Wapiti Formation Research Articles

Fluvial Sequence Stratigraphy: The Wapiti Formation, West-Central Alberta, Canada

Abstract Outcrop exposures and high-resolution subcrop data allow the description and mapping of four stratigraphic discontinuities in the fully nonmarine strata of the Campanian–Maastrichtian Wapiti Formation (Western Interior foreland basin, Alberta, Canada). This framework defines four unconformity-bounded depositional sequences (A–D), based on sequence stratigraphic methodology, well-log patterns, and facies analysis. In ascending order, sequence A records the transition from the underlying marine facies of the Puskwaskau Formation into the Wapiti fluvial facies, and consists of strongly progradational and aggradational stacking patterns. Sequences B and C show a similar pattern of basal amalgamated channel-fill deposits that grade upwards into floodplain-dominated strata. Finally, sequence D is dominated by channelized sediments and extensive overbank facies. An aggradational stacking pattern suggests deposition under high-accommodation conditions. Maximum flooding surfaces are interpreted within fine-grained deposits in the upper portions of sequences C and D. They are tied to regionally extensive coals that accumulated more than 250 km away from the coeval shoreline. This study provides new evidence that major coal seams may represent the extension of marine maximum flooding surfaces into the downstream-controlled fluvial realm. Furthermore, the new stratigraphic framework of subaerial unconformities and maximum flooding surfaces provides the means of subdividing the previously undifferentiated fully nonmarine Wapiti Formation into depositional sequences and component systems tracts.

Bentonite chemical features as proxy of late Cretaceous provenance changes: A case study from the Western Interior Basin of Canada

Bentonite beds are fairly common in both marine and terrestrial Upper Cretaceous (Campanian–Maastrichtian) deposits of the Western Interior Basin of western Canada and northwestern United States. A detailed stratigraphic, sedimentologic, geochemical (X-ray fluorescence), and mineralogical (X-ray diffraction) study of twenty-one bentonites from the Puskwaskau and Wapiti formations in the Grande Prairie area (west-central Alberta, Canada) is here presented. Major and trace-element concentrations from altered volcanic ashes document the presence in the study area of predominantly trachyandesitic and rhyolitic volcanogenic products, resulted from intense volcanic arc to within-plate pyroclastic activity. Concentration values of high field strength elements (HFSE) and selected large ion lithophile elements (LILE) (e.g. Nb, Zr, Th, and Y) obtained by X-ray fluorescence spectroscopy strongly support the presence of multiple volcanic sources. Integrated paleoenvironmental and geochemical criteria for provenance determination indicate a bimodal occurrence of basic and acid volcanic products interpreted as reflection of source areas characterized by different tectonic setting and magmatic composition. A comparative analysis of geochemical compositions between Grande Prairie bentonites and 30 known volcanic beds from central and southern Alberta, Manitoba and Montana 1. documents a trend toward more acidic and alkali-depleted volcanic products during the late Campanian–early Maastrichtian interval, and 2. suggests a well constrained stratigraphic and geographic subdivision of the non-marine successions of the foreland basin on the basis of geochemical characteristic of volcanic ash beds. Furthermore, geochemical “fingerprints” of several decimeter to meter thick bentonite beds have been coupled with volcanic ash subsurface signature in order to investigate their role as marker beds. This multiple-approach provides a reliable tool for basin-scale identification and correlation of non-marine sedimentary successions.

Stratigraphy of the Upper Cretaceous Wapiti Formation, west-central Alberta, Canada

The lithostratigraphic interval between the marine Puskwaskau Formation (Smoky Group, Santonian–Campanian) and the fluvial Scollard Formation (early Maastrichtian) in west-central Alberta and easternmost British Columbia (Canada) is represented by the nonmarine deposits of the Wapiti Formation. Its subdivision into regionally mappable stratigraphic units and the correlation of such units with the better known successions of central and southern Alberta are the main goals of this study. We present a detailed stratigraphic revision of the Wapiti Formation in the Grande Prairie region, where the entire succession crops out extensively and intensive oil and gas exploration activity provides excellent subsurface control. This study indicates that the Wapiti Formation consists in five stratigraphic units: their description has been based in particular on facies analysis and well-log signatures. In ascending order, units 1 to 5 record major differences in depositional architecture related to variation in accommodation and climatic conditions. Upper and lower contacts of these units are represented by regionally mappable subaerial unconformities or conformable facies contacts. Three major coal zones are identified within the Wapiti Formation, the Basal, Red Willow, and Cutbank: coals referred to these intervals have been documented in both outcrop and subsurface in the entire study area, thus representing a reliable tool for regional correlations. Furthermore, results presented here indicate that the maximum flooding surfaces of the Bearpaw seaway and the Drumheller Marine Tongue, both marine reference units in central and southern Alberta, lie, respectively, within coals of unit 3 and the Red Willow coal zone.

A high latitude vertebrate fossil assemblage from the Late Cretaceous of west-central Alberta, Canada: evidence for dinosaur nesting and vertebrate latitudinal gradient

This study reports on a new microvertebrate locality from the Campanian (c 74 My) fluvial beds of the Wapiti Formation in the Grande Prairie area (west-central Alberta, Canada). This locality represents deposition on a low-gradient, waterlogged alluvial plain approximately 300 km to the north west of the Bearpaw Sea. Detailed sedimentological analyses suggest an environment characterized by a high-sinuosity channel system responsible for widespread oxbow lakes, bogs and marshes. A total of 260 identifiable elements were recovered from three distinct sites at the Kleskun Hill Park, documenting a diverse terrestrial and fresh-water palaeocommunity. The recovered fossils include those from hatchling- to nestling-sized hadrosaurid dinosaurs, indicating the presence of a nesting ground in the area. This is the first evidence for dinosaur nesting site in the Wapiti Formation and simultaneously an extremely rare evidence of high-latitude dinosaur nesting, the northernmost in North America to date. A large number of teeth of the small theropod Troodon are associated with baby hadrosaurids in the site supporting a northern affinity of this taxon as well as a previously proposed predator–prey association. Other dinosaurs are less common at the locality and include large and small theropods (i.e. tyrannosaurid, Saurornitholestes, Richardoestesia, Paronychodon, and dromaeosaurid) and five ornithischian taxa. Fish, squamate, turtle, and mammal elements were also identified. Collectively, the vertebrate fossil assemblage from the locality allows palaeocommunity reconstruction in the Wapiti Formation. The importance of the data collected from the new locality is twofold: first, they represent the first comprehensive report from a geographically significant area located between the well-sampled fossil localities of southern Alberta and the high-latitude localities of Alaska. Furthermore, the reconstructed vertebrate fauna support latitudinal gradient of vertebrate distribution along the Western Interior region during the Late Cretaceous.

Geological characterization and potential for carbon dioxide (CO2) enhanced oil recovery in the Cardium Formation, central Pembina Field, Alberta

Research Article| June 01, 2008 Geological characterization and potential for carbon dioxide (CO2) enhanced oil recovery in the Cardium Formation, central Pembina Field, Alberta Shahin E. Dashtgard; Shahin E. Dashtgard Department of Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada Search for other works by this author on: GSW Google Scholar Maja B.E. Buschkuehle; Maja B.E. Buschkuehle Strike Oil Lilmited, Perth, Australia Search for other works by this author on: GSW Google Scholar Brent Fairgrieve; Brent Fairgrieve Energy Resources Conservation Board, Calgary, AB, Canada Search for other works by this author on: GSW Google Scholar Habtemicael Berhane Habtemicael Berhane Energy Resources Conservation Board, Calgary, AB, Canada Search for other works by this author on: GSW Google Scholar Bulletin of Canadian Petroleum Geology (2008) 56 (2): 147–164. https://doi.org/10.2113/gscpgbull.56.2.147 Article history received: 16 Jan 2008 accepted: 06 May 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Shahin E. Dashtgard, Maja B.E. Buschkuehle, Brent Fairgrieve, Habtemicael Berhane; Geological characterization and potential for carbon dioxide (CO2) enhanced oil recovery in the Cardium Formation, central Pembina Field, Alberta. Bulletin of Canadian Petroleum Geology 2008;; 56 (2): 147–164. doi: https://doi.org/10.2113/gscpgbull.56.2.147 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract Injection of CO2 into the Cardium Formation, central Pembina Field, Alberta was initiated in 2004 in two inverted 5-spot waterflood patterns. The purpose of this flood was to assess the economic viability of enhanced oil recovery (EOR) using CO2. To study CO2 behaviour within the reservoir and assess long-term risks of CO2 leakage and storage potential, a geological and hydrogeological model was developed for the Cardium Formation, and for both the underlying and overlying strata. The injection zone, Cardium Formation, was sub-divided into four permeable and three impermeable reservoir units. The underlying and overlying strata were subdivided based on their geological potential to contain CO2 over the long-term (5,000 years).Permeable reservoir units in the Cardium Formation include the lower, middle and upper sandstones, and the conglomerate. Most of the storage capacity of the Cardium Formation is contained within the three sandstone beds, which exhibit average porosities between 14.8 percent and 16.4 percent. Permeability in the sandstones increases predictably with increasing porosity, but is variable from sandstone to sandstone. The lower sandstone has the lowest average permeability (9.5 md), which is about half the average permeability of the middle and upper sandstones (21.4 and 19.8 md, respectively). There is no relation between porosity and permeability in the conglomerate. The conglomerate on average is 50 percent more permeable (33 md) than the middle and upper sandstones; although, permeability may exceed one Darcy in individual beds. The higher permeability of the conglomerate results in it acting as a “thief” zone for injected CO2. This tendency is further compounded by both the endemic use of hydraulic fractures (which propagate vertically) to stimulate oil production, and the positive buoyancy of CO2 relative to water.The Cardium Formation at Pembina occurs within the middle of the 650 m thick Colorado Group shale. The effectiveness and integrity of the overlying shale succession, as a seal for the Cardium Formation, is vital to the long-term storage of CO2. Leakage through this shale is very unlikely as it is thicker than 300 m and separates two aquifers with significantly different regional pressure regimes (the Cardium Formation was originally over-pressured whereas the overlying Wapiti Formation is sub-hydrostatically pressured). You do not currently have access to this article.

Heart Mountain, Wyoming, detachment lineations: Are they in microbreccia or in volcanic tuff?

Research Article| September 01, 1991 Heart Mountain, Wyoming, detachment lineations: Are they in microbreccia or in volcanic tuff? WILLIAM G. PIERCE; WILLIAM G. PIERCE 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar WILLIS H. NELSON; WILLIS H. NELSON 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar ANTONI K. TOKARSKI; ANTONI K. TOKARSKI 2Polish Academy of Science, Krakow, Poland 31-002 Search for other works by this author on: GSW Google Scholar EWA PIEKARSKA EWA PIEKARSKA 2Polish Academy of Science, Krakow, Poland 31-002 Search for other works by this author on: GSW Google Scholar Author and Article Information WILLIAM G. PIERCE 1U.S. Geological Survey, Menlo Park, California 94025 WILLIS H. NELSON 1U.S. Geological Survey, Menlo Park, California 94025 ANTONI K. TOKARSKI 2Polish Academy of Science, Krakow, Poland 31-002 EWA PIEKARSKA 2Polish Academy of Science, Krakow, Poland 31-002 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1991) 103 (9): 1133–1145. https://doi.org/10.1130/0016-7606(1991)103<1133:HMWDLA>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation WILLIAM G. PIERCE, WILLIS H. NELSON, ANTONI K. TOKARSKI, EWA PIEKARSKA; Heart Mountain, Wyoming, detachment lineations: Are they in microbreccia or in volcanic tuff?. GSA Bulletin 1991;; 103 (9): 1133–1145. doi: https://doi.org/10.1130/0016-7606(1991)103<1133:HMWDLA>2.3.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 SocietyGSA Bulletin Search Advanced Search Abstract The concept of tectonic denudation followed by deposition of lower middle Eocene Wapiti Formation volcanic rocks on the exposed Heart Mountain detachment has been challenged by Hauge. His "extending allochthon" interpretation requires that the Wapiti Formation be fault emplaced and that lineations in a volcanic tuff overlying the fault north of Jim Smith Peak be fault striae in "microbreccia." Our re-examination of the field evidence in minute detail indicates that these lineations were produced by flowage of volcanic rocks on a thin layer of air-fall tuff. The following lines of evidence indicate that this tuff was deposited on the detachment surface during the brief interval that the denuded surface was exposed. (1) Field relations indicate that the Wapiti volcanic rocks are younger than the detachment, and so they could not have been fault emplaced. (2) Lineations occur only on the upper surface of Wapiti Formation tuff; none were found at the contact of the tuff with the detachment surface. (3) The reported direction of translation indicated by the lineations is not consistent. Many lineations in the tuff indicate north and northeast movement—a direction that is consistent with lineations produced by lava flowing from a known vent but inconsistent with a southeast direction of detachment movement. (4) The lineations are restricted to the northwestern part of the area covered by the Wapiti Formation, which is also consistent with their derivation as volcanic flow lineations from a known vent. If the Wapiti had been tectonically emplaced, fault striae should occur elsewhere on the detachment surface, but none have been observed. (5) The lower contact of the tuff with the detachment surface, as seen in thin sections, is irregular, suggesting that it is a depositional rather than a fault contact. (6) The contact between the tuff and overlying Wapiti, as seen in thin sections, is also irregular, as would be expected if the Wapiti volcanic breccia had been deposited on the tuff. Thin sections of the "microbreccia" suggest that it is a sedimentary rock, not a "fault rock." (7) A remnant of the tectonic carpet of all-carbonate fault breccia lying on the detachment surface, unmixed with the overlying Wapiti volcanic rock, is compatible with the depositional emplacement of the Wapiti but is not compatible with Wapiti Formation being moved many kilometers across the carpet of all-carbonate fault breccia and not removing or becoming mixed with it. 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.

The case for tectonic denudation by the Heart Mountain fault—A response

Two basic concepts pertaining to the history of the Heart Mountain fault of northwestern Wyoming have recently been challenged; one, that there was tectonic denudation, and two, that volcanic rock of the Wapiti Formation was deposited on the exposed fault surface. Tectonic denudation is believed to have occurred as a consequence of the upper plate having broken into numerous blocks that separated as movement progressed along a nearly horizontal fault surface, thus leaving the fault surface exposed between blocks. Volcanic rocks of the Wapiti Formation were then deposited both on the exposed fault surface and against and over the upper-plate blocks. Two formations of Eocene volcanic rocks are involved. The older volcanic unit, the Cathedral Cliffs Formation, and the Paleozoic carbonate rocks are part of the upper plate of the Heart Mountain fault and moved with it, whereas the younger Wapiti Formation was deposited on the fault surface after movement had ceased. In an alternate interpretation recently advanced by T. A. Hauge, subdivisions of the Absaroka Volcanic Supergroup, of which the Cathedral Cliffs and Wapiti Formations are units, are not recognized. The upper plate of the Heart Mountain detachment is interpreted as having been a single, continuous allochthon composed largely of volcanic rocks with small amounts of Paleozoic rocks. During Heart Mountain faulting, extension of the once-continuous slab of Paleozoic sedimentary rock is alleged to have been accompanied by the formation of ten or more grabens, now filled predominantly by Absaroka volcanic rocks. This interpretation further proposes that the volcanic rocks were emplaced while the separating blocks of Paleozoic strata were still moving and that the basal part of the volcanic rock between these blocks is in fault contact rather than depositional contact with the strata beneath the Heart Mountain fault. Many lines of geologic field evidence indicate that the Wapiti Formation is younger than the Heart Mountain fault and was deposited on the technically denuded fault surface. (1) Wapiti rocks bury the break-away fault. (2) Fault breccia at the base of the upper-plate carbonate blocks is composed entirely of carbonate fault breccia and has no volcanic component. (3) Small blocks of upper-plate rocks have been displaced by gravity from the upper part of the allochthon to the detachment fault surface. (4) Eocene stream-channel deposits locally cut into the surface of tectonic denudation and also have been displaced on the Heart Mountain fault. (5) The volume of Wapiti Formation filling the spaces between allochthonous blocks in proportion to the volume of those blocks is much too great for the Wapiti to have been allochthonous. (6) Clastic dikes of carbonate fault breccia penetrate Wapiti volcanic rocks. (7) Some of these clastic dikes of fault breccia contain Precambrian xenoliths and wood phenoclasts requiring surface exposures of the fault breccia before injection as dikes. (8) Wapiti volcanic rocks having chilled borders are in tightly bonded contact with upper-plate Paleozoic rocks. (9) Faults present in the upper-plate blocks do not penetrate the overlying Wapiti Formation. (10) Volcanic fault breccia is absent where volcanic rocks overlie carbonate fault breccia. (11) A mound of carbonate fault breccia is not mixed with overlying Wapiti Formation. The continuous allochthon interpretation is based on several erroneous assumptions that cannot be supported by field observations. (1) Faults to transport and emplace the Wapiti Formation onto and along the Heart Mountain fault do not exist. (2) The contact between volcanic rocks and the allochthon west of Corral Creek at the west end of Cathedral Cliffs, cited by Hauge as a fault in an extending allochthon, is a depositional contact. (3) The volcanic rock adjoining allochthonous Paleozoic rocks north of Pilot Creek cannot be part of an extending allochthon because (a) it is Cathedral Cliffs Formation, which is pre–Heart Mountain fault, and (b) its direction of movement is horizontal rather than down dip, as required in an extending allochthon. (4) Most of the igneous dikes were intruded after the Heart Mountain fault movement ceased, and so they could not accommodate significant extension of the upper plate. (5) Striae reported as indicating fault emplacement of volcanic rock (Wapiti Formation) on the Heart Mountain fault actually lire flow features, formed as the Wapiti Formation was deposited on the exposed fault surface. Tectonic denudation is the only model that is consistent with evidence observable in the field. Although the process by which tectonic denudation was accomplished remains enigmatic, tectonic denudation remains a constraining fact in any model for the origin of the Heart Mountain fault.

Magnetostratigraphic Correlation of Eocene Rocks from the Absaroka Mountains, Wyoming: ABSTRACT

A paleomagnetic framework has been established for the correlation of the Eocene section throughout the southern and eastern Absaroka Mountains of northwestern Wyoming, and it has been tested against biostratigraphic and rock stratigraphic markers. Correlation is based on the magnetic polarity of volcanic and volcaniclastic rocks samples collected from nine sites that include Togwotee Pass, the East Fork basin, the Owl Creek and Cottonwood Creek drainages, Phelps Mountain, Carter Mountain, and along the South fork and North fork of the Shoshone River. The remnant magnetization of these samples reflects the polarity of the earth's magnetic field when the rocks were deposited. Magnetic polarity zonations, determined at individual sections, were correlated throughout the region and established horizons that are contemporaneous to within a few thousand years. This represents a method for timing volcanic, tectonic, and depositional events that is more precise than any other technique currently known. In addition, the method provides absolute ages if the polarity zonations can be matched to the pattern of Eocene geomagnetic reversals. Using this approach, it has been determined that (1) the Wiggins Formation in the Carter and Phelps Mountain areas is similar in age to the Tepee Trail Formation in the southeastern Absarokas; (2)more » the Pitchfork Formation is a transitional facies between the Aycross and Wapiti Formations; and (3) the Eocene section from the upper Willwood to the lower Wiggins was deposited between 52 and 47 Ma.« less

Coal Quality, Coal Rank Variation and its Relation to Reconstructed Overburden, Upper Cretaceous and Tertiary Plains Coals, Alberta, Canada

Near-surface coals in the Alberta plains occur in Upper Cretaceous and Tertiary sediments, the former represented by the Belly River Group, Horseshoe Canyon Formation, and Wapiti Formation, and the latter by the Scollard Member of the Paskapoo Formation. Statistical techniques were used to document both the distribution of and the interrelationships among the components of proximate and ultimate analysis and calorific value determinations. The coals discussed range in rank from subbituminous C to high-volatile bituminous C. These coals are variable in ash content and low in sulfur content. The relationships among calorific value (dry basis, in kJ/kg) and ash (dry basis, in %) and calorific value (moist mineral-matter-free basis, in kJ/kg) and equilibrium moisture (MEQ, in %) were determined to be CVD = 29,677 - 315.17 ashD, and CVMMMF = 31,816 - 442.05 MEQ, respectively. The maximum depth of coal seam burial (DOB, in m) was reconstructed on the basis of previously published graphs, relating the equilibrium moisture loss to depth of coal seam burial, using the relationship: log10MEQ = 1.865 - 0.000416 DOB. A least-squares regression analysis of calorific value (MMMF basis, in k /kg) on the calculated depth of burial (DOB, in m) yielded the equation, CVMMMF = 14,748 + 6.25 DOB, indicating a coalification gradient, determined on the reconstructed overburden, of 6.25 kJ/kg/m (0.82 Btu/lb/ft) of depth (or overburden). Near-surface coals in the Alberta plains increase in rank toward the west-southwest (toward the foothills and mountains region) because of progressively greater amounts of overburden that existed in that direction during the Tertiary. Erosion has since removed between 900 and 1,900 m (3,000 and 6,200 ft) of sediment, with the greatest amount of removal occurring in a west-southwest direction.

Coal Quality and Overburden Reconstruction of Upper Cretaceous and Tertiary Coal-Bearing Formations, Plains Area, Alberta: ABSTRACT

Statistical analyses of chemical data obtained from 685 coal samples have been carried out to determine the distribution of coal quality in the Alberta plains. Distributions of components of proximate and ultimate analyses and heating value for each of the major Upper Cretaceous and Tertiary coal-bearing units, namely Belly River Group, Wapiti Formation, Horseshoe Canyon Formation, and Scollard Formation, were investigated. A least-squares regression analysis of all data, regardless of formation, of calorific value, CV (Kcal/kg), corrected to a moist mineral matter free basis, on equilibrium moisture, MEQ, yielded the equation CV = 7599-105.58 MEQ. The maximum depth of coal seam burial, D (meters), was reconstructed on the basis of published graphs relating equilibrium moisture loss to depth of burial of coal seams. The resulting equation was log[10]MEQ = 1.865-0.000416(D). This equation facilitated reconstruction of both the maximum paleotopographic elevation and the amount of sediment removal from the plains area of Alberta. Near surface coals (shallower than 300 m) varied in rank from subbituminous to high volatile bituminous C, with rank increasing in a west-southwest direction (i.e., toward the foothills and mountains region) because of the progressively greater amounts of overburden that existed in that direction during Tertiary time. Erosion has since removed between 880 and 1,900 m of sediment, with the greatest amount of removal occurring in a west-southwest direction. An average coalification gradient of 1.67 of Kcal/kg/m (0.91 BTU/lb/ft) was determined by using the reconstructed overburden. End_of_Article - Last_Page 614------------

The Heart Mountain break-away fault, northwestern Wyoming

The Heart Mountain break-away fault was the last of the four phases of the Heart Mountain detachment fault to be discovered and is the only fault of this type yet recognized and described. The descriptive term, “break-away fault,” was introduced in 1960 for the steep surface along which the rocks of the Heart Mountain decollement fault mass separated from the stationary block on the west. The break-away fault, located near the northeast entrance to Yellowstone National Park, has a known linear extent of 37 km. The northern one-third trends north, and the remainder trends southeast and south. Rocks on its western side are Paleozoic carbonate rocks and Eocene volcanic rocks; the volcanic rocks are pre–Heart Mountain fault in age. The rocks on its eastern side are younger and consist of Eocene volcanic rocks which were deposited against and over the fault. Thus the break-away fault is unusual in that one side is a fault surface and the other side is a depositional surface, and in that respect is similar to parts of the bedding-plane phase of the Heart Mountain detachment fault. Slickensides and brecciation in the Madison Limestone adjoining the break-away indicate horizontally directed compressive shear. Movement was probably right lateral, and then laterally southeastward away from the fault at an angle of about 45°. To the north, in Wolverine Pass and in the valley of Soda Butte Creek, the break-away fault extends down to a bed in the basal part of the Bighorn Dolomite where it joins or terminates at the bedding plane phase of the Heart Mountain detachment fault; movement of upper-plate rocks away from the break-away fault increases from about 0.25 km at the northernmost trace of the fault to more than 1.5 km on the south side of Soda Butte Creek valley. Several kilometres southeastward, in Cache Creek valley, the Heart Mountain break-away fault terminates downward in volcanic rocks of the undivided Lamar River and Cathedral Cliffs Formations and joins a low-angle fault in those rocks. This low-angle fault probably steps downward to the east where it reaches the Heart Mountain detachment fault surface. Three kilometres farther to the southeast, the break-away fault is presumably represented by a low-angle fault in these volcanic rocks that probably also steps down to the northeast beneath the volcanic cover to join the Heart Mountain detachment fault. Erosion in this area probably has removed rocks that contained the high-angle part of the fault. The south end of the break-away fault is overlapped and concealed by the Wapiti Formation. It presumably continues southward, but it probably does not join a normal fault near Black Mountain, although Voight (1974) has suggested that it does.

Crandall Conglomerate, An Unusual Stream Deposit, and Its Relation to Heart Mountain Faulting

The Crandall Conglomerate (Eocene) is a channel deposit, more than 350 ft (100 m) thick, believed to have formed as a result of preliminary movement of the Heart Mountain detachment fault in northwestern Wyoming. Initial movement of the Heart Mountain fault opened a deep rift in which the conglomerate was deposited. The rift was less than a mile (1.6 km) wide and was bordered by 2,000-ft (600 m) cliffs, mostly of Paleozoic limestone. Before the gravel was deposited, unconfined Cambrian shale below the rift was deformed into the Blacktail fold, a sharp anticline without apparent roots, while streams carried away the upwelling shale and cut a channel several hundred feet deep. The debris that accumulated in this channel is the Crandall Conglomerate. Deposition of the conglomerate was followed by Cathedral Cliffs volcanism, by movement on the Reef Creek detachment fault, and by the main movement on the Heart Mountain detachment fault. The main movement on this fault left the lower part of the conglomerate in place but carried the upper part with deposits of the upper plate roughly 15 mi (24 km) southeastward. Most of the deposits of the lower plate rest directly on the Blacktail fold. Of the 15 known deposits of Crandall Conglomerate, five are in place but have been overridden by the upper plate of the Heart Mountain fault, and ten have been transported as part of the upper plate. After this movement, volcanic rocks of the Wapiti Formation blanketed the region.

Igneous Activity, Metamorphism, and Heart Mountain Faulting at White Mountain, Northwestern Wyoming: Reply

The spire of brown volcanic rock at White Mountain, long regarded as a filled volcanic conduit associated with eruption of the Eocene Wapiti Formation, is actually an erosional remnant of volcaniclastic sedimentary rocks of the Eocene Cathedral Cliffs Formation that has been transported 10 to 15 mi southeastward as part of a Heart Mountain detachment fault block. Prevolcanic Paleozoic carbonate rocks, which comprise the western part of this block, are metamorphosed and strongly folded, in contrast to the rocks of other Heart Mountain fault blocks. This metamorphism ends abruptly downward at the Heart Mountain fault plane. Rounded fragments of metamorphosed carbonate rock in Heart Mountain fault breccia and in related clastic dikes show that the metamorphism occurred before the faulting, presumably as a result of the Cathedral Cliffs igneous activity. Igneous rock fragments in the Heart Mountain fault breccia at White Mountain seem to have been derived from allochthonous sills and dikes that predate the Heart Mountain fault. Therefore these fragments are not evidence for volcanic activity during Heart Mountain faulting, nor for introduction of volcanic gases along the fault plane as suggested by Hughes (1970a). A fault plate would have to be large and coherent to be buoyed up by volcanic gas or other fluids. The present widespread distribution of the remnants of the upper plate indicates that the upper plate broke up to form a number of fault blocks very soon after the Heart Mountain faulting began.

Igneous Activity, Metamorphism, and Heart Mountain Faulting at White Mountain, Northwestern Wyoming

The spire of brown volcanic rock at White Mountain, long regarded as a filled volcanic conduit associated with eruption of the Eocene Wapiti Formation, is actually an erosional remnant of volcaniclastic sedimentary rocks of the Eocene Cathedral Cliffs Formation that has been transported 10 to 15 mi southeastward as part of a Heart Mountain detachment fault block. Prevolcanic Paleozoic carbonate rocks, which comprise the western part of this block, are metamorphosed and strongly folded, in contrast to the rocks of other Heart Mountain fault blocks. This metamorphism ends abruptly downward at the Heart Mountain fault plane. Rounded fragments of metamorphosed carbonate rock in Heart Mountain fault breccia and in related clastic dikes show that the metamorphism occurred before the faulting, presumably as a result of the Cathedral Cliffs igneous activity. Igneous rock fragments in the Heart Mountain fault breccia at White Mountain seem to have been derived from allochthonous sills and dikes that predate the Heart Mountain fault. Therefore these fragments are not evidence for volcanic activity during Heart Mountain faulting, nor for introduction of volcanic gases along the fault plane as suggested by Hughes (1970a). A fault plate would have to be large and coherent to be buoyed up by volcanic gas or other fluids. The present widespread distribution of the remnants of the upper plate indicates that the upper plate broke up to form a number of fault blocks very soon after the Heart Mountain faulting began.