Crevasse Splay Facies Research Articles

DETERMINATION OF HYDROCARBON ZONE AND DEPOSITIONAL ENVIRONMENT FACIES IN TALANG AKAR FORMATION, SOUTH SUMATRA BASIN AT "EPURA" FIELD

The EPURA field is one of the oil and gas producing fields in the South Sumatra Basin, where well completion has been carried out in the Talang Akar Formation, and the production test results are interpreted to mean that in wells EP-13, EP-14, EP-15, EP-16, EP-17 and EP-23 contain several reservoir zones that have the potential to contain hydrocarbons. This research with facies interpretation analysis uses data from six wells (wireline, mudlog, RCAL and lithology data), so it is hoped that it can provide more detailed information for the development of an oil and gas field. The analysis carried out is in the form of facies analysis, depositional environment, electrofacies and facies correlation. From the research results, it was found that the Talang Akar Formation has depositional facies in the form of a fluvial, which in this study is the Lower Talang Akar Formation with depositional facies in the form of channel, Crevasse Splay, point bar and flood plain. Based on the analysis results, the Talang Akar Formation is divided into 3 reservoir zones, namely Zone EP-1, EP-2, and EP-3. After going through all stages of petrophysical analysis, it was found that zones with high hydrocarbon potential were found in wells EP-13, EP-23 and EP-16. The wells with low hydrocarbon potential are EP-14, EP-15 and EP-17 wells. The zone of highest hydrocarbon potential in prospect wells is in the EP-1 zone with a Crevasse Splay facies association and has thick sandstone lithology characteristics with medium to fine grain size.

Karakteristik Lapisan Batubara pada Cekungan Bentarsari Terhadap Pola Sebaran Di Daerah Bentar Dan Sekitarnya Kecamatan Salem Kabupaten Brebes

The Kaliglagah Formation in the Bentarsari area, Salem District, Brebes Regency, Central Java Province is included in the Bentarsari Basin. This formation is a coal-bearing formation in the Bentarsari Basin of Late Pliocene age and is composed of layers of claystone, sandstone and coal. The coal seams in this formation were analyzed megascopically to determine the type of characteristics based on taking outcrop profiles in the research area and analyzed using the Horne classification approach, 1978 so that the depositional environment and facies of the formation of the coal seams were found. The results of the two analyzes were then used to determine the characteristics and distribution patterns of the coal seams of the Kaliglagah Formation. Characteristics The coal seam in the study area was deposited in the Crevasse splay facies, in the transitional lower delta plain depositional environment according to Horne, 1978. The distribution pattern of coal with a northwest-southeast trend, the withdrawal of coal distribution obtained three seams, namely a seam with a thickness of 1.21 m at Lp 4 , seam b with a thickness of 0.82 m on Lp 4, on Lp 2 the thickness of the coal seam is 0.03 m on seam b upper, 0.02 m on seam b middle and seam c lower 0.1 m, and 0.04 m on seam b upper and 0.03 m on seam b lower Lp 5 and seam c with a thickness of 1.65 m on seam b upper and seam c lower on Lp 1.

Distribution Characteristics of Quaternary Channel Systems and Their Controlling Factors in the Qiongdongnan Basin, South China Sea

The study of deepwater channels is important for the understanding of the sedimentary evolution mechanism and the sedimentary process of the marginal sea. In 2019, thick pore-filling gas hydrate with high saturation was firstly discovered in the Quaternary sands of the Qiongdongnan Basin (QDNB), which expanded the reservoir types of gas hydrates in the South China Sea. However, the distribution of sand-related channels is not well characterized, which limits the ability to predict sand reservoirs with gas hydrate. Using integrated 2D/3D seismic, multi-beam, well logging, and coring data, the current study documents the distribution characteristics of channel systems in the Quaternary strata and discusses their controlling factors. The integrated analysis shows that the channel-related sedimentary facies include channel-filling facies, levee facies, crevasse splay facies, and lobes facies. A total of six periods of channel systems is identified in the Quaternary strata. There are obvious distribution differences between the Channel 1 and Channel 3 systems when comparing the western, middle, and eastern sections: the channels in the western and eastern sections are mainly dominated by near straight V-shaped channels, while the middle section mainly consists of large braided channels, where channel-levee sedimentary facies developed. Compared with the distribution of the Central Canyon that developed in the Miocene, the Channel 1 and Channel 3 systems in the western section show southward migration since the Miocene. The distribution and evolution of Quaternary channels were likely collectively controlled by seafloor morphology, tectonic movement, sea-level fluctuations, and provenance supply. Tectonic movement controls seafloor morphology, which directly controls the flow of channels and their distribution characteristics; provenance supply determines the scale and sedimentary characteristics of each channel. The periodic changes in sea-level determine the evolution of multi-stage channel systems. This study has implications for the prediction of gas hydrate–bearing sands in the Quaternary QDNB and deepens our understanding of the Quaternary tectonic and sedimentary evolution in the QDNB.

PRESERVATION OF NEUROPTERIS OVATA IN ROOF SHALE AND IN FLUVIAL CREVASSE-SPLAY FACIES (LATE PENNSYLVANIAN, SYDNEY COALFIELD, CANADA). PART I: AN INFRARED-BASED CHEMOMETRIC MODEL

ABSTRACTAnalytical questions relating to the influence of sedimentation on the preservation states of Carboniferous plant fossils are seldom addressed in the literature. Here we address specifically the influence facies differences have on preservation states and suggest how they can be analyzed. The case study involves the seed fern Neuropteris ovata (Hoffmann) that occurs as opaque pinnules in the roof shale and as transparent pinnules in an associated crevasse-splay of the basal Cantabrian in age, Point Aconi Coal Seam, Sydney Coalfield, Canada. The color differences imply different molecular pathways for organic matter transformation over geological time, which resulted in production of compression fossils in the roof shale and fossilized-cuticle in the crevasse-splay, respectively. Fourier transform infrared spectroscopy methods are used to quantify functional groups, and the derived data are chemometrically evaluated. Results indicate that the compressions are, as anticipated, characterized in the crevasse-splay facies by a predominantly aromatic composition. The fossilized-cuticles, however, are mainly characterized by oxygen-containing aliphatics, confirming the influence of facies changes on preservation states of the species studied. Implications for preservation, taxonomy, and paleoecology are emphasized.

Anatomy and dimensions of fluvial crevasse-splay deposits: Examples from the Cretaceous Castlegate Sandstone and Neslen Formation, Utah, U.S.A.

Crevasse-splay deposits form a volumetrically significant component of many fluvial overbank successions (up to 90% in some successions).Yet the relationships between the morphological form of accumulated splay bodies and their internal facies composition remains poorly documented from ancient successions. This work quantifies lithofacies distributions and dimensions of exhumed crevasse-splay architectural elements in the Campanian Castlegate Sandstone and Neslen Formation, Mesaverde Group, Utah, USA, to develop a depositional model. Fluvial crevasse-splay bodies thin from 2.1m (average) to 0.8m (average) and fine from a coarsest recorded grain size of lower-fine sand to fine silt away from major trunk channel bodies. Internally, the preserved deposits of splays comprise laterally and vertically variable sandstone and siltstone facies associations: proximal parts are dominated by sharp and erosional-based sandstone-prone units, which may be structureless or may comprise primary current lineation on beds and erosional gutter casts; medial parts comprise sets of climbing-ripple strata and small scale deformed beds; distal parts comprise sets of lower-stage plane beds and complex styles of lateral grading into fine-grained floodbasin siltstones and coals. Lithofacies arrangements are used to establish the following: (i) recognition criteria for crevasse-splay elements; (ii) criteria for the differentiation between distal parts of crevasse-splay bodies and floodplain fines; and (iii) empirical relationships with which to establish the extent (ca. 500m long by 1000m wide) and overall semi-elliptical planform shape of crevasse-splay bodies. These relationships have been established by high-resolution stratigraphic correlation and palaeocurrent analysis to identify outcrop orientation with respect to splay orientation. This permits lateral changes in crevasse-splay facies architecture to be resolved. Facies models describing the sedimentology and architecture of crevasse-splay deposits preserved in floodplain successions serve as tools for determining both distance from and direction to major trunk channel sandbodies.

Storm-reworked shallow-marine fans in the Middle Triassic Baise area, South China

Shallow-marine fans have been analyzed for sedimentary characteristics and genetic mechanisms far less commonly than deep-marine fans. Based on outcrop observations, this study reveals that large-scale submarine fans in the Middle Triassic Baise area, south China, consisted of a braided channel-levee facies complex in the inner fans; sinuous channel-levee facies complex, overbank facies and crevasse splay facies in the medial fans; and sand sheet facies in the outer fans, which present different lithology assemblages and depositional successions. The lithofacies of dominant massive sandstone, secondary graded sandstone and laminated sandstone from bottom to top is similar to the Bouma sequence, indicative of gravity flow processes. However, the laminated sandstones mostly bear sedimentary structures of gutter casts, wave-generated ripple marks, hummocky cross-bedding, wave-generated cross-bedding and ripple bedding, and were thus attributed to frequent storm reworking processes. Moreover, discontinuous deposition recorded by abrupt sediment grain-size changes, distinct interfaces and divergent paleocurrent orientations occurred between the laminated sandstones and the underlying massive (or graded) sandstones. Accordingly, storm reworking processes together with abundant fossils of Daonella, Ammonite and Crinoidea indicate a shallow-marine paleo-environment. As a whole, this study provides a good example of large-scale shallow-marine fans and laminated sandstones resulted from storm reworking.

New sedimentological and palynological data from surface Miocene strata in the central Amazonas Basin areaNew sedimentological and palynological data from surface Miocene strata in the central Amazonas Basin area

The scarcity of stratigraphic data has hindered the demarcationof the outcropping area of Miocene deposits of the AmazonBasin, represented informally by the Novo Remanso Formation.Moreover, this unit is characterized by a sparse and irregular geographicdistribution due to its sedimentological features and rare fossilcontent. Miocene deposits cropping out in central Amazonas Basinarea were described in sedimentological terms and analyzed palynologically.All analyses were undertaken in samples collected at theUatumaRiver banks (Itapiranga and Sao Sebastiao do Uatuma cities).Lithostratigraphic data shows that Novo Remanso Formation consistsof sandstones, with subordinate conglomerates and pelites, characteristicof a meandering fluvial paleosystem, with fluvial channel, pointbar, floodplain and crevasse splay facies. The palynoflora retrieved fromfive samples consists exclusively of continental-origin palynomorphsdominated by angiosperms species. Trilete spores are well represented,while gymnosperms pollen grains are minor components. The presenceof Psilastephanoporites tesseroporus, Syncolporites poricostatus, Jandufouriaseamrogiformis and Polypodiaceoisporites potoniei ensure these depositsfits into the Grimsdalea magnaclavata palynozone (Regali et al.1974a, b), and the Grimsdalea magnaclavata/Crassoretitriletes vanraadshoovenipalynozones of Jaramillo et al. (2011) considered MiddleMiocene age. This age is confirmed by the zonation of Jaramillo et al.(2011), based on the LADs of Bombacacidites baumfalki (11.57Ma)and Crototricolpites annemariae (12.91Ma); and the FAD of Psilastephanoporitestesseroporus (14.00Ma). With these new data presentedherein, it is possible to assume that the Miocene strata represented bythe Novo Remanso Formation covers a larger area in the basin thanpreviously considered, and that it may be extended for about 300 kmuntil the Manacapuru village, indicating a Miocene subsidence phase.

New sedimentological and palynological data from surface Miocene strata in the central Amazonas Basin area

ABSTRACT The scarcity of stratigraphic data has hindered the demarcation of the outcropping area of Miocene deposits of the Amazon Basin, represented informally by the Novo Remanso Formation. Moreover, this unit is characterized by a sparse and irregular geographic distribution due to its sedimentological features and rare fossil content. Miocene deposits cropping out in central Amazonas Basin area were described in sedimentological terms and analyzed palynologically. All analyses were undertaken in samples collected at the Uatumã River banks (Itapiranga and São Sebastião do Uatumã cities). Lithostratigraphic data shows that Novo Remanso Formation consists of sandstones, with subordinate conglomerates and pelites, characteristic of a meandering fluvial paleosystem, with fluvial channel, point bar, floodplain and crevasse splay facies. The palynoflora retrieved from five samples consists exclusively of continental-origin palynomorphs dominated by angiosperms species. Trilete spores are well represented, while gymnosperms pollen grains are minor components. The presence of Psilastephanoporites tesseroporus, Syncolporites poricostatus, Jandufouria seamrogiformis and Polypodiaceoisporites potoniei ensure these deposits fits into the Grimsdalea magnaclavata palynozone (Regali et al. 1974a, b), and the Grimsdalea magnaclavata/Crassoretitriletes vanraadshooveni palynozones of Jaramillo et al. (2011) considered Middle Miocene age. This age is confirmed by the zonation of Jaramillo et al. (2011), based on the LADs of Bombacacidites baumfalki (11.57Ma) and Crototricolpites annemariae (12.91Ma); and the FAD of Psilastephanoporites tesseroporus (14.00Ma). With these new data presented herein, it is possible to assume that the Miocene strata represented by the Novo Remanso Formation covers a larger area in the basin than previously considered, and that it may be extended for about 300 km until the Manacapuru village, indicating a Miocene subsidence phase.

Mechanisms of volcaniclastic aggradation in fluvial systems influenced by explosive volcanism: An example from Neoproterozoic Hammamat Group, Wadi Queih area, Central Eastern Desert, Egypt

Wadi Queih basin records different continental settings that interacted with explosive volcanism. This paper discusses the contrasting aggradational mechanisms in fluvial systems strongly influenced by explosive volcanism which took place during sedimentation of the Queih basin. Six main facies associations composed of 12 lithofacies have been recognized in the Neoproterozoic succession filling the Queih basin: (1) lava flows and pedogenically modified pyroclastics facies association, (2) debris-flow-dominated alluvial fan facies association, (3) sheetflood-dominated alluvial fan facies association, (4) crevasse-splay facies association, (5) lacustrine facies association, and (6) loess facies association. These facies assemblages are typical of low-sinuosity rivers flowing through unsymmetrical half graben basin. Petrographical and geochemical data of the Queih sediments indicate a predominantly continental volcanic block provenance and stable craton to fault-bounded basement uplift. Low values of Chemical and Plagioclase Index of Alteration (CIA and PIA) are consistent with low intensity source rock weatherning under prevailing semi-arid to arid climate.During deposition of the lower member of the Queih basin, common fall and flow tuff events occurred, indicating syn-eruptive conditions. In contrast, deposition of the upper member occurred in a fluvial–aeolian setting without input of primary volcaniclastic detritus, indicating inter-eruptive conditions. The change in depositional mode from the lower to upper is considered to be due to a change in the balance between the sedimentation rate and the rate of lake-level rise. Lithofacies stacking and rapid lateral changes of lithological units in conjunction with interformational unconformities and basin margin faults suggest tectonically induced sedimentation. Volcanism can also influence basin evolution and the delicate balance between erosion, sedimentation, and prevalent transport processes is affected the Queih basin by volcanic input. Thus, the Queih basin records the response of fluvial system to large, volcanism-induced sediment loads.

Sedimentology of the coal-bearing Mist Mountain Formation, Line Creek, Southern Canadian Cordillera: relationships to coal quality

A detailed sedimentological investigation of the Jurassic–Cretaceous Mist Mountain Formation in the southern Canadian Cordillera was undertaken to determine what, if any, sedimentological factors control coal quality and seam geometry. In the Line Creek area, the Mist Mountain Formation is divisible into two units based on abundance and lateral continuity of facies. The lower unit consists of alternating laterally extensive coal seams and thick, widespread channel sandstones interspersed with crevasse splay and flood plain facies sediments. The lower unit was deposited in an interdeltaic coastal plain environment protected from marine incursion by the beach ridge–dune sandstones of the underlying Morrissey Formation. The upper unit of the Mist Mountain Formation was deposited in a distal alluvial–fluvial flood plain environment and has similar facies to the lower unit but coal seams and channel sandstones are less laterally continuous and thinner than in the lower unit. Channel sandstones decrease in number and thickness up-section, and are replaced by an increasing abundance of coal seams, flood plain and crevasse splay facies sediments. Seam geometry and ash data indicate that clastic sedimentation had only limited influence on peat (coal) accumulation in the Mist Mountain Formation. While the geometry of the seams reflects the proximity of under- and overlying channel sandstones, neither abundance nor mineralogy of the coal ash reflects changes in surrounding clastic sediments. The Mist Mountain Formation peat mires were thus not obviously influenced by coeval fluvial activity. Characteristics of the lower unit suggest peat mires developed only during hiatus in clastic deposition, whereas upper unit coals appear to have formed in at least partially domed mires contemporaneous with clastic sedimentation. The vitrinite content of the coal increases up-section at the expense of semifusinite, possibly reflecting an increase in the proportion of arborescent vegetation in the mire with time and a lower susceptibility to fires.

Variations in fluvial deposition on an alluvial plain: an example from the Tongue River Member of the Fort Union Formation (Paleocene), southeastern Powder River Basin, Wyoming, U.S.A.

The Tongue River Member of the Paleocene Fort Union Formation is an important coal-bearing sedimentary unit in the Powder River Basin of Wyoming and Montana. We studied the depositional environments of a portion of this member at three sites 20 km apart in the southeastern part of the basin. Six lithofacies are recognized that we assign to five depositional facies categorized as either channel or interchannel-wetlands environments. (1) Type A sandstone is cross stratified and occurs as lenticular bodies with concave-upward basal surfaces; these bodies are assigned to the channel facies interpreted to be the product of low-sinuosity streams. (2) Type B sandstone occurs in parallel-bedded units containing mudrock partings and fossil plant debris; these units constitute the levee facies. (3) Type C sandstone typically lacks internal structure and occurs as tabular bodies separating finer grained deposits; these bodies represent the crevasse-splay facies. (4) Gray mudrock is generally nonlaminated and contains ironstone concretions; these deposits constitute the floodplain facies. (5) Carbonaceous shale and coal are assigned to the swamp facies. We recognize two styles of stream deposition in our study area. Laterally continuous complexes of single and multistoried channel bodies occur at our middle study site and we interpret these to be the deposits of sandy braided stream systems. In the two adjacent study sites, single and multistoried channel bodies are isolated in a matrix of finer-grained interchannel sediment suggesting deposition by anastomosed streams. A depositional model for our study area contains northwest-trending braided stream systems. Avulsions of these systems created anastomosed streams that flowed into adjacent interchannel areas. We propose that during late Paleocene a broad alluvial plain existed on the southeastern flank of the Powder River Basin. The braided streams that crossed this surface were tributaries to a northward-flowing, basin-axis trunk stream that existed to the west.

Reservoir Description of a Sand-Rich Submarine Fan Complex for a Steamflood Project: Upper Miocene Potter Sandstone, North Midway Sunset Field, California: ABSTRACT

Nearly 650 m of cores from the upper Miocene Potter sandstone in Mobil's Alberta/Shale property, North Midway Sunset field, California, were examined to determine depositional facies, sand-body geometry, and reservoir quality for a proposed steamflood project. The Potter represents a sand-rich submarine fan complex with braided-channel, meandering-channel, levee, and crevasse-splay facies. The braided-channel facies (gravel and coarse sand) is thick (up to 100 m), sheetlike (> 500 m wide), and highly permeable (10,000 + md). The meandering-channel facies (coarse to medium sand) is up to 20 m thick, over 400 m long, lenticular in geometry, and exhibits an upward decrease in permeability (e.g., 9000 to 500 md) related to grain size that fines upward. The levee facies (in bioturbated sand) is up to 21 m thick, shows variable geometry, and is generally low in permeability (100-1500 md). The crevasse splay (medium sand) is up to 12 m thick, sheetlike (> 300 m wide), and shows moderately high permeability (2000-8000 md). The braided-channel facies was a product of density-modified grain flows, and the remaining three facies were deposited by turbidity currents. Steam flooding of the Potter reservoir should perform extremely well because the entire reservoir is composed of relatively clean sandmore » and the reservoir lacks both horizontal and vertical permeability barriers.« less

Adverse Effects of Crevasse-Splay Deposits in an Appalachian Coal Mine, Eastern Kentucky: ABSTRACT

Facies analysis of highwall exposures, roof and pillar information, and 56 core descriptions indicate that a series of narrow, bifurcating paleochannels and associated sheet sandstones in an eastern Kentucky coal mine were deposited by at least three crevasse-splay and overbank flooding events that occurred during and immediately following peat accumulation in a fluviolacustrine flood-basin environment. The proximal crevasse facies is channel-form, dominantly gray, very fine to fine-grained sandstone exhibiting ripple-drift, current-ripple, and small-scale trough cross-bedding, abundant micaceous laminae, and common disseminated plant and stem debris. The proximal crevasse channels grade laterally, and are incised into distal splay sandstones, shales, claystones, and coal riders. Sandstones of the distal splay facies are gray, sheet form to wedge shaped, shaly to very fine grained, and exhibiting ripple-drift, irregular, and massive bedding, disseminated and well-preserved plant and stem fossils, micaceous concentrations, coal spar, and rooting structures. Shales of the distal splay facies are gray and laminated, with abundant, well-preserved plant and stem fossils, sideritic nodules, claystone, and coal laminae. Economic problems resulting from the crevasse-splay facies include 1) multiple washouts of the coal seam, 2) increased parting thickness and frequency, 3) split wedges in the coal seam, and 4) significant roof stability problems. Largemore » roof falls in the crevasse-splay (stackrock) roofs result from 1) thin bedding of facies, 2) rapid lateral and vertical changes of facies, 3) internal bedding weaknesses, such as fossil plant and micaceous concentrations, sideritic nodules, and coal spar, 4) thin coal riders and streaks in the roof, and 5) slickensided shale beneath sandstone channels. Mapping of the crevasse-splay facies may help to predict coal quality and roof stability problems in unmined areas.« less

Relationships Between Sedimentation, Depositional Environments, and Coal Quality: Upper Potomac Coalfield, West Virginia and Maryland: ABSTRACT

Evaluations were made of sedimentation patterns and depositional environments from approximately 450 core logs and 225 surface exposures in the Upper Potomac coalfield. The relationships between the clastic depositional facies and the distribution and quality of the Bakerstown and upper Freeport coals were also investigated. Data from 61 Bakerstown and 35 upper Freeport coal samples from selected cores indicate a change from uniform coal quality to highly variable coal quality when moving from related interchannel and bay-fill facies to channel, channel-fill, levee, and crevasse-splay facies. Areas of uniform coal quality range from 20-26% ash and 55-62% fixed carbon (weight percent, dry basis), whereas areas of highly variable coal quality range from 26-54% ash and 33-55% fixed carbon. The channel and related facies represent areas where increased fresh water was introduced into the topogenous swamp system, causing increased microbial degradation and the concentration of authigenic minerals within the peat material. These conditions, combined with the introduction of detrital minerals, resulted in areas of lower quality coal.

Facies and Depositional Environments of the Energy Shale Member (Pennsylvanian) and their Relationship to Low-sulfur Coal Deposits in Southern Illinois

ABSTRACT Thick deposits of Energy Shale (Carbondale Formation, Desmoinesian) are associated with low-sulfur coal deposits in the underlying Herrin (No. 6) Coal Member in southern Illinois. The Energy Shale consists of wedges up to at least 26 m thick, which thin away from the Walshville channel (interpreted as a major channel deposit), and local pods or lenses which occur farther from the channel. Facies recognition and interpretation of depositional environments are based on paleoecology, lithology, sedimentary structures, vertical and lateral relationships, and geometry. Supplementary evidence was obtained from total sulfur content and boron content. Six facies are recognized in the areas studied. The thickest and coarsest facies is adjacent to the Walshville channel and is characterized by numerous fining-upward channel-fill sandstones, siltstones, and silty shales. This facies is interpreted as a series of crevasse-distributary channel-fill, levee, and interchannel deposits formed in the proximal portions of the splays. The proximal splay facies grades laterally into a distal splay facies, which consists of shale with abundant plant remains, thin coal beds (splits from the Herrin Coal), rare siderite concretions, and siltstone lenses. The distal splay facies grades laterally into or overlies shale with laterally persistent siderite layers, interpreted as a nonmarine bay facies. The nonmarine bay facies grades vertically and late ally into shale, which is bioturbated and contains euryhaline bivalves and is interpreted as a brackish to marine bay facies. The brackish to marine bay facies grades vertically into shale, containing a moderately diverse marine fauna with some small, possibly stunted, individuals. This facies is interpreted as a marginal marine deposit. Local lenses of organic-rich, dark gray to black shale underlie isolated pods of the marginal marine facies and probably were deposited in freshwater ponds developed on the Herrin peat swamp. The Walshville channel, the proximal and distal crevasse-splay facies of the Energy Shale, and possibly the black shale pond facies of the Energy Shale were partly contemporaneous with Herrin peat deposition. The sulfur content of the Herrin Coal is highest beneath the proximal splay and marginal marine facies of the Energy Shale and is lowest (less than 1.5%) beneath the distal splay facies and the nonmarine bay facies. The sulfur content of the Herrin Coal is related to the thickness, permeability, and environment of deposition of the facies of the overlying Energy Shale.

Fluvial plain/lacustrine facies transition in the Cretaceous Sindong Group, south coast of Korea

Along the south coast of Korea, a 250 m stratigraphic interval corresponding to the uppermost Hasandong and lowermost Jinju Formations of the Cretaceous Sindong Group has been studied in terms of facies transition. The interval displays a passage from a fluvial plain facies association consisting of floodplain, levee, crevasse splay and channel facies to a lacustrine facies association composed of crevasse splay, channel, overbank sheet splay, marginal lake, open lake and stream mouth bar facies. Between these two associations a transitional facies association occurs in which some facies of both associations alternate. In the lacustrine association, shallow marginal lake deposits including channel facies are gradually replaced upwards by deeper open lake deposits made up of open lake and stream mouth bar facies. During the Hasandong/Jinju period, small channels, which originated in the uplifted areas beyond the fault(s)-bounded western margin of the Gyeongsang Basin, flowed through alluvial fans developed along the fault(s) and a fluvial plain to a lake which occupied the central part of the basin. As a result, the lake shoreline was non-coincident with the basin margin. Sinuosity of the streams increased downstream, reaching a maximum near the shoreline, but decreased in the marginal lake areas. The fluvial plain was progressively submerged by the transgression of a non-deltaic shoreline, resulting in a deepening of the depositional sites from a fluvial plain through a marginal lake to an open lake setting. Intermittent channel overflows deposited levee and crevasse splay facies in the fluvial plain, and crevasse splay and overbank sheet splay facies in the marginal lake. Stream mouth bars were developed at the ends of the sublacustrine channels by hyperpycnal density flows operated mainly during floods. The non-deltaic shoreline was formed due to: (1) maintenance of shallow and wide marginal lake areas; (2) dispersal of sediments by small channels; (3) continuous shifting of the channels and their mouths; and (4) direct transport of coarser sediments to the open lake and their subsequent wide dispersions.

In-Situ Leaching of South Texas Uranium Ores: Part 3-Post-Leach Assessment of Recovery and Sweep Efficiency

Summary This paper reports results of a post-leach study following nearly 3 years' uranium in-situ leaching in a south Texas ore body. Wells drilled in strategic locations were logged [including delayed fission neutron (DFN) and gamma ray logs] and cored and the recovered core chemically analyzed. Overall uranium recovery for the total 11.9-m [39-ft] ore zone was about 70%, estimated from core and log data. Although ammonia analyses gave evidence of some leachate contact at some time over the whole interval, uranium recovery was not uniform over the total 11.9 m [39 ft]. The upper half of the ore zone appears to have been leached exhaustively, showing not only complete uranium depletion but zero reducing capacity. In the lower half of the interval, however, there was evidence of severe reservoir stratification. There were two narrow, visually oxidized bands from which uranium had been leached. These were interposed between three zones containing strong uranium shows, which had been totally or partially bypassed by the leaching fluid. Lithological cross sections suggested that, in the bypassed zones, a higher degree of sand compaction or the presence of clayballs or clay streaks caused lower permeability, thereby presence of clayballs or clay streaks caused lower permeability, thereby severely limiting the accessibility of the uranium mineral to the injected fluids. Introduction In the past few years in-situ leaching has become an important alternative to open-pit and shaft-mining recovery of uranium. In-situ leaching has a high potential for recovering reserves not presently minable by conventional techniques and with minimal disturbance of the surface environment. Water requirements are much less than in a conventional mine, and undesirable tailings ponds are not needed. Many leaching studies have been reported for south Texas, including case histories of field operations and commercial-size projects. Great interest in this technology is indicated by the more than 12 pilot and commercial in-situ projects in operation in south Texas in 1981. Reservoir engineering aspects of in-situ uranium leaching are similar in some respects to oilfield waterflooding operations. Factors affecting in-situ leaching performance include areal sweep efficiency, vertical stratification, and permeability/porosity variations. Unlike waterflooding, however, leachate/ore contact is fundamentally the most important aspect of in-situ uranium leaching and in many instances the most difficult to achieve. Since most uranium exists in a chemically reduced form, contact between uranium mineral and fluid-containing oxidant is required to form a soluble product. Most leachate/ore contacting problems result from reservoir stratification, specifically where there are adjacent channels of widely varying permeabilities. When uranium occurs in the lower-permeability layers, contact with leachate is sometimes difficult or impossible. The contacting problems encountered with in-situ leaching contrast with uranium ore processing mills, where a high surface area is exposed by mechanical means. Very little documentation is available for post-leach analyses of in-situ uranium leaching projects, partly because of the large expenditure of time and money necessary to complete a post-leach study and the many technical problems associated with such a project. An important problem associated with any post-leach analysis is obtaining a "control" sample before the injection of leachate. A representative control sample is particularly difficult to obtain if horizontal correlation is not good -- particularly difficult to obtain if horizontal correlation is not good -- i.e., if the formation is laterally heterogeneous in mineralogy or permeability, or if there is cross bedding (non-horizontal layering). The permeability, or if there is cross bedding (non-horizontal layering). The later validity of the post-leach analysis will depend largely on how much preleach information was obtained, and how accurately the data describe the preleach information was obtained, and how accurately the data describe the formation. This is especially dependent on the type of logs available and the number and location of the determinations. The uranium ore body in which the present coring was performed lies in the Oligocene-Miocene Catahoula formation of south Texas. These deposits are commonly found in ancient fluvial sediments along the flanks of major fluvial channel-fill and occasional crevasse-splay facies. They frequently show the characteristic C-shape roll-type geometry, with mineralization at the interface of oxidized sediments and reduced pyritic sands. JPT p. 1018

Two Depositional Models for Pliocene Coastal Plain Fluvial Systems, Goliad Formation, South Texas Gulf Coastal Plain: ABSTRACT

The Goliad Formation consists of four depositional systems--the Realitos and Mathis bed-load fluvial systems in the southwest and the Cuero and Eagle Lake mixed-load fluvial systems in the northeast. Detailed facies analysis indicates that Goliad bed-load and mixed-load fluvial systems represent two contrasting depositional environments. Five facies are recognized in the Realitos and Mathis bed-load fluvial systems: (1) primary channel-fill facies, (2) chaotic flood channel-fill facies, (3) complex splay facies, (4) flood plain facies, and (5) playa facies. Both channel-fill and splay deposits consist primarily of gravel, sandy gravel, and coarse to medium gravelly sand. Primary channel-fill deposits are characterized by large-scale accretionary foresets and trough cross-beds, localized scour-and-fill structures, and massive beds. Fining upward trends are crudely developed to absent, and no diagnostic vertical sequence of sedimentary textures and structures has been recognized. Chaotic flood channel-fill deposits are characterized by erratic interbedding of coarse and fine units, and of erosional and accretionary feat res. Individual beds have chaotic or poorly ordered textural profiles, and an absence of well-developed internal structures. Extensive flocks of stacked scour-and-fill structures are common. Complex splay deposits share characteristics of both crevasse and sheet splays. A model for Realitos-Mathis depositional environments shows arid-climate braided stream complexes with extremely coarse sediment load, highly variable discharge, and marked channel instability. Broad, shallow, straight to slightly sinuous primary channels were flanked by wide flood channels. These acted as part of the flood plain under most conditions, but as channels during high intensity flood flow. Flood channels passed laterally into broad, low-relief flood plains. Small playas occupied topographic lows near large channel axes. Three facies are recognized in the Cuero and Eagle Lake mixed-load fluvial systems: (1) channel-fill facies, (2) crevasse splay facies, and (3) flood plain facies. Channel-fill deposits consist of coarse to medium sand and gravelly sand, with a variety of large- and intermediate-scale sedimentary structures. Small-scale structures are common in finer grained beds. Fining-upward sequences are moderately well developed and commonly stacked. Crevasse splay deposits consist of medium to fine sand and silt, with abundant small-scale sedimentary structures. A model for Cuero-Eagle Lake depositional environments shows coarse-grained meander belts in a semi-arid climate. Slightly to moderately sinuous meandering streams were flanked by low, poorly developed natural levees. Crevasse splays were common, but tended to be broad and ill-defined. Extensive, low-relief flood plains occupied interaxial areas. While a number of models for coarse-grained meander belts exist in the literature, there are few models for arid-climate, gravel-rich braided stream complexes. These systems are likely to be characterized by extreme hydrodynamic complexity, which will be reflected in the resultant sedimentary package. The model proposed for the Realitos and Mathis fluvial systems may aid in recognition of analogous ancient depositional systems. In addition, since facies characteristics exercise broad controls on Goliad uranium mineralization, the proposed depositional models aid in defining target zones for Goliad uranium exploration. End_of_Article - Last_Page 484------------

Estuarine and Fluvial Systems, Lower Mesaverde Group (Campanian), Northwestern Colorado: ABSTRACT

Stacked shoreline sandstones near the base of the Mesaverde Group are well exposed along the southern flank of Rangely dome, northwestern Colorado. Overlying these marine deposits is a thick sequence of carbonaceous siltstones that encase elongate lenticular sandstones. This sequence records the evolution from estuarine to fluvial channels formed along the western margin of the Cretaceous Western Interior seaway. Sections 180 to 250 m (590 to 820 ft) long, were measured along a trend perpendicular to paleoshoreline. Several individual sandstones were studied in detail to develop depositional models. Data from over 300 well logs provided information regarding regional distribution and stratigraphic relationships of the systems. Two major stratigraphic successions were reco nized. Thin (0.5 to 2 m, 20 in. to 6.6 ft) bioturbated and root-mottled fine sandstones, interbedded with pervasive siltstones occur immediately over the marine shoreline deposits in both sequences. The sandstones are interpreted as storm washover deposits. At Gillam Draw in the eastern portion of the outcrop study area, the washover sandstones are overlain by 50 to 60 m (165 to 195 ft) of bioturbated shales and siltstones. Ripplestratified, upward-fining, fine to very fine sandstone lenses occur in this interval. These lenses are 4 to 8 m (13 to 26 ft) thick, have erosional bases, and have well-developed lateral-accretion bounding surfaces. Ophiomorpha and other trace fossils suggest an estuarine influence. The sandstone lenses are point bar deposits formed along meandering tidal creeks. Si tstones, coals, and 8 to 12 m (26 to 39 ft) thick lenticular sandstones overlie the tidally influenced interval. The sandstone lenses change significantly in geometry, bounding surface relationships, and textural trends within this succession. Stratigraphically lower sandstones form broad (100 to 200 m, 330 to 660 ft wide) belts. Individual sandstone bodies within the lenses have erosional bases and prominent lateral-accretion surfaces. Trough cross-bedding near the base is overlain by ripple stratification. These broad, lenticular sandstones represent fluvial meander-belt deposits. Sandstone lenses become narrower and lack accretionary surfaces higher in the section. These younger sandstones are multi-storied, rather than multilateral, channel deposits and are flanked by extensive crevasse splay facies. They are interpreted as confined anastomosing fluvial channels. West of Gillam Draw, the anastomosing fluvial system directly overlies shoreface and storm washover deposits. The multistoried lenticular sandstones are thicker (20 to 30 m, 66 to 100 ft). Sedimentation kept pace with subsidence in the eastern, basinward sections. Lower reaches of streams were tidally influenced even though the area was not inundated by marine waters. The western succession represents aggraded fluvial systems formed inland from the coast. Both sequences are characteristic of areas of rapid subsidence. End_of_Article - Last_Page 525------------

Effects of overbank deposition on the quality and maceral composition of the Herrin (No. 6) coal (Pennsylvanian) of Southern Illinois

A detailed study of the effects of overbank deposition on the quality and maceral composition of the Herrin (No. 6) Coal Member (Carbondale Fm., Middle Pennsylvanian) in southern Illinois was done using proximate, total-sulfur and maceral analyses. Channel samples were taken of the Herrin (No. 6) Coal and descriptions of the rocks overlying the coal were made at nine locations. the Herrin (No. 6) Coal in the study area is known to 3ave a high ash content toward the Walshville Channel (a channel sandstone possibly representing a distributary channel that existed during Herrin peat deposition). Sulfur content is knwon to in crease markedly where marine or marginal marine rocks directly overlie the coal and decrease where overlain by thick non-marine shale. Three types of overbank deposits are found in the study area accounting for the changes in coal quality and composition. Overbank flooding as sheet flow off the levee of the Walshville Channel introduced suspended material into the peat swamp. The suspended material either produced numerous shale laminae or intermixed with the peat, producing an increased ash content of the resultant coal close to the Walshville Channel. Contemporaneous with the introduction of clastic material by overbank flooding, partial oxidation of the peat occurred. Oxygenated flood water was able to oxidize the peat, increasing the pseudovitrinite content of the resultant coal. Fire splay deposits forming the partings, occurred when the swamp was flooded after a dry period or a swamp fire. The build-up of crevasse splay deposits forming the Energy Shale helped decrease sulfur content of the Herrin (No. 6) Coal in portions of the study area. The non-marine, shaly distal crevasse splay facies formed an impermeable barrier to downward movement of sulfate ion-bearing marine water during deposition of the marine units above the Energy Shale. High-sulfur coal is associated with the sandy crevasse distributary channel-fill facies and bay-fill facies of the Energy Shale or where the Energy Shale is not present. The crevasse distributary channel-fill facies allowed marine water to permeate through it, reaching the peat and resulting in high-sulfur coal. High-sulfur coal found where the bay-fill facies or other marine units directly overlie the coal is a result of marine water being able to permeate the peat directly.