{"title":"The Blanco Basin Formation (Eocene), San Juan Mountains region, Colorado and New Mexico","authors":"B. Brister","doi":"10.56577/ffc-43.321","DOIUrl":"https://doi.org/10.56577/ffc-43.321","url":null,"abstract":"","PeriodicalId":325871,"journal":{"name":"San Juan Basin IV","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130356024","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The fluvial lower Eocene San Jose Formation represents the last preserved period of deposition in the Laramide San Juan Basin. The basal Cuba Mesa Member of the formation is a nearly basinwide, coarsegrained sheet sandstone composed of mult ilateral and multistoried low-sinuosity tluvial channels. The Cuba Mesa is locally thickened where sheet sandstones are vertically amalgamated. The Cuba Mesa thins by intertongu ing with mudrock and pinches out along the basin axis where the San Jose Formation conformably overlies the Paleocene Nacimiento and Animas Formations in northern New Mexico and Colorado. The Cuba Mesa Member unconformably overlies Paleocene and Mesozoic strata toward margins of the basin, with as much as 90° of angular discordance. Floodplain mudrock and di sconnec ted sheet sandstones of the Regi na Member were deposited laterally adjacent to and above the Cuba Mesa Member. Mudrock of the Regina Member also intertongues with the lobate. sandstone-dominated Ditch Canyon Member (named here ) and Llaves Member. The Ditch Canyon Member represents southeast-directed fluvial deposition in the northwestern San Juan Basin from the Four Comers pla tform and southwestern San Juan upli ft . The Llaves Member was deposited on the eastern side of the bas in by west-southwest-flowing streams and is sedimentologically and stratigraphically similar to, but not continuous with. the Ditch Canyon Member. The Llaves Member is overlain by the siltstonedominated Tapicitos Member. The Tapicitos was derived from uplifts east of the basin. Grain size in the Regina Member decreases toward the San Juan and Nacimiento uplifts, due to minimal erosion of coarse-grained sediment from these active, reverse-fau lted monoclines . Small drainage basins along these active mountain fronts eroded most ly fine-grained sediment from Phanerozoic strata. Coarse-grained sediment of the Di tch Canyon and Llaves Members was deposited by fluvial systems that emanated from different paleo-drainage basins within structural reentrants between basin-marginal uplifts. The Cuba Mesa Member was deposited during late Paleocene through early Eocene subsidence in the center of the San Juan Basin with concurrent erosion and possibly slow sedimentation nearer basin margins . Synsedimentary angu lar unconformities within the Regina Member show that the Regina, Llaves and Ditch Canyon Members were deposited during episodic monoclinal fo lding near the Nacimiento fault.
{"title":"Stratigraphy, sediment dispersal and paleogeography of the lower Eocene San Jose Formation, San Juan Basin, New Mexico","authors":"L. Smith","doi":"10.56577/ffc-43.297","DOIUrl":"https://doi.org/10.56577/ffc-43.297","url":null,"abstract":"The fluvial lower Eocene San Jose Formation represents the last preserved period of deposition in the Laramide San Juan Basin. The basal Cuba Mesa Member of the formation is a nearly basinwide, coarsegrained sheet sandstone composed of mult ilateral and multistoried low-sinuosity tluvial channels. The Cuba Mesa is locally thickened where sheet sandstones are vertically amalgamated. The Cuba Mesa thins by intertongu ing with mudrock and pinches out along the basin axis where the San Jose Formation conformably overlies the Paleocene Nacimiento and Animas Formations in northern New Mexico and Colorado. The Cuba Mesa Member unconformably overlies Paleocene and Mesozoic strata toward margins of the basin, with as much as 90° of angular discordance. Floodplain mudrock and di sconnec ted sheet sandstones of the Regi na Member were deposited laterally adjacent to and above the Cuba Mesa Member. Mudrock of the Regina Member also intertongues with the lobate. sandstone-dominated Ditch Canyon Member (named here ) and Llaves Member. The Ditch Canyon Member represents southeast-directed fluvial deposition in the northwestern San Juan Basin from the Four Comers pla tform and southwestern San Juan upli ft . The Llaves Member was deposited on the eastern side of the bas in by west-southwest-flowing streams and is sedimentologically and stratigraphically similar to, but not continuous with. the Ditch Canyon Member. The Llaves Member is overlain by the siltstonedominated Tapicitos Member. The Tapicitos was derived from uplifts east of the basin. Grain size in the Regina Member decreases toward the San Juan and Nacimiento uplifts, due to minimal erosion of coarse-grained sediment from these active, reverse-fau lted monoclines . Small drainage basins along these active mountain fronts eroded most ly fine-grained sediment from Phanerozoic strata. Coarse-grained sediment of the Di tch Canyon and Llaves Members was deposited by fluvial systems that emanated from different paleo-drainage basins within structural reentrants between basin-marginal uplifts. The Cuba Mesa Member was deposited during late Paleocene through early Eocene subsidence in the center of the San Juan Basin with concurrent erosion and possibly slow sedimentation nearer basin margins . Synsedimentary angu lar unconformities within the Regina Member show that the Regina, Llaves and Ditch Canyon Members were deposited during episodic monoclinal fo lding near the Nacimiento fault.","PeriodicalId":325871,"journal":{"name":"San Juan Basin IV","volume":"90 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133456499","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Coalbed methane from the Fruitland Formation, San Juan Basin, New Mexico","authors":"Douglas M. Bland","doi":"10.56577/ffc-43.373","DOIUrl":"https://doi.org/10.56577/ffc-43.373","url":null,"abstract":"","PeriodicalId":325871,"journal":{"name":"San Juan Basin IV","volume":"146 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117046575","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Paleocene Nacimiento Fonnation of the San Juan Basin is as much as 525 m thick and consists of nonmarine fluvial and lacustrine strata de posited in the Laramide San Juan Basin. South of Kutz Canyon, in the southern San Juan Bas in, we divide the Nacimiento Formation into (in ascending order) the Arroyo Chijuillita , Ojo Encino and Escavada Members . The Arroyo Chijuillita Member is as much as 134 m thick and consists mostly of drab gray, olive and ye llow bentoni tic mudstones, wh ite trough-crossbedded sandstone and minor beds of lignite. It confonnably overlies, grades into and interfingers with the unde rl ying Paleocene Ojo Alamo Sandstone . The base of the Ojo Encino Member is a resistant, trough-crossbedded sandstone complex he re named the Penistaja Bed . The Penistaja Bed is as much as 60 m thick and is overlain by as much as 122 m of Ojo Encino Member strata-mostly variegated red , green and black bentonitic mudstones and troughcrossbedded sandstones. Thin (up to 50 cm) beds of silcrete and th icker beds of trough-crossbedded sandstone characterize the overlying facavada Member, which is as much as 88 m th ick. The Cuba Mesa Member of the San Jose Fonnation unconfonnably overlies the Escavada Member of the Nacimiento Fonnation. Locally, this unconfonnity is a disconfonn ity, but across the southern San Juan Basin it is sl ightly angular. The three members of the Nacimiento Formation can be correlated on a li thologic basis across the southern San Juan Basin in surface measured sections and in the subsurface by geophysical well logs. These correlations also demonstrate that the two fossil mammal zones that yield Puercan faunas, the Ectoconus and Taenio/ab is zones, are disc rete, superposed assemblage zones. Fossili ferous zones that yield Puercan and Torrej,rn ian faunas are separated by a 45 m "barren " interval. The De/ratherium and Pantolambda zones of the Torrejonian are largely success ive but overlap to so me extent. Recent ly defined biochronologic zonation of the Puercan and Torrejon ian land mammal "ages·· (Pu0Pu3, To l-To3) are based on the first appearance of key taxa and are only loosely based on biostratigraphic zonation. Biostrat igraphy of the Nacimiento Formation and correlation of Torrejonian fa unas of western North America suggest that Tetraclaenodon shou ld not be used to define the base of To2. Fossil mammals and magnetostratigraphy document that most of the Nacimiento Formation is of early Paleocene age (chrons 2927, Dan ian), al though its uppennost strata may be of earl y late Paleocene age (ch ron 26 , early Thanetian). The Paleocene mammals of the Nacimiento Format ion document a significant diversificat ion of paleoplacentals during the early Paleocene and continue to provide a standard by which the earl y Cenozoic diversi fication of the Eutheria is calibrated and interpreted . 265
{"title":"Stratigraphy and mammalian biostratigraphy of the Paleocene Nacimiento Formation, southern San Juan Basin","authors":"T. Williamson, S. Lucas","doi":"10.56577/ffc-43.265","DOIUrl":"https://doi.org/10.56577/ffc-43.265","url":null,"abstract":"The Paleocene Nacimiento Fonnation of the San Juan Basin is as much as 525 m thick and consists of nonmarine fluvial and lacustrine strata de posited in the Laramide San Juan Basin. South of Kutz Canyon, in the southern San Juan Bas in, we divide the Nacimiento Formation into (in ascending order) the Arroyo Chijuillita , Ojo Encino and Escavada Members . The Arroyo Chijuillita Member is as much as 134 m thick and consists mostly of drab gray, olive and ye llow bentoni tic mudstones, wh ite trough-crossbedded sandstone and minor beds of lignite. It confonnably overlies, grades into and interfingers with the unde rl ying Paleocene Ojo Alamo Sandstone . The base of the Ojo Encino Member is a resistant, trough-crossbedded sandstone complex he re named the Penistaja Bed . The Penistaja Bed is as much as 60 m thick and is overlain by as much as 122 m of Ojo Encino Member strata-mostly variegated red , green and black bentonitic mudstones and troughcrossbedded sandstones. Thin (up to 50 cm) beds of silcrete and th icker beds of trough-crossbedded sandstone characterize the overlying facavada Member, which is as much as 88 m th ick. The Cuba Mesa Member of the San Jose Fonnation unconfonnably overlies the Escavada Member of the Nacimiento Fonnation. Locally, this unconfonnity is a disconfonn ity, but across the southern San Juan Basin it is sl ightly angular. The three members of the Nacimiento Formation can be correlated on a li thologic basis across the southern San Juan Basin in surface measured sections and in the subsurface by geophysical well logs. These correlations also demonstrate that the two fossil mammal zones that yield Puercan faunas, the Ectoconus and Taenio/ab is zones, are disc rete, superposed assemblage zones. Fossili ferous zones that yield Puercan and Torrej,rn ian faunas are separated by a 45 m \"barren \" interval. The De/ratherium and Pantolambda zones of the Torrejonian are largely success ive but overlap to so me extent. Recent ly defined biochronologic zonation of the Puercan and Torrejon ian land mammal \"ages·· (Pu0Pu3, To l-To3) are based on the first appearance of key taxa and are only loosely based on biostratigraphic zonation. Biostrat igraphy of the Nacimiento Formation and correlation of Torrejonian fa unas of western North America suggest that Tetraclaenodon shou ld not be used to define the base of To2. Fossil mammals and magnetostratigraphy document that most of the Nacimiento Formation is of early Paleocene age (chrons 2927, Dan ian), al though its uppennost strata may be of earl y late Paleocene age (ch ron 26 , early Thanetian). The Paleocene mammals of the Nacimiento Format ion document a significant diversificat ion of paleoplacentals during the early Paleocene and continue to provide a standard by which the earl y Cenozoic diversi fication of the Eutheria is calibrated and interpreted . 265","PeriodicalId":325871,"journal":{"name":"San Juan Basin IV","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126878604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
-Crocodilian fossils from the Fruitland, Kirtland, Nacimiento and San Jose Formations in the San Juan Basin (Upper Cretaceous-lower Eocene) represent the genera Akanthosuchus (Nacimiento Formation), Allognathosuchus (Nacimiento and San Jose Formations), Brachychampsa (Fruitland and Kirtland Formations), Diplocynodon (Nacimiento Formation), Goniopholis (Fruitland and Kirtland Formations), Leid_vosuchus (Fruit land. Kirtland, Nacimiento and San Jose Formations) and Thoracosaurus 9 (Fruitland Formation). The San Juan Basin taxa document some evolutionary turnover in crocodilians at the Cretaceous-Tertiary boundary and suggest that the feeding ecology of extant crocodilians was present among the Late Cretaceous-early Eocene crocodilians.
{"title":"Cretaceous-Eocene crocodilians from the San Juan Basin, New Mexico","authors":"S. Lucas","doi":"10.56577/ffc-43.257","DOIUrl":"https://doi.org/10.56577/ffc-43.257","url":null,"abstract":"-Crocodilian fossils from the Fruitland, Kirtland, Nacimiento and San Jose Formations in the San Juan Basin (Upper Cretaceous-lower Eocene) represent the genera Akanthosuchus (Nacimiento Formation), Allognathosuchus (Nacimiento and San Jose Formations), Brachychampsa (Fruitland and Kirtland Formations), Diplocynodon (Nacimiento Formation), Goniopholis (Fruitland and Kirtland Formations), Leid_vosuchus (Fruit land. Kirtland, Nacimiento and San Jose Formations) and Thoracosaurus 9 (Fruitland Formation). The San Juan Basin taxa document some evolutionary turnover in crocodilians at the Cretaceous-Tertiary boundary and suggest that the feeding ecology of extant crocodilians was present among the Late Cretaceous-early Eocene crocodilians.","PeriodicalId":325871,"journal":{"name":"San Juan Basin IV","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123261777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Lucas, T. Williamson, L. Smith, Bruce Wright-Dunbar, B. Kues, Gretchen K. Hoffman, A. Hunt, D. Love, V. McLemore, R. Hadley
Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico.
{"title":"First-day road log: From Cuba to La Ventana, San Luis, Cabezon, Mesa Portales, Mesa de Cuba and return to Cuba","authors":"S. Lucas, T. Williamson, L. Smith, Bruce Wright-Dunbar, B. Kues, Gretchen K. Hoffman, A. Hunt, D. Love, V. McLemore, R. Hadley","doi":"10.56577/ffc-43.1","DOIUrl":"https://doi.org/10.56577/ffc-43.1","url":null,"abstract":"Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico.","PeriodicalId":325871,"journal":{"name":"San Juan Basin IV","volume":"25 9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131369912","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Lucas, A. Hunt, T. Williamson, B. Kues, V. McLemore
Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico.
{"title":"Third-day road log: From Cuba to La Jara, Regina, Almagre Arroyo, Llaves, Gallina, Arroyo del Agua, Coyote, Youngsville and Abiquiu Dam","authors":"S. Lucas, A. Hunt, T. Williamson, B. Kues, V. McLemore","doi":"10.56577/ffc-43.53","DOIUrl":"https://doi.org/10.56577/ffc-43.53","url":null,"abstract":"Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico.","PeriodicalId":325871,"journal":{"name":"San Juan Basin IV","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129871508","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Precious- and base-metal districts in Rio Arriba and Sandoval Counties, New Mexico","authors":"V. McLemore","doi":"10.56577/ffc-43.385","DOIUrl":"https://doi.org/10.56577/ffc-43.385","url":null,"abstract":"","PeriodicalId":325871,"journal":{"name":"San Juan Basin IV","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130849866","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Topography in the northeastern tributary watersheds to the Chaco River is characterized by either subplanar alluvial surfaces or badland topography. The Alamo and Ah-shi-sle-pah watersheds contain extensive badland topography, whereas the Coal Creek and Tsaya basins are characterized by broad alluvial surfaces. Correlation of geomorphic surfaces between the drainage basins allows comparison of the responses each basin had to baselevel falls. The two oldest geomorphic surfaces extended beyond present-day drainage divides; drainage divides and the resulting proportions of sandstone and mudrock bedrock lithologies were inherited during the incision of these surfaces. Three younger geomorphic surfaces formed during periodic downcutting of the drainages. The character of drainage-basin evolution during regional dissection is a function of initial basin shape, relative relief of the drainage basin, distribution and proportion of mudrock to sandstone bedrock units, and distribution and preservation of sandy surficial deposits. Sandstone outcrop, elongate low-relief morphology, and accumulation of extensive sandy surficial deposits reduced sediment yield and downcutting in the Tsaya basin. Extensive badland development in the Ah-shi-sle-pah basin was augmented by the dominance of mudrock bedrock in the basin, a high drainage-basin relief ratio, and minimal preservation of sandy surficial deposits. INTRODUCTION SURFICIAL GEOLOGY The subtle topography in the northern tributaries to the Chaco River is interrupted locally by regions characterized by bedrock outcrop, high erosion rates and a badland topography. The Alamo, Coal Creek, Tsaya and Ah-shi-sle-pah drainage basins north of the Chaco River display a wide range of landforms and surficial processes characteristic of the region. The purposes of this paper are to describe the geomorphic history of the region and to discuss those geomorphic factors that have influenced drainage-basin evolution and the present distribution of the region's distinct landforms. The northern tributary drainage basins to the Chaco River are oriented across the strike of northeast-dipping Cretaceous and Paleogene sandstones, mudrocks, coal and minor conglomerate in the southwestern San Juan Basin (Fig. 1). Bedrock formations crop out at similar distances upstream from the Chaco River in each of the drainage basins. Although similar bedrock units crop out in each basin, variable thicknesses of bedrock units results in different proportions of sandstone-tomudrock among the study basins (Table 1). Many of the low relief, vegetated landforms in the northern tributary drainage basins of the Chaco River are capped by alluvium that is part of a topographically stepped Pleistocene and Holocene sequence (Fig. 4). Regional correlation of these deposits allows comparison of the differing downcutting histories of the basins. These alluvial deposits range in topographic position from present-day drainage divides to terraces to valley floors
{"title":"Quaternary history and landscape development of some tributary drainage basins north of Chaco River","authors":"L. Smith","doi":"10.56577/ffc-43.391","DOIUrl":"https://doi.org/10.56577/ffc-43.391","url":null,"abstract":"Topography in the northeastern tributary watersheds to the Chaco River is characterized by either subplanar alluvial surfaces or badland topography. The Alamo and Ah-shi-sle-pah watersheds contain extensive badland topography, whereas the Coal Creek and Tsaya basins are characterized by broad alluvial surfaces. Correlation of geomorphic surfaces between the drainage basins allows comparison of the responses each basin had to baselevel falls. The two oldest geomorphic surfaces extended beyond present-day drainage divides; drainage divides and the resulting proportions of sandstone and mudrock bedrock lithologies were inherited during the incision of these surfaces. Three younger geomorphic surfaces formed during periodic downcutting of the drainages. The character of drainage-basin evolution during regional dissection is a function of initial basin shape, relative relief of the drainage basin, distribution and proportion of mudrock to sandstone bedrock units, and distribution and preservation of sandy surficial deposits. Sandstone outcrop, elongate low-relief morphology, and accumulation of extensive sandy surficial deposits reduced sediment yield and downcutting in the Tsaya basin. Extensive badland development in the Ah-shi-sle-pah basin was augmented by the dominance of mudrock bedrock in the basin, a high drainage-basin relief ratio, and minimal preservation of sandy surficial deposits. INTRODUCTION SURFICIAL GEOLOGY The subtle topography in the northern tributaries to the Chaco River is interrupted locally by regions characterized by bedrock outcrop, high erosion rates and a badland topography. The Alamo, Coal Creek, Tsaya and Ah-shi-sle-pah drainage basins north of the Chaco River display a wide range of landforms and surficial processes characteristic of the region. The purposes of this paper are to describe the geomorphic history of the region and to discuss those geomorphic factors that have influenced drainage-basin evolution and the present distribution of the region's distinct landforms. The northern tributary drainage basins to the Chaco River are oriented across the strike of northeast-dipping Cretaceous and Paleogene sandstones, mudrocks, coal and minor conglomerate in the southwestern San Juan Basin (Fig. 1). Bedrock formations crop out at similar distances upstream from the Chaco River in each of the drainage basins. Although similar bedrock units crop out in each basin, variable thicknesses of bedrock units results in different proportions of sandstone-tomudrock among the study basins (Table 1). Many of the low relief, vegetated landforms in the northern tributary drainage basins of the Chaco River are capped by alluvium that is part of a topographically stepped Pleistocene and Holocene sequence (Fig. 4). Regional correlation of these deposits allows comparison of the differing downcutting histories of the basins. These alluvial deposits range in topographic position from present-day drainage divides to terraces to valley floors ","PeriodicalId":325871,"journal":{"name":"San Juan Basin IV","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132086662","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
-The Gavilan Mancos Oil Pool is one of several naturally fractured oil reservoirs producing from the Mancos Formation on the eastern side of the San Juan Basin. Commercial production is the result of the concentration. on slructure, of natural fractures wi1hin carbonale-cemenled sandstone and calcareous shale intervals of the Mancos Formalion. Fracturing of lhe rock column resulted from the formalion of the Gavilan dome by compressional forces associated with right lateral movement along the Nacimiento fault zone. Ac companying the fracturing process was the metasomatic formation of ankerite within calcareous portions of the rock column by tectonic dolomitization. Sulfide mineralization also formed by this mechanism. Detailed sample examination and thin section analysis of drill cuttings enabled recognition of the correct relationship between fracturing and the dolomite content of the rock. An understanding of lhe influence of tectonic dolomitization on the Gavilan Mancos Oil Pool will aid in additional exploralion efforts on the ea,tem side of the San Juan
{"title":"Tectonic dolomitization in the Gavilan Mancos oil pool, Rio Arriba County, New Mexico","authors":"A. Emmendorfer","doi":"10.56577/ffc-43.123","DOIUrl":"https://doi.org/10.56577/ffc-43.123","url":null,"abstract":"-The Gavilan Mancos Oil Pool is one of several naturally fractured oil reservoirs producing from the Mancos Formation on the eastern side of the San Juan Basin. Commercial production is the result of the concentration. on slructure, of natural fractures wi1hin carbonale-cemenled sandstone and calcareous shale intervals of the Mancos Formalion. Fracturing of lhe rock column resulted from the formalion of the Gavilan dome by compressional forces associated with right lateral movement along the Nacimiento fault zone. Ac companying the fracturing process was the metasomatic formation of ankerite within calcareous portions of the rock column by tectonic dolomitization. Sulfide mineralization also formed by this mechanism. Detailed sample examination and thin section analysis of drill cuttings enabled recognition of the correct relationship between fracturing and the dolomite content of the rock. An understanding of lhe influence of tectonic dolomitization on the Gavilan Mancos Oil Pool will aid in additional exploralion efforts on the ea,tem side of the San Juan","PeriodicalId":325871,"journal":{"name":"San Juan Basin IV","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125470188","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：