Sangre De Cristo Formation Research Articles

Paleosols of the upper Paleozoic Sangre de Cristo Formation, north-central New Mexico: Record of early Permian palaeoclimate in tropical Pangaea

The lower Permian (Wolfcampian) Sangre de Cristo Formation of northern New Mexico consists of silty mudstones and laterally discontinuous sandstones deposited on an aggrading alluvial plain. Locally, mudstones display a variety of pedogenic features. Common mudstone fabrics vary from platy to prismatic; some beds display prominent pedogenic slickensides. Drab-colored root traces are common throughout the section, as are calcareous nodules, which vary from small bodies with diffuse boundaries to vertically stacked, discrete, cm-scale nodules (rhizocretions), and less commonly form coalescing horizons. Vertisols occur only in the lower portion of the ca. 90-m measured section. Most of the mudstone beds contain calcretes that are immature (calcic Protosols to calcic Argillisols), but the lower to middle portion of the section also contains mature calcrete horizons (argillic Calcisols and Calcisols).Intercalated micritic limestone beds with sharp contacts containing root traces, are of laterally variable thickness and grade to nodular calcretes. These are interpreted as floodplain pond carbonates that have undergone pedogenic alteration (palustrine limestones), indicating long periods of exposure under strongly seasonal climatic conditions. The isotopic composition of the pedogenic carbonate displays a substantial range of values, but most of the range of variation in isotopic composition is accounted for by isotopically heavier carbonate (both carbon and oxygen) precipitated in shallow ponds subject to intense pedogenic reworking (palustrine carbonate).During the early Permian, northern New Mexico was situated in a near equatorial position (ca. 4° N). The overall character of the paleosols suggests a persistent warm, semi-humid, seasonal climate throughout most of the interval of deposition during the Wolfcampian, but with episodically increased aridity during formation of the more mature calcretes. No long-term trend of climate change is evident in the stratigraphic section examined for this study.

Plant architecture and spatial structure of an early Permian woodland buried by flood waters, Sangre de Cristo Formation, New Mexico

Abstract Natural molds of 165 stems were found in life position in a 1 m-thick sandstone bed, lower Permian (Wolfcampian), Sangre de Cristo Formation, northern New Mexico. The sandstone represents a single flood event of a river sourced in the Ancestral Rocky Mountains. Most of the flood-buried plants survived and resumed growth. The stem affinities are uncertain, but they resemble coniferophytic gymnosperms, possibly dicranophylls. Stem diameters (N = 135) vary from 1 to 21 cm, with three strongly overlapping size classes. Modern forest studies predict a monotonically decreasing number (inverse square law) of individuals per size class as diameter increases. This is not seen for fossil stems ≤ 6 cm diameter, reflecting biases against preservation, exposure, and observation of smaller individuals. Stems ≥ 6 cm diameter obey the predicted inverse square law of diameter distribution. Height estimates calculated from diameter-to-height relationships of modern gymnosperms yielded heights varying from ~ 0.9 m to > 8 m, mean of ~ 3 m. Mean stand density is approximately 2 stems/m 2 (20,000 stems/hectare) for all stems > 1 cm diameter. For stems > 7.5 cm or > 10 cm diameter, density is approximately 0.24 stems/m 2 (2400 stems/hectare) and 0.14 stems/m 2 (1400 stems/hectare). Stem spatial distribution is random (Poisson). Mean all-stem nearest-neighbor distance (NND) averages 36 cm. Mean NND between stems > 7.5 cm and > 10 cm diameter is approximately 1.02 m and 1.36 m. NND increases in approximate isometry with stem diameter, indicating conformation to the same spatial packing rules found in extant forests and other fossil forests of varying ages. Nearest-neighbor distance distribution passes statistical testing for normality, but with positive skew, as often seen in extant NND distributions. The size-frequency distribution of the stems is similar to those of Jurassic, early Tertiary, and extant woodlands; the early Permian woodland distribution line has the same slope, but differs in that the overall size range increases over time (Cope's rule). The early Permian woodland is self-thinning; its volume versus density relationship shows a self-thinning exponent between − 1.25 and − 1.5, within the range seen in some extant plant stands (− 1.21 to − 1.7).

A Linear Programming Approach to Determine the Normative Composition of Sedimentary Rocks

The analysis of modal and normative composition of sedimentary rocks is widely used for studying their sources and tectonic settings. The normative calculation of the mineral composition of rocks in this study is formulated as a linear programming problem and is solved by means of the simplex method. This enables both simultaneous and successive subtraction of a set of basic minerals from a rock sample represented by its chemical composition {SiO2...LOI}. Such an approach provides a more exact calculation of the contribution of basic minerals in the rock. This mathematical approach is used to study two representative sets of sandstones and fine-grained rocks from a Meso- to Neoproterozoic marginal basin of southeastern Siberia (Uchur–Maya region, Yakutia) and a Pennsylvanian-Lower Permian uplifted continental block in Colorado, USA. The calculated normative mineral compositions of the Siberian sandstones are consistent with the observed modal compositions. These sandstones vary from K- Feldspar rich arkoses at the base of the sequence (the Uchur Group, lower Riphean) to quartz arenites or lithic sandstones and wacke in transgressive successions of the middle-upper Riphean. Arkoses and quartz arenites are dominant in Meso- to Neoproterozoic Siberia. These samples represent craton interior uplifted basement and quartzose, recycled orogen provenance of a stable craton in Rodinia. There are higher but consistent discrepancies between the calculated and observed compositions for the Pennsylvanian to Lower-Permian arkoses and quartz arenites (Sangre de Cristo, Belden, and Maroon Formations). The differences between the predicted and observed mineralogy may be due to uncertainties in the modes in the matrix and cement of the sandstones. This normative program should supplement modal calculations and provide better genetic constructions, especially in case of matrix-rich sandstones.

Syndepositional thrust-related deformation and sedimentation in an Ancestral Rocky Mountains basin, Central Colorado trough, Colorado, USA

Pennsylvanian–Permian synorogenic deposits (Minturn and Sangre de Cristo Formations) of the Central Colorado trough record an interplay of deformation and sedimentation in an Ancestral Rocky Mountains basin. The Central Colorado trough was a north-trending basin bordered by basement-involved highlands of the Uncompahgre uplift on the west and the Ancestral Front Range and Apishapa uplift on the east. Stratigraphic data show that the Central Colorado trough was an asymmetric basin in which coarse-grained sediments were deposited adjacent to the Sand Creek–Crestone thrust fault system of the Uncompahgre uplift. These deposits pinch out eastward against the Apishapa uplift along the eastern margin of the basin. Lithofacies analysis shows that the Central Colorado trough was filled by fan-delta, fluvial-delta, and turbidite deposits of the Middle Pennsylvanian Minturn Formation and by alluvial-fan, braided-stream, and meandering-stream deposits of the Upper Pennsylvanian–Permian Sangre de Cristo Formation. Geologic mapping has identified three syndepositional structures in the strata of the Central Colorado trough that indicate Pennsylvanian–Permian shortening: (1) the Gibson Peak growth syncline in the footwall of the Crestone thrust fault, which formed by syndepositional rotation of the Crestone Conglomerate Member of the Sangre de Cristo Formation during thrust displacement; (2) the Sand Creek thrust fault, which cuts the lower part of the Crestone Conglomerate Member but is covered by younger deposits of the Crestone Conglomerate Member; and (3) an intraformational angular unconformity in the Sangre de Cristo Formation that separates folded strata from overlying less deformed strata. All three structures indicate general east-west shortening during deposition. We interpret the Central Colorado trough as a flexural basin on the basis of syndepositional thrust-related structures, basin asymmetry, and lithofacies distribution. Displacement on the east-verging Sand Creek–Crestone thrust fault system appears to have controlled uplift of the central part of the Uncompahgre uplift and also subsidence in the adjacent basin. The Apishapa uplift, located along the eastern margin of the basin, is interpreted as a possible flexural forebulge related to crustal loading of thrust sheets along the western margin of the Central Colorado trough. Geologic mapping, subsurface data, and identification of syndepositional structures has also led to a better understanding of post-Paleozoic deformation of Pennsylvanian–Permian strata of the Central Colorado trough and the structural evolution of the present Sangre de Cristo Mountains.

The geochemistry of shales, siltstones and sandstones of Pennsylvanian–Permian age, Colorado, USA: implications for provenance and metamorphic studies

A series of shales and sandstones found near the source of the Sangre de Cristo, Belden, and Maroon Formations from central Colorado were examined petrographically and were analyzed for major and selected trace elements, including the REE. The sandstones from the Belden Formation have higher quartz/feldspar ratios than do those from the Maroon and Sangre de Cristo Formations. Also, the alkali feldspar (i.e., orthoclase, microcline, perthite)/plagioclase ratio decreases in the order Sangre de Cristo Formation>Maroon Formation>Belden Formation, but the CIW′ (chemical index of weathering=molecular [Al 2O 3/(Al 2O 3+Na 2O)]∗100) decreases in the order Belden Formation>Sangre de Cristo Formation>Maroon Formation. This suggests that the Belden Formation had a more plagioclase-rich granitoid source and more intense weathering of the source than did the Maroon and Sangre de Cristo Formations. Also, the variation in the elemental composition within the terrigenous sediment may be explained in terms of the variation in the observed minerals. Elemental ratios critical of provenance are statistically the same between the finer sediment of the Maroon and Sangre de Cristo Formations and fall within the range of a granitoid provenance, suggesting a similar granitoid source composition for the two formations. The fine sediment from the Belden Formation, however, has significantly more negative Eu anomalies and lower La/Sc and Th/Cr ratios than those of the Maroon and Sangre de Cristo Formations, suggesting a more differentiated granitoid source for the Belden than for the Maroon and Sangre de Cristo Formations. Most elemental concentrations or ratios vary by a factor of 0.12 to 60 between adjacent fine and coarse sediment (<1-m distances). Thus, it is not recommended that metasedimentary sequences similar in composition to this study be examined to determine element mobility during metamorphism as the variation due to sedimentary processes is so large.

A new species of Limnoscelis (Amphibia, Diadectomorpha) from the Late Pennsylvanian Sangre de Cristo Formation of central Colorado

A new species of Limnoscelis (Amphibia, Diadectomorpha) from the Late Pennsylvanian Sangre de Cristo Formation of central Colorado

Minturn and Sangre de Cristo Formations of Southern Colorado--A Prograding Fan-Delta to Alluvial-Fan Sequence Shed from Ancestral Rocky Mountains: ABSTRACT

The Middle Pennsylvanian Minturn Formation and the Pennsylvanian and Permian Sangre de Cristo Formation of the northern Sangre de Cristo Range form a 4,000-m (13,000-ft) thick, progradational sequence of fan-delta and alluvial-fan deposits. This sequence was deposited along the western margin of the central Colorado trough during faulting and uplift of the late Paleozoic Uncompahgre highland of the Ancestral Rocky Mountains. The Minturn Formation is composed mostly of sandstone and shale deposited by fan deltas that prograded into the central Colorado trough. The Minturn of the northern Sangre de Cristo Range is divisible into (1) a turbidite-bearing facies, (2) a limestone-bearing facies, and (3) a red-bed facies. The turbidite-bearing facies is interpreted as deposits of fan deltas that prograded onto the sea bottom below wave base. The limestone-bearing facies is interpreted as deposits of fan deltas that prograded onto a shallow sea bottom above wave base. Turbidites and shallow-marine limestones, although they make up only a minor part of the Minturn Formation, are mutually exclusive deposits that serve to distinguish the two facies. In the limestone-bearing facies, sandstones containing deltaic fore ets overlie thin shallow-marine limestones and are considered diagnostic of that facies. Both facies contain thick intervals of sandstone and shale interpreted as deltaic and alluvial deposits. Where it onlaps the Uncompahgre highland, the lower part of the Minturn Formation contains quartzose and arkosic red beds of probable alluvial origin. The continental Sangre de Cristo Formation conformably overlies the Minturn Formation basinward, but it unconformably overlies Minturn Formation and Precambrian basement near the Uncompahgre highland. The Sangre de Cristo Formation contains (1) a sandstone facies deposited on the distal surfaces of alluvial fans, and (2) a conglomerate facies (Crestone Conglomerate Member) deposited on the proximal surfaces of alluvial fans. The sandstone facies consists of fining-upward cycles of red conglomeratic sandstone and siltstone interpreted as braided-stream deposits. The conglomerate facies consists of poorly sorted conglomerates interpreted as debris-flow and mudflow deposits, and sorted conglomerate and sandstone interpreted as streamflow and sheetflow deposits. End_of_Article - Last_Page 854------------

Late Paleozoic Tectonism in Central Colorado: ABSTRACT

Detailed mapping and stratigraphic and sedimentologic studies within thick sequences of Pennsylvanian and Permian strata of central Colorado show that most of the major faults called Laramide underwent significant displacements in the late Paleozoic. Abrupt eastward facies changes from fine- to coarse-grained sediments and from gray to red strata, and abrupt thinning of the section across the faults indicate that the north-northwest-trending Gore, Mosquito-Weston, Williams Range, and Elkhorn faults were offset as much as 8,000-9,000 ft during the deposition of the Minturn and Maroon strata during the Pennsylvanian and Permian Periods. The Hartsel uplift was faulted as much as 6,000-8,000 ft along its bounding, north-northwest-trending Agate Creek and Santa Maria faults, thereby splitting South Park into several local depositional basins during the Pennsylvanian and Permian. Lithofacies evidence within Madera (Minturn) strata, and a Permian angular unconformity between the lower and upper members of the Sangre de Cristo Formation show that the north-northwest-trending Pleasant Valley fault was offset as much as 11,000 ft during the Pennsylvanian and Permian. Abrupt facies End_Page 613------------------------------ changes within the Madera and Sangre de Cristo Formations, overlap of the Crestone Conglomerate onto Precambrian rocks, and the presence of unconformities within the late Paleozoic section indicate that several faults in the Crestone (Sangre de Cristo Range) and southern Wet Mountain areas were displaced significantly in the late Paleozoic. End_of_Article - Last_Page 614------------

Upper Pennsylvanian vertebrates from the Sangre de Cristo formation of Central Colorado

Upper Pennsylvanian vertebrates from the Sangre de Cristo formation of Central Colorado

Stratigraphy and History of Raton Basin and Notes on San Luis Basin, Colorado-New Mexico

Raton Basin: The Raton basin of northeastern New Mexico and southeastern Colorado is a Laramide structural basin bounded on the west by the Sangre de Cristo uplift, on the north by the Wet Mountains uplift and Apishapa arch, and on the east by the Sierra Grande arch. The basin is asymmetrical and the northerly trending axis generally is near the Sangre de Cristo uplift. The intrabasinal Cimarron arch separates the structurally deeper northern part of the Raton basin from the shallower, southern, Las Vegas sub-basin. During most of Paleozoic time the Raton basin and its bounding uplifts were part of the relatively stable continental backbone. The oldest known sedimentary rocks in the basin are marine beds of Devonian(?) and Mississippian age. In Early Pennsylvanian time the Rowe-Mora and Central Colorado geosynclinal basins were formed in the area of the present Sangre de Cristo uplift and the western half of the present Raton basin. The basins were bounded on the west by the intermittently rising San Luis uplift, and on the east and north by the ancestral Sierra Grande, Apishapa, and Wet Mountains uplifts. A mainly marine unstable shelf facies of the Magdalena Group of Pennsylvanian age in the Las Vegas sub-basin is 1,500-2,500 feet thick. These rocks grade abruptly northward into a marine geos nclinal facies which is as much as 6,000 feet thick in the Las Vegas sub-basin. The Magdalena Group is absent from the Cimarron arch, but it probably is present in the western half of the northern Raton basin where it may be 4,000 feet thick. Orogenic debris of the Sangre de Cristo Formation of Pennsylvanian and Early Permian age was derived mainly from the San Luis uplift, filled the Rowe-Mora and Central Colorado basins, and lapped onto Precambrian rocks of the other bounding uplifts. The Sangre de Cristo Formation is 700-3,500 feet thick at the south, and 6,000-9,500 feet thick at the north. Higher Permian rocks, and Upper Triassic and Upper Jurassic rocks have average aggregate thicknesses ranging from 2,300 feet at the south to 1,100 feet at the north. These deposits blanketed the region of the present Raton basin and buried the late Paleozoic, Sierra Grande, and Apishapa uplifts. Cretaceous marine shale interbedded with some sandstone blanketed the entire region. The Cretaceous rocks are about 4,500 feet thick at the north, and remnants in the Las Vegas sub-basin are 900-1,000 feet thick. The terrestrial latest Cretaceous and early Tertiary rocks, which are about 12,000 feet in aggregate maximum thickness in the northern part of the Raton basin, were derived mainly from the rejuvenated San Luis uplift. During early and middle Tertiary time, the San Luis uplift and the western parts of the Paleozoic Rowe-Mora and Central Colorado basins were elevated to form the Sangre de Cristo uplift. The present Raton basin, Wet Mountains uplift, and the Apishapa, Las Animas, and Sierra Grande arches were formed in early Tertiary time. The Raton basin has been a basinal area for most of its history since Early Pennsylvanian time. Thick marine sediments of Pennsylvanian and Cretaceous ages probably were sources of petroleum. Potential traps, both stratigraphic and structural, are known to exist in many parts of the basin, although these traps are mainly untested. Encouraging shows of oil and gas have been found in Pennsylvanian rocks in the Las Vegas sub-basin, and in Cretaceous rocks in several parts of the basin, but there has been no commercial production. San Luis Basin: In middle and late Tertiary time the ancient San Luis uplift was tilted eastward and its eastern part foundered to form the San Luis basin, which is the northern part of the complex Rio Grande trough. The northwestern part of the San Luis basin merges into the eastern flank of the San Juan Mountains uplift. The southwestern part of the basin is bounded by the east-tilted Brazos uplift. The eastern and northern boundaries of the basin are a complex fault zone along the western margin of the Sangre de Cristo uplift which merges, around the northern end of the basin, with the Sawatch and Gunnison uplifts. Much of the San Luis basin is filled with middle to upper Tertiary and Quaternary terrestrial sediments and interbedded andesite and basalt that are at least 5,000 feet thick locally. This basin fill rests on lower and middle Tertiary volcanics that are related to the volcanics of the San Juan Mountains. Because the region of the San Luis basin was a part of the Paleozoic and Mesozoic San Luis uplift, it is doubtful that extensive areas of Paleozoic or Mesozoic rocks are preserved beneath the lower to middle Tertiary volcanics. The stratigraphy and geologic history of the San Luis basin are not encouraging for petroleum possibilities. End_Page 2041------------------------------

Tectonic and Sedimentary History of Raton Basin and Notes on San Luis Basin: ABSTRACT

The Raton basin of northeastern New Mexico and southeastern Colorado is a Laramide structural basin bounded on the west by the Sangre de Cristo uplift, on the north by the Wet Mountains uplift and Apishapa arch and on the east by the Sierra Grande and Las Animas arches. The basin is strongly asymmetrical and the northerly-trending axis is near the Sangre de Cristo uplift. The intrabasinal Cimarron arch separates the structurally deeper northern part of the Raton basin from the shallower, southern, Las Vegas subbasin. During most of Paleozoic time the Raton basin and its bounding uplifts were part of the relatively stable Continental backbone. The oldest known sedimentary rocks in the basin are Devonian (?). In Early Pennsylvanian the Rowe-Mora basin was formed in the area of the present Sangre de Cristo uplift and the western half of the present Raton basin. The Rowe-Mora basin was bounded on the west by the intermittently rising San Luis uplift and on the east and north by the ancestral Sierra Grande Apishapa and Wet Mountains uplifts. An unstable-shelf facies of the Magdalena Group of Pennsylvanian age in the southern part of the Rowe-Mora basin is 1,500-2,500 feet thick. These rocks grade abruptly northward into a geosynclinal facies which is as much as 6,000 feet thick in the Las Vegas subba in. The Magdalena Group is absent from the Cimarron arch, but it probably is present in the western half of the northern part of the Raton basin where it may be 4,000 feet thick. Orogenic debris of the Sangre de Cristo Formation of Pennsylvanian and Early Permian age was derived mainly from the San Luis uplift, filled the Rowe-Mora basin, and lapped into Precambrian rocks of the other bounding uplifts. The Sangre de Cristo Formation is 700-3,500 feet thick at the south, and 6,000-10,000 feet thick at the north. Higher Permian rocks and Upper Triassic and Upper Jurassic rocks have average aggregate thicknesses ranging from 2,300 feet at the south to 1,100 feet at the north. These deposits blanketed the entire region and buried most of the late Paleozoic uplifts. Cretaceous shales interbedded with some sandstones also blanketed the region. These rocks are about 4,500 feet thick at the north, and remnants in the Las Vegas subbasin are 900-1,000 feet thick. The latest Cretaceous and early Tertiary rocks, which are about 12,000 feet in aggregate maximum thickness in the northern part of the Raton basin, were derived mainly from the rejuvenated San Luis uplift. During early and middle Tertiary the western part of the Paleozoic Rowe-Mora basin was elevated to form the Sangre de Cristo uplift, and the present Wet Mountains uplift and the Apishapa, Las Animas, and Sierra Grande arches were formed. In late Tertiary the San Luis uplift was tilted eastward and its eastern part foundered to form the northern part of the complex Rio Grande trough. The San Luis basin in southcentral Colorado is the northeastern part of this tilted and faulted block. The western part of the basin merges into the eastern flank of the San Juan dome. The eastern and northern boundaries are a complex fault zone along the western margin of the Sangre de Cristo uplift which merges, around the northern end of the basin, with the Sawatch and Gunnison uplifts. Much of the San Luis basin is filled with upper Tertiary and Quaternary sediments and interbedded andesites and basalts that are at least 2,000 feet thick locally. This basin fill rests on lower and middle Tertiary volcanics that are related to the volcanics of the San Juan Mountains. Because the region of the San Luis basin was a part of the Paleozoic and Laramide San Luis uplift, it is doubtful that extensive areas of Paleozoic and Mesozoic rocks are preserved beneath the volcanics. End_of_Article - Last_Page 1875------------

Permian Shoreline of Central New Mexico

Permian rocks of the Santa Fe-Las Vegas area, New Mexico, exhibit many shoreline characteristics, and a single cycle onlap-offlap sequence. Ripple marks, cross-bedding, bars and channels, fossils, beach-rock, facies changes, gypsum, supposed halite prints, mud cracks, traits, pebble sizes, and rock thicknesses are used to interpret this pattern. The shoreline was oriented roughly north-south, or northeast-southwest. Local hills or small mountains, and a wide coastal plain, were on the west and northwest. The sea extended toward the east and southeast. In early Permian time, the sea was advancing; in middle Permian time, retreating. The onlap-offlap cycle produced a wedge-shape body of marine Permian sediments which feathered out along a line west of the present Rio Grande. The Sangre de Cristo Formation (of upper Pennsylvanian and lower Permian age) is dominantly maroon shale, with about 20 per cent sandstone and conglomerate, representing continental deposition. The Yeso Formation is primarily orange-colored ripple-marked siltstones representing the tidal flat environment, but the upper part of the formation includes several beachrock units. The Glorieta Formation is highly cross-bedded clean sand which apparently accumulated in the near-shore environment. The Lagunita Formation is beachrock, formed early in the regressive stage. The Bernal Formation is orange-colored siltstone thought to represent the tidal flat, and supposedly deposited in middle Permian time. No late Permian rocks are known in the area. Coastal plain sediments accumulated again duri g the Triassic (Santa Rosa and Chinle Formations). Ripple marks, cross-bedding, bars, and facies changes are used to give orientations. Ripple marks, mud cracks, trails, and evaporites are used to provide information about water depths. Ripple marks, beachrock, and fossils are used to interpret specific environments. A tropical or sub-tropical climate is inferred.

Probable Triassic Rocks Along Eastern Front of Sangre de Cristo Mountains, South-Central Colorado

Sedimentary rocks of Triassic age generally have been thought to be missing from outcrops in the Sangre de Cristo Mountains of Colorado where at most places the Entrada sandstone of Jurassic age rests unconformably on rocks that have been assigned to the Sangre de Cristo formation of Pennsylvanian and Permian age. Two units of probable Triassic age have been separated from the top of the Sangre de Cristo formation; one is here described and named the Johnson Gap formation. The other is correlated with the Lykins formation of central Colorado and in this report is referred to as the Lykins(?) formation. The Johnson Gap formation crops out for 8 mi. or more N. of the Colorado-New Mexico boundary, and is correlated with a part of the Dockum group of Triassic age of northern New Mexico. The Lykins(?) formation crops out in the area of Huerfano Park and locally along the eastern front of the Sangre de Cristo Mountains as far S. as the North Fork of the Purgatoire River. Fossil wood found near the top of the unit has been determined as Triassic(?) in age. The Johnson Gap formation and the Lykins(?) formation differ lithologically and probably are not correlative. The Johnson Gap consists mainly of gray silty conglomeratic limestone interbedded with gray and light red silty and siliceous limestone, red siliceous siltstone, greenish gray and brown plastic shale, and gray fine-grained quartzose sandstone. The Lykins(?) is made up of brownish red, purplish red, and buff sandstone, siltstone, and shale, and a few thin light gray limestone beds. It is probably older than the Johnson Gap formation in that the Lykins(?) formation seems to grade into the underlying Sangre de Cristo formation, whereas the Johnson Gap formation overlies the Sangre de Cristo unconformably. The striking lithologic similarity of the rocks of the Lykins(?) formation along the eastern front of the Sangre de Cristo Mountains to those of the most southerly exposures of the Lykins formation 20 mi. ENE. of Canon City, Colorado, suggests that the rocks once were probably continuous throughout S.-central Colorado, but were locally removed by erosion following a post-Triassic uplift in the general area of the Wet Mountains.

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------------

Rocky Mountain Association of Geologists Symposium on Pennsylvanian Rocks of Colorado: ABSTRACT

The Rocky Mountain Association of Geologists, Denver, Colorado, published in 1958 a volume with this title in conjunction with its field conference on Pennsylvanian rocks of the Maroon basin. Pennsylvanian tectonism was dominated by vigorous growth of northwest-trending mountain ranges (Frontrangia and Uncompahgria) and their attendant depositional troughs. These obliterated the amoeboid patterns of gentle epeirogeny in Colorado established during early and middle Paleozoic time. Pennsylvanian depositional history began in Colorado with the accumulation of a red clay regolith, the Molas formation, upon the maturely dissected Mississippian Leadville limestone. Four Pennsylvanian basins (or troughs), the Denver, the Maroon, the Paradox, and the Raton, between and adjacent to Uncompahgria and Frontrangia, contain abundant thicknesses of all lithologic types common to cratonic sediments. Two basins in western Colorado, the Maroon and the Paradox, exhibit extensive evaporites, he Paradox and Eagle sequences. All the basins contain large volumes of red, arkosic conglomerates and finer clastics (the Fountain, Maroon, Cutler, and Sangre de Cristo formations) which grade laterally into marine limestones, shales, and sandstones with or without passing through an evaporite facies. Western Colorado marine sequences bear the names Hermosa group, Morgan formation, and Weber sandstone. In the Raton basin the Sangre de Cristo and Madera formations, predominantly clastic, comprise the section. In the Denver basin, only the Fountain arkose facies crops out (except for a trace of Glen Eyrie claystone near Colorado Springs); the series terms Morrow, Atoka, Des Moines, Missouri, and Virgil have been borrowed from the Mid-Continent region as subdivisions. The uplifts attained maximum development in the Des Moines epoch and continued tectonically active into middle Permian time. Pennsylvanian deposition carried over without hiatus into the Wolfcamp epoch of the Permian period. The existing Uncompaghre uplift and the Frontrange uplift (now masked by the Laramidian Front and Park Ranges) are part of the present tectonic pattern of Colorado. The bulk of Colorado oil has been produced from three reservoir classes: (1) Cretaceous sandstone lenses scattered across the Denver basin, (2) the Weber sandstone of the Rangely pool in the Maroon basin, (3) the Hermosa carbonate reservoirs in the Paradox basin. The latter two, Permo-Pennsylvanian in age, are outstandingly important. The size and youth of Pennsylvanian carbonate pools indicate large reserves in these rocks. End_of_Article - Last_Page 1779------------

Pennsylvanian and Permian Stratigraphy in Sangre de Cristo Mountains Between La Veta Pass and Westcliffe, Colorado

Structurally complex Pennsylvanian and Permian strata comprise the bulk of the Sangre de Cristo Range between La Veta Pass and Westcliffe in south-central Colorado. They are at least 14,000 feet thick near Crestone in the northern part of the area, and more than 9,000 feet thick at La Veta Pass on the south. The sediments are predominantly arkosic clastics, eroded from Precambrian crystalline rocks of the San Luis-Uncompahgre highland on the West, and rapidly deposited in a narrow, northwest-trending geosyncline. This sector of the Sangre de Cristos is nearly parallel with the geosyncline and situated near its western side. The terrigenous clastics become finer-grained and Desmoinesian limestones become abundant southeastward, reflecting southward decrease in uplift of th highland and a more basinward position of the southern exposures. The Kerber formation (Morrowan ?), oldest Pennsylvanian unit in this area, apparently can be recognized only at Grayback Mountain, west of Huerfano Park; presumably it was partly removed by erosion prior to Atokan deposition. The name Deer Creek formation is proposed for beds previously called Clastic member of the Sandia, from Huerfano River south to the New Mexico border. At its type locality west of Huerfano Park, this formation is late Atokan, 1,119.2 feet thick, and consists of variegated sandstones, siltstones, conglomerates, and shales chiefly of fluvial origin, with interbedded marine limestone and terrigenous clastics in the upper part. The Deer Creek formation is differentiated by its redbeds. The Madera formation contains Fusulina rockymontana (Roth and Skinner) and is of Desmoinesian age. At La Veta Pass it is about 3,068 feet thick and is divided into the lower, Gray limestone member, 533 feet thick; the Arkosic limestone member, 2,369 feet thick; and the upper, Whiskey Creek Pass limestone member, 166 feet thick. The first two members accumulated under alternating marine and fluvial environments. The increasing predominance of continental sediments in the Arkosic limestone member reflects eastward migration of the shoreline. The Whiskey Creek Pass limestone records stability in both depositional and source areas. The Madera grades northward into its stratigraphic equivalent, the Minturn formation. The Minturn is at least 5,000 feet thick and consists chiefly of grayish to greenish sandstones, conglomerates, and shales or siltstones. It is mainly fluvial, but marine sediments occur at several horizons. Near the top, a calcareous zone containing marine fossils is probably equivalent to the Whiskey Creek Pass limestone. Overlying the Madera near La Veta Pass and Pass Creek Pass is a sandstone section about 1,000 feet thick, in fault contact with the overlying Sangre de Cristo formation. It is here named the Pass Creek sandstone. The Sangre de Cristo formation, of late Pennsylvanian (?) and probably Permian (Wolfcamp) age, contains up to 8,000 feet or more of predominantly fluvial strata. It is differentiated from underlying units by its redbeds. Two members are recognized in the northern part of the area: the Lower member, characterized by piedmont cyclothems; and the Crestone conglomerate. The latter, a thick fanglomerate, is the only positive evidence of mountains in the San Luis-Uncompahgre highland, and is the last record of Paleozoic orogeny in this area.

Tectonic History of Raton Basin with Special Reference to Late Paleozoic: ABSTRACT

During early Pennsylvanian time the ancient Apishapa Sierra Grande, a linear mildly positive element trending 45° W. of the present strike of the Sierra Grande uplift, extended across the Raton basin and connected with the strongly positive Front Range element. Seas surrounded the ancient Apishapa Sierra Grande except on the extreme northwest where it connected with the old Front End_Page 786------------------------------ Range. Marshall Kay's zeugogeosyncline of Colorado and northern New Mexico bounded the west side of the mildly positive ancient Apishapa Sierra Grande and the east side of the mildly positive Uncompahgre. In early Pennsylvanian time relatively small quantities of arkosic clastics were carried into adjacent seas from the ancient Apishapa Sierra Grande and the Uncompahgre. The Front Range, however, yielded vast quantities of arkosic debris toward seas on the east during Atokan and Desmoinesian time. Orogenic activity along the Front Range is recorded in the coarse clastic Fountain formation which grades laterally into early Pennsylvanian marine sediments as well as late Pennsylvanian marine sediments. Shortly after Cherokee time a major alteration occurred in the tectonic framework of south-central and southeastern Colorado. The Uncompahgre was strongly uplifted along its east side and the ancient Apishapa Sierra Grande subsided to receive coarse arkosic clastics during late Pennsylvanian time. This writer believes the Sangre de Cristo formation in the Raton basin area is Missouri and Virgil in age, representing a near-source clastic deposit with few interfingering marine limestones. Subsidence of the Raton basin area during Missouri and Virgil time was not uniform. A subsiding east-west trough developed along the New Mexico-Colorado border in the Raton basin, connecting with the north-south subsiding Colorado and northern New Mexico zeugogeosyncline. The present configuration of t e Apishapa and Sierra Grande uplifts developed during Missouri and Virgil time as linear features bounding the more rapid subsiding east-west trough along the Colorado-New Mexico border. Uplift on the west side of the Uncompahgre near the close of the Pennsylvanian period caused regional tilting toward the east, producing an unconformity at the top of the Sangre de Cristo formation. Rocks of known Permian Leonard age do not interfinger with arkoses of the Sangre de Cristo formation but rest unconformably on Sangre de Cristo rocks and pinch out by onlap along the west side of the Raton basin. Except for minor erosion during early Triassic time, the Raton basin area received sediments during the Mesozoic era until the late Cretaceous Laramide orogeny. The Colorado and northern New Mexico zeugogeosyncline was the center of strong Laramide uplift, creating the Sangre de Cristo Mountains, and minor Laramide uplift gave rise to the present Apishapa and Sierra Grande topographic features. End_of_Article - Last_Page 787------------

STRATIGRAPHY IN THE PERMO-PENNSYLVANIAN ZEUGOGEOSYNCLINE OF COLORADO AND NORTHERN NEW MEXICO

The Permo-Pennsylvanian zeugogeosyncline of Colorado and northern New Mexico, unique among the troughs of the western United States, was a rapidly subsiding basin with highlands on both sides. Its development was progressive. The Morrow strata were deposited in the northern half of the trough. Following the retreat of the Morrow sea, the Atoka sea entered the southern part of the trough. This sea remained until Desmoinesian time, and the Atoka and Desmoines faunas are mixed. Marine sedimentation reached a climax in Cherokeean time when a seaway traversed the length of the trough. In later Permo-Pennsylvanian time, the sea was confined to the ends of the trough, but thick deposits of nonmarine sediment accumulated in the center of the trough. Upper Pennsylvanian or Wolfcamp strata are several thousand feet thick. Four principal lithologic units can be recognized: (1) the Belden and Kerber formations of Morrowan, Atokan, and possibly Desmoinesian age; (2) the Clastic member of the Sandia formation of Atokan age; (3) the Minturn and Madera formations, mainly of Cherokeean age; and (4) the Maroon and Sangre de Cristo formations, late Pennsylvanian or Wolfcampian in age. Four minor lithologic units occur at the ends of the trough: (1) the Yeso formation of Leonardian age; (2) the San Andres formation of Permian age; (3) the Weber sandstone of Pennsylvanian and Permian (?) age; and (4) the State Bridge formation of Guadalupian age. The Jacque Mountain limestone of the Gore area may correlate with a bed which the writer has named the Whiskey Creek Pass limestone member of the Madera formation. If this correlation is correct, this layer can be used as a datum plane over much of the trough. Cotylosaur and pelycosaur bones occur in the Sangre de Cristo formation in Fremont County, Colorado. These reptiles have not been found previously in this region.