Cambrian Section Research Articles

Updated Isopach Maps of Prairie du Chien, Trempealeau, and Munising of Michigan Basin: ABSTRACT

As part of an ongoing project concerning the Lower Ordovician and Cambrian sections of the Michigan basin, consistent correlations from modern electrical logs have been used to develop structural and isopach maps of the Prairie du Chien, Trempealeau, and Munising of the Michigan basin. The Prairie du Chien is subdivided into the upper Bruggers sandstone, the middle Foster formation, and the lower Umlor formation. The bruggers is thickest in the area of the common boundary between Kalkaska, Crawford, Missaukee, and Roscommon Counties. The Foster and Umlor are thickest in Gladwin County. The Trempealeau is thickest in the area of the common boundary between Bay, Midland, and Gladwin Counties. A secondary area of thickening also occurs in the extreme southwest, toward Berrien County. The Munising Formation is thickest toward the southeast, despite the fact that it is entirely truncated by an erosional unconformity in extreme southeastern Michigan. An area of secondary thickening is present in the central basin, near Missaukee and Clare Counties.

Oil and Gas Developments in Western Canada in 1985

Western Canadian petroleum industry activity soared to record levels in 1985, exceeding the 1980 record by 25%. This was the third successive annual increase following the 1981-1982 slump. The signing of the Western Accord by the federal government and the provinces of British Columbia, Alberta, and Saskatchewan brought oil-price decontrol and numerous incentives in the form of tax relief and new marketing strategies for oil and gas throughout western Canada. Provincial government incentives and new royalty holidays bolstered western Canada drilling activity. Total number of wells drilled increased 26% in 1985, to 11,071 wells. Exploratory drilling rose 15% to 3,293 wells, while development drilling reached a record level of 7,778 wells, up 32% from 1984. Exploratory succ ss rate dropped from 60% to 57%, with 1,250 oil discoveries and 620 gas discoveries. Development success rate remained constant at 89%, with 5,044 oil completions and 1,900 gas completions. Exploratory drilling activity rose in every area, while development drilling increased in all areas but Manitoba and the Northwest Territories-Arctic region. Average well depth decreased in every province but Manitoba, which increased slightly, and the Northwest Territories-Arctic region, which remained constant. Land sale revenue approached record levels, increasing 28% to $1,037 million,(FOOTNOTE 3) but was still shy of the 1980 record of $1,311 million. Alberta's 25 Crown land sales generated $796 million, Saskatchewan's 4 Crown land sales generated $149 million, British Columbia's 5 Crown land sal s generated $88 million, and Manitoba's 2 Crown land sales generated $4.2 million. Average price per hectare decreased in all provinces but Manitoba, which increased to a new record level of $272/ha. Exploratory and development drilling in Alberta continued to dominate western Canada with 61% of the total activity. Devonian reservoirs yielded prominent discoveries at Driftpile, Cindy, Evi, Bat Lake, Trout, Kidney, and Shekilie, while Cretaceous strikes were made at Thornbury and Bow Island. Multimillion-dollar expansions and developments of oil sands projects were announced by Dome, Murphy, and Westmin at Lindbergh, Esso at Cold Lake, BP and Petro-Canada at Wolf Lake, and Dome at Primrose. Syncrude announced a record production year of 7.46 million m3 of synthetic crude during 1985. Saskatchewan activity hit record levels as the provincial government continued royalty holidays and encouraged gas exploration with new provincial policies. Exploration activity was concentrated in the Weyburn-Midale Mississippian trends, with development of Petro-Canada's Cretaceous Salt Lake oil field nearly complete by year end. The $650-million Newgrade heavy oil upgrader received the go-ahead for construction in the Regina area, whereas Husky's $3.2-billion upgrader was still being held up by ongoing federal, provincial, and company fiscal negotiations. British Columbia improved provincial incentives for oil and gas drilling and generated a new strategy for gas marketing. Development continued in the Desan area, and exploratory gas successes were attained in the Weasel and Alces areas. At year end, the provincial government was negotiating for control over offshore resources, and indications were pointing to the collapse of the $2.5-billion LNG project to supply liquefied natural gas to several Japanese utilities. A significant Lower Mississippian oil discovery in the Daly area of Manitoba spurred land sale prices to record highs during 1985. Development activity was centered in the Daly-West Daly area and around the 1980 Jurassic oil discovery at Waskada. The introduction of the Canada Petroleum Resources Act and the abolition of the Petroleum Incentives Program, together with declining world oil prices, will change the future exploration approach in frontier areas. Significant oil and gas discoveries in the Beaufort region were made at Nipterk and Adlartok, while the Arctic Islands region had a major gas find at Cape Allison, as drilling activity tapered off by 6% during 1985. Delineation of the 1984 Cretaceous gas and condensate discovery at Tuk was a disappointment, but proved to be a pleasant surprise when testing produced significant amounts of oil and gas from the uphole Tertiary section. Gas and condensate discoveries were also made in the Lower Cambrian section of the Tweed Lake area. The first commercial oil production project in the north, at Norman Wells, was connected to southern markets with the completion of the Zama pipeline by Esso Resources and Interprovincial Pipeline, nearly 65 years after the first discovery well was drilled. In addition, the first production in 17 years of Arctic exploration was shipped by tanker from Panarctic's Bent Horn oil field on Cameron Island to a refinery in Montreal. Instability within OPEC pushed Middle East oil production upward and sent world oil prices spiraling downward at year end. Exploration budgets were being reviewed as cash flow diminished from reduced returns on production. The year 1985 established new record highs in drilling activity for western Canada, but tougher times appeared to be ahead for 1986. FOOTNOTE 3. Money in Canadian dollars. End_Page 1231------------------------------

Early Cambrian innovation in shallow subtidal environments: Paleoenvironments of Early Cambrian shelly fossils

Contrary to onshore-offshore patterns described for several Phanerozoic clades, evolutionary innovations leading to the earliest shelly Metazoa did not originate in nearshore, stressed marine habitats. Paleoecological analyses of the Early Cambrian fauna and strata of the White-Inyo Mountains of California indicate that major shelly taxa and trace fossils appeared offshore from shallow-water, physically stressed environments and only later spread to nearshore habitats. Other lowermost Cambrian stratigraphic sections elsewhere in the world show similar patterns. The contrast in pattern of community evolution between the Early Cambrian and the remaining Phanerozoic suggests either temporally variable control on position of evolutionary innovation or a need for reexaminution of the data.

Hydrocarbon Potential in Paradox Basin: an Overview: ABSTRACT

The petroleum-rich Paradox basin of southeastern Utah and southwestern Colorado remains an exploration frontier. With current production and exploration programs focusing on algal mound limestones in the Pennsylvanian Paradox Formation and deeper Mississippian structures, numerous other zones with hydrocarbon potential exist. Floored by a complexly faulted Precambrian basement, there is ample evidence suggesting that both source beds and reservoir rocks comprise much of the Cambrian section underlying the region. Although successfully developed at Lisbon field, Devonian sandstones and Mississippian carbonates have only been peripherally explored in other parts of the basin and much remains to be learned about deeper evaporite sequences in the Paradox Formation where tur idite deposits are known or inferred to exist between source bed shales and dolomites. Migration reservoirs exist in the Laramide structures that rim and occupy parts of the basin. Permian tar sand deposits estimated to hold 4-8 billion bbl of oil in place remain to be developed where an exhumed stratigraphic trap in the White Rim Sandstone is exposed west of the confluence of the Colorado and Green Rivers. Additionally, carbon dioxide gas deposits associated with Tertiary intrusives in the region require further delineation and development for coal slurry and enhanced oil recovery projects. Accordingly, the basin is expected to continue being developed for its resources for several decades. End_of_Article - Last_Page 848------------

Geology of Scipio Pass Quadrangle, Millard County, Utah: ABSTRACT

The Scipio Pass quadrangle is comprised of three separate packages of stratigraphy: (1) the Canyon Range Precambrian and Cambrian allochthonous section, (2) the Pavant allochthon of Paleozoic carbonates and quartzites, and (3) a thick Cretaceous to Quaternary blanket of coarse clastics that unconformably overlies the other packages. A fourth package, the Pavant autochthon, is inferred in the subsurface. Mesozoic rocks of this package crop out farther south where the Jurassic Navajo Sandstone is overlain in thrust contact by the Cambrian Tintic Quartzite. Based on lithology and biostratigraphic evidence, the heretofore undivided Cambrian section of the Pavant allochthon correlates well with the End_Page 942------------------------------ East Tintic section to the north, but differs notably from the Cambrian section of the Canyon Range allochthon, which closely parallels the House Range stratigraphy. Juxtaposition of two separate Cambrian packages is attributed to a major Cretaceous thrusting episode during the Sevier orogeny. The Canyon Range allochthon placed Precambrian and Cambrian rocks on top of Cambrian through Devonian rocks of the Pavant allochthon. Later detachment of the Pavant allochthon emplaced the Paleozoic section over the Mesozoic rocks farther east. Movement of the Pavant allochthon carried the Canyon Range allochthon piggyback. Folding of both allochthonous sheets occurred, and Precambrian klippen of the Canyon Range allochthon are preserved, in two major synclinal troughs. Miocene to Holocene blo k faulting elevated and exhumed both the Canyon and Pavant Ranges from beneath their cover of self-derived conglomerates. End_of_Article - Last_Page 943------------

Precambrian-Cambrian transition problem in western North America: Part II. Early Cambrian skeletonized fauna and associated fossils from Sonora, Mexico

A skeletonized fauna of possible Tommotian age (earliest Cambrian) has been discovered in the Caborca region, Sonora, in a unit considered approximately equivalent to the basal part of the Wood Canyon Formation of the Death Valley region. Probable metazoan traces occur about 900 m stratigraphically below the shelly fossils and may be among the oldest trace fossils known in the southern Cordillera. About 1,200 m stratigraphically below the shelly fossils, a new filamentous algal microbiota has been found in silicified wackestone from the El Arpa Formation. These new fossil occurrences, found within three stratigraphically correlated upper Proterozoic through Middle Cambrian sections from the Caborca region, have significant paleobiologic and biostratigraphic implications for the “Precambrian-Cambrian boundary” and Proterozoic paleobiology in western North America.

Revised stratigraphy of the Long Reach area, southern New Brunswick: evidence for major, northwestward-directed Acadian thrusting

In the Long Reach area of southern New Brunswick, a new stratigraphic succession has been delineated; it consists of Precambrian (?) volcanic rocks, Cambrian sedimentary, volcanic and hypabyssal rocks, Silurian sedimentary rocks, and Devonian plus Precambrian (?) heterogeneous, granitoid rocks. The northern boundary of this succession is postulated to be a northwestward-directed thrust fault of Acadian age. Other Acadian thrust faults are interpreted in the area and major reverse movement of the same age occurred along the Belleisle Fault.Mafic and felsic volcanic rocks that were previously thought to be either Precambrian or Silurian are demonstrably part of the Lower Cambrian section. Some of the granitoid rocks intrude Silurian strata and therefore cannot be basement to the Cambrian succession. Other granitoid rocks appear to be older and may be Precambrian in age.

Environments and Dynamics of Clastic Sediment Dispersal Across Cambrian of Grand Canyon: ABSTRACT

End_Page 1004------------------------------The transgressive Grand Canyon Cambrian contains basal fluvial sands (Tapeats Sandstone) and overlying shallow marine sands and shales (Bright Angel Shale) in which textures and structures permit a detailed reconstruction of clastic sediment dispersal across a broad cratonic margin. Dominantly trough cross-bedded basal Tapeats Sandstone, containing buried regolith in bed-rock depressions, a low-variance, unimodal paleocurrent trend down the regional paleoslope, and well to moderately sorted medium to coarse-grained sands, records pre-vegetation bed-load fluvial sedimentation. Bed-load sands (> 200 mµ) mature from arkosic to orthoquartzitic within 5 to 10 m of the base. Finer, suspension-transported sands remain subarkosic through the entire 250 to 500 m of Cambrian section implying rapid dispersal. The Bright Angel Shale is composed of shallowing upward sedimentary cycles 1 to 6 m thick. Lower parts of the cycles are thinly interbedded fine sand and shale layers whose sedimentary structures and textures record level-bottom storm resuspension, dispersal, and deposition (sand layers) alternating with quiescent periods of finer silt and clay dispersal and accumulation. Bed-load transported sands are absent. Sand bed thickness up to a maximum (5 to 20 cm) represents variation in storm intensities with maximum thicknesses controlled by water depth, which limits volume in suspension. Upper parts of cycles are cross-laminated fine sands with glauconite and U-shaped or vertical burrows. These represent shoaling phases with increased bottom agitation, decreased sedimentation rate, and winnowing bypass of silts and clays. Organism structures, tadpole ripples, and rare mud cracks record shallowing. Cycle caps are 1 to 20-cm thick layers of medium to very coarse quartz sand, hematitic ooids, phosphatic, and dolomite cemented clasts that record phases of emergence and complete bypass of all suspension load. Recently recognized dunes 3 to 5 m in height provided bed load dispersal at the close of sedimentation cycles. Structures and textures suggest dunes are eolian. End_of_Article - Last_Page 1005------------

Shelly microfossils near the Precambrian–Cambrian boundary, Mackenzie Mountains, northwestern Canada

Our understanding of early metazoan evolution is being revolutionized by recent discoveries of pre-trilobite faunas. A fascinating aspect of this evolution is the appearance and development of metazoan skeletal parts near the Precambrian–Cambrian boundary. Fossils of these parts are best known from the lowermost stage (Tommotian) of the Cambrian in Siberia which contain archaeocyathids and small shelly fossils, the latter commonly of phosphatic composition1–3. Although the sudden, in terms of geological time, appearance of metazoan hard parts near the boundary is recognized as an outstanding evolutionary event, none of the proposals given to explain the ‘Cambrian explosion’ (see refs 4–6) has been widely accepted. Additional information from areas outside Siberia is now needed to broaden our knowledge on early Metazoa, and to assist a geological team, the Precambrian–Cambrian Boundary Working Group of the International Union of the Geological Sciences, that is locating, defining and correlating the Precambrian–Cambrian boundary on a world-wide basis. Here we report the discovery of a small fauna of microfossils near the boundary in the Mackenzie Mountains. New forms are present and a known species is used for correlation with the classic Precambrian–Cambrian sections in Siberia and successions elsewhere.

RECENT SEISMIC STUDIES UPGRADE THE PETROLEUM PROSPECTS OF THE TOKO SYNCLINE, GEORGINA BASIN

The Georgina Basin covers an area of 325,000 sq km in the Northern Territory and Queensland. Most of the basin contains less than 500m of Palaeozoic sediments, but the Toko Syncline, in Queensland, contains up to 5000m of Middle Cambrian to Middle Ordovician shallow marine carbonate, sandstone and shale. The syncline is bounded on its western margin by the Toomba-Craigie Fault systemHydrocarbon shows are known within the Middle Cambrian to Middle Ordovician strata and some of the rocks have fair source rock potential. Potential reservoir rocks are vuggy dolostones and sandstone. Ordovician siltstones and shales may provide cap-rocks. The southern, deepest part of the syncline appears to have been protected from flushing. AOD Ethabuka-I well, drilled in the southern part, encountered gas in the Ordovician, but drilling problems prevented penetration of the deeper section.A Bureau of Mineral Resources (BMR) seismic survey in 1977, linked lines shot on earlier surveys, tied to wells and examined the Toomba Fault system. The results show that two previously unidentified reflectors represent the top of Upper Cambrian Georgina Limestone and the base of the Middle Cambrian section. Substantial thickening of Ordovician and slight thinning of Middle and Upper Cambrian strata occurs southeast along the axis of the syncline. Southeast progradation of some Middle Cambrian strata and possible bioherms were observed. The Toomba Fault is a high-angle reverse fault and several possible anticlines are present in the adjacent folded and faulted zone. The two largest ones, the Ethabuka and Mirrica Structures, were partially outlined by Alliance Oil Development (AOD). They are shown to lie within a larger structure which has a minimum vertical closure of 700m over a minimum area of 130 sq km. Possible stratigraphic traps are located on the northeastern flank and along the axis of the syncline.The seismic work has better defined the prospective section and confirmed closure on a large structure. The next step in exploration should be to drill the Mirrica-Ethabuka Structure, where about 1500m of section remains to be tested.

Cambrian Stratigraphic Nomenclature and Ground‐Water Prospecting Failures on the Hualapai Plateau, Arizona

ABSTRACTThe best potential aquifers underlying the 600 mi 2 Hualapai Plateau of northwestern Arizona are (1) the Cambrian Rampart Cave Member of the Muav Limestone and (2) interbedded Tertiary sedimentary and volcanic rocks that locally fill old canyons on the plateau. These target aquifers have been identified on the basis of spring locations on the flanks of the plateau, primarily along the walls of the Grand Canyon to the north and east. Total ground‐water discharge from springs along the plateau is approximately 4 ft3/sec.To date the largest production from a test well on the plateau is 120 gal/min from Tertiary rocks. The Cambrian rocks have frustrated development in part because of small permeabilities, small recharge (0.1 in/yr minimum), and the fact that the rocks are well drained.The complex stratigraphic nomenclature used to describe the Cambrian rocks in the region has inadvertently contributed to prospecting failures. The Cambrian section is characterized by thick interbedded limestones and shales, with the basal limestone being the principal target aquifer. These relationships have not been adequately conveyed to managers and drillers, with the result that critical test holes have been terminated in shales that overlie the target aquifer. Dry holes have been the result.

Basement Rocks of Barrow Arch, Alaska, and Circum-Arctic Paleozoic Mobile Belt

Silurian fossils from steeply dipping slate and graywacke underlying the Prudhoe Bay oil field, and Ordovician and Silurian fossils from similar rocks in the Barrow test wells indicate that rocks of about the same lithology and age as the Neruokpuk Formation in the Brooks Range-Barn Mountains area continue west in the subsurface and form the basement of the Barrow arch. This belt of highly deformed, weakly metamorphosed, predominantly siliceous strata, including volcanic rocks, is part of an early Paleozoic geosyncline that was deformed, intruded by Silurian and Devonian granite, and deeply eroded by the end of the Devonian. Similar rocks affected by the same orogeny form the Innuitian fold belt in the Canadian Arctic Islands, but the connection between the two fold belts is obscured by rocks of mainly younger age in the Mackenzie River delta region and by water along the west side of Banks Island. South of the Mackenzie River delta, the Richardson trough with its graptolitic shale and chert section separates carbonate strata of the Yukon shelf of northern Yukon Territory and east-central Alaska from the Mackenzie carbonate platform lapping onto the Canadian shield. Now that the Neruokpuk Formation in the Barn Mountains is known to include graptolitic shales and cherts of the same age as, and of partly similar lithology to, those in the nearby Richardson trough, it seems likely that deep-water pelagic sedimentation continued from the Neruokpuk geosyncline into the Richardson trough. The argillaceous rocks of the Richardson trough, unlike those of the Neruokpuk geosyncline or Cordilleran geosyncline, grade downward into argillaceous limestone that lies on a Cambrian platform section. In the Ogilvie Mountains at the south end of the trough, shales interfinger with limestones, indicating that the trough was constricted into narrow channels and was separated partly from the Cordilleran geosyncline farther south. These relations indicate that the Richardson trough was not a basin of oceanic type or proportions but may be an aulacogen that developed across the Yukon shelf from an Arctic sea-floor-spreading center.

Middle and Early Late Cambrian Algal Biostromes and Regional Dolomitization in Great Basin: ABSTRACT

Middle and early Late Cambrian stratigraphic sections from southeastern California, across eastern Nevada, to northern Utah are characterized by the rhythmic repetition of dolomitic algal biostromes and dolomitized pelletiferous calcisiltite. Stratigraphic and petrographic criteria indicate deposition on a very wide, shallow, low-gradient shelf on which extensive calcareous algal mats formed. Penesaline conditions, resulting in part from the combination of the width and shallowness of the shelf, led to production of brines and syndiagenetic dolomitization of the algal mats. Syndiagenesis is suggested by associated intraformational breccias composed chiefly of dolomitized algal debris in a matrix of calcisiltite and by a few erosion pits cut to depths of several inches. Subaqueously formed cracks across wrinkled mats, probably caused by the drag of passing waves, appear to represent an incipient stage in the formation of the breccias. The pelletiferous calcisiltite is a more seaward deposit and is believed to be composed largely of detritus washed from the algal-mat environment. Seaward refluxion of the brines led to the dolomitization of these rocks. Rhythmic repetition of these environmentally controlled lithic types reflects a set of conditions which alternately inhibit and enhance algal growth. End_of_Article - Last_Page 726------------

New data on composition and properties of Lower Cambrian crude oils in Lena region, Irkutsk oil and gas basin

Two groups of oils are considered: condensates and light oils from the terrigenous Lower Cambrian section, and oils occurring in the halogen-carbonate section. Preliminary conclusions on different cycles of oil formation in the terrigenous and carbonate complexes are drawn from the study of chemical composition, optical activity, and distribution of microelernents in the oils. The Parfenovo horizon of Markovo field is considered as a differentiated oil and gas deposit. -- Author.

General Geology and Hydrocarbons of the Northern Amadeus Basin, Australia: ABSTRACT

The Amadeus basin is a structural depression extending easterly from the Canning basin in Western Australia to the Great Artesian basin in Queensland. It covers about 80,000 square miles and contains up to 30,000 feet of late Proterozoic and early Paleozoic marine and continental sediments. The marine cycle of deposition started in late Proterozoic time and terminated in late Ordovician. No unconformity is present at the base of the Paleozoic sequence and both Proterozoic and Paleozoic beds are unaltered except along the northern margin of the basin where low grade metamorphic facies were developed in End_Page 349------------------------------ the sediments during the Pertnjara orogeny in Devonian time. The marine sequence consists of clastics, carbonates, and evaporites. They were deposited in shallow water, shelf environments as is shown by algal growths, biohermal and biostromal carbonates, abundant ripple marks and abundant cross laminations in sandstones, and by widespread coquinoid facies in Ordovician shales. Silled or barred basins with restricted circulation of marine waters existed from time to time during the marine cycle as is shown by salt deposits in the upper Proterozoic and Cambrian sections and by thick accumulations of dark shales with abundant pyrite in late Proterozoic and Ordovician sediments. The marine cycle of deposition was terminated by the Pertnjara orogeny. This orogenic episode created a welt north of the Amadeus basin and a bordering foredeep whose depoaxis follows the present northern margin of the basin. Marine sediments were stripped from the rising welt, transported southward, and dumped into the subsiding foredeep where they now form a thick apron of poorly sorted, coarse clastic deposits. Salt tectonics has played an important role in the growth of structures in the northern Amadeus basin. Thick salt deposits in the Bitter Springs formation of late Proterozoic age constituted a semi-plastic layer near the base of the Proterozoic sequence. Sedimentary loading on this layer produced flowage and initiated salt anticlines and salt domes. These structures grew during late Proterozoic and early Paleozoic deposition as is shown by crestal stratigraphic convergence and local unconformities confined to one structure. The evaporite layer also provided a lubricated zone along which slippage was localized during the Pertnjara orogeny, and it may be responsible in part for the large nappes and overthrusts along the northern margin of the basin. The anticlines and salt domes initiated by salt flowage were formed early in the history of deposition and thus constituted potential traps for hydrocarbons long before the Pertnjara orogeny. However, folding during the Pertnjara orogeny greatly increased structural relief on the anticlines and thereby created traps having large volumetric capacities. Two of these large structures have been tested with encouraging results. The Exoil-Magellan-United Canso groups have discovered a large wet-gas accumulation, possibly with an appreciable oil leg, in Ordovician reservoirs on the Mereenie anticline in the western part of the Amadeus basin. They also discovered a non-commercial gas accumulation in Proterozoic sediments on the Ooraminna anticline in the eastern part of the Amadeus basin. A third test of a small structure near the Ooraminna anticline encountered non-commercial oil shows in Cambrian sediments. In addition, the Australian Bureau of Mineral Resources discovered oil-saturated sands in Ordovician sediments penetrated by a well being drilled as a test for phosphates. With the exception of shallow water bores, no other wells have been drilled to date in this basin. End_of_Article - Last_Page 350------------

Middle Cambrian Section in Vicinity of Currant Creek, Nevada: ABSTRACT

A regional study of the White Pine Range, eastcentral Nevada, has disclosed in the vicinity of Currant Creek a previously undescribed Middle Cambrian section. Approximately 4,000 feet of strata composed dominantly of thin-bedded limestone and shales, lies directly above the Lower Cambrian Prospect Mountain quartzite, and below the Upper Cambrian Dunderberg formation. Though faulted, the section has yielded rich trilobite faunas representing in ascending order the Middle Cambrian zones: Albertella, Glossopleura and Bathyuriscus-Elrathina. The Bolaspidella zone may be present but is not recognizable because of structural complexities and scarcity of fossils. The Currant Creek section has been compared with that of the Pioche District, Nevada; House Range, Utah; and the Bear River Range, Utah-Idaho. Comparisons indicate that the Albertella zone of Currant Creek is similar to that of the Upper Pioche shale, Highland Peak Range, and the Naomi Peak limestone member of the Langston formation, Bear River Range. The Glossopleura zone is particularly well-developed in the Currant Creek section and the faunal assemblage is remarkably similar to that of the Spence shale of the Bear River Range. It may represent a westward extension of the extracratonic faunal environment postulated for the Spence shale and Langston limestone. End_of_Article - Last_Page 1773------------

Cambrian Rocks of Southern Snake Range, Nevada

The southern Snake Range of Nevada lies between the Cambrian sections at Pioche and Eureka, Nevada, and Gold Hill and the House Range, Utah. The Cambrian rocks of the area include about 5,000 feet of beds assigned to the Prospect Mountain quartzite, Pioche shale, and the following new formations: Pole Canyon limestone (Middle Cambrian), Lincoln Peak formation (Middle and Upper Cambrian), Johns Wash limestone (Upper Cambrian), and Corset Spring shale (Upper Cambrian). Several hundred feet of uppermost Cambrian rock are left unassigned. The Middle and Upper Cambrian measured sections are separated by a thrust fault in the lower part of the Lincoln Peak formation. Mapping the southern Snake Range has shown that the new formations are practical units but has not provided a more complete section.

1951 Western Utah Field Trip Review: ABSTRACT

The Intermountain Association of Petroleum Geologists conducted its 1951 field trip through the Canyon, House, and Confusion ranges of west central Utah within the Basin and Range Province. Rocks of the Canyon Range have recently been assigned to the Cambrian and pre-Cambrian with contiguous Cretaceous conglomerates whereas previously considered as of Carboniferous and Tertiary age. The 10,000-foot Cambrian section of the House Range was studied in conjunction with close-up observations of the Wheeler Amphitheater, Rainbow Canyon (Marjum Pass), and the Notch Peak granite mass. The Confusion Range includes rocks of each Paleozoic period from Ordovician through Permian with an aggregate section of about 20,000 feet. A thin Triassic mask is also present in isolated outcrops. The Confusion Range is generally synclinal with an extended and interrupted east limb. Both normal and reverse faulting may be observed along with textbook anticlines, notwithstanding spectacular examples of major overturning. Three exploratory wells are now being drilled as a result of recent geologic research in west central Utah. End_of_Article - Last_Page 960------------

The Cambrian section in the Logan Quadrangle, Utah and vicinity

The Cambrian section in the Logan Quadrangle, Utah and vicinity

Cambrian formations and sections in part of Cordilleran trough

Field and laboratory studies have shown that the older type Cambrian sections in Nevada, Utah, and Wyoming are not usable for correlation, and that published faunal lists are incomplete and partly erroneous. In 1936 and 1937, fossils were accurately zoned in seven remeasured sections: Pentagon, Prairie Reef, and Scapegoat, Montana; Wind River Canyon, Wyoming; Blacksmith Fork and House Range, Utah; and Highland Range, Nevada. The terms DuNoir and Gallatin are not applicable to the Wind River Canyon section which is now divided into the Depass (Albertan) and Boysen (Croixan) formations. The St. Charles (Croixan) formation in the original Blacksmith Fork section is redefined, as the upper 827 feet contain Ordovician fossils. The name Tatow limestone is applied to the youngest Waucobian rocks in the House Range. The upper 370 feet of the original Pioche shale in the Highland Range contains Albertan species and is named the Comet shale, the name Pioche being retained for the 600 feet of Waucobian rocks underlying the Comet and resting upon the Prospect Mountain formation. Few Middle Cambrian formations south of Montana can be correlated on evidence from fossils, other than the basal Ute with the Chisholm and Gordon, the upper Howell with the Damnation, and, doubtfully, the Wheeler and Marjum with the Pentagon. The Kochaspis upis fauna in the Steamboat limestone of Montana seems to be younger than the Marjumia-Neolenus fauna in the upper part of the Marjum limestone in the House Range.