Splay Facies Research Articles

Depositional and Diagenetic History of Hosston Formation (Travis Peak), Nuevo Leon Group, Trawick Field, Nacogdoches County, Texas: ABSTRACT

ABSTRACT Five major lithofacies were identified in the Hosston Formation of Trawick Field, Nacogdoches County, Texas. These were identified based upon vertical changes in sedimentary structures, textures, and lithologic composition. Facies identified in the Hosston Formation included: (1) a clean, crossbedded, tidal-channel facies, (2) a sandy, bioturbated, tidal-flat facies, (3) thin, rapidly deposited, crevasse splay deposits, (4) interdistributary bay sands, silts, and muds and (5) partially reworked distal deltaic sandstones. Distinct differences are observed between the upper and lower Hosston facies due to the transition from a lower, more continental fluvio-deltaic system to an upper, marginal marine delta-fringe system. In the lower Hosston, only the channel, crevasse splay, and interdistributary bay facies are significant. The regressive nature of the formation is documented through changes in color and detrital constituents as well as in the presence of prodelta muds and shallow carbonates found exclusively in the upper Hosston. The Hosston Formation has characteristically low porosity and permeability values. Variations in the reservoir quality of Hosston sands is controlled both by environment of deposition and diagenesis. Two diagenetic pathways are postulated. In the first, extensive silica and phyllosilicate cementation dramatically reduce reservoir potential and porosity values rarely exceed 2 percent. In the second, early hydrocarbon migration inhibits additional cementation and therefore suppresses further porosity reduction. Samples following this pathway have porosities of up to 30 percent. Late stage diagenetic events include cementation by calcite and anhydrite as well as isolated occurrences of intergranular albite cementation. Channel sands of the lower Hosston maintain the highest consistent reservoir qualities.

Facies and Depositional Environments of Energy Shale Member (Carbondale Formation, Pennsylvanian), Southwestern Jefferson County, Illinois: ABSTRACT

The Energy Shale directly overlies the Herrin (No. 6) Coal Member in southwestern Jefferson County. Five facies of the Energy are recognized in the study area. The depositional environment is interpreted as a large quiet-water bay into which periodic influxes of coarse-grained sediments from the nearby Walshville channel were deposited as crevasse splays. The bay-fill deposits include a nonmarine and a brackish-marine facies; the latter has higher sulfur and boron contents and a sparse marine fauna. Both bay-fill facies are faintly laminated gray shales, and both grade laterally into and underlie deposits of the distal portion of crevasse splays. The distal splay facies is dominantly siltstone with lenticular bedding. The proximal splay facies grade laterally into and are interbedded with the distal splay deposits, and are divided into a channel facies (characteristically a well-sorted sandstone that contains microcross-bedding, clay drapes, contorted bedding, and a shale clast lag-deposit) and an interchannel facies (characterized by massive and flaser-bedded sandstones). Sulfur and boron content of the proximal and distal splay deposits is considerably less than that of the brackish-marine bay deposits, suggesting a nonmarine origin. Energy Shale facies have a direct influence on the sulfur content of the underlying Herrin (No. 6) Coal. In areas where thick (> 20 ft, 6 m) nonmarine bay-fill deposits overlie the coal, the sulfur content of the coal is less than 1%. Where the coal is overlain by thick proximal splay deposits, the sulfur content is 2 to 3%. This increase in sulfur content is attributed to downward percolation of sulfate-rich marine waters of a later transgression through the permeable sandstone. Where the coal is overlain by thin brackish-marine Energy or by the Anna Shale, the sulfur content averages 4 to 5%. End_of_Article - Last_Page 1454------------

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

Depositional Environments in an Alluvial-Lacustrine System: Molluscan Paleoecology and Lithofacies Relations in Upper Part of Tongue River Member of Fort Union Formation, Powder River Basin, Wyoming: ABSTRACT

The upper part of the Tongue River Member of the Fort Union Formation (Paleocene) in the northern Powder River basin, Wyoming, contains assemblages of excellently preserved nonmarine mollusks which occur in laterally continuous outcrops of diverse lithologic sequences and sedimentary structures. These attributes offer a unique opportunity for interdisciplinary interpretation of depositional environments based on molluscan paleoecology and lithofacies relations. Taphonomic histories of mollusk assemblages as reflected by molluscan biofabric (size, End_Page 478------------------------------ shape, orientation, and distribution of faunal elements), and the taxonomic composition, diversity, and abundance representation of species in assemblages are of particular importance in interpretations of paleoecology and depositional environments. Three facies are recognized vertically within an alluvial-lacustrine system. The interfluvial lake and lake splay facies is characterized by sequences of coarsening-upward detritus, abundant continuous limestone beds, and few beds of discontinuous coal and continuous carbonaceous shale. Limestones, contain two lacustrine mollusk assemblages: a locally reworked assemblage dominated by the bivalve Plesielliptio (two species), and the gastropods Viviparus, Lioplacodes (three species), and Clenchiella; and a quiet-water assemblage dominated by sphaeriid bivalves. This facies reflects development of numerous lakes bordered by well-drained backswamps in interfluvial flood basins. Lakes were repeated infilled by carbonate mud, splay detritus, and backswamp deposits. The interfluvial crevasse splay-crevasse channel facies is characterized by sequences of coarsening-upward detritus and few discontinuous limestone beds, separated vertically by thick, continuous coal and carbonaceous shale beds. This facies includes small crevasse channel sandstones which scour into splay sandstones. Biofabric of lacustrine mollusk assemblages, which are identical in composition (but with dwarfed species of Plesielliptio) to locally reworked lacustrine assemblages of the interfluvial lake and lake splay facies, reflects deterioration of lakes through active infilling by crevasses. The fluvial channel and interchannel facies is typified by thick channel sandstones laterally separated by sequences of coarsening-upward detritus, overbank sediments, and rare limestones. This facies includes thick, continuous coal and carbonaceous shale beds. Muddy-substrate flood basin lakes are characterized by an untransported lacustrine mollusk assemblage differing from those of the interfluvial lake and lake splay facies in both composition and relative abundance of species. Transported mollusk assemblages dominated by the gastropod Hydrobia eulimoides occur in crevasse sandstones. Relative to northerly flowing major channels, proximal and distal parts of splay deposits can be differentiated by their mollusk assemblage composition. The fluvial channel and interchannel facies re lects deposition on flood basins that were formerly occupied by lake, crevasse, and backswamp deposits. Thick, continuous coal beds reflect the spread of backswamps from interchannel depressions to abandoned major channel ridges. Cessation of fluvial channel and interchannel sedimentation was marked by widespread lacustrine deposition. The vertical sequence of facies just described also reflects the areal distribution of deposits of major channels that pass laterally into overbank and crevasse splay channel areas, which in turn merge into large and small lakes. Alluvial-lacustrine deposition in the upper part of the Tongue River Member is similar to that of anastomosed reach of the Saskatchewan River, Canada, as reported in a 1980 study by Smith and Putnam. End_of_Article - Last_Page 479------------

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.

Depositional History and Correlation Problems of the Anderson-Dietz Coal Zone, Southeastern Montana

The Roland, Smith, Anderson, and Dietz coal beds of the Tertiary Fort Union Formation in Big Horn County, Montana, split and merge in a complex pattern which makes standard methods of correlation by stratigraphic interval impossible. The splitting and merging of the coal beds can be related to the distribution of the associated rocks, particularly the sandstone beds which can be divided into crevasse splay and channel fill facies. The elastic partings and intervals between coal beds represent short term input of crevasse splay elastics into interdistributary peat swamps or the longer-term migration of fluvial channels through them. This interpretation means that the coal beds studied in Big Horn County are not separate isochronous beds but are irregularly distributed throughout the stratigraphic interval containing them, and coal beds near the base of the interval can frequently be physically correlated with coal beds near the top of the interval. It is therefore recommended that coal correlations not be carried over long distances or that new names not be assigned to coal beds within the interval without very detailed stratigraphic support.

High-Constructive, Tidally Influenced Deltaic Sedimentation in Arkoma Basin: Desmoinesian Hartshorne Sandstone: ABSTRACT

The Hartshorne Sandstone and associated fine-grained facies of the Arkoma basin were deposited in a high-constructive, tidally influenced delta system which prograded longitudinally from east to west in an elongate, foreland basin during Ouachita suturing. Prodelta facies (generally mapped as upper Atoka) consists of dark gray, nonfossiliferous shales. Delta front facies deposited near the mouth of an active distributary channel include interlaminated siltstones and sandstones of distal bar origin and ripple-bedded and trough cross-bedded sandstones of distributary-mouth bar origin. Delta front facies deposited in interdistributary areas consists of lenticular, wavy, and flaser-bedded sandstones, siltstones, and shales deposited under the influence of tidal currents. Delta plain facies is sandstone, siltstone, shale, and coal deposited in distributary channels, interdistributary bays, crevasse splays, marshes, and swamps. Distributary channel sandstone bodies display shoestring geometry (50 to 60 m thick), 1 to 3 km wide, tens of km lon ) and internally are unidirectionally trough cross-bedded. Their linear geometry and thickness relative to other delta facies suggest that channels were structurally localized, that the delta was elongate, or a combination of the two. Interdistributary bay facies comprise locally fossiliferous shale and silty shale. Crevasse splay facies coarsen upward from shale through ripple-bedded sandstone to trough cross-bedded sandstone. Marsh and swamp facies are carbonaceous shale and coal. In Arkansas, the Hartshorne displays a single, progradational sequence of prodelta, delta front, and delta plain facies. In Oklahoma, the prodelta and delta front facies are capped by a complex assemblage of delta plain facies which records at least three episodes of active sedimentation followed by delta plain abandonment. Understanding the genesis of these delta plain facies will enhance petroleum and coal exploitation efforts within the Hartshorne of the Arkoma basin. End_of_Article - Last_Page 1499------------

Facies, Paleoecology, and Depositional Environments of Energy Shale Member (Pennsylvanian) and Their Relation to Low-Sulfur Coal Deposits, 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 in southern Illinois. The Energy Shale consists of wedges, up to 85 ft (25.9 m) thick, which thin away from the Walshville Channel (interpreted as a major distributary channel deposit in the study area). Facies recognition and interpretation of depositional environments are based upon lithology, sedimentary structures, vertical and lateral relations, geometry, and paleoecology as well as organic matter content and total sulfur content. Four facies are recognized in the surface mines studies. The thickest and coarsest facies is adjacent to the Walshville Channel and is characterized by numerous fining-upward channel-fill sequences of sandstone, siltstone, and silty shale. It is interpreted as a series of crevasse distributary channel-fills in the proximal parts of splays. This proximal splay facies grades laterally into shale with abundant plant remains, thin coal beds (splits from the Herrin No. 6 coal) and some siderite concretions. It is interpreted as the distal deposits of crevasse splays. The distal splay facies grades laterally into what is interpreted as an interdistributary bay-fill facies consisting of shale with laterally persistent siderite layers. Sixteen miles (25.8 km) from the Walshville Channel, a zo e at the top of this facies is extensively burrowed and contains pectinoid bivalves, indicating some marine influence. The bay-fill facies grades laterally and vertically into shale, containing a moderately diverse marine fauna composed mostly of stunted individuals. It is interpreted as a marginal marine facies. The Walshville Channel and the crevasse splay facies of the Energy were partly contemporaneous with Herrin peat deposition. The sulfur content of the Herrin No. 6 coal is highest beneath the marginal marine facies (the thinnest) and the proximal splay facies (the thickest) of the Energy Shale. End_of_Article - Last_Page 1283------------

Uranium Host Depositional Systems of Texas Gulf Coastal Plain--Influence of Genetic Facies on Mineralization Pattern: ABSTRACT

ABSTRACT Significant reserves of uranium have been delineated in the Jackson, Catahoula, and Oakville Formations of the south and central Texas Coastal Plain. The Jackson includes (1) a major barrier/lagoon system, consisting of strike-parallel barrier bar and associated small cuspate and bayhead delta sand units, which lies south of the San Marcos arch and (2) a fluvial-dominated delta system consisting of dip-oriented fluvial and distributary channel, and delta margin sands, which infilled the Houston embayment northeast of the arch. The overlying Catahoula and Oakville Formations comprise several major dip-oriented fluvial systems containing bedload and mixed-load channel sands and assocaited crevasse splay, floodplain, and lacustrine facies. Uranium was introduced into the sediments by coastward-migrating ground water and concentrated along mobile, Eh-defined hydrochemical boundaries. The volume, direction, and downdip extent of oxidizing ground-water flux was directly affected by bulk permeability, facies heterogeneity, and trend and degree of vertical interconnection of permeable elements within each system. Consequently, the regional distribution as well as local geometry, trend, internal complexity, and size of individual uranium deposits reflect the genetic facies framework of the host depositional system. Depositional patterns, subsequent ground-water flow geometry, and cross-stratal flux of extrinsic reductants (H2S and hydrocarbon gases) were also affected by major strike-parallel zones of faulting and by local piercement salt domes. Relatively shallow mineralization fronts, which have been the objective of exploration to date, dominantly occur at margins of major sand facies or along fault zones where flow patterns were disturbed and intrinsic or extrinsic reductants were most available. Understanding ground-water flow patterns within major coastal plain depositional systems will enhance predictive capability of both regional and local exploration programs. 1. Publication authorized by Director, Bureau of Economic Geology, The University of Texas at Austin End_of_Record - Last_Page 245-------

Virgil and Wolfcamp Fluvial, Deltaic, and Inter-Deltaic Embayment Depositional Systems in North and West-Central Texas: ABSTRACT

Virgil and lower Wolfcamp sediments on the Eastern shelf were deposited within 3 depositional systems--Bowie fluvial system, Cisco delta system, and Lake Hubbard interdeltaic embayment system--which are the subjects of this report. Complementary shelf-edge bank, slope, and basin systems, to be discussed by William E. Galloway, complete the facies tract. Bowie fluvial facies compose tabular and belted sandstone bodies characterized by braided and coarse-grained meander-belt sequences and sedimentary structures. Fine-grained meander-belt facies generally becoming finer upward, lateral accretionary point bar deposits, and characteristic sedimentary structures commonly occur high in the Bowie fluvial system, indicating decreasing tectonic activity in source areas. Basal fluvial channel facies normally cut subjacent deltaic facies and may overlie rocks of previous depositional episodes. Cisco deltaic facies are composed of prograding, prodelta mudstones that become coarser upward, delta front, channel-mouth bar and distributary channel sandstones, and aggradational crevasse splay facies, delta-plain mudstones, and coal or organic-rich clays. Local sandstone bars of destructional origin may fringe the delta facies. Lake Hubbard interdeltaic embayment facies flank deltaic lobes and are composed of mudstone, thin extensive sheet sandstone, and thin impure detrital coal. Some sheet sandstones reflect strandplain accretion, but more commonly they are reworked delta-front sands. Deltas prograded rapidly westward across the slowly subsiding Eastern shelf. Sediments from the east supplied crevassing delta lobes until avulsion of over-extended systems occurred. Delta construction, accompanied by deposition of complementary facies within nearby interdelta embayments, restricted open-shelf limestone facies to areas downslope or in areas of abandoned deltas. Channels were cut deeply into subjacent facies as prograding deltas extended fluvial erosion and deposition far across older deltaic facies. Marine processes slowly modified abandoned, compacting, and subsiding deltas. Winnowed sediment was swept into interdeltaic embayment mudflats and strandplains. In the absence of local terrigenous sediment, shelf limestones transgressed upslope and along the coast to coale ce over marsh-stabilized deltaic and interdeltaic areas. All environments could occur simultaneously, shifting with distribution of delta sites to produce repetitive End_Page 151------------------------------ sequences of thin superposed depositional systems. Deposition of fluvial and deltaic facies was rapid; deposition of destructional and transgressive facies represents most of the time consumed by deposition. Depositional systems shifted westward through time as the eastern flank of the basin was filled. End_of_Article - Last_Page 152------------