ABSTRACT

This paper discussses the paleozoic tectonic features, stratigraphy, structures, and oil and gas possibilities of northeastern New Mexico and adjacent states.

Paleozoic highlands began to appear in the area as early as Mississippian time. This resulted in either non-deposition or limited deposition and/or erosion of Mississippian sediments, particularly along the trend of the modern Rocky Mountain Front. Pennsylvanian sediments record at least two intervals of uplift in the highlands. Accelerated upheavals accurred from late Pennsylvanian through Wolfcamp time in the Permian.

The major highlands included the Uncompahgre - San Luis-Canyoncito axes of Colorado and New Mexico and the Colorado Front Range. The southern end of the latter was expressed in Pennsylvanian time by a pair of west-northwest trending uplifts -- the Apishapa and Sierra Grande. During part of the Permian a northeast-southwest trending uplift --the Sierra Grande - Las Animas Arch--occupied the northeast corner of New Mexico and adjacent Colorado. East of the Sierra Grande part of the arch and on the general trend of the Amarillo Mountains stood the Bravo Dome high of the Texas Panhandle. Several modern ranges of the Sangre de Cristo Mountains of northeastern New Mexico occupy the sites of influential Paleozoic highs. These are the north-south trending Las Vegas-Mora-Rincon ranges, paralleled on the west, in part, by the Central Sangre de Cristo and the Truchas Range. The Pedernal Hills to the south mark the site of a more extentive Paleozoic highland--the Pedernal Uplift. This crystalline uplift was aligned generally north-south, curving to the northeast toward the Sierra Grande Arch on the northern end. The east-west Matador Arch of the Texas Panhandle formed the southern border of the Palo Duro Basin and apparently terminated with a west-southwest trend in Roosevelt County, New Mexico.

A number of structural and sedimentary basins bordered on and were influenced by the above highlands. The major structure was the generally north-south trending Central Colorado zeugogeosyncline between the Uncompahgre - San Luis and Front Range highlands. The northern portion included the Canyon City and Colorado Springs embayments of the southern Denver Basin. East of the Las Animas Arch was the Hugoton embayment of the Anadarko Basin of southwestern and adjacent Colorado and Oklahoma. Southeastward from this arch and north of the Bravo Dome was the Dalhart Basin. East of the modern Sangre de Cristos and astride the New Mexico - Colorado border was the Raton Basin. To the south was a relatively long, narrow extension of the zeugogeosyncline, the Rowe-Mora Basin with a possible southeastward extension between the Pedernal Uplift and the Sierra Grande Arch. The Palo Duro Basin, of uncertain extent, occupied the area between the Matador Arch and the Amarillo Mountains.

The stratigraphy of Northeastern New Mexico, Pennsylvanian through Tertiary, is discussed in some detail and compared with similar units in the adjacent areas. The general stratigraphic

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relationships are shown in the accompanying chart. A maximum sedimentary thickness in excess of 20,000 feet is indicated for the deepest basin deposits. Tertiary and Quaternary surface rocks of igneous origin cover a large part of the area in northeastern New Mexico and adjacent Colorado.

Surface and subsurface structures are of three general ages: late Penn-sylvanian, Permian and Laramide. Pennsylvanian structures are localized and consist of uplift in the basement rock, folding, thrust faulting and attendant jointing. Biohermal structures also occur locally in the shallow parts of some of the basins. Partial truncation of the fold structures occurred in late Pennsylvanian and/or transitional Permo-Pennsylvanian time. Uplifts during the early Permian affected the primary dips of sediments bordering the highlands. The Sierra Grande-Las Animas Arch became defined as such, but like its neighboring positive areas, was gradually overlapped and covered by Leonard and/or Guadalupian sediments. Laramide orogeny began in late Cretaceous time and continued intermittently through the Oligocene of Tertiary time. Incomplete records indicate probable reactivation and modification of some major Permian and Pennsylvanian faults, beginning in the Late Cretaceous. The crystalline cores of the Southern Rockies were uplifted in broad, plunging anticlinal arches, accompanied by strong compression from the west. Upthrusts, reverse faults and overthrusts trend generally N.15W. to N.45E. and are paralleled by singly and doubly plunging folds. Folds along the Rocky Mountain Front are overturned or steeply inclined to the east. Some of the older local highs were re-elevated at this time.

Gentle folding continued in the Eocene along with intrusions in the form of stocks, necks, dikes and sills. Lava sheets covered areas of appreciable extent. Possibly the most intense Tertiary deformation occurred during the Oligocene and created a generally northeast trending set of structures, including steep normal faults, gravity faults, folds and uplifts. Late Tertiary time was marked by additional local faulting--mainly gravity types in en echelon pattern, along with general uplift in the mountain cores and differential warping of blocks bounded by the major faults.

Oil and gas exploration in the major basins has been fitfull and inadequate. Many of the well records are sketchy and inaccurate. However, encouraging shows and some commercial production have been indicated for all of the areas. Potential source beds occur in the Mississippian, Pennsylvanian and Cretaceous. Associated sands and conglomerates offer favorable carrier beds. These, in combination with the structural features mentioned above--including reefs, buried hills and stratigraphic traps--offer numerous possibilities for reservoirs. The most promising shows of oil and gas have come from basal Pennsylvanian sandstones (Atoka and Morrow), Pennsylvanian limestones (Des Moines, Missouri and Virgil) and Cretaceous (Dakota) sandstone and sandy shales (Pierre).

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