments that had accumulated in are not known from the immediate area. This middle Desmoinesian age just east of Dugout the sedimentary trough in front of the orogenic latter group includes sedimentary, igneous, and Mountain, may be a turbidite. The Chaetetes- belt between South America (Gondwana) and metamorphic rocks, the ages and sources of bearing limestone is both underlain and overlain North America (Euramerica). The sedimentary which are not known. From a third, much rarer, conformably by dark, thin-bedded shales and mass could not be accommodated in the trough group of limestone boulders in the upper part of sandstones from which no diagnostic fossils have and so was forced as an accretionary wedge, the Haymond, Palmer and others (1984) identi- been reported. The major change in depositional referred to as the "Marathon allochthcn" by fied Middle Cambrian faunas that they believed pattern, however, above these beds is at the base Ross and Ross (1985), onto the southern margin originated from the cratonic carbonate margin of the fluvial and near-shore conglomerates of of the North American craton. Accretion of this 100 to 200 km southeast of their present loca- the conglomerate member of the Gaptank For- sedimentary wedge had extensive structural tion. Girty (in King, 1937) reported extensive mation. The base of this conglomerate member ramifications for the region north and west of shallow-water faunas from several larger lime- marks an erosional hiatus of five Desmoinesian the Glass Mountains. It resulted in major stone blocks and made tentative comparisons fusulinid zones (that is, most of the Desmoines- movements on the fault-bounded platform and with Lower Pennsylvanian (Morrowan) faunas. ian) and at least two zones at the base of the basin topography constituting the Central basin Sellards (1931) and Baker (1932) reported on Missourian, a span of -14 m.y. As the Platform, Diablo Platform, Eastern Shelf, and collections from limestone blocks in the same Chaetetes-bearing limestone is part of the Hay- Midland and Delaware basins (Kluth and area that were examined by F. B. Plummer, who mond depositional phase of the succession and Coney, 1981). Its oblique motion across ancient, believed those collections included Middle lies within (rather than on) the Marathon alloch- nearly north-south, zones of crustal weakness Pennsylvanian faunas. Above the main boulder beds, the upper WOLF CAMP HILLS member of the Haymond Formation is -1,000 NEAL ft (300 m) of rhythmic, sandy carbonaceous RANCH c shales and sandstones. In its type area, the high- FM. i. est Haymond is exposed in the axis of a syncline, and the type section lacks a stratigraphic top. Haymond lith.ologies are exposed in the northeastern part of the Marathon Basin (Figs. 4 and 5), where King (1937) was able to measure as much as 1,800 ft (545 m) of Haymond beds beneath a Chaetetes-bearing limestone. In the upper part of these exposures, -400 ft (120 m) below the Chaetetes-bearing bed, King located boulder-bearing beds that he correlated with those in the upper part of the type Haymond. These boulder beds are rich in Caballos Novacu- lite and Maravillas chert and limestone clasts, in LEONARD MT. contrast to the boulder beds near Housetop 10 B Mountain, which have appreciable amounts of LENOX HILLS FM. Tesnus sandstone, Pennsylvanian limestone, and rhyolite cobbles (King, 1980). Flores (1972, GAPTANK FM. Figure 5. Gaptank and Neal Ranch 1975, 1978) proposed that these beds were a (Middle Missourian) Formations in the northern part of the braided-fan delta, although not everyone has ac- Marathon Basin, showing relationship cepted this interpretation (McBride, 1975). HAYMOND FM. (Upper Desmoinesian) of facies and of unconformities. These The top of the Haymond Formation is not units are overlain unconformatily by exposed in the Haymond type area, and so its the Lenox Hills and Brooks Ranch upper stratigraphic boundary has been deter- Formations and underlain unconform- mined by defining the base of the overlying Gap- ably by the Haymond Formation. tank Formation in the northeastern part of the Data from Ross (1963a, 196:5, and Marathon Basin. King (1930b) published a de- 1967).

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also loaded the cratonic margin immediately to reasons discussed above, Ross (1967) restricted Tank. The limestone bed at the base of this the north of the allochthon, which created fore- the type Gaptank Formation to shallow-water member can be traced westward for 2 mi (3 deeps, the Val Verde and Marfa basins, into shelfal clastics and carbonates that were depos- km), where it gradually thins, becomes darker in which Late Pennsylvanian and early Wolf- ited on the surface of the Marathon allochthon. color, and pinches out into sandstones and campian turbidites were rapidly deposited. The These are Missourian and Virgilian in age. shales. Higher limestones in this member form a Marathon allochthon (Fig. 3) formed a highland In the type section of the Gaptank Formation, low, discontinuous limestone cuesta westward that effectively formed the southern boundary of the conglomerate member -550 ft (165 m) along the base of the Glass Mountains to the the Permian basin region. Shelf sediments of the thick (Figs. 4 and 5A) rests unconformably on Wolf Camp Hills. The individual limestones Gaptank Formation were deposited on the faulted and folded strata of Desmoinesian and form an off-lapping series of shelf-edge carbon- eroded surface of this highland, which was not older age. The conglomerates are predominantly ate banks that cumulatively total -800 ft (240 unlike the present topographic surface of the well-rounded, size-sorted limestone cobbles. m). They are of latest Missourian to Virgilian in northern part of the Marathon basin from Leon- Most are derived from the Dimple Limestone or age. From the western end of the Wolf Camp ard Mountain to Gap Tank. A wide channel the Chaetetes-bearing limestone bed, both of Hills to Leonard Mountain, the Gaptank Forma- and fore-basin separated the highlands of the which are exposed nearby. Smaller clasts in- tion is not exposed, presumably because the allochthon from the Diablo Platform and con- clude nearly all of the lithologies represented in limestone member was not deposited in this area nected the Permian basin to an ocean to the the Paleozoic succession exposed in the northern or was formed a few miles south of the present southwest at this time. part of the Marathon Basin. The five main beds mountain front and subsequently has been of conglomerate pinch out rapidly toward the eroded. Missourian and Virgilian Series north, where they intertongue with limy and At Leonard Mountain, a 200-ft (60-m) chert- shaly sandstones containing lower middle Mis- pebble conglomerate, a 40-ft (12-m) limestone Gaptank Formation. The name "Gaptank sourian faunas (Ross, 1965, 1967). The lowest of Missourian age, and a 150-ft (45-m) covered Formation" was originally applied by Udden {in conglomerate bed is the most extensive. These interval represent the Gaptank Formation (Fig. Udden and others, 1916) to Upper Pennsylva- conglomerates were deposited in fluvial, beach, 5B). The Gaptank shelf apparently was only a nian strata at the locality known as Gap Tank in bar, and river-mouth spit environments. few miles wide, and this shallow-shelf facies is the Stockton Gap in the northeastern part of the The middle member of the Gaptank Forma- exposed only from Leonard Mountain to just Marathon Basin. Originally, it included at the tion consists of 550 ft (160 m) of mainly sand- east of the Allison Ranch, -20 mi (32 km), top some rocks of Wolfcampian age (Neal stone and shale, with 3 or 4 limestone beds. The where it is covered by younger rocks. Ranch Formation), which Udden (1917) later sandstones are similar to those between the con- The cuesta formed by the limestone member excluded from the formation. In the original glomerate lenses in the underlying member, and is in part discontinuous, because the limestones description, the base of the Gaptank Formation the limestones first appear as thin, discontinuous are a series of off-lapping shelf-edge, shelf, and was not well defined. King (1930b) chose the beds in the shale-rich units. These are upper back-shelf limestones that become younger to lower Desmoinesian Chaetetes-bearing lime- Missourian. the west. Each of the shelf limestones passes stone bed, a bed within the Marathon alloch- Only the lower part of the limestone member westward into a deeper-water tongue before thon, as the base of the Gaptank Formation. For of the Gaptank Formation is exposed at Gap pinching out into shaly and sandy beds. Succes- sive shelf limestones built out over clastic wedges of sandstone to form new limestone shelves that prograded basinward. Locally, as in the Wolf Camp Hills, repeated but gentle fold- ing of the underlying allochthon continued dur- ing Late Pennsylvanian time and resulted in minor unconformities within the Gaptank lime- stones. Such unconformities are particularly notable in the part of the section containing the Uddenites-beanng shale bed in the Wolf Camp Hills. The highest of these shelf-edge carbonates is exposed in the Wolf Camp Hills, where it has been called the "gray limestone bed or member" (King, 1930b). It is important in being one of several "marker" beds that has featured in var- ious attempts to define a Pennsylvanian-Per- mian boundary in the Glass Mountains. Litho- logically, it is similar to the other shelf-edge carbonates of the Gaptank Formation and can be traced 5-6 mi (9-10 km) east of the Wolf Camp Hills before it is truncated by erosional channels in the Lenox Hills Formation. Ross (1963a, 1965) showed that the fusulinid faunas from this bed were Virgilian (Pennsylvanian) in age.

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Triassic (?) o/

Figure 6. Facies relationships and regional unconformities in the Lenox Hills, Skinner Ranch, Hess, Cathedral Mountain, Road Canyon, Word, Capitan, arid Tessey Formations in the Glass Mountains. Leonardian nomenclature modified from Cooper and Grant (1966). Othet data from King (1930a, 1937) and Ross (1960,1962,1963a, 1963b).

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Permian: Wolfe; unpian Series beds," although clearly useful in recognizing im- 1959, 1963a). In Dugout Mountain and in the portant lithologic differences, have only been Lenox Hills, this unit forms the lower par; of the Neal Ranch Formation. The lowest Wolf- quoted (as here) but never seriously raised to escarpment and rests on strongly folded and campian beds, the Neal Ranch Formation formal stratigraphic status. The "Dugout beds" faulted beds of Pennsylvanian and early Wolf- (Ross, 1959,1963a), rest unconformably on the represent the filling of a fore-basin and include campian age (Baker's "Dugout beds") £.nd lo- shelf-edge limestones of the Gaptank Formation distal turbidites of Desmoinesian age and pro- cally on outliers of older Paleozoic beds in the in the Wolf Camp Hills and at Gap Tank (Fig. gressively more proximal turbidite facies of Late Dugout Creek thrust sheet. At the south eastern 5A). The Neal Ranch Formation, if deposited in Pennsylvanian and earliest Wolfcampian age. end of Leonard Mountain, the Lenox Hil ls For- the intervening .12 mi (20 km), has been re- Locally, fairly shallow-water carbonates of Neal mation rests on a 150-ft (45-m) covered interval moved by pre-Lenox Hills erosion. The Neal Ranch age make up some of the thicker beds, of undetermined beds that lie above shallow- Ranch Formation is a succession of ~12 cyclical such as adjacent to the Lenox Hills area (Ross, water Gaptank shelf limestones. Farther east, shales and calcarenites having numerous, small, 1963a). near the Wolf Camp Hills, it consists of a per- circular bioherm:; ~3 ft (1 m) high and 10-20 ft sistent conglomerate and shale section that cov- (3-10 m) in diameter. The bioherms are rich in Middle Wolfcampian Orogeny and the ers and truncates the Neal Ranch Formation. fossils, including sponges, bryozoans, corals, Dugout Allochthon Eastward, it locally cuts through the upper parts brachiopods, and the fusulinids Pseudoschwager- of the limestone member of the Gaptank ina, Paraschwagerina, Schwagerina, and ad- After deposition of the Neal Ranch Forma- Formation. vanced species of Triticites. West of the Wolf tion and beds of equivalent age in the "Dugout The base of the Lenox Hills Formation is an Camp Hills, the Neal Ranch Formation abruptly beds" succession, thrusting was renewed (Ross, unconformity that is nearly everywhere marked loses its bioherms and calcarenites and passes 1963a, 1978). This tectonic event, termed the by the accumulation of conglomerates and into a shaly succession that is covered by allu- "Dugout orogeny" by Ross and Ross (1985), coarse clastic deposits (Ross, 1963a). In Dugout vium. The topographic high caused by the mas- also deformed and resulted in the lithification of Mountain, a thick conglomeratic delti front sive shelf-edge gray limestone bed thus contin- the "Dugout beds" into a cohesive allochthon passes into sandy fore-delta beds having a few ued to act as a residual high area around which called the "Dugout allochthon" by Ross and fossiliferous, calcarenitic marine limestones. In small, early Wolfcampian bioherms could Ross (1985). Its deformation was much like the the Lenox Hills, the transgressive basal unit con- accumulate. history of the older Marathon allochthon. Most tains large, tumbled blocks of penecontempo- The Neal Ranch Formation is overlain un- of the Dugout allochthon is covered by younger raneous limestone bioherms, indicating steep conformably and truncated eastward by con- Permian strata or, to the east, by the older Mara- slopes and strong wave and current action. glomerates at the base of the Lenox Hills thon allochthon, which overrode part of it from These are overlain by prograding delta and fore- Formation. The Neal Ranch exposure at Gap the southeast. The sole thrust of the Dugout al- delta deposits similar to those at Dugout Tank rests on lower Virgilian limestones and lochthon is not exposed but is believed to have Mountain. At Leonard Mountain, the lower part was protected from erosion by being dropped been penetrated by a number of wells drilled in of the Lenox Hills Formation is a thick w edge of down by a small. post-Neal Ranch-pre-Lenox the area, including the Slick-Urschel, Decie No. conglomerates that filled a channel and "hat are Hills fault (Ross, 1963a). 1, at the base of the Lenox Hills, which passed overlain by coarse deltaic deposits. Here, bio- "Dugout Beds," Western Marathon Basin. through a probable thrust at a depth of 1,600 ft herms formed adjacent to the delta and eventu- West of the Dugout Creek thrust fault (Fig. 4) in (490 m) (Hall, 1956). This well then drilled ally built a massive reef-like feature that forms the western part of the Marathon basin, a se- through another 5,000 ft (1,500 m) of early the southeastern point of the mountain. Just quence of turbidites, conglomerates, sandstones, Wolfcampian and Late Pennsylvanian turbidites north of the Hess Ranch house, at the entrance shales, and limestones includes strata of Des- and basinal facies before passing into a lower to Hess Canyon, the edge of the bioherm,il facies moinesian, Missourian, Virgilian, and early Desmoinesian shelf carbonate. The remainder of is exposed. Eastward, this facies passes into fine- Wolfcampian (Neal Ranch) ages (Baker, this well drilled cratonic shelf facies and bot- grained carbonates and becomes interbedded 1928; King, 1930b, 1937; Ross, 1963a; Cys, tomed in Ellenburger Dolostone at a depth of with silt- and shale-rich beds. Just west of the 1977). King (1930b, 1937) assigned beds ex- 9,637 ft (2,920 m). The westward extent of the Wolf Camp Hills, the conglomeratic lower part posed in the axis of an anticline just east of nearly buried Dugout allochthon is difficult to of the Lenox Hills Formation appeal's from Dugout Mountain to the Haymond Formation, determine, however; it may not extend beyond under the alluvium and can be traced aistward on the basis of Lthologic similarities and a col- the edge of the Capitanian carbonate-shelf build- as a series of conglomerate-filled channels to lection of middle Desmoinesian fossils from a up at the western boundary of the Glass Moun- Gap Tank and eastward to near the old Allison limestone turbidite that he used as the local base tains, a distance of only 4-5 mi (6-8 km) west Ranch house. The silty and shaly bed:; above of his Gaptank Formation, even though the bed of the Slick-Urschel, Decie No. 1. The northern have a few marine limestone tongues in the was younger than the ChaetetesAxaxvng lime- extent of this allochthon (Fig. 3) was shown by vicinity of the Wolf Camp Hills; however, east- stone near Gap Tank. Moore and others (1981) to be ~7 mi (11.5 km) ward they become mainly clastic red beds. north of the Glass Mountains escarpment and Wilde (1984) named this clastic red-bed facies Baker (1928) recognized the strong lithologi- buried beneath 5,000-6,000 ft (1,500-1,800 m) the "Brooks Ranch Formation." cal differences !>etween these western basinal of Permian sediments. The western extent was beds and their coeval shelf facies to the northeast The Lenox Hills Formation represents the delimited by Ammon (1981), Keller and others and proposed the name "Dugout beds" for synorogenic and early postorogenic deposits that (1981), and Pearson (1978, 1981) and is dis- them. As this was before most stratigraphers and formed on the western and northern ma rgins of cussed in the Marfa basin part of this paper. biostratigraphers had tried to separate fossil the combined Dugout and Marathon alloch- zones, depositicmal environments, and rock Lenox Hills Formation. The upper part of thons. As such, the Lenox Hills Formation rep- units, Baker's proposal was criticized unduly by the Wolfcampian Series in the Glass Mountains resents a diverse set of marine, marginal-marine, King (1930b). Since then, Baker's "Dugout (Fig. 6) is the Lenox Hills Formation (Ross, and nonmarine facies that are traceable laterally

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along the entire lower face of the Glass Moun- ian) fauna (Ross, 1963a), and the base of the medium-bedded limestone and thin-bedded tains and is the lowest and oldest unit that post- type Leonard Formation was revised to exclude chert that pass upward into dark sandstone, dates major thrusting in the Marathon-Dugout these beds. The Leonard Formation on Leonard shale, and thin calcarenitic limestones. It is fold belt. The top of the Lenox Hills Formation Mountain is composed mostly of thin- to overlain by a massive, reefal to biohermal shelf is marked by an unconformity. After the Lenox Hills Formation was deposited, it was broadly West of Shaffer warped, and in places, as at the southern end of Dugout Mountain, subsequent erosion has (Guadalupian reef) nearly cut through it.

Leonardian Series

Udden (1917) named strata that formed the crest and north slopes of Leonard Mountain the "Leonard Formation." King (1930b) showed that the massive bed at the base of the forma- Pinto Canyon tion, which forms the southeastern point on Leonard Mountain, was traceable into beds just north of the Hess Ranch house at the entrance to Hess Canyon. These lower beds later were shown to carry a Lenox Hills (upper Wolfcamp-

Pinto Canyon Fm North of Shatter (Leonardian) Sierra Alta and Cibolo Creek ^T (Leonardian?)

Cibolo Fm. 1-1000 r300 (late Wolfcampian)

200 500 100 Pinto Canyon 104°15' -\-30°00 0 0 Alta Fm. Feet Meters (early Wolfcampian?) Mina Grande Fm. 3000 feet not shown Ross Mine Fm.

Figure 7. Late Paleozoic TT1 Pinto Canyon Fm. stratigraphie units in the Marfa Basin succession as Cibolo Fm. exposed in the Chinati >X] Alta Fm. Mountains and their corre- lation with units in the Glass Cieneguita Fm. Mountains. Data from Am- Cieneguita Fm. 0 5 MILES nion (1981), Amsbury (1958), i u Keller and others (1981), Luff 0 5 KM. (1981), Rigby (1953), Rix (1953a, 1953b), and Skinner (1940). 29°45'-\- (Desmoinesian) 104°30'

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limestone, the Road Canyon Formation clude all three of these subdivisions, and, ten eastward with time (Fig. 6) and was located (= "Word number 1 limestone" of King, 1930b, years after Furnish's proposal, "Leonardian" is nearly 1-1.5 mi (2-3 km) east of the Old Word 1937). still used in that wider sense, I propose here the Ranch house just prior to the beginning of Road The Glass Mountains escarpment rises name "Cathedralian Stage" as a replacement Canyon deposition. abruptly east of the Hess Ranch house and is name for (and thus abandon) Furnish's re- Hess Formation. The Hess Formatior is the held up by resistant reefal and lagoonal lime- stricted use of the "Leonardian" Stage. back-reef and lagoonal facies of this reef trend stones to which Udden (1917) applied the Skinner Ranch Formation. The type section and is composed chiefly of fine-grained, thick- to name "Hess Formation." These beds continue of the Skinner Ranch Formation is on the medium-bedded limestones that can be traced eastward, forming the crest of the Glass Moun- southwestern face of Leonard Mountain (Fig. many miles to the east. Some sandstones, silt- tains until they arc finally covered by Cretaceous 6), below the westernmost knob (Cooper and stone, and shale intertongue with these lime- strata several miles east of Gap Tank. Udden Grant, 1964). It consists of 509 ft (153 m) of stones and thicken gradually to the east. Locally, (1917) believed that the Hess Formation lay be- thin-bedded to massive calcarenitic and calciru- dolostone is common in the upper part of the neath the Leonard Formation, because both the ditic limestones, with some interbedded silt- Hess. Several unconformities are traceable reef facies (Hess) and the more clastic western stone, shale, and chert. Additional studies by through this facies (Fig. 6), including one at the facies (Leonard) shifted eastward with time, so Cooper and Grant (1966), Rogers (1978), base of the "Hess fossil bed" of King (1930b) (= that the more clastic facies appears to lie consis- Flores and McMillan (1981), Flores and others Taylor Ranch Member), another 250-600 ft tently on the reef facies. King (1937) recognized (1977, 1978), Cys and Mazzullo (1981), and (75-180 m) higher in the succession, and that this was a classic example of changes caused Cys (1981) showed the Skinner Ranch had a another 200-300 ft (60-90 m) below the base by lateral shifts of contrasting facies and pointed complicated depositional history. Rogers (1978) of the Road Canyon Formation. out that the total thicknesses of the Leonard and showed that the two limestone tongues, the Cathedral Mountain Formation. The Cath- the Hess were mutually complementary, one Decie Ranch and Sullivan Peak Members, edral Mountain Formation (Cooper and Grant, thickening as the other thinned. which extend to the southwest of Leonard 1964) lies conformably on the Skinner Ranch By 1939 (Adams and others, 1939), the Leon- Mountain, are composed of limestone clastics Formation and is composed of yellow to dark ard Formation (and its Hess Limestone Mem- that include large, rounded blocks derived from gray siliceous shales, siltstones, and sandstones ber) had become the North American reference erosion of the Lenox Hills Formation below, as with a number of clastic (calcarenitic and calci- section for the Leonardian Series of the Permian. well as displaced and jumbled bioliths dislodged ruditic) limestones. The Cathedral Mountain in- Several comprehensive studies have described from contemporaneous Skinner Ranch bio- cludes much of the former Leonard Formation the faunas, includ ing brachiopods (R. E. King, herms and patch reefs. This reworking of large as mapped by King (1930b). It thickens to >900 1931; Cooper and Grant, 1972-1977), fusulinids Lenox Hills limestone blocks explains why sev- ft (270 m) to the southwest of Leonard Moun- (Dunbar and Skinner, 1937; Ross, 1960,1962), eral typically upper Wolfcampian species, found tain and thins to <200 ft (60 m) to the east, and cephalopods (Bose, 1917; Miller and Fur- in rare isolated samples, were thought previously where it intertongues with bioherms anc. small nish, 1940). to range from the Lenox Hills into the Skinner reefs in the upper part of the Skinner Ranch Ranch. These species include Eoparafusulina Cooper and Grant (1964) divided the Leon- Formation a short distance east of the Old Word linearis (Dunbar and Skinner) (Ross, 1962), ardian Series (Fij>. 6) into the Skinner Ranch Ranch house. Pseudoschwagerina (as reported by G. L. Wilde, Formation (with three members), the Hess The Cathedral Mountain Formation was 1975, personal commun.), and probably a Formation, and the Cathedral Mountain Forma- deposited in deeper water west and northwest of number of species of brachiopods that are com- tion and revised it to include the Road Canyon the Skinner Ranch shelf-edge limestone (King, mon in these clasts (Cooper and Grant, Member as a newly named unit for the Word 1937; Cys, 1981). Most of the limestone beds 1972-1977). number 1 limestone bed of King (1930b). This within the Cathedral Mountain are debris from bed contains the ammonoid Perrinites hilli that The succession at Leonard Mountain appears those shelf-edge limestones. In contrast to the is otherwise found only in Leonardian beds. to represent the facies in which the Skinner coarse clastics of the Decie Ranch and Sullivan Later they (Cooper and Grant, 1966) recognized Ranch bioherms were forming, because, there, Peak Members, Cathedral Mountain deposition a number of additional members in these forma- some of the bioherms are in place, whereas oth- was generally finer-grained and in deeper, less tions and raised the Road Canyon to formation ers are dislodged. The massive, reefal Lenox agitated water of the Hovey Channel. rank and transferred it to the Leonardian Series. Hills dolostone at the southeastern end of Leon- Road Canyon Formation. The Road Can- Within the Leonardian Series, three or four ard Mountain, furthermore, appears to have yon Formation (Fig. 6) (Cooper and Grant, major depositional breaks occur. These separate stood in local topographic relief above the lower 1964, 1966) was defined as the former first three distinctive faunal zones based on studies of beds of the Skinner Ranch, so that erosion of limestone member of the Word Formation fusulinids and ammonoids (Ross, 1960, 1962; that, or of similar topographic prominence of (King, 1930b) and unconformably overlies the Furnish, 1973), for which Furnish (1973) se- Lenox Hills limestones, was the possible source Cathedral Mountain Formation. The Road lected three stage names, in ascending order: the for reworked Lenox Hills blocks in the Skinner Canyon Formation in turn is overlain conform- Aktaskinian Stage, represented by faunas in the Ranch Formation. The present line of strike ably by the Word Formation (restricted). Along western Glass Mountains in the Skinner Ranch southwest from Leonard Mountain is angled strike, the Road Canyon Formation changes Formation; the "leonardian" Stage, represented slightly to the west of the depositional strike and thickness and lithology. Near the Hovey anti- by faunas in the Cathedral Mountain Formation gradually includes more westerly, clastic depos- cline, it is a shallow-water limestone (Ross, in the western Glass Mountains; and the Road- its along the edge of the Hovey Channel. 1963b). To the east, it includes some siliceous ian Stage, represented by the faunas in the Road East of Leonard Mountain, the Skinner shales, siltstones, and thin-bedded limestone and Canyon Formation in the central Glass Moun- Ranch Formation passes into shelf-edge lime- dolostone. One or two miles east of the Old tains. As the name "Leonardian Series" is stones that are rich in bioherms and small to Word Ranch house, it becomes mainly dolo- widely used in the much broader sense to in- large patch reefs. The reef trend climbs gradually stone and is difficult to separate from strati-

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Figure 8. Relationships of Marfa Basin to the Diablo Platform, Hovey Channel, and Dugout and Marathon allochthons. Isopachous lines show generalized thickness of Pennsylvanian and Permian basinal sediments. Cross sections aligned along northwest-southwest are shown in Figure 9. Data from Amnion (1981), Luff (1981), and Moore and others (1981).

graphically higher and lower back-reef dolo- It appears (Ross, 1963b) that the Road Can- house during Cathedral Mountain deposition. stones. Southwest of Leonard Mountain, the yon Formation was deposited on a surface of There is a strong likelihood, because of paleo- Road Canyon Formation becomes a dark gray, some relief caused, in part, by ~ 150 ft (45 m) of topographic relief, that the type section of the deeper water, shaly limestone. Yellow to dark uplift along the Hovey anticline before Road Road Canyon Formation includes the equiva- gray, fine sandstones, dark shales, and thin lime- Canyon deposition. This uplift permitted the lents of both the first and second limestone stones occupy this stratigraphie interval west of rapid westward extension of the carbonate shelf members of the Word Formation of King Dugout Mountain. from its position near the Old Word Ranch (1930b) (compare Ross, 1963b, Fig. 2 with

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stratigraphic sections in Cooper and Grant, Ochoan(?) that the remainder was Missourian. The shales 1964, and Cys, 1981). that form the type section of the Alta Formation Tessey Limestone. Along the northern side yielded no diagnostic fauna. The lower part of Guadalupian of the Glass Mountains massive, almost non- the Cibolo Formation has a diverse upper Wolf- bedded limestones (Fig. 6) lie above the Gilliam campian fauna (equivalent to the Lenox Hills Word Formation. The Word Formation Member of the Capitan Limestone and reach a faunas in the western part of the Glass Moun- (Fig. 6), like the underlying Road Canyon For- thickness of -1,000 ft (300 m). Originally tains). The upper 50 ft (16 m) of the Cibolo mation, consists o:"an eastern dolostone facies, a named the "Tessey Limestone" by Udden Formation, Udden's yellow limestone member, carbonate shelf-ec.ge bioherm and reef facies, a (1917), these limestones have been difficult to contains a Leonardian fauna typical of the lower deeper water siliceous shale and clastic lime- correlate, because they have only a few, non- part of the Skinner Ranch Formation (Decie stone facies, and in the southwest, a basinal diagnostic fossils. King (1930b) correlated these Ranch and Poplar Tank Members). sandstone facies. The numbered limestone outcrops with an anhydrite, limestone, and West of Shafter, Skinner (1940) found that members of King (1930b) are tongues of the dolomite section penetrated in the Vacuum Oil Ross and Cartwright's sections contained only shelf-edge facies l.hat can be traced for only a Co., Elsinore No. 1 well a few miles to the Guadalupian faunas and were younger than the few miles east of the Hovey anticline, where northeast (Fig. 6) and considered them a south- sections to the northeast studied by Udden they intertongue with dark siliceous shale. ern extension of the Ochoan evaporites that had (1904). At Pinto Canyon, Skinner found that Southwest of the Hovey anticline, limestone been altered by surface processes to calcite. the 450 ft (135 m) at the top of the succession units are more difficult to trace, and those beds contained Word (lower Gaudalupian) faunas. may represent other limestone tongues that are MARFA BASIN Beneath these beds, there are 400 ft (170 m) of not physically continuous with those in the Word nonfossiliferous sandstones that bear a general Ranch-Hovey anticline area. West of the Marathon orogenic belt, the resemblance to the Perrinites-beAring beds in the By the end of Wordian deposition, reef Marfa basin (Figs. 7,8,9) was the last of a series Ojo Bonito section and to the Cathedral Moun- growth and movements on the Hovey anticline of cratonic fore-deep basins and appears analo- tain Formation of the Glass Mountains. Rigby constricted this channel to <5.5 mi (9 km) wide. gous to the Val Verde basin to the north and east (1953) and Amsbury (1958) demonstrated that Capitan Limestone. The Capitan Limestone of the Marathon orogenic belt. Our knowledge the Pinto Canyon section is composed of deep- (Fig. 6) lies above the Word Formation with of the Marfa basin is limited to outcrops brought water turbidites and submarine slide blocks. apparent conformity. It, like the underlying to the surface by Tertiary intrusions in the Skinner (1940) and Cys (1975) indicated that beds, may be divided into a shelf-edge reef facies, Chinati Mountains and -20 deep drill holes, of the sections studied by Udden (1904) hear in which the reefs are thick and massive; a back- which fewer than a dozen reach the Ordovician Sierra Alta and by Ross and Cartwright '1935) reef thin-bedded dolostone facies; and a deeper Ellenburger Limestone. in the Shafter Mining District also are mainly water clastic limestone, shale, and siltstone The late Paleozoic strata (Fig. 7) of the basinal deposits, that is, turbidites. For the beds facies. In the northwestern part of the Glass Chinati Mountains were first studied a few miles west of Shafter, Rix (1953a, 1953b) proposed Mountains, the Capitan is thickest, -1,800 ft north of Shafter by Udden (1904), who named the names "Ross Mine Formation" for the (550 m). The lower part is a massive, partially the Cieneguita, Alta, and Cibolo Formations in Word age equivalent and "Mina Grande For- dolomitized reef (Vidrio Member; Udden, 1917) the area northwest of Sierra Alta. He believed mation" for the Capitan age equivalent. that passes upward and eastward into thin- they were Pennsylvanian in age, with the possi- The late Paleozoic basinal strata in the sub- bedded, back-reel: dolomitic limestones (Gilliam bility that the upper part of the Cibolo might be surface of the Marfa Basin (Fig. 8) lie on Member; Udden, 1917). The Vidrio reef facies Permian. Later, Baker (1927, 1929) examined Desmoinesian and earlier Paleozoic cratonic forms the high, westernmost cuesta of the Glass stratigraphic sections near Ojo Bonito, several shelf-facies rocks (Ammon, 1981; Keller and Mountains and has steep depositional dips west- miles northwest of Udden's sections, and in others, 1981; Luff, 1981; Pearson, 1978,1981). ward into the Hovey Channel. Along the south- Pinto Canyon, at the northwest end of the The thickest area of Pennsylvanian and Permian west end of these outcrops, dark gray, basinal, Chinati Mountains, and erroneously assumed basinal sediments (Fig. 7) is bounded on siliceous shale, siltstone, and thin-bedded lime- that he was dealing with Udden's Alta and the north by the Walnut Draw fault and on stone intertongue with the Vidrio reef succession Cibolo Formations at both localities. He did the south by the Chalk Draw fault (Fig. 1). to form the Altuda Member (King, 1930b, recognize that the lithologies were markedly These faults have been active in Mesozoic and 1937). different and that the entire fauna was of Cenozoic time, and so it is not clear if this dis- The facies relationships of the Capitan Lime- Permian age. At yet another locality, 3-4 mi tribution is the result of original deposition or of stone in the western Glass Mountains indicate (5-6 km) to the southeast of Udden's localities, subsequent erosion. The lithologies and ages of that the outer edge of the carbonate shelf pro- in the Shafter Mining District, Ross and Cart- the Paleozoic rocks exposed in the Chinati graded rapidly westward several miles early in wright (1935) described -1,100 ft (330 m) of Mountains are closely similar to those of the this interval of deposition. This progradation re- massive dolomitic limestone and dark shale that "Dugout beds" and the overlying Lencx Hills sulted in a widening of the back-reef facies in they correlated with the Cibolo Formation. through Capitan and Altuda Formations in the the northeastern Glass Mountains and an exag- These outcrops, except for those near Ojo western part of the Marathon Basin and Glass gerated depositional relief into the Hovey Bonito, were re-examined by Skinner (1940), Mountains, indicating a similar depositional Channel. By the end of the Capitan deposition, who studied the fauna in considerable detail and history. the Capitan reefs from the Diablo Platform established the basic age correlations with strata Post-Paleozoic History joined with those from the Glass Mountains side in the Glass Mountains succession (Fig. 7). He to close the Hovey Channel and restrict circu- demonstrated that the lowest part of Udden's The Glass Mountains and Marathon Basin, lation in the Delaware Basin. Cieneguita Formation was Desmoinesian and area remained a slight topographic high during

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Silurian and Devonian'

Upper Cambrian and Ordovician

Dagger Flat Ss. (Cambrian)

S.E. -Marathon Orogenic Belt- N.W. /^v Diablo Platform Gaptank and Neal Ranch Fms. (Missourian.Virgilian, early Wolfcampian) Craton Allochthon of folded and faulted Upper Cambrian through Lower Pennsylvanian basinal strata.

Middle Pennsylvanian Hells Half Acre-Devils Backbone Fault Zone Complex Mississipptan and Lower (Folding and faulting of thrusts Pennsylvanian Silurian and and duplexing of thrusts post dates Devonian the Dimple Ls.. which is contained in fault zone and in overridden Marathon Upper Cambrian Allochthon) and Ordovician

\ ? Cratonic margin \ S.E. N.W. - Marathon Orogenic Belt Diablo Platform Figure 9. Schematic recon- Hovey structions without horizontal or Lenox Hills Fm.^ Hueco Ls. Channel •Sea Level— 'Marathon Allochthon of vertical scale show the effects of folded and faulted Upper i/t^n two major thrust events in the it AUochthon of Cambrian through Middle Pennsylvanian Middle folded and faulted Middle ^ ^ ^basinal strata - (reactivation of some Y ^ Pennsylvanian* 1 development of the Hovey Pennsylvanian through ^Astructures at end of early Wolfcampian)^ "^Ssjearly Wolfcampian \ Mississippian and Channel. Sections are aligned basinal strata ll \Dugout Creek thrust zone complex Lower Pennsylvanian ^ r/Vj'Dugout tt »folding and faulting of thrust fault and v northwest-southwest, as in Fig- Silurian - Devonian' vT i-V^, Beds) /^duplexing of fault zone post dates Hells Half Acre - Virgilian strata, which are caught up in ' Devils Backbone ure 8 (modified from Ross, Upper Cambrian - Ordovician ^ fault zone, and likely post dates early V Fault Complex Wolfcampian strata). (second renewed movement 1981; Ross and Ross, 198S). k of structures possible. Data from many sources, includ- : but difficult to date) Shelf strata^ ing King (1930b, 1937, 1980), Buried craton Ross (1963a, 1965, 1967), DeMis (1985), Tauvers (1985), *N ? Cratonic margin and others.

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the Mesozoic. Triassic(?) nonmarine sediments the present uplifted structural position of the but apparently two or more discrete allochthons lapped onto the area on the north and west; Glass Mountains and Marathon Basin. Late that behaved structurally as a compound alloch- however, not until the Cretaceous did extensive Cenozoic extensional events are largely respon- thon unit during the orogenic episode at the end marine inundations cover the entire area. Exten- sible for the basic intrusive and extrusive rocks of the Middle Pennsylvanian (Figs. 9-1, 9 -2). sive Cretaceous and Tertiary sedimentary and in the region, such as the Davis Mountains to the Recently, DeMis (1985) redescribed this Hells igneous rocks cover most of the Marfa Basin. west and Iron Mountain and smaller intrusive Half Acre-Devils Backbone thrust fault com- The Marfa Basin lies within the eastern bound- plugs and dikes in the Marathon Basin and Glass plex in the southeastern part of the Marathon ary of the Basin and Range province, which Mountains area. basin (Figs. 1, 8, 9). His description clearly sug- accounts for the Tertiary faulting and extensive gests a complex, subparallel duplexed thrust basic igneous intrusions, such as the Davis CONCLUSIONS fault system in which renewed faulting and fold- Mountains. ing occurred along an earlier thrust fault zone. In Late Cretaceous and early Tertiary times, Oceanic early and middle Paleozoic turbidites The renewed movement involved Dimple Lime- compression from, the west deformed much of and cherts in the Marathon fold belt sequence stone being caught within the complexly de- the region immediately west of the Glass Moun- are succeeded by extremely thick accumulations formed duplex fault zone. These particular tains and Marathon Basin. The Del Norte of clastic siliceous and limestone turbidites that Dimple Limestone blocks have not been dated Mountains along the western edge of the Mara- were deposited from Mississippian into Early and, therefore, could be Morrowan, Atokan, or thon Basin are on the eastern edge of this major Permian time. The late Paleozoic turbidites are Desmoinesian in age. The beds on the southeast belt of diastrophism. Gradual post-Paleozoic up- known from two or more allochthonous masses side of the Hells Half Acre-Devils Backbone lift of the buried portions of the Diablo Platform of strongly deformed sediments. The oldest, the fault system are Tesnus and older. Those on the (a horst) that underlie parts of the Marathon and Marathon allochthon (as referred to by Ross and northwest side have Dimple and Haymond beds Dugout allochthons apparently has caused Ross, 1985), is probably not a single allochthon in addition. This suggests (1) an early thrust fault

KILOMETERS

MILES

Figure 10. Tectonic map of Euramerica and the Marathon-Ouachita orogenic belt during the later part of the Paleozoic Era. Loca tion of possible transform faults after Thomas (1983) and position of advancing orogenic fold belt interpreted from Palmer and others (1984). (Modified from Ross, 1979; Ross and Ross, 1985).

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of late Mississippian to early Morrowan age likely the result of the transpressional collision of orogenic belt were progressively incorporated (Fig. 9-1) which deformed only Tesnus and South America (Gondwana) and North Amer- into the orogenic belt and repeatedly thrust and older strata and (2) a duplex thrust faulting ica (Euramerica) during the late Paleozoic deformed until the middle Wolfcampian, when event at the end of the Middle Pennsylvanian (Ross, 1979, 1981; Kluth and Coney, 1981; forward (northwestward) motion on this section which deformed Dimple and Haymond in addi- Thomas, 1983). Thomas (1983) suggested that of the orogenic belt ceased. The Marfa basin tion to older strata (Fig. 9-2). the direction of movement on the various seg- was one of the last of these frontal fore-basins King (1937) had considered the Hells Half ments of the Marathon-Ouachita orogen was and received basinal deposits as late as early Acre thrust fault to be one of the oldest thrust controlled by older, late Precambrian or earliest Guadalupian time. faults exposed in the region; DeMis (1985) con- Paleozoic transform faults, which gave the sidered it to be one of the youngest. As a com- North American craton a zigzag margin (Fig. ACKNOWLEDGMENTS plex duplexed thrust fault system involving one 10). One transform fault, referred to here as the or more periods of renewed movement, both "Val Verde transform fault system," lies between My special thanks to June R. P. Ross, West- King and DeMis could be correct. the Val Verde basin and the Marathon orogenic ern Washington University, for many discus- The compound Marathon allochthon formed belt and accounts for the absence of major late sions about the geology of this interesting part of an orogenic highland along which Late Pennsyl- Paleozoic thrust faulting within the Val Verde West Texas, for help in field work in the region, vanian and earliest Permian shallow-water basin (Webster, 1980; Nicholas and Rozendal, and for aid in editing this summary. I also thank carbonates and clastics were deposited on a 1975), in contrast to the history of repeated C. L. Hendrick, S. J. Mazzullo, R. L. Nicholas, relatively narrow, wave-cut shelf. The Marathon northwestward-directed thrusting in the Mara- N. Schneidermann, R. G. Stevenson, P. R. allochthon was sufficiently massive to cause thon and Dugout allochthons. Tauvers, and W. A. Thomas for reviewing the additional loading of the immediately adjacent Much of the history of the Permian basin is manuscript, which has benefited from their con- cratonic margin, which created deeper, trough- closely associated with the history of the Mara- structive suggestions, and the Gulf Oil Explora- like fore-deeps into which Late Pennsylvanian thon orogenic belt. The timing of depositional tion and Production Company and Chevron and early Wolfcampian turbidites accumulated changes in the Permian basin closely corre- U.S.A., Inc. for permission to publish this paper. in great thicknesses. Continued thrusting in the sponds to the timing of tectonic events and middle Wolfcampian resulted in the deforma- depositional changes in the Marathon basin, tion of the thick Pennsylvanian and early Wolf- Glass Mountains, and Marfa basin. The com- REFERENCES CITED campian turbidites to form the Dugout alloch- pound Marathon allochthon, and later the com- Adams, J. 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H„ 1931, Erratic boulders of large size 1963a, The standard Wolfcampian Series (Permian), Glass Mountains, p. J 83-205. in the West Texas Carboniferous [abs.]: Geological Society of America Texas: Geological Society of America Memoir 88,205 p. Cys, J. M., and Mazzullo, S. J., 1981, Lithofacies and sedimentation of Lower Bulletin, v. 42, p. 200. 1963b, Fusulinids from the Word Formation (Permian), G ass Moun- Permian carbonates Df the Leonard Mountain area, Glass Mountains, King, R. E„ 1931 (1932), Geology of the Glass Mountains, Texas; Pan 2, tains, Texas: Cushman Foundation for Foraminiferal Research Con- western Texas: A discussion: Society of Economic Paleontologists and Faunal summary and correlation of the Permian formations with tributions, v. 14, p. 17-31. Mineralogists, Permits Basin Section, Publication 81-20, p. 163-168. description ofbrachiopods: University of Texas Bulletin 3042,245 p. 1965, Late Pennsylvanian Fusulindae from the Gaptank formation, DeMr's, W. 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REVISED MANUSCRIPT RECEIVED DECEMBER 17,1985 Geological Survey Professional Paper 1157,40 p. 1960, Fusulinids from the Hess Member of the Leonard Formation, MANUSCRIPT ACCEPTED DECEMBER 18,1985

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