Mountain Geologist最新文献

{"title":"Late Paleozoic Yuma Arch, Colorado and Nebraska: Implications for Oil Exploration in Pennsylvanian Carbonate Reservoirs","authors":"J. P. Rogers, M. Longman, W. Pearson, G. Wahlman, R. Kettler, Joseph Walseth, J. Dixon, M. Thomasson","doi":"10.31582/rmag.mg.52.1.5","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.1.5","url":null,"abstract":"The Yuma Arch is herein proposed as a major structural element forming the northeast margin of the Denver Basin. This previously little-recognized regional geological feature has significance in exploration for oil in this area of the basin. It was initially uplifted during the Paleozoic, but is largely masked by late Cretaceous - early Tertiary tectonic events. Limited pre-Cretaceous exploration drilling has not defined the precise location of the axis of the arch, but subsurface studies show that it occupies most of Yuma, Sedgwick and Phillips counties, Colorado, and Deuel County, Nebraska. The immediate west flank of the arch lies in parts of Washington and Logan counties, Colorado, and most significantly in Cheyenne County, Nebraska, where initial Paleozoic exploration has been focused around the discovery of Bird Oil Field in 1982, a small but unique, over-full, domal trap. Preservation of several cores from Pennsylvanian boreholes in Cheyenne County, Nebraska, facilitated study of cyclical Missourian-Virgilian carbonate reservoirs that provide significant future potential objectives for exploration on the underexplored arch. These cores also provided key biostratigraphic data that helped to clarify the correlation of classical Pennsylvanian strata. Studies of Paleozoic source rocks and migration pathways were conducted over the central and northeastern Denver Basin. These studies indicate that the immediate west flank and the crest of the Yuma Arch provide a significant regional catchment for oil in Paleozoic strata, and should be a target for future exploration. Processing and interpretation of aeromagnetic data provided a means to characterize the Precambrian crystalline core of the arch, and to define areas for seismic imaging of mobile basement block margins that appear to have initiated and sustained the growth of low-relief Paleozoic structural traps. This study reinforces the significant decoupling between pre-salt (Precambrian and Pennsylvanian) and post-salt (Cretaceous and Tertiary) geological processes in this area.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128051988","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":"Appendix I: Fusulinid Biostratigraphy of Upper Pennsylvanian Cores from Cheyenne County, Nebraska","authors":"G. Wahlman","doi":"10.31582/rmag.mg.52.1.59","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.1.59","url":null,"abstract":"Other cores were examined from the study area, but they covered parts of the stratigraphic section that did not have any fusulinid-bearing horizons. From the four cores analyzed here, over 100 petrographic thin-sections were examined for fusulinid biostratigraphy, and an additional 90 oriented-fusulinid thin-sections were made from 50 fusulinid-bearing samples. Also, data from an Amoco fusulinid biostratigraphic chart (made by George Verville in the 1980's) from a nearby fifth cored well, the Ohio #3 Pahl, Cheyenne County, Nebraska, were evaluated and correlated with new data from the other four cored wells. The Ohio #3 Pahl fusulinid dataset was particularly significant because the cores included lower Virgilian and Desmoinesian intervals, which had not been cored in the four newly-sampled wells. Another Amoco fusulinid chart with good data from the Shell #A-16 Green in adjacent Logan County, Colorado, was also evaluated and correlated with data from the new wells, and was instrumental in constructing a reliable Pennsylvanian fusulinid zonation for the study area.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132105158","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":"Appendix III: High-Sensitivity Aeromagnetic Analysis","authors":"W. Pearson","doi":"10.31582/rmag.mg.52.1.72","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.1.72","url":null,"abstract":"","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127711826","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":"Appendix II: Geochemistry of Paleozoic Oils - Denver Basin","authors":"R. Kettler","doi":"10.31582/rmag.mg.52.1.64","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.1.64","url":null,"abstract":"","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133407251","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":"Dinosaur Footprints from the Dakota Group of Eastern Colorado","authors":"M. Lockley","doi":"10.31582/rmag.mg.24.4.107","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.4.107","url":null,"abstract":"Dinosaur footprints from the Dakota Group In eastern Colorado are known from at least eight different locations but are essentially undocumented, and unprotected. Detailed analysis reveals that trackways from two sites include front foot (manus) impressions of ornithopods, which are probably the most distinctive yet described The tracks shed light on the morphology and gait of large ornithopods, which were probably of iguanodontid affinity The tracks can be assigned to the ichnogenus Caririchnium which also occurs in South America The lack of skeletal remains in the Dakota Group and the good quality of many tracks suggests that footprints should be examined more care- fully for the useful paleoecologic census information they provide in some cases they may be used for local stratigraphic correlation.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113957445","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":"Mississippian Ratcliffe and Nesson Reservoirs, Rosebud Field, Williams County, North Dakota","authors":"Karen T. Dean","doi":"10.31582/rmag.mg.24.4.95","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.4.95","url":null,"abstract":"Rosebud is a Ratcliffe and Nesson held, located ln the central part of the Willrston basin. The field has five producing wells, but 1s not completely defined Rosebud field may have 5 to 15 additional locations and the potentla1 for recoverable reserves ln excess of one million barrels of oil Production IS controlled by a combination of structure and stratigraphic pinchout of porosity Ratclifte production IS from an algal buildup and is the primary reservoir in the field Nesson production is from a carbonate shoal facies. Rosebud fields located on an east plunging structural nose with 13 ft (4 m) of closure at the Nesson level. Both Ratcliffe and Nesson porosity are best developed along the crest of the structure A fairway of Ratcliffe algal buildups and Nesson shoals offer additional exploration opportunities in a relatively undefined area of the Williston basin","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127229121","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":"A Wrench Fault/Thrust-Fold Clay Model Study and Comparison with the Bonanza-Zeisman Area of the Eastern Big Horn Basin","authors":"D. Stone","doi":"10.31582/rmag.mg.24.4.87","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.4.87","url":null,"abstract":"The kinernatics and geometry of some of the basement-involved structures observed in the central Rocky Mountain foreland province have been investigated by means of a series of simple clay models. In these models, a relatively rigid Precambrian crystalline basement is simulated with plasticine oil-base clay (OBC) and the overlying, relatively ductile sedimentary section IS simulated with colored layers of a salt, cornstarch, and water mixture (SCW). In the model described here, a vertical cut and two perpendicular cuts dipping 30\" were made in a block of OBC and lubricated. Horizontal layers of uncut SCW were laid over the cut block of OBC Horizontal compression was applied parallel to the vertical cut so that shortening along one side was greater than along the other side. Shortening was manifest in the differential development of perpendicular thrust-folds which accompanied left-lateral s11p along the buried vertical fault plane. In the overlying, unfaulted SCW layers, a plunge was created on both fold trends, and the anticlinal hinges above OBC thrust locations were deflected sinistrally across the buried wrench fault zone. There are some basic similantries, but also important differences, in the geometry of the deformed clay model and the structure observed in the Bonanza-Zeisman area of the eastern Big Horn basin of Wyoming. A significant component of left slip along a postulated northeast-trending wrench fault zone buried in the basement of the Bonanza-Zeisinan area 1s inferred from the northeastern alignment of sinistral deflections and abrupt terminations of thrust-fold structures which trend perpendicular to the zone Although the numbers of thrust-fold structures developed along either side of the postulated Bonanza-Zeisman wrench fault zone are not equal as in the clay model, the total horizontal shortening measured along either side of the fault line approximately balances. The inferred left-lateral slip on the postulated wrench fault zone 1s thought to be the result of Laramide reactivation of a pre-existing Pre-Cambrian fracture or shear zone","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123984641","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":"Government Draw Bentonite Beds: A Newly Identified Stratigraphic Marker in the Virgin Creek Member of the Pierre Shale, Central South Dakota","authors":"T. C. Nichols, A. F. Chleborad, D. S. Collins","doi":"10.31582/rmag.mg.24.3.77","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.3.77","url":null,"abstract":"A grouping of four bentonite beds, herein named the Government Draw Bentonite Beds, is identified as a stratigraphic marker within the Virgin Creek Member of the Pierre Shale. The beds are found west of Pierre, South Dakota, over an area of at least 130 mi/sup 2/ where no other markers within the Virgin Creek Member have been identified. In this area, the Government Draw is a potential tool needed to determine the stratigraphic and structural relationships within the upper part of the Pierre Shale, heretofore little known. A better understanding of structural elements found in the Pierre Shale is needed to unravel the Late Cretaceous and younger geologic history of the area. This is part of a study to characterize Cretaceous shales for subsurface engineering construction undertaken by the US Government to evaluate the feasibility of using shales as a medium for disposal of toxic waste.","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":"132941740","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 Precambrian Metamorphic Rocks Along South Hardscrabble Creek, Wet Mountains, Colorado","authors":"J. Noblett","doi":"10.31582/rmag.mg.24.3.67","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.3.67","url":null,"abstract":"Proterozoic metamorphic rocks exposed along South Hardscrabble Creakier typical those in the Wet Mountains on the east side of the Ilse fault, lacking the northeast trending, 1-mr (1 6 km) wavelength folds of rocks to the west They are folded isochronally implying that this IS not a stratigraphic succession, but map units can be described and analyzed Three major units were recognized 1) amphibolite, 2) birotate gneiss, and 3) granitic gneiss Manor rock types include metagabbro and sillimanite-bearing quartzite The amphibolite and metagabbro have compositions suggesting that they originated as tholeiitic basalts The birotate gneiss probably had both shale and greywacke protoliths The mineralogy, textures, and chemistry of the granitic gneisses indicate Igneous origin, probably as late tectonic granitic intrusions of crustal derivation","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":"115392714","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":"A Preliminary Report on the Bentonite Beds of the Lower Virgin Creek Member of the Pierre Shale, Stanley County, South Dakota","authors":"D. S. Collins","doi":"10.31582/rmag.mg.24.3.81","DOIUrl":"https://doi.org/10.31582/rmag.mg.24.3.81","url":null,"abstract":"The Virgin Creek Member of the Pierre Shale has been divided by earlier workers into lower and upper zones based on weathering and shale differences Within the study area in Stanley County, South Dakota, the lower Virgin Creek contains 49 bentonite beds, whereas only seven bentonite beds have been observed in the upper Virgin Creek Of the bentonite beds of the lower Virgin Creek, the Government Draw Bentonite Beds, a doublet bentonite bed with a row of concretions, and bentonite bed 20 are the best markers for correlation from stream valley to stream valley However, because of the variation in number and thickness of both shale and bentonite beds from site to site, it is difficult to use the other bentonite beds as correlation tools The variation of number and thickness of shale and bentonite beds IS due to bioturbation, current activity, differential compaction, basin subsidence, and merging and splitting of bentonite beds As a result of the variation, the exact position of the upper and lower contacts of the Virgin Creekland the contact between the upper and lower Virgin Creek with respect to a selected marker bed IS quite variable Three distinctive concretion horizons have the potential of also being used as stratigraphic markers within the study area They include a nodule zone between two bentonite beds, barite(?) concretions that locally mark the lower contact of the Virgin Creek, and a set of concretions at the contact between the upper and lower Virgin Creek","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":"129891012","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}