Pedernal Uplift Research Articles

Detrital zircon geochronology of quartzite clasts in the Permian Abo Formation, Sacramento Mountains, New Mexico, USA

More than 2500 m of Paleozoic strata, ranging in age from Cambrian to Permian occur in the Sacramento Mountains of New Mexico, making these rocks the largest and most complete exposures of Paleozoic strata in North America. The core of the Sacramento Mountains reveals compressional structures associated with the Pennsylvanian-Permian Ancestral Rocky Mountain orogeny. The Permian Abo Formation is 120–450 m in thickness, and consists of interbedded sandstone, conglomerate, limestone and shale and rests above the Ancestral Rocky Mountain unconformity. U-Pb analysis of detrital zircons extracted from quartzite clasts in basal conglomerates reveal a maximum depositional age of their protolith to be 1110 ± 15 Ma. Most (∼40%) of the detrital zircon age spectrum is Grenville (1000–1300 Ma) in age, with a peak age of 1209 Ma. Midcontinent Granite-Rhyolite (1300–1500 Ma) ages comprise about 33% of the data, and have a peak age of 1431 Ma. Smaller age populations of Yavapai-Mazatzal (1600–1800 Ma; age peak =1676 Ma), Trans-Hudson (1800–2000 Ma; peak age = 1820 Ma), and Archean (>2.5 Ga, age peak = 2819 Ma) also are present. U-Pb detrital zircon ages from these quartzite clasts indicate that they were likely derived from the Proterozoic Lanoria Formation, which is exposed now in the Franklin Mountains >150 km to the south. The Lanoria is identical to the Abo clasts in terms of maximum depositional age and detrital zircon age peaks. The protolith sandstone of these quartzite clasts and quartzites of the Lanoria were derived from the Grenville high-lands of the Llano region of central Texas, and then transported west to the Rodinian continental margin at ∼1110 Ma, where they were eventually buried and metamorphosed to quartzite. These quartzites were subsequently uplifted and eroded during the Ancestral Rocky Mountain orogeny and transported north and west along the Pedernal Uplift to the adjacent Orogrande Basin during the early Permian.

Structurally Dependent Source Rock Maturity and Kerogen Facies, Estancia Basin, New Mexico: ABSTRACT

The Estancia basin of central New Mexico is an asymmetric, north-south trending structural depression that originated during the Pennsylvanian. The present-day basin covers 1,600 mi{sup 2} (4,100 km{sup 2}). It is bounded on the east by the late Paleozoic Pedernal uplift, on the west by the Tertiary-age Manzano and Los Pinos Mountains, on the north by the Espanola basin, and on the south by Chupadera Mesa. Depth to Precambrian basement ranges from 9,000 ft (2,700 m) in a narrow graben in the eastern part of the basin to less than 1,500 ft (460 m) on a shelf to the west. Basin fill consists primarily of Pennsylvanian and Wolfcampian sandstones and shales in the graben and sandstones, shales, and marine limestones on the shelf Mature to marginally mature dark-gray to black Pennsylvanian shales are probable source rocks. Thermal Alteration Index ranges from 2.0 to 3.2. Shales become thermally mature with depth in the eastern graben. On the western shelf, shales become mature to the west as a result of increased heating from the Rio Grande rift. Total organic carbon exceeds 0.5% in many shales, sufficient for hydrocarbon generation. Kerogen types are mixed algal, herbaceous, and woody, indicating that gas, or possiblymore » gas mixed with oil, was generated. Kerogens in shales of the eastern graben are entirely continental, gas-prone types. In limestones and shales of the western shelf, kerogens have a mixed marine and continental provenance, indicating that both oil and gas may have been generated on thermally mature parts of the shelf.« less

Stratigraphy and Depositional Environment of Lower San Andres Formation in Subsurface and Equivalent Outcrops: Chaves, Lincoln, and Roosevelt Counties, New Mexico

This paper establishes correlations from subsurface to outcrop and develops a depositional model for the lower San Andres Formation in New Mexico. Five cyclic carbonate-evaporite sequences, numbered consecutively upward as units 1, 2, 3, 4, and 5, were identified from measurement of approximately 1,750 ft (534 m) of section in the Hondo Canyon area of Lincoln County and examination of approximately 400 ft (122 m) of core from six wells in the Levelland-Slaughter trend of Chaves and Roosevelt Counties. An idealized sequence consists of open-marine, restricted subtidal, intertidal, and supratidal facies capped by anhydrite (in the subsurface) or an evaporite dissolution zone (in outcrop). Lateral facies changes in outcrop indicate that the Pedernal uplift provided a locus f r emergent conditions at low relative sea level stands through the deposition of unit 3. Units 4 and 5 are incomplete, highly variable sequences. Lateral facies changes are not present in outcrop, indicating that the Pedernal uplift exerted little influence on the deposition of these units. Preserved anhydrite cores capping P1 and P2 sequences (equivalent to units 4 and 5) range up to 15 ft (5 m) thick, are relatively pure, commonly lack underlying intertidal/supratidal carbonates, and contain some gypsum ghosts, indicating that part of the anhydrite was deposited subaqueously. We present a depositional model involving both subaqueous (salina) and subaerial (sabkha) deposition of the anhydrite. The model accounts for the purity and thickness of the evaporite caps, the rarity of subaerial exposure features, variations in the nature of the dolomite/anhydrite transition, and the accumulation and preservation of thick subaqueous evaporites north of the study area.

Paleosols of Late Pennsylvanian cyclic strata, New Mexico*

ABSTRACTCyclically deposited siliciclastic and carbonate rocks of the Late Pennsylvanian (Virgilian, Holder Formation) of south‐central New Mexico were deposited on a narrow shelf between the Pedernal uplift and the Orogrande basin. In the Dry Canyon area, Sacramento Mountains, shelf‐to‐basin palaeotopography is indicated by onlapping beds and primary dips. Calcareous alteration zones are developed on the tops of major carbonate units. These detailed studies confirm earlier interpretations that alteration zones represent subaerial exposure events and provide new evidence for and further documentation of a paleosol environment. The paleosols contain: (1) rhizoliths; (2) tangential needle fibres of calcite; (3) five types of alveolar texture; (4) upward oriented ‘ribbon spar’; (5) brownish and clear isopachous spar; (6) blackened grains; (7) random needle fibres of calcite; (8) coated grains; (9) micritized grains; (10) glaebules; (11) desiccation cracks; (12) possible Microcodium; and (13) well‐developed laminated crusts. Isopachous cements, upward‐oriented cements (which mark the former tops of capillary fringes), dark colour and shallow depth of penetration of rhizoliths (less than 1 m) indicate significant paleosol formation in waterlogged (hydromorphic) and drier conditions. Pennsylvanian palaeohydrogeology of the system is reflected in the type of paleosol alteration.Paleosols developed on subtidal strata and paleosols which drape tens of metres of palaeotopography indicate cyclic sedimentation was not controlled by delta lobe switching. Local tectonic up and down movement would be an unlikely mechanism to explain the repeated tens of metres of relative sea‐level fluctuation. Eustatic sea‐level fluctuations, induced by Late Pennsylvanian Gondwana glaciation, probably were of the correct magnitude and frequency to have caused the Holder cycles.

Morrowan Sedimentation in the Orogrande Basin,"West Texas and South-Central New Mexico: ABSTRACT"

Morrowan strata in the Hueco and Franklin Mountains reflect deposition within a shallow, gradually subsiding, carbonate shelf lagoon. Postulated environments fluctuated between open shelf lagoon with localized shoaling, restricted inner shelf lagoon, and peritidal settings. Variations in depth were slight, probably not exceeding several tens of meters within the photic zone. The La Tuna Formation (Franklin Mountains) was deposited near the axis (center) of the Orogrande basin; the lower division of the Magdalena limestone (Hueco Mountains), 30 mi east, was deposited 20-30 mi west of the paleoshoreline. Physiographically, the Orogrande sea was a small gulf, offering a certain degree of protection from the Morrowan seaway to the south. Sedimentologically, it was a wide expanse of predominantly quiet-water carbonate sedimentation with subordinate argillaceous influex and coarser peripheral clastics. The Orogrande basin, a stratigraphic feature, corresponds to a blanket deposit of shallow epeiric carbonates. Climatic and orographic effects are invoked to explain the contrasting style of clastic sedimentation in the Delaware and orogrande basins, east and west of the Pedernal uplift. Analysis of Morrowan carbonates reveals no evidence of cyclicity, major transgressions or regressions, or local tectonic activity. Deposition was stable and in equilibrium with a gradually subsiding shallow basin. Based onmore » lithologic, faunal, biostratigraphic, and paleogeographic criteria, the lower division is both laterally and temporally equivalent with the La Tuna Formation. Accordingly, the latter term is advocated in favor of the former, which lacks both priority and formal status.« less

Abo Formation Alluvial Facies and Associated Basin Fill, Sacramento Mountains, New Mexico: ABSTRACT

Outcrops of the Abo Formation (Wolfcampian to early Leonardian age) in the Sacramento Mountains of south-central New Mexico record the evolution of a dry alluvial fan system as it was deposited off the pedernal uplift into the Orogrande basin. The location and orientation of present-day outcrops allow us to observe an inferred east-to-west transverse facies tract consisting of: (1) proximal alluvial fans (lower Abo), which are contiguous in places with underlying Laborcita Formation fan-deltaic sediments; (2) medial anastomosed streams (middle Abo); and (3) distal low-gradient mud-dominated flood basins characterized by either distributary streams (upper Abo) or clastic tidal flats (Lee Ranch Tongue of the Abo) with associated marine carbonates (Pendejo Tongue of the Hueco Formation). Tectonism in the Pedernal highlands, which climaxed during the Late Pennsylvanian, apparently continued well into the Wolfcampian in this region, as evidenced by a major basal Abo unconformity and distinct stacked megasequences of lower Abo alluvial fan lithofacies. However, by the middle Abo, tectonic activity had quiesced and the uplift began eroding and retreating to the north and east. By the late Abo, a pediment surface had formed that was subsequently onlapped by upper Abo and eventually Yeso Formation sediments.

Siliciclastic-Carbonate Interactions in Laborcita Formation, Sacramento Mountains, New Mexico: ABSTRACT

Outcrop exposures of the Laborcita Formation (Wolfcampian) reveal an active depositional environment with abrupt lateral and vertical changes between fan-deltaic and carbonate sediments. The siliciclastic source area was to the east, in the Pedernal uplift. Fan-delta lobe shifting was important in producing the cyclic nature of deposition. Away from the area affected by the fan-deltas, deposits are increasingly calcareous. Shales are the predominant lithology in the Laborcita Formation, due to the abundance of carbonate-inhibiting terrigenous matter, especially in restricted areas. A few digitate stromatolites and Archeolithophyllum sp. mounds indicate subaerial exposure. Toward the edge of the narrow shelf, large phylloid-algal buildups (20 m or 65 ft thick) occur. An exposure in Coyote Canyon, near the northern end of the Laborcita exposure, shows an onlapping sequence of several mounds. This mound zone was terminated when muds and fine to medium-grained terrigenous sands migrated in and inhibited growth of the carbonate-producing organisms. The terrigenous sediments were in turn overlain by grainstones exhibiting lon , low-angle (15°) cross-bedding, which dips landward (southeast). Individual grainstone beds are thin (0.5-1.5 m or 1.6-5 ft), extend along strike laterally for about 2.5 mi (4 km), and are composed largely of bioclastic carbonate grains (not oolitically coated) with 5% quartz grains. Direction of migration was southwest to northeast. Gradual emergence is recorded by the Laborcita Formation. With continual progradation of terrigenous deposits, interrupted by marine incursions resulting in deposition of shallow-water carbonated deposits, the transitional Laborcita Formation was ultimately overlain by the terrigenous Abo Formation. End_of_Article - Last_Page 256------------

Depositional Trends In Upper Paleozoic Terrigenous Clastic Rocks, Sacramento Mountains, New Mexico

Field analysis of terrigenous elastic units lying within the upper Pennsylvanian-lower Permian cyclic elastic/ carbonate sequence (Holder and Labore/ta Formations) of the northern Sacramento Mountains, New Mexico, illustrates a marine to non-marine environmental progression as infilling of the Orogrande basin occurred. The oldest units studied, flat-based sandstone bodies A, B and C (Virgilian), coarsen upward texturally and dis­ play large-scale (up to 5m thick) foresets, hummocky stratification, bimodal or polymodal cross-stratification trends, and abundant burrows. These characteristics indicate that siliciclastic shelf bars were present on a storm­ dominated and tide-influenced shelf. Higher in the section, units D (upper Virgilian) and E (lower Wolfcampian) exhibit fluvially influenced depositional features such as concave-up erosional bases, upward-fining textural sequences and unimodal or asymmetric, bimodal paleocurrent distributions. Units D and E are interpreted as estuarine and fan deltaic deposits, respectively Several upward-coarsening fan-deltaic sequences were recognized in the study area suggesting that delta shifting , rather than sea level fluctuations, was a significant local cause of cyclicity. The sequence of units A-E may represent the relatively continuous progradation of terrigenous elastic sediments from the Pedernal uplift into the Orogrande basin during late Paleozoic time.

Evolution of a Fluvial Clastic Wedge, Abo Formation (Wolfcampian), Sacramento Mountains, New Mexico: ABSTRACT

Outcrops of the Abo Formation (Wolfcampian) in the northern and central Sacramento Mountains of south-central New Mexico record the evolution of fluvial systems within a major clastic wedge. This wedge was derived from the Pedernal uplift and prograded westward into the Orogrande basin. Regionally, the Abo Formation thickens from 60 m (197 ft) in the central Sacramentos, to over 545 m (1,788 ft) in the northern portion of the range, a distance of approximately 29 km (18 mi). Superposed on the regional pattern are local thickness variations of up to 91 m (300 ft). These occur within distances as small as 0.4 km (0.25 mi), and represent local tectonic and paleotopographic controls on sedimentation. Clast-supported cobble conglomerates, associated with laminated mudstones and discontinuous coarse arkosic sandstones, are present near the base of the Abo Formation. The conglomerate lenses range from 0.5 to 20 m (1.5 to 66 ft) thick, and from 15 m (49 ft) to several kilometers wide. They exhibit poor stratification, occasional clast imbrication, and near horizontal to concave-upward erosional bounding surfaces. Locally, nodular CaCO3 occurs in beds or scattered throughout the associated mudstones. The central portion of the sequence is characterized by abundant conglomeratic medium to very coarse-grained arkosic sandstone lenses interbedded with laminated mudstones. These lenses range from 0.25 to 10 m (0.8 to 33 ft) in thickness, and 10 to 110 m (33 to 361 ft) in width. Commonly, several lenses will coalesce, forming laterally extensive belts. Both erosional and depositional (lateral accretion) bounding surfaces are well developed within individual lenses. Low-angle, large-scale trough cross-bedding is the dominant stratification type within these units, however, small to large-scale tabular foresets occur, as do planar, ripple, and small-scale trough stratification. Occasionally, individual units fine upward in grain size and/or scale of structures. This sandstone-rich horizo varies laterally in thickness, and grades upward into a mudstone-rich horizon at the top of the Abo Formation. The upper interval of the Abo sequence contains infrequent fine to coarse-grained arkose lenses enclosed in laterally extensive red mudstones. Paleosols and caliche horizons are present, but not common, in the mudstones. The basal conglomeratic horizon of the clastic wedge represents braided stream deposition at the distal end of arid alluvial fans associated with the tectonically active Pedernal uplift. Caliche and paleosols developed in the overbank mud drapes and levees of these deposits. The conglomerates grade into arkosic sandstones, reflecting the intense weathering and erosion of the granitic core of the uplift. The multilateral sandstone lenses characteristic of the mid portion of the Abo Formation were deposited in low-sinuosity, coarse-grained (bed-load) meander belts; however, higher sinuosity, mixed-load channel and crevasse splay deposits also occur locally. Finally, as the Pedernal source area was buried by its own debris, thick, broad flood-plain deposition predominated. Sandstones ass ciated with the red mudstones were deposited in shallow ephemeral channels and crevasse splays. End_of_Article - Last_Page 550------------

Exploration Geology and Depositional Modeling of a Continental Tight Sand Reservoir, Abo Formation, Chaves County, New Mexico: ABSTRACT

The Wolfcampian-Leonardian age Abo Formation has been the major objective of exploration efforts in southeastern New Mexico since 1980. The Abo Formation in Chavez County consists of red and green mudstones and shales interbedded with very fine-grained reddish-orange sandstones. The sandstones are subarkosic arenites deposited in a fluvial/delta plain environment on the northwest shelf of the Permian basin. Producing sandstones are characterized by very low in-situ permeabilities (0.006 to 0.01 md) and porosities (determined from CNL density logs) ranging from 5 to 12%. Petrographic analysis of the producing zones yields only traces of visible porosity (^approx 1%), indicating the relative importance of fractures to total porosity. The importance of this secondary porosit is substantiated by the concentration of production within an area of major southwest-northeast-trending buckles that result in folded and fractured zones parallel to their strike. Abo sediments were derived from the predominantly granitic Pedernal uplift to the north and west of the producing area. The prograding fluvial/delta plain is evidenced by calcareous mudstones at the base of the Abo with calcite fracture fillings grading upward into anhydritic mudstones containing anhydrite fracture fillings and bird's-eye lenses. In general, three main producing zones are found in the upper Abo Formation. These sandstones occur either as a single thick (6 to 10 m, 20 to 33 ft) sand or several thin (2 to 4 m, 6.5 to 13 ft) sands separated by thin mudstones. Changes in thickness and character o these three major sands represent lateral shifts in subaerially deposited, braided paleochannels. The relatively homogenous mudstone intervals between producing sands and at the base of the section represent delta switching and tidal backreef (submarine) deposition. Gas wells in the Abo initially produce from 200 to 4,000 MCFGPD of dry (1,000 Btu) gas after considerable acidizing and fracturing. The modeling of the depositional environment of the Abo is critical to the selection of prime drilling locations. Paleochannel development and trends, as well as significant interbedded mudstone intervals, are essential for good Abo potential. Several stratigraphic and diagenetic trapping processes may result in hydrocarbon accumulations within these anastomosed fluvial sandstones. Channel fills are most commonly contained laterally and vertically by mudstones. Differing amounts of calcite and anhydrite cement and argillaceous matrix within the sandstones may create diagenetic traps within the channels. The best Abo wells are located in areas where paleoc annels are well developed and intersect southwest-northeast-trending structural zones. The completion of these wells can be complicated by inadequate cementing prior to fracturing resulting in the fracturing of containing mudstones and shales instead of gas-bearing perforated sandstone intervals. The relatively shallow, 950 to 1,300 m (3,100 to 4,300 ft), depths to encounter pay, combined with the higher allowable tight gas (107) price in the Abo, have stimulated significant activity in this new play that is certain to expand as the reservoir and trapping mechanism is better understood. End_of_Article - Last_Page 476------------

A Spectrum of Late Paleozoic Siliciclastic Shelf-Bars, Sacramento Mountains, New Mexico: ABSTRACT

Study of several Pennsylvanian-Permian shelf sandstones in the northern Sacramento Mountains, New Mexico, suggests that siliciclastic shelf-bars were migrating on a high-energy shelf adjacent to the Pedernal uplift. These shelf-bars had sufficient relief, 2 to 6 m (6.5 to 20 ft), to provide the clear-water, agitated conditions requisite to carbonate grain-shoal development in areas of low clastic influx. The carbonate and siliclastic cycles can be End_Page 436------------------------------ explained by a relatively simple progradational cyclic model without invoking major sea level fluctuations. A typical cycle contains 3 major components: (1) shelf-bar stones; and (3) interbar siltstones. Shelf-bar sandstones, 1 to 6 m (3 to 20 ft) thick, are typically overlain by carbonate grainstone/packstone facies 1.5 to 6 m (5 to 20 ft) thick, which are grainstone/packstone facies, 1 to 6 m (3 to 20 ft) thick, which are in turn overlain by siltstones, 1 to 6 m (3 to 20 ft) thick, thus completing the cycle, 4 to 18 m (13 to 59 ft) total thickness. Shelf-bar sandstones in the Holder Formation (Virgilian) are lenticular concavo-convex sand bodies, 2.5 to 6 m (8 to 20 ft) thick, with flat depositional bases. Average grain-size (4^phgr - 0^phgr) and maximum clast size (12 mm, 0.5 in.) increases upward. Seaward dipping (W - NW) accretion foresets, up to 0.6 m (2 ft) thick, and bimodal trough cross-stratification, 10 to 30 cm (4 to 12 in.) thick, characterize lower sandstone facies. Hummocky cross stratification, 7 to 9 cm (2.8 to 3.5 in.) thick, 1.2 to 2.5 m (3.9 to 8 ft) wavelength, is common along accretion foreset surfaces and the tops of many of these sets are rippled and burrowed. Syndepositional deformation structures are common. Missourian and Virgilian shelf-bar sandstones were rapidly deposited by storm-induced currents and were modified by fair-weather tidal oscillatory flow and biological processes. In contrast with Virgilian shelf-bar sandstones, Wolfcampian bars are thinner, 1.5 to 2 m (5 to 6.5 ft) thick, coarser grained, and locally have erosional bases. Bimodal through cross-stratification is well-developed at the expense of seaward dipping accretion foresets which if present, are poorly developed. Hummocky cross-stratification and burrows are rarely present, whereas ripples and syndepositional deformation structures are common. Average grain size coarsens-upward crudely. These Wolfcampian shelf-bars were deposited in shallow water subject to strong tidal currents, which winnowed finer sediments, produced distinct bimodality in sedimentary structures, and prevented the bars from achieving significant depositional relief. Carbonate units, 1 to 5 m (3 to 16 ft) thick, decrease in micrite and increase in abundance of allochems upward in the vertical sequence. Sedimentary structures are similar to those of the associated siliciclastic shelf-bars, indicating a change in sediment-supply without significant change in hydrodynamic conditions. Carbonate units are thinner, 1 to 2 m (3 to 6.5 ft), become less important volumetrically in Wolfcampian sediments as compared with those in Virgilian rocks. The spectrum of high energy siliciclastic shelf-bar sandstones, and the presence of fan-deltaic and fluvial deposits in overlying sediments (Wolfcampian) suggests that the shelf adjacent to the Pedernal uplift continuously prograded into the Orogrande basin. Shifting clastic influx along depositional strike caused drastic local changes in shoreline configuration, longshore currents, and subsequent clastic and carbonate sediment distribution patterns. End_of_Article - Last_Page 437------------

New Mexico Lineament of the Colorado Rockies Front

The Colorado Rockies end in the Sangre de Cristo Range between Santa Fe and Las Vegas, New Mexico. At this latitude the Colorado Rockies are bipronged, consisting of the Santa Fe Range on the west and the Las Vegas Range on the east, with a synclinorium lying between the two. South of the end of the Santa Fe front a mild line of deformation continues for 60 mi along a monocline between Glorieta Mesa and the Estancia Valley downwarp. This trend dies out near the southern end of the Pedernal uplift near U.S. Highway 60. The eastern front of the Colorado Rockies dies out at the end of the Las Vegas Range a few miles south of Las Vegas. Recent mapping in eastern New Mexico reveals a lineament of structures aligned southward from the Las Vegas front for nearly 200 mi. The principal elements of this alignment are the Anton Chico monocline, Leon anticline, Vaughn sag, Nalda shear zone, Tinnie fold belt, and Dunken uplift. Lesser folds and faults connect the above features along the lineament. These structures may reflect movement on a basement fracture zone which also determined the alignment of the eastern front of the Rockies.

Late Paleozoic Sediments Derived From Pedernal Uplift: ABSTRACT

The Pedernal uplift, elongated northward from southern Otero County, New Mexico, to the present-day position of Pedernal Hills, was a late Paleozoic feature 40-75 mi wide and about 225 mi long; at the time of maximum development, the uplift connected southward with the Diablo platform and northeastward with Sierra Grande arch and Amarillo-Wichita uplift. This is Hill's (1958) Pedernal-Sacramento-Otero uplift, Adams' (1962) Pedernal arch, and Meyer's (1966) Pedernal uplift, but differs from Galley's (1958) Pedernal massif which he extended northeastward to encompass the southern Sierra Grande arch. The southern Pedernal area was beneath pre-Pennsylvanian seas, which derived their minor detritus from Penasco dome of northern New Mexico and southern Colorado. The Pedernal uplift emerged during Early Pennsylvanian time. Sediments which became sandstone, dark shale, and silty limestone were deposited westward in Orogrande and Estancia basins and eastward in Delaware basin. During Desmoinesian time, there was wide expansion of shallow seas; the Pedernal barely was awash, and provided only silt and clay for the limestone-choked seas, except for some deltaic subgraywacke in the Orogrande basin. Uplift of the northern part of the Pedernal uplift during late Desmoinesian time supplied arkose northeastward to the Rowe-Mora basin and westward to the Joyita-Los Pinos area and Estancia basin Beginning in late Missourian, the uplift took on the aspect of a tilted fault block, with the western edge higher (especially near Ruidoso) and providing more detritus westward into the Orogrande and Estancia basins, whereas only minor amounts of fine-grained materials swept eastward into the Delaware basin. These conditions continued into Virgilian time, culminating during the late Virgilian and early Wolfcampian with the westward dumping of a thick sequence of subgraywacke, arkose, and red to dark shale. Early Wolfcampian sediments derived from the west side of the Pedernal uplift range from quartzite and granite-cobble conglomerate to red shale, but by middle Wolfcampian the major detritus source was the Uncompahgre highland of north-central New Mexico and southwestern Colorado. Reddish clastics from this highland flooded Wolfcampian seas southeastward where Abo redbeds intertongue with Hueco Limestone. By late Wolfcampian time, most of the Pedernal uplift was buried beneath redbeds; only locally, as at the present-day Pedernal Hills and Pajarita Mountain, did remnant Precambrian-rock monadnocks rise above the red clastic flood. Higher remnants supplied minor detritus to lagoonal seas during Leonardian time. End_of_Article - Last_Page 537------------

Sedimentational Influence of Pedernal Uplift: ABSTRACT

Depositional and erosional features outline the late Paleozoic Pedernal uplift as a narrow northward-elongated landmass, connected southward with the Diablo platform and northeastward with the Sierra Grand arch and Amarillo-Wichita uplift. During pre-Pennsylvanian Paleozoic time, north-central and central New Mexico was periodically uplifted epeirogenically, but this bears little resemblance to late Paleozoic Pedernal uplift. Pedernal should not be applied to the massif in east-central New Mexico (southern part of Sierra Grande arch). Ordovician, Silurian, and Mississippian strata probably were deposited in most of New Mexico and adjoining areas, and Devonian beds in most of southern and western New Mexico, but were removed from large areas during subsequent erosion periods. Early Ordovician El Paso-Manitou was eroded in Middle Ordovician time; later Ordovician Cable Canyon-Harding and Montoya-Fremont as well as Silurian Fusselman Dolomite were partly removed during Late Silurian-Early Devonian time; and only a remnant of Mississippian was left in central New Mexico by erosion during Late Mississippian-Early Pennsylvanian time. Erosional and sedimentational patterns trend east-west for earlier Paleozoic strata, with a positive-trending feature in north-central New Mexico, contrasting with Pennsylvanian and early Pe mian northward trends related to the Pedernal uplift and its adjoining basins, Orogrande and Estancia on the west, and Delaware on the southeast. The northern New Mexico massif supplied some Cambrian sands, some Middle Ordovician Simpson sand and silt, and Late Devonian and Early Mississippian silt and clay. The Pedernal uplift area in south-central New Mexico was covered by early and middle Paleozoic seas, and did not become a detritus-source upland until Early Pennsylvanian time. During Pennsylvanian and early Wolfcampian time it provided much sediment to flanking basins; most of the uplift was worn down and was buried by floods of northern redbed material during late Wolfcampian time. Only remnant hills remained in the sandy seas of Leonardian time. End_of_Article - Last_Page 197------------

Distribution and Facies of Pennsylvanian Rocks of Sangre de Cristo Mountains and Raton Basin, New Mexico: ABSTRACT

In Pennsylvanian and early Permian time north-central New Mexico and the adjacent part of Colorado were the site of the Rowe-Mora geosyncline--a narrow, north-trending depositional basin bounded on the west by the ancestral San Luis-Uncompahgre highland and on the east by the ancestral Sierra Grande uplift. The southern part of the geosyncline was divided by the Pedernal uplift, the main trough being at the west, and the Las Vegas sub-basin at the east. Sediments of the Magdalena group of Pennsylvanian age were deposited as a predominantly marine suite during formation of the geosyncline, and sediments of the overlying Sangre de Cristo formation of Pennsylvanian and Permian age were deposited as a predominantly non-marine suite which finally filled the geosyncline. During Laramide orogeny the troughal part of the geosyncline was elevated to form the Sangre de Cristo uplift and the shallower eastern part was downfolded to form the Raton basin. Rocks of the Magdalena group exhibit two facies. Thick limestone and sandstone and interbedded shale were deposited on a shelf in the southern part of the geosyncline. These rocks are as much as 2,500 feet thick. The shelf facies thickens northward and grades rapidly into a geosynclinal facies. The gradation occurs along a belt trending northeastward across the mountains and into the subsurface of the southern part of the Raton basin. The geosynclinal facies is dominantly black shale containing thick beds of sandstone and thin beds of limestone. This facies originally was more than 10,000 feet thick in the deeper part of the trough and is more than 5,000 feet thick in the subsurface of the western part of the Raton basin in Mora County. In the southern part of the geosyncline on the Pedernal uplift, the shelf facies of the Magdalena group is truncated locally by the Sangre de Cristo formation. At the east side of the Las Vegas sub-basin the shelf facies is truncated by the Sangre de Cristo formation, which rests on Precambrian rocks of the ancestral Sierra Grande uplift. At the north in Colfax County, on much of the eastern limb of the Raton basin, the Sangre de Cristo formation or Triassic rocks rest on Precambrian rocks of the ancestral Sierra Grande uplift. A thick sequence of the geosynclinal facies of the Magdalena group is present in the mountains at the west. These rocks wedge out beneath the Sangre de Cristo formation in the subsurface of the western part of the Raton basin. Thick black shales of the geosynclinal facies might be sources of petroleum; however, the interbedded sandstones and limestones are tight. Sandstones of the shelf facies generally are more porous and permeable. Limestones of the shelf facies could be the best reservoirs, and shows of oil and End_Page 1093------------------------------ gas have been reported from these rocks in the Las Vegas sub-basin and near the southern end of the mountains. Small bioherms and associated calcareous clastic rocks occur at places in the shelf facies, particularly near the western margin of the Pedernal uplift, and may be present also in the subsurface along the eastern margin of the uplift and along the northeast-trending belt of transition from shelf to geosynclinal facies. Combination stratigraphic and structural traps may occur along the belts of wedge-out of the Magdalena on the Pedernal uplift and the west flank of the ancestral Sierra Grande uplift. Whether suitable reservoir rocks are present in these areas of wedge-out is not known. A thin but widespread sequence of Devonian(?) and Mississippian age contains cavernous limestone and breccia, but these rocks lie beneath possible source beds and rest on Precambrian crystalline rocks. End_of_Article - Last_Page 1094------------

Pennsylvanian Paleogeology and Search for Oil in Lucero Basin, Central New Mexico: ABSTRACT

The Lucero basin of central New Mexico was an area of Pennsylvanian sedimentation representing a significant widening of the central New Mexico seaway or accessway from the Paradox geosyncline on the north to the Sonoran geosyncline on the south. Several such basins along this accessway include the Lucero, San Mateo, and Orogrande, all of which have slightly different post-depositional geologic histories. This accessway, of which the Lucero basin is a part, ranged from 50 to 130 miles in width, and received up to 3,000 feet of Pennsylvanian sediments which form the Sandia, Madera, and Red Tanks formations. This seaway was in existence between Atokan and Virgilian time but was widest during Desmoinesian and Missourian time. Pennsylvanian marine sedimentation was limited on the west by the Zuni positive, on the east by a long sinuous platform west of the Estancia basin and the Pedernal positive, and on the northeast by the Penasco positive. Fine clastic sediments from the Zuni and medium to coarse sediments from the Penasco make up less than one-fourth of the Pennsylvanian section which is predominantly limestone. The sharp downwarp of the Estancia basin on the east, as a southerly basin of the central Colorado-Sangre de Cristo seaway, resulted in entrapment of westerly moving coarse clastics from the Pedernal uplift. The Sandia-Manzanita-Manzano-Joyita tectonic alignment (of Tertiary age) was a long narrow platform or sill which separated the thick clastic-filled Pennsylvanian section of the Estancia basin from the somewhat thinner but normal basinal and shelf carbonate section of the Lucero basin. Bioherms grew on the gently shelving east sides of the central New Mexico accessway as indicated by outcrops of calcarenite mounds containing Chaetetes sp. corals in the Sandia and Manzano mountains. Inasmuch as the Pennsylvanian outcrops at Monte de Belen and Gray Mesa along the Lucero uplift show basinal lithologic character in Desmoinesian and early Missourian strata and the entire section thins to zero westward onto the Zuni positive, it is likely that similar reefoid masses will be found in the subsurface in the area surrounding the corner common to Catron-Socorro-Valencia counties. Because of Laramide folding and Tertiary faulting, the eastern two-thirds of the Pennsylvanian Lucero basin is buried deeply beneath the valley fill of the Rio Grande trench, and parts of the platform between the Estancia basin on the east and the Lucero basin on the west now stand high as the Sandia-Manzano block-fault mountains. End_of_Article - Last_Page 1108------------

Pennsylvanian and Related Sediments of Upper Pecos Valley, New Mexico

More than 3,000 feet of Pennsylvanian sediments accumulated in the northern New Mexico extension of the Colorado zeugogeosyncline. The thickness north of Pecos is 2,836 feet. Sedimentation was influenced by several major bordering uplands: (1) Uncompahgre-San Luis uplift, (2) Pedernal uplift, (3) Sierra Grande-Las Animas arch, and (4) Front Range. Four facies representing two formations of cyclic deposition are recognized. Each facies corresponds with a distinct member: (1) lower Limestone member of Sandia, consisting of alternating sandstones and limestones, (2) upper Clastic member of Sandia, consisting of sandstones, shales, and coal, (3) lower Gray Limestone member of Madera, consisting of shales and cherty limestones, (4) Arkosic Limestone member of Madera, consistin of arkoses, red and green shales, and thin limestones. Uplift of the borderlands was accelerated in Late Pennsylvanian and Early Permian time. This resulted in sea withdrawal, local flexuring and erosion of Madera sediments, and increased continental sedimentation. The basins and uplifts are shown on a paleotectonic map.