Arbuckle Group Research Articles

Bedded Cherts in the Early Ordovician Arbuckle Group of Southwestern Oklahoma

Bedded cherts are a rarely occurring but environmentally significant facies in the Early Ordovician Arbuckle Group. Two such units have been identified: one in the Cool Creek Formation and one in the Kindblade Formation. In each, microcrystalline calcite and dolomite alternate in thin laminae with microcrystalline silica in units up to 25 cm in thickness. The areal extent of the bedded cherts encompasses more than 130 km{sup 2}. It is hypothesized that the interlaminated cherts and micrites were deposited in very shallow marine conditions. A relatively small part of the Oklahoma Aulacogen was cut off from open ocean circulation, resulting in an isolated lagoon. The chert/micrite couplets may represent seasonal deposits in the lagoon. During seasonal flooding, slightly deeper water resulted in algal growth with accompanying precipitation of carbonates and solution of detrital quartz sand. During the dry season, the dissolved silica precipitated, resulting in thin layers of microcrystalline chart. Some carbonate layers contain small pseudomorphs after what may have been gypsum and anhydrite crystals and nodules, indicating that salinities increased enough to permit formation of evaporites. At least ten couplets occur in the thickest units, suggesting that the lagoon existed for ten wet-dry seasons.

Oils and source rocks from Pauls Valley, Anadarko Basin, Oklahoma, U.S.A.

Thirty oils from the Pauls Valley area of the Anadarko Basin, Oklahoma, have been analyzed for n-alkane, terpane and sterane distributions in an effort to classify genetically related oils. Ten rock samples from the area were also analyzed in an attempt to relate oil types to their possible source rocks. The Pauls Valley area, located near the southeast corner of the Anadarko Basin, has producing formations ranging in age from Middle Ordovician to Late Pennsylvanian. Trapping mechanisms responsible for the accumulation of hydrocarbons vary from purely structural traps, to fractured reservoirs, to up-dip truncations of reservoirs and up-dip pinchouts of sandstones. Results show that 85% of oils in the area probably have a common source, the Woodford Shale. A group of oils reservoired in the Viola Group exhibit distinct geochemical characteristics and are thought to have a different source. The differences between the oils from these two sources include: enhanced C 24 tetracyclic terpane concentrations relative to C 26 tricyclic terpanes; diminished C 28–30 tricyclic terpanes relative to T s and T m ; diminished C 30-steranes relative to their C 29 counterparts; predominance of C 35 over C 34 extended hopanes and an even/odd predominance of the normal alkane distribution. Extracts from the Viola Group generally exhibit the same qualities as the associated oils and the limestone is proposed as their probable source rock. The predominance of C 29-steranes for oil samples which appear to have a marine source (inferred by their n-alkane distribution, the presence of C 30-steranes and high levels of tricyclic terpanes) suggests that caution be used in the interpretation of terrigenous sources based on the high abundance of C 29-steranes. The Deese Group, the Springer Formation, the Sylvan Shale, and the Arbuckle Group are not likely sources for the oils analyzed from the Pauls Valley area. Differences in API gravity and color, previously used to classify oils in this region, are not source-related but are related to maturation and migration effects.

Geochemical and isotopic constraints on the diagenetic history of a massive stratal, late Cambrian (Royer) dolomite, Lower Arbuckle Group, Slick Hills, SW Oklahoma, USA

The diagenetic history of the late Cambrian massive Royer dolomite from the lower Arbuckle Group, Slick Hills, SW Oklahoma, USA, has been evaluated through comprehensive geochemical analyses. The dolomite probably formed during early diagenesis from contemporaneous late Cambrian seawater, evidenced by similar 87Sr 86Sr ratios (from 0.70891 to 0.70913) of most (70%) dolomite samples, to coeval late Cambrian seawater (from 0.7089 to 0.7092). Very light δ 18 O values (−10.2 to −12.9‰, PDB), however, indicate that the dolomite was significantly modified during burial. Correlation of various geochemical parameters (Sr, Fe, δ 18 O, and 87Sr 86Sr ) demonstrates that dolomite samples with increased modification are characterized by lower Sr and higher Fe concentrations, lighter δ 18 O values, and less radiogenic 87Sr 86Sr ratios. This correlation, coupled with the light δ 18 O values of the dolomite, demonstrates that meteoric water, recharged into overlying carbonates, was responsible for burial modification of the dolomite. Geochemical comparison of the dolomite with associated limestone and quantitative modelling of δ 18 O, Sr, and 87Sr 86Sr variation during water-rock interaction suggest that the dolomite underwent long-lasting modification. The timing of meteoric modification was coincident with the development of regional overlying unconformities corresponding to emergence of the carbonate platform. Similar diagenetic modification has probably been responsible for 18O depletion and trace element modification of ancient dolomites in many other areas, although many of these dolomites have been interpreted to have formed either in mixing-zone environments or in subsurface environments.

Evidence for Existence of Sabkhalike Conditions in Upper Arbuckle Group, Slick Hills, Southwestern Oklahoma: ABSTRACT

In the Slick Hills of southwestern Oklahoma, the Ordovician upper Arbuckle Group carries a cryptic record of evaporite precipitation. This record is particularly well developed in the Cool Creek and, to a lesser extent, the West Spring Creek formations. Principal lines of evidence supporting this conclusion are (1) salt pseudomorphs (after gypsum( )) preserved in chert and, less commonly, in limestone (principal pseudomorphing minetals are calcite and dolomite), (2) molds of salts in cherts, (3) traces of anhydrite and celestite within chert nodules, (4) collapse breccias the authors interpret as resulting from the solution of sulfate deposits, (5) dolomite beds that have appropriate isotope values, and (6) length-slow and other varieties of chert indicative of waters of high ionic strength, some of which are the distinctive cauliflower variety. In addition, a number of features suggest that waters of unusual composition (ie., modified seawater) were present on the Arbuckle platform from time to time. These features include rare bedded (primary( )) cherts, subaqueous shrinkage cracks, and ooids of unusual and variable textures. Their conclusion is that during upper Arbuckle Group deposition, particularly Cool Creek deposition, the vast Arbuckle platform was periodically exposed and a sabkhalike environment developed in which dolomitization andmore » gypsum/anhydrite precipitation took place. Subsequent reestablishment of fully marine conditions resulted in the early removal of the sulfates, leaving only a cryptic evaporite signature. Our interpretation can be supported in a general sense by the fact that (1) the fauna of the Cool Creek Formation is impoverished by comparison with adjacent formations, (2) the area was in a suitable climatic zone, and (3) the widespread occurrence of detrital quartz in the Cool Creek is compatible with exposure of the platform and consequent movement of clastics into the area.« less

Arbuckle Group Depositional Cycles, Southern Oklahoma: ABSTRACT

Arbuckle Group Depositional Cycles, Southern Oklahoma: ABSTRACT

Evaluation of the Maximum Allowable Injection Pressure for Industrial Waste Disposal Wells in Northeast Oklahoma

Limitations on the pressure of injected fluids are necessary to preclude the initiation or extension of fractures. For formations within 2,000 ft (600 m) of the surface, the least principal stress which is exceeded during fracturing is often the overburden pressure. Density logs from 17 wells in the study area were integrated to evaluate the overburden pressure gradient of the Arbuckle Formation in northeastern Oklahoma. The regional gradient of 1.08 to 1.14 psi/ft (24.4 to 25.8 kPa/m) depth appears reasonable when compared with published data for the overlying Pennsylvanian sands. Under Oklahoma Rule 818, the maximum total pressure gradient for Class I industrial waste disposal wells shall not exceed sixty-five percent of the established overburden pressure gradient. In accordance with this Rule, injection pressure gradients less than 0.70 to 0.74 psi/ft (15.9 to 16.8 kPa/m) are permissible in the Arbuckle Group of Northeast Oklahoma. Information obtained while fracturing and acidizing the formation to improve injectivity, confirms the absence of fracturing at the allowable injection pressure gradients.

Cottonwood Creek-Hewitt Trend Arbuckle Play (Southern Oklahoma): Example of Complexly Faulted and Fractured Karst Trap: ABSTRACT

The Hewitt field (T4, 5S, R1, 2W), located along the northwest-southeast-trending Wichita-Criner Hills anticlinorium, is the ninth largest field in Oklahoma with ultimate recovery projected to exceed 250 million bbl. The development of the anticlinorium was initiated by the Wichita orogeny during the Morrowan, forming north-south-trending folds. During the Atokan, extensive erosional forces removed thick sequences and exposed the Ordovician Arbuckle Group. The uplift was subsequently covered by Deese and Hoxbar clastic sediments during the Middle Pennsylvanian. The Late Pennsylvanian Arbuckle orogeny produced compressional stress from the southwest and resulted in refolding of the uplift features and movement along high-angle faults. The recent discovery of prolific hydrocarbon reserves in Ordovician carbonates (Canadian, Arbuckle Group) has renewed interest along this prolific trend. The productive reservoir in the Hewitt-Cottonwood Creek area is the dolomitic Brown zone (Kindblade Formation), located approximately 1000 ft below the top of the Arbuckle group. The zone consists of crystalline dolomite, 500-600 ft thick, with adequate porosity and permeability developed to form significant reservoirs due to karstification of the extensive fracture systems. The Bray zone (West Spring Creek Formation-upper Arbuckle Group) has production in the Healdton and southwestern Lone Grove fields from fractured, arenaceous, finely granular dolomite and more » may be an additional possible reservoir. The combination of good untested reservoirs located on structural features associated with block faulting, as illustrated by seismic sections across the Criner fault, gives an excellent indication that the trend may have great future potential within a mature province. « less

Conodont Biostratigraphy of Lower Ordovician Rocks, Arbuckle Group, Southern Oklahoma: ABSTRACT

The Arbuckle Group of southern Oklahoma displays the only complete exposure of the shallow-water carbonates that characterize the Lower Ordovician of interior North America. Trilobites have been described from some parts of this sequence and sporadic occurrences of other invertebrates are known, but much of the sequence is sparingly fossiliferous. As a consequence, these magnificent exposures have not contributed notably to continuing efforts toward development of a comprehensive biostratigraphic scheme for the Lower Ordovician of the North American platform. Samples collected at 25-ft intervals through the Arbuckle Group along and adjacent to Interstate Highway 35 on the south flank of the Arbuckle anticline near Ardmore, Oklahoma, produced conodonts in abundances ranging from a few tens to over a thousand elements per kilogram and displaying good to excellent preservation with low CAI. These conodonts document a biostratigraphic continuum that provides a standard for correlation of Lower Ordovician rocks in the subsurface of central US and of the many localized and incomplete outcrops of generally equivalent strata in the Ozark and Upper Mississippi Valley regions. The stratigraphic continuity of the collections makes the I-35 section an ideal standard reference section for graphic correlation of Lower Ordovician rocks containing conodonts of the Mid-Continent more » Province. « less

Fracture Density and Spacing Along Washita Valley Fault, Arbuckle Mountains, Oklahoma: ABSTRACT

The authors document fracture density and spacing associated with the Washita Valley fault, a major strike-slip fault. The Washita Valley fault strikes northwest-southeast with up to 80 mi of exposure in southern Oklahoma and may be an early bounding fault of the Southern Oklahoma aulacogen (Ardmore/Marietta basins). Horizontal displacement on the fault has been estimated to be up to 40 mi, with vertical displacement on the order of 10,000 ft. Samples collected from traverses across the Washita Valley fault have been analyzed. The traverses cross the fault at different stratigraphic levels from Proterozoic igneous basement, through the Cambrian-Ordovician Arbuckle Group, Ordovician Simpson and Viola Groups, to the Silurian-Devonian Hunton Group. Several types of fracture systems are documented that reflect mechanical stratigraphy, burial depth during deformation, and episodic movement on the fault. The fractures in the study area include open fracture systems, calcite-filled fractures, tension gashes, and fractures related to pressure solution. The samples were cut parallel to the strike of the fault, vertical-normal to the fault, and horizontal-normal to the fault. These cuts allow examination of the total fracture strain, characterization of the fractures, and statistical analysis of fracture density. From these data, fracture density is shown to decrease exponentiallymore » moving away from the primary fault zone. The increased understanding of fracture patterns and characteristics will assist future exploration and development programs involving carbonate reservoirs associated with strike-slip systems.« less

Porosity Development in Quartz-Rich, Oolitic Limestones of Upper Arbuckle Group: A Response to Unloading: ABSTRACT

The upper Arbuckle Group of southern Oklahoma is composed of a thick sequence of carbonates deposited in shallow, epicontinental seas. Several concentrations of quartz sandy detritus, two of which are significant markers in outcrop, are found in the Kindblade and Cool Creek Formations. Both units are composed of varying amounts of quartz sand, ooids, peloids, clasts, and micrite matrix cemented by calcite, silica, and minor dolomite. After a complex postdepositional history of burial, tectonism, and uplift, removal of overburden resulted in relaxation of compressive forces and the development of microfractures between and within grains in the mixed mineralogy units. Equidimensional voids formed around the outer edges of syntaxial quartz overgrowths as calcite spar separated from silica spar. Relatively thin cortices pulled away from large nuclei resulting in spherical voids within ooids. Multiple microfractures in the radial cortices connect the inner spherical pores to interparticle porosity. A system of microfractures between crystal boundaries in the calcite cement links the pores. Porosity development varies laterally within the quartz sandy, oolitic units and is, in part, dependent on the original burial depth and the amount of overburden removed. Microfractures in subsurface units, if present, may not be as well developed. Alternatively, microfracturing maymore » be enhanced as a result of subsurface dissolution.« less

Evidence of Paleokarstic Phenomena and Burial Diagenesis in Ordovician Arbuckle Group of Oklahoma: ABSTRACT

Cores from various localities in south-central and north-central Oklahoma display surprisingly similar suites of karstic and diagenetic phenomena. Vadose dissolution tubes, solution-enlarged fractures, collapse breccias, and vugular porosity, where present are considered evidence of karstification. Primary speleothemic precipitates were not readily observed; either they were not present or were obscured by later hydrothermal dolomitization. A complex history of exposure and subsidence is recorded in these rocks. Immature karst profiles may have subsided at rapid rates under conditions that prevented low-temperature phreatic cementation, thus preserving the open pore network of the karst profile. Deep burial diagenesis is evidenced by the appearance of highly ferroan baroque dolomite cement partially or entirely occluding vugular and fracture porosity. In addition, host-rock carbonates were extensively replaced by typical thermal xenomorphic dolomite. Cathodoluminescent microscopy indicates that the hydrothermal dolomite is uniform in composition and was precipitated under highly reducing conditions. Dolomite cementation was arrested when oil migrated into the remaining pore space. A complex multistage fracture network is present in cores from the Healdton oil field. Early fracture systems are healed by highly ferroan, dull luminescent baroque dolomite, and later fractures are cemented with nonferroan, brightly luminescent cement.

Paleomagnetism of the Cambro‐Ordovician Arbuckle Group and associated deposits in the southern Oklahoma Aulacogen: Evidence for block rotations

The magnetization in hydrocarbon‐impregnated Arbuckle Group limestones from the southern margin of the Southern Oklahoma Aulacogen (Limestone Hills) is secondary and resides in magnetite. The magnetization (Declination/Inclination=128°/2°, α95=7.6°, k=79) fails a fold test and is post Pennsylvanian. The corresponding pole position (146°E, 30°N), however, does not coincide with the post‐Pennsylvanian Apparent Polar Wander Path (APWP). Some Permian speleothems that fill caves in these rocks contain magnetizations that are also anomalous. Shallow remanent inclinations from the folded limestones and speleothems suggest that the most likely time of remanence acquisition was the Permian. The directions are at least 30° in declination from the expected directions based on the inferred ages of the magnetizations. This discrepancy can be explained by a horizontal counterclockwise rotation, consistent with left‐lateral wrench faulting, during deformation of the aulacogen.

Paleomagnetic Dating of Dedolomitization in Cambrian-Ordovician Arbuckle Group Limestones and Pennsylvanian Collings Ranch Conglomerate, Southern Oklahoma: ABSTRACT

Paleomagnetic and petrographic techniques have been used to date dedolomitization in stratigraphic and tectonic dolomites exposed in the Arbuckle Mountains, southern Oklahoma. The authors examined red dedolomites and their dolomite precursors from the Cambrian-Ordovician Arbuckle Group and dolomite clasts in the Pennsylvanian Collings Ranch Conglomerate. Authigenic hematite is associated with the dedolomite and precipitated as a result of the dedolomitization process. Dedolomite is associated with paleokarst and fractures, burrows, Liesegang bands, and red rims on conglomerate clasts. Magnetic directions from these dedolomitized rocks range from Dec = 145/sup 0/ to 154/sup 0/ and Inc = 2/sup 0/ to 9/sup 0/, with ks greater than 50 and /alpha/95s less than 5. The directions are constrained by fold tests to be post-structural (Late Pennsylvanian to Early Permian) and in the Collings Ranch to post-depositional. These directions correspond to a reversed Pennsylvanian pole position and the magnetizations are interpreted as chemical remanent magnetizations (CRM) acquired when hematite precipitated during dedolomitization.

Paleomagnetic Dating of Liesegang Bands

ABSTRACT Paleomagnetic analysis, in conjunction with petrographic studies, is used in this study to date the formation of hematite Liesegang bands in the Ordovician Upper Arbuckle Group in southern Oklahoma. The hematite bands form symmetrical patterns on both sides of calcite-filled fractures in dolomitic beds. The bands decrease in abundance and become more diffuse away from the fractures. Paleomagnetic specimens from distinctly banded dolomite near the fractures contain a relatively strong chemical remanent magnetization (CRM) with a southeasterly declination and shallow inclination. Samples farther from the fractures which are less distinctively banded or have no bands contain a weaker and less stable magnetization. Samples were collected from both flanks of the Arbuckle Anticline (late Pennsylvanian folding), and a fold test indicates that the CRM is postfolding. The pole position for the CRM corresponds to the Permian ( 280 Ma) part of the Apparent Polar Wander Path for stable North America. Petrographic evidence, stable demagnetization to above 600°C, and rock magnetic experiments indicate that the CRM resides i hematite. These results suggest that the Liesegang bands formed in the Early Permian, probably by precipitation of hematite from fluids that emanated from the fractures. The fluids also apparently caused dedolomitization and precipitation of calcite in intercrystalline pore spaces. Probable sources of the iron in the bands include these fluids, as well as iron released from dedolomitization and from oxidation of pyrite.

Evidence for a relationship between hydrocarbons and authigenic magnetite

Establishing a relationship between hydrocarbon migration and the precipitation of authigenic magnetite in sedimentary rocks is of significant interest with respect to (1) elucidating mechanisms for remagnetization and establishing the origin of secondary magnetizations residing in magnetite, (2) developing a method to date hydrocarbon migration events by determining the time of remanence acquisition by palaeomagnetic methods, and (3) evaluating whether searching for anomalous concentrations of diagenetic magnetic minerals and/or aeromagnetic anomalies is justified as a relatively inexpensive exploration tool. The direct association of hydrocarbon migration and the precipitation of authigenic magnetite has, however, not been established. In this paper we report palaeomagnetic, rock magnetic, petrographic and geochemical results of a study of samples from Permian spelebthems and gilsonite found in the Ordovician Arbuckle Group in southern Oklahoma. The results indicate that there is a genetic relationship between hydrocarbon migration and the precipitation of authigenic magnetite.

Southeast Hoover Field: Model of Foreland Tectonics of Arbuckle Region, Southern Oklahoma: ABSTRACT

The Southwest Hoover field, located on the northern side of the Arbuckel Mountains, typifies the structural style common to the foreland of southern Oklahoma. This oil field, which produces primarily from the upper Arbuckle Group carbonates, was created in response to the Late Pennsylvanian Arbuckle orogeny. Various interpretations of the mode of deformation have been proposed such as wrench faulting, gravity sliding, and overthrusting. This research supports the idea of moderately dipping thrust faults created by northeast-southwest compression. Paleozoic rocks, originally deposited on the northern edge of the Southern Oklahoma aulacogen, have been transported to the northeast on southwest-dipping thrust faults, and now comprise the leading edge of the Arbuckle Mountains. In a detailed study, the Southeast Hoover field was reinterpreted in light of the compressional thrust-fault theory. Large-scale structural closure controls the location of hydrocarbon accumulation in the Arbuckle Group. Structures in the shallower horizons are characterized by detached anticlines that were created as a response to volume adjustments in adjacent upward-tightening synclines. Fault cutoff lengths and hanging-wall cutoff angles provide clues to predeformation fault-plane geometry. Comparison of the Southeast Hoover field with other structures in the Arbuckle region indicates a close similarity of style, which suggests this studymore » can be used as a geologic model for interpreting foreland oil fields throughout southern Oklahoma.« less

Gravity-Slide Thrusting and Folded Faults in Western Arbuckle Mountains, Oklahoma: ABSTRACT

End_Page 1318------------------------------One or more major gravity-slide thrusts have been documented in the Eola, Southeast Hoover, and Southwest Davis oil fields, and in the western Arbuckle Mountains, Garvin and Murray Counties, Oklahoma. The gravity-slide area initially covered portions of at least nine townships; it was more than 30 mi (50 km) long and 5-6 mi (8-10 km) wide. It involved a stratigraphic sequence greater than 5,000 ft (1,500 m), extending from the lower Springer Formation into the upper portion of the Arbuckle Limestone. The major slides moved to the northeast and northwest, probably in the Middle Pennsylvanian. Slides and faults were subsequently isoclinally folded in the Late Pennsylvanian. The tensional updip segment of the major folded slide fault now coincides with the trace of the Washita Valley fau t. The compressional end of the slide coincides with the Reagan fault in the east and the frontal Eola fault in the west. In the Lake Classen area the latest folding has turned all formations involved in the slide--and the associated faults--to a near-vertical position. Thus, the slide is exposed in a profile view on the south limb of the overturned Washita Valley syncline. On the north normal limb of the Washita Valley syncline, the slide is exposed in plan view, with the Dougherty anticline and related folds representing compressional folding at the toe of the slide. Several tectonic breccias near the top of the Kindblade Formation of the Arbuckle Group probably mark the orogenic event. End_of_Article - Last_Page 1319------------

Gravity Slide Thrusting and Folded Faults in Western Arbuckle Mountains and Vicinity, Southern Oklahoma

Documentation for one or more major gravity slide thrusts and numerous lesser slides is recognized in the Eola, Southeast Hoover, and Southwest Davis oil fields, and in the Western Arbuckle Mountains, Garvin and Murray Counties, Oklahoma. The gravity slide area initially covered portions of at least nine townships; it was more than 30 mi (50 km) long and 5 to 6 mi (8 to 10 km) wide. It involved a stratigraphic sequence > 5,000 ft (1,500 m) extending from the lower Springer Formation into the upper portion of the Arbuckle Limestone. The major slides moved to the northeast and northwest, probably in Middle Pennsylvanian. The slides and the faults were subsequently isoclinally folded in Late Pennsylvanian. Small depositional structures within beds ranging from upper Arbuc le through the Viola Limestone indicate the area was seismically active during deposition and probably also was subject to gravity sliding in the early Paleozoic. The tensional updip segment of the major folded slide fault now coincides with the trace of the Washita Valley fault. The compressional end of the slide coincides with the Reagan fault in the east and the frontal Eola fault in the west. In the Lake Classen area the latest folding has turned all the formations involved in the slide, and the associated faults, to a near-vertical position. Thus, the slide is exposed in a profile view on the south limb of the overturned Washita Valley syncline. On the north normal limb of the Washita Valley syncline, the slide is exposed in plan view, with the Dougherty anticline and related fo ds representing compressional folding at the toe of the slide. The major slide fault and the Washita Valley fault now share the same trace, but separate movements are still recognizable, the slides having moved north, northeast, and northwest followed by thrusting and probably left-lateral displacement along the Washita Valley fault. Compressional folding and thrusting in the toe of the slide, and extensional faulting along the trailing edge are both recognized. Several tectonic breccias near the top of the Kindblade Formation of the Arbuckle Group probably mark the orogenic event. Tectonic breccias within the fault zone also are interpreted in several wells in the Eola field, and in the past have been identified as Eola conglomerate (Pontotoc). The Arbuckle Group, which had been beneath at least 5,000 ft (1,500 m) of younger strata, was exposed immediately following the slide, which explains the inclusion of boulders and cobbles of this group of formations as major constituents in the earliest known Middle Pennsylvanian conglomerates in this area. The interpretation also explains the absence of any record in the geologic column of the sequential erosion of strata overlying the Arbuckle Group.

Storm Deposits (Tempestites) in Ordovician Cratonic Carbonates (Arbuckle Group, South-Central Oklahoma): ABSTRACT

The Early Ordovician Kindblade Formation (Arbuckle Group), exposed in the Arbuckle Mountains of south-central Oklahoma, is a shallow marine epicontinental carbonate sequence that contains numerous storm deposits. Similar deposits also occur in other Arbukle Group units, although not as abundantly as in the Kindblade Formation. The storm deposits (tempestites) are of two types, proximal and distal; the latter dominates in terms of both number and aggregate thickness. Distal tempestites consist of a fining upward sequence, 5 to 50 cm (2 to 20 in.) thick, that overlies an eroded hardground or firmground. The sequence consists of a lag lithoclastic grainstone that grades up into a laminated peloidal grainstone and then into mudstone. Firmgrounds are characterized by hummocky, sharp, and erosional contacts (relief 2 to 7 cm, 0.75 to 2.75 in.) with grainstone-filled erosive pockets. Hardgrounds are characterized by sharp hummocky-to-convolute surfaces (relief < 4 cm, 1.5 in.), which are mineralized and bored. Primary sedimentary features such as laminations, burrows, and allochems are truncated at the surfaces, and borings are filled with unsorted lithoclasts. The lithoclasts at the base of the sequence are bored, generally well rounded, discoid in shape, and consist of mudstone, peloidal packstone, and oolitic grainstone. Infiltration fabrics within the lithoclastic grainstone include cement-filled shelter voids beneath large clasts and internal sediment perched on the upper surfaces of lithoclasts. The overlying peloidal grainstones contain ripple cross-la inations, plane-laminations, and hummocky cross-stratification as well as rare escape burrows. The overlying mudstone is sparsely fossiliferous and bioturbated with burrows either selectively dolomitized or infilled with lithoclastic grainstone. Although there are many examples of the ideal sequence described above, complex composite or amalgamated beds are also common. Proximal tempestites consist of coarse lithoclastic flat pebble conglomerate beds approximately 1 m (3.25 ft) thick that are interbedded with ooid grainstone and overlie mudstone. The contact between the units is sharp and erosional. The lithoclasts are of variable composition and may be up to 20 cm (7.75 in.) in diameter. The two types of tempestites occur in crude cycles, which consist of distal deposits overlain by proximal tempestites and ooid grainstones. The cycles are interpreted as shallowing-upward progradational sequences. The abundance of the storm deposits in the section, approximately one every 20 cm (7.75 in.), indicates that hundreds of storm-induced events are recorded in the Kindblade Formation. The tempestites represent rare catastrophic events, while the hardgrounds-firmgrounds are discontinuity surfaces that represent gaps in the sequence. End_of_Article - Last_Page 471------------

Control of Arbuckle (Cambrian-Ordovician) Production by Block Faulting: ABSTRACT

The Central Kansas uplift is a collapsed arch which was eroded to granite on both sides of a central graben during the post-Mississippian. Uplift and collapse produced a myriad of horst and graben blocks affecting the Arbuckle Group below the so-called pre-Pennsylvanian unconformity. Arbuckle production comes from horst blocks, and about 75% of the Arbuckle production on the uplift comes from blocks within the central graben. Mapping Arbuckle structures as fault blocks rather than as erosional features allows a completely different use of subsurface data and can lead to many unsuspected field extensions and wildcat prospects. End_of_Article - Last_Page 1324------------