Pub Date : 1987-07-01DOI: 10.31582/rmag.mg.24.3.55
S. Mattox, M. Weiss
Recent work in central Utah has outlined the broader features of the area's thrust geometry. Although individual interpretations differ, most models indicate the region is similar to better understood segments of the Cordilleran thrust belt. Poor and limited seismic data and the paucity of drill-hole information has hindered the investigation of the south- west quadrant of the Gunnison Plateau. Detailed surface mapping of a centrally located quadrangle has provided strati- graphic evidence for a previously unrecognized Cretaceous-Paleocene thrust fault. The present expression of the thrust surface requires reactivation with a reverse sense of motion during Tertiary extension. Drastic facies changes in the Late Cretaceous-Early Paleocene North Horn Formation occur over a short distance - essentially across a fault. The gray, eastern lithofacies is dominated by massive conglomerate, sandstone, and oncolitic limestone. Maximum thickness is 253 m (830 ft). Clast composition indicates a local source/positive area of Cretaceous lndianola Group. The thinner 38 m (126 ft), red, western lithofacies consists of pebbly sandstone, sandstone, and mudstone. Reddish brown mudstones and intrac lasts suggest red beds, possibly the Cretaceous Cedar Mountain Formation and/or the Jurassic Twist Gulch Formation and Arapien Shale, as a primary source. After careful consideration of several hypotheses, the only valid conclusion seems to be the presence of thrusted Indianola, creating a topo- graphic barrier between the two separate and unique basins. Two major structural features can be traced to the north, an area of better seismic and drill-hole data. The southern terminus of the Wasatch fault zone, has been interpreted by numerous investigators as eithera reactivated Cretaceous thrust (with a reverse sense of motion) or a high-angle planar Tertiary normal fault. The Escarpment fault, the eastern boundary of a Basin and Range graben, has also been presented in both configurations (listric or high-angle planar). No observations were made to support a listric geometry for the Fayette fault. The Escarpment fault, however, appears to have been active during North Horn time, thrusting lndianola conglomerate into a topographic/structural high. The upper plate underwent a reversed sense of motion in the Tertiary to create the present Chriss/Mellor graben.
{"title":"Reactivation of a Cretaceous Thrust Surface by Basin-and-Range Extension, Southwestern Gunnison Plateau, Central Utah","authors":"S. Mattox, M. Weiss","doi":"10.31582/rmag.mg.24.3.55","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.3.55","url":null,"abstract":"Recent work in central Utah has outlined the broader features of the area's thrust geometry. Although individual interpretations differ, most models indicate the region is similar to better understood segments of the Cordilleran thrust belt. Poor and limited seismic data and the paucity of drill-hole information has hindered the investigation of the south- west quadrant of the Gunnison Plateau. Detailed surface mapping of a centrally located quadrangle has provided strati- graphic evidence for a previously unrecognized Cretaceous-Paleocene thrust fault. The present expression of the thrust surface requires reactivation with a reverse sense of motion during Tertiary extension. Drastic facies changes in the Late Cretaceous-Early Paleocene North Horn Formation occur over a short distance - essentially across a fault. The gray, eastern lithofacies is dominated by massive conglomerate, sandstone, and oncolitic limestone. Maximum thickness is 253 m (830 ft). Clast composition indicates a local source/positive area of Cretaceous lndianola Group. The thinner 38 m (126 ft), red, western lithofacies consists of pebbly sandstone, sandstone, and mudstone. Reddish brown mudstones and intrac lasts suggest red beds, possibly the Cretaceous Cedar Mountain Formation and/or the Jurassic Twist Gulch Formation and Arapien Shale, as a primary source. After careful consideration of several hypotheses, the only valid conclusion seems to be the presence of thrusted Indianola, creating a topo- graphic barrier between the two separate and unique basins. Two major structural features can be traced to the north, an area of better seismic and drill-hole data. The southern terminus of the Wasatch fault zone, has been interpreted by numerous investigators as eithera reactivated Cretaceous thrust (with a reverse sense of motion) or a high-angle planar Tertiary normal fault. The Escarpment fault, the eastern boundary of a Basin and Range graben, has also been presented in both configurations (listric or high-angle planar). No observations were made to support a listric geometry for the Fayette fault. The Escarpment fault, however, appears to have been active during North Horn time, thrusting lndianola conglomerate into a topographic/structural high. The upper plate underwent a reversed sense of motion in the Tertiary to create the present Chriss/Mellor graben.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1987-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122333491","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}
Pub Date : 1987-04-01DOI: 10.31582/rmag.mg.24.2.33
T. Ahlbrandt, W. Groen
The Goshen Hole uplift 1s a little recognized and sparsely explored feature in the northern end of the Denver Julesburg basin We believe there is excellent hydrocarbon potential on the uplift principally In Cretaceous (Hygiene, Niobrara, Wall Creek, Muddy, Dakota). Jurassic (Canyon Springs), Permian and Pennsylvanian objectives. There are diverse stratigraphic anomalres observed on seismic data in these horizons as well as numerous paleo structures. Basement tests are approximately in the 10.000 to 11,000 ft (3.048 - 3.353 m) range. The uplift has had recurrent movement since the Pennsylvanian; however a period of uplifting occurred in the Upper Cretaceous beginning by at least early Campanian time with intermit- tent uplift rn the Cenozoic. There are numerous subsurface shows and source beds in Paleozoic and Mesozoic horizons and oil seeps on the uplift which enhance the exploitations potential of this area
Goshen Hole凸起是Denver Julesburg盆地北端一个鲜为人知且勘探较少的特征，我们认为主要在白垩纪凸起(Hygiene, Niobrara, Wall Creek, Muddy, Dakota)具有良好的油气潜力。侏罗纪(峡谷泉)，二叠纪和宾夕法尼亚目标。在这些层位的地震资料中发现了各种各样的地层异常和大量的古构造。地下室测试大约在10,000至11,000英尺(3.048 - 3.353米)范围内。自宾夕法尼亚纪以来，隆起反复运动;然而，至少在坎帕纪早期开始的上白垩世出现了一段隆升期，并在新生代出现了间歇性隆升。区内古生界和中生界有大量的地下展露和烃源层，隆起处有大量的原油渗漏，提高了该区的开发潜力
{"title":"The Goshen Hole Uplift: A Brief Review of its History and Exploration Potential","authors":"T. Ahlbrandt, W. Groen","doi":"10.31582/rmag.mg.24.2.33","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.2.33","url":null,"abstract":"The Goshen Hole uplift 1s a little recognized and sparsely explored feature in the northern end of the Denver Julesburg basin We believe there is excellent hydrocarbon potential on the uplift principally In Cretaceous (Hygiene, Niobrara, Wall Creek, Muddy, Dakota). Jurassic (Canyon Springs), Permian and Pennsylvanian objectives. There are diverse stratigraphic anomalres observed on seismic data in these horizons as well as numerous paleo structures. Basement tests are approximately in the 10.000 to 11,000 ft (3.048 - 3.353 m) range. The uplift has had recurrent movement since the Pennsylvanian; however a period of uplifting occurred in the Upper Cretaceous beginning by at least early Campanian time with intermit- tent uplift rn the Cenozoic. There are numerous subsurface shows and source beds in Paleozoic and Mesozoic horizons and oil seeps on the uplift which enhance the exploitations potential of this area","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1987-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122422126","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}
Pub Date : 1987-04-01DOI: 10.31582/rmag.mg.24.2.44
W. W. Locke
One of the greatest needs in Quaternary stratigraphy is for information regarding subsurface units and the relations between them Low-energy (hammer) seismic surveying has the potential to provide that information inexpensively and unobtrusively In reconnaissance studies m Rocky Mountain National Park, Colorado, the Pinedale and Bull Lake tills, colluvium, alluvium, and weathered and fresh bedrock can be differentiated m the shallow subsurface (30 m) by this method Seismic velocities with units are constant *5%, and are generally constant _+ 10% for deposits present at several localities The ability of the method to discriminate among unconsolidated sediments of various ages and origins suggests that rt has potential for pedologic, geomorphic, and environmental applications
{"title":"Low-Energy Seismic Survey of Quaternary Materials, Rocky Mountain National Park, Colorado","authors":"W. W. Locke","doi":"10.31582/rmag.mg.24.2.44","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.2.44","url":null,"abstract":"One of the greatest needs in Quaternary stratigraphy is for information regarding subsurface units and the relations between them Low-energy (hammer) seismic surveying has the potential to provide that information inexpensively and unobtrusively In reconnaissance studies m Rocky Mountain National Park, Colorado, the Pinedale and Bull Lake tills, colluvium, alluvium, and weathered and fresh bedrock can be differentiated m the shallow subsurface (30 m) by this method Seismic velocities with units are constant *5%, and are generally constant _+ 10% for deposits present at several localities The ability of the method to discriminate among unconsolidated sediments of various ages and origins suggests that rt has potential for pedologic, geomorphic, and environmental applications","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1987-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128086546","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}
Pub Date : 1987-04-01DOI: 10.31582/rmag.mg.24.2.30
P. Hennings, J. Sprang
The geometry of the uppper basement surface displacement field in structures uplrfted by reverse faults can be used to predlct fault surface geometry at depth A method a described that uses sllp lmes whlch define the motion of the uplifted basement block and assumes that faults are curved and become parallel to the reg~onal basement surface beyond the lateral extent of the associated rotated block The method assumes constant shortening mth depth, 1s a "balanced" base- ment model, and provldes an estimate of the amount of horlzontal shortening. The method 1s applled to an example struc- ture ln the northeastern Blghorn Mountam, Wommng
{"title":"A Method for Estimating Fault Geometry from Rotated Basement Blocks Using Slip Lines","authors":"P. Hennings, J. Sprang","doi":"10.31582/rmag.mg.24.2.30","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.2.30","url":null,"abstract":"The geometry of the uppper basement surface displacement field in structures uplrfted by reverse faults can be used to predlct fault surface geometry at depth A method a described that uses sllp lmes whlch define the motion of the uplifted basement block and assumes that faults are curved and become parallel to the reg~onal basement surface beyond the lateral extent of the associated rotated block The method assumes constant shortening mth depth, 1s a \"balanced\" base- ment model, and provldes an estimate of the amount of horlzontal shortening. The method 1s applled to an example struc- ture ln the northeastern Blghorn Mountam, Wommng","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1987-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124431006","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}
Pub Date : 1987-04-01DOI: 10.31582/rmag.mg.24.2.50
D. S. Collins, T. C. Nichols
A knowledge of past overburden thickness is useful for designing underground structures such as waste repositories. This study attempts to determine d a correlation can be made between a geologic estimate and two types of geotechnical calculations of past overburden thickness. i%r the PierreHayes, South Dakota area, we have found that of the hw geotechnical determinations, the in-situ pressuremeter is better than the laboratory consolidation determination as an indicator of past overburden thickness. In the PierreHayes area, Late Cretaceous Pierre Shale is the only bedrock present, but clasts of the Miocene Ogallala Formation were found in the Pleistocene deposits, suggesting that rocks of the Ogallala Formation once covered this area Based on the geologic estimate, the Ogallala surface was 1,100 fl higher than the present surface. Of the two types of geotechnical data acquired for the Hayes site, the laboratory over consolidation ratios indicate a past overburden thickness value of 2,300 fl, whereas the in-situ pressuremeter over consolidation ratios indicate 1,318 IY. We, therefore, believe that in-situ determination is a better indicator of past overburden that the laboratory results. However why the two test results dir7er to this degree is unknown at present.
{"title":"Comparing Geotechnical to Geologic Estimates for Past Overburden in the Pierre-Hayes, South Dakota Area: An Argument for In-situ Pressuremeter Determination","authors":"D. S. Collins, T. C. Nichols","doi":"10.31582/rmag.mg.24.2.50","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.2.50","url":null,"abstract":"A knowledge of past overburden thickness is useful for designing underground structures such as waste repositories. This study attempts to determine d a correlation can be made between a geologic estimate and two types of geotechnical calculations of past overburden thickness. i%r the PierreHayes, South Dakota area, we have found that of the hw geotechnical determinations, the in-situ pressuremeter is better than the laboratory consolidation determination as an indicator of past overburden thickness. In the PierreHayes area, Late Cretaceous Pierre Shale is the only bedrock present, but clasts of the Miocene Ogallala Formation were found in the Pleistocene deposits, suggesting that rocks of the Ogallala Formation once covered this area Based on the geologic estimate, the Ogallala surface was 1,100 fl higher than the present surface. Of the two types of geotechnical data acquired for the Hayes site, the laboratory over consolidation ratios indicate a past overburden thickness value of 2,300 fl, whereas the in-situ pressuremeter over consolidation ratios indicate 1,318 IY. We, therefore, believe that in-situ determination is a better indicator of past overburden that the laboratory results. However why the two test results dir7er to this degree is unknown at present.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1987-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132387375","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}
Pub Date : 1987-01-01DOI: 10.31582/rmag.mg.24.1.26
R. Nusbaum, S. Gant
Variable degrees of widespread alkali metasomatism have been detected within Wah Wah Springs Tuff samples collected in southwestern Utah. Highly altered samples show (1) strong periodic enrichment trends for alkali metals (except Na) at the expense of alkaline earth elements (except Ba), and (2) complete to partial replacement of andesine phenocrysts by K-feldspar: Mildly altered samples show (1) similar but less extreme enrichments and depletions compared to highly altered samples, and (2) no megascopic evidence of alteration. Cs is the most sensitive of the elements enriched by the alteration, followed by Rb and K20. Greater tendency toward fixation of heavy alkalis at low temperatures accompanying the addition of K-feldspar and the reduction of andesine explains. relative alteration trends. The lack of prvximal mineralization and widespread nature of alkali metasomatism associated with minor pmpylitic alteration suggests fossil geothermal activity in this part of Utah.
{"title":"Alkali Metasomatism and Fossil Geothermal Activity: Wah Wah Springs Tuff, Utah","authors":"R. Nusbaum, S. Gant","doi":"10.31582/rmag.mg.24.1.26","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.1.26","url":null,"abstract":"Variable degrees of widespread alkali metasomatism have been detected within Wah Wah Springs Tuff samples collected in southwestern Utah. Highly altered samples show (1) strong periodic enrichment trends for alkali metals (except Na) at the expense of alkaline earth elements (except Ba), and (2) complete to partial replacement of andesine phenocrysts by K-feldspar: Mildly altered samples show (1) similar but less extreme enrichments and depletions compared to highly altered samples, and (2) no megascopic evidence of alteration. Cs is the most sensitive of the elements enriched by the alteration, followed by Rb and K20. Greater tendency toward fixation of heavy alkalis at low temperatures accompanying the addition of K-feldspar and the reduction of andesine explains. relative alteration trends. The lack of prvximal mineralization and widespread nature of alkali metasomatism associated with minor pmpylitic alteration suggests fossil geothermal activity in this part of Utah.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115192377","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}
Pub Date : 1987-01-01DOI: 10.31582/rmag.mg.24.1.10
R. Perman
The Dad Sandstone Member is a progmding unit of sandstone and minor mudstone that sepamtes upper and lower shale members of the Lewis Shale. Outcrops of this Maestrichtian-age unit have been examined in southcentml W)vming along the eastern margin of the Great Divide basin north of Rawlins, and in the Hanna basin to the east. These outcmps form two groups with very different chamcteristics, including thickness of sendstone and interbedded mudstone units, sedimen- tary structures, and fossils. In the western part of the area studied, the Dad Sandstone is interpreted to represent progmda- tion in the lower delta-fmnt reglon of the Sheridan delta that existed to the northwest. In the eastern portion of the study area the Dad Sandstone probably represents upper shorefece iacies of interdistributary barrier bars. These deposits mey be related to either the Sheridan delta to the north, or a north-trending uplift to the south. The Dad Sendstone in the eastern part of the study area is probably slightly younger than In the western part of the study area.
{"title":"Deltaic Deposits of the Upper Cretaceous Dad Sandstone Member of the Lewis Shale, South-Central Wyoming","authors":"R. Perman","doi":"10.31582/rmag.mg.24.1.10","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.1.10","url":null,"abstract":"The Dad Sandstone Member is a progmding unit of sandstone and minor mudstone that sepamtes upper and lower shale members of the Lewis Shale. Outcrops of this Maestrichtian-age unit have been examined in southcentml W)vming along the eastern margin of the Great Divide basin north of Rawlins, and in the Hanna basin to the east. These outcmps form two groups with very different chamcteristics, including thickness of sendstone and interbedded mudstone units, sedimen- tary structures, and fossils. In the western part of the area studied, the Dad Sandstone is interpreted to represent progmda- tion in the lower delta-fmnt reglon of the Sheridan delta that existed to the northwest. In the eastern portion of the study area the Dad Sandstone probably represents upper shorefece iacies of interdistributary barrier bars. These deposits mey be related to either the Sheridan delta to the north, or a north-trending uplift to the south. The Dad Sendstone in the eastern part of the study area is probably slightly younger than In the western part of the study area.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134265545","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 Late Tnassic Higham Gnt m southeastern ldaho and western H$aming IS comprised pmdommantly of coarse to medrum- grarned sandstone and pebble conglomerate wrth mrnor mudstone Lithofacies present include: Massive to crudely horizon- tally bedded pebbly conglomerate (Gm), trough crossbedded sandstone (St), planar crossbedded sandstone (Sp), horizon- tally stratified sandstone (Sh), ripple crosslaminated sandstone (Sr), and finely laminated sandstone and mudstone (FI). Deposition occurredm a South Saskatchewan/Platte River-type braided fluvialcomplex wrth the development of longitudinal bars and gravel lags (Gm), straightcrested transverse bars (Sp), and sinuouscrested transverse bars and dunes (St). Perrodic, high-velocity flow resulted m development of upper flow regime plane beds (Sh). Minor episodes of flood plain rnundation produced werbank deposits (FI). Application of the South Saskatchewan and Platte River brarded stream models to the Higham Gnt is m good agreement with provenance studres (Schmitt and Hazen, in preparation) which postulate a sediment source area in the Ancestral Rocky Mountains uplift, a distance of 500-700 km to the southeast Sediment transport distances in both the South Saskatchewan and Platte braided fluvial systems closely approximate this distance.
{"title":"Sedimentation of the Late Triassic Higham Grit in a South SaskatchewanlPlatte River-Type Braided Stream Complex, Southeastern ldaho and Western Wyoming","authors":"J. Schmitt, D. R. Hazen","doi":"10.31582/rmag.mg.24.1.1","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.1.1","url":null,"abstract":"The Late Tnassic Higham Gnt m southeastern ldaho and western H$aming IS comprised pmdommantly of coarse to medrum- grarned sandstone and pebble conglomerate wrth mrnor mudstone Lithofacies present include: Massive to crudely horizon- tally bedded pebbly conglomerate (Gm), trough crossbedded sandstone (St), planar crossbedded sandstone (Sp), horizon- tally stratified sandstone (Sh), ripple crosslaminated sandstone (Sr), and finely laminated sandstone and mudstone (FI). Deposition occurredm a South Saskatchewan/Platte River-type braided fluvialcomplex wrth the development of longitudinal bars and gravel lags (Gm), straightcrested transverse bars (Sp), and sinuouscrested transverse bars and dunes (St). Perrodic, high-velocity flow resulted m development of upper flow regime plane beds (Sh). Minor episodes of flood plain rnundation produced werbank deposits (FI). Application of the South Saskatchewan and Platte River brarded stream models to the Higham Gnt is m good agreement with provenance studres (Schmitt and Hazen, in preparation) which postulate a sediment source area in the Ancestral Rocky Mountains uplift, a distance of 500-700 km to the southeast Sediment transport distances in both the South Saskatchewan and Platte braided fluvial systems closely approximate this distance.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134435006","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}
Faults that cut poorly consolidated debris* deposits on Sen Francisco Mountain, a Pleistocene composite wlcano in northern Arizona, form a complex, branching graben end a broad horst. The faults cen be no older then 0.46 Ma, the maximum age of the debris fan end be no younger than 0.25 Ma, the minimum age of a dach leva flow that cowred the fan's epex end blocked the drelnage of a sheem that dissected the floor ofthe graben. Topographic pmfiles reveal the fault scarps and demonstrate that the fan suhx has been offset by faulting. The displacements probably occumd during reedvation of older north-northeast- end north-northeast-trending structums in the rocks of the southern Colorado Plateau below the wkenlc deposits. The time of faulting is normally constrained in the late Pleistocene; it is the youngest dated faulting event in northcentral Arizona.
{"title":"Geomorphic Evidence for Youngest Dated Faults in North-Central Arizona","authors":"R. Holm","doi":"10.31582/rmag.mg.24.19","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.19","url":null,"abstract":"Faults that cut poorly consolidated debris* deposits on Sen Francisco Mountain, a Pleistocene composite wlcano in northern Arizona, form a complex, branching graben end a broad horst. The faults cen be no older then 0.46 Ma, the maximum age of the debris fan end be no younger than 0.25 Ma, the minimum age of a dach leva flow that cowred the fan's epex end blocked the drelnage of a sheem that dissected the floor ofthe graben. Topographic pmfiles reveal the fault scarps and demonstrate that the fan suhx has been offset by faulting. The displacements probably occumd during reedvation of older north-northeast- end north-northeast-trending structums in the rocks of the southern Colorado Plateau below the wkenlc deposits. The time of faulting is normally constrained in the late Pleistocene; it is the youngest dated faulting event in northcentral Arizona.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1987-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132798395","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}
Pub Date : 1986-10-01DOI: 10.31582/rmag.mg.23.4.113
Carol J. Bibler, J. Schmitt
The Horsethief Formation (upper Campanian) of the Northern Disturbed Belt and western Sweetgrass Arch area of Montana, was deposited along the western margin of the Western Interior Cretaceous Seaway. Investigation of the Horsethief in an area extending northwest of Augusta, Montana and southwest of Choteau, Montana indicates that deposition occurred along a barrier-island coastline. Deposits in the lower part of the Horsethief (Horsethief-Bearpaw Transition Unit) are transgressive in nature whl1e those in the upper part are regressive. Several distinct lithofacies within the Horsethief Formation lend themselves to paleoenvironmental interpretation on the basis of texture, sedimentary structures, paleocurrent indicators, and faunal content. Lower shoreface sediments consist of a thick sequence of interbedded mudstone, siltstone, and horizontally stratified and ripple cross-laminated sandstone. Predominantly trough cross-bedded sandstone with abundant Ophiomorpha characterizes the upper shoreface. Sandstones of the foreshore and backshore are horizontally to subhorizontally bedded. Marsh-tidal flat sediments consist of carbonaceous siltstone, claystone, sandstone and shale; the siltstone and sandstone is commonly ripple cross-laminated. Shoreward-dipping wedge-planar cross-stratification represents deposition within flood-tidal deltas. Horsethief Formation sandstones include: 1) volcarenites, 2) chertarenites, 3) feldspathic volcarenites, and 4) feldspathic chertarenites. Abundance of volcanic rock fragments increases upward in the Horsethief, suggesting that the regressive nature of the Upper Horsethief may be due in part to influx of volcanogenic sediment from the west.
{"title":"Barrier-Island Coastline Deposition and Paleogeographic Implications of the Upper Cretaceous Horsethief Formation, Northern Disturbed Belt, Montana","authors":"Carol J. Bibler, J. Schmitt","doi":"10.31582/rmag.mg.23.4.113","DOIUrl":"https://doi.org/10.31582/rmag.mg.23.4.113","url":null,"abstract":"The Horsethief Formation (upper Campanian) of the Northern Disturbed Belt and western Sweetgrass Arch area of Montana, was deposited along the western margin of the Western Interior Cretaceous Seaway. Investigation of the Horsethief in an area extending northwest of Augusta, Montana and southwest of Choteau, Montana indicates that deposition occurred along a barrier-island coastline. Deposits in the lower part of the Horsethief (Horsethief-Bearpaw Transition Unit) are transgressive in nature whl1e those in the upper part are regressive. Several distinct lithofacies within the Horsethief Formation lend themselves to paleoenvironmental interpretation on the basis of texture, sedimentary structures, paleocurrent indicators, and faunal content. Lower shoreface sediments consist of a thick sequence of interbedded mudstone, siltstone, and horizontally stratified and ripple cross-laminated sandstone. Predominantly trough cross-bedded sandstone with abundant Ophiomorpha characterizes the upper shoreface. Sandstones of the foreshore and backshore are horizontally to subhorizontally bedded. Marsh-tidal flat sediments consist of carbonaceous siltstone, claystone, sandstone and shale; the siltstone and sandstone is commonly ripple cross-laminated. Shoreward-dipping wedge-planar cross-stratification represents deposition within flood-tidal deltas. Horsethief Formation sandstones include: 1) volcarenites, 2) chertarenites, 3) feldspathic volcarenites, and 4) feldspathic chertarenites. Abundance of volcanic rock fragments increases upward in the Horsethief, suggesting that the regressive nature of the Upper Horsethief may be due in part to influx of volcanogenic sediment from the west.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1986-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114023275","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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