Deadwood Formation Research Articles

Petroleum Potential of Winnipeg Sandstone in South Dakota: ABSTRACT

The term Group includes all strata which underlie the Red River Formation and overlie the Precambrian basement complex. The upper unit, a greenish-gray, noncalcareous marine shale, is called the Icebox Shale or Winnipeg shale in the Williston basin, and it ranges from 0 to more than 100 ft (30 m) in thickness. Outcrops in the Black Hills contain Middle Ordovician fossils. The lower unit consists mainly of quartzose sandstone ranging from 0 to 465 ft (141 m) or more in thickness. In the northern Black Hills, most of the sandstone is included in the Deadwood Formation and is Late Cambrian in age, but the uppermost beds are Early and Middle(?) Ordovician. In the Williston basin, the terms Black Island and Winnipeg Sandstone have been used to denote the sandstones hich underlie the Icebox or Winnipeg shale. The disconformity which separates Black Island and Deadwood sandstones cannot be traced with confidence into the subsurface of South Dakota, where the entire sequence appears to be a blanket of sandstone containing only thin interbeds of dolomite and shale. Therefore, the term Winnipeg Sandstone is used to denote all the sandstone between the Winnipeg shale and the Precambrian basement. End_Page 1330------------------------------ The Winnipeg Sandstone is present throughout most of the Williston basin and extends into the Kennedy basin. At its featheredge (zero isopach), it is overlapped by the Winnipeg shale. The sand appears to have originally extended farther because isolated remnants occur in a few wells on the Pierre arch. An erosional episode is believed to have removed the sand from areas east of its present regional limit except in a few downwarped or downfaulted areas. This episode was followed by a rapid advance of the Middle Ordovician sea, during which no sand was deposited. The Winnipeg shale was deposited immediately after this transgression. The overlap creates a regional seal over the Winnipeg Sandstone reservoir. The Winnipeg shale is a mature petroleum source bed in the northern part of the Williston basin. Maturation and migration probably occurred by Permian time when the Winnipeg was buried beneath about 6,000 ft (1,800 m) of younger beds. Although some of the petroleum migrated upward into the Red River Formation, the underlying Winnipeg Sandstone was an ideal conduit for lateral migration. Documented Winnipeg shows indicate that oil migrated at least as far as Mellette County, South Dakota. One of the shows appears to be a fossil oil field, indicating that entrapment and accumulation did occur. Isopachs of the Minnelusa to Winnipeg interval indicate preferential directions of lateral migration. Live oil shows suggest the possibility of commercial accumulations. The Winnipeg Sandstone is thick, porous, and permeable. Depending on local conditions, a Winnipeg oil well might yield up to 500,000 bbl or more. Anticlines located basinward from the regional pinch-out of the Winnipeg Sandstone are the most logical exploration targets. Subsurface mapping and interpretation of aerial photographs and Landsat images suggest several large structures capable of containing major oil fields. End_of_Article - Last_Page 1331------------

GROUND WATER RESOURCES IN BEDROCK AQUIFERS ALONG THE INTERNATIONAL BOUNDARY IN THE SOUTHERN PRAIRIES

Adequate quantities of ground water for domestic and small municipal supplies are normally found within a few hundred feet of the surface on the southern Canadian Prairies. The potential exploitation of ground water in deeper bedrock aquifers has not generally been considered. The proposed exploitation of ground water in the Madison Limestone for development of coal reserves in the north-central United States and the experimental study of low-grade geothermal energy extraction from the Winnipeg and Deadwood Formations at the University of Regina have focussed attention on these bedrock aquifers.Past, present and proposed studies of the bedrock aquifers in the Great Plains region of the United States and Canada are reviewed. Studies on the Canadian side of the border should be given priority in order to evaluate the hydrogeological and environmental effects of the developments and to provide the necessary knowledge for evaluation of transboundary ground water problems in these areas.

Geology of Paleozoic Strata in West-Central Saskatchewan: ABSTRACT

The study area is located just south of the Precambrian shield between the Meadow Lake escarpment and the Alberta-Saskatchewan boundary. It is approximately 350 km long and 70 km wide and constitutes part of the Middle Devonian Meadow Lake basin, which is the southeastern portion of the early Elk Point basin. The Paleozoic strata comprise clastic rocks of the Cambrian Deadwood Formation and dominantly carbonate rocks End_Page 826------------------------------ of the Middle Devonian Elk Point Group. The Deadwood clastics are quartzose sandstone, sand, subordinate shale, and conglomerate. Locally, in the northernmost part of the area, they have been removed by pre-Devonian erosion. The carbonate sequence of the Elk Point Group is divided into lower and upper subgroups. The Lower Elk Point subgroup contains the Meadow Lake Formation (new) which is subdivided into lower and upper members. The basal formation of the Upper Elk Point subgroup, the Winnipegosis is present in the area. The younger formations of these southwest-dipping Devonian strata are absent owing to erosion or nondeposition. The Devonian carbonate rocks are overlain unconformably by clastic sediments of the Lower Cretaceous Mannville Group. The common occurrence of fractured and brecciated carbonate rocks within the Meadow Lake Formation indicates salt solution and can be correlated with the extensive rock salt deposits of the Lower Elk Point subgroup in central Alberta. The depositional edge of one of these salt deposits, the Cold Lake Salt, can be traced. Accessory copper, lead, and zinc minerals are present locally in clastic rocks of the Deadwood Formation and also in the Devonian carbonate rocks. Gas shows have been reported from the upper member of the Meadow Lake Formation. Meadow Lake limestone of economic significance was recently discovered near Pinehouse Lake. End_of_Article - Last_Page 827------------

A Fish from the Upper Cambrian of North America

Phosphatic dermal fragments of Anatolepis, interpreted as a heterostracan fish (class Agnatha), have been discovered in the Deadwood Formation of Late Cambrian age in northeastern Wyoming. This discovery extends back the age of the earliest known vertebrate fossils by approximately 40 million years. Other occurrences of Anatolepis in North America, Greenland, and Spitzbergen show that these fish had a widespread geographic distribution in Late Cambrian and Early Ordovician marine environments.

A Fish from the Upper Cambrian of North America

Phosphatic dermal fragments of Anatolepis , interpreted as a heterostracan fish (class Agnatha), have been discovered in the Deadwood Formation of Late Cambrian age in northeastern Wyoming. This discovery extends back the age of the earliest known vertebrate fossils by approximately 40 million years. Other occurrences of Anatolepis in North America, Greenland, and Spitzbergen show that these fish had a widespread geographic distribution in Late Cambrian and Early Ordovician marine environments.

Helium Source-Rock in Southwestern Saskatchewan

ABSTRACT Helium-enriched natural gas occurs in Upper Cambrian silicified siltstones and mudstones overlying a pronounced basement topographic high (the Aikens anomaly) nine miles north of Swift Current, Saskatchewan. Relief of 600 ft, relative to the regional basement elevation, can be attributed to the massive structure and stability to weathering of the undeformed and unmetamorphosed porphyritic rhyolite forming the topographic anomaly. Delayed neutron-activation analysis of a rhyolite core sample from B. A. Wilhelm 1-9 indicates 4.9 ppm. U, only slightly above the western Canada basement average of 4.3 ppm. U. However, core samples from M.O.W.S. Cantuar 2-21 and M.O.W.S. Fosterton 15.3, 20 and 25 mi to the west respectively, contain 24.1 and 15.7 ppm. U. Compositionally both rocks are porphyritic granites. Textural features suggest epizonal emplacement. The suggested origin of the helium accumulation is: A Late Hudsonian volcanic-plutonic centre developed west of the present site of Swift Current. Pre - Upper Cambrian erosion formed a series of hills above this complex. Upper Cambrian transgression (Deadwood Formation) buried the hills. Authigenic silica tightly sealed parts of the siltstone and mudstone overlying the Aikens anomaly. Circulating formation fluids carried helium from the subcrop of uranium-rich porphyritic granites along the Precambrian-Cambrian unconformity to the highest adjacent topographic feature.

Stratigraphy of Upper Cambrian-Lower Ordovician Subsurface Sequence in Williston Basin

Trilobites and brachiopods of Late Cambrian and Early Ordovician ages were obtained from seven wells that penetrated the Deadwood Formation in the Williston basin in Montana and North Dakota. The sections contain a basal transgressive sandstone overlain by interbedded limestone pebble conglomerate, dark shale, and light colored sandstone. On the east in North Dakota the section becomes markedly sandy. In these eastern sections it is difficult to place the Deadwood-Winnipeg boundary exactly, but in Montana there is a sharp lithic contact which represents a significant subaerial erosion break in the section. In Montana Dicellomus of Dresbachian age is present in the basal sandstone. The Elvinia, Conaspis, Ptychaspis-Prosaukia, and Saukia zones of Franconian and Trempealeauan ages occur in the overlying 287 feet. There is no evidence of a depositional break between the Upper Cambrian and the Lower Ordovician, and beds at this level carry the transitional Apoplanias faunule. An arbitrary boundary is placed at the first appearance of Symphysurina and (or) the associated Euloma. Faunas of the Lower Ordovician trilobite Zones A, B, C, D, E, and G (of Ross [1951] and Hintze [1953]) have been found. Intercalated graptolite shales permit correlation with Berry's Lower Ordovician graptolite Zones 1, 2, and 3. On the basis of the faunas the Deadwood can be correlated with formations throughout the anadian Rockies, Montana, Wyoming, Utah, Nevada, Colorado, New Mexico, Texas, and Missouri. Lithofacies exhibit many lateral changes within the basin. No persistent units can be recognized for the entire basin, but local facies members useful for mapping in smaller areas are distinguished. Reconstruction of paleogeographic conditions for the Late Cambrian shows the region as a wide, shallowly inundated coastal shelf with a west-northwesterly slope. A positive transcontinental arch between Laurentia and Siouxia forms a low sandy eastern shore or a maze of islands and shallow straits connecting with the upper Mississippi Valley region. The recurring transgressions of the middle Dresbachian, the early Franconian, and the middle Trempealeauan were not accompanied by upwarping of the land areas and may have been caused by eustatic sea-level changes. Shoaling in the Late Cambrian moved the shoreline gradually westward to western North Dakota. The Saukia zone trilobite genera died out, but dendroid graptolites persisted on the oxygenated shoals. Slow deposition of carbonate oo es, muds, and glauconites continued in the basin sites. The appearance of Euloma, Symphysurina, and Hystricurus marks the beginning of a new marine transgression which altered the shore topography and eventually carried the Zones A and B assemblages into the upper Mississippi Valley. Depositional thickening of the basal Lower Ordovician strata from the Richey to the Pine and Cabin Creek fields near the Montana-North Dakota border suggests that the axis of the earliest basin depocenter was in the direction of the Pine and Cabin Creek fields. During Zones D-E time, widespread carbonate shoals supported a gastropod-brachiopod fauna allied to assemblages of the central interior states. By Zones F-G time, the eastern sections were markedly sandy. Zone G faunas are the youngest Early Ordovicia assemblages known in the basin. The continued shoaling and eventual cessation of deposition probably occurred throughout the Williston basin during Zone H time, or definitely before the end of the Early Ordovician. Although no hydrocarbons are known in the Deadwood, it is suggested that the Deadwood shales may be source rocks. Stratigraphic entrapment of these postulated hydrocarbons may have occurred in Winnipeg strata or in sandy Deadwood facies during Early to Middle Ordovician time along the then newly formed eastern rim of the basin.

Sedimentary and Tectonic History of North Dakota Part of Williston Basin

The Williston basin is a structural and sedimentary basin which includes 51,600 square miles in North Dakota. It contains sedimentary rocks of every geologic period from the Cambrian through the Tertiary and its history can be divided conveniently into the Sequence subdivision (Sauk Tippecanoe, Kaskaskia, Absaroka, Zuni, Tejas) based on the major unconformities within the preserved section. The maximum known sedimentary thickness is 15,128 feet in a well in McKenzie County in western North Dakota. The Upper Cambrian to Lower Ordovician Epochs are represented by the Deadwood Formation, which is a stable shelf deposit extending eastward from the Cordilleran geosyncline. The Williston structural basin began to be filled in Middle Ordovician time with a relatively thin clastic sequence (Winnipeg Group) followed by predominantly carbonate deposition (Red River, Stony Mountain, and Stonewall Formations). Carbonate deposition continued through Early and Middle Silurian time (Interlake Formation) followed by a period of erosion marked by a major unconformity. During the Middle and Upper Devonian Epochs the Williston basin was a part of the larger western Canada basin of deposition which was characterized by predominantly carbonate deposition with a thick evaporite in the lower part (Prairie Formation) and cyclical carbonate with some thin clastic and evaporite beds in the upper part (Duperow, Nisku, Three Forks). Deposition was continuous or nearly continuous into the Mississippian, but the center of the Madison depositional basin was nearly coincident with the present Williston basin. Mississippian deposition began with predominantly carbonate deposition, evaporites increasing in the upper part. The evaporites are mostly halite in the central basin area and anhydrite toward the flanks of the basin. Predominantly clastic deposition (Big Sn wy Group) followed the evaporites; another unconformity is at the top of the Big Snowy. The Pennsylvanian and Permian Periods are represented by clastics with minor carbonates (Minnekahta Formation) and some evaporites. This was a time of slight subsidence, with the Williston basin area a part of a larger depositional area extending south and west. Similar conditions continued through the Triassic with deposition of fine-grained clastics and some evaporites, which are overlain by some non-marine redbeds and another unconformity. As the Williston structural basin had little effect on Jurassic or Cretaceous sedimentation, these periods are represented by eastward extensions of the predominantly fine-grained clastics from the Rocky Mountain area seas. The Tertiary Period is represented by a wedge of predominantly non-marine beds which thicken westward toward the Rocky Mountain area.

Sedimentary and Tectonic History of North Dakota Portion of Williston Basin: ABSTRACT

The Williston basin is a structural and sedimentary basin which covers 51,600 square miles in North Dakota and contains sedimentary rocks of every geologic period from the Cambrian through the Tertiary. The maximum known thickness is 15,128 feet in a well in McKenzie County in Western North Dakota. The Upper Cambrian to Lower Ordovician Epochs are represented by the Deadwood Formation which represent stable shelf deposits extending eastward from the Cordilleran geosyncline. The Williston structural basin began in Middle Ordovician time with a relatively thin clastic sequence (Winnipeg Group) followed by predominantly carbonate deposition (Red River, Stony Mountain and Stonewall Formations). Carbonate deposition continued through Lower and Middle Silurian (Interlake Formation) followed by a period of erosion marked by a major unconformity. During the Middle and Upper Devonian Epochs the Williston basin was a part of the larger western Canada basin of deposition which was marked by predominantly carbonate deposition with a thick evaporite in the lower part (Prairie Formation) and cyclical carbonates with some thin clastic and evaporite beds in the upper part End_Page 1881------------------------------ (Duperow, Nisku, Three Forks). Deposition was continuous or nearly continuous into the Mississippian, but the center of the Madison depositional basin was nearly coincident with the present Williston basin. It began with predominantly carbonate deposition with increasing evaporites in the upper part. The evaporites are mostly halite in the central basin area with anhydrite toward the flanks of the basin. Predominantly clastic deposition (Big Snowy Group) followed the evaporites and this was followed by another unconformity. The Pennsylvanian and Permian periods are represented by clastics with minor carbonates (Minnekahta Formation) and some evaporites. This was a time of slight subsidence with the Williston basin area being part of a larger depositional area extending to the south and west. Similar conditions continued through the Triassic with fine grained clastics and some evaporites being deposited, followed by some non-marine redbeds and another unconformity. The Williston structural basin had little effect on Jurassic or Cretaceous sedimentation so these periods are represented by eastward extensions of the predominantly fine grained clastics from the Rocky Mountain area seas. The Tertiary Period is represented by a wedge of predominantly non-marine beds which thickens westward toward the Rocky Mountain area. End_of_Article - Last_Page 1882------------

Ordovician and Silurian of Central and Southern Parts of Williston Basin: ABSTRACT

Ordovician and Silurian rocks, mainly dolomitic limestone and dolomite, underlie the eastern half of Montana, nearly all of North Dakota and a large portion of South Dakota. They reach a thickness of about 2,000 feet near the basin center (where the cover exceeds 12,000 feet) but are bevelled radially by pre-Devonian and later surfaces of unconformity. Only Ordovician rocks escaped removal from areas of present-day outcrop at the southern rim of the basin. For historical reasons the outcrop and subsurface nomenclature of the stratigraphic column differ, but a series of sedimentary units which can be traced in basin-wide stratal continuity exists. The Bighorn dolomite of the Pryor-Bighorn Mountains in Montana is demonstrably continuous with and equivalent to the combined Red River, Stony Mountain and Stonewall formations of the northern part of the basin. Similarly, the Whitewood dolomite of South Dakota equates with a small section of the lowest Red River. Sedimentary thickness and distribution maps reveal former contiguity of the Williston and Nebraska-Iowa-Illinois depositional areas. During pre-Stony Mountain sedimentation the northern Nebraska and northeastern Iowa areas lay on the southern flank of a Red River basin centered in North Dakota. Ordovician sedimentation (post-Beekmantown Deadwood formation) commenced with deposition of a sandstone on an erosion surface cut across Cambrian and Precambrian rocks. It continued with a shale and sandstone formation (Winnipeg, Simpson) which overstepped the initial sandstone and behaved as a basal deposit to the overlying carbonates of the Red River (Viola), and Stony Mountain-Stonewall (Maquoqueta) formations. The lower three-quarters of the Red River comprise an uninterrupted succession of marine fossiliferous limestones, highly dolomitized at their periphery, but the upper quarter is a strongly rhythmic carbonate-evaporite sequence. These evaporites spread over most of the basin interior, the earliest having the greatest extent. An influx of shale in the lower part of the overlying Stony Mountain abruptly smothered the evaporite rhythms. Evidence of facies variation within the lower Stony Mountain, coupled with a shift in the center of maximum accumulation of later formations points to appreciable re-disposition of sedimentary influences. Evaporite rhythms returned after the shale incursion and lasted through the remaining Stony Mountain and the Stonewall formations. Silurian rocks, the Interlake group (Hunton), are almost wholly dolomite, characteristically pale in color and micrograined. Evaporitic anhydrite beds occur locally but have either the spread nor the rhythmic succession of those in the Ordovician. Correlation and subdivision of Interlake group sections is much aided by the existence of several persistent sandy non-sequential End_Page 956------------------------------ beds. The Interlake is variably eroded, but everywhere affected by the great pre-Devonian unconformity. End_of_Article - Last_Page 957------------

Lower Paleozoic Rocks of Northern Williston Basin and Adjacent Areas

Cambrian, Ordovician, and Silurian strata of Manitoba, Saskatchewan, northern North Dakota, and northeastern Montana comprise two vertically separated parts: a lower sequence of non-carbonate clastic beds ranging from Cambrian to Upper Ordovician, and an upper sequence of dolomitic limestones and dolomites ranging from Upper Ordovician to Silurian. The rocks floor all the northern part of the Williston Basin, reach more than 3,000 feet in thickness, and are unconformably overlain by Middle Devonian or younger beds. The formations cropping out along the northeastern side of the basin can be traced (in the form of para-time-rock units) by means of subsurface sections across the entire area. The full sequence in upward order is: Deadwood formation, Winnipeg formation; Red River, Stony Mountain, and Stonewall formations (Bighorn group); and Interlake group. The clastic Deadwood and Winnipeg formations are separated by an unconformity of probable post-earliest Ordovician pre-Middle Ordovician age. The carbonate succession above records numerous small hiati, but no major breaks of sedimentation. Toward the end of Red River carbonate deposition marked cyclic alternation between thin evaporitic anhydrites and fossiliferous-fragmental limestones occurred. The evaporites extend through a wide arc on the northern and western sides of the basin. Lateral (updip) changes from limestones to dense dolomites cause divergence between the marker bed and facies boundaries: lithologic features typical of the upper part of the Bighorn group appear to descend into the Red River formation toward the basin margin. Shales at the base of the overlying Stony Mountain formation seem to be the result of slight tectonic adjustment on the southeastern side of the basin, but the carbonate-evaporite cycles returned during later Stony Mountain and Stonewall deposition. Interlake group deposits are characterized by dense dolomites with pseudo-oolitic and fragmental beds. Sedimentation was interrupted by several small non-sequential beds of highly rounded quartz-sand grains and silts. These horizons are utilized as para-time-rock markers. Isopach maps reveal a progressive movement of the axis of the basin from a nearly east-west trend during Red River deposition to a north-northwest-south-southeast trend during Interlake deposition. Petroleum accumulations (either shows or producible quantities) occur at many porous levels in the succession, particularly in stratigraphic traps developed by the upper Red River and Stony Mountain-Stonewall evaporite cycles on the western side of the basin (south-central Saskatchewan, western North Dakota, and northeastern Montana), and in paleotopographic or tectonic structures over truncated Interlake porosities at the pre-Middle Devonian unconformity. Both kinds of trap are analogous to Mississippian reservoirs and cap rocks in the northeastern part of the basin. The areal distribution of presently known oil occurrences is directly related to the distribution of highly saline formation waters.

Commercial Oil in Cambrian Beds, Lost Soldier Field, Carbon and Sweetwater Counties, Wyoming

The possibility of finding oil in the basal sands of the Cambrian of Wyoming has long been a matter of speculation. The Cambrian, where well developed, consists of marine shales and limestones in the upper part and a rather thick series of coarse-grained sandstones near the base. Several comparatively shallow tests had been drilled to test the Cambrian on large, well closed structures prior to 1930 but the results were either negative or the reported showings were in doubt. A deep test to granite on the South Oregon Basin field in 1945 found definite indications of oil saturation in basal sands of the Cambrian but due to mechanical difficulties no free oil was recovered from the well. A test to granite in the Lost Soldier field, Sweetwater County, Wyoming, in 1948 resulted in the first commercial well in the Cambrian in the Rocky Mountain region. During the year two additional wells were drilled through the Cambrian in the Lost Soldier field. One of these was completed as a commercial flowing well but the other found the formation too dense to produce. In the same year a producing well was completed in the Cambrian on the adjoining Wertz dome. The Cambrian, which is represented by the Deadwood formation in this area, is ordinarily hard and quartzitic but where oil-bearing it is softer and more friable. The total thickness of the Cambrian is as much as 700 feet but the oil-bearing zone is near the base, almost in contact with the basement complex. It is the writer's belief that the oil produced at Lost Soldier and Wertz from the Cambrian is not indigenous to that formation but has migrated laterally from overlying oil-bearing reservoirs after accumulation in the structure. The writer believes that a well could be drilled at the crest of the Lost Soldier dome, which would yield oil from the basement complex if that formation were penetrated above the oil-water contact in the Tensleep sand.

Developments in Rocky Mountain Region in 1948

Two hundred and seventy-seven exploratory wells were drilled in the Rocky Mountain region during 1948. Of these, 73 were successful. This represented a gain over the previous year, 1947, when, of 185 exploratory wells, 49 were successful. Permian and Pennsylvanian objectives provided the most new discoveries. New pools discovered by the Sinclair-Wyoming Oil Company in the Deadwood formation of Cambrian age at Wertz and Lost Soldier, Sweetwater County, Wyoming, and by the Pure Oil Company in the Mesa Verde formation at West Poison Spider, Natrona County, Wyoming, were of great significance as neither of these formations had hitherto been productive in the Rocky Mountain states. Other important discoveries were in the basal Amsden at Big Wall and Melstone in central Montana and in the Hermosa formation at Dove Creek and Boundary Butte in the Four Corners area of Colorado and Utah. A deeper-pool discovery in the Weber formation at Ashley Valley, Uintah County, by the Equity Oil Company provided the source for the first commercial oil production in Utah. Geophysical work increased during 1948, with the center of activity in Wyoming. Production of crude oil showed gains corresponding with the increased rate of exploratory drilling. Development drilling progressed rapidly particularly at Mush Creek, Weston County, Wyoming, where 88 new producers are reported. At Rangely, the development of the Weber Sand pool neared completion at the close of the year.

STRATIGRAPHY AND METAMORPHISM IN A PART OF THE NORTHERN BLACK HILLS AND THE HOMESTAKE MINE, LEAD, SOUTH DAKOTA

The pre-Cambrian rocks of the northern Black Hills which have been mapped and studied by the staff of the Homestake Mining Company comprise sedimentary formations with a total stratigraphic thickness of about 20,000 feet. The oldest formations, the Poorman and Homestake, are dominantly ankeritic carbonate and iron-magnesium carbonate respectively. The younger formations, the Ellison, Northwestern, Grizzly, and Flag Rock, are dominantly argillaceous rocks with some quartzites and other rock types. Pre-Cambrian intrusive rocks, originally gabbroic, cut the pre-Cambrian sedimentary rocks; and the whole succession is overlain unconformably by the Cambrian Deadwood formation, and everything is cut by Tertiary intrusive rocks.

Developments in Rocky Mountain District in 1940

There were no major discoveries of oil and gas in unproved areas in the Rocky Mountain district in 1940, most of the drilling being restricted to inside locations in major fields. In Wyoming, good showings of oil encountered in the Shannon sandstone member of the Steele shale (Upper Cretaceous) in the Cole Creek field during deeper drilling in 1937 and thereafter, were tested further in 1940 and commercial production found; one relatively small oil well was drilled in the North Labarge field, Sublette County, 2½ miles north of the nearest production in the Labarge field; and wells deepened a few feet in the Tensleep sandstone (Pennsylvanian) in the Mahoney field, Carbon County, and to the basal member of the Tensleep in the Lost Soldier field, Sweetwater County, were good oil wells. During 1940, commercial amounts of oil were first found in the Tensleep in the East Mahoney (West Ferris) field, Carbon County. No new producing zones were found elsewhere in t e Rocky Mountain district during 1940. However, in February 1941, commercial amounts of oil were first found in the Sundance formation (Upper Jurassic) in the Wilson Creek field, Rio Blanco County, Colorado. In Wyoming, the Frannie field, Park County, was extended almost ½ mile northwestward into Carbon County, Montana; Sundance production was extended eastward about ½ mile in the Lance Creek oil field, Niobrara County; the present north end of the Labarge oil field was extended westward by relatively active drilling; and Tensleep sandstone production was extended about ¼ mile northeast inthe Wertz oil field, Carbon County. Gas production in the Frontier sandstone (Upper Cretaceous) was extended about ½ mile northwestward in the Muskrat field, Fremont County, and almost ½ mile southeastward in the near-by Big Sand Draw field. In the Hiawatha field, Sweetwater County, commercial gas was found in the Wasatch formation (Eocene) about a mile north of the nearest produ er. In Colorado, a good Morrison (Upper Jurassic) sand well was found in the Wilson Creek oil field, Rio Blanco County, 3/4 mile southwest of the nearest producer; and on the east side of the Hiawatha oil and gas field, Moffat County, one relatively large oil well and one relatively small one were found in sandstones of the Wasatch formation. During the year, very few important wildcat wells were drilled in the district. In Montana, a 7,116-foot dry hole was drilled through the Sundance sand on the Absarokee structure, Stillwater County. In Wyoming, a 6,302-foot dry hole was drilled to Pennsylvanian beds in the Middle Baxter Basin area, being the first well to test certain lower zones in the Rock Springs uplift; a 4,243-foot dry hole was completed in the Deadwood formation (Cambrian) on the Bull Creek structure, Crook County; and an 8,343-foot dry hole was completed in the Tensleep sandstone on North Geary dome, Natrona County. A new depth record for drilling in Wyoming was established at 10,121 feet in the Badger Basin field, Park County. Several relatively short pipe lines were completed in the district during 1940, one of the larger being the 100-mile line between the Billy Creek gas field, Johnson County. Wyoming, and the Big Sand Draw gas line at Casper.

Developments in Rocky Mountain Region in 1940: ABSTRACT

There were no major discoveries of oil and gas in unproved areas in the Rocky Mountain district in 1940, most of the drilling being restricted to inside locations in major fields. In Wyoming, good shows of oil encountered in the Shannon sandstone member of the Steele shale (Upper Cretaceous) in the Cole Creek field during deeper drilling in 1937 were tested further in 1940 and commercial production found; one relatively small oil well was drilled in the North Labarge field, Sublette County, about two miles northwest of the nearest production in the Labarge field; and wells deepened a few feet in the Tensleep sandstone (Pennsylvanian) in the Mahoney field, Carbon County, and to the basal member of the Tensleep in the Lost Soldier field, Sweetwater County, were good oil wells. During 1940, commercial amounts of oil were first found in the Tensleep in the East Mahoney (West Ferris) field, Carbon County. No new producing zones were found elsewhere in the Rocky Moun ain district during 1940. However, in February, End_Page 938------------------------------ 1941, commercial amounts of oil were first found in the Sundance formation (Upper Jurassic) in the Wilson Creek field, Rio Blanco County, Colorado. In Wyoming the Frannie field, Park County, was extended almost one-half mile northwestward into Carbon County, Montana; Sundance production was extended eastward and southeastward about one location in the Lance Creek oil field, Niobrara County; the Labarge oil field was extended westward by relatively active drilling; and Tensleep sandstone production was extended about ¼ mile northeast in the Wertz oil field, Carbon County. Gas production in the Frontier sandstone (Upper Cretaceous) was extended about ½ mile northwestward in the Muskrat field, Fremont County, and less than ½ mile southeastward in the near-by Big Sand Draw field. In the Hiawatha field, Sweetwater County, commercial gas was found in the Wasatch formation (Eocene) about a mile north of the nearest produc r. In Colorado, a good Morrison (Upper Jurassic) sand well was found in the Wilson Creek oil field, Rio Blanco County, 3/4 mile southwest of the nearest producer; and on the east side of the Hiawatha oil and gas field, Moffat County, one relatively large oil well and one relatively small one were found in sandstones of the Wasatch formation. During the year, very few important wildcat wells were drilled in the district. In Montana, a 7,116-foot dry hole was drilled through the Sundance sand on the Absarokee structure, Stillwater County. In Wyoming, a 6,302-foot dry hole was drilled to Pennsylvanian beds in the Middle Baxter Basin area, being the first well to test certain lower zones in the Baxter Basin fields; a 4,243-foot dry hole was completed in the Deadwood formation (Cambrian) on the Bull Creek structure, Crook County; and an 8,343-foot dry hole was completed in the Tensleep sandstone on North Geary dome, Natrona County. A new depth record for drilling in Wyoming was established at 10,121 feet in the Badger Basin field, Park County. Several relatively short pipe lines were built in the district during 1940, one of the larger ones being the 100-mile line between the Billy Creek gas field, Johnson County, Wyoming, and the Big Sand Draw gas line at Casper. End_of_Article - Last_Page 939------------

Ordovician Fossils From Upper Part of Type Section of Deadwood Formation, South Dakota

In the northern Black Hills, Middle (?) Ordovician fossils have been found to occur throughout approximately 70 feet of shale and siltstone beds immediately below the typical Whitewood dolomite. These beds and their faunas are discussed, and it is concluded that the strata involved should be included tentatively, at least, with the overlying Whitewood formation (Ordovician), rather than with the underlying Deadwood formation (Cambrian) as has been done heretofore.

Suggestions as to the Description and Naming of Sedimentary Rocks

To attempt a thoroughgoing logical classification of sedimentary rocks is beyond the scope of this article. Unless Grabau's compounding of prefixes into one dinosaurian term is deemed objectionable, his classification can scarcely be bettered. Here only two lines of suggestion are offered. One aims at systematizing field descriptions of rocks. The other deals with problems of nomenclature which chiefly arose during the writer's examination of three hundred specimens and eighty thin sections of the so-called Deadwood formation in the Bighorn Mountains, Wyoming.