The Tunp Member of the Wasatch Formation in the Fossil basin of southwestern Wyoming was deposited by debris flows containing abundant, very poorly sorted to unsorted coarse debris in a mudstone matrix. Deposition occured on alluvial fans where small braided streams reworked the toes of the debris flows generating minor fluvial deposits. Tunp sediments are preserved in three separate north-south trending belts adjacent to the northern Fossil basin and deposits in each belt had separate sources in discrete highlands. The Tunp on Commissary Ridge was generated by passive uplift of the Absaroka sheet over a ramp in the Darby thrust. The deposits on Rock Creek and Dempsey ridges are related to motion on the Tunp thrust. The Tunp on Boulder Ridge was derived from the hanging wall of the Crawford thrust but it is not clear whether this was a passive or active source. Stratigraphic relations of these Tunp deposits with dated beds in the Wasatch and Green River formations indicate that the belts of Tunp are successively older to the west and that passive rotation of the Absaroka sheet preceded movement on the Tunp thrust which, in turn, preceded the generation of a source on the Crawford. Deposition of the Tunp therefore records a sequence, progressively younger to the west, of minor adjustments to compression during the last phase of thrusting.
{"title":"Stratigraphy and Tectonic Significance of the Tunp Conglomerate in the Fossil Basin, Southwest, Wyoming","authors":"D. Hurst, J. Steidtmann","doi":"10.31582/rmag.mg.23.1.6","DOIUrl":"https://doi.org/10.31582/rmag.mg.23.1.6","url":null,"abstract":"The Tunp Member of the Wasatch Formation in the Fossil basin of southwestern Wyoming was deposited by debris flows containing abundant, very poorly sorted to unsorted coarse debris in a mudstone matrix. Deposition occured on alluvial fans where small braided streams reworked the toes of the debris flows generating minor fluvial deposits. Tunp sediments are preserved in three separate north-south trending belts adjacent to the northern Fossil basin and deposits in each belt had separate sources in discrete highlands. The Tunp on Commissary Ridge was generated by passive uplift of the Absaroka sheet over a ramp in the Darby thrust. The deposits on Rock Creek and Dempsey ridges are related to motion on the Tunp thrust. The Tunp on Boulder Ridge was derived from the hanging wall of the Crawford thrust but it is not clear whether this was a passive or active source. Stratigraphic relations of these Tunp deposits with dated beds in the Wasatch and Green River formations indicate that the belts of Tunp are successively older to the west and that passive rotation of the Absaroka sheet preceded movement on the Tunp thrust which, in turn, preceded the generation of a source on the Crawford. Deposition of the Tunp therefore records a sequence, progressively younger to the west, of minor adjustments to compression during the last phase of thrusting.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1986-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116875880","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 : 1986-01-01DOI: 10.31582/rmag.mg.23.1.14
I. Wong, J. Humphrey
On 14 August 1983, a small earthquake of Richter magnitude 3.4 occurred near the town of Cimarron in southwestern Colorado. The analysis of data collected from seismographic stations located within the intermountain U.S. suggests the earthquake occurred on the Cimarron fault, a major west-northwest trending Precambrian fault which has experienced displacement possibly since Oligocene time. A fault plane solution determined for the earthquake exhibits normal faulting on a moderately dipping, west-northwest- or east-west-trending fault plane in good agreement with the geologic observations of the Cimarron fault. The fault plane solution also displays a north-northeast trending minimum compressive stress suggesting that this earthquake occurred in response to a reactivation of the Cimarron fault in an extensional tectonic stress field similar to that observed in the Rio Grande rift to the southeast or the Southern Great Plains to the east. The location and the faulting characteristics of the Cimarron earthquake represent the best evidence to date that associates an earthquake with a known major fault in Colorado.
{"title":"The 14 August 1983 Cimarron, Colorado Earthquake and the Cimarron Fault","authors":"I. Wong, J. Humphrey","doi":"10.31582/rmag.mg.23.1.14","DOIUrl":"https://doi.org/10.31582/rmag.mg.23.1.14","url":null,"abstract":"On 14 August 1983, a small earthquake of Richter magnitude 3.4 occurred near the town of Cimarron in southwestern Colorado. The analysis of data collected from seismographic stations located within the intermountain U.S. suggests the earthquake occurred on the Cimarron fault, a major west-northwest trending Precambrian fault which has experienced displacement possibly since Oligocene time. A fault plane solution determined for the earthquake exhibits normal faulting on a moderately dipping, west-northwest- or east-west-trending fault plane in good agreement with the geologic observations of the Cimarron fault. The fault plane solution also displays a north-northeast trending minimum compressive stress suggesting that this earthquake occurred in response to a reactivation of the Cimarron fault in an extensional tectonic stress field similar to that observed in the Rio Grande rift to the southeast or the Southern Great Plains to the east. The location and the faulting characteristics of the Cimarron earthquake represent the best evidence to date that associates an earthquake with a known major fault in Colorado.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1986-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114239018","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}
Debate over the question of whether basement rocks folded or faulted during the Laramide orogeny in the Wyoming province of the Rocky Mountain foreland has raged for many years. Proponents of one view or the other have drawn support for their case from theoretical arguments, from experimental laboratory results, from interpretations of seismic and subsurface borehole data, and from direct observation of surface outcrops and subsurface mine exposures. An analysis of the validity and applicability of these various approaches included the generation of synthetic seismic sections and an evaluation at balanced cross sections. This analysis indicated that the notion of a folded basement is supported only by the interpretation of seismic and borehole data whereas the concept of brittle deformation of the basement is supported by all of these lines of reasoning, interpretation, and observation. The conclusion is that structural basement did not fold during the Laramide orogeny.
{"title":"A Case for Brittle Deformation of the Basement During the Laramide Revolution in the Rocky Mountain Foreland Province","authors":"V. Matthews","doi":"10.31582/rmag.mg.23.1.1","DOIUrl":"https://doi.org/10.31582/rmag.mg.23.1.1","url":null,"abstract":"Debate over the question of whether basement rocks folded or faulted during the Laramide orogeny in the Wyoming province of the Rocky Mountain foreland has raged for many years. Proponents of one view or the other have drawn support for their case from theoretical arguments, from experimental laboratory results, from interpretations of seismic and subsurface borehole data, and from direct observation of surface outcrops and subsurface mine exposures. An analysis of the validity and applicability of these various approaches included the generation of synthetic seismic sections and an evaluation at balanced cross sections. This analysis indicated that the notion of a folded basement is supported only by the interpretation of seismic and borehole data whereas the concept of brittle deformation of the basement is supported by all of these lines of reasoning, interpretation, and observation. The conclusion is that structural basement did not fold during the Laramide orogeny.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1986-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121579607","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 : 1986-01-01DOI: 10.31582/rmag.mg.23.1.19
J. Steidtmann, L. Middleton
The established mid-Tertiary stratigraphy along the southern margin of the Wind River Range is of questionable chronologic validity because of the difficulty in discriminating among the several tuffaceous units and because lithologic criteria have been used as chronostratigraphic indicators. Field observations and zircon fission-track ages suggest certain revisions of, and additions to, this stratigraphy. These include: 1) recognition of the Cathedral Bluffs Tongue of the Wasatch Formation at Reds Cabin monocline, 2) establishment of a late Oligocene or early Miocene age for the South Pass Formation and 3) recognition that there are middle Miocene deposits previously mapped as Arikaree that consist of reworked Arikaree shed off the upthrown side of the Continental fault. The implications of these findings are that the Continental fault, now a collapse feature, was a tear fault during the early Eocene, that there are most likely Oligocene rocks north of the Continental fault, that there was late Oligocene or early Miocene uplift in the core of the Wind River Range and that the range collapsed in the middle Miocene.
{"title":"Eocene-Pliocene Stratigraphy Along the Southern Margin of the Wind River Range, Wyoming: Revisions and Implications from Field and Fission-Track Studies","authors":"J. Steidtmann, L. Middleton","doi":"10.31582/rmag.mg.23.1.19","DOIUrl":"https://doi.org/10.31582/rmag.mg.23.1.19","url":null,"abstract":"The established mid-Tertiary stratigraphy along the southern margin of the Wind River Range is of questionable chronologic validity because of the difficulty in discriminating among the several tuffaceous units and because lithologic criteria have been used as chronostratigraphic indicators. Field observations and zircon fission-track ages suggest certain revisions of, and additions to, this stratigraphy. These include: 1) recognition of the Cathedral Bluffs Tongue of the Wasatch Formation at Reds Cabin monocline, 2) establishment of a late Oligocene or early Miocene age for the South Pass Formation and 3) recognition that there are middle Miocene deposits previously mapped as Arikaree that consist of reworked Arikaree shed off the upthrown side of the Continental fault. The implications of these findings are that the Continental fault, now a collapse feature, was a tear fault during the early Eocene, that there are most likely Oligocene rocks north of the Continental fault, that there was late Oligocene or early Miocene uplift in the core of the Wind River Range and that the range collapsed in the middle Miocene.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1986-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134309018","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 : 1985-10-01DOI: 10.31582/rmag.mg.22.4.167
R. Gries
The San Juan Sag is a foreland basin formerly adjacent to and west of the Laramide northern Sangre de Cristo uplift. Latest Laramide wrench faulting and Miocene rifting split this bounding uplift and formed the San Luis basin adjacent to and east of the sag. Concurrent volcanism concealed the San Juan Sag with over 10,000ft of intermediate-type volcanic deposits and its presence remained in doubt until oil occurrences in the volcanic rocks encouraged exploration for the underlying sedimentary rocks. Recent drilling through the volcanic field has revealed the presence of Eocene elastic sediments, the Cretaceous Lewis, Mancos and Dakota formations and Jurassic Morrison, Junction Creek, Entrada, and possibly Wanakah formations. Additionally, oil and gas shows were found and production established as a result of drilling in 1984.
圣胡安凹陷是一个前陆盆地，原与Laramide北部Sangre de Cristo隆起相邻并以西。最新的Laramide扭断作用和中新世裂陷作用使这一边界隆起分裂，形成了与凹陷相邻及以东的圣路易斯盆地。同期火山活动掩盖了圣胡安凹陷超过10,000英尺的中型火山矿床，其存在一直受到怀疑，直到在火山岩中发现石油，鼓励了对下伏沉积岩的勘探。最近在火山场的钻探发现了始新世弹性沉积物的存在，白垩纪Lewis、Mancos和Dakota地层以及侏罗纪Morrison、Junction Creek、Entrada地层，可能还有Wanakah地层。此外，由于1984年的钻探，发现了石油和天然气显示并建立了生产。
{"title":"San Juan Sag: Cretaceous Rocks in a Volcanic-Covered Basin, South Central Colorado","authors":"R. Gries","doi":"10.31582/rmag.mg.22.4.167","DOIUrl":"https://doi.org/10.31582/rmag.mg.22.4.167","url":null,"abstract":"The San Juan Sag is a foreland basin formerly adjacent to and west of the Laramide northern Sangre de Cristo uplift. Latest Laramide wrench faulting and Miocene rifting split this bounding uplift and formed the San Luis basin adjacent to and east of the sag. Concurrent volcanism concealed the San Juan Sag with over 10,000ft of intermediate-type volcanic deposits and its presence remained in doubt until oil occurrences in the volcanic rocks encouraged exploration for the underlying sedimentary rocks. Recent drilling through the volcanic field has revealed the presence of Eocene elastic sediments, the Cretaceous Lewis, Mancos and Dakota formations and Jurassic Morrison, Junction Creek, Entrada, and possibly Wanakah formations. Additionally, oil and gas shows were found and production established as a result of drilling in 1984.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1985-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130790447","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 : 1985-10-01DOI: 10.1306/AD462A9C-16F7-11D7-8645000102C1865D
S. Sonnenberg
Pennsylvanian Morrow sandstones are oil and gas productive throughout a large area in southeast Colorado. The Sorrento field is a recent major Morrow discovery with recoverable reserves estimated at over 10 million barrels of oil from an area of 3200 acres (1295 ha) at depths of 5400 to 5600 ft (1646 to 1707 m). Minor production also occurs from the Mississippian Spergen Formation, the Mississippian Saint Louis Formation, and the Pennsylvanian Marmaton Group. On the basis of subsurface mapping, productive Morrow sandstones are interpreted to be fluvial valley-fill deposits, consisting mainly at channel sandstones. These deposits are encased in marine shale and range in thickness from O to 55 ft (O to 16.7 m); net pay ranges from 5 to 30 ft (1.5 to 9.1 m). Porosities average 19% and permeabilities range from 1 to 4000 md. Isopach maps of the Morrow and associated stratigraphic intervals indicate that paleostructure influenced Morrow depositional patterns. Morrow channel sandstones accumulated in paleostructural low areas created by movements on basement fault blocks. Structural nosing is present in the same location and trend as the Morrow channels, indicating structural inversion. Analyses of stratigraphic intervals above the Morrow indicate that the structural inversion occurred during the Early and Middle Pennsylvanian. The field is regarded as a combination structural-stratigraphic trap. Knowledge of paleostructural control on reservoir facies provides a new idea for exploration for Morrow reservoirs in southeast Colorado.
{"title":"Tectonic and Sedimentation Model For Morrow Sandstone Deposition, Sorrento Field Area Denver Basin, Colorado","authors":"S. Sonnenberg","doi":"10.1306/AD462A9C-16F7-11D7-8645000102C1865D","DOIUrl":"https://doi.org/10.1306/AD462A9C-16F7-11D7-8645000102C1865D","url":null,"abstract":"Pennsylvanian Morrow sandstones are oil and gas productive throughout a large area in southeast Colorado. The Sorrento field is a recent major Morrow discovery with recoverable reserves estimated at over 10 million barrels of oil from an area of 3200 acres (1295 ha) at depths of 5400 to 5600 ft (1646 to 1707 m). Minor production also occurs from the Mississippian Spergen Formation, the Mississippian Saint Louis Formation, and the Pennsylvanian Marmaton Group. On the basis of subsurface mapping, productive Morrow sandstones are interpreted to be fluvial valley-fill deposits, consisting mainly at channel sandstones. These deposits are encased in marine shale and range in thickness from O to 55 ft (O to 16.7 m); net pay ranges from 5 to 30 ft (1.5 to 9.1 m). Porosities average 19% and permeabilities range from 1 to 4000 md. Isopach maps of the Morrow and associated stratigraphic intervals indicate that paleostructure influenced Morrow depositional patterns. Morrow channel sandstones accumulated in paleostructural low areas created by movements on basement fault blocks. Structural nosing is present in the same location and trend as the Morrow channels, indicating structural inversion. Analyses of stratigraphic intervals above the Morrow indicate that the structural inversion occurred during the Early and Middle Pennsylvanian. The field is regarded as a combination structural-stratigraphic trap. Knowledge of paleostructural control on reservoir facies provides a new idea for exploration for Morrow reservoirs in southeast Colorado.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1985-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121064841","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 : 1985-10-01DOI: 10.31582/rmag.mg.22.4.149
G. Mitchell
The Upper Permian and Lower Triassic rocks in the northwestern Paradox basin are closely related even though they are separated by a significant unconformity. Careful analysis of surface and subsurface data provides a framework to relate underlying units to deposition of suprajacent units. The Black Dragon Member of the Triassic Moenkopi Formation infilled the topography on the underlying Permian units. The thickness of the Black Dragon Member is inversely related to the thickness of the underlying White Rim Sandstone. The upper portion of the Black Dragon Member was deposited primarily in coastal marine environments with a very low westward depositional slope. An oolite-bearing carbonate shelf present during subsequent Sinbad Member deposition was also controlled, in part, by thickness distribution of the Permian White Rim Sandstone. The Torrey Member was deposited on the Sinbad Member in a fine-grained, elastic-dominated, low energy, very flat coastal environment. The Moody Canyon Member (uppermost Moenkopi) was deposited in a subaqueous environment, probably marine. The Emery uplift, a pre-White rim tectonic element, did not affect deposition of the White Rim, Kaibab or Moenkopi strata. The San Rafael Swell is a Laramide tectonic feature that is offset from and unrelated to the Emery uplift or deposition of the Permian and Triassic units.
悖论盆地西北部的上二叠统和下三叠统岩石虽被明显的不整合区分开，但两者关系密切。对地表和地下数据的仔细分析提供了将下伏单元与上覆单元的沉积联系起来的框架。三叠系Moenkopi组黑龙段充填了下伏二叠纪单元的地形。黑龙段厚度与下伏白缘砂岩厚度成反比。黑龙段上部主要沉积于沿海海相环境，向西沉积坡度极低。在随后的Sinbad段沉积过程中形成的含鲕粒碳酸盐陆架也在一定程度上受到二叠纪白缘砂岩厚度分布的控制。Torrey段沉积在Sinbad段上，是一个细粒、弹性为主、低能量、非常平坦的海岸环境。穆迪峡谷成员(最上面的Moenkopi)沉积在水下环境中，可能是海洋环境。前白缘构造元素砂砂隆升对白缘、Kaibab和Moenkopi地层的沉积没有影响。San Rafael Swell是Laramide构造特征，与二叠纪和三叠纪单元的em砂隆升或沉积相抵消，但与之无关。
{"title":"The Permian-Triassic Stratigraphy of the Northwest Paradox Basin Area, Emery, Garfield, and Wayne Counties, Utah","authors":"G. Mitchell","doi":"10.31582/rmag.mg.22.4.149","DOIUrl":"https://doi.org/10.31582/rmag.mg.22.4.149","url":null,"abstract":"The Upper Permian and Lower Triassic rocks in the northwestern Paradox basin are closely related even though they are separated by a significant unconformity. Careful analysis of surface and subsurface data provides a framework to relate underlying units to deposition of suprajacent units. The Black Dragon Member of the Triassic Moenkopi Formation infilled the topography on the underlying Permian units. The thickness of the Black Dragon Member is inversely related to the thickness of the underlying White Rim Sandstone. The upper portion of the Black Dragon Member was deposited primarily in coastal marine environments with a very low westward depositional slope. An oolite-bearing carbonate shelf present during subsequent Sinbad Member deposition was also controlled, in part, by thickness distribution of the Permian White Rim Sandstone. The Torrey Member was deposited on the Sinbad Member in a fine-grained, elastic-dominated, low energy, very flat coastal environment. The Moody Canyon Member (uppermost Moenkopi) was deposited in a subaqueous environment, probably marine. The Emery uplift, a pre-White rim tectonic element, did not affect deposition of the White Rim, Kaibab or Moenkopi strata. The San Rafael Swell is a Laramide tectonic feature that is offset from and unrelated to the Emery uplift or deposition of the Permian and Triassic units.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1985-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130099792","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 : 1985-10-01DOI: 10.31582/rmag.mg.22.4.192
W. Hansen
The Upper Green River flows southward out of the Green River Basin through a series of deep canyons across the Uinta Mountains in a course that post-dates the deposition of the Bishop Conglomerate (Oligocene); the ancestral Green flowed east to the Mississippi, probably by way of the North Platte. Basinal subsidence in Eocene time had produced 3 large, well-known, interconnected lakes on both sides of the Uinta Mountains--Fossil Lake and Lake Gosiute on the north side and Lake Uinta on the south. Lake-to-lake connections are indicated by a remarkably well preserved fauna common to all three lakes, the famous Green River fish fauna. Most of these fish had Mississippi River affinities, hence, the Continental Divide in Eocene time was west of the lakes. The Colorado River system did not yet exist. After the lakes disappeared, drainage was generally eastward across the present Continental Divide, until the Green River was captured near Green River, Wyo. by south-flowing drainage in middle Pleistocene time, ca., 600,000 years ago. Capture of the Upper Green River as recently as middle Pleistocene time, if a valid hypothesis, must take into account the marked differences between the endemic and indigenous fish fauna of the Green River and that of the North Platte. The Green is postulated to have been captured at the height of a glacial stage when the Green River Basin was a frigid semidesert and its fish population had been forced far downstream by the hostility of the glacial climate. Indigenous nonendemic cold-water fauna of the Green River/Upper Colorado River Basin - salmonids, cottids, and others - are geologically recent arrivals from the Columbia River Basin; they probably transferred to the Green during an interglacial stage, then spread throughout the Upper Colorado River system during the colder water phase of a succeeding glacial stage. Several possible transfer points exist along the Green/Bear and Green/Snake River divides.
{"title":"Drainage Development of the Green River Basin In Southwestern Wyoming and its Bearing on Fish Biogeography, Neotectonics, and Paleoclimates","authors":"W. Hansen","doi":"10.31582/rmag.mg.22.4.192","DOIUrl":"https://doi.org/10.31582/rmag.mg.22.4.192","url":null,"abstract":"The Upper Green River flows southward out of the Green River Basin through a series of deep canyons across the Uinta Mountains in a course that post-dates the deposition of the Bishop Conglomerate (Oligocene); the ancestral Green flowed east to the Mississippi, probably by way of the North Platte. Basinal subsidence in Eocene time had produced 3 large, well-known, interconnected lakes on both sides of the Uinta Mountains--Fossil Lake and Lake Gosiute on the north side and Lake Uinta on the south. Lake-to-lake connections are indicated by a remarkably well preserved fauna common to all three lakes, the famous Green River fish fauna. Most of these fish had Mississippi River affinities, hence, the Continental Divide in Eocene time was west of the lakes. The Colorado River system did not yet exist. After the lakes disappeared, drainage was generally eastward across the present Continental Divide, until the Green River was captured near Green River, Wyo. by south-flowing drainage in middle Pleistocene time, ca., 600,000 years ago. Capture of the Upper Green River as recently as middle Pleistocene time, if a valid hypothesis, must take into account the marked differences between the endemic and indigenous fish fauna of the Green River and that of the North Platte. The Green is postulated to have been captured at the height of a glacial stage when the Green River Basin was a frigid semidesert and its fish population had been forced far downstream by the hostility of the glacial climate. Indigenous nonendemic cold-water fauna of the Green River/Upper Colorado River Basin - salmonids, cottids, and others - are geologically recent arrivals from the Columbia River Basin; they probably transferred to the Green during an interglacial stage, then spread throughout the Upper Colorado River system during the colder water phase of a succeeding glacial stage. Several possible transfer points exist along the Green/Bear and Green/Snake River divides.","PeriodicalId":101513,"journal":{"name":"Mountain Geologist","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1985-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127190882","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 : 1985-07-01DOI: 10.31582/rmag.mg.22.3.94
J. P. Matheny, M. Picard
Results of a sedimentological study of the Emery Sandstone Member of the Mancos Shale (Upper Cre- taceous) in southern Castle Valley, Utah, are presented. Depositional environments, paleogeography, textural and mineralogrcal characteristics and possible sediment sources are determined. Tidal flat deposits are dominant in the Emery, but subtidal (shoreface) and offshore deposits also occur. The paleotidal range is estimated to have been between 1 3 and 1.7 m Many asymmetrrc, transgressive-regres- srve cycles of two drfferent magnitudes and periods are present. They formed in response to minor fluctua-tions in sea level combrned wrth slight varrations m the subsidence rate. The Emery Sandstone was deposited m the foreland of the Sevier orogenic belt. The average orientatron of the paleoshoreline, as determrned by paleocurrent analysis, was N. 9" W. Sediment was probably transported southward from the Utah-Idaho- Wyomrng border area by longshore currents. Well-sorted, subrounded to subangular, very fme-grained subarkose is the dominant rock type in the Emery Dolomite and calcrte are the major cements Average porositres, based on thin sectron analysis, are less than 2 percent. Abundant chert grains and reworked authigenrc quartz overgrowths suggest a sedimentary source terrain. The observed amounts of feldspar could have been derived from Mesozorc sedimentary rocks exposed in the Sevier orogenrc belt
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