F. Goff, C. Goff, S. Chipera, D. Schiferl, Laurie S. Waters, Emiko Konishi, N. Iverson, J. Gindreau
Detailed geologic mapping combined with petrologic and geochemical analyses and a low-altitude aerial drone survey were used to investigate the development of monoliths and walls of altered Bandelier Tuff at Goblin Colony (GC) 11 km south of the southern Valles Caldera rim in New Mexico. The monoliths and walls consist of eroded spires, fins, spire and fin clusters, columns, and steam pipes of bright orange to tan tuff. Mapping shows that nonwelded to poorly welded unit 1 (Qbt 1 ) of the Tshirege Member of the Bandelier Tuff (1.23 Ma) filled a preexisting southwest-trending canyon cut into a complex sequence of eroded Miocene volcanic lava flows, domes, dikes, and volcaniclastic debris flows and sandstones. A dacite dike and plug zone about 1.5 km long formed a hydrologic boundary on the southeastern margin of the canyon before tuff (ignimbrite) emplacement. Thin sections of altered tuff show growth of feathery and blocky zeolite minerals in glass shards, pumice, and pore spaces and on feldspar (sanidine) surfaces. Patches of secondary hematite-limonite are also common, resulting in the intense orange colors of tuff at GC. X-ray diffraction (XRD) analyses reveal that the zeolites are mordenite with lesser clinoptilolite, with the zeolites forming primarily at the expense of rhyolitic glass. Scanning electron microscope (SEM) images verify that zeolites are growing primarily on glass and in voids. XRD also reveals that the ignimbrite contains exceptionally low quantities of vapor-phase minerals, tridymite, cristobalite, and excess alkali feldspar, even if unaltered by zeolites. Whole-rock chemical analyses of altered tuff are not as revealing as other techniques but show relative increases in water, Al 2 O 3 , total Fe 2 O 3 , MgO, CaO, K 2 O, and P 2 O 5 and decreases in SiO 2 and Na 2 O when compared with equivalent analyses of fresh tuff from the Pajarito Plateau. Concentrations of TiO 2 and MnO are unaffected. An aerial drone survey was flown over GC to examine the orientation of structures. Vertical spires, fins, and clusters of zeolite-altered tuff are broadly aligned in a northeast–southwest pattern on the upper (north) part of GC. However, the drone survey revealed that most spires, fins, and clusters developed along elongate or curving cracks 10 to 50 m long in random orientations. Unaltered tuff surrounds the various features. Two imposing walls of zeolite-altered tuff also developed in a general northeast–southwest trend, but the north wall displays a pronounced southward undulation, and the south wall is cut by en echelon faults or fractures. Between the walls is a modern eroded ravine about 35 m deep. Columns and steam pipes of zeolite-altered tuff are found in the upper to middle portions of GC and plunge 70° to 60° northwest. The columns display considerable zeolite alteration, are best exposed in the uppermost north part of GC, and are surrounded by unaltered tuff. Steam pipes protrude from the south face of the north wall; their r
{"title":"The Goblin Colony: Spectacular Monoliths and Walls of Altered Bandelier Tuff South of the Valles Caldera, New Mexico","authors":"F. Goff, C. Goff, S. Chipera, D. Schiferl, Laurie S. Waters, Emiko Konishi, N. Iverson, J. Gindreau","doi":"10.58799/nmg-v44n1.1","DOIUrl":"https://doi.org/10.58799/nmg-v44n1.1","url":null,"abstract":"Detailed geologic mapping combined with petrologic and geochemical analyses and a low-altitude aerial drone survey were used to investigate the development of monoliths and walls of altered Bandelier Tuff at Goblin Colony (GC) 11 km south of the southern Valles Caldera rim in New Mexico. The monoliths and walls consist of eroded spires, fins, spire and fin clusters, columns, and steam pipes of bright orange to tan tuff. Mapping shows that nonwelded to poorly welded unit 1 (Qbt 1 ) of the Tshirege Member of the Bandelier Tuff (1.23 Ma) filled a preexisting southwest-trending canyon cut into a complex sequence of eroded Miocene volcanic lava flows, domes, dikes, and volcaniclastic debris flows and sandstones. A dacite dike and plug zone about 1.5 km long formed a hydrologic boundary on the southeastern margin of the canyon before tuff (ignimbrite) emplacement. Thin sections of altered tuff show growth of feathery and blocky zeolite minerals in glass shards, pumice, and pore spaces and on feldspar (sanidine) surfaces. Patches of secondary hematite-limonite are also common, resulting in the intense orange colors of tuff at GC. X-ray diffraction (XRD) analyses reveal that the zeolites are mordenite with lesser clinoptilolite, with the zeolites forming primarily at the expense of rhyolitic glass. Scanning electron microscope (SEM) images verify that zeolites are growing primarily on glass and in voids. XRD also reveals that the ignimbrite contains exceptionally low quantities of vapor-phase minerals, tridymite, cristobalite, and excess alkali feldspar, even if unaltered by zeolites. Whole-rock chemical analyses of altered tuff are not as revealing as other techniques but show relative increases in water, Al 2 O 3 , total Fe 2 O 3 , MgO, CaO, K 2 O, and P 2 O 5 and decreases in SiO 2 and Na 2 O when compared with equivalent analyses of fresh tuff from the Pajarito Plateau. Concentrations of TiO 2 and MnO are unaffected. An aerial drone survey was flown over GC to examine the orientation of structures. Vertical spires, fins, and clusters of zeolite-altered tuff are broadly aligned in a northeast–southwest pattern on the upper (north) part of GC. However, the drone survey revealed that most spires, fins, and clusters developed along elongate or curving cracks 10 to 50 m long in random orientations. Unaltered tuff surrounds the various features. Two imposing walls of zeolite-altered tuff also developed in a general northeast–southwest trend, but the north wall displays a pronounced southward undulation, and the south wall is cut by en echelon faults or fractures. Between the walls is a modern eroded ravine about 35 m deep. Columns and steam pipes of zeolite-altered tuff are found in the upper to middle portions of GC and plunge 70° to 60° northwest. The columns display considerable zeolite alteration, are best exposed in the uppermost north part of GC, and are surrounded by unaltered tuff. Steam pipes protrude from the south face of the north wall; their r","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71179843","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":"San Diego Mountain: A �Rosetta Stone� for Interpreting the Cenozoic Tectonic Evolution of South-Central New Mexico","authors":"W. Seager, S. Kelley, Jacob O. Thacker, R. Kelley","doi":"10.58799/nmg-v44n2.24","DOIUrl":"https://doi.org/10.58799/nmg-v44n2.24","url":null,"abstract":"Hogbacks of the","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71179485","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}
Spencer G. Lucas, William A. DiMichele, Joseph M. Karnes
{"title":"Unusual Sandstone Cylinders from the Lower Permian Glorieta Sandstone, Northern New Mexico","authors":"Spencer G. Lucas, William A. DiMichele, Joseph M. Karnes","doi":"10.58799/nmg-v44n3.63","DOIUrl":"https://doi.org/10.58799/nmg-v44n3.63","url":null,"abstract":"","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136305012","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}
We document calcareous paleosols from Upper Pennsylvanian (lower Virgilian) strata of the Burrego Member of the Atrasado Formation in the Cerros de Amado of Socorro County, New Mexico. The Burrego paleosols are an excellent example of a scarce, climate-sensitive lithology in the Pennsylvanian strata of New Mexico. These paleosols contain mostly stage II to III carbonate horizons, and their overall morphology suggests deposition and pedogenesis under subhumid, seasonally dry conditions. This conclusion is consistent with paleobotanical and other data that indicate such climate conditions were widespread on Late Pennsylvanian Pangea. The mean value of the oxygen-isotope ratios from Burrego paleosol carbonates compares well with the values from Virgilian paleosols of the San Juan, the eastern Midland and Chama basins of New Mexico-Texas, suggesting similar conditions of temperature and paleoprecipitation. Application of the diffusion-reaction model to the mean carbon-isotope composition of the carbonate suggests a paleo-pCO2 of approximately 400 ppmV, which is also consistent with estimates from correlative carbonate deposits that formed farther east in Late Pennsylvanian Pangea.
我们记录了新墨西哥州Socorro县Cerros de Amado的Atrasado组Burrego成员的上宾夕法尼亚(下弗吉尼亚)地层的钙质古土壤。Burrego古土壤是新墨西哥州宾夕法尼亚地层中稀缺的、对气候敏感的岩性的一个很好的例子。这些古土壤主要含有II至III期碳酸盐层，其整体形态表明在半湿润、季节性干燥的条件下沉积和成土。这一结论与古植物学和其他数据一致，表明这种气候条件在晚宾夕法尼亚泛大陆广泛存在。Burrego古土壤碳酸盐的氧同位素平均值与新墨西哥-德克萨斯州圣胡安盆地、东部米德兰盆地和Chama盆地的Virgilian古土壤的氧同位素平均值比较好，表明了相似的温度和古降水条件。将扩散反应模型应用于碳酸盐岩的平均碳同位素组成，表明其古pco2约为400 ppmV，这也与晚宾夕法尼亚盘古大陆形成的相关碳酸盐岩沉积的估计相一致。
{"title":"Late Pennsylvanian Calcareous Paleosols from Central New Mexico: Implications for Paleoclimate","authors":"S. Lucas, L. Tanner","doi":"10.58799/nmg-v43n1.3","DOIUrl":"https://doi.org/10.58799/nmg-v43n1.3","url":null,"abstract":"We document calcareous paleosols from Upper Pennsylvanian (lower Virgilian) strata of the Burrego Member of the Atrasado Formation in the Cerros de Amado of Socorro County, New Mexico. The Burrego paleosols are an excellent example of a scarce, climate-sensitive lithology in the Pennsylvanian strata of New Mexico. These paleosols contain mostly stage II to III carbonate horizons, and their overall morphology suggests deposition and pedogenesis under subhumid, seasonally dry conditions. This conclusion is consistent with paleobotanical and other data that indicate such climate conditions were widespread on Late Pennsylvanian Pangea. The mean value of the oxygen-isotope ratios from Burrego paleosol carbonates compares well with the values from Virgilian paleosols of the San Juan, the eastern Midland and Chama basins of New Mexico-Texas, suggesting similar conditions of temperature and paleoprecipitation. Application of the diffusion-reaction model to the mean carbon-isotope composition of the carbonate suggests a paleo-pCO2 of approximately 400 ppmV, which is also consistent with estimates from correlative carbonate deposits that formed farther east in Late Pennsylvanian Pangea.","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71179910","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":"In Memory of Philip J. Sterling","authors":"T. Parkhill, Davy Wentworth","doi":"10.58799/nmg-v42n1.60","DOIUrl":"https://doi.org/10.58799/nmg-v42n1.60","url":null,"abstract":"","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71179238","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}
M. Petronis, R. Trujillo, J. Lindline, J. Zebrowski
The Española Basin is one of a series of interconnected, asymmetrical basins in the Rio Grande rift that includes a number of northand northeast-striking faults that accommodated block tilting and basin subsidence. The western margin of the Española Basin, in particular, is characterized by a greater than 17-km wide zone of normal and oblique-slip faults. To clarify the involvement of block rotation in the tectonic evolution of the Española Basin, we carried out a paleomagnetic study of mafic intrusions (Rio del Oso dike swarm) that are genetically related to regionally extensive basalt flows of the mid-Miocene Lobato Formation. The primary hypothesis tested was that these intrusions experienced some degree of vertical axis rotation associated with mid-Miocene to recent continental rifting. In situ paleomagnetic results from forty-two sites yield a group mean declination (D) of 344.0°, an inclination (I) of 41.1°, α95 of 6.1°, and k of 14.1. The group mean result is discordant to the <10 Ma pole of D=356.0°, I=54.4°, α95 = 3.3° with a statistically significant inferred rotation (R) of -12.0°± 7.2° and flattening of +13.3° ± 5.5° relative to the <10 Ma pole field direction. These discordant results indicate that a modest degree of counter-clockwise vertical axis rotation occurred in this region, which is likely associated with Rio Grande rifting north of the Jemez Mountains. It is possible that oblique motion along the Santa Clara fault and/ or the Cañada del Almagre fault facilitated the vertical axis rotation. The results from this study imply that vertical axis rotation is common to extensional rift systems and should be considered when modeling continental extension.
Española盆地是里约热内卢大裂谷中一系列相互连接的不对称盆地之一，该裂谷包括许多北向和东北向的断裂，可容纳地块倾斜和盆地沉降。特别是Española盆地的西缘，其特征是一个超过17公里宽的正滑和斜滑断裂带。为了明确块体旋转在Española盆地构造演化中的作用，我们对基性侵入体(里约热内卢del Oso岩脉群)进行了古地磁研究，这些侵入体与中中新世Lobato组区域广泛的玄武岩流动有遗传关系。经检验的主要假设是，这些侵入体经历了与中新世中期到近代大陆裂陷有关的某种程度的垂直轴旋转。42个地点的原位古地磁结果显示，群平均赤纬(D)为344.0°，倾角(I)为41.1°，α95为6.1°，k为14.1。组平均结果与<10 Ma极D=356.0°，I=54.4°，α95 = 3.3°不一致，相对于<10 Ma极场方向，推断旋转(R)为-12.0°±7.2°，平坦化(+13.3°±5.5°)具有统计学意义。这些不一致的结果表明，该地区发生了一定程度的逆时针垂直轴旋转，这可能与Jemez山脉北部的里约热内卢大裂谷作用有关。沿圣克拉拉断层和/或Cañada del Almagre断层的斜向运动可能促进了垂直轴的旋转。研究结果表明，纵轴旋转是伸展裂谷系统的共同特征，在模拟大陆伸展时应予以考虑。
{"title":"Paleomagnetic Data Bearing on Vertical Axis Rotation of the Rio del Oso dike swarm, Western Espa�ola Basin, New Mexico","authors":"M. Petronis, R. Trujillo, J. Lindline, J. Zebrowski","doi":"10.58799/nmg-v42n2.61","DOIUrl":"https://doi.org/10.58799/nmg-v42n2.61","url":null,"abstract":"The Española Basin is one of a series of interconnected, asymmetrical basins in the Rio Grande rift that includes a number of northand northeast-striking faults that accommodated block tilting and basin subsidence. The western margin of the Española Basin, in particular, is characterized by a greater than 17-km wide zone of normal and oblique-slip faults. To clarify the involvement of block rotation in the tectonic evolution of the Española Basin, we carried out a paleomagnetic study of mafic intrusions (Rio del Oso dike swarm) that are genetically related to regionally extensive basalt flows of the mid-Miocene Lobato Formation. The primary hypothesis tested was that these intrusions experienced some degree of vertical axis rotation associated with mid-Miocene to recent continental rifting. In situ paleomagnetic results from forty-two sites yield a group mean declination (D) of 344.0°, an inclination (I) of 41.1°, α95 of 6.1°, and k of 14.1. The group mean result is discordant to the <10 Ma pole of D=356.0°, I=54.4°, α95 = 3.3° with a statistically significant inferred rotation (R) of -12.0°± 7.2° and flattening of +13.3° ± 5.5° relative to the <10 Ma pole field direction. These discordant results indicate that a modest degree of counter-clockwise vertical axis rotation occurred in this region, which is likely associated with Rio Grande rifting north of the Jemez Mountains. It is possible that oblique motion along the Santa Clara fault and/ or the Cañada del Almagre fault facilitated the vertical axis rotation. The results from this study imply that vertical axis rotation is common to extensional rift systems and should be considered when modeling continental extension.","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71179425","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}
Invertebrate trace fossils from the Albian Mesilla Valley Formation (Washita Group) at Cerro de Cristo Rey, Sunland Park, NM represent the following ichnotaxa: Ancorichnus isp., Arenicolites isp., Bergueria isp., Bichordites sp., Cardioichnus foradadensis, C. biloba, Chondrites intricatus, Cochlichnus anguineus, Coprulus oblongus, Gordia marina, Helicodromites isp., Lockeia isp., Ophiomorpha nodosa, Palaeophycus tubularis, P. striatus, P. heberti, Planolites isp., Protovirgularia dichotoma, Rhizocorallium commune var. irregulare (with Coprulus oblongus), Skolithos isp., Spongeliomorpha isp., S. sublumbricoides, S. oraviense, Taenidium isp., Thalassinoides isp., T. paradoxicus, Treptichnus isp., a chimney structure (Chomatichnus?), and the biofilm Rugalichnus (“Kinneyia”). This is the first study of the invertebrate ichnology of any of the shallow marine units at Cerro de Cristo Rey. The Mesilla Valley Formation contains a medium/high diversity ichnoassemblage, including fugichnia (i.e., Skolithos), fodichnia (i.e., Chondrites), domichnia (i.e., Ophiomorpha, Thalassinoides), repichnia (Protovirgularia), paschichnia (i.e., Palaeophycus), and cubichnia (i.e., Bergaueria, Cardioichnus, Lockeia), as well as compound traces and composite traces. This ichnoassemblage was preserved in tempestites (storm deposits) from below wave base on the upper/middle continental shelf during Oceanic Anoxic Event 1d and contains ichnotaxa representative of the proximal Cruziana ichnofacies (with Skolithos influence).
新墨西哥州桑兰公园Cerro de Cristo Rey的Albian Mesilla Valley Formation (Washita Group)的无脊椎动物化石代表了以下ichno类群:Ancorichnus isp;砂粒石;， bergeria isp。二叶球粒陨石、弓形锥虫、长尾锥虫、长尾锥虫、长尾锥虫、长尾锥虫、长尾锥虫。， Lockeia isp。叶面蛇苔、管状古蛇苔、纹状蛇苔、叶面蛇苔、扁豆蛇苔。，双歧原菌属，不规则根腐菌属(与长尾菌属)，长尾菌属。海绵状植物。，半伞状伞，鸟状伞，带状伞。Thalassinoides的翻译结果:， T. paradoxicus, treptichus。，烟囱结构(Chomatichnus?)和生物膜Rugalichnus (Kinneyia)。这是第一次对基督山浅海单位的无脊椎动物技术进行研究。Mesilla Valley组包含了中/高多样性的昆虫组合，包括fugichnia(即Skolithos)、fodichnia(即Chondrites)、domichnia(即Ophiomorpha、Thalassinoides)、repichnia(即Protovirgularia)、paschichnia(即Palaeophycus)和cubichnia(即Bergaueria、Cardioichnus、Lockeia)，以及复合痕迹和复合痕迹。该鱼类组合在海洋缺氧事件1d期间保存在上/中大陆架波底下的风暴沉积中，包含具有代表性的近Cruziana鱼相(受Skolithos影响)的鱼类分类群。
{"title":"Ichnology of the Lower Cretaceous (Albian) Mesilla Valley Formation, Cerro de Cristo Rey, southeastern New Mexico, USA","authors":"Eric J. Kappus, S. Lucas","doi":"10.58799/nmg-v42n1.3","DOIUrl":"https://doi.org/10.58799/nmg-v42n1.3","url":null,"abstract":"Invertebrate trace fossils from the Albian Mesilla Valley Formation (Washita Group) at Cerro de Cristo Rey, Sunland Park, NM represent the following ichnotaxa: Ancorichnus isp., Arenicolites isp., Bergueria isp., Bichordites sp., Cardioichnus foradadensis, C. biloba, Chondrites intricatus, Cochlichnus anguineus, Coprulus oblongus, Gordia marina, Helicodromites isp., Lockeia isp., Ophiomorpha nodosa, Palaeophycus tubularis, P. striatus, P. heberti, Planolites isp., Protovirgularia dichotoma, Rhizocorallium commune var. irregulare (with Coprulus oblongus), Skolithos isp., Spongeliomorpha isp., S. sublumbricoides, S. oraviense, Taenidium isp., Thalassinoides isp., T. paradoxicus, Treptichnus isp., a chimney structure (Chomatichnus?), and the biofilm Rugalichnus (“Kinneyia”). This is the first study of the invertebrate ichnology of any of the shallow marine units at Cerro de Cristo Rey. The Mesilla Valley Formation contains a medium/high diversity ichnoassemblage, including fugichnia (i.e., Skolithos), fodichnia (i.e., Chondrites), domichnia (i.e., Ophiomorpha, Thalassinoides), repichnia (Protovirgularia), paschichnia (i.e., Palaeophycus), and cubichnia (i.e., Bergaueria, Cardioichnus, Lockeia), as well as compound traces and composite traces. This ichnoassemblage was preserved in tempestites (storm deposits) from below wave base on the upper/middle continental shelf during Oceanic Anoxic Event 1d and contains ichnotaxa representative of the proximal Cruziana ichnofacies (with Skolithos influence).","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71179108","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}
Located about 19 km (12 mi) southeast of Las Cruces in Doña Ana County, New Mexico, Bishop Cap is a rugged peak at the southern end of the Organ Mountains. At an elevation of 1,651 m (5,419 ft), Bishop Cap rises about 335 m (1,100 ft) above the alluvial fans at its base. The miter-shaped peak looks like a bishop’s cap, hence the name. Bishop Cap is on a westward-tilted fault block between the Organ Mountains of New Mexico and the Franklin Mountains of West Texas. Its western side is a monocline-like flexure that dips to the west beneath Quaternary alluvial-fan deposits. The oldest strata exposed at Bishop Cap are along the eastern base of the peak. They are Mississippian marine rocks capped by the Late Mississippian (Chesterian) Helms Formation. A limestone-dominated Pennsylvanian section about 256 m thick makes up most of Bishop Cap, and these strata rest with evident disconformity on olive-gray shale of the Helms Formation. During the early 20th Century, fluorite was mined at Bishop Cap and in the surrounding hills, and published descriptions of the mining geology and stratigraphy first appeared in the 1920s (Seager, 1973, 1981). The lithostratigraphic nomenclature long applied to the Pennsylvanian strata at Bishop Cap has been that of Nelson (1940), names he introduced at Vinton Canyon in the northern Franklin Mountains to the south. Nelson (1940) coined the names (ascending order) La Tuna, Berino, and Bishop’s Cap members of the Magdalena Formation. At Vinton Canyon, these strata and an overlying unnamed interval of Pennsylvanian strata comprise a stratigraphic section about 823 m thick (Harbour, 1972). At Bishop Cap, Seager (1973, 1981) mapped the Pennsylvanian strata as the La Tuna and Berino formations of the Magdalena Group (ironically, Nelson’s “Bishop’s Cap Member” is not exposed at Bishop Cap, having been removed by
{"title":"Gallery of Geology: The Pennsylvanian section at Bishop Cap, Do�a Ana County, New Mexico","authors":"S. Lucas, K. Krainer","doi":"10.58799/nmg-v42n2.79","DOIUrl":"https://doi.org/10.58799/nmg-v42n2.79","url":null,"abstract":"Located about 19 km (12 mi) southeast of Las Cruces in Doña Ana County, New Mexico, Bishop Cap is a rugged peak at the southern end of the Organ Mountains. At an elevation of 1,651 m (5,419 ft), Bishop Cap rises about 335 m (1,100 ft) above the alluvial fans at its base. The miter-shaped peak looks like a bishop’s cap, hence the name. Bishop Cap is on a westward-tilted fault block between the Organ Mountains of New Mexico and the Franklin Mountains of West Texas. Its western side is a monocline-like flexure that dips to the west beneath Quaternary alluvial-fan deposits. The oldest strata exposed at Bishop Cap are along the eastern base of the peak. They are Mississippian marine rocks capped by the Late Mississippian (Chesterian) Helms Formation. A limestone-dominated Pennsylvanian section about 256 m thick makes up most of Bishop Cap, and these strata rest with evident disconformity on olive-gray shale of the Helms Formation. During the early 20th Century, fluorite was mined at Bishop Cap and in the surrounding hills, and published descriptions of the mining geology and stratigraphy first appeared in the 1920s (Seager, 1973, 1981). The lithostratigraphic nomenclature long applied to the Pennsylvanian strata at Bishop Cap has been that of Nelson (1940), names he introduced at Vinton Canyon in the northern Franklin Mountains to the south. Nelson (1940) coined the names (ascending order) La Tuna, Berino, and Bishop’s Cap members of the Magdalena Formation. At Vinton Canyon, these strata and an overlying unnamed interval of Pennsylvanian strata comprise a stratigraphic section about 823 m thick (Harbour, 1972). At Bishop Cap, Seager (1973, 1981) mapped the Pennsylvanian strata as the La Tuna and Berino formations of the Magdalena Group (ironically, Nelson’s “Bishop’s Cap Member” is not exposed at Bishop Cap, having been removed by","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71179436","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}
A pilot study has yielded the first infrared stimulated luminescence (IRSL) age from the upper part of the eolian Blackwater Draw Formation near its type locality in the Southern High Plains of Texas. The age on potassium feldspar is 294 ± 32 ka (50°C IRSL) and 347 ± 40 ka (290°C post-IR IRSL) and averaged 300 to 350 ka. Both ages are significantly earlier than previously reported thermoluminescence (TL) ages. A Middle Pleistocene age of the upper Blackwater Draw Formation is consistent with its mature argillic soil Bt horizon and the overprint of a well-developed calcic soil Bk horizon. The deposition of the Blackwater Draw Formation also pre-dates the Mescalero sand sheet of southeastern New Mexico, a late Pleistocene component of which has been miscorrelated with the Blackwater Draw. The tendency to regard all red eolian sands in the region as the Blackwater Draw Formation may be mistaken, overlooking younger red eolian sand bodies with less mature soil development.
{"title":"Middle Pleistocene IRSL age of the upper Blackwater Draw Formation, Southern High Plains, Texas and New Mexico, USA","authors":"S. Hall, R. Goble","doi":"10.58799/nmg-v42n1.31","DOIUrl":"https://doi.org/10.58799/nmg-v42n1.31","url":null,"abstract":"A pilot study has yielded the first infrared stimulated luminescence (IRSL) age from the upper part of the eolian Blackwater Draw Formation near its type locality in the Southern High Plains of Texas. The age on potassium feldspar is 294 ± 32 ka (50°C IRSL) and 347 ± 40 ka (290°C post-IR IRSL) and averaged 300 to 350 ka. Both ages are significantly earlier than previously reported thermoluminescence (TL) ages. A Middle Pleistocene age of the upper Blackwater Draw Formation is consistent with its mature argillic soil Bt horizon and the overprint of a well-developed calcic soil Bk horizon. The deposition of the Blackwater Draw Formation also pre-dates the Mescalero sand sheet of southeastern New Mexico, a late Pleistocene component of which has been miscorrelated with the Blackwater Draw. The tendency to regard all red eolian sands in the region as the Blackwater Draw Formation may be mistaken, overlooking younger red eolian sand bodies with less mature soil development.","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71179202","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}
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