Pub Date : 2021-08-02DOI: 10.31582/rmag.mg.58.3.249
M. Longman, Virginia Gent, J. Hagadorn
We integrate new and previous stratigraphic and petrographic data for the mid-Turonian Codell Sandstone to interpret its provenance, depositional characteristics, and environments. Our focus is on sedimentologic, X-ray diffraction, and X-ray fluorescence analyses of cores and thin sections spread throughout the Denver Basin, augmented by interpretation and correlation of well logs, isopach maps, outcrops, and provenance data. Although we treat the Codell as a single mappable unit, it actually consists of two geographically disjunct sandstone packages separated by a southwest-northeast-trending gap, the NoCoZo, short for No Codell Zone. The Codell is everywhere capped by a significant unconformity and across much of the northern Denver Basin rests unconformably on the underlying shales of the Carlile Shale. In the southern Denver Basin, the Codell commonly contains two parasequences, each of which becomes less muddy upward. Biostratigraphic and geochonologic data suggest that the unit represents deposition over a relatively brief time, spanning ~0.4 Ma from ~91.7 to ~91.3 Ma. The Codell is predominantly a thin (<50 ft) sheet-like package of pervasively bioturbated coarse siltstone and very fine-grained sandstone dominated by quartz and chert grains 50 to 100 μm in diameter. The unit is more phosphatic than the underlying members of the Carlile Shale, and its grain size coarsens to medium-grained in the northern part of the basin. An unusual aspect of the Codell across our study area is the generally excellent grain sorting despite the presence of an intermixed clay matrix. This duality of well sorted grains in a detrital clay matrix is due to the bioturbation that dominates the unit. Such burrowing created a textural inversion that obscures most of the unit’s primary sedimentary structures, except for thin intervals dominated by interlaminated silty shale and very fine sandstone. A relatively widespread and unburrowed example of this bedded facies is preserved in a thin (<10 ft) interval that extends across most of the northern Denver Basin where it is informally called the middle Codell bedded to laminated lithofacies. Sparse beds with hummocky or swaley cross-stratified and ripple cross-laminated fine-grained sandstone are present locally in this bedded facies. We hypothesize that Codell sediments were derived from a major deltaic source extending into the Western Interior Seaway from northwestern Wyoming, and that the Codell was deposited and reworked southward on the relatively flat floor of the Seaway by waxing and waning shelf currents as well as storms and waves. Codell sediments were spread across an area of more than 100,000 mi2 in this epeiric shelf system that spans eastern Colorado, southeastern Wyoming, western Kansas, parts of Nebraska and beyond.
{"title":"Sedimentology, petrography, and deposition of the Upper Cretaceous Codell Sandstone in the Denver Basin","authors":"M. Longman, Virginia Gent, J. Hagadorn","doi":"10.31582/rmag.mg.58.3.249","DOIUrl":"https://doi.org/10.31582/rmag.mg.58.3.249","url":null,"abstract":"We integrate new and previous stratigraphic and petrographic data for the mid-Turonian Codell Sandstone to interpret its provenance, depositional characteristics, and environments. Our focus is on sedimentologic, X-ray diffraction, and X-ray fluorescence analyses of cores and thin sections spread throughout the Denver Basin, augmented by interpretation and correlation of well logs, isopach maps, outcrops, and provenance data. Although we treat the Codell as a single mappable unit, it actually consists of two geographically disjunct sandstone packages separated by a southwest-northeast-trending gap, the NoCoZo, short for No Codell Zone. The Codell is everywhere capped by a significant unconformity and across much of the northern Denver Basin rests unconformably on the underlying shales of the Carlile Shale. In the southern Denver Basin, the Codell commonly contains two parasequences, each of which becomes less muddy upward. Biostratigraphic and geochonologic data suggest that the unit represents deposition over a relatively brief time, spanning ~0.4 Ma from ~91.7 to ~91.3 Ma. The Codell is predominantly a thin (<50 ft) sheet-like package of pervasively bioturbated coarse siltstone and very fine-grained sandstone dominated by quartz and chert grains 50 to 100 μm in diameter. The unit is more phosphatic than the underlying members of the Carlile Shale, and its grain size coarsens to medium-grained in the northern part of the basin. An unusual aspect of the Codell across our study area is the generally excellent grain sorting despite the presence of an intermixed clay matrix. This duality of well sorted grains in a detrital clay matrix is due to the bioturbation that dominates the unit. Such burrowing created a textural inversion that obscures most of the unit’s primary sedimentary structures, except for thin intervals dominated by interlaminated silty shale and very fine sandstone. A relatively widespread and unburrowed example of this bedded facies is preserved in a thin (<10 ft) interval that extends across most of the northern Denver Basin where it is informally called the middle Codell bedded to laminated lithofacies. Sparse beds with hummocky or swaley cross-stratified and ripple cross-laminated fine-grained sandstone are present locally in this bedded facies. We hypothesize that Codell sediments were derived from a major deltaic source extending into the Western Interior Seaway from northwestern Wyoming, and that the Codell was deposited and reworked southward on the relatively flat floor of the Seaway by waxing and waning shelf currents as well as storms and waves. Codell sediments were spread across an area of more than 100,000 mi2 in this epeiric shelf system that spans eastern Colorado, southeastern Wyoming, western Kansas, parts of Nebraska and beyond.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121616926","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 : 2019-08-01DOI: 10.31582/rmag.mg.56.3.231
J. McGuire, J. Craddock, D. Malone, S. Malone
The Ordovician Lander Sandstone, which occurs unconformably above the Cambrian Gallatin Limestone and beneath the Bighorn Dolomite, occurs in the Bighorn, Powder, and Wind River basins of Wyoming. The Lander ranges from 0-10 m in thickness and consists of texturally and compositional mature, cross bedded quartz arenite. This study uses detrital zircon U-Pb geochronology to elucidate its provenance. Samples were collected from two localities along the eastern flank of the Bighorn Mountains near Buffalo, Wyoming: a roadcut on US 16 just west of the Clear Creek thrust and from along Crazy Woman Canyon Road. The results showed a statistical similarity between the two samples, and that zircon ages are predominantly Proterozoic in age (~75%) while the minority ages were Archean (25%). Probability density plots of the two-source areas show that the peak ages for Crazy Woman Canyon (n=90) are ~1840, 2075 and 2695 Ma and the US 16 peak ages (n=141) are ~1825, 2075, and 2725 Ma. The detrital zircon age spectra for these samples indicate that the Lander was not derived from local Archean basement and was not recycled from the underlying Cambrian. The Lander has a provenance in either the Trans-Hudson Province and adjacent rocks in present day Saskatchewan and Manitoba more than 1000 km to the north or from the Peace River Arch, an early Paleozoic highlands in northwestern Alberta and northeastern British Columbia. The Lander zircons have a similar provenance to eolian zircons in the Bighorn Dolomite and to other Ordovician sandstones on the Cordilleran Continental margin and central Idaho. The Lander provenance is distinct from the Ordovician St. Peter Sandstone, which occurs extensively east of the Transcontinental Arch. We interpret that the Lander was derived on the late Ordovician shoreline, and then transported via prevailing winds across the Laurentian shelf from east to west during sea level low stand, and then distributed throughout the shelf by currents.
奥陶系陆氏砂岩，不整合地出现在寒武纪加勒廷石灰岩之上和大角白云岩之下，分布在怀俄明州的大角、粉和风河盆地。着陆器厚度在0 ~ 10 m之间，由结构和成分成熟的交错层状石英砂岩组成。本文利用碎屑锆石U-Pb年代学对其物源进行了研究。样本是从怀俄明州布法罗附近的大角山东侧的两个地方收集的:在美国16号公路上的一条路堑，就在Clear Creek thrust以西，以及沿着疯狂女人峡谷路。结果表明，两样品的锆石年龄具有统计学上的相似性，锆石年龄以元古代(~75%)为主，太古宙(25%)为少数。两源区的概率密度图显示，疯女人峡谷(n=90)的峰值年龄为~1840、2075和2695 Ma，美国16 (n=141)的峰值年龄为~1825、2075和2725 Ma。这些样品的碎屑锆石年龄谱表明，着陆器不是来自当地太古宙基底，也不是来自下伏的寒武纪。“着陆器”的起源可以是横跨哈德逊省和邻近的岩石，在今天的萨斯喀彻温省和马尼托巴省以北1000多公里处，或者来自和平河拱门，阿尔伯塔西北部和不列颠哥伦比亚省东北部的一个早期古生代高地。陆源锆石与大角白云岩中的风成锆石以及科迪勒拉大陆边缘和爱达荷中部的其他奥陶系砂岩具有相似的物源。Lander的物源与奥陶系圣彼得砂岩不同，后者广泛分布在横贯大陆拱门以东。我们认为陆陆架起源于晚奥陶世的海岸线，在海平面低潮期通过盛行风由东向西穿过劳伦森陆架，然后通过洋流分布在整个陆架上。
{"title":"Detrital zircon U-Pb geochronology of the Ordovician Lander Sandstone, Bighorn Mountains, Wyoming","authors":"J. McGuire, J. Craddock, D. Malone, S. Malone","doi":"10.31582/rmag.mg.56.3.231","DOIUrl":"https://doi.org/10.31582/rmag.mg.56.3.231","url":null,"abstract":"The Ordovician Lander Sandstone, which occurs unconformably above the Cambrian Gallatin Limestone and beneath the Bighorn Dolomite, occurs in the Bighorn, Powder, and Wind River basins of Wyoming. The Lander ranges from 0-10 m in thickness and consists of texturally and compositional mature, cross bedded quartz arenite. This study uses detrital zircon U-Pb geochronology to elucidate its provenance. Samples were collected from two localities along the eastern flank of the Bighorn Mountains near Buffalo, Wyoming: a roadcut on US 16 just west of the Clear Creek thrust and from along Crazy Woman Canyon Road. The results showed a statistical similarity between the two samples, and that zircon ages are predominantly Proterozoic in age (~75%) while the minority ages were Archean (25%). Probability density plots of the two-source areas show that the peak ages for Crazy Woman Canyon (n=90) are ~1840, 2075 and 2695 Ma and the US 16 peak ages (n=141) are ~1825, 2075, and 2725 Ma. The detrital zircon age spectra for these samples indicate that the Lander was not derived from local Archean basement and was not recycled from the underlying Cambrian. The Lander has a provenance in either the Trans-Hudson Province and adjacent rocks in present day Saskatchewan and Manitoba more than 1000 km to the north or from the Peace River Arch, an early Paleozoic highlands in northwestern Alberta and northeastern British Columbia. The Lander zircons have a similar provenance to eolian zircons in the Bighorn Dolomite and to other Ordovician sandstones on the Cordilleran Continental margin and central Idaho. The Lander provenance is distinct from the Ordovician St. Peter Sandstone, which occurs extensively east of the Transcontinental Arch. We interpret that the Lander was derived on the late Ordovician shoreline, and then transported via prevailing winds across the Laurentian shelf from east to west during sea level low stand, and then distributed throughout the shelf by currents.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130012453","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 : 2015-10-01DOI: 10.31582/rmag.mg.52.4.47
C. Burberry, R. Joeckel, J. Korus
The geologic structures of the central Midcontinent of the USA are largely buried and known only from geophysical datasets, coupled with sparse well control and limited outcrop. Such unconstrained geophysical models preclude a deeper assessment of possible continental interior seismic hazards, which have the potential to cause appreciable damage. Within the study area in southeastern Nebraska and northeastern Kansas is an area of elevated seismic risk, with a spatial relationship to the Nemaha Tectonic Zone and the Midcontinent Rift System. Using sequential restorations of three published cross sections within Nebraska and Kansas this study demonstrates that the Nemaha Tectonic Zone and Midcontinent Rift System have each been reactivated several times since the end of the Mississippian (the details of deformation prior to the Mississippian are not considered). Our reconstructions indicate that in addition to major Pennsylvanian-Early Permian fault reactivation during the Ancestral Rocky Mountain orogeny there was also deformation both prior to the post-Mississippian unconformity associated with uplift on the Nemaha Tectonic Zone and after the deposition of late Early-early Late Cretaceous sediments in the study area, potentially due to the Laramide orogeny. Results also indicate that the magnitude of the far-field stresses is sufficient to cause seismogenic reactivation on favorably oriented pre-existing faults. This history of reactivation of geologic structures in the central Midcontinent suggests that seismic hazards in the region in the present cannot be ruled out. Though dangerous large earthquakes are uncommon in the continental interior, seismic activity along the structures in the study area would threaten several large population centers and the potential for this activity should not be ignored.
{"title":"Post-Mississippian tectonic evolution of the Nemaha Tectonic Zone and Midcontinent Rift System, SE Nebraska and N Kansas","authors":"C. Burberry, R. Joeckel, J. Korus","doi":"10.31582/rmag.mg.52.4.47","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.4.47","url":null,"abstract":"The geologic structures of the central Midcontinent of the USA are largely buried and known only from geophysical datasets, coupled with sparse well control and limited outcrop. Such unconstrained geophysical models preclude a deeper assessment of possible continental interior seismic hazards, which have the potential to cause appreciable damage. Within the study area in southeastern Nebraska and northeastern Kansas is an area of elevated seismic risk, with a spatial relationship to the Nemaha Tectonic Zone and the Midcontinent Rift System. Using sequential restorations of three published cross sections within Nebraska and Kansas this study demonstrates that the Nemaha Tectonic Zone and Midcontinent Rift System have each been reactivated several times since the end of the Mississippian (the details of deformation prior to the Mississippian are not considered). Our reconstructions indicate that in addition to major Pennsylvanian-Early Permian fault reactivation during the Ancestral Rocky Mountain orogeny there was also deformation both prior to the post-Mississippian unconformity associated with uplift on the Nemaha Tectonic Zone and after the deposition of late Early-early Late Cretaceous sediments in the study area, potentially due to the Laramide orogeny. Results also indicate that the magnitude of the far-field stresses is sufficient to cause seismogenic reactivation on favorably oriented pre-existing faults. This history of reactivation of geologic structures in the central Midcontinent suggests that seismic hazards in the region in the present cannot be ruled out. Though dangerous large earthquakes are uncommon in the continental interior, seismic activity along the structures in the study area would threaten several large population centers and the potential for this activity should not be ignored.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127948416","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}
Compartmentalization within shoreface and deltaic reservoirs is key to trapping gas in the Iles Formation of the southern Piceance Basin. There are two types of reservoirs: 1) compartmentalized gas-saturated Corcoran and Cozzette sandstones, and 2) continuous water-saturated Rollins sandstones. Compartmentalized sandstones are interpreted to have been deposited during a time of relatively low accommodation with relatively low sediment supply while more connected sandstones were deposited during a time of relatively high accommodation and a much higher sediment supply. The compartmentalization is due to 1) location within the overall parasequence stacking pattern; 2) facies variability within the deltaic and wave-dominated deposits; and 3) further partitioning due to the superposition of multiple types of erosion surfaces ultimately related to low accommodation rates. The continuous sandstones are more connected because they were apparently deposited during a period of time when rates of progradation were more regular and overall accommodation and sedimentation were higher.
{"title":"Stratigraphic Trapping Mechanisms in the Iles Formation, Piceance Basin, Colorado","authors":"M. Kirschbaum, S. Cumella","doi":"10.31582/rmag.mg.52.4.5","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.4.5","url":null,"abstract":"Compartmentalization within shoreface and deltaic reservoirs is key to trapping gas in the Iles Formation of the southern Piceance Basin. There are two types of reservoirs: 1) compartmentalized gas-saturated Corcoran and Cozzette sandstones, and 2) continuous water-saturated Rollins sandstones. Compartmentalized sandstones are interpreted to have been deposited during a time of relatively low accommodation with relatively low sediment supply while more connected sandstones were deposited during a time of relatively high accommodation and a much higher sediment supply. The compartmentalization is due to 1) location within the overall parasequence stacking pattern; 2) facies variability within the deltaic and wave-dominated deposits; and 3) further partitioning due to the superposition of multiple types of erosion surfaces ultimately related to low accommodation rates. The continuous sandstones are more connected because they were apparently deposited during a period of time when rates of progradation were more regular and overall accommodation and sedimentation were higher.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133911094","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 : 2015-10-01DOI: 10.31582/rmag.mg.52.4.27
Ryan C. Thompson
The mechanisms and timing of fracturing are important parameters to predicting intensely fractured trends with enhanced reservoir permeability and production potential. Fracture analyses were used to test hypotheses for the structural development of the Wind River Basin in Wyoming that include: 1) pre-Laramide regional compression; 2) Laramide ENE-WSW horizontal compression and left-slip faulting; and 3) multiple post-Laramide hypotheses: a) near-surface mechanisms; b) regional extension due to a variety of causes; and/or c) localized extensional reactivation and backsliding of thrust faults during release of compression and collapse of basin-bounding arches. Fracture data collected from Cambrian- to Eocene-aged formations throughout the basin included 1,900 joints and minor faults measured at 45 outcrop stations and 14,775 fractures compiled from 39 micro-resistivity image log interpretations. Inferred stress axes were calculated using eigenvector averaging and show two distinct stages of deformation: 1) Laramide ENE-WSW horizontal shortening followed by 2) post-Laramide extension consistent with modern stresses. Post-Laramide fractures in the basin parallel NW-SE striking joints observed across the Rocky Mountain foreland, except in the vicinity of E-W trending basin-bounding arch margins where these fractures closely parallel arch-bounding thrust faults. Fracture analyses are consistent with Laramide shortening followed by localized extension in proximity to both basin-bounding master thrusts and smaller productive structures in the basin. Seismic-based models show backsliding on these thrusts related to arch/anticline collapse. Recent wells at Frenchie Draw gas field have high initial production rates and probably intersected off-structure, intensely fractured trends along the margins of what appears to be a collapsed anticline.
{"title":"Post-Laramide, Collapse-Related Fracturing and Associated Production; Wind River Basin, Wyoming","authors":"Ryan C. Thompson","doi":"10.31582/rmag.mg.52.4.27","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.4.27","url":null,"abstract":"The mechanisms and timing of fracturing are important parameters to predicting intensely fractured trends with enhanced reservoir permeability and production potential. Fracture analyses were used to test hypotheses for the structural development of the Wind River Basin in Wyoming that include: 1) pre-Laramide regional compression; 2) Laramide ENE-WSW horizontal compression and left-slip faulting; and 3) multiple post-Laramide hypotheses: a) near-surface mechanisms; b) regional extension due to a variety of causes; and/or c) localized extensional reactivation and backsliding of thrust faults during release of compression and collapse of basin-bounding arches. Fracture data collected from Cambrian- to Eocene-aged formations throughout the basin included 1,900 joints and minor faults measured at 45 outcrop stations and 14,775 fractures compiled from 39 micro-resistivity image log interpretations. Inferred stress axes were calculated using eigenvector averaging and show two distinct stages of deformation: 1) Laramide ENE-WSW horizontal shortening followed by 2) post-Laramide extension consistent with modern stresses. Post-Laramide fractures in the basin parallel NW-SE striking joints observed across the Rocky Mountain foreland, except in the vicinity of E-W trending basin-bounding arch margins where these fractures closely parallel arch-bounding thrust faults. Fracture analyses are consistent with Laramide shortening followed by localized extension in proximity to both basin-bounding master thrusts and smaller productive structures in the basin. Seismic-based models show backsliding on these thrusts related to arch/anticline collapse. Recent wells at Frenchie Draw gas field have high initial production rates and probably intersected off-structure, intensely fractured trends along the margins of what appears to be a collapsed anticline.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133824614","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}
In late 2009, the EOG Resources Jake 2-01H horizontal well (Sec. 1, T11N, R63W, Weld County, CO) re-opened the Niobrara oil play in the DJ basin. The play for EOG was built on comprehensive geologic scrutiny across the entire DJ basin of Colorado and Wyoming. Niobrara tests in the original Hereford field, four miles east of the Jake discovery, had bypassed Niobrara pay. This data, along with a 1991-vintage horizontal well with a vertical core through the Niobrara B Chalk in the original Hereford field, set up the prospect around the Jake discovery. A proprietary 40 square-mile 3-D seismic survey acquired and processed between May and July 2009 provided data for well-location planning. Determination of current-day maximum horizontal stress of N55°E in the Lamotta 5-01M monitoring well led to the drilling of the Jake 2-01H, although the Jake well was not the original planned location for the first horizontal test in the prospect area. Since the Jake discovery, EOG has drilled 71 Niobrara horizontal wells in Hereford field, and industry has drilled more than 4400 horizontal wells in the entire DJ basin Niobrara play.
{"title":"A Short History of the “Jake” Niobrara Horizontal Oil Discovery, Weld County, Colorado","authors":"D. Anderson, J. Melby, J. Folcik","doi":"10.31582/rmag.mg.52.3.5","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.3.5","url":null,"abstract":"In late 2009, the EOG Resources Jake 2-01H horizontal well (Sec. 1, T11N, R63W, Weld County, CO) re-opened the Niobrara oil play in the DJ basin. The play for EOG was built on comprehensive geologic scrutiny across the entire DJ basin of Colorado and Wyoming. Niobrara tests in the original Hereford field, four miles east of the Jake discovery, had bypassed Niobrara pay. This data, along with a 1991-vintage horizontal well with a vertical core through the Niobrara B Chalk in the original Hereford field, set up the prospect around the Jake discovery. A proprietary 40 square-mile 3-D seismic survey acquired and processed between May and July 2009 provided data for well-location planning. Determination of current-day maximum horizontal stress of N55°E in the Lamotta 5-01M monitoring well led to the drilling of the Jake 2-01H, although the Jake well was not the original planned location for the first horizontal test in the prospect area. Since the Jake discovery, EOG has drilled 71 Niobrara horizontal wells in Hereford field, and industry has drilled more than 4400 horizontal wells in the entire DJ basin Niobrara play.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116047891","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 : 2015-07-01DOI: 10.31582/rmag.mg.52.3.13
K. Rudolph, W. Devlin, J. Crabaugh
Three scales of sedimentary cyclicity are observed in the Campanian to Maastrichtian-aged strata of southwestern Wyoming based on sedimentary stacking patterns, facies successions, paleontological data and geometric criteria from outcrop, and subsurface data. The largest scale of sequence stratigraphic interpretation is of 10-15 million years duration per cycle and is designated as second order. Second-order cyclicity is represented by profound sequence boundaries and maximum-flooding surfaces that are related to regional tectono-subsidence drivers. The 2nd-order sequence boundaries at the base of the Ericson Formation (Moxa Unconformity) and the base of the Fort Union Formation (Laramide Unconformity) locally erode thousands of feet of section on discrete structural highs, but also show evidence of uplift on a broader scale. Both unconformities terminate long successions of marine shoreline progradation. Second-order maximum flooding surfaces are present within thick marine mudstone successions of the Baxter-Niobrara and Lewis formations. These intervals represent the deepest water deposits in the Upper Cretaceous and are associated with important regional seals and source rocks. The large-scale tectono-cyclicity is composed of an aggregate of smaller-scale, 3rd- and 4th-order sequences and their component systems tracts. In addition to the second-order sequences described above, third-order sequence boundaries are interpreted at the base of the Blair Formation, base of the Chimney Rock Member of the Rock Springs Formation, and at the base of the Canyon Creek Member of the Ericson Formation. Third-order maximum flooding surfaces are in the middle Blair Formation, middle Black Butte Member of the Rock Springs Formation, and in the upper part of the Rusty Member of the Ericson Formation. At least 7 additional 4th-order sequences can be interpreted within these successions. The higher-order cycles are shorter in duration and smaller in magnitude (i.e., thinner and with a smaller degree of change in environments or bathymetry within a cycle). The sequence stratigraphic interpretation approach is observationally based and consistent across these scales. However, finer-scale sequence stratigraphic interpretations, especially at the 4th-order scale, are subject to additional subjectivity. An important challenge is to separate apparent cyclicity related to factors such as local to regional shifting of depocenters (autocyclicity) from regionally correlative cyclicity (allocyclicity) within the high-frequency sequences. Examples of this are provided, most clearly for the lower portion of the Blair Formation. Such considerations are important economically, as this is the scale that controls sandstone reservoir and mudstone seal architecture within petroleum fields. Standard systems tracts criteria using parasequence stacking patterns are extended to non-marine strata by use of the degree of amalgamation (net/gross) of the fluvial sandstones. This approach
{"title":"Upper Cretaceous Sequence Stratigraphy of the Rock Springs Uplift, Wyoming","authors":"K. Rudolph, W. Devlin, J. Crabaugh","doi":"10.31582/rmag.mg.52.3.13","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.3.13","url":null,"abstract":"Three scales of sedimentary cyclicity are observed in the Campanian to Maastrichtian-aged strata of southwestern Wyoming based on sedimentary stacking patterns, facies successions, paleontological data and geometric criteria from outcrop, and subsurface data. The largest scale of sequence stratigraphic interpretation is of 10-15 million years duration per cycle and is designated as second order. Second-order cyclicity is represented by profound sequence boundaries and maximum-flooding surfaces that are related to regional tectono-subsidence drivers. The 2nd-order sequence boundaries at the base of the Ericson Formation (Moxa Unconformity) and the base of the Fort Union Formation (Laramide Unconformity) locally erode thousands of feet of section on discrete structural highs, but also show evidence of uplift on a broader scale. Both unconformities terminate long successions of marine shoreline progradation. Second-order maximum flooding surfaces are present within thick marine mudstone successions of the Baxter-Niobrara and Lewis formations. These intervals represent the deepest water deposits in the Upper Cretaceous and are associated with important regional seals and source rocks. The large-scale tectono-cyclicity is composed of an aggregate of smaller-scale, 3rd- and 4th-order sequences and their component systems tracts. In addition to the second-order sequences described above, third-order sequence boundaries are interpreted at the base of the Blair Formation, base of the Chimney Rock Member of the Rock Springs Formation, and at the base of the Canyon Creek Member of the Ericson Formation. Third-order maximum flooding surfaces are in the middle Blair Formation, middle Black Butte Member of the Rock Springs Formation, and in the upper part of the Rusty Member of the Ericson Formation. At least 7 additional 4th-order sequences can be interpreted within these successions. The higher-order cycles are shorter in duration and smaller in magnitude (i.e., thinner and with a smaller degree of change in environments or bathymetry within a cycle). The sequence stratigraphic interpretation approach is observationally based and consistent across these scales. However, finer-scale sequence stratigraphic interpretations, especially at the 4th-order scale, are subject to additional subjectivity. An important challenge is to separate apparent cyclicity related to factors such as local to regional shifting of depocenters (autocyclicity) from regionally correlative cyclicity (allocyclicity) within the high-frequency sequences. Examples of this are provided, most clearly for the lower portion of the Blair Formation. Such considerations are important economically, as this is the scale that controls sandstone reservoir and mudstone seal architecture within petroleum fields. Standard systems tracts criteria using parasequence stacking patterns are extended to non-marine strata by use of the degree of amalgamation (net/gross) of the fluvial sandstones. This approach ","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130224639","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}
New U-Pb zircon and 40Ar/39Ar crystallization ages for latest Mesozoic to Cenozoic plutonic rocks in the western San Juan Mountains provide insight into the timing and interplay of mantle and crustal magmatism over the past 80 Ma. Subduction-driven magmatism in the Laramide (75-60 Ma) generated alkalic intermediate to mafic magmas. These were emplaced as laccoliths and stocks along northeast trends that were likely controlled by crustal-scale zones of weakness with Proterozoic ancestry. The transition from Laramide subduction to slab rollback and delamination was marked by incipient regional extension and widespread emplacement of plutons. Oligocene plutons of gabbro to granite were mostly peripheral to 29-27 Ma caldera complexes that formed over a regional subvolcanic batholith. Alkaline mantle magmas that accompanied the semi-continuous intrusion of shallow felsic to intermediate plutons from 25 to 4 Ma produced diatreme-dike complexes and dike swarms across the northern San Juan Basin. Emplacement of plutons from 75-4 Ma caused localized uplift that had a major influence on landscape evolution, and often were linked to zones of mineralization. Late Mesozoic to Cenozoic plutonic events in the western San Juan Mountains record a long-term shift to more bimodal magmatism. Injection of mantle melts from 25 to 4 Ma during incipient crustal extension accompanied elevated thermal gradients over the region, as evidenced by resetting of cooling ages in some Laramide intrusive rocks. The preservation of xenocrystic zircons in 75-4 Ma plutonic rocks provides evidence for variable magmatic conditions with an overall increase in the thermal state of Oligocene melts proximal to caldera systems and all plutons emplaced after 18 Ma. High geothermal gradients caused by the long duration of magmatism and increased mantle contributions may have permitted more prolonged assembly and slower cooling in some plutons.
{"title":"New U-Pb Zircon and 40AR/39AR Age Constraints on the Late Mesozoic to Cenozoic Plutonic Record in the Western San Juan Mountains","authors":"D. Gonzales","doi":"10.31582/rmag.mg.52.2.5","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.2.5","url":null,"abstract":"New U-Pb zircon and 40Ar/39Ar crystallization ages for latest Mesozoic to Cenozoic plutonic rocks in the western San Juan Mountains provide insight into the timing and interplay of mantle and crustal magmatism over the past 80 Ma. Subduction-driven magmatism in the Laramide (75-60 Ma) generated alkalic intermediate to mafic magmas. These were emplaced as laccoliths and stocks along northeast trends that were likely controlled by crustal-scale zones of weakness with Proterozoic ancestry. The transition from Laramide subduction to slab rollback and delamination was marked by incipient regional extension and widespread emplacement of plutons. Oligocene plutons of gabbro to granite were mostly peripheral to 29-27 Ma caldera complexes that formed over a regional subvolcanic batholith. Alkaline mantle magmas that accompanied the semi-continuous intrusion of shallow felsic to intermediate plutons from 25 to 4 Ma produced diatreme-dike complexes and dike swarms across the northern San Juan Basin. Emplacement of plutons from 75-4 Ma caused localized uplift that had a major influence on landscape evolution, and often were linked to zones of mineralization. Late Mesozoic to Cenozoic plutonic events in the western San Juan Mountains record a long-term shift to more bimodal magmatism. Injection of mantle melts from 25 to 4 Ma during incipient crustal extension accompanied elevated thermal gradients over the region, as evidenced by resetting of cooling ages in some Laramide intrusive rocks. The preservation of xenocrystic zircons in 75-4 Ma plutonic rocks provides evidence for variable magmatic conditions with an overall increase in the thermal state of Oligocene melts proximal to caldera systems and all plutons emplaced after 18 Ma. High geothermal gradients caused by the long duration of magmatism and increased mantle contributions may have permitted more prolonged assembly and slower cooling in some plutons.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126137084","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 : 2015-04-01DOI: 10.31582/rmag.mg.52.2.43
D. Sweet, Corbin R. Carsrud, A. Watters
The Fountain Formation is an important unit recording ancestral Rocky Mountain tectonics and paleogeography along the Front Range urban corridor. The age of the formation constrains timing of uplift of the ancestral Front Range and Ute Pass uplift and subsidence of adjacent basins. Yet, age models for the Fountain Formation are crude and varied. Specifically, available biostratigraphic data suggest an entirely Pennsylvanian age for the Fountain Formation, however historical lithostratigraphic assignment of the Lyons Formation atop the Fountain Formation south of Lyons, Colorado allows for a significant early Permian component of deposition. New stratigraphic and sedimentologic data recorded from the Ingleside Formation and the Lower Permian unit at Manitou Springs, Colorado demonstrate: 1) a conformable contact between the upper Fountain Formation and Lower Permian strata at both localities and 2) close grain size and framework mineralogy comparisons at both localities. These data suggest that the Lower Permian at Manitou Springs, Colorado best correlates to the Ingleside Formation, rather than the previously mapped Lyons Formation. This newly proposed lithostratigraphic correlation aligns with the available biostratigraphic data that the Fountain Formation is a Pennsylvanian unit with little to no Lower Permian component. An entirely Pennsylvanian age for the Fountain Formation indicates that active uplift of the ancestral Front Range and delivery of first-cycle arkose had ceased by the latest Pennsylvanian.
{"title":"Proposing an Entirely Pennsylvanian Age for the Fountain Formation through New Lithostratigraphic Correlation along the Front Range","authors":"D. Sweet, Corbin R. Carsrud, A. Watters","doi":"10.31582/rmag.mg.52.2.43","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.2.43","url":null,"abstract":"The Fountain Formation is an important unit recording ancestral Rocky Mountain tectonics and paleogeography along the Front Range urban corridor. The age of the formation constrains timing of uplift of the ancestral Front Range and Ute Pass uplift and subsidence of adjacent basins. Yet, age models for the Fountain Formation are crude and varied. Specifically, available biostratigraphic data suggest an entirely Pennsylvanian age for the Fountain Formation, however historical lithostratigraphic assignment of the Lyons Formation atop the Fountain Formation south of Lyons, Colorado allows for a significant early Permian component of deposition. New stratigraphic and sedimentologic data recorded from the Ingleside Formation and the Lower Permian unit at Manitou Springs, Colorado demonstrate: 1) a conformable contact between the upper Fountain Formation and Lower Permian strata at both localities and 2) close grain size and framework mineralogy comparisons at both localities. These data suggest that the Lower Permian at Manitou Springs, Colorado best correlates to the Ingleside Formation, rather than the previously mapped Lyons Formation. This newly proposed lithostratigraphic correlation aligns with the available biostratigraphic data that the Fountain Formation is a Pennsylvanian unit with little to no Lower Permian component. An entirely Pennsylvanian age for the Fountain Formation indicates that active uplift of the ancestral Front Range and delivery of first-cycle arkose had ceased by the latest Pennsylvanian.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125071544","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 : 2015-04-01DOI: 10.31582/rmag.mg.52.2.71
C. Stevens
Unusual tubular calcareous nodules occur in reddish-brown siltstones in the upper 150 m of the Pennsylvanian Minturn Formation in northwestern Colorado. These nodules have an inner core extending the length of the specimens and consisting of sparry calcite and/or siliciclastic material. This core is surrounded by several concentric zones of crudely laminated micritic limestone with variously shaped small cavities filled with clear calcite. The outer parts of the nodules generally consist of clotted micrite with some siliciclastic material incorporated near the contact with the surrounding sediment. Several nodules were later fractured, some with the cracks partially filled with micrite and others filled with sparry calcite. These nodules may be microbialites that encrusted small reed-like plants that grew in a salt marsh, a shallow coastal lake, or a pool on a muddy tidal flat. These plants later decayed allowing access of siliciclastic sediment into the hollow core.
{"title":"Tubular Calcareous Nodules from the Pennsylvanian Minturn Formation of Colorado","authors":"C. Stevens","doi":"10.31582/rmag.mg.52.2.71","DOIUrl":"https://doi.org/10.31582/rmag.mg.52.2.71","url":null,"abstract":"Unusual tubular calcareous nodules occur in reddish-brown siltstones in the upper 150 m of the Pennsylvanian Minturn Formation in northwestern Colorado. These nodules have an inner core extending the length of the specimens and consisting of sparry calcite and/or siliciclastic material. This core is surrounded by several concentric zones of crudely laminated micritic limestone with variously shaped small cavities filled with clear calcite. The outer parts of the nodules generally consist of clotted micrite with some siliciclastic material incorporated near the contact with the surrounding sediment. Several nodules were later fractured, some with the cracks partially filled with micrite and others filled with sparry calcite. These nodules may be microbialites that encrusted small reed-like plants that grew in a salt marsh, a shallow coastal lake, or a pool on a muddy tidal flat. These plants later decayed allowing access of siliciclastic sediment into the hollow core.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132085102","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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