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Research about San Juan Basin

Source-linked reports with geographic coverage including San Juan Basin.

At least 19 recordsLinked to original sources
USGS2023

Progradational-to-retrogradational styles of Palaeogene fluvial fan successions in the San Juan Basin, New Mexico

Basin-scale outcrop analyses of fluvial architecture in the Palaeogene San Juan Basin, New Mexico, document lateral and vertical trends in channel, floodplain and palaeosol characteristics. Herein, the uppermost part of the Palaeocene Nacimiento Formation and lower Eocene Cuba Mesa and Regina Members of the San Jose Formation are identified as deposits of large fluvial fans based on trends observed across the basin. Stratigraphic trends suggest two packages originated by fluvial fan progradation. Progradation of the lower fan system provides a new explanation for the transitional nature of a disconformity at the Nacimiento–San Jose Formation contact, previously thought to be a low-angle unconformity. The two fan systems are separated by a retrogradational interval that culminates in a depositional hiatus at the contact between the Cuba Mesa and Regina Members. This, combined with poor age constraints, indicates that the duration of the disconformity at the base of the Cuba Mesa Member may have been overestimated. Furthermore, the succession is interpreted as deposits of variable-discharge rivers, based on the combined abundance of upper flow regime and high deposition rate sedimentary structures indicative of intense flooding events, preservation of in-channel bioturbation and paedogenic modification indicating periods of prolonged dryness, lack of identifiable bar strata and alternations of poorly drained and well-drained floodplain deposits with pedofacies indicating alternating wet–dry cycles. This dataset adds to a growing body of evidence linking the formation of large fluvial fans to discharge variability and thus to hydroclimates with significant inter- and intra-annual precipitation variability and intense rainfall. A long-term stratigraphic shift from poorly drained to well-drained floodplain deposits across two progradational fan successions indicates that a predictive model suggesting downstream decreases in soil drainage conditions is not encompassing of all large fan systems, and instead suggests a transition to a more arid climate across the Palaeocene–Eocene boundary.

New Mexico↗
USGS2012

Direct U-Pb dating of Cretaceous and Paleocene dinosaur bones, San Juan Basin, New Mexico: COMMENT

Based on U-Pb dating of two dinosaur bones from the San Juan Basin of New Mexico (United States), Fassett et al. (2011) claim to provide the first successful direct dating of fossil bones and to establish the presence of Paleocene dinosaurs. Fassett et al. ignore previously published work that directly questions their stratigraphic interpretations (Lucas et al., 2009), and fail to provide sufficient descriptions of instrumental, geochronological, and statistical treatments of the data to allow evaluation of the potentially complex diagenetic and recrystallization history of bone. These shortcomings lead us to question the validity of the U-Pb dates published by Fassett et al. and their conclusions regarding the existence of Paleocene dinosaurs.

New Mexico↗
USGS2007

Pliocene and Quaternary deposits in the northern part of the San Juan Basin in southwestern Colorado and northwestern New Mexico

Unconsolidated late Cenozoic deposits in the northern part of the San Juan Basin range in age from late Pliocene to Holocene. Most of the deposits are alluvial gravel composed of resistant quartzite, sandstone, and igneous, metamorphic, and volcanic rocks derived from the uplifted central core of the San Juan Mountains 20-50 miles (32-80 kilometers) north of the basin. Alluvial deposits are most voluminous in the Animas Valley, but deposits of gravel of the same general age are present in the La Plata, Florida, Los Pinos, and Piedra River valleys as well. Alluvial gravel forms tabular deposits, generally about 20 feet (6 meters) thick, that are exposed beneath a sequence of terraces at many levels above the rivers. Gravel layers 360 feet (110 meters) or less above the Animas River are glacial outwash. The gravel layers begin at the south toes of end moraines and extend discontinuously downvalley at least 10-20 miles (16-32 kilometers). Farther south, distinction between outwash and nonglacial alluvium is problematical. Alluvial gravel beneath higher terraces does not grade to end moraines. Glacial till forms a series of end moraines at the north edge of the town of Durango. The oldest moraines are farthest downvalley, are higher above the river, and have more mature surficial soils than do moraines farther north. The two youngest moraines, the Animas City moraines, are interpreted to be Pinedale in age. They have narrow, ridgelike crests and form nearly unbroken arcs across the valley floor. Small segments of still more weathered moraines, the Spring Creek moraines, are 170-230 feet (52-70 meters) above the river and are 660-990 feet (200-300 meters) farther downvalley. The oldest moraines, the Durango moraines, are on the north end of the unnamed mesa on which Fort Lewis College is located. The base is about 180 feet (55 meters) above the river. These oldest moraines may be of Bull Lake age. Alluvial fans, pediment gravel, and landslides are scattered at several levels in various valleys within the northern San Juan Basin. Except where the Lava Creek B volcanic ash (0.639 mega-annum) is interbedded in them, these crudely bedded accumulations of sandy or clayey material washed from side drainages and added little to our reconnaissance stratigraphic study. Scattered landslide deposits consist of unsorted, mixed soil and fragments of rock. Loess and local silty and clayey sheetwash alluvium 6-12 feet (2-4 meters) thick form a veneer on low terraces. On higher terraces, such as Red Mesa east of the La Plata River and Florida Mesa east of the Animas River, loess and sheetwash alluvium generally are about 20 feet (6 meters) thick but can be as thick as 40-50 feet (12-15 meters) in places on Florida Mesa. When using the Lava Creek B volcanic ash as a time datum, apparently the timing of late Cenozoic continental deposition in the region was broadly similar to that in the Denver Basin-Front Range region and some other glaciated mountain ranges in the Rocky Mountains. A more accurate dating of Quaternary alluviation must await a thorough dating of the deposits. Thick, extensive outwash gravel indicates enhanced deposition during glacial epochs.

Colorado, New Mexico↗
USGS2002

Dinosaurs that did not die: Evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone, San Juan Basin, New Mexico

Palynologic and paleomagnetic data confirm a Paleocene age for the Ojo Alamo Sandstone (and its contained dinosaurs) throughout the San Juan Basin of New Mexico. The recently reported discovery of 34 skeletal elements from a single hadrosaur in the Ojo Alamo provides unequivocal evidence that these bones were not reworked from underlying Cretaceous strata. Geochemical studies of samples from several single-dinosaur-bone specimens from the Paleocene Ojo Alamo Sandstone and the underlying Late Cretaceous (Campanian) Kirtland Formation show that mineralized bones from these two rock units contain distinctly different abundances of uranium and rare-earth elements and demonstrate that Cretaceous and Paleocene bones were mineralized at different times when mineralizing fluids had distinctly different chemical compositions. These findings indicate that the dinosaur bone from the Paleocene Ojo Alamo is indigenous and not reworked. These data show that a relatively diverse assemblage of dinosaurs survived the end-Cretaceous asteroid-impact extinction event of 65.5 Ma. The San Juan Basin’s Paleocene dinosaur fauna is herein named the Alamoan fauna. Magnetic-polarity chronology shows that these survivors lived for about one million years into the Paleocene and then became extinct around 64.5 Ma. We suggest that a plausible survival mechanism for this Lazarus fauna may have been the large numbers of buried dinosaur eggs, laid just before the asteroid impact occurred. These buried eggs would have provided a safe haven for developing dinosaur embryos for the first one to two years after the impact, thereby making it possible for them to survive the worst of the impact’s early devastation.

Colorado, New Mexico↗
USGS2000

Evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone, San Juan Basin, New Mexico

Dinosaur fossils from the Ojo Alamo Sandstone, San Juan Basin, New Mexico, have been a puzzle to geologists for decades because other stratigraphic and paleontologic evidence indicates that this formation is Paleocene in age. The Paleocene age of the Ojo Alamo is based on the following evidence: (1) the lowermost part of the Nacimiento Formation, which conformably overlies and intertongues with the Ojo Alamo Sandstone in the Ojo Alamo type area in the southern part of the basin, contains Paleocene (Puercan) mammalian fossils; (2) plant megafossils collected from the Ojo Alamo indicate a Tertiary age for this rock unit; (3) pollen-productive rock samples collected from the Ojo Alamo at several localities in the basin have, without exception, yielded Paleocene-age palynomorph assemblages, and conversely, no Cretaceous pollen has ever been reported from Ojo Alamo rock samples. We report here the first discovery of Paleocene palynomorphs from Ojo Alamo Sandstone outcrops in the northern San Juan Basin. The pollen-producing rock samples were collected from a coaly, carbonaceous shale bed 12-m above the base of the Ojo Alamo and 3-m below the level of a large hadrosaur femur (1310-mm long and weighing about 130 kg) collected from this site. The bone was recovered from a cobble-to-boulder conglomeratic sandstone but shows no evidence of abrasion by erosion indicating almost instant burial after death of the animal and early mineralization of the femur. It is our opinion that this bone was not reworked from underlying Cretaceous strata. The data from the San Juan River site indicate that dinosaurs did not die out at the end of the Cretaceous in the San Juan Basin, but lived on for as much as a few hundred thousand years into the Paleocene before finally becoming extinct.

New Mexico↗
USGS1997

Precise age of C33N-C32R magnetic-polarity reversal, San Juan Basin, New Mexico and Colorado

Polarity-chron boundary C33n-C32r has been identified in the Upper Cretaceous continental Farmington Sandstone Member of the Kirtland Shale in Hunter Wash in the southwest part of the San Juan Basin of New Mexico, and in the marine Lewis Shale at Chimney Rock, Colorado, in the northeast part of the basin. Single- and multiple-crystal laser fusion 40 Ar/ 39 Ar ages of sanidine crystals from volcanic ash beds bracketing the C33n-C32r polarity reversal at Hunter Wash establish its age as 73.50 ± 0.18 Ma. The reversal apparently occurs within the Baculites compressus Western Interior ammonite zone and within the Edmontonian land-vertebrate faunal zone. An 8 Ma hiatus separates Cretaceous and Tertiary rocks in the southern San Juan Basin. These findings provide a precise new interpolated Late Cretaceous tie point for geologic time scales, provide the basis for the direct correlation of Western Interior ammonite zones to European open-ocean faunal zones, and establish the first direct tie between continental and marine fossil zones within the Western Interior of North America.

Colorado;New Mexico↗
USGS1991

Oil-generating coals of the San Juan Basin, New Mexico and Colorado, U.S.A.

Coal beds of the Upper Cretaceous Fruitland Formation in the San Juan Basin of northwestern New Mexico and southwestern Colorado have significant liquid hydrocarbon generation potential as indicated by typical Rock-Eval Hydrogen Indexes in the range of 200–400 mg hydrocarbon/g organic carbon (type II and III organic matter). Small, non-commercial quantities of oil have been produced from the coal beds at several locations. The oils are characterized by high pristane/phytane ( ca 4) and pristane/ n -C 17 ratios ( ca 1.2), abundant C 21+ alkanes in the C 10+ fraction with a slight predominance of odd carbon-numbered n -alkanes, abundant branched-chain alkanes in the C 15+ region, and a predominance of methylcyclohexane in the C 4 -C 10 fraction. The oils are indigenous to the Fruitland Formation coals and probably migrated at thermal maturities corresponding to vitrinite reflectance values in the range 0.7–0.8%. Although the oils found to date are not present in commercial amounts, these findings illustrate the potential of some coals to generate and expel oil under conditions of moderate thermal heating.

Colorado, New Mexico↗
USGS1991

Organic matter variations in transgressive and regressive shales

Organic matter in the Upper Cretaceous Mancos Shale adjacent to the Tocito Sandstone in the San Juan Basin of New Mexico was characterized using organic petrology and organic geochemistry. Differences in the organic matter found in these regressive and transgressive offshore marine sediments have been documented and assessed within a sequence stratigraphic framework. The regressive Lower Mancos Shale below the Tocito Sandstone contains abundant well preserved phytoclasts and correspondingly low hydrogen indices. Total organic carbon values for the regressive shale are low. Sediments from the transgressive systems tract (Tocito Sandstone and overlying Upper Mancos Shale) contain less terrestrially derived organic matter, more amorphous non-structured protistoclasts, higher hydrogen indices and more total organic carbon. Advanced stages of degradation are characteristic of the phytoclasts found in the transgressive shale. Amorphous material in the transgressive shale fluoresces strongly while that found in the regressive shale is typically non-fluorescent. Data from pyrolysis-gas chromatography confirm these observations. These differences are apparently related to the contrasting depositional styles that were active on the shelf during regression and subsequent transgression. It is suggested that data from organic petrology and organic geochemistry provide greater resolution in sedimentologic and stratigraphic interpretations, particularly when working with basinward, fine-grained sediments. Petroleum source potential for the regressive Lower Mancos Shale below the Tocito Sandstone is poor. Based on abundant fluorescent amorphous material, high hydrogen indices, and high total organic carbon, the transgressive Upper Mancos Shale above the Tocito Sandstone possesses excellent source potential. This suggests that appreciable source potential can be found in offshore, fine-grained sediments of the transgressive systems tract below the condensed section and associated downlap surface. Organic petrology can be used to accurately predict petroleum source potential. The addition of simple fluorescence microscopy greatly enhances this predictive ability because non-generative amorphous material is generally non-fluorescent. Organic petrology must also be used to properly evaluate the utility of T max from programmed pyrolysis as a thermal maturity indicator. Organic matter dominated by autochthonous amorphous protistoclasts exhibits lower T max values than that which is composed of mostly phytoclasts.

New Mexico↗
USGS1986

The non-transferability of a Cretaceous coal model in the San Juan Basin of New Mexico and Colorado

The San Juan Basin of northwest New Mexico and southwest Colorado contains several Upper Cretaceous coal-bearing formations. The coals in these formations were deposited in environments associated with repeated transgressions and regressions of the Western Interior seaway in Late Cretaceous time. A detailed subsurface and surface study of the coal beds in one of these units, the Fruitland Formation, formed the basis for a coal-depositional model (Fassett and Hinds, 1971). This model basically shows that the thickest Fruitland coals formed landward of thickly stacked sandstone beds of the regressive-marine Pictured Cliffs Sandstone. Transferability of the Fruitland coal model was tested by comparing it to another San Juan Basin coal-bearing rock unit, the lower Menefee Formation. Lower Menefee coal deposits were formed in association with the Point Lookout Sandstone, an older regressive-marine unit. The purpose of this comparison was to see if thick lower Menefee coal beds were also concentrated adjacent to thick vertical shoreface-sandstone buildups. This comparison showed that even though thick sandstone buildups were found in the Point Lookout, no thick coal beds were found in the lower Menefee Formation adjacent to them. This test suggests that certain coal depositional models may have limited value as predictive tools and must be used with caution by coal explorationists. Even more importantly, potential coal-bearing areas should never be written off simply because they do not fit a previously described model.

Colorado, New Mexico↗
USGS1983

Data for ground-water studies of the San Juan Basin, New Mexico (1982-83)

Ground-water data that can be used for futher hydrologic studies in the San Juan structural basin of New Mexico are reported. Descriptions and a location map of 64 observation wells, a list of water levels measured in the observation wells, water-level hydrographs of 32 wells, 15 partial chemical analyses of water samples from wells, and descriptions and a location map of 264 potential observations wells are included. The latter are wells for which good records exist. Their potential for use as observation wells needs to be verified in the field. (USGS)

New Mexico↗
USGS1981

Erodibility of selected soils and estimates of sediment yields in the San Juan Basin, New Mexico

Onsite rainfall-simulation experiments were conducted to derive field-erodibility indexes for rangeland soils and soils disturbed by mining in coal fields of northwestern New Mexico. Mean indexes on rangeland soils range from 0 grams (of detached soil) on dune soil to 121 grams on wash-transport zones. Mean field-erodibility-index values of soils disturbed by mining range from 16 to 32 grams; they can be extrapolted to nearby coal fields where future mining is expected. Because field-erodibility-index data allow differentiation of erodibilities across a variable landscape, these indexes were used to adjust values of K, the erodibility factor of the Universal Soil Loss Equation. Estimates of soil loss and sediment yield were then calculated for a small basin following mining. (USGS)

New Mexico↗
USGS1967

Core description from GB-1 (Gasbuggy 1) in the northeastern part of the San Juan Basin, Rio Arriba County, New Mexico

The core herein described came from the first test hole drilled for Project Gasbuggy--a project designed to stimulate gas production by the use of nuclear explosives from the Pictured Cliffs Sandstone in the northeastern part of the San Juan Basin, N. Mex. Project Gasbuggy is a cooperative experiment principally involving the El Paso Natural Gas Co., the Atomic Energy Commission, and the U.S. Bureau of Mines. Permission to describe the core from the well was kindly granted by these three organizations.

New Mexico↗