Central Kansas Uplift Research Articles

Generation of Pseudo-synthetic Seismograms from Gamma-Ray Well Logs of Highly Radioactive Formations

The conventional synthetic seismogram is created with a sonic and a density log; however, the sonic log can be replaced with the resistivity, neutron, gamma-ray or spontaneous potential log to produce a pseudo-sonic (PS) log. More recent techniques involve combining an SP log and a GR log to produce a PS log. In the past, a drawback in using GR logs for the PS is the presence of highly radioactive and often organic-rich layers possessing abnormally high GR readings. To improve the pseudo-sonic log produced from the gamma-ray log, a technique was developed to statistically treat the outliers from the wells in the Hugoton Embayment that encountered predominantly shale, sandstone, limestone, and dolomite and whose logged sections included both normal and abnormally high GR readings. To demonstrate a wider-range application of our method, the procedure was applied to wells from the Hugoton Embayment, Central Kansas Uplift, Sedgwick Basin, Salina Basin, Forest City Basin and Nemaha Uplift. The correlation coefficients between the PS and the conventional sonic for the six basins were 0.75, 0.92, 0.86, 0.91, 0.77, and 0.70, respectively. Also, the match between the resulting conventional synthetic seismogram and the pseudo-synthetic seismogram from a blind test well for each area was quite good. Provided the outliers have been properly treated, the GR log is a viable tool for creating pseudo-sonic logs and pseudo-synthetic seismograms for exploration in oil and gas basins where there are few wells with sonic logs or where sonic log quality is poor.

Mississippian (Osagean) Shallow-Water, Mid-Latitude Siliceous Sponge Spicule and Heterozoan Carbonate Facies

Mixtures of biosiliceous and heterozoan-dominated carbonate deposits are commonly interpreted as recording cold-water polar or deep basinal conditions. However, a growing body of literature is documenting examples from the rock record that show these deposits accumulated in shallow-water middle- to low-latitude environments. The continued recognition of ancient neritic heterozoan carbonate and biosiliceous accumulations is broadening our understanding of the various paleoenvironmental controls on their development.
 Early-Middle Mississippian time was characterized by the development of biosiliceous and carbonate accumulations in North America. This study focuses on Osagean cherty dolomitic strata in cores from the Schaben field in Kansas, which is located in Ness County on the southwest flank of the Central Kansas uplift (CKU). During the Osagean, Kansas was located at approximately 20° S latitude, within the tropical to subtropical latitudinal belt. Study area strata are characterized by shallow-water inner-shelf carbonates that were deposited on a gently southward-sloping shelf (ramp). Two depositional sequences (DS1 and DS2) are identified in cores and are separated by a sequence boundary (SB1) that evidences subaerial exposure. The primary facies in the two depositional sequences include 1) Mudstone-Wackestone (MW); 2) Sponge Spicule-Rich Wackestone-Packstone (SWP); 3) Echinoderm-Rich Wackestone-Packstone-Grainstone (EWPG); and 4) Dolomitic Siltstones and Shale facies. Other features identified in cores include 1) Silica Cementation and Replacement; 2) Silica Replaced Evaporites; 3) Brecciation and Fracturing; and 4) Calcite Cementation and Replacement.
 The abundance of echinoderm facies with other diverse fauna, evidence of extensive reworking by burrowing organisms, and only rare occurrence of evaporites suggest subtidal deposition in a normal to slightly restricted marine inner-shelf setting for DS1. After the SB1 subaerial exposure event, marine conditions returned but the depositional environment over the study area changed compared to that for much of DS1 deposition. The volumetric increase of sponge-spicule wackestone and packstone (SWP) with less diverse fauna, abundance of early evaporites (replaced by silica), and evidence for shallowest water to subaerially exposed conditions throughout DS2 suggest deposition in more restricted environments that likely ranged from restricted inner shelf/protected embayment to evaporative lagoon and possibly supratidal flat.
 One of the more significant characteristics in DS2 is the dominance of siliceous sponge spicule facies and heterozoan carbonates that were deposited in shallow-water and restricted environments. This study and others from numerous periods in the geologic record are indicating that shallow-marine, mid-latitude biosiliceous and heterozoan carbonates may be more common than previously thought. Especially interesting are the examples from Mississippian (Osagean-Meramecian) strata in North America that show similar facies associations with DS2 strata of this study.
 The predominance of Early-Middle Mississippian heterozoan carbonate and biosiliceous (spiculitic) deposits, and lack of photozoan deposits, in the mid-latitude shallow-shelf setting in Kansas and surrounding areas was likely due to abundant nutrients and dissolved silica derived from basinal and/or terrestrial sources. Based on available evidence, upwelling of basinal waters rich in nutrients and dissolved silica appears to have been a primary control on shelf margin and shelf facies. Upwelling even may have had a primary imprint on shallow-water, inner-shelf areas, especially during transgression(s). Nutrients and dissolved silica from terrestrial sources may have contributed to the facies associations in shallowest water, inner-shelf areas. However, the available evidence suggests that terrestrial sourced nutrients and dissolved silica were not the dominant control.
 The results of this study have implications from a petroleum reservoir standpoint. The DS2 sponge spicule, heterozoan carbonate, and silica-replaced evaporite facies in this study form reservoirs in Schaben field and another nearby field composed of similar facies. Because regional upwelling is likely to have had at least some control, facies similar to DS2 strata may form important reservoirs in Lower-Middle Mississippian strata that were deposited in shallow-water inner shelf/ramp settings elsewhere in Kansas and North America.
 Continuing studies of the controls on biosiliceous and heterozoan carbonate deposition and diagenesis in mid-latitude neritic settings will improve our understanding and predictive capabilities.

A Petroleum System for the Salina Basin in Kansas Based on Organic Geochemistry and Geologic Analog

The Salina Basin historically has been an “exploration desert”—a home of dryholes. Although this basin, which underlies much of north-central Kansas, may never be a prolific source of hydrocarbons, recent research into the maturation and geochemistry of organic matter and oils in Kansas can provide guidelines for a new exploration strategy. The Salina Basin is similar to the oil-productive Forest City Basin in northeastern Kansas in many ways. Both basins originated as a single large basin (i.e., the North Kansas Basin) prior to the rise of the Nemaha Uplift in Late Mississippian-Early Pennsylvanian time. Their Paleozoic stratigraphy thus is similar and the axes of both basins are presently at approximately the same depth. Thermal maturation modeling and available organic-matter maturation data indicate that the lower Paleozoic rocks in the axes of both basins are in the early stages of oil generation. In the Forest City Basin the Ordovician Simpson Group is the deepest known hydrocarbon source-rock—oil-reservoir interval, and by analogy, exploration tests in the Salina Basin, at a minimum, should penetrate through this stratigraphic interval. Ordovician Simpson Group shales in the Forest City Basin are the source rocks for a geochemically distinct oil, which also occurs in Ordovician reservoirs in the extreme southern end of the Salina Basin. To increase the odds of success in an exploration program in the Salina Basin, wildcat wells should be drilled where thermal maturation is greatest. The broad NW–SE-trending basin axis is the most logical area. Exploration tests along this axis in the northern end of the basin may have an extra advantage as organic matter in the Simpson Group may be more thermally mature because of greater burial depth during the Cretaceous. Along the eastern margin of the nearby Central Kansas Uplift and Pratt Anticline, several Paleozoic geologic structures, some of which contain major oil fields, are attributable to tectonic reactivation along the western margin of the Precambrian Central North American Rift System (CNARS). Prospective structural trends in the Paleozoic section of the Salina Basin are anticipated to be associated with this underlying tectonic boundary. The western margin of the CNARS trends NNE–SSW where it passes under the axis of the Salina Basin in northeastern Lincoln and southeastern Mitchell counties. This area is sparsely drilled, with less than two tests per township. If an exploration program can define lower Paleozoic structural closures in this region, these structures may represent the best chance for future petroleum discoveries.

Abstract: Is the Mississippian of Kansas a Viable Petroleum Target After a Century of Exploration? 

The Mississippian rocks in Kansas have produced about 16% of the oil and 1 1 % of the gas of the total in the past 100 years. The Mississippian units are predominately uniform carbonates (mostly limestone), but are missing on the higher positive structures such as the Central Kansas Uplift and Nemaha Anticline. Production of petroleum is from both structural and stratigraphic traps. The present configuration of structures, formed near the end of the Mississippian when the North and South American plates collided, overprinted the previous structures and caused a change in the previous structural and sedimentary regimes in the region. An influx of upper Paleozoic clastics alternating rhythmically with carbonates signaled the onset of the Quachita Orogeny and major changes and provided the seal for the reservoirs. Mississippian units (up to 1,700 feet thick) include (from oldest to youngest): Kinderhookian, Osagean, Meramacian, and Chesteran; unconformably overlie the Siluro-Devonian or Ordovician units and are unconformably overlain by rocks of Pennsylvanian age - (from oldest to youngest) Morrowan, Atokan, or Desmoinesian. Since discovery of oil in the Mississippian in 19 16 in the Virgil field (Greenwood County), production from Mississippian rocks has accounted for slightly more than 13% of the state’s total oil and gas production. Although historically most of the Mississippian oil has been produced from the Salina and Sedgwick Basins, the increasing contribution of Mississippian oil to total production is primarily the result of exploration in the Hugoton Embayment in western Kansas. Information from 16,000 qualified wells was used to quality check formation data from 43,000 operator reported wells. Separating these new discoveries by date and comparing their spatial distribution to historical production provides a better understanding of emerging trends and new areas for exploration.

Mississippian Chat Reservoirs, South Kansas: Low-Resistivity Pay in a Complex Chert Reservoir 

Mississippian chert of variable character and diagenetic history defines a unique and prolific series of reservoirs in south-central Kansas and northern Oklahoma. Known collectively as the chat, these reservoirs occur beneath, and are partly associated with, a major regional unconformity separating Mississippian and Pennsylvanian deposits. Chat fields occur in an arcuate fairway extending approximately 160 km along the flanks of the southward-plunging Pratt anticline, a southern extension of the Central Kansas uplift. Initial discoveries were made in the 1920s and 1930s, with major expansion of the trend in the 1940s and 1950s. Chat wells have been among the most productive in the southern midcontinent, yielding oil and gas at rates up to 1500 bbl, or 40 mmcf, per day from depths of 909-1515 m. The better reservoirs have exceptional porosities (30-50%), but moderate permeabilities (20-100 md); fracturing is assumed to play an important role in reservoir performance. Few detailed characterizations of chat reservoirs exist to date. Recent study has identified three reservoir types: (1) in-situ spiculitic chert, (2) in-situ brecciated and partly weathered spiculitic chert, and (3) highly weathered, transported chert conglomerate. These types can be broadly categorized according to paleostructural position. Current depositional models interpret the chert as mainly primary in origin, related to subtidal sponge spicule bioherms along a subtle shelf break. Entrapment is predominantly stratigraphic in nature; bioherms grade laterally into impermeable carbonate and are truncated updip beneath the sub-Pennsylvanian unconformity. Total production from the chat trend is on the order of 381 million bbl oil and 2.3 tcf gas. New infill drilling, field expansion, and enhanced recovery projects in the 1990s have helped revitalize interest in the chat. Future exploratory and development efforts should add significant new data to the characterization of these complex and highly profitable reservoirs.

Long-Term Production Results of Polymer Treatments on Producing Wells in Western Kansas

Summary This paper describes the analysis of the long-term oil production performance of 37 near-well polymer treatments on 26 producing wells in western Kansas to determine incremental oil recovery resulting from the treatments. Estimated incremental oil recovery from the 37 treatments was 76,500 STB of oil from 39,600 Ibm of polymer injected, or 1.93 STB/lbm of polymer injected. The polymer treatment types giving the best oil recovery performance were solutions of anionic polyacrylamide (ungelled) and cationic polyacrylamide gelled in situ with the chromium reduction/oxidation process. Both gave incremental oil recoveries of 2.6 STB oil/Ibm of polymer injected and had average treatment lifetimes exceeding 1 year. Introduction Polymer treatments of injection and production wells have been used extensively for fluid diversion and to increase oil recovery. Injection of high-molecular-weight polymers increases the viscosity of the injected water and reduces the permeability of the porous medium to water. In producing-well treatments, the injected aqueous polymer solution preferentially flows into zones that exhibit high permeability to water and subsequently restricts the flow of water when the well is put back on production. Polymer injection has two effects: the water production rate decreases substantially and the pressure drawdown into the wellbore often increases greatly, resulting in an increased oil production rate. During the 1970's, Phillips Petroleum Co. conducted 37 polymer treatments on 26 producing wells in western Kansas. All but one of the treatments were on wells completed in the Arbuckle dolomite formation. The formation has been characterized as a highly fractured, vuggy dolomite with varying amounts of chert and with reservoir characteristics varying from field to field throughout the Central Kansas Uplift. Permeability ranges from 50 to 5,000 md; porosity ranges from 1% to 20%, with an average of 15%. The oil zone is estimated to be 5 to 50 ft thick; the total Arbuckle zone is up to 300 ft. Oil viscosity ranges from 3 to 13 cp. The reservoir drive mechanism is primarily bottomwater drive, and the wells are completed at the top of the formation to delay the onset of water production. Water production comes primarily from coning. Because of the natural fracture network, vertical permeability is high and there are few vertical barriers to restrict water coning.

Depositional Environments and Facies Analysis of the Cherokee Group in West-Central Kansas

The Cherokee Group of early Desmoinesian Pennsylvanian age in west-central Kansas is comprised of a mixed siliciclastic and carbonate sequence. It was deposited in environments that are transitional from continental to marginal marine as the Hugoton Sea transgressed the Mississippian unconformity on to the Central Kansas uplift. Sandstones of the Cherokee Group are important oil reservoirs in west-central Kansas, but they are highly variable and difficult to predict. Core studies and subsurface analysis reveal two persistent and widespread limestone beds that form useful stratigraphic markers within the Cherokee. They provide a framework for facies analysis and regional mapping that may be useful as a predictive tool for oil exploration. Six basic lithofacies are interpreted from lithologies and sedimentary structures observed in cores obtained from four wells in eastern Ness County: (1) basal Pennsylvanian conglomerate, (2) fluvial sands, (3) fine-grained tidal flat deposits, (4) shallow-marine limestones, (5) shoreline sands and tidal channel sands, and (6) braided stream, sandy conglomerates. These facies are correlative with components of an ideal Kansas cyclothem. Two transgressive-regressive cycles are identified and maximum transgression is correlated with two widespread limestone beds. Following burial of the Mississippian karstic surface, deposition of peritidal sediments occurred on a uniform shallowmore » shelf, punctuated by periods of subaerial exposure and weathering. Clastics derived from the eroding Central Kansas uplift were probably supplied to the coastal plain by braided streams and reworked by coastal processes.« less

Petroleum Potential of Lower and Middle Paleozoic Rocks in Nebraska Portion of Mid-Continent: ABSTRACT

Central North America during the Paleozoic was characterized by northern (Williston) and southern (Anadarko) depositional regimes separated by a stable Transcontinental arch. Nebraska lies on the southern flank of this arch and contains the northern zero edges of the lower and middle Paleozoic rocks of the southern regime. Most of these rocks are secondary dolomites with zones of excellent intercrystalline porosity. The Reagan-LaMotte Sandstones and the overlying Arbuckle dolomites are overlapped by Middle Ordovician rocks toward the Transcontinental arch. Rocks equivalent to the Simpson consist of a basal sand (St. Peter) and overlying interbedded gray-green shales and dolomitic limestones. An uppermost shale facies is present in the Upper Ordovician (Viola-Maquoketa) eastward and southward across Nebraska. The dolomite facies extends northward into the Williston basin. The Silurian dolomites, originally more widely deposited, are overlapped by Devonian dolomites in southeastern Nebraska. Upper Devonian rocks exhibit a regional facies change from carbonate to green-gray shale to black shale southeastward across the Mid-Continent. Mississippian carbonates overlap the Devonian westward and northward across the Transcontinental arch. Pennsylvanian uplift and erosion were widespread, producing numerous stratigraphic traps. Sands related to the basal Pennsylvanian unconformity produce along the Cambridge arch. Arbuckle, Simpson, Viola, and Hunton production ismore » present in the Forest City basin and along the Central Kansas uplift. Although source rocks are scarce and the maturation is marginal, current theories of long-distance oil migration encourage exploration in the extensive lower and middle Paleozoic reservoirs in this portion of the Mid-Continent.« less

Composition and stable-isotope geochemistry of natural gases from Kansas, Midcontinent, U.S.A.

More than 28·10 12 ft. 3 (79·10 10 m 3) of natural gas and 5.3·10 9 bbl (8.4·10 8 m 3) of oil have been produced in Kansas, U.S.A., from Paleozoic carbonate and sandstone reservoirs on structural uplifts and shallow embayments along the northern margin of the Anadarko basin. A heavily-explored, geologically well-characterized state, Kansas is an excellent place to study hydrocarbon migration and to test geochemical models for the origin of natural gases. Immature to marginally-mature rocks of eastern Kansas (Cherokee and Forest City basins) produce mixed microbial and thermogenic gases. Gases in this region have wetness = 0.03–51%, methane δ 13C = −65 to −43‰ and methane δD = −260 to −150‰. Gases from central and western Kansas (Nemaha uplift to Hugoton embayment) are entirely thermogenic and have wetness =4–51%, methane δ 13C = −48 to −39‰ and methane δD = −195 to −140‰. Ethane and propane δ 13C-values throughout Kansas vary from −38 to −28‰ and from −35 to −24‰, respectively. Mature thermogenic gas (generated from source rocks in southwestern Kansas and the Anadarko basin with 1.0% ≤ R o ≤ 1.4%) is recognized throughout the state. Lateral migration into shallow reservoirs on the Central Kansas and northern Nemaha uplifts and in the Cherokee basin probably occurred along basal Pennsylvanian conglomerates and weathered Lower Paleozoic carbonates at the regional sub-Pennsylvanian unconformity. Early thermogenic gas (generated by local source rocks with R o ≤ 0.7%) is recognized in isolated fields in the Salina and Forest City basins, in Ordovician reservoirs beneath the sub-Pennsylvanian unconformity in the Cherokee basin, and in reservoirs generally above the unconformity in the Cherokee and Sedgwick basins, the eastern Central Kansas uplift and the Hugoton embayment.

Microearthquakes in Kansas and Nebraska 1977–87

Abstract The Kansas Geological Survey has operated a microearthquake seismograph network since mid-1977. The network now consists of fifteen stations located in the eastern half of Kansas and Nebraska. Locatable microearthquakes with duration magnitudes less than 3.2 occur at the rate of roughly 20 per year in the two-state area, with most of the events ranging from 1.4 to 2.5 in local magnitude. The microearthquake pattern observed over the past ten years is consistent with the pattern of historical earthquakes reported since 1867. Much of the activity occurs along the Nemaha Ridge, a buried Precambrian uplift that runs from roughly Omaha, Nebraska, southward across Kansas to near Oklahoma City. This geological structure has been the site of several earthquakes of MM Intensity VII over the past 125 years. Some seismicity is observed along the northwest flank of the Midcontinent Geophysical Anomaly in Kansas, but little is observed in the Nebraska or Iowa portions of this Precambrian feature. The Central Kansas Uplift, which is a buried anticline similar in age to the Nemaha Ridge, has been the site of several felt earthquakes since 1982. A trend of earthquakes extending northeastward across central Nebraska is not associated with any prominent known geologic structure. All the seismicity in central and eastern Kansas can be roughly correlated to known geologic structures.

Review of Carbonate Sand-Belt Deposition of Ooid Grainstones and Application to Mississippian Reservoir, Damme Field, Southwestern Kansas

Ooid shoals are present (1) in the high-energy zones of carbonate ramps, (2) across broad shelves, and (3) along rimmed carbonate shelf edges. Shoals generally form as depositional strike-oriented or dip-oriented sand bodies in these settings. Marine sand belts, locally present along the shelf edge of the Great Bahama Little Bahama Banks, are depositional strike-oriented sand shoals made of flood ramps, shields, and channels that terminate in spillover lobes. Their geometry results from an interplay between storm-generated and tide-generated currents with the sea floor. Mississippian oolitic limestones (St. Louis Limestone B-zone), whose geometries resemble modern Bahamian ooid shoals, produce oil and are current exploration targets in southwestern Kansas (Hugoton embayment). Thus, a sedimentological and stratigraphic study of a producing field (Damme field, Finney County, Kansas) and a comparison to modern ooid sand bodies were justified. The St. Louis Limestone is overlain by the Ste. Genevieve Limestone (nonproductive) in Damme field. Both formations consist of five lithofacies: (1) skeletal wackestones in an open marine shelf, (2) porous, skeletal, ooid grainstone in a marine sand belt, (3) sandy, peloid-ooid, skeletal grainstone in a mobile grain shoal, (4) quartz-arenite in a tidal inlet, and (5) fenestral lime mudstone in an intertidal mud flat. Porous grainstones of lithofacies 2 form an elongate (northwest-southeast), lenticular body 10 mi (16 km) long, 2 mi (3.2 km) wide, and up to 18 ft (5.5 m) thick. Its shape and geometry are nearly the same as the marine sand belts of the Bahamas. Lithofacies arrangements indicate two styles of shallowing-upward depositional cycles; the lower St. Louis cycle was deposited during a relative sea level rise, and the overlying Ste. Genevieve cycles were deposited after a relative drop of sea level, an event signalled by the influx of siliciclastic sediments into the carbonate shelf from the Central Kansas uplift and/or Transcontinental arch.

Deltaic Sedimentation on a Carbonate Shelf: Stanton Formation (Upper Pennsylvanian), Southeastern Kansas

The Pennsylvanian epicontinental sea periodically covered much of Mid-Continent North America during Missourian time, burying local siliciclastic source areas in Kansas--such as the Nemaha uplift and Central Kansas uplift--with carbonate sediments. During regressive depositional phases in the Missourian (Late Pennsylvanian), siliciclastic sediments were transported into Kansas mainly from the southeast. The five members of the latest Missourian Stanton Formation (in ascending order: Captain Creek Limestone, Eudora Shale, Stoner Limestone, Rock Lake Shale, and South Bend Limestone), form a transgressive-regressive-transgressive sequence, in which the black phosphatic shale of the Eudora Member represents maximum transgression and the sandy Rock Lake shale represents maximum regression. In southernmost Kansas, the regressive Stoner Limestone Member grades into a siliciclastic sequence, most of which is assigned to the Rock Lake Shale Member. Detailed study of surface and subsurface data from these siliciclastics show that deltaic systems prograded into the cratonic sea from Ouachita sources. Analyses of texture and sedimentary structures in lithic samples and of geophysical well-log characteristics indicate that early during Stanton regressive deposition, a fluvially dominated deltaic lobe complex prograded northwestward across the Oklahoma-Kansas border and initiated Stanton siliciclastic deposition in the detrital-facies belt in southeastern Kansas. This lobe complex was eventually abandoned as the sediment sources shifted northward along the eastern margin of the ea, and a later deltaic lobe complex (represented by the Onion Creek Sandstone) prograded along the southern limit of the carbonate platform (Stoner Limestone Member) to the north. Textural and compositional characteristics of Stanton siliciclastics indicate that they were derived from preexisting sedimentary rocks. Pennsylvanian plate collisions that formed the Ouachita and Appalachian Mountains resulted in the uplift of early Paleozoic sedimentary rocks. Sediments derived from these rocks were transported northward and westward, particularly during regressive episodes resulting in punctuation of the dominantly carbonate Missourian Series with siliciclastics in southeastern Kansas. Although very little petroleum has been produced from the siliciclastic portions of the Stanton Formation, similar sedimentary complexes may be more productive. It is hoped that this work may serve as a guide for exploration efforts in this and other complexes in similar tectonic settings.

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------------

A Mid-Continent Basin: A Reappraisal: ABSTRACT

One of the largest unevaluated basins in the Mid-Continent is the Salina basin in Kansas and its extension into eastern Nebraska. The purpose of this study is to update all older data, reconstruct new maps, and reappraise the potential for further exploration. The last comprehensive publications on the area were in 1948 and 1956. The Salina basin includes 12,700 mi2 (33,000 km2) in north-central Kansas, and approximately 7,000 mi2 (18,000 km2) in east-central Nebraska. The basin is delineated by the zero isopach of Mississippian rocks bordering the basin. The Central Kansas uplift borders the basin on the southwest and Nemaha ridge on the east; the southern limit is an ill-defined saddle in the vicinity of T17S. Boundaries of the Nebraska basin are less well defined, but the axis of the basin trends directly north from the Kansas border along the boundary of Ts10 and 11W, to 41°N lat., and then bifurcates to the northwest toward the Siouxiana arch and northeast for an unknown distance. Conventional structure maps have been constructed on several horizons, and a series of cross sections depicts anomalous structures. Recent gravity, magnetic, and seismic reflection profiling also provide information on basement tectonics which may influence structures in the younger sediments. Basement depth ranges from 600 ft (180 m) on the northeast Nemaha ridge boundary of the basin, to a depth of 4,750 ft (1,450 m) or -3,000 ft ( -915 m) below sea-level datum in Jewell County; therefore, there may be an approximate total of 10,000 mi3 (42,000 km3 of sediments for future exploration. End_of_Article - Last_Page 1323------------

Kansas Earthquakes - 1979

This report includes a summary of microearthquakes located by the Kansas Geological Survey seismograph network during 1979. The network now consists of thirteen stations, nine of which are telemetered to Lawrence, Kansas. Locations and magnitudes are provided for 19 earthquakes in Kansas and Missouri. Statistical parameters obtained from the location computer program HYP071 are also listed. Magnitudes are calculated using an empirical relation derived by Jim Lawson of the Oklahoma Geophysical Observatory. Three distinct earthquake trends have been observed associated with the Humboldt fault zone, the Midcontinent Geophysical Anomaly, and the Central Kansas Uplift.

Petrology of Arbuckle Group, Central Kansas: ABSTRACT

The Arbuckle Group (Late Cambrian and Early Ordovician) in Kansas is mostly crystalline dolomite with abundant chert in the upper part. The Arbuckle is entirely in the subsurface, and there are only scattered cores, mostly from the upper part. Depositional constituents and textures have been reported only from the chert. Study of thin sections from three cores from the Central Kansas uplift reveals abundant evidence of depositional components, as well as diagenetic features of dolomitization and porosity. Despite virtually complete dolomitization, it is often possible to identify primary grain types, fabrics, and textures, and by comparison with better preserved examples, to interpret less well-preserved features. Identifiable grain types include oolites, pellets, intraclasts (of micrite, pellets, and oolites), and skeletal grains, including gastropods, echinoderms, and bivalves. Crenulate, laminated dolomite, interpreted as stromatolites, recurs. Depositional textures range from mudstone to packstone. The dolomite is microcrystalline to coarsely crystalline, with porosity ranging erratically from 1 to 22%. Pore types are: (1) intercrystal (most common), supplemented and interconnected by (2) solution-enlarged fractures, (3) moldic, from solution of depositional grains, (4) fenestral, and (5) primary interparticle. Partly dissolved dolomite crystals have collapsed, compacted, and probably contributed to fracturing. Small, closely spaced fractures may be open or plugged by crystals mobilized from surrounding dolomite, thereby isolating bodies of dolomite with high intercrystal porosity. Laminae of low-porosity dolomite, presumably controlled by depositional texture, contribute also to porosity variability. Most large pores are reduced by dolomite cement. Other scarce cements are anhy rite and sparry calcite, which fills oomolds and fractures. End_of_Article - Last_Page 960------------

Future Petroleum Potential of Pre-Cretaceous Rocks of Eastern Colorado: ABSTRACT

Throughout Permian time, eastern Colorado, like western Kansas, was on the shelf area of the Anadarko basin; and the Las Animas arch, as reflected on top of the pre-Pennsylvanian unconformity, was a south-trending nose in the north part of the Anadarko basin. This relation was very similar to that of the Central Kansas uplift, from which over 2 billion bbl of oil has been produced from pre-Cretaceous rocks. Many other geologic similarities can be discerned between the Las Animas arch and the Central Kansas uplift. The two most dissimilar factors are (1) that the pre-Pennsylvanian unconformable surface on the Central Kansas uplift is underlain chiefly by Cambro-Ordovician rocks, whereas on the Las Animas arch, Mississippian rocks underlie most of the area; and (2) that the dip of the pre-Permian beds in northeastern Colorado was reversed during the Laramide orogeny. The entire pre-Pennsylvanian sequence in eastern Colorado and western Kansas demonstrates a very subnormal but continuous pressure system. Over most of eastern Colorado, the Mississippian is the porous and permeable stratigraphic unit of this very low-pressure system. Fluids will migrate from the higher energy Pennsylvanian system to the lower energy Mississippian. Thus, the Mississippian is capable of deriving hydrocarbons transversely as well as laterally. Since 1965, exploratory interest has been primarily in Mississippian reservoirs, although some Pennsylvanian oil and gas fields also have been found. Since 1965, 20 Mississippian and Pennsylvanian oil and gas fields have been found and over 200 wildcat wells have been drilled. The data from these wells have resulted in new interpretations of hydrocarbon accumulations. Early Pennsylvanian growth strongly influenced Mississippian accumulations, and recent refinements in seismic techniques have allowed definition of these growth features. By incorporating recent subsurface interpretations with the extensive seismic control available, numerous prospects are being defined and doubtless will result in additional pre-Cretaceous discoveries. End_of_Article - Last_Page 660------------

Future Petroleum Potential of Pre-Cretaceous Rocks of Eastern Colorado: ABSTRACT

Throughout Permian time, eastern Colorado, like western Kansas, was on the shelf area of the Anadarko basin; and the Las Animas arch, as reflected on top of the pre-Pennsylvanian unconformity, was a south-trending nose in the north part of the Anadarko basin. This relation was very similar to that of the Central Kansas uplift, from which over 2 billion bbl of oil has been produced from pre-Cretaceous rocks. Many other geologic similarities can be discerned between the Las Animas arch and the Central Kansas uplift. The two most dissimilar factors are (1) that the pre-Pennsylvanian unconformable surface on the Central Kansas uplift is underlain chiefly by Cambro-Ordovician rocks, whereas on the Las Animas arch, Mississippian rocks underlie most of the area; and (2) that the dip of the pre-Permian beds in northeastern Colorado was reversed during the Laramide orogeny. The entire pre-Pennsylvanian sequence in eastern Colorado and western Kansas demonstrates a very subnormal but continuous pressure system. Over most of eastern Colorado, the Mississippian is the porous and permeable stratigraphic unit of this very low-pressure system. Fluids will migrate from the higher energy Pennsylvanian system to the lower energy Mississippian. Thus, the Mississippian is capable of deriving hydrocarbons transversely as well as laterally. Since 1965, exploratory interest has been primarily in Mississippian reservoirs, although some Pennsylvanian oil and gas fields also have been found. Since 1965, 20 Mississippian and Pennsylvanian oil and gas fields have been found and over 200 wildcat wells have been drilled. The data from these wells have resulted in new interpretations of hydrocarbon accumulations. Early Pennsylvanian growth strongly influenced Mississippian accumulations, and recent refinements in seismic techniques have allowed definition of these growth features. By incorporating recent subsurface interpretations with the extensive seismic control available, numerous prospects are being defined and doubtless will result in additional pre-Cretaceous discoveries. End_of_Article - Last_Page 660------------

Mississippian Rocks Of Western Kansas

Mississippian rock reservoirs in western Kansas have produced large quantities of oil and gas. The potential for additional production of hydrocarbons is great both at the top of and within the sequence of rocks. In western Kansas, Mississippian rocks, all marine (except for some Chesteran rocks) and all in the subsurface, are correlated with rocks of the Kinderhookian, Osagian, Meramecian, and Chesteran States. Unconformities set off dominantly carbonate Mississippian rocks from Pennsylvanian rocks above and Cambrian to Devonian rocks below. Diagenetic alterations, facies changes, and karst complicated the establishment of lateral stratigraphic equivalents. Dolomitization, silicification of fossils, and chertification are widespread. Conodont faunas recovered as acetic acid insoluble residues from cores are correlated with conodont biostratigraphic zones of the type area of Mississippian rocks. Reworked Devonian and Kinderhookian conodonts preserved in Kinderhookian rocks are evidence that part of the study area once contained Devonian rocks. The primary sediment source of Osagian and Meramecian rocks was biogenetic. Sediments were deposited in warm, shallow seas which fluctuated in depth. Thin intraformational conglomerate beds, quasibrecciated limestone beds, and local beds of anhydrite are known in upper Meramecian rocks. An increased content of clastic (quartz) rocks in upper Meramecian strata marks an important change in sediment source. Areas of provenance of siliceous sediments were the Central Kansas uplift and the Las Animas arch. In Chesteran rocks, sandstone, siltstone, and thin limestone beds predominate. A normal sequence of Osagian and Meramecian rocks was deposited in south-central Kansas but was diagenetically altered. The cherty facies, developed only locally, includes rocks of Osagian and Meramecian ages. The term Cowley Formation should be dropped.

Mississippian Rocks of Western Kansas: ABSTRACT

In western Kansas, Mississippian rocks, all marine and all in the subsurface, are correlated with rocks of the Kinderhookian, Osagian, Meramecian, and Chesteran Stages. Unconformities separate dominantly carbonate Mississippian rocks from Pennsylvanian rocks above and Cambrian to Devonian rocks below. Karst, diagenetic alternations, and facies changes complicate the problem of establishing lateral stratigraphic equivalents. Dolomitization, silicification of fossils, and chertification are widespread. Conodont faunas recovered as acetic acid insoluble residues from cores are correlated with conodont biostratigraphic zones of the type are of Mississippian rocks. Part of the study area once contained Devonian rocks; evidence of this is the presence of reworked Devonian and Kinderhookian conodonts preserves in Kinderhookian rocks. The primary sediment source of Osagian and Meramecian rocks was organic. Sediments probably were deposited in warm, shallow seas. Thin intraformational conglomerate beds, quasi-brecciated limestone beds, and local beds of anhydrite are known in upper Meramecian rocks. An increased content of clastic (quartz) rocks in upper Meramecian strata marks a change in sediment source. Siliceous sediments were provided from areas of provenance from the Central Kansas uplift and the Las Animas arch. In Chesteran rocks, sandstone, siltstone, and thin limestone beds predominate. A normal sequence of Osagian and Meramecian rocks was deposited in south-central Kansas. The term Formation should be dropped; the cherty Cowley facies is developed only locally. End_of_Article - Last_Page 1688------------