Rierdon Formation Research Articles

Mixed sediment deposition in a retro-arc foreland basin: Lower Ellis Group (M. Jurassic), Wyoming and Montana, U.S.A.

The “lower” Ellis Group (M. Jurassic) of northern Wyoming and southern Montana affords an excellent opportunity to examine the influence of tectonics, sea-level change, and incipient topography on facies dynamics and the evolution of mixed sediment ramp deposits. The Sawtooth, Piper, and Gypsum Spring formations (Bajocian to Callovian) represent sedimentation along the forebulge of a retro-arc foreland basin. The “lower” Ellis Group records deposition during two transgressive–regressive cycles, (1) a Bajocian-age cycle dominated by evaporites and red shales, and (2) a Bathonian-age cycle characterized by carbonates, evaporites, and red shales. These cycles are capped by a Callovian-age cycle distinguished by carbonates and red shales that is represented by the “lower” Sundance and Rierdon Formations. Transgressive episodes favored intensified chemical sediment production resulting in thick units deposited in subtidal to peritidal environments. Regressive periods are characterized by supratidal redbed progradation and subsequent shallowing–upward cycles. The depositional cycles in the lower Ellis Group developed due the interplay between sea-level change and tectonic subsidence related to the evolution of a retro-arc foreland basin. Differential subsidence before, during, and after deposition created paleohighs that locally influenced accommodation space and, thereby, complicated depositional and erosional patterns. This paper provides a regional framework for further analysis of the depositional history of the lower Ellis Group by addressing the stratigraphic relationships between the Sawtooth, Piper, and Gypsum Spring Formations.

Combined tide and wave influence on sedimentation patterns in the Upper Jurassic Swift Formation, south‐eastern Alberta

In south‐eastern Alberta, the Oxfordian Swift Formation comprises two unconformity‐bounded sequences. Sequence 1 consists of the shale member. It unconformably overlies Bathonian calcareous shale of the Rierdon Formation and consists dominantly of shale with uncommon hum‐ mocky cross‐stratified siltstone. The shale member comprises up to four parasequences that show a subtle upward‐fining stacking pattern, suggesting overall deepening in a storm‐dominated fully marine basin. Deposition of the shale member was terminated by a fall in relative sea‐level, which in turn initiated sequence 2. During lowstand, a network of north‐east‐ to south‐west‐trending meandering channels incised the top of sequence 1. Despite the preserved morphology of these channels, observations in core suggest that lowstand deposits are absent. These strata were most likely thoroughly reworked by ravinement processes associated with the ensuing transgression and are recorded only by a thin chert pebble lag. Also associated with transgression were significant changes in the physical and ecological conditions in the local Swift basin. These changes were related to modifications in basin configuration and the development of a low‐energy strait, which probably formed as a result of uplift of the Sweetgrass Arch. Within this newly configured basin, brackish‐water conditions prevailed, and sedimentation was dominated by suspension deposition of mud. Bed‐load sediment, composed mostly of very fine and fine sand, made up only a small part of the total sediment flux into the area and was transported principally by low‐energy combined flows with variable‐speed microtidal currents and a low‐energy oscillatory component related to storm waves. Sand was generally deposited in the form of small, discontinuous sand ridges that developed locally throughout the study area – it is these features that form the principal hydrocarbon reservoir bodies in the Swift Formation in the study area. After initiation, ridges built upwards and migrated laterally in response to transport and preferential local deposition of bed‐load sediment. Although common near the unconformity along the top of sequence 1, sand ridges also occur at several higher stratigraphic levels in sequence 2. These latter ridges, however, are not associated with regionally correlatable discontinuities but, instead, were initiated by local bed irregularities, possibly related to breaking internal waves, and were supplied with new sediment transported into the study area. The origin of these sand ridges is therefore not related to changes in relative sea‐level but, instead, to intrabasinal processes in a low‐energy strait.

Oil families in Mannville Group reservoirs of southwestern Alberta, Western Canada sedimentary basin

Lower Cretaceous oils in southern Alberta have been assessed using column chromatography, sulphur analysis, gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). These oils can be divided into four oil families, E, Q, EQ and F, on the basis of biomarker characteristics. Family E oils are characterized by low pristane/phytane ratios and a C 35 homohopane prominence. Family Q oils are identified by the presence of so-called “Q compounds” (Q/R ratio > 0.5) and have high C 27 diasterane to regular sterane ratios. Family EQ oils are a mixture of Family E and Family Q oils, with biomarker characteristics intermediate between these two families and low abundance of “Q compounds” (Q/R ratio < 0.5). Family F oils have high saturate/aromatic ratios, high pristane/phytane ratios (> 1.2) and no C 35 homohopane prominence. Oil-source rock correlation to available source rock data suggest that Family E oils are derived from the Upper Devonian-Mississippian Exshaw Formation and Family Q oils correlate to the Lower Cretaceous Ostracode Zone. Family F oils are likely derived from shales of the Upper Jurassic Rierdon Formation, however additional geochemistry data from this potential source rock are required to confirm this interpretation.

Ostracods from the Rierdon Formation (Jurassic) of Montana: GEOLOGICAL NOTES

ABSTRACT Ostracods from the Rierdon Formation (Jurassic) of Montana have been examined in order to refigure the original species of Procytheridea Peterson, and background information concerning the studied locality, section and ostracod assemblages is given herein.

Petrofabric stress analysis of the Dry Creek Ridge anticline, Montana

Macrofracture analysis and dynamic analysis of calcite twin lamellae and quartz deformation lamellae detail the stress history during evolution of the Dry Creek Ridge anticline — a multilayered, multilithologic fold near Livingston, Montana. This study analyzes data from sandstone and limestone units in the Jurassic Rierdon, Swift, and Morrison Formations and in the Cretaceous Kootenai Formation. During the early stages of folding, σ 1 was parallel to layering and was oriented normal to the anticlinal axis. A fracture system, F 1 , formed in all layers in response to this stress state. As predicted from mechanical bending theory, a neutral surface developed as folding proceeded. The location of this surface is indicated by petrofabric data and approximates the Kootenai-Morrison contact. In the lower portion of the anticline, σ 1 remained parallel to bedding, although locally the stress rotated. In the upper portion, σ 1 became reoriented normal to bedding. At this time (or later during fold growth), the lower units deforming in the compressional domain (σ 1 parallel to layering) of a single mechanical plate subdivided into two separate plates. The stratigraphically lower of these units (Rierdon Formation) was then located in the extensional domain of a mechanical plate (σ 1 normal to layering). During this stage of deformation, the upper portion of the fold (Morrison and Kootenai Formations) did not change behavior. The stress history of this anticline agrees in general with published theoretical models and explains the superposition of several fracture sets at one position in a fold.

Marine Jurassic of Northern Rocky Mountains and Williston Basin

Regional studies indicate that the pattern of sedimentation within the Jurassic seas of the northern Rocky Mountains was influenced by several associated paleotectonic elements. The major negative-trending units were the Alberta and Twin Creek troughs and the Williston basin. The major positive-trending elements were the Belt island and the Sheridan arch. Regionally the marine Jurassic can be separated into lithogenetic units whose characteristics appear to be directly related to the presence of sedimentary environments, the nature of which was governed by the position and relative activity of the various paleotectonic elements. The Piper and Rierdon formations and their equivalents are each separated into three regional units of member rank. The lithologic nature of these units is believed to be related in a large way to the position of Belt island and its effect upon the salinities, temperature, and current distribution in the waters of the Twin Creek trough and the Williston basin and the intervening Montana-Wyoming shelf area. Much of the misunderstanding concerning the Jurassic stratigraphy of the Williston basin is believed to be caused by an inadequate knowledge of the regional nature of the Jurassic units.

Jurassic Subsurface in Southern Alberta: ABSTRACT

Jurassic rocks underlie all of southern Alberta from its eastern and southern boundaries to the Rocky Mountain front on the west. The northern boundary is roughly crescent shape, approximately coinciding with the South Saskatchewan River and its tributary, the Oldman River, to within a few miles of Lethbridge. From that point the boundary trends northwest, passing a few miles east of Calgary. On Alberta plains, Jurassic strata are readily divisible into three formations, which were originally described and named in Montana, and which are, in ascending order, Sawtooth, Rierdon, and Swift. In Alberta Foothills, Jurassic strata are called the Fernie formation, which is roughly the equivalent of the three formations of the Plains. Jurassic strata in southern Alberta rest unconformably on the Rundle formation of Mississippian age. On the Plains they are overlain unconformably by the basal sandstones of the Blairmore formation which have been correlated with the Cutbank and Sunburst sands of Montana. The unconformity at the top of the Jurassic truncates the formations so that they wedge out northward; consequently, the Swift, being the uppermost, has a very limited distribution in Alberta having been eroded completely from the crest of the Sweetgrass arch and remaining only in the extreme southeastern corner of Alberta and in a narrow belt paralleling the Foothills. The Rierdon and Sawtooth formations extend northward approximately to the limits of the Jurassic as defined. In the Foothills the Fernie is overlain y Kootenay sandstone and shale. The Sawtooth formation consists of two sandstone members, separated by green, pyritic, non-calcareous shale. The upper sand is a reservoir for oil and gas in several small fields in Alberta. The formation has a maximum thickness of about 235 feet. The Rierdon formation is made up of an alternation of gray calcareous shale and greenish gray limestone with some pyrite, glauconite, and iron-stone, and has a maximum thickness of 200 feet. The Swift formation lies unconformably on the Rierdon and has a maximum thickness of 150 feet. It consists of glauconitic sandstone, siltstones, concretions, dark gray shale, and usually has chert pebbles at the base. Facies changes take place from west to east in the Sawtooth, Rierdon, and Swift formations so that at the eastern boundary of Alberta they may be readily correlated with the Gravelbourg, End_Page 414------------------------------ Shaunavon, and Vanguard formations of Saskatchewan. However, they are not the exact equivalents of these formations since some overlapping occurs. End_of_Article - Last_Page 415------------

Jurassic System in Williston Basin

The Jurassic system in the Williston Basin is divided into the thin non-marine Morrison formation at the top and the thick marine Ellis group below. The Ellis group includes the Upper Jurassic Sundance formation and the Middle Jurassic Piper formation. No Lower Jurassic rocks are known. Over most of the basin the Piper overlies Triassic Spearfish rocks, except in the north, where it overlies Mississippian or Devonian. The center of Jurassic deposition was in western North Dakota, and a less extensive Jurassic basin was in southern Saskatchewan. Grain size and relative amount of clastic material decrease eastward, and limestones and calcareous shales are more abundant in the areas of thickest accumulation. The lower part of the Piper formation contains red shales and gypsum, and in places it is difficult to separate from underlying Triassic strata. Members of the Sundance formation defined in the Black Hills can not now be recognized in the basin, and the Rierdon formation of the Ellis group in Montana is not a readily mappable unit in North Dakota. Oil has been produced in Wyoming, Montana, and Saskatchewan from rocks equivalent to the Sundance and Piper. Sundance sandstones and Piper limestones have suitable porosity and may be found to be productive on structure elsewhere in the basin.

Jurassic System in the Williston Basin: ABSTRACT

The Jurassic system in the Williston basin is divided into the thin non-marine Morrison formation at the top and the thick marine Ellis group below. The Ellis group includes the Upper Jurassic Sundance formation and the Middle Jurassic Piper formation. No Lower Jurassic rocks are known. Over most of the basin the Piper overlies Triassic Spearfish rocks, except in the north, where it overlies Mississippian or Devonian. The center of Jurassic deposition was in western North Dakota, and a less important Jurassic basin was in southern Saskatchewan. Grain size and relative amount of clastic material decrease toward the east, and limestones and calcareous shales are more abundant in the areas of thickest accumulation. The lower part of the Piper formation contains red shales and gypsum, and it is commonly difficult to separate it from underlying Triassic strata. Members of the Sundance formation defined in the Black Hills can not now be recognized in the basin, and the Rierdon formation of the Ellis group in Montana is not a readily mappable unit in North Dakota. Oil has been produced in Wyoming and Saskatchewan from rocks equivalent to the Sundance and Piper. Sundance sandstones and Piper limestones have suitable porosity and may be found to be productive on structure elsewhere in the basin. End_of_Article - Last_Page 2617------------

Marine Jurassic Formations of Southern Alberta Plains

The Jurassic sediments of the Southern Alberta Plains, known only from subsurface work, are described as to lithology, thickness, distribution, stratigraphic relationships, and geologic history. The three-fold subdivision of the Ellis group into Swift formation, Rierdon formation, and Sawtooth formation, established in Montana, is recognizable and applicable in Alberta. A major unconformity between the Jurassic beds and the underlying Paleozoic limestone influences the distribution of the Sawtooth formation. Late Jurassic or early Cretaceous erosion truncating the Jurassic formations from south to north has determined the present extent and northern boundaries of these formations in Southern Alberta.

Marine Jurassic of Black Hills Area, South Dakota and Wyoming

In the Black Hills area the marine Jurassic rocks comprising the Gypsum Spring and formations represent the upper Bajocian, Bathonian, Callovian, and Oxfordian stages of the Middle and Jurassic. A minor disconformity was developed during the upper Bathonian and a major, regional disconformity during the middle to upper Callovian. Subdivisions of the formation from base to top are herein defined as the Canyon Springs sandstone member, the Stockade Beaver shale member, the Hulett sandstone member, the Lak member, and the Redwater shale member. Sandy sediments in the lower four members were probably derived locally from the east or southeast, in the upper member mainly from the west. The Gypsum Spring formation represents the first widespread invasion and withdrawal of marine waters during the Jurassic in the Western Interior region. It is Middle Jurassic in age and correlative with the Gypsum Spring and Sawtooth formations farther west. The Canyon Springs sandstone member and the Stockade Beaver shale member represent a widespread marine invasion at the beginning of the Jurassic and are correlative with the lower part of the formation of north-central Wyoming, the Lower Sundance of central Wyoming, and the Rierdon formation of Montana. The overlying marine Hulett sandstone member is correlative with similar sandstone in the Lower Sundance formation in central Wyoming. It is probably present in North Dakota and southeastern Montana. It is missing in the outcrop in Montana but may be represented there by shale or sha y limestone at the top of the Rierdon formation. It probably passes westward in Wyoming into the upper part of the Twin Creek limestone. The Lak member consists of redbeds, is apparently non-marine, and is correlative at least in part with the Entrada and Preuss sandstones farther west. It is possibly present in North Dakota but has not been identified in Montana. The Redwater shale member represents the last Jurassic marine invasion in the Western Interior region of the United States. It is mainly or entirely Oxfordian in age and correlative with highly glauconitic sandstone and shale farther west, variously called Swift formation, Stump sandstone, Curtis formation, and Upper Sundance formation.

Marine Jurassic Formations of Sweetgrass Arch, Montana

The marine Jurassic rocks of the Sweetgrass arch in western north-central Montana have been assigned to the Ellis formation. As a result of measuring and sampling eleven Jurassic sections around the Sweetgrass arch and from examining numerous well cuttings, the writer concludes that the Ellis consists of three major lithologic divisions that should be recognized as formations, and that the Ellis should be raised to group rank. The formations of the Ellis group from oldest to youngest are herein named Sawtooth, Rierdon, and Swift. The Sawtooth formation consists of three members, a basal fine-grained sandstone, a medial dark gray shale containing a few dark limestone beds, and an upper member of light gray calcareous siltstone, fine-grained sandstone, or sandy, oolitic limestone. The Sawtooth is as little as 8 feet in thickness on the Kevin-Sunburst dome. It thickens eastward to 200 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The lower two members pass into redbeds east of the Sweetgrass Hills and on the southeast flank of the South arch. The Rierdon formation consists mainly of gray limy shale and nodular limestone. It seems to overlie the Sawtooth formation conformably. It is as little as 72 feet in thickness on the Kevin-Sunburst dome, but thickens eastward to 180 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The Swift formation is composed of two members along the Rocky Mountain Front and eastward across the Kevin-Sunburst dome at least as far as the Sweetgrass Hills. The lower member is dark non-calcareous shale, highly glauconitic at the base. The upper member is gray fine-grained flaggy glauconitic sandstone containing abundant black-gray micaceous shale partings. On the South arch the formation consists of fine-grained flaggy sandstone which is locally pebbly at the base. In the vicinity of the Little Belt Mountains the formation is massive fine-grained sandstone containing a prominent basal conglomerate. The Swift attains its maximum thickness of 166 feet in the Pondera field. The formation has been removed by pre-Kootenai erosion from most of the Cut Bank area, and from a small area west of the Whitlash field. All the formations are fossiliferous. According to Imlay, the Sawtooth is upper Bathonian, the Rierdon is upper Bathonian and Callovian, and the Swift is Divesian and Argovian. The South arch was an island through most of the Bathonian and Callovian stages. At the close of the Callovian the marine waters retreated from the area. During the early Divesian the Sawtooth and Rierdon formations were locally thinned by erosion and possibly removed from some areas. Later in the Divesian marine waters transgressed the entire area and remained until the close of the Argovian.

Marine Jurassic Formations of Sweetgrass Arch, Montana

The marine Jurassic rocks of the Sweetgrass arch in western north-central Montana have been assigned to the Ellis formation. As a result of measuring and sampling eleven Jurassic sections around the Sweetgrass arch and from examining numerous well cuttings, the writer concludes that the Ellis consists of three major lithologic divisions that should be recognized as formations, and that the Ellis should be raised to group rank. The formations of the Ellis group from oldest to youngest are herein named Sawtooth, Rierdon, and Swift. The Sawtooth formation consists of three members, a basal fine-grained sandstone, a medial dark gray shale containing a few dark limestone beds, and an upper member of light gray calcareous siltstone, fine-grained sandstone, or sandy, oolitic limestone. The Sawtooth is as little as 8 feet in thickness on the Kevin-Sunburst dome. It thickens eastward to 200 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The lower two members pass into redbeds east of the Sweetgrass Hills and on the southeast flank of the South arch. The Rierdon formation consists mainly of gray limy shale and nodular limestone. It seems to overlie the Sawtooth formation conformably. It is as little as 72 feet in thickness on the Kevin-Sunburst dome, but thickens eastward to 180 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The Swift formation is composed of two members along the Rocky Mountain Front and eastward across the Kevin-Sunburst dome at least as far as the Sweetgrass Hills. The lower member is dark non-calcareous shale, highly glauconitic at the base. The upper member is gray fine-grained flaggy glauconitic sandstone containing abundant black-gray micaceous shale partings. On the South arch the formation consists of fine-grained flaggy sandstone which is locally pebbly at the base. In the vicinity of the Little Belt Mountains the formation is massive fine-grained sandstone containing a prominent basal conglomerate. The Swift attains its maximum thickness of 166 feet in the Pondera field. The formation has been removed by pre-Kootenai erosion from most of the Cut Bank area, and from a small area west of the Whitlash field. All the formations are fossiliferous. According to Imlay, the Sawtooth is upper Bathonian, the Rierdon is upper Bathonian and Callovian, and the Swift is Divesian and Argovian. The South arch was an island through most of the Bathonian and Callovian stages. At the close of the Callovian the marine waters retreated from the area. During the early Divesian the Sawtooth and Rierdon formations were locally thinned by erosion and possibly removed from some areas. Later in the Divesian marine waters transgressed the entire area and remained until the close of the Argovian.