bluuebunny/crossref_metadata_2025 huggingface dataset:
Facies Associations and Depositional Environments of the Mississippian Endicott Group in the National Petroleum Reserve – Alaska (NPRA)
Authors: Wilson Gregory C. , McGowen Joseph H. , Veldhuis Jerry H.
Published: November 2010

The base of the Middle Ellesmerian Megasequence of Hubbard et al. (1987) in the National Petroleum Reserve - Alaska (NPRA) is the non-marine to marginal marine Mississippian Endicott Group. It overlies a highly irregular erosional surface on pre-Mississippian basement complex and is mostly overlain by and transitional with the Mississippian-Pennsylvanian Lisburne Group shallow water carbonates. A late Devonian to early Mississippian breakup of the Basement Complex created the Meade, Ikpikpuk, and Umiat basins in the NPRA. Owing to accommodation within these basins and erosional relief at the top of Basement Complex outside the basins, the distribution of the Endicott Group across the NPRA is highly variable. Seismic correlation and limited well data suggests the basins were filled with as much as 5,400 m (17,700 ft) of clastics and carbonates of the Endicott and Lisburne groups. These same rocks are locally absent between basins and are thin to absent along the coast of NPRA. Core of the Endicott Group in NPRA is limited to four wells, but is only plentiful in the East Simpson 2 well. This core is interpreted to represent the Kekiktuk Formation of the Endicott Group and is comprised of coal and what appear to be crevasse splay sandstone and flood basin mudstone associated with a fan delta system and shallow lacustrine swamp. Limited Endicott core from the Inigok 1 well is tightly quartz-cemented pebbly sandstone and granule conglomerate that appears to be of fluvial origin. Reservoir potential of the Endicott Group within the deep basins is low, but there may be limited potential in the thin, shallower accumulations along the NPRA coast.
Lithologies of the Basement Complex (Devonian And Older)in the National Petroleum Reserve – Alaska
Authors: Dumoulin Julie A.
Published: November 2010

Rocks of the basement complex (Devonian and older) were encountered in at least 30 exploratory wells in the northern part of the NPRA. Fine-grained, variably deformed sedimentary rocks deposited in a slope or basinal setting predominate and include varicolored (mainly red and green) argillite in the Simpson area, dark argillite and chert near Barrow, and widespread gray argillite. Chitinozoans of Middle-Late Ordovician and Silurian age occur in the dark argillite and chert unit. Sponge spicules and radiolarians establish a Phanerozoic age for the varicolored and gray argillite units, both of which contain local interbeds of chert-rich sandstone and silt-stone. Conglomerate and sandstone, also chert-rich but interbedded with mudstone and coal and of Early-Middle Devonian age, occur in the Topagoruk area; these strata formed in a fluvial environment. At East Teshekpuk, granite of probable Devonian age was penetrated. Brecciated, quartz-veined rock of uncertain protolith that may be part of the basement complex was encountered in the Ikpikpuk well. Seismic data indicate that angular unconformities truncate all sedimentary units of the basement complex in NPRA. Rocks correlative in age and lithofacies with the dark argillite and chert unit occur in the subsurface near Prudhoe Bay. Other argillite units in NPRA have similarities to basement rocks in the subsurface adjacent to ANWR and the Ordovician-Silurian Iviagik Group at Cape Lisburne, but lack the interbedded limestones found in the ANWR strata, and are less metamorphosed than, and compositionally distinct from, the Iviagik. The Topagoruk conglomerate and the East Teshekpuk granite resemble the Ulungarat formation and the Okpilak batholith, respectively, in the northeastern Brooks Range.
Petroleum Plays and Systems in the National Petroleum Reserve - Alaska
Authors: Houseknecht David W.
Published: November 2010

The North Slope of Alaska has re-emerged as one of the most active exploration provinces in the United States. Recent exploration successes, economic benefits of applying innovative exploration and production technologies, evolving industry demographics, rising oil and natural gas prices, and the anticipation that North Slope natural gas resources may become economically viable and marketable through a planned pipeline have stimulated a renewed intensity in leasing and exploration activity. The focus of NPRA exploration appears to include both structural and stratigraphic objectives that may include strata spanning much of the stratigraphic column. The purpose of the core workshop is to prove an opportunity to examine a large collection of core from all major stratigraphic units present in NPRA. The chapters in this volume provide a current perspective on the genesis and petroleum potential of each stratigraphic interval.
Geology of the Capitan Shelf Margin - Subsurface Data from the Northern Delaware Basin
Authors: Garber Raymond A. , Grover George A. , Harris Paul M.
Published: November 2010

Facies relations determined from outcrop studies have been used in conjunction with subsurface data to better understand the geologic evolution, depositional facies, and diagenesis of the Capitan shelf margin. These studies have centered on a 2400 ft (731 m) portion of a 4800 ft (1463 m) continuous core from the Gulf PDB-04 research well that is located in Eddy County, New Mexico, at the northern end of the Delaware Basin.

The evolution of the Capitan shelf and margin was examined after (a) the establishment of time lines for shelf-to-basin correlations in the Late Guadalupian and (b) the confirmation of the stratigraphic units penetrated in the PDB-04 well. Subsurface and outcrop data revealed that the evolution of the 2.5 m.y. duration Capitan shelf margin occurred in two major growth phases: a 1.5 m.y. duration phase during Seven Rivers time when over 80% of the total progradation, over half of the total aggradation, deposition of thick carbonate debris units on the slope and basin margin, and influx of over 60% of the total siliciclastics of the Bell Canyon Formation occurred. A subsequent, 1.0 m.y. growth phase during Yates and Tansill time is dominated by aggradation, steepening of the margin, and corresponds with abundant clastic deposition on the shelf. Maximum progradation of up to 12 miles (19 km) occurred along the northern rim of the basin, where progradation rates in excess of 7500 µm/year are measured.

Detailed shelf-to-basin correlations have revealed that three major processes were responsible for the profound progradation and differentiation of Capitan growth into two major phases: (a) fluctuations of sea level, (b) maximum emplacement of allochthonous carbonate debris along the basin margin during Seven Rivers time, and (c) that abundant siliciclastics bypassed the actively prograding shelf margin and were an important foundation for the progradation. Because the Capitan was a deeply submerged reef during most of its growth, progradation occurred during both
Lateral Variability of the Capitan Reef Complex, West Texas and New Mexico
Authors: Pray Lloyd C.
Published: November 2010

The Delaware Basin is a pear-shaped, NNW-SSE elongate, intracratonic basin, about 250 km long and 150 km wide at its bulging northwestern end. The Capitan Reef Complex forms a narrow carbonate belt along the rim of the Delaware Basin for some 600-700 km, but outcrops occur only along about one-sixth of its rim. Most of these are in the Guadalupe Mountains where they fringe the Northwestern Shelf, but some occur in the Apache Mountains and fringe the Diablo Plateau, and also in the Glass Mountains where they fringe the Southern Shelf (index map of Fig. 1).

The most extensive and laterally continuous exposures are in the Guadalupe Mountains, and most subsurface data is from the area east and southeast of the Guadalupes. By far the most sedimentologic research has been of outcrops of the Guadalupe Mountains. Here excellent exposures, tectonic simplicity, and the large scale of the dramatic shelf-to-basin transitions have, justifiably, made the Permian of this area, and especially the Capitan Reef and its associated facies, a world-famous sedimentologic model.

But the extensive research over more than half a century on the Guadalupe outcrops (and on the petroleum-bearing area adjacent to them) has created two dangerous impressions: (1) that the Capitan Reef and its associated facies are well understood, and (2) that the "model" derived from study of the Guadalupe Mountains outcrops can be safely extrapolated along the remainder of the Capitan trend rimming the Delaware Basin. Despite major progress in recent decades as concerns "what is where" and "how did it form," much remains to be learned to arrive at a satisfactory sedimentologic understanding of the Capitan Reef and its associated facies. Moreover, the available surface and subsurface evidence indicates that considerable depositional and diagenetic lateral variability exists along the Capitan trend, and application of sedimentologic principles indicates that considerable lateral variability should be expected.
Characterization of an Upper Guadalupian Barrier-Island Complex from the Middle and Upper Tansill Formation (Permian), East Dark Canyon, Guadalupe Mountains, New Mexico
Authors: Parsley M. J. , Warren J. K.
Published: November 2010

The youngest Guadalupian shelf deposits in the Permian Basin region of West Texas and southeastern New Mexico are exposed in the Tansill Formation in East Dark Canyon, Guadalupe Mountains, New Mexico (Figs. 1 and 2). Previous investigations of the Capitan Limestone have suggested that Ochoan deposition was foreshadowed by Delaware Basin shallowing conditions (Babcock, 1974; Toomey and Babcock, 1983) and increasing restriction of basinal and shelf waters (Given and Lohmann, 1985) at the end of the Guadalupian. The deposits of the middle and uppermost Tansill Formation (Tyrrell et al., 1978) in East Dark Canyon provided the opportunity to describe and interpret the latest pulses of Guadalupian back-reef sedimentation in the barrier-island complex of the shelf.
Peritidal Facies of the Guadalupian Shelf Crest, Walnut Canyon, New Mexico
Authors: Neese Douglas G.
Published: November 2010

The facies succession of shelf carbonates in the upper Yates and lower Tansill formations shows a complex progression of environmental conditions across the shelf through time. An interval approximately 50 m thick centered about the easily recognizable contact between the Yates and Tansill formations was studied in an outcrop belt 3.5 km wide and 11 km long parallel to, and 1 to 8.5 km shelfward of, the Capitan Limestone (Walnut Canyon, New Mexico). The stratigraphic interval includes three major outcrop-defined carbonate units; in ascending order, the Hairpin Dolomite (Yates Formation), Triplet Dolomite (Yates Formation), and Basal Tansill Dolomite (Fig. 1), which have been subdivided into eight fabric-specific facies (Neese and Schwartz, 1977).

The geological literature of the Guadalupian shelf is extensive; King (1948), Newell et al. (1953), and Hayes (1964) concentrated primarily on broad stratigraphic relationships, lithologic features, and biota of shelf sediments and their reef and basinal equivalents. More genetic sedimentologic considerations of the Guadalupian shelf strata and their environments have been presented by Dunham (1972), Smith (1974), Pray and Esteban (1977), Neese (1979), Sarg and Lehmann (1986), and Tye (1986). The focus of this study is on the facies relationships of the grainstone and packstone facies of Dunham (1972) and Smith (1974).
Stratigraphy and Sedimentology of the Back-Reef Upper Queen-Lower Seven Rivers Strata, Goat Seep-Capitan Reef Complexes (Middle-Late Guadalupian, Permian), Southeast New Mexico
Authors: Sarg J. F. (Rick)
Published: November 2010

The uppermost 27 m of the Shattuck Member of the Queen Formation (Middle Guadalupian) and the lower 156 m of the overlying Seven Rivers Formation (Late Guadalupian) represent portions of two depositional sequences (Fig. 1). A subaerial sabkha surface near the top of the Shattuck Member is interpreted to be a sequence boundary and separates the two sequences. This disconformity is widespread over the Permian Basin, correlates with a toplap surface at the Goat Seep platform margin, and suggests a major sea-level drop at the end of Goat Seep deposition. Deposition of the basin-restricted Manzanita Member of the Cherry Canyon Formation is interpreted to have occurred during this lowstand in sea level. The immediately overlying 7 to 11 m of the topmost Shattuck contains fossilized and dolomitized Permian soil caliche (dolocalcrete). The dolocalcrete occurs in a repeated series of soil profiles overlain by evaporite solution residues. These dolocalcrete cycles are interpreted to have been deposited during a time of slowly rising sea level toward the end of the Manzanita lowstand and just prior to deposition of the Capitan Reef Complex (Sarg, 1985).

The dolocalcretes consist of nodular, massive, and mottled textures containing clotted and fractured micrite, microspar, equant spar-filled solution channels, coated fractures, and pisolites similar to modern caliche fabrics. Profiles are thin (approximately 0.5 m) and incomplete, and record short-lived soil-forming conditions with little external addition of CaCO3. The upper surfaces of the dolocalcretes are hard and undulatory, and erosional in part. The overlying evaporite solution residues are composed of interbedded green/red clayey siltstone and thin, discontinuous zones of red calcitic dolomite. The dolomite consists of small angular clasts of microcrystalline dolomite in a coarsely crystalline calcite matrix. Overlying dolomite beds are commonly brecciated (Sarg, 1977, 1985).
The Massive Facies of the Capitan Limestone Guadalupe Mountains, Texas and New Mexico
Authors: Babcock Jack A. , Yurewicz Donald A.
Published: November 2010

The Guadalupe Mountains provide dramatic exposures of the Capitan Limestone along the northwest margin of the Delaware Basin. These exposures provide unparalleled opportunities to examine lateral and vertical variations in the Capitan Limestone along a portion of the basin margin. Our work (Babcock, 1974, 1977; Yurewicz, 1976, 1977a) focused on outcrops of the massive facies of the Capitan Limestone in Slaughter, McKittrick, Walnut, and Dark canyons, and was supplemented by studies in Big, Rattlesnake, Bear, and Pine Springs canyons and Jurnigan Draw. These exposures show distinct, progressive changes in the Capitan as it prograded into the Delaware Basin. This paper summarizes those observations (Table 1). In order to document changes within the Capitan, we have divided it into three informal stratigraphic units: the lower, middle, and upper Capitan equivalent to the Seven Rivers, Yates, and Tansill formations on the shelf (Fig. 1). It is important to emphasize that our observations, although extensive, are not necessarily representative of the entire reef trend or even the entire exposed trend in the Guadalupe Mountains.
Large-Scale Channel Development within the Capitan Reef Complex - Evidence from Carlsbad Caverns
Authors: Harwood Gill M.
Published: November 2010

Carlsbad Caverns have formed within the uppermost Capitan reef and, where the cavern margins have not been coated with cave formations, allow examination of three-dimensional transects through the reef and adjacent facies. This study was made within Left Hand Tunnel, which is developed mostly on one stratigraphic-level within the reef facies (Fig. 1a). Although in situ reef is developed both at the entrance to the tunnel and further along the tunnel, mapping has identified an area, commencing near the western end of the tunnel, where large rotated blocks of reef facies sediments are present (Fig. 1b). A further, smaller area of rotated reef facies blocks is present near the eastern end of the tunnel (Fig. 1b). These areas are interpreted as paleochannels which developed within the reef. The western paleochannel is some 230 m wide by over 25 m deep. The size of the eastern paleochannel cannot be determined as the surrounding areas are covered by cave formations.
An Investigation of the Use of Paleomagnetic Techniques in a Carbonate Terrane - The Capitan Reef Complex, Southwestern U.S.A.
Authors: Darke Gill
Published: November 2010

Paleomagnetic methods have been used to obtain both qualitative and quantitative data concerning the depositional and diagenetic environments of rocks from the Capitan Reef Complex (Guadalupian, Upper Permian) in the Guadalupe Mountains of West Texas and New Mexico, southwestern U.S.A. The natural remanent magnetism (NRM) of rocks can be dated using paleomagnetic methods. This information on absolute ages can place constraints on the timing of depositional and diagenetic events. The study of magnetic minerals in rocks can also yield qualitative data concerning the nature of the system in which those minerals developed.
Simulation of the Capitan Shelf Margin (Late Permian, Guadalupian) of West Texas/New Mexico, A Response to Eustatic Change and an example of the use of Sedpak
Authors: Kendall C. G. St. C. , Strobel J. , Tang J. , Bezdek J. , Moore P. , Cannon R. , Biswas G.
Published: November 2010

The interactive computer simulation, SEDPAK, can track the sedimentary geometries produced by the filling of a two-dimensional basin from both sides, with a combination of clastic sediment and in situ carbonate growth (Strobel et al., 1987, 1988; Heiland-Hansen et al., 1988; Scaturo et al., 1988). The simulation program is implemented in 'C' and has been executed on Apollo and Sun workstations using graphical plotting functions based on the 'X' windows system. Sediment geometries are plotted on the graphics terminal as they are computed, so the user can immediately view the results. Then, based on these observations, the parameters can be repeatedly changed and the program rerun till the user is satisfied with the resultant geometry.

SEDPAK models geometries of clastic and carbonate sediments as they evolve through time and respond to depositional processes that include tectonic movement, eustasy, and sedimentation. Clastic modeling includes sedimentary bypass and erosion and sedimentation in alluvial and coastal plains, marine-shelf, basin-slope, and basin-floor settings. Carbonate modeling includes progradation, the development of hard grounds, downslope aprons, keep up, catch up, back step, and drowned reef facies, as well as lagoonal and epeiric facies. Also included is the capability to model extensional vertical faulting of the basin, sediment compaction, and isostatic response to sediment loading.
Subaqueous Gravity Flows in the Rader Member, Capitan Reef Complex (Permian), Delaware Mountains, West Texas
Authors: Lawson Ellen C.
Published: November 2010

The Rader Member contains coarse, allochthonous carbonate debris deposited on low-angle slopes (<10°) basinward of a ~500 m, higher-angle (30°) foreslope (Rigby, 1953; King, 1948). Subaqueous gravity flows fill channels which have up to 40 m of relief. Bed thickness for a single flow ranges from <1 m to as much as 15 m. Some mass flows are traceable >6.5 km parallel to depositional strike and extend >17 km southeast from the toe-of-slope into the Delaware Basin. A previously undocumented, prominent basin-sloping erosion surface occurs at the base of the mass flows and truncates 55 m of section in the toe-of-slope (Fig. 1). The angle of truncation is as high as 7° in the toe-of-slope and diminishes to <1° along the basin slope.

Subaqueous gravity flows in the Rader section exhibit features which suggest deposition from debris flows, turbidity flows, and possibly from density-modified grain flows (or grain flow-debris flow (Hampton, 1979)). Features which imply a debris-flow origin include poorly sorted and graded debris, a wide range of clast sizes, chaotic orientation of clasts, matrix support, and some large rafted clasts near the top of the bed. Atypical features observed are a fine, quartz-rich sand matrix with a small amount of mud (<1%) and appreciable rounding of the clasts. Rader debris flows were competent to carry limestone boulders up to 10 m across in their longest exposed dimension.
Depth Evolution of the Delaware Basin - Castile/Salado Transition
Authors: Hovorka Susan D.
Published: November 2010

Ochoan evaporites of the Castile and Salado formations in the Delaware Basin contain information about the final stages of basin evolution, specifically regarding the nature of the connection to the ocean and stability of local sea level. Core from the Gulf PDB-03 research well, Menton area, Loving County, Texas, was examined from near the base of the Castile Formation to the uppermost preserved halite in the Salado Formation (Figs. 1 and 2) to investigate evaporite depositional environments, especially with respect to paleodepth. A list of criteria for interpretation of paleodepth was developed (Table 1). These criteria are based on (1) comparison of observed evaporite fabrics with similar fabrics in modern and other ancient examples, and (2) interpretation of how observed evaporite processes would effect fabrics in different settings. Comparison of depth criteria with sequences of fabrics observed in the Castile and Salado formations shows systematic textural variation from the base to the top of individual depositional cycles as well as the entire sequence (Figs. 1 and 2).
The Geology of Lechuguilla Cave, New Mexico
Authors: Jagnow David H.
Published: November 2010

Lechuguilla Cave is located 3½ miles WNW of Carlsbad Cavern in the headwaters of Lechuguilla Canyon. The more shelfward position of this cave, combined with its great depth, allows the geologist a rare opportunity to study the very heart of the Permian-age Capitan Reef Complex.
The Evolution of the Delaware Basin - Preliminary Results
Authors: Hill Carol A.
Published: November 2010

This paper summarizes an ongoing research project on the Delaware Basin studying interrelationships between oil-gas, sulfur deposits, Mississippi Valley-type (MVT) ores, and cave genesis. Such an integrated approach was taken by Hill (1987), who suggested that basinal H2S - generated by oil-anhydrite reactions at the Castile-Bell Canyon contact - was the ultimate source for the sulfuric-acid speleogenesis of Guadalupe caves and for MVT ores in carbonate rock along the margins of the basin.
The Role of Hydrogen Sulfide in the Evolution of Caves in the Guadalupe Mountains of Southeastern New Mexico
Authors: DuChene Harvey R. , McLean John S.
Published: November 2010

Part of the Permian Capitan Reef Complex is exposed in the Guadalupe Mountains of southeastern New Mexico and western Texas (Fig. 1). The reef complex includes the Capitan Limestone and the carbonate backreef beds of the Artesia Group that comprise a lithosome called the Capitan aquifer (Hiss, 1976). This lithosome contains well-developed solution openings that range from microscopic to voids the size of Carlsbad Cavern. This solution porosity was once thought to be caused by weak carbonic acid in the phreatic zone within the Capitan aquifer (Bretz, 1949). During the last 15 years, however, workers have obtained evidence indicating that sulfuric acid may be a major cause of carbonate dissolution (Egemeier, 1973; Jagnow, 1977; Palmer et al., 1977; Maslyn, 1979; Davis, 1980; Kirkland, 1982; and Hill, 1987). Sulfuric acid is generated when oxygen (O2) is introduced into solutions containing dissolved hydrogen sulfide (H2S) gas (Hill, 1987).

Hydrogen sulfide is common in subsurface formations in southeastern New Mexico (Bjorklund and Motts, 1959; Hinds and Cunningham, 1970, pp. 4 and 7). In southeastern New Mexico and elsewhere along the subsurface trend of the Capitan reef, H2S is present in accumulations of oil and gas and in associated saline water (Schram, 1956a, p. 103, and 1956b, p. 307; Wilson, 1956, p. 179; and Roswell Geological Society Symposium Committee, 1956a, p. 181, and 1956b, p. 291).
Architectural Controls on the Recovery of Hydrocarbons From Sandstone Reservoers
Authors: Tyler Noel , Finley Robert J.
Published: November 2010

Development of the 330-billion-bairel oil resource remaining in United States reservoirs after conventional primary and secondary recovery will be dependent on the advanced understanding of facies relations and compartmentalization inherent in reservoir depositional systems. Style of deposition, as reflected in internal reservoir architecture, defines flow units that determine how a reservoir drains, where hydrocarbons remain unrecovered at the interwell (macroscopic) scale, and what approaches will be effective in accessing unrecovered oil. A substantial part of the unrecovered oil resource is nonresidual oil that, although mobile in the reservoir, remains unrecovered owing to poor contact by existing wells and vertical or areal bypassing by the waterflood front.

Because heterogeneity style is a product of depositional system, it is predictable and can be characterized in terms from low to high in a lateral and vertical sense. For sandstones, the wave-dominated deltas, barrier cores, and sand-rich strand plains show a low degree of heterogeneity in both dimensions, whereas the highly aggradational backbarrier fans, fluvially dominated deltas, and fine-grained meander belts show a higher intensity of heterogeneity. Other systems can be similarly classified. The resulting matrix leads to delineation of targeted approaches to incremental oil recovery specifically tailored to the distribution of remaining oil saturation. Such approaches, optimized to the character of the depositional system, may include geologically targeted infill drilling, selective recompletion, horizontal drilling, and strategic cross-reservoir flooding involving flood redesign and profile modification. Such techniques are herein termed Advanced Secondary Recovery (ASR) and represent advancements in technology that will lead to near- and mid-term improvements in efficiency that set the stage for later approaches to Enhanced Oil Recovery (EOR).
Hierarchies of Architectural Units in Terrigenous Clastic Rocks, and Their Relationship to Sedimentation Rate
Authors: Miall Andrew D.
Published: November 2010

Sedimentation rates vary by eleven Orders of magnitude and the physical scale of depositional units varies by fourteen orders of magnitude. These variations suggest a hierarchical ordering of depositional units in clastic sedimentary deposits.

A tentative grouping of architectural units has been constructed, based primaril on the recurrence interval of the depositional events: Group 1 deposits are the product of events taking tens of seconds to a few minutes, such as the burst-and-sweep activitiy of a fluid boundary layer. Group 2 deposits are those formed in a few minutes to a few hours, and include ripples and dune depositional increaments. Group 3 deposits are those forming in a few hours to a day or two, including diurnal tidal bundles. Group 4 deposits form in days to a few months, and include such processes as neap-spring tidal cycles:group 4 deposits also encompasse the spacing of many storm events. Group 5 deposits represent one to a few years, such as seasonal events (spring runoff, glacial varves), and occasional violent storrms. Group 6 is for sedimentary processes of a hundred to thousands of years duration, including the evolution of fluvial macroforms, eolian dunes and tidal sand-wave fields. Group 7 represents longterm geomorphic processes, over thousands to tens of thousands of years, such as channel and draa migration. Group 8 processes extend over tens to hundreds of thousands of years, and represent such depositional elements as channel belts, ergs and sand-ridge fields. Fifth-order stratigraphic sequences, many generated by Milankovitch causes, are also of this rank. Group 9 processes are of hundreds of thousands to a few million years duration, such as fourth-order stratigraphic cycles (e.g., major cyclothems, shelf coarsening-upward cycles driven by thrust-loading events, etc). Deposits assigned to group 10 are those taking a few millions to tens of millions of years, including third-order stratigraphic cycles.

Instantaneous sedimentation rates are of a similar order of magnitude within each group, ranging from 105 m/ka for the smallest scale of deposit, to 10-1 m/ka for groups 9 and 10. Deposits of each group may be defined, in some cases, by enclosing bounding surfaces. Hierarchiesof such surfaces have been erected for fluvial and eolian deposits and for some suites of estuarine and shelf bedforms.

Investigations of each group require different techniques. Deposits up to group 7 and possibly 8 may be documented in expectionalyy good outcrop. Studies of moderm deposits of groups 6 to 8 may be carried out using high-resolution geophysical techniques. Groups 7 to 10 require investigation and reconstructio using basin-mapping techniques based on careful correlation. Subsurface well and seimic data may be employed.
Photomosaics of Outcrops
Authors: Wizevich Michael C.
Published: November 2010

Photomosaics can be useful tools for understanding and communicating geologic features expressed on outcrop faces. In order to utilize photomosaics properly, maximum resolution and minimum geometric distortion of the features is necessary. Maximum resolution is best obtained by using quality equipment and by attending to proper technique. In some cases increasing contrast will improve resolution; various methods can be utilized.

Sufficient overlap of photographs in the construction of photomosaics will remove distortion in most situations. A common problem is perspective distortion, the convergence of vertical lines. This occurs when the film plane and outcrop face are not parallel and results in curved or "smiling" mosaics. When it is not feasible to obtain parallelism, several methods can be used to help correct this problem. In many situations fitting a 35-mm camera with a perspective control lens is the simplest and most economical strategy for reducing or eliminating the problem.
The Large-Scale Architecture of The Fluvial Westwater Canyon Member, Morrison Formation (Upper Jurassic), San Juan Basin, New Mexico
Authors: Cowan E. Jun
Published: November 2010

The Westwater Canyon Member of the Morrison Formation (Upper Jurassic) has previously been interpreted as consisting of fluvial “channel systems” tens of kilometers wide and tens of meters thick. Reinvestigation of the member indicates that these “channel systems” actually represent post-depositional aquifer conduits, defined instead by differing sandstone colors, rather than primary depositional features. The member is composed of amalgamated, individual fining-up sandstone sheets each about 5-10 m thick. The absolute widths of these sheet sandstone bodies are at least 1 km and possibly exceed several kilometers. The width.thickness range of the sandstone sheets are well within the typical values of sandstone body dimensions reported from other fluvial sandstones, and are interpreted to represent aggradational channel-belts. Sandstone bodies thicker than about 12 m are the result of amalgamation of these individual unit sandstone bodies, and do not represent individual channel belts as interpreted previously.

Internally, the sheets contain abundant concave-up troughs typically 30 m wide and 5 m thick, filled both laterally and vertically with inclined parallel- to low-angle cross-stratified sandstone, in places exhibiting parting lineation. The laterally-limited extent of these large troughs and nature of their internal fills suggest that they represent short-lived scour fills rather than confined elongated channels. The concave-up erosional base, a negative feature, was most likely formed due to large-scale flow separation within a wider and shallower channel. Physical conditions similar to stream-flow convergence at channel confluences may be responsible for their formation. The abundant preservation of these troughs in the Westwater Canyon Member is consistent with the expected poor preservation of positive barforms in a sweeping, sandy-braided channel belt.

Review of the literature indicates that inferred channelbelt sandstone bodies mostly fall within the thickness range of 1 to 12 m, irrespective of their interpreted fluvial style. Post-depositional large-scale reservoir conduits are also expected to fall within this range for sandy fluvial systems-. Deviations from this range are due to amalgamation of the sandstone bodies or increased grain-size heterogeneity, resulting in an increase and decrease, respectively, of the conduit size.
Architectural-Facies Analysis of Nonmarine Depositional Systems in The Upper Triassic Chinle Formation, Southeastern Utah
Authors: Dubiel Russell F.
Published: November 2010

The Upper Triassic Chinle Formation in southeastern Utah is a sequence of continental strata deposited in a back-arc cratonic basin. Archi tectural-faries analysis of exposures in sub-parallel canyons and in cliffs surrounding structural uplifts reveals an intricately interbedded fluvial-deltaic-lacustrine system characterized by: 1. mobile fluvial-channel belts consisting of stacked, high- and low-sinuosity channel complexes; 2. overbank deposits, including levees, paleosols, marshes, and small floodplain lakes interiingered with crevasse splays and lacustrine deltas; and 3. extensive lacustrine-basin, lacustrine-mudflat, and eolian sandsheet strata deposited throughout the entire study area. Stratigraphic panels of closely-spaced measured sections oriented both perpendicular and parallel to depositional dip depict the facies architecture both within the extra-channel strata and the relations of the extra-channel deposits to adjacent channel complexes.

In the Shinarump and Monitor Butte Members in the lower part of the Chinle Formation, fluvial-channel complexes interfinger with extra-channel facies. These extra-channel facies include levees, crevasse splays, and wetland complexes consisting of lacustrine deltas, lakes, and marshes. In the Moss Back and Petrified Forest Members in the middle part of the Chinle, fluvial-channel complexes interfinger with floodplain strata characterized by paleosols and crevasse splays. Locally, paleosol horizons and lake and marsh deposits serve as marker beds in three dimensions. The Owl Rock and Church Rock Members in the upper part of the Chinle are dominated by laterally extensive lacustrine-basin, lacustrine-mudflat, and minor eolian sandsheet strata that extended throughout the study area.
Variations in Alluvial Architecture Across The Oligo-Miocene Huesca Fluvial System, Ebro Basin, Spain
Authors: Hirst J.P.P.
Published: November 2010

The Huesca System is interpreted as a terminal, distributive fluvial system. Flow across this ‘fluvial fan’ was largely through a network of well-defined channels and the deposits typically consist of channel-sandstone bodies enclosed within floodplain fines. Amalgamation of the sandstone units varies depending on the location within the system. Lateral profiles are used to show that there are systematic and broadly quantifiable variations in the alluvial architecture across the system.

A precise apex for this distributive system cannot be determined, and thus a datum line has been constructed within the proximal region. This datum has enabled plots to be constructed showing medial to distal variations. The results indicate 1. the proportion of in-channel sediment decreased distally; 2. the sandstone bodies thin distally and thus the paleochannels were becoming shallower, and 3. sheet sandstones deposited by laterally unstable channels are prevalent medially, whereas more stable channels, indicated by ribbon sandstones, were more common distally. The decrease in channel depth and in-channel component are probably the result of evaporative water loss, channel bifurcation and gradient decrease. The increased channel stability distally is interpreted to be the result of reduced ability to erode the banks, more frequent avulsion and ephemeral flow.

The alluvial architecture of the ‘peripheral areas’ of the system, adjacent to the thrust front that defines the northern margin of the basin, differs slightly from the main part of the system. The main difference is the higher frequency of ribbon sandstones in the peripheral areas. This may be due to the tectonic instability of the area near the thrust front and periodic inundation by the marginal alluvial fans. Also, these marginal fans would have increased the flow paths of streams into the peripheral parts of the main system.

The study has applications to hydrocarbon exploration in analogous sequences. Radial variations in reservoir potential are indicated and the extents of sandstone bodies in the subsurface may be estimated from the width-thickness relationship determined from the medial part of the system.
Three-Dimensional Reservoir Architecture of a Valley-Fell Sequence and a Deltaic Aggradational Sequence
Authors: Eschard R. , Ravenne C. , Houel P. , Knox R.
Published: November 2010

In the Middle Jurassic series of the Cleveland basin (Northeastern England), the Scalby Formation comprises two main members, interpreted as a valley-fill complex overlain by a deltaic aggradational series. The valley was incised during a relative sea-level drop and infilled during a stepped relative sea-level rise by a retrogradational fluvial to estuarine complex. The valley fill is composed of three superposed sandsheet prisms showing, respectively, 1. fluvially dominated straight channels, 2. tidally influenced meander belts, and 3. a mixed fluvial-tidal meander belt The deltaic aggradational member corresponds to highstand deposits. Small ribbons or meandering channels are isolated in shaly floodplain and lacustrine facies.

A precise three-dimensional reservoir reconstruction has been carried out on a 1-km2 area using cliff sections, drill cores, wireline logs and petrophysical measurements. Accurate reservoir reconstructions are presented here as large cross sections in terms of lithology, porosity and permeability. At Cloughton, the valley-fill member consists of a lower and upper prism. Each corresponds to a channel-fill stage with a basal aggradational fluvial unit overlain by an estuarine or paralic transgressive unit The basal prism displays a fluvial stacked-chaanel unit with side bars and sand or clay plugs, the tops of which are truncated by a transgressive surface. The unit is overlain by an estuarine sand-flat complex. The upper prism corresponds to tidally-influenced meander belts with hectometric point bars composed of argillaceous sandstone and siltstone. It is capped by shaly marsh deposits, corresponding to the period of maximum flooding of the valley fill. The aggradational deltaic member consists mainly of delta-plain shales with multistory ribbon channels and wide meander belts.

The best potential reservoirs are located in the basal fluvial sucked channels of the valley fill. Reservoir qualities decrease in the estuarine sand-flat complex and are very poor in the mixed fluvial-tidal meander belts. The small ribbon channels generally constitute good but small disconnected reservoirs. The sequence stratigraphy of the Scalby Formation shows that reservoir geometry and architecture could be controlled by minor relative sea-level variations.
Constructing a Three-Dimensional Rock-Property Model of Fluvial Sandstones in The Peoria Field, Colorado
Authors: Chapin Mark A. , Mayer David F.
Published: November 2010

Fluid-flow units and fluid-flow barriers are distinguished through mapping distributions of facies and bounding surfaces of coalesced channel belts within the Lower Cretaceous J Sandstone in the Peoria field, Colorado. Measured rock properties (porosity, permeability, relative permeability, and capillary pressure) were calibrated to facies, which were distinguished by common associations of grain sizes, clay content, and sedimentary structures. The three-dimensional distribution of rock properties in the J sandstone reservoir was obtained through facies mapping. Within a meander belt, trough cross-stratified and clean, ripple-laminated point-bar sandstones act as flow units, and clay-rich abandonment fills act as flow barriers. Hydraulic communication between vertically stacked channel belts depends on the thickness and continuity of muddy sandstones having abundant clay inclusions that commonly overlie basal scour surfaces. The effect of smaller scale sedimentary bounding surfaces on fluid flow was not measurable at the scale of the well spacing and engineering data available. Compartmentalization of the reservoir is indicated by two elevations of oil-water contacts along the downdip, west flank of the field. This is explained by a concentration of abandonment-fill facies and a lack of hydraulic communication between coalesced channel belts in the center of the field. Pre- and post-injection production patterns are explained by the geologic model.
Regional to Subregional Facies Architecture of River-Dominated Deltas in The Alberta Subsurface, Upper Cretaceous Dunvegan Formation
Authors: Bhattacharya Janok P.
Published: November 2010

The Dunvegan Formation (mid-Cenomanian) comprises a thick clastic wedge deposited in the West Alberta foreland basin. This wedge consists of a complex series of interbedded shales, siltstones, and sandstones and has been subdivided into seven allomembers (A-G), each separated by widespread flooding surfaces.

Allomember E consists of four offlapping, shingled, heterolithic sedimentary units that progressively built seaward to the southeast. Isolith maps of the sandstones within these shingles reveal deltaic morphologies consisting of well-developed sandy depositional lobes fed by sandy distributary channels separated by mudstone-dominated interchannel and interlobe areas. The plan-view morphologies and facies successions in the lobes are typical of prograding river-dominated delta fronts.

Superposition of sandbodies within each shingle reveals the autocyclic fashion in which the sedimentary basin was filled. The arcai pattern and scale of overlapping depositional delta lobes are similar to those of the Mississippi delta during the last 5 ka.
Architectural Patterns in Large-Scale Gilbert-Type Delta Complexes, Pleistocene, Gulf of Corinth, Greece
Authors: Ori Gian gabriele , Roveri Marco , Nichols Gary
Published: November 2010

Large-scale Gilbert-type delta deposits occur on the southern side of the Gulf of Corinth in Greece. They accumulated adjacent to the very steep margins of listric-fault blocks. The deltaic complexes consist of very thick (up to 700 m) foreset packages that pass into bottomset strata, which, in turn. pass into thin-bedded turbidites. Topset deposits are well preserved and are the keys to interpreting the fan-delta bodies in architectural terms. The geometric pattern is discussed in terms of accommodation, that is the vertical space made available for the sedimentation. Where there is no accommodation, the topset environment is bypassed and, geometrically, toplap boundaries occur. With increasing accommodation, fluvial topset strata are formed: they pass downdip into the foreset beds. At higher accommodation values, transgressive deposits occur. If accommodation is too high, the transgressive sediments are drowned and foreset beds form on top.
Sedimentology of a Sequence Boundary Within The Nonmarine Torrivio Member, Gallup Sandstone (Cretaceous), San Juan Basin, New Mexico
Authors: Miall Andrew D.
Published: November 2010

The Gallup Sandstone of northwest New Mexico consists of a series of sandstone tongues, deposited in strandplain environments, interbedded with fine-grained marine sediments of the Mancos Shale. The uppermost tongue includes shales and thin sandstones of the "nonmarine Gallup" and a prominent sandstone unit, the Torrivio Member. The latter has been interpreted as fluvial in origin. Earlier work by other researchers interpreted the Torrivio as the basal member of a transgressive sequence, which includes in its upper part open-marine shelf deposits of the upper Mancos Shale.

The nonmarine Gallup contains some evidence of marine influence and is interpreted here as a back-barrier tidal-flat or lagoonal deposit The overlying Torrivio Member is fluvial in its lower part, but some sections along the west and south flank of San Juan Basin contain tidal sand waves in the upper part of the member. A prominent bounding surface separates fluvial from tidally influenced beds in some localities, and it is suggested here that this is the position of the main sequence boundary, marking the time of maximum regression. The succession up to this bounding surface is that of a regressive, strandplain to fluvial parasequence. Above the surface, tidal deposits, probably representing estuarine sand shoals, form the base of a transgressive sequence.

Maximum regression may record the time of lowest relative sea level. However, there is no independant evidence of sea-level change. Current models that purport to explain changes in fluvial accomodation space with reference to changes in base level are flawed, and an alternative model of regional tectonism and resulting increases in sediment supply cannot be ruled out as a mechanism for the generation of fluvial tongues in foreland basins, such as the Torrivio Member.
Evolution of Middle Eocene Tide-Dominated Deltaic Sandstones, Lagunillas Field, Maracaibo Basin, Western Venezuela
Authors: Maguregui Jesus , Tyler Noel
Published: November 2010

Interpretations of net-sand/percent-sand maps, well-log cross sections, vertical log-pattem trends, core descriptions, and log facies suggest that several aggradational tide-dominated deltaic cycles were deposited in Lagunillas field. Western Venezuela, during a widespread transgressive event at the end of the Middle Eocene. Reservoir lithofacies present are estuarine distributary-channel sandstones, tidal sand-ridge sandstones, prodelta/shelf assemblages, and tidal-channel facies. Geometries of the sandstone bodies are highly dip elongate and strike lenticular. These shoestring sands maintain their widths in a landward direction (west) and splay outward at their seaward limit (east), where loci of sand deposition occurred. Eastward, the sequence thickens concomitant with a decrease in sand-to-shale ratio. Individual correlatable depositional units are interpreted to be discrete delta lobes established during progradation of estuarine distributary systems. These single delta lobes shifted laterally along strike during infilling of deltaic depositional axes. Laterally persistent low-resistivity shale markers stratigraphically bound several delta lobes, which together constitute one of five deltaic cycles present in the upper reservoirs of the field.
Architecture of Modern Subtidal Dunes (Sand Waves), Bay of Bourgneuf, France
Authors: Berné Serge , Durand Jacques , Weber Olivier
Published: November 2010

Improvements of geophysical acquisition and processing techniques and coring data give a new insight into the architecture of large subaquatic dunes. A field of dunes, with amplitudes ranging from 0.7 to 9.4 m. has been studied in the Bay of Bourgneuf. near the Loire inlet, France. Results show that the bedforms have steep lee sides and distinct asymmetry, and that the internal structure consists of steeply-dipping cross-strata truncated by several orders of bounding surfaces. The true dip angle of the laminae, measured on a core collected from a 3.6-m-high dune, suggests the existence of sandflow or sandfall processes, similar to those previously described in eolian dunes or small intertidal bedforms. The combined effect of waves and tidal currents is proposed to explain the strong asymmetry of the structures and the origin of bounding surfaces. Even if these dunes can be considered as tidal bedforms, seismic and core data suggest that the internal structure is probably the result of episodic, rather than cyclic, processes. If compared to the sand waves described by Visser from sheltered environments, this type of sandbody should be difficult to interpret in the stratigraphic record, because it does not display any "tidal criteria" (tidal bundles, mud couplets).