Geology of the Four Corners Country最新文献

{"title":"The lower and upper contacts of the Upper Jurassic Bluff Sandstone Member of the Morrison Formation in southeastern Utah","authors":"R. B. O'Sullivan","doi":"10.56577/ffc-61.101","DOIUrl":"https://doi.org/10.56577/ffc-61.101","url":null,"abstract":"An eolian sandstone, about 92 m thick, forms cliffs around the town of Bluff, Utah. The unit includes what has been termed the Bluff Sandstone Member of the Upper Jurassic Morrison Formation, but its base has been placed at 6 different levels within a stratigraphic interval of about 39 m by various geologists. This has led to much uncertainty as to where the contact with the underlying Middle Jurassic Wanakah Formation is best defined. The top of the member has also been placed at 2 different stratigraphic levels, about 24 m apart.","PeriodicalId":283482,"journal":{"name":"Geology of the Four Corners Country","volume":"4 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":"115606163","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":"New interpretations of alluvial and paleo-vegetation records from Chaco Canyon, New Mexico","authors":"","doi":"10.56577/ffc-61.231","DOIUrl":"https://doi.org/10.56577/ffc-61.231","url":null,"abstract":"A BSTRACT — The alluvial stratigraphy, vegetation history, and paleoecology of Chaco Canyon are re-evaluated. The alluvial units are Fajada (middle-late Pleistocene), Pre-Gallo (undated), Gallo (6.7 to 2.8 ka), Chaco (2.1 to 1.0 ka), and Bonito (0.8 to 0.1 ka). A new alluvial unit, Pre-Gallo, is a small erosional remnant that may be late Pleistocene or early Holocene in age. The hot-dry climate of the mid-Holocene and accompanying low stream flow resulted in the accumulation of local sand in the canyon, forming the Gallo unit. A shift to less arid climate by 2.5 ka and increased stream flow flushed out much of the Gallo sand. Greater stream flow throughout the drainage basin resulted in clay overbank deposition across the canyon floor, forming the Chaco unit. The canyon floor provided a habitat for a molluscan fauna consisting of two freshwater snails and six terrestrial snails. The end of the accumulation of the Chaco unit occurred ca. 1.0 ka with a shift in climate to dry conditions and the downcutting of the Bonito channel. The Bonito channel was filling by ca. 0.8 ka, based on buried potsherds. The vegetation of the Chaco area has been a desert-shrub grassland since the end of the Pleistocene. Within that framework, a pinyon-juniper woodland thrived on sandstone substrates during the late Pleistocene-early Holocene. However, mid-Holocene aridity led to the demise of the woodlands, leaving behind a few individuals of pinyon pine and juniper on sandstone escarpments. Reduced rainfall, high evaporation, and increased soil alkalinity promoted the expansion of chenopod shrubs during the mid-Holocene. Moister conditions by 2.5 ka resulted in a reduction in chenopod shrubs and expansion of pinyon pine and juniper in isolated stands on local escarpments and in higher areas of sandy soils within the desert shrub grassland, similar to present-day vegetation patterns. Slight shifts in regional climate after ca. 1.0 ka to dry then wet conditions, while significant to fluvial geomorphology, does not show up in the local vegetation record.","PeriodicalId":283482,"journal":{"name":"Geology of the Four Corners Country","volume":"6 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":"131414466","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":"Stratigraphic nomenclature of rock strata adjacent to the Cretaceous-Tertiary interface in the San Juan Basin","authors":"J. Fassett","doi":"10.56577/ffc-61.113","DOIUrl":"https://doi.org/10.56577/ffc-61.113","url":null,"abstract":"During the last two decades, several changes in the stratigraphic nomenclature of rocks adjacent to the CretaceousPaleogene (K-T) boundary in the San Juan Basin have been recommended. All of these changes have been suggested by vertebrate paleontologists working in limited areas (those containing vertebrate fossils) in the southern part of the San Juan Basin. Because of their provincial view of the formations under discussion and a clear lack of understanding of the North American Stratigraphic Code, these geologists’ suggested stratigraphic changes do not stand close scrutiny and are thus rejected. Suggested deletion of the lithic component of two formations: the Ojo Alamo Sandstone of Paleocene age, and the Upper Cretaceous Farmington Sandstone Member of the Kirtland Formation is rejected. Recommendations were to eliminate the word “Sandstone” from the names of these two rock units and substitute the word “Formation” in their stead. Because these rock units are characterized by their sandstone components, the use of the word Sandstone in both instances is in accordance with the Stratigraphic Code and thus no change in nomenclature is warranted. It has been suggested that the Ojo Alamo Sandstone be divided into two members in the southwest part of the San Juan Basin; the Naashoibito and Kimbeto Members, and only consist of one member in the southeast part of the basin. No lithologic criteria have been established for a two-member Ojo Alamo in the southwest part of the basin, thus this subdivision is rejected. Moreover, the suggestion that the Ojo Alamo consists of a single member in the southeast part of the basin is contrary to the Stratigraphic Code. A formation cannot consist of a single member. It has been recommended that the long established names for subdivisions of the Kirtland Formation: lower shale member, Farmington Sandstone Member, and upper shale member, be changed to the Hunter Wash Member, Farmington Sandstone Member, and the De-na-zin Member, respectively. Because these new names apply to exactly the same lithologic intervals as the old names, there is no valid reason to change the old names that had been in print in various media for 76 years, prior to these suggested name changes. The Stratigraphic Code rejects frivolous changes to long-established nomenclature, therefore, these name changes are rejected. Furthermore, the Hunter Wash name has been previously applied to other rocks in this stratigraphic section in this same area, thus the use of the name “Hunter Wash” for the lower member of the Kirtland Formation has been preempted and is thus improper. It has been suggested that a sandstone bed named the Bisti Bed marks the base of the Kirtland Formation throughout the San Juan Basin. This implies that the Bisti Bed can be traced continuously throughout the San Juan Basin. It is abundantly clear that no such bed exists in the lower Kirtland Formation throughout the basin. Random fluvial channel-sandstone beds occur sporadical","PeriodicalId":283482,"journal":{"name":"Geology of the Four Corners Country","volume":"3 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":"114334710","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":"New insight into the timing and history of diatreme-dike complexes of the northeastern Navajo volcanic fiedl, southwestern Colorado","authors":"D. Gonzales, B. Turner, R. Burgess, C. Holnback, M. Critchley","doi":"10.56577/ffc-61.163","DOIUrl":"https://doi.org/10.56577/ffc-61.163","url":null,"abstract":"The northern extent of the Navajo volcanic field (NVF) is defined by several diatreme complexes that evolved from swarms of north-northeast-trending mafic dikes exposed near Mesa Verde National Park (MVNP). Field evidence indicates that the eruptive phases were generated by multi-stage degassing and fluidization of mantle magmas. This produced diatreme buds that developed along dikes, lateral eruptions that scoured and were injected into adjacent sedimentary strata, and the formation of dome-shaped blind diatremes. New 40Ar/39Ar age constraints on mafic dikes exposed near MVNP indicate a time of emplacement of ~24 Ma, within the accepted age range of magmatism for the NVF. Swarms of mafic dikes with similar composition to NVF rocks are exposed as far north as Placerville, approximately 75 kilometers north of MVNP. Mafic dikes exposed near Mt. Wilson yield a 40Ar/39Ar age of ~7 Ma. The younger dikes are either part of NVF magmatism or another distinct period of potassic magmatism in the region. Oligocene to Miocene mafic dikes exposed from MVNP to Placerville are potassic to ultrapotassic alkaline basalts to basaltic andesites with mineral associations that are similar to those found in minette dikes in other parts of the Navajo volcanic field. All of these rocks have chemical affinities that are consistent with partial melting of metasomatized lithospheric mantle with possible minor contributions from other mantle sources. The protracted period of Oligocene to Miocene potassic magmatism in southwestern Colorado makes up part of mantle magmatism that led to the emplacement of mafic-dike swarms across the northern margin of the San Juan basin after 30 Ma. The dominant north-to-northeast trends of these dike swarms lend evidence for incipient west to northwest rifting in southwestern Colorado that is aligned with a regional zone of crustal anisotropy (Colorado Mineral belt), and high heat flow related partial melting in the mantle (the Aspen anomaly). Regional extension and influx of mantle magmas into the crust in southwestern Colorado in the Middle to Late Tertiary were a probable catalyst to crustal melting in the adjacent San Juan volcanic field, and potassic mantle magmas in particular may have made an important contribution to the production of these crustal magmas.","PeriodicalId":283482,"journal":{"name":"Geology of the Four Corners Country","volume":"28 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":"114809777","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 engimatic Late Cretaceous mcDermott Formation","authors":"D. Gonzales","doi":"10.56577/ffc-61.157","DOIUrl":"https://doi.org/10.56577/ffc-61.157","url":null,"abstract":"The Late Cretaceous McDermott Formation is a distinctive maroon to purple unit that is exposed on the northwestern margin of the San Juan Basin. Previous workers have argued that this unit is composed of volcaniclastic deposits that were derived from a volcanic complex in the vicinity of the La Plata Mountains. There is no evidence for any volcanic features or events associated with the intrusive complex in the La Plata Mountains, and definitive field and petrologic evidence for volcanic deposits within the McDermott Formation has not been documented. The igneous material in the McDermott Formation is dominated by pebbleto boulder-sized fragments of diorite and monzonite that are similar to intrusive rocks exposed in the La Plata Mountains laccolithic complex. The deposits in the McDermott Formation mostly fine upward, and were deposited as debris flows and hyperconcentrated flows along with minor dilute stream flows. An alternative hypothesis for the origin of this controversial unit is that dome collapse of the La Plata Mountains intrusive complex was created by magmatic inflation and roof-flank detachment creating gravity slides that were remobilized by streams flowing to the south and southeast. Reduction in lithostatic pressure may have also allowed for sudden release of pressure on the underlying magma body which could have produced minor volcanic-flank eruptions. This model is consistent with the dominant type of igneous material in the unit, and the fluvial-dominated systems that are preserved in these rocks.","PeriodicalId":283482,"journal":{"name":"Geology of the Four Corners Country","volume":"101 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":"133927565","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":"Implications of U-Pb ages of detrital zircons in Mesozoic strata of the Four Corners region for provenance relations in space and time","authors":"W. Dickinson, G. Gehrels","doi":"10.56577/ffc-61.135","DOIUrl":"https://doi.org/10.56577/ffc-61.135","url":null,"abstract":"U-Pb ages for individual detrital zircons in sandstone record the ages of igneous source rocks in which zircon and accompanying quartz crystals formed because zircon U-Pb ages are not reset by either sedimentary or diagenetic processes. Ages of detrital zircons reflect ultimate sand sources in basement rocks but allowance must be made in provenance interpretations for potential recycling of resistant zircon grains from more proximate sources in sedimentary assemblages. Our database for Mesozoic strata in the Four Corners region includes 2213 concordant or nearly concordant U-Pb ages of detrital zircons from 24 samples (Triassic to Cretaceous). Chinle channel sands were derived largely from the Ouachita orogen where uplifted on the northern shoulder of the pre-Gulf of Mexico rift system, from which Ouachita-derived sand was carried westward by paleoriver systems ~1500 km long with headwaters in the Ouachita foreland. Southern tributaries of central Chinle paleorivers contributed detritus from Precambrian basement and the Cordilleran magmatic arc lying south of the Colorado Plateau. Eolian dune sands of Glen Canyon and San Rafael ergs were derived largely from pre-Atlantic rift highlands along the Appalachian belt, transported to deltas or floodplains in the northern Rocky Mountains region by a transcontinental paleoriver system ~2000 km long carrying Appalachian-derived sediment, and delivered southward to the Colorado Plateau ergs by the paleowinds recorded by dune crossbedding. Salt Wash (Morrison) and Burro Canyon (including Jackpile) fluvial sands were largely reworked from older Jurassic eolianites forming sedimentary cover over the Mogollon paleohighlands, but Westwater Canyon (Morrison), Cretaceous (Toreva-Gallup-Menefee ) fluvial and fluviodeltaic sands contain prominent components of detrital zircon derived from Proterozoic Mogollon basement and its sedimentary cover, and from the Mesozoic Cordilleran magmatic arc lying still farther south.","PeriodicalId":283482,"journal":{"name":"Geology of the Four Corners Country","volume":"45 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":"129605004","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":"Gemstone deposits of the Four Corners region, USA","authors":"R. Eveleth, V. Lueth","doi":"10.56577/ffc-61.221","DOIUrl":"https://doi.org/10.56577/ffc-61.221","url":null,"abstract":"— Collecting of gem olivine (peridot), pyrope garnet, and chrome diopside has occurred in the four corners region prior to the arrival of Europeans and probably long before. These gemstones are derived from lower crustal and mantle xeno-liths entrained in the volcanic necks and tuffs of the Navajo Volcanic Field. Subsequent weathering has liberated these minerals from their matrices leaving residual deposits of gemstones. Another concentration mechanism for these gems is reworking by ants and subsequent accumulations on their hills. Although these stones have been gathered, traded, or sold around the south-west for over 500 hundred years, perhaps longer, commerical mining is not likely given cultural prohibitions and low volume of commerical material.","PeriodicalId":283482,"journal":{"name":"Geology of the Four Corners Country","volume":"4 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":"117228951","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":"Detrital zircon evidence for derivation of arkosic sand in the eolilan Narbona Pass Member of the Eocene-Oligocene Chuska Sandstone from Precambrian basement rocks in central Arizona","authors":"W. Dickinson, S. Cather, G. Gehrels, K. Zeigler","doi":"10.56577/ffc-61.125","DOIUrl":"https://doi.org/10.56577/ffc-61.125","url":null,"abstract":"The Narbona Pass Member of the Chuska Sandstone, exposed only along the crest of the Chuska Mountains (Arizona–New Mexico), is the central remnant of the Oligocene Chuska erg, which is inferred to have occupied ~125,000 km2 of the southeastern Colorado Plateau within a subcircular area surrounded by Oligocene volcanic fields. The high paleotopography of active volcanic edifices delimited the lateral extent of erg deposition except to the west, which was upwind for eolian sand transport. The dominant arkosic petrofacies of the Narbona Pass Member, as exposed at Narbona Pass near Crystal (NM) and at Buffalo Pass near Lukachukai (AZ), was derived mainly from Precambrian basement in central Arizona. The principal subpopulations of detrital zircons (n=100 grains) by U-Pb age are 1770-1640 Ma (~70% with age peak at 1700 Ma), reflecting derivation from the Yavapai-Mazatzal belt of southwest Laurentia, and 1460-1400 Ma (~15% with age peak at 1425 Ma) derived from anorogenic granite bodies intrusive into Yavapai-Mazatzal basement. Precambrian detritus was apparently carried northward to alluvial plains deposited west of the Chuska erg and deflated to feed sand into the erg interior. Other remnants of the Chuska erg along the northern flank of the Mogollon-Datil volcanic field, in the subsurface of the Albuquerque basin of the Rio Grande rift, and near Whiskey Lake in the southernmost Chuska Mountains are petrographically distinct from the arkosic petrofacies of the erg interior, and were evidently derived from other sources as yet untested by detrital zircons. The areal variability of erg sand implies either different pathways for sand transport across the expanse of an integrated Chuska erg or segmentation of the Chuska erg into multiple subdivisions that were partly separated by inselbergs of the pre-Oligocene erg substratum.","PeriodicalId":283482,"journal":{"name":"Geology of the Four Corners Country","volume":"51 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":"114306557","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":"Geology of the southern San Juan Basin - Third day road log from Farmington south to the Bisti Badlands and east to Barrel Spring locality","authors":"J. Fassett","doi":"10.56577/ffc-61.55","DOIUrl":"https://doi.org/10.56577/ffc-61.55","url":null,"abstract":"","PeriodicalId":283482,"journal":{"name":"Geology of the Four Corners Country","volume":"2 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":"134140887","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":"Correlation of the upper part of the Middle Jurassic San Rafael Group in northeast Arizona, northwest New Mexico, and southeast Utah","authors":"R. B. O'Sullivan","doi":"10.56577/ffc-61.91","DOIUrl":"https://doi.org/10.56577/ffc-61.91","url":null,"abstract":"In east-central Utah, the Middle Jurassic San Rafael Group consists, in ascending order, of the Page Sandstone, Carmel Formation, Entrada Sandstone, Curtis Formation, and Summerville Formation, with a combined thickness of about 365 m. In northwestern New Mexico, the sequence, only about 80 m thick, consists of the Entrada Sandstone overlain by the Wanakah Formation the basal part of which is the distinctive Todilto Limestone Member. The San Rafael Group includes a mixture of terrestrial, marine, and marginal marine deposits. An unconformity, termed “J-3”, underlies the Curtis Formation and can be traced into northwestern New Mexico where it lies near the middle of the Wanakah Formation. Previously, the Curtis Formation had been correlated with the Todilto Limestone Member. However, the Todilto lies beneath the J-3 unconformity and is separated from it by about 20 m of strata. All of the Summerville Formation is truncated by another unconformity, termed “J-5”, in east-central Utah, and the formation does not extend into New Mexico and adjacent areas.","PeriodicalId":283482,"journal":{"name":"Geology of the Four Corners Country","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":"125517579","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}