Dolomitic Sandstone Research Articles

Kaibab Limestone and Associated Strata, Circle Cliffs , Utah

Exposed Permian rocks studied in the Circle Oiffs region are the upper part of the White Rim Sandstone Formation of the Cutler Group and the overlying Kaibab Limestone. The former is composed of calcareous and dolomitic sandstones and sandy dolomites formed under stable tectonic conditions in a nearshore marine environment by reworking of the underlying aeolian portion of the White Rim Member. The Kaibab Limestone is actually a slightly calcareous, partly sandy, glauconitic dolomite which was chiefly a biomicrite before dolomitization. It formed in shallow, though quiet, marine waters under tectonically quiescent conditions. It disconformably overlies the White Rim Sandstone. Detrital intertidal and very shallow subtidal sediments of the lowermost Moenkopi Formation (Triassic), mostly chert breccias, overlie the irregular, partly channeled surface of the Kaibab Limestone. This ' attests to post-Kaibab emergence and erosion. Uniformity of lithologies and thicknesses of individual Permian beds traced across the Circle Cliffs Anticline demonstrate the absence of a late Permian paleostructure.

Recognition of Petroleum-bearing Traps by Unusual Isotopic Compositions of Carbonate-cemented Surface Rocks

Research Article| July 01, 1974 Recognition of Petroleum-bearing Traps by Unusual Isotopic Compositions of Carbonate-cemented Surface Rocks Terrence J. Donovan; Terrence J. Donovan 1U.S. Geological Survey Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Irving Friedman; Irving Friedman 1U.S. Geological Survey Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Jim D. Gleason Jim D. Gleason 1U.S. Geological Survey Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Geology (1974) 2 (7): 351–354. https://doi.org/10.1130/0091-7613(1974)2<351:ROPTBU>2.0.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Terrence J. Donovan, Irving Friedman, Jim D. Gleason; Recognition of Petroleum-bearing Traps by Unusual Isotopic Compositions of Carbonate-cemented Surface Rocks. Geology 1974;; 2 (7): 351–354. doi: https://doi.org/10.1130/0091-7613(1974)2<351:ROPTBU>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Unusual carbon and oxygen isotopic compositions characterize outcropping dolomitic sandstone of Permian age over the Davenport oil field, Oklahoma. The δC13PDB ranges from −5.1 to −11.3/mil and the δO18SMOW ranges from +28.8 to +48.8/mil. Areal distribution of both isotopic ranges is systematic and closely reflects the distribution of petroleum in the producing interval at a depth of 1,000 m (3,300 ft). The 20/mil positive oxygen range in these surface rocks suggests evaporative fractionation of ground water controlled by the near-surface expansion of vertically migrating dry natural gas from the underlying deposit. The rather light, though unexceptional, carbon values, unlike those reported for other hydrocarbon-derived carbonate rocks, indicate only partial chemical or biochemical oxidation of the gas, suggesting further that the leakage rate was relatively rapid.At the Cement oil field, Oklahoma, similar relations in surface rocks occur, but the carbon isotopic values are exceptionally light (−5.5 to −39.2/ml relative to PDB), indicating significant near-surface oxidation of slowly seeping hydrocarbons of low molecular weight.The occurrence of carbonate rocks derived from the chemical oxidation or bacterial conversion of hydrocarbons is well known (Thode and others, 1953; S. R. Silverman and others, unpub. data; Russell and others, 1967; Hathaway and Degens, 1968; Mamchur, 1969; Davis and Kirkland, 1970). Such carbonates typically have δC13PDB values more negative than about −25/mil. Similarly, unusual isotopic signatures have been documented in carbonate-cemented sandstone and calcitized gypsum cropping out over the Cement oil field in the southeastern part of the Anadarko basin of Oklahoma (Donovan, 1974). There, the rock cements display carbon isotopic ratios that are increasingly light and oxygen ratios that are increasingly heavy toward the crest of the anticlinal structure. These trends are limited areally and are systematic in their patterns, reflecting the subsurface distribution of petroleum. Both liquid and gaseous hydrocarbons have leaked from the Cement reservoirs; much of the hydrocarbon was oxidized and the carbon incorporated into the interstitial carbonate cements of the overlying rocks. Rapid vertical leakage of gas, expansive under depressurization, resulted in preferential evaporation of H2O16, compared with H2O18 from near-surface ground waters. This evapo-escape to the atmosphere. Rayleigh distillation proceeds if escape rates cause evaporation of ground water at rates faster than the replacement or recharge rate of meteoric water. Rocks whose isotopic compositions reflect an intermediate mix of these contrasting processes have not yet been found but presumably exist. The existence of these kinds of isotopically anomalous carbonate cements would prove useful in petroleum exploration independently of other kinds of geochemical indicators. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Microbiota from the Late Proterozoic Tindir Group, Alaska

Preliminary investigation of carbonaceous sediments from the late Proterozoic Tindir Group, east-central Alaska, reveals the presence of abundant single-celled and spherical colonial nannofossils interpreted to represent blue-green algae. Similar micro-organisms, particularly Sphaerocongregus Moorman, have been reported from the late Proterozoic Hector Formation of southwestern Alberta, Canada. The fossils reported here come from beds tentatively considered to represent the upper Tindir Dolomitic Sandstone and Shale member, stratigraphically above the Basalt and Red Beds member, for which an age of no more than 850 m.y. has been suggested. However, it is possible that the fossiliferous sequence is correlative with the lower Tindir Dolomite and Shale member which immediately underlies the Basalt and Red Beds member, and which contains a stromatolitic structure known in beds 950 m.y. old and older elsewhere.

Clastic dykes in the Namurian shales of Co. Leitrim, Republic of Ireland

SummaryA description is given of the numerous thin dolomitic sandstone dykes cutting dark marine shales of E1a age in Co. Leitrim. They are almost wholly confined to the Dough–Thur Mountain area, which is cut by the Caledonoid trending Ox Mountain and Belhavel Faults. It is thought probable that movement along one of these faults, possible in E1c times, conferred thixotropic properties to a sand horizon in the marine shales and also produced fractures in the shales up which the sand was intruded.

Stratigraphy of Chaffee Group (Upper Devonian), West-Central Colorado

During the Late Devonian, sediments deposited in shallow marine, brackish, and tidal mud-flat environments accumulated in west-central Colorado. This sedimentary sequence comprises the Chaffee Group, which is divided into two formations; the lower third, the Parting Formation, consists predominantly of detrital rocks; the upper two thirds of the group, the Dyer Formation, is composed of carbonate rocks. The Parting Formation is divided into three stratigraphic units, designated A, B, and C, in ascending order. Unit A is chiefly quartzose sandstone. Unit B is composed of four persistent beds which, in ascending order, are shale, thin dolomite, shale, and sandy dolomite or dolomitic sandstone that contains dolomite pebbles. Unit C consists of lenses and beds of quartzose sandstone, sandy shale, and sandy dolomite. On the east and northeast all three units change in facies to quartzose sandstone. The Parting Formation is principally a transgressive sequence, but the middle dolomite bed and the top bed of unit B represent regressive phases. The source for the detrital sediments was a crystalline highland flanked by sedimentary rocks, located east and northeast of the study area. This highland persisted throughout Chaffee deposition, but yielded more detritus to the Parting Formation. The maximum advance of the Devonian sea occurred during upper Parting and lower Dyer deposition. The Dyer Formation is a regressive carbonate sequence that can be divided into two carbonate members. The lower member consists of dark-gray, dolomitic, fossiliferous limestone, and herein is named the Broken Rib Member. The upper member consists of light-gray dense, stromatolitic dolomite, and herein is named the Coffee Pot Member. The Broken Rib Member apparently reflects deposition in a sublittoral environment. The stromatolites of the Coffee Pot Member are interpreted as having formed by the trapping and binding action of blue-green algae, which grew in the littoral zone. Intraformational breccias formed by the disruptive action of waves on desiccation polygons are associated with the stromatolites.

Geology of Central Grant Range, Nevada

Approximately 26,000 ft (7,930 m) of Paleozoic carbonate and subordinate clastic sedimentary rocks is exposed in the central Grant Range. Cambrian quartzite, shale, and minor limestone are the oldest exposed rocks in the area. The overlying 11,200 ft (3,416 m) consists of limestone, dolomite, shale, and minor quartzite and sandstone; this sequence begins with the Ordovician Pogonip Group and ends with the Mississippian Joana Limestone. The overlying strata are Upper Mississippian and Pennsylvanian shale, and minor sandstone and limestone. The Paleozoic sequence is overlain unconformably by Cenozoic sedimentary and volcanic rocks. Three major low-angle faults that separate younger rocks from older are exposed in the area. They are, in ascending order, the Grant Canyon, Heath Canyon, and Beaty Canyon faults. The Grant Canyon fault emplaces gently dipping Middle Cambrian limestone and shale over steeply dipping Lower Cambrian Prospect Mountain Quartzite. Rocks considered to be Lower Ordovician are separated from overlying Cambrian units by the Heath Canyon fault. The Beaty Canyon fault generally carries concordant Silurian through Pennsylvanian strata over Lower Ordovician rocks. Relative eastward movement of the upper plate rocks is demonstrated by folds in the lower plates, which are overturned to the east. In addition, five subordinate low-angle faults are recognized. Synorogenic regional metamorphism, predating the faulting, converted part of the Cambrian and Lower Ordovician strata into tectonically banded marbles, and chlorite-muscovite and biotite phyllites. Postmetamorphic low-angle faulting resulted in superposed local mylonitization. Medium- to high-grade calc-silicate rocks are associated with a granitic intrusion. Folding within the range is locally intense, and high-angle faulting, with the exception of the range front fault or faults, is mostly of small displacement. A Mesozoic age of metamorphism and thrusting is inferred from regional evidence.

MINERALOGY OF THE LOWER JURASSIC IN WEST CENTRAL ALBERTA

ABSTRACT The Lower Jurassic in the Rocky Mountain House area of central Alberta includes the lower part of the Fernie Formation, which may be subdivided into two distinct lithologic units: the Nordegg Member, and the Poker Chip Shale Member. These units were studied by power X-ray diffraction to determine semiquantitative values of mineralogy. The values were verified by data from atomic-absorption spectrometry and insoluble-residue calculations. Quartz, calcite, and dolomite comprise the essential minerals of the Nordegg Member, with pyrite, siderite, and bituminous matter as accessories. On the basis of these minerals and the lithologic data, three major facies can be identified: a dolomitic sandstone along the eastern margin, which passes westerly into a bioclastic limestone, and a chert farther to the west. Deposition of the Nordegg Member was on a stable shelf with a shoreline lying to the east, and deeper waters to the west. Two possible ultimate sources for the abundant silica required for biogenic deposition of chert are available—volcanic ash from central British Columbia, or silica carried in solution by streams flowing westerly off the Precambrian Shield area. Mineralogy of the Poker Chip Shale Member is less variable, with quartz, illite and kaolinite being the essential constituents and pyrite, siderite, and glauconite the accessory minerals. No facies relationships were observed in the Poker Chip Shale Member, but a depositional environment similar to that of the Nordegg Member is suggested.

Petrography-Porosity Relations in Carbonate-Quartz System, Gatesburg Formation (Late Cambrian), Pennsylvania

The Gatesburg Formation of Late Cambrian age in central Pennsylvania consists of cyclic deposits ranging from nearly pure dolomite to nearly pure quartzite containing less than 5 percent clay and 2 percent other minerals. Principal-components and multiple-regression analyses of the petrographic variables of size, shape, sorting, and packing indicate that the degree of packing (quartz-grain to quartz-grain contacts) is the primary property influencing intergranular porosity. The degree of packing accounts for 36 percent of the total variation in porosity explained by linear multiple-regression analysis. Principal-components analysis shows these two variables to be significantly related to each other or associated with common causes. This carbonate-quartz system is interpre ed as a beach-lagoon-dune sedimentary system. Development of intergranular porosity, ranging from 2 to 20 percent, is related causally to a quartz-grain supported framework that isolates and preserves pores where the quartz-carbonate ratio is equal to or greater than 1:1. Of the variables tested, statistically significant correlations were found between (1) packing and amount of quartz, (2) packing and porosity, and (3) amount of quartz and porosity. Almost 50 percent of the total variation in porosity is explained by packing and the amount of quartz; however, the partial correlation coefficient (r13.2) between porosity and amount of quartz, with the influence of packing removed, is not significant (r13.2 = 0.173 at the 5 percent significance level). An unexpected c nclusion is that intergranular porosity is not related to grain size in this system. Permeability values determined for the dolomitic sandstone, dolomitic quartzite, and orthoquartzite are several orders of magnitude higher than those for the sandy dolomite, and range from less than 0.01 to 1,361 md in the carbonate-quartz system. Results and conclusions of this investigation should be applicable to other carbonate-quartz systems of similar cyclic character.

Lacq Gas Field, France: ABSTRACT

The Lacq gas field, France's most important, was discovered in 1951 by geophysical methods. The field is just north of the major overthrust separating the southern edge of the Aquitaine basin from the Nord Pyrenees foredeep. Directly under the field is a paleo-high flanked by two strongly subsided basins: the Arzacq basin on the north and Upper Cretaceous flysch trough on the south. The gas is trapped in a roughly elliptical anticlinal structure in which differential subsidence has played the major role. The gas has a 15.4 percent H2S content and occurs under strong pressure (9,700 psi at 13,200 ft) in uppermost Jurassic dolomitic strata, Purbeckian-Wealdian sandstone, and Neocomian limestone and dolomite. Reservoirs characteristics of these rooks are poor (5 percent porosity; 0.1 md permeability at best) and production is possible only because of intense fracturing on the upper part of the structure. Production of the field is presently 700 MMcf per day of raw gas and in-place reserves are evaluated at 8.8 trillion cu ft. End_of_Article - Last_Page 555------------

Dolomite from the continental slope off southern California

ABSTRACT A 500-pound, manganese-covered dolomite boulder was recovered from the ocean bottom near the continental slope off southern California, at 33°44N latitude 120°45W longitude. The dolomite has a massive appearance although a few barely discernible planar features may be bedding. Perfect dolomite rhombs are intergrown in a matrix of anhedral quartz with minor amounts of zeolites and detrital minerals. Characteristically, each dolomite rhomb has an inclusion at its center, which are similar to those in the cement of a dolomitic sandstone at Point Fermin, California. The dolomite may be a less-clastic, more calcareous facies of the Point Fermin dolomitic sandstone. Alternatively, it may be a dolomitized foraminiferal ooze. In which case it could be a fragment of a lithified deep-sea ooze, possibly part of seismic layer two.

DESCRIPTION AND PALEOECOLOGY OF A TREMADOC DENDROID GRAPTOLITE FROM NORTHERN NEW YORK

A new species of Dictyonema from dolomitic sandstones close to the top of the Bucks Bridge Formation from a locality in the town of Potsdam, New York, is described; associated discoidal gastropods suggest a Tremadoc age. Ecological interpretation shows that this dendroid was sessil-benthonic in clusters or “gardens” in a relatively shallow-water littoral environment, the bottom containing numerous tubes apparently formed by a tunneling organism.

The Petrography of Pennsylvanian Chert Breccias and Conglomerates; Rocky Mountain Group, Banff, Alberta

ABSTRACT Chert sharpstone breccias are preserved some stratigraphic sections of the Kananaskis Formation (Pennsylvanian) of the Rocky Mountain Group the Banff area, Alberta. The breccias incorporate, or occur immediately above, or above and below, an organic chert whose fauna dates the formation (McGugan & Rapson, 1960). In other sections a mature chert conglomerate is developed and contains numerous sharpstone fragments. Similar sharpstone fragments are mixed with slump breccias of laminated dolomitic sandstone. Petrographic observation indicates the following sequence of events: Chert Breccias. (1) Preservation of the microfauna a silty carbonate mud. (2) Replacement of the calcareous organisms by silica and polymerization of silica around or within the organic debris to form a gel nodule or lens. (3) Syneresis or contraction of the latter to give a brecciated surface to the nodule or lens. (4) Crystallization of the silica and cementation of the primary cryptocrystalline breccia by microcrystalline silica, the whole still an unconsolidated silty carbonate mud. (5) Selective replacement of the microcrystalline silica by dolomite with consequent isolation of the chert splinters. (6) Further replacement of microcrystalline and cryptocrystalline silica by dolomite, with slight displacement of the fragments and the introduction of detrital ma erials. The stages can be traced outward from the center of the organic chert nodules. Brecciation must have taken place in situ before complete consolidation of either matrix or nodule. Breccio-conglomerates. The sharpstone fragments were removed from some areas of formation, transported without rounding and mixed with (a) a pre-existing mature gravel, (b) a penecontemporaneous slump breccia. A third type of silicification cements both round and sharpstones and apparently replaces the dolomite matrix. The geochemical and environmental conditions necessary for such phenomena are discussed. The environment suggested is an evaporitic one cut by local distributaries and modified by a retreating sea. A simile is drawn with the present-day environment along the southeast coast of South Australia (Alderman & Skinner, 1957).

Possible Early Devonian Seaway in Northern Rocky Mountain Area: ABSTRACT

A seaway may have occupied a geosynclinal trough in Washington and Oregon during Early Devonian time. Its existence is postulated from the distribution and sedimentary environment of isolated deposits of Early Devonian and probably Early Devonian age in the northern Rocky Mountains. Regional evidence suggests that the Beartooth Butte formation of Early Devonian age was laid down along the eastern margin of a sea and on the landmass that bordered it in southern and central Montana and northern Wyoming. The Williston basin area in North Dakota was apparently a part of the landmass. The Water Canyon, Maywood, and Ghost River formations which may be in part correlative with the Beartooth Butte were laid down in a nearshore, shallow-water marine environment in northern Utah an southern Idaho, western Montana, and west-central Alberta, respectively. These lie west of the marginal marine deposits of the Beartooth Butte but several hundred miles east of the postulated north-south axis of the seaway. Discontinuous deposits of the Beartooth Butte formation, which formerly was considered to be a local channel filling at a few localities in northern Wyoming, have now been widely recognized. The formation consists of grayish red and yellowish gray silty dolomite and dolomitic siltstone, sandstone, conglomerate, and breccia. It is generally less than 10 feet but locally as much as 170 feet thick. The continental beds of the Beartooth Butte were laid down on a land surface of generally low relief with karst topography in places. Redbeds filling channels and sinkholes were derived mostly from red soils that had developed on carbonate rocks possibly in a humid, tropical, or subtropical climate. Marginal marine beds of the formation were probably deposited in estuaries, bays, and lagoons a ong a drowned coast characterized by long, narrow marine embayments. The Water Canyon formation of Early Devonian age in northern Utah is about 400 feet thick. It is composed of intraformational breccia, silty dolomite, cherty dolomite, and dolomitic sandstone and sandy dolomite containing End_Page 416------------------------------ fish remains. The lower part of the Maywood formation in western Montana is 200 feet thick and may be of Early Devonian age. It is composed of thin-bedded silty dolomite and dolomitic siltstone with imbedded crystals of dolomite pseudomorphous after halite and, like the Water Canyon formation, dolomitic sandstone containing fish remains. The upper part of the Ghost River formation in west-central Alberta is lithologically similar to the lower part of the Maywood and may also be of Early Devonian age. Discontinuous shallow-water, near-shore marine deposits of these three formations were probably laid down at the mouths of bays. The probable subsurface occurrence of the Beartooth Butte formation and its tentative correlatives provides a hitherto unrecorded and untested stratigraphic trap that might be considered in planning petroleum exploration. End_of_Article - Last_Page 417------------

Montoya Dolomite and Fusselman Dolomite in Silver City Region, New Mexico

Rocks of the Montoya dolomite of Late Ordovician age and the Fusselman dolomite of Silurian age, exposed in the Silver City region of southwest New Mexico, show marked similarities in lithology, sequence, and thickness to rocks of the same formations as reported farther east. The sections in the Silver City region, described here in detail for the first time, are at Bear Mountain, northwest of Silver City; at Lone Mountain, southeast of Silver City; and near Georgetown, northeast of Silver City. The Montoya dolomite is divisible into the same four units recognized farther east in New Mexico and Texas, and the same names are applied to them: from the base up they are the Cable Canyon sandstone member, 11-28 feet of coarse-grained dolomitic sandstone; the Upham member, 52-9 feet of massive dolomite; the Aleman cherty member, about 75 feet of distinctive interlaminated dolomite and chert; and the Cutter member, about 200 feet of massive dolomite. The Cutter member is separated by a generally sharp and distinct lithologic break from the overlying Fusselman dolomite, which is composed of about 100-300 feet of gray massive dolomite. The contact is marked by two lithologic contrasts: the Cutter is light gray and dense, and the Fusselman dark gray and vuggy. Fossils collected from the Cutter member at Bear Mountain are of Late Ordovician age. Pentameroid brachiopods near the middle of the Fusselman dolomite in its thickest occurrence--at Lone Mountain--are of Middle or Late Silurian age, but corals near the base of the Fusselman suggest that the lower part may b of Late Ordovician age. The subdivision and nomenclature of the Montoya and Fusselman have had an involved history since the two formations were originally differentiated and named by Richardson in 1908. The major developments in this history, especially those since Kelley and Silver's work in 1952, are reviewed and are summarized diagrammatically, in order to provide a background for the discussion of the Montoya and Fusselman at Silver City. Most workers have now accepted Kelley and Silver's (1952) proposal to raise the Montoya to group status and to consider its subdivisions, which are valid lithogenetic units, as formations. Reference to the Montoya as a formation in this paper reflects the current usage of the U. S. Geological Survey but does not preclude group status of the Montoya in areas where its component members are so exposed as to fulfill the other requirement of a formation, that of mappability.

Some ore occurrences of the Mississippi Valley type in equatorial Africa

The Mindouli deposit (equatorial Africa), which consists of copper, lead, and zinc minerals occurring as replacements of massive dolomite (Schisto-calcaire) or younger Precambrian coarse-grained sandstones adjacent to a fault zone, and locally in veins along the faults, is described as representative of a number of Mississippi Valley-type ore deposits in the lower Congo region.

UPPER CROIXAN STRATIGRAPHY, UPPER MISSISSIPPI VALLEY

In the Upper Mississippi Valley Croixan strata above the Franconia formation consist of dolomite and dolomitic siltstone and sandstone overlain by massive nondolomitic sandstone. Previous classifications of this succession have employed both faunal and lithologic criteria for discrimination of formations and members. The strata can readily be divided on lithologic characters alone, and such divisions are markedly time-transgressive from shoreward to basinward facies. The terminology adopted represents a return to early lithologic classifications in which the St. Lawrence and Jordan formations are recognized as the dolomitic strata and the massive sandstone, respectively. The St. Lawrence is further divided into the Black Earth member (sandy and silty dolomite) and the Lodi member (dolomitic siltstone and fine-grained silty and dolomitic sandstone). Faunal zones are largely independent of the lithologic units. It is urged that the term Trempealeau, previously employed as a formation name to include all these strata and also as a stage name, be restricted to Trempealeauan Stage.

Carboniferous and Permian Stratigraphy of the Oquirrh Basin, Northwestern Utah: ABSTRACT

The Oquirrh basin, the dominant element in the late Paleozoic history of northwestern Utah and adjacent areas, first developed near the eastern margin of the Cordilleran miogeosyncline in medial Mississippian time. From then until the medial Permian, it existed continuously with alternate times of extension and contraction, the extensions being generally northwestward toward central Idaho and southwestward toward northeastern Nevada. Times of increased tectonism, which appear to be represented in accentuation of subsidiary basins and rise of marginal positive areas, with attendant contraction of the sea, were Meramecian and early Chesterian, Morrowan-Lampasan, Missourian-Virgilian, and early Wolfcampian. Times of decreased tectonism with less rapid depression and wider sp eading of the marine waters were Desmoinesian and Leonardian-early Guadalupian. Particularly noteworthy are the Logan-Milligen sub-basin of early Chesterian time, the main basin in Wolfcampian time, and the Diamond Creek and Lower Park City sub-basins of late Wolfcampian and early Leonardian time. In the latter, dolomite, red and buff sandstone, and anhydrite were deposited to notable thicknesses. The eastern margin of the Oquirrh basin was exceptionally abrupt and the remarkable change of facies exhibited there is accentuated by overthrusting which has moved the basin facies tens of miles eastward on to the shelf facies. End_of_Article - Last_Page 2612------------

Geology of Rocky Mountain Front Ranges Near Bow River, Alberta

The front ranges of the Rocky Mountains near the Bow River, Alberta, are a fine example of the thrust-fault type of structure which characterizes the eastern Canadian Rockies. The ranges consist largely of repeated sequences of Paleozoic strata dipping 40° W. and separated by subsequent valleys eroded in Mesozoic or Upper Paleozoic beds. Cambrian to Upper Cretaceous strata are exposed. The map area is traversed by the Calgary-Banff highway and the main line of the Canadian Pacific Railway and, although visited by many geologists since the 1880's, it has not heretofore been mapped. The map area, which consists of three fault blocks that repeat most of the Paleozoic section, is bounded on the east by a major folded thrust fault which throws Middle Cambrian rocks over Upper Cretaceous strata. This fault marks the boundary between the Rocky Mountains and the Foothill belt. The Cascade Coal Basin is the westward limit of mapping. Middle Cambrian strata along the mountain front are overlain unconformably by the Ghost River formation of questionable Devonian age. This is overlain conformably by Upper Devonian dolomites and limestones and these are followed by Lower, Middle, and Upper Mississippian shales and limestones, Pennsylvanian quartzitic and dolomitic sandstones, Permian (?) chert and quartzite Triassic shaly siltstone, Jurassic black shale, and Lower Cretaceou or Jurassic sandstones, shales, and coal. No igneous rocks are exposed in this part of the Rocky Mountains. The great thrust faults, displacements on which are measured in miles, in some places develop drag folds, but the fault planes are clean breaks with little or no gouge, and the strata on both sides approach parallelism with the fault planes.

NOTABLE FEATURES IN THE MIDDLE PERMIAN MARLS OF SOUTH YORKSHIRE AND NORTH NOTTINGHAMSHIRE

PART I. PEBBLE BANDS IN THE MIDDLE MARLS. The most conspicuous elements in the Eastern Permian Marls of this country are generally marl, sandy marl sometimes approximating to definite siltstone, hard dolomitic sandstone very variable in thickness and gypsum, well developed in many pit sinkings and occasionally in superficial exposures. Fairly pure sand beds are sometimes encountered but usually a certain percentage of calcite or dolomite occurs throughout. It is seldom that pebbles are mentioned in these deposits so that particular interest attaches to the recent exposure in the districts of Letwell, Firbeck and Lindrick in South Yorkshire of several well developed and sometimes consolidated bands of pebbles. During the laying of a new water-main which connects the Sheffield supply to some of the outlying villages in the south of Yorkshire the trench-line passed through a sequence of Permian strata from the lowest to the highest members of the formation. Of major importance were the sections in the Middle Permian Marls since in the Letwell and Firbeck areas several pebble-bands were exposed in the trench, the pebble beds being interstratified with the normal marly strata. At Lindrick a pebble bed was recently exposed at the base of a new sand quarry, details of which will follow later in this paper. Before dealing with the individual sections a few words concerning the general geology of the district would be of advantage. Letwell village lies some 12 miles east of Sheffield and is situated on a rather prominent portion of ground about ...