Geology of the Taos Region最新文献

{"title":"The San Luis Basin to the Espa�ola Basin - Third-day Road Log from Talpa to the Rio Grande del Rancho Valley, U.S. Hill, Vadito, and Pe�asco","authors":"P. Bauer, A. Read, K. Kelson, B. Kues, S. Aby, Wiliam R. Muehlberger, Ren A. Thompson, G. S. Austin, Gary A. Smith","doi":"10.56577/ffc-55.77","DOIUrl":"https://doi.org/10.56577/ffc-55.77","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":224165,"journal":{"name":"Geology of the Taos Region","volume":"17 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":"126551404","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":"Middle-Upper Miocene stratigraphy of the Velarde Graben, North-Central New Mexico: Tectonic and paleogeographic implications","authors":"D. Koning, S. Aby, N. Dunbar","doi":"10.56577/ffc-55.359","DOIUrl":"https://doi.org/10.56577/ffc-55.359","url":null,"abstract":"A BSTRACT . — Geologic mapping and correlation of tephras in and near the Velarde graben supports the southward extension of the Cieneguilla member of Leininger (1982) into the graben, refines the stratigraphic relationships of various lithostratigraphic units, and has produced better estimates of vertical stratigraphic displacement on several graben faults. The Velarde graben is a 6-10 km-wide, northeast-trending extensional feature in the northern Española Basin of the Rio Grande rift. It coincides with a 19 km-long gravity low between the north tip of Black Mesa and the town of Hernandez to the southwest. In the general area of the Velarde graben, the Santa Fe Group is differentiated into seven lithostratigraphic units assigned to the Tesuque Formation. Some of these units were originally assigned to the Chamita Formation in previous studies. However, we propose abandoning the Chamita Formation, and reassigning its strata to the Tesuque Formation, because 1) strata assigned to the Tesuque Formation correlate into the Chamita type section, and 2) in the absence of the Ojo Caliente Sandstone Member it is not possible to map a contact between the Chamita and Tesuque formations with confidence. Vertical stratigraphic displacements along the border faults of the Velarde graben since 7.7-8.4 Ma range from as low as 65 m on the Rio de Truchas fault to 435 m on the Santa Clara fault. On the southern tip of Black Mesa, comparison of vertical slip rates for the Santa Clara fault over two time periods yields slightly higher vertical slip rate values for 3-8 Ma (48-56 m/Myr) compared to 0-3 Ma (35-48 m/Myr). On the gravity high separating the Velarde graben from another gravity low to the south, a vertical slip rate calculated for the Santa Clara fault gives 48-50 m/Myr for time after 9.9 Ma. Increasing slip rates on the Velarde graben faults in the late Miocene may have induced west-northwestward progradation of alluvial slope facies (lithosome A) derived from the Sangre de Cristo Mountains.","PeriodicalId":224165,"journal":{"name":"Geology of the Taos Region","volume":"1 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":"114174924","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":"Cenozoic structural development of the Taos area, New Mexico","authors":"P. Bauer, K. Kelson","doi":"10.56577/ffc-55.129","DOIUrl":"https://doi.org/10.56577/ffc-55.129","url":null,"abstract":"A BSTRACT . —New, detailed geologic maps of Precambrian and Paleozoic bedrock, Tertiary basin fill, Quaternary surficial deposits, and the faults that cut them all, provide important controls on the geometry and kinematics of tectonism in the Taos area, from Laramide shortening to modern rifting. The three major fault systems that intersect in the Taos area are much more complex than previously described. The north-striking, 8-km-wide, strike-slip Picuris-Pecos fault system cuts deposits younger than about 5 Ma. The Picuris-Pecos fault is truncated by the Embudo fault, a major sinistral, antithetic rift transfer zone between the San Luis and Española rift basins. The Embudo fault is a complex system of left-oblique, north-down, strike-slip fault strands that is over 2 km wide. Pliocene basalt offset by the Embudo fault southwest of Pilar suggests a post-3-Ma minimum throw rate of 35 m/m.y. and a minimum average net slip rate of 130 m/m.y. The northeastern terminus of the Embudo fault is at the Rio Grande del Rancho drainage, where the east-striking Embudo fault system swings northward and smoothly merges with the dominantly dip-slip Cañon section of the rift-bounding Sangre de Cristo fault. The transition zone from the Embudo fault to the Sangre de Cristo fault is coincident with the Picuris-Pecos fault system and the Miranda graben. The Picuris-Pecos fault projects northward across the Taos embayment and aligns with the Questa section of the Sangre de Cristo fault. In the San Luis Basin directly north of the Embudo fault, is the buried, north-trending, 13-km-wide, 5000-m-deep Taos graben. We speculate that this graben may be the sinistrally displaced equivalent of the Miranda and Rio Grande del Rancho grabens. Our mapping also yields information on the timing of tectonism in the southeastern San Luis Basin. Substantial strike-slip faulting occurred in the Taos area at least until 18 million years ago, well past the 27 Ma onset of extension in the San Luis Basin. During early extension, prior to development of the Embudo fault, the Picuris-Pecos fault system, and its now-buried northward extension, may have represented the eastern rift margin. The transition from Laramide shortening to rift extension is indistinct, and at least some Laramide transverse faults probably evolved into rift normal faults in a transtensional(?) setting. The change to pure extension may have coincided with a middle Miocene change in crustal extensional strain rate, and may have also triggered the initial development of the modern Embudo fault.","PeriodicalId":224165,"journal":{"name":"Geology of the Taos Region","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":"125110524","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":"Proterozoic rocks of the Pilar Cliffs, Picuris Mountains, New Mexico","authors":"P. Bauer","doi":"10.56577/ffc-55.193","DOIUrl":"https://doi.org/10.56577/ffc-55.193","url":null,"abstract":"A .—The Cenozoic Embudo fault zone has juxtaposed the crystalline rocks of the Picuris Mountains against the Plio- cene rocks of the San Luis Basin near the village of Pilar. A combination of north-down faulting and late Cenozoic erosion by the Rio Grande has produced several miles of spectacular exposures of south-dipping Paleoproterozoic rocks along the Pilar cliffs. An impressive ductile shear zone separates the Ortega Formation quartzite from the Glenwoody Formation schist. The Glenwoody Formation is composed of feldspathic quartz-muscovite and quartz-eye schist that probably represents metamor- phosed, altered, phenocrystic, felsic volcanic rocks. The Ortega Formation of the Hondo Group is a remarkably clean, 1-km-thick, metamorphosed quartz arenite that is overlain by a metamorphosed siliclastic sequence of interlayered quartzites and pelitic schists of the Rinconada Formation. All supracrustal rocks have undergone a progressive ductile deformational history that involved the formation of pervasive penetrative foliations and lineations, major fold sets, and a variety of ductile shear zones. The Pilar cliffs section forms the north limb of the large, shallowly plunging, east-trending, overturned Hondo syncline. The south-dipping contact (Pilar shear zone) between the Glenwoody Formation and the overlying, upright Ortega Formation in the Pilar cliffs is a ductile shear zone preserving evidence for both early north-vergent shearing and late south-vergent shearing. The Pilar shear zone is probably not a major tectonic break, but instead is one of the south-dipping imbrication structures that are recognized in and around the Ortega Formation in northern New Mexico. In the southern Picuris Mountains, the Hondo Group section is bounded by a second south-dipping ductile shear zone (Plomo fault) along which the overturned Vadito Group has been thrust northward over the Hondo Group. The Ortega and Glenwoody Formations belong to the northeast-trending Yavapai-Mazatzal transition zone, and are part of the 1.70-1.69 Ga rhyolite-quartzite association of the Southwest that is thought to have accumulated in volcanic/sedimentary basins on juvenile, but relatively stable, continental crust. The preferred stratigraphic/structural model states that the Glenwoody Formation is the youngest Vadito Group unit exposed in the range, and was faulted out in the southern Picuris Mountains during the Mazatzal orogeny when the older Yavapai volcanogenic basement and its quartzitic cover were thrust northward at ca. 1.65 Ga as continental crust to the south collided with the Laurentian craton. Later collapse of the mountain belt (or 1.4 Ga intracontinental tectonism) resulted in south-directed movement of the Ortega Formation over the Glenwoody Formation.","PeriodicalId":224165,"journal":{"name":"Geology of the Taos Region","volume":"17 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":"127547714","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":"The Picuris Formation: A late Eocene to Miocene sedimentary sequence in northern New Mexico","authors":"S. Aby, P. Bauer, K. Kelson","doi":"10.56577/ffc-55.335","DOIUrl":"https://doi.org/10.56577/ffc-55.335","url":null,"abstract":".—New geologic mapping and 12 new 40 Ar/ 39 Ar ages from the Picuris Formation have provided new information on this noteworthy Tertiary sedimentary unit in Taos County, New Mexico. Where exposed along the northern and southern flanks of the Picuris Mountains, the formation is composed of: 1) a lower, basement- and volcanic-derived, highly weathered, conglomerate, sandstone, and siltstone member; 2) a middle, tuffaceous/pumicious sandstone member; and 3) a volcaniclastic pebble-conglomerate to mudstone member. Although compositional and textural variability exists within the members and between exposures, and some interfingering of the upper two members occurs, for simplicity we informally refer to them as the lower conglomerate member, the middle tuffaceous member, and the upper volcaniclastic member. The lower conglomerate member is derived from local Proterozoic basement and, in the northeastern Picuris Mountains, from a mixed basement/volca-nic source. The volcaniclastic components of the upper two members are derived from the Latir volcanic field with additions from Proterozoic sources. In some areas the upper volcaniclastic member also contains Paleozoic clasts. The lower conglomerate member contains and/or underlies ash layers dated at ca. 34.5 Ma. The middle tuffaceous member contains a 27.9 Ma ash in the north and overlies the 28.3 Ma Llano Quemado breccia. The middle tuffaceous member in the south contains 27.7-23.0 Ma pumice clasts. The upper volcaniclastic member contains volcanic clasts that range in age from 27.3-18.6 Ma. A basalt clast from near the base of the upper volcaniclastic member in the south, dated at 19.8 Ma, provides a maximum age for the southern part of the upper volcaniclastic member. Because the Picuris Formation spans a time range of greater than 34.5 Ma to less than 18.6 Ma, sedimentation may span the time between the end of Laramide shortening and onset of Rio Grande rift extension. The upper volcaniclastic member of the Picuris Formation may be equivalent to the Miocene Chama-El Rito Member of the Tesuque Formation of the Santa Fe Group.","PeriodicalId":224165,"journal":{"name":"Geology of the Taos Region","volume":"58 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":"131532336","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":"Evolution of the southeastern San Luis Basin margin and the Culebra embayment, Rio Grande rift, southern Colorado","authors":"A. R. Wallace","doi":"10.56577/ffc-55.181","DOIUrl":"https://doi.org/10.56577/ffc-55.181","url":null,"abstract":"A BSTRACT . —The Culebra half-graben and horst in southern Colorado form the southern half of the asymmetric San Luis graben-horst system along the Rio Grande rift. The Blanca Peak horst forms the northern margin of the Culebra half-graben and is linked with the Sangre de Cristo horst to the north. These elements comprise the Culebra reentrant, an eastward recess in the rift margin south of Blanca Peak. Rifting in the Culebra horst-graben system began at about 25 Ma, and Santa Fe Group sediments were shed westward into alluvial fans and the developing depocenter. Clasts of progressively older source lithologies were carried to the depocenter, reflecting early uplift of the Culebra horst through at least 18.7 Ma, and sedimentation continued to at least 3.7 Ma. The drainage divide in the rising horst shifted westward, eventually limiting the alluvial sources to the west- ern side of the modern range. Blanca Peak was not a topographic high during these stages of sedimentation. The structurally active part of the Culebra horst-graben system coincides with the thrust-faulted west side of a Laramide arch. Normal faulting along the western side of the Culebra horst began in the late Oligocene and was most active from the late Miocene to the present. The dominant faults strike northeast and are down-dropped into the basin, creating at least 4600 m of total offset. Rifting reactivated Laramide tear faults to form northwest-striking normal faults. The interaction between the rift-parallel faults and the oblique reactivated tear faults created a compartmentalized fault system and demonstrates a clear Laramide influence on rift-related faulting. Initial uplift of the Blanca Peak horst began in the early Miocene, but substantial uplift did not take place until the late Miocene and Pliocene. Since that time, uplift of the Culebra horst and Blanca Peak horsts overlapped in time and, in part, in space. The Culebra reentrant is a product of contrasting uplift styles along the margins of the two horsts and conjecturally some clockwise rotation of the Blanca Peak horst.","PeriodicalId":224165,"journal":{"name":"Geology of the Taos Region","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":"114714339","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":"Structure of the Sangre de Cristo Mountains between Taos and Mora based on an integrated geophysical analysis","authors":"O. Quezada, C. Andronicos, G. Keller","doi":"10.56577/ffc-55.257","DOIUrl":"https://doi.org/10.56577/ffc-55.257","url":null,"abstract":"A BSTRACT .- The southern Sangre de Cristo Mountains in New Mexico record much of the geological history of southwestern North America. Here we use a combination of geophysical data with geological ground truth to define the subsurface structure of part of this region. Our analysis indicates that a Proterozoic ductile fold and thrust belt exposed in the northern Rincon Range extends in the subsurface at least 25 km to the southwest of its surface expression. This fold and thrust belt likely links to similar fold and thrust structures exposed to the south and west in the Rio Mora, Truchas, Picuris and Tusas Mountains. Cross-cutting these structures, and offsetting the Great Unconformity, is a series of gently west dipping normal faults. These faults likely developed during Rio Grande rifting, although their gentle dips may be inherited from Laramide compressional structures. No structures related to Ancestral Rocky Mountains deformation were imaged in the subsurface. However, the distributions of Paleozoic rocks require that the Rainsville and Taos Troughs were major basins formed during Ancestral Rocky Mountain deformation. No evidence for the reactivation of Proterozoic structures was observed on the seismic data. Thus the structure of the southeastern Sangre de Cristo Mountains is the result of superposed deformation events that occurred in the Proterozoic, Late Paleozoic and the Cenozoic.","PeriodicalId":224165,"journal":{"name":"Geology of the Taos Region","volume":"103 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":"133379020","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":"Plio-Pleistocene incision history of the Rio Ojo Caliente, northern Espa�ola Basin, and overview of the Rio Grande system in northern New Mexico","authors":"D. Newell, D. Koning, K. Karlstrom, L. Crossey, M. Dillon","doi":"10.56577/ffc-55.300","DOIUrl":"https://doi.org/10.56577/ffc-55.300","url":null,"abstract":"A BSTRACT . —The Rio Ojo Caliente, a tributary to the Rio Chama in the Española Basin, exhibits a well-preserved flight of Plio-Pleistocene terrace deposits. Ten terraces identified along the Rio Ojo Caliente consist of several meters of river gravels deposited onto straths cut on Precambrian and Tertiary rock. Strath heights range from 3 to 165 m above the river and correlate to straths beneath dated terraces along the Rio Chama and Rio Grande. River gravels at ~270 m above the Rio Ojo Caliente directly underlie the 3.65 Ma Black Mesa basalt, representing topographic inversion of a southwest-flowing ancestral Rio Grande. Two topographically lower terraces are associated with the ~1.6 Ma Guaje pumice (~160 m) and 0.62 Ma Lava Creek B ash (~110 m). These three surfaces constrain a variable incision history with rates, using basal strath heights, that average 65 m/m.y. from 3.65 to 1.6 Ma, 30 m/m.y from 1.6 to 0.62 Ma, and 175 m/m.y. from 620 ka to present. New longitudinal profile data support and expand the hypothesis of Wells et al. (1987) that increased incision in the Española Basin since ~600 ka involved piracy of the San Luis Basin drainages by Española Basin drainages in the middle Pleistocene. Likewise, we concur that major knickpoints in the longitudinal profile of the Rio Grande and its tributaries upstream from the Rio Chama represent young transients due to the integration of the two basins. The pattern of knickpoints and convex profiles in the mainstem and tributaries could represent a passing transient wave of incision. South of the mainstem knick-zone, tributary knickpoints occur within convex profiles at progressively higher elevations; north of the mainstem knick-zone, tributaries have simpler concave profiles. Bedrock strength is a strong factor in localizing knickpoints, but does not fully explain this pattern. study in the context of Plio-Pleistocene climate change and regional tectonism over the same period.","PeriodicalId":224165,"journal":{"name":"Geology of the Taos Region","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":"130780500","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":"Pennsylvanian trilobites from the Sangre de Cristo and Jemez Mountains, north-central New Mexico","authors":"B. Kues","doi":"10.56577/ffc-55.326","DOIUrl":"https://doi.org/10.56577/ffc-55.326","url":null,"abstract":"A BSTRACT . —Trilobites are rare in marine Pennsylvanian strata of New Mexico. More than 100 specimens from Morrowan to Virgilian strata in the Sangre de Cristo and Jemez Mountains, belonging to five species, are described here. These are: aff. Paladin sp. (Morrowan), Sevillia trinucleata (Herrick) (upper Atokan-lower Desmoinesian), Sevillia sevillensis Weller (lower Desmoinesian), Ditomopyge scitula (Meek and Worthen) (Desmoinesian-middle Virgilian), and Ameura missouriensis (Shumard) (Atokan-middle Virgilian). These trilobites represent a depauperate but geographically widely distributed North American Pennsylvanian trilobite fauna. The taxa aff. Paladin sp., Ditomopyge scitula , and Ameura missouriensis appear to have preferred shallow, carbonate-shelf environments in which they occur with stenohaline groups such as brachiopods, bryo- zoans, and crinoids. Less commonly, the latter two species also occur in limestone assemblages dominated by bivalves and gastropods. The two species of Sevillia , on the other are in dark-gray shales of the Formation, interdistributary bay they occur with large numbers of and bivalves.","PeriodicalId":224165,"journal":{"name":"Geology of the Taos Region","volume":"69 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":"114144116","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":"Unconformable and cross-cutting relationships indicate major Precambrian faulting on the Picuris-Pecos Fault System, Southern Sangre de Cristo Mountains, New Mexico","authors":"S. Fankhauser, E. Erslev","doi":"10.56577/ffc-55.206","DOIUrl":"https://doi.org/10.56577/ffc-55.206","url":null,"abstract":"A .—What is the age of the Picuris-Pecos fault system? Its 37 km dextral separation of Precambrian lithologic belts makes it the largest well-documented strike-slip system in the southern Rocky Mountains. Numerous studies focusing on regional stratigraphic relationships, basin geometries and structural patterns have variously assigned the major strike slip on the Picuris-Pecos fault system to Precambrian, Ancestral Rocky Mountain, and Laramide orogenies. New field and petrographic observations were collected from the southern Picuris-Pecos fault system in the southern Sangre de Cristo Mountains. In Deer Creek Canyon, an exceptionally broad and resistant zone of brecciated granitic gneiss is exposed adjacent to folded, but not brecciated, Paleozoic limestones and siliciclastic rocks. The induration of the crush breccias and protocataclasites along with their microcline + chlorite +/- biotite assemblages and lack of void space fillings suggest that brecciation occurred during Precambrian low-grade metamorphic conditions near the brittle-ductile transition. Phanerozoic deformation appears to be dominated by narrow zones of unconsolidated fault gouge cutting the crystalline rocks and associ ated folding of the Paleozoic strata. In addition, easily excavated shales and weathered granitic grus showing cataclastic breccia textures are locally exposed between crystalline breccias and overlying, minimally-deformed Mississippian and Pennsylvanian limestones. These apparent erosional nonconformities indicate that major brecciation occurred prior to the late Paleozoic. Furthermore, two northwest-striking bands of Mississippian limestone, 24 and 10 meters in length respectively, crosscut both the brecciated rocks and the overall trend of the Picuris-Pecos fault system. Compositional, faunal and textural similarities between several carbonate bands and the lowermost Mississippian carbonate rocks indicate that they are penecontemporaneous clastic dikes injected from above into coherent Precambrian crystalline breccias. If the spectacular breccias in Deer Creek Canyon are related to the dextral strike-slip displacements along the Picuris Pecos fault system, then these displacements are Precambrian, not Phanerozoic. This conclusion contradicts hypotheses invoking large dextral strike-slip displacements on north-striking faults during both Laramide and Ancestral Rocky Mountain orogenies and reopens the possibility of major Proterozoic dextral strike-slip faulting in the southern Rocky Mountains.","PeriodicalId":224165,"journal":{"name":"Geology of the Taos Region","volume":"13 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":"116208218","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}