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39-826: The San Juan Basin is a geologic structural basin located near the Four Corners region of the Southwestern United States . The basin covers 7,500 square miles and resides in northwestern New Mexico , southwestern Colorado , and parts of Utah and Arizona . Specifically, the basin occupies space in the San Juan , Rio Arriba , Sandoval , and McKinley counties in New Mexico, and La Plata and Archuleta counties in Colorado. The basin extends roughly 100 miles (160 km) N-S and 90 miles (140 km) E-W. The San Juan Basin

78-631: A northward course towards Asia. In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America. Europe was an island chain. Populating some of these islands were endemic dwarf dinosaur species. In the Late Cretaceous, the hadrosaurs , ankylosaurs , and ceratopsians experienced success in Asiamerica (Western North America and eastern Asia). Tyrannosaurs dominated

117-536: A very different dinosaurian fauna, with most predators being abelisaurids and carcharodontosaurids ; and titanosaurs being among the dominant herbivores. Spinosaurids were also present during this time. Birds became increasingly common, diversifying in a variety of enantiornithe and ornithurine forms. Early Neornithes such as Vegavis co-existed with forms as bizarre as Yungavolucris and Avisaurus . Though mostly small, marine Hesperornithes became relatively large and flightless, adapted to life in

156-453: Is a large-scale structural formation of rock strata formed by tectonic warping ( folding ) of previously flat-lying strata into a syncline fold. They are geological depressions , the inverse of domes . Elongated structural basins are a type of geological trough . Some structural basins are sedimentary basins , aggregations of sediment that filled up a depression or accumulated in an area; others were formed by tectonic events long after

195-551: Is an asymmetric structural depression in the Colorado Plateau province, with varying elevation and nearly 3,000 feet (910 m) in topographic relief. Its most striking features include Chaco Canyon (northwestern New Mexico, between Farmington and Santa Fe ) and Chacra Mesa . The basin lies west of the Continental Divide , and its main drainage is the southwest- to west-flowing San Juan River , which eventually joins

234-492: Is especially known for gas reservoirs from its coal-bed methane formations. The San Juan Basin contains the largest coal-bed methane field in the world and ranks second in total gas reserves. During the mid- Paleozoic , the San Juan Basin was part of the ancient landmass called Laurentia ; this was a supercontinent that contained much of current-day North America . The ancient landmass called Gondwana contained most of

273-474: Is it particularly evident that a true systematic decline was ever in place, especially with the discovery of smaller pterosaur species. Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian of North America . In the northern hemisphere, cimolodont , multituberculates , metatherians and eutherians were the dominant mammals, with the former two groups being

312-491: Is likely from established gas, coal, and coalbed methane mining and processing." The region emitted 590,000 metric tons of methane every year between 2002 and 2012—almost 3.5 times the widely used estimates in the European Union ’s Emissions Database for Global Atmospheric Research. 36°16′N 107°54′W  /  36.27°N 107.90°W  / 36.27; -107.90 Structural basin A structural basin

351-614: The Colorado River in Utah. Climate of the basin is arid to semiarid , with an annual precipitation of 15 in (380 mm) and an average annual temperature of around 50 °F (10 °C). The San Juan Basin has been a major producer of oil and natural gas since the early 20th century, with currently more than 300 oil fields and over 40,000 drilled wells throughout the area. As of 2009, cumulative production reached 42.6 trillion cubic feet of gas and 381 million barrels of oil. The area

390-535: The Cutler Formation . The Permian continued to be a time of terrestrial deposits, including late-Permian eolian deposits. The Cretaceous was a time of three major transgressive-regressive cycles, as eustatic changes in sea-level caused fluctuations on the Western Interior Seaway's shoreline. The San Juan Basin was conveniently located in the western margin of the seaway and recorded these cycles in

429-671: The Leadville Limestone and the Pinkerton Trail Formations. Once the supercontinents collided (see Tectonic Evolution above), the subsidence of the Paradox Basin and the uplift of the Uncompahgre highlands allowed for enormous amounts of sediment to shed off the highlands via Permian fluvial systems. The Rico Formation represents the transition from Pennsylvanian marine deposits to Permian terrestrial deposits of

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468-515: The San Jose Formation ) brought the basin to its current-day configuration. Little is known about Precambrian units due to poor outcrop exposure and poor well-control. Precambrian rocks consist of quartzite , schist , and granite , and rocks are overlain unconformably by younger Paleozoic units. Little is known about the stratigraphy of the Paleozoic. Of the >40,000 wells drilled in

507-1012: The Central Basin Platform, the Four Corners Platform, and the Chaco Slope (a.k.a. the Chaco Homocline ). The basin is bound on the northwest by the Hogback Monocline (separating the Central Basin and Four Corners platforms), on the northeast by the Archuleta Anticlinorium, on the east by the Nacimiento Uplift, and on the south by the Zuni Uplift. Prior to collision , Mississippian- and Pennsylvanian-aged units were deposited during various marine environments, e.g.

546-813: The Cretaceous Period derived from the German name Kreidezeit , and T is the abbreviation for the Tertiary Period (a historical term for the period of time now covered by the Paleogene and Neogene periods). The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era. "Tertiary" being no longer recognized as a formal time or rock unit by the International Commission on Stratigraphy ,

585-847: The K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers. Non- avian dinosaur fossils are found only below the Cretaceous–Paleogene boundary and became extinct immediately before or during the event. A very small number of dinosaur fossils have been found above the Cretaceous–Paleogene boundary, but they have been explained as reworked fossils , that is, fossils that have been eroded from their original locations then preserved in later sedimentary layers. Mosasaurs , plesiosaurs , pterosaurs and many species of plants and invertebrates also became extinct. Mammalian and bird clades passed through

624-605: The Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident. The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions. Due to plate tectonics , the Americas were gradually moving westward, causing the Atlantic Ocean to expand. The Western Interior Seaway divided North America into eastern and western halves; Appalachia and Laramidia . India maintained

663-619: The San Juan Basin on the northeast. During the late Jurassic , continental collision of the Farallon and North American plates resulted in low-angle ("flat slab") subduction beneath the western margin of the United States. Pressure on the underlying lithosphere resulting in a "depression" of the continents interior, and this allowed for the formation of the Inner Cretaceous Seaway ( a.k.a. Western Interior Seaway ). This began

702-843: The San Juan Basin target the Dakota Sandstone, the Point Lookout Sandstone, and the Pictured Cliffs Sandstone. Plays consist of stratigraphic traps mostly concentrated in the Central Basin Platform. In 2014 NASA researchers reported the discovery of a 2,500 square miles (6,500 km) methane cloud floating over the Basin. The discovery was based on data from the European Space Agency ’s Scanning Imaging Absorption Spectrometer for Atmospheric Chartography instrument from 2002 to 2012. The report concluded that "the source

741-629: The San Juan Basin, i.e. nearly 250 of the >300 fields source Upper Cretaceous units. Major oil plays in the San Juan Basin target the Dakota Sandstone, the Gallup Sandstone, the Tocito Sandstone, and the El Vado Sandstone Member. The source rock for these units was the black, organic-rich marine shale of the stratigraphically lower Mancos Formation . Most of the oil fields described below are at or nearing depletion. Major gas plays in

780-415: The San Juan Basin, only about 12 have penetrated deep enough to come in contact with Paleozoic units. Additionally, poor outcrop exposure and lateral facies changes complicate the defining and correlation of these units. The Cretaceous-aged units are the most well-understood and the most productive units in the San Juan Basin. The Inner Cretaceous Seaway's western extent was along the San Juan Basin, and

819-485: The basin is still actively producing today. While the majority of production has occurred in Cretaceous-aged units, the Paleozoic rocks of the Four Corners Platform have successfully produced from over two-dozen fields from Devonian, Mississippian, and Pennsylvanian-aged units. The Paleozoic units deepen in a northeast direction where they cross from the oil- to the gas-window; subsequently, Paleozoic fields yield gas in

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858-519: The boundary with few extinctions, and evolutionary radiation from those Maastrichtian clades occurred well past the boundary. Rates of extinction and radiation varied across different clades of organisms. Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater , in combination with increased volcanic activity , such as that recorded in

897-646: The large predator niche in North America. They were also present in Asia, although were usually smaller and more primitive than the North American varieties. Pachycephalosaurs were also present in both North America and Asia. Dromaeosaurids shared the same geographical distribution, and are well documented in both Mongolia and Western North America. Additionally therizinosaurs (known previously as segnosaurs) appear to have been in North America and Asia. Gondwana held

936-659: The late Mesozoic /early Cenozoic (e.g. Fruitland Formation and the Kirtland Shale) . Eocene / Oligocene volcanism resulted in large volcanic aprons that covered thousands of square-kilometers, and these volcanic fields sourced the Cenozoic units the Ojo Alamo (sourced from the west), and the Animas and Nacimiento formations (sourced from the northeast). Uplift in the northwest (and subsequent erosion), and continued deposition (e.g.

975-636: The most common mammals in North America. In the southern hemisphere there was instead a more complex fauna of dryolestoids , gondwanatheres and other multituberculates and basal eutherians ; monotremes were presumably present, as was the last of the haramiyidans , Avashishta . Mammals, though generally small, ranged into a variety of ecological niches, from carnivores ( Deltatheroida ), to mollusc-eater ( Stagodontidae ), to herbivores (multituberculates, Schowalteria , Zhelestidae and Mesungulatidae ) to highly atypical cursorial forms ( Zalambdalestidae , Brandoniidae ). True placentals evolved only at

1014-403: The northeast and oil in the southwest. Furthermore, Paleozoic field locations roughly align with the northeast-trending Hogback monocline. Future Paleozoic plays will target natural gas, and these will include untested carbonates in the Central Basin Platform and potentially undiscovered plays in the Four Corners Platform. Cretaceous-aged units account for the majority of gas and oil production in

1053-528: The northwest resulted in over 2,000 feet (610 m) of erosion in the southeast. As compression shifted to extension and the formation of the Rio Grande Rift began, volcanism dominated the area throughout much of the Eocene and Oligocene . Uplift in the northwest and continued deposition brought the basin to its current-day configuration. The San Juan Basin is an asymmetrical syncline with three components:

1092-531: The numerous teleost fishes, which in turn evolved into new advanced and modern forms ( Neoteleostei ). Ichthyosaurs and pliosaurs , on the other hand, became extinct during the Cenomanian-Turonian anoxic event . Near the end of the Cretaceous Period, flowering plants diversified. In temperate regions, familiar plants like magnolias , sassafras , roses , redwoods , and willows could be found in abundance. The Cretaceous–Paleogene extinction event

1131-407: The open sea. Though primarily represented by azhdarchids , other forms like pteranodontids , tapejarids ( Caiuajara and Bakonydraco ), nyctosaurids and uncertain forms ( Piksi , Navajodactylus ) are also present. Historically, it has been assumed that pterosaurs were in decline due to competition with birds, but it appears that neither group overlapped significantly ecologically, nor

1170-495: The sedimentary layers were deposited. Basins may appear on a geologic map as roughly circular or elliptical, with concentric layers. Because the strata dip toward the center, the exposed strata in a basin are progressively younger from the outside in, with the youngest rocks in the center. Basins are often large in areal extent, often hundreds of kilometers across. Structural basins are often important sources of coal , petroleum , and groundwater . Late Cretaceous During

1209-496: The southern continents, e.g. South America and Africa . During the late- Mississippian (~320 million years ago), the landmasses of Laurentia and Gondwana collided to form the giant landmass of Pangea . This continental collision resulted in several pivotal orogenic (mountain building) episodes. The collision of supercontinents Gondwana and Laurentia resulted in the Alleghanian and Ouachita orogenies. The Alleghanian Orogeny

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1248-456: The state of New Mexico. As of 2009, cumulative production reached 42.6 trillion cubic feet of gas and 381 million barrels of oil. The first documented oil play in the San Juan Basin occurred in 1911 on the Chaco Slope. The well was drilled to a depth of 100 m and produced only 12 barrels of oil per day. The first documented gas play occurred ten years later in the Central Basin Platform. The well

1287-591: The stratigraphy (see Stratigraphy below). The westernmost extent of the seaway (a.k.a. maximum transgression) was recorded by the Lewis Shale , which eventually graded into the Pictured Cliffs and the Fruitland Formation as the shoreline made its final retreat. The Western Interior Seaway's shoreline regression resulted in ample swamps, lakes, and flood plains; this resulted in the coal -rich formations of

1326-408: The three major transgressive-regressive episodes that occurred during this time are recorded in the mid- to upper-Cretaceous stratigraphy. The San Juan Basin contains ample fuel resources, including oil, gas, coal, and uranium. The basin has produced from over 300 oil fields and nearly 40,000 wells, most of which are sourced from Cretaceous-aged rocks. Furthermore, 90% of the wells have been drilled in

1365-610: The transition from terrestrial sedimentation during the late Paleozoic and early Mesozoic to a shallow marine basin, as waters from the Arctic and Gulf regions poured into the center of the continent. During late Cretaceous to early Tertiary , compressional forces (continued subduction of the Farallon Plate) continued to act and caused the uplift of the modern Rocky Mountains via the Laramide Orogeny . Early-Tertiary tilting towards

1404-433: The very end of the epoch; the same can be said for true marsupials . Instead, nearly all known eutherian and metatherian fossils belong to other groups. In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and penguin-like polycotylid plesiosaurs (3 meters long) and huge long-necked elasmosaurs (13 meters long) also diversified. These predators fed on

1443-505: Was 300 m deep and resulted in a gas pipeline to carry and market gas to nearby cities. The following years resulted in many oil and gas discoveries that subsequently spiked interest in San Juan resources. The 1930s brought upon the first pipeline to transport gas outside of the basin. The 1980s brought upon the discovery of the coal-bed methane resources, resulting in a drilling spike during the 1980s and 1990s. Production has since leveled out, but

1482-537: Was a large-scale mass extinction of animal and plant species in a geologically short period of time, approximately 66  million years ago (Ma). It is widely known as the K–T extinction event and is associated with a geological signature, usually a thin band dated to that time and found in various parts of the world, known as the Cretaceous–Paleogene boundary (K–T boundary). K is the traditional abbreviation for

1521-623: Was the collision of Africa with the current-day southeastern United States, and resulted in the Appalachian Mountains . The Ouachita Orogeny was the collision of South America with the current-day Gulf-region, and resulted in the Ancestral Rockies - a northwest trending intercontinental mountain belt mainly through Texas, New Mexico, and Colorado. The Ancestral Rockies gave way to the Uncompahgre Mountain Range , which bound

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