bluuebunny/crossref_metadata_2025 huggingface dataset:
National Petroleum Reserve – Alaska Core Workshop 2001
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. Until recently, this activity was focused mostly on State lands and waters, as well as the Federal offshore immediately adjacent to the State-Federal boundary.

The 1994 discovery of the Alpine field (>400 mmbo reserves) on the Colville River delta and the production performance of the nearby Tarn field (>70 mmbo reserves) stimulated exploration interest in the National Petroleum Reserve - Alaska (NPRA). Consequently, a lease sale was held in eastern NPRA in May 1999, the first onshore Federal lease sale on the North Slope in 15 years. Of approximately 4 million acres offered in that lease sale, more than 867,000 acres were leased for nearly $105 million in total successful bids. Three wells were drilled on NPRA leases during the winter 2000 season and many more are planned for drilling during the winter 2001 season. Results of the winter 2000 exploration drilling remain proprietary.

The focus of NPRA exploration appears to include both structural and stratigraphic obj ectives that may include strata spanning much of the stratigraphic column. The purpose of the core workshop is to provide an opportunity to examine
Sequence Stratigraphy and Sedimentology of Beaufortian Strata (Jurassic – Lower Cretaceous) In The National Petroleum Reserve – Alaska (Npra)
Authors: Houseknecht David W.
Published: November 2010

Beaufortian strata (Jurassic - earliest Cretaceous) in NPRA have become a focus of exploration since the 1994 discovery of the nearby Alpine oil field. Interpretation of sequence stratigraphy and depositional facies from a regional 2-D seismic grid and well data has resulted in the definition of four major depositional sequences that each display unique stratal geometries and thickness trends across NPRA.

Sequence K1 (Lower-Middle Jurassic) accumulated in a depocenter in northcenteral NPRA. Constituent depositional sequences include lowstand (LST), transgressive (TST), and highstand (HST) systems tracts. Sequence K2 (Oxfordian-Kimmeridgian) is a composite of higher-order depositional sequences that each reflects a forced regression, which caused widespread erosion across northcentral NPRA and accumulation of the derived sediment at the shelf margin in lowstand systems tracts. Subsequent flooding of the shelf resulted in deposition of transgressive systems tracts that commonly include well-winnowed, upper shoreface sandstones capped by a condensed section of fissile shale, forming good stratigraphic trapping potential. Sequence K3 (Valanginian) displays relatively distal facies character, suggesting high relative sea level during most of the depositional history. An important exception is the presence of a transgressive systems tract at the base of K3 that contains winnowed, shoreface sandstones. Sequence K4 (Hauterivian) is a shelf-margin wedge that developed as the result of tectonic uplift along the Barrow Arch. It comprises lowstand and transgressive systems tracts that display stratal geometries suggesting dynamic incision and synsedimentary collapse of the shelf margin.

Cores of Beaufortian strata from NPRA exploration wells display a variety of key stratigraphic surfaces and depositional facies. When integrated with the regional grid of public domain seismic data, these provide a unique opportunity for interpreting the sequence stratigraphy and depositional systems oil-prospective strata in a frontier province.
Stratigraphy and Lithofacies of Lisburne Group Carbonate Rocks (Carboniferous – Permian) in the National Petroleum Reserve – Alaska
Authors: Dumoulin Julie A. , Bird Kenneth J.
Published: November 2010

Carbonate rocks of the Lisburne Group (Carboniferous-Permian) occur widely throughout northern Alaska. In the NPRA, seismic mapping and well penetrations show that the Lisburne occurs throughout the subsurface except in northernmost NPRA where it is missing by depositional onlap. Lisburne strata encountered in 11 exploratory wells in the northern part of the NPRA are essentially undeformed, consist of limestone and lesser dolostone, sandstone, siltstone, and shale, encompass a wide array of chiefly shallow-water facies, and range in age from Early Mississippian to Permian. Basins and platforms that formed during Mississippian (and possibly Devonian) time greatly affected depositional patterns of the Lisburne. Total thickness of the Lisburne in northern NPRA wells varies from almost 4000 ft in the Ikpikpuk-Umiat Basin to 300 ft on the north edge of the Fish Creek Platform. Lisburne strata of Mississippian age are found in northeastern NPRA, comprise three subunits (lower limestone, middle dolostone, and upper limestone) and are oldest (Osagean) in the Ikpikpuk-Umiat Basin. All wells that penetrated the Lisburne in northern NPRA encountered rocks of Pennsylvanian age; these intervals are mainly limestone and characterized by decameter-scale shallowing-upward sequences. Lisburne sections of prob-able Early-middle Permian age range from thin (≤60 ft) intervals of dolostone and limestone in the Fish Creek Platform area to thick (500-1000 ft) successions of interbedded limestone and siliciclastic sediment in the Ikpikpuk-Umiat Basin and northwestern NPRA. Abundant non-carbonate detritus, primarily quartz and chert with locally notable plagioclase feldspar and metamorphic lithic clasts, occurs throughout the Lisburne Group in northern NPRA. Per-mian strata and a persistent non-carbonate detrital component are also seen in the Lisburne in subsurface beneath the Chukchi Sea (Hanna Trough) to the northwest, but are not found in Lisburne successions elsewhere in Alaska.
Stacked Island Facies in Tansill Outer-Shelf Platform, Dark Canyon, Guadalupe Mountains, New Mexico
Authors: Mazzullo S. J. , Bischoff W. D. , Hedrick C. L.
Published: November 2010

The Tansill Formation (Permian, Guadalupian) comprises the youngest back-reef platform facies of the Capitan Reef in the Guadalupe Mountains of New Mexico and Texas (Fig. 1). Here the Tansill is divided into "outer-shelf" and "shelf-crest" facies which pass landward into coeval bedded evaporites and sandstones (Pray, 1977; Mazzullo and Hedrick, 1985). The shelf-crest facies, consisting of peritidal dolomites with conspicuous pisolites, tepees, and some sandstones, is interpreted as a linear, low-lying island complex situated 1.6 km (1 mile) landward of the Capitan Reef (Pray, 1977; Mazzullo and Hedrick, 1985). It is therefore analogous to other island complexes of the Tansill in the subsurface (Ordonez, 1984) as well as to modern outer-shelf islands in Belize (Mazzullo and Reid, 1986). The outer-shelf facies consists mainly of biograins tones and, locally, patch-reefs deposited in shallow, high-energy environments (Mazzullo and Hedrick, 1985). Outcrops in an abandoned quarry near the mouth of Dark Canyon include spectacular exposures of stacked island deposits in the outer-shelf facies tract of the middle Tansill platform (Fig. 2A and B). These exposures lie within 0.8 km (0.5 miles) of the subsurface Capitan Reef shelf margin and are physically separated from contiguous shelf-crest facies (Fig. 2D). The occurrence of these islands is of particular significance in interpreting the depositional history of the Tansill platform, and their study provides critical information on sedimentation and diagenesis as they are related to relative sea-level fluctuations.
Depositional Facies and Cycles in Yates Formation Outcrops, Guadalupe Mountains, New Mexico
Authors: Borer J. M. , Harris P. M.
Published: November 2010

Four outcrops in the Guadalupe Mountains are investigated in order to evaluate two current models that describe the depositional setting of siltstones and sandstones in the Upper Guadalupian, Yates Formation. The outcrops are described and placed in their relative position along a dip-oriented cross section that is representative of the Yates Formation on the Northwest Shelf. Facies relations and cyclic stratigraphic sequences suggest that the siliciclastics were transported across a very shallow to subaerially exposed shelf during eustatic sea-level low stands and were trapped on the shelf during subsequent sea-level rises. Clastics near the shelf margin were reworked during the sea-level rises.
Shallow Marine Sheet Sandstones, Upper Yates Formation, Northwest Shelf, Delaware Basin, New Mexico
Authors: Candelaria Magell P.
Published: November 2010

Numerous studies have documented the lateral and vertical facies sequences of the Guadalupian-age Capitan-proximal carbonates of the Yates and Tansill formations on the Northwest Shelf of the Delaware Basin, New Mexico (Dunham, 1972; Hurley, 1978; Smith, 1974; Neese and Schwartz, 1977; Pray and Esteban, 1977). However, in contrast, relatively few detailed sedimentologic studies of the less abundant siliciclastic units that are interbedded with the shelf carbonates have been reported (Smith, 1974; Candelaria, 1982, 1983, 1988; Thorkelson, 1983). The lack of sedimentologic studies of the shelf sandstones has been due, no doubt, to the notable, and disconcerting apparent widespread, absence of visible primary stratification and bedforms indicative of physical processes and depositional environment. As a result, most interpretations of the shelf sandstone depositional environment have been made a priori and have remained largely unchallenged and unverified.

Candelaria (1982, 1983, 1988) described the sedimentological characteristics and lateral facies distribution of the upper two siliciclastic intervals of the Yates Formation as exposed along the outermost 5 km of the Northwest Shelf in the southeastern Guadalupe Mountains, New Mexico (Fig. 1). The two upper Yates sandstones are continuously traceable across the study area and well beyond (east) into the subsurface. The lateral continuity and uniformity of interval thickness on depositional strike is remarkable as is the absence of channeling within the sands or incisement into the subjacent carbonate units.
Facies Mosaic of the Lower Seven Rivers Formation, Mckittrick Canyon, New Mexico
Authors: Hurley Neil F.
Published: November 2010

This paper summarizes a detailed investigation of the sedimentology and stratigraphic setting of the lower Seven Rivers Formation in the Guadalupe Mountains, New Mexico (Hurley, 1978). Work is confined to superb exposures in North McKittrick Canyon of a lateral facies transition from bedded shelf carbonates and siliciclastic sediments to the massive facies of the lower Capitan Limestone. The major research questions addressed are:

1. What depositional processes and environments characterize the complex facies mosaic of the lower Seven Rivers Formation and the shelfward edge of the lower Capitan Limestone?

2. Did the shelf-to-basin profile in earliest Capitan time differ from later Capitan times (Yates and Tansill) where this transition has been more thoroughly studied?

3. What is the nature of the Seven Rivers to Capitan facies transition, and what does this transition imply as to growth rate of the early Capitan?
Stratigraphy and Sedimentology of the Shattuck Member (Queen Formation) and Lowermost Seven Rivers Formation (Guadalupian), North Mckittrick and Dog Canyons, Guadalupe Mountains, New Mexico and West Texas
Authors: Wheeler Christopher
Published: November 2010

The Permian Basin Complex is characterized by a prograding and aggrading shelf-marginal megafacies which is flanked by a shelf megafacies and a basinal megafacies. Guadalupian units of the shelf-marginal megafacies are the Goat Seep Dolomite and the younger, overlying Capitan Limestone. Shelf strata equivalent to these shelf-marginal units comprise the Artesia Group. The subdivisions of the Artesia Group are the Grayburg, Queen, Seven Rivers, Yates, and Tansill formations. In the Grayburg, Seven Rivers, and Tansill, a broad band of shelf carbonates separates the shelf-margin megafacies from bedded evaporites and evaporite-bearing carbonates further shelfward (Fig. 1). Similar rocks and relationships occur in the Queen and Yates, but, in addition, the Queen and Yates contain several siliciclastic intervals which extend like sheets across the shelf and up to the shelf margin. The Shattuck is one of these siliciclastic intervals. The origin of the siliciclastic intervals is still controversial, some workers advocating predominantly subaqueous transport over a submerged shelf, while others argue for predominantly eolian transport during low sea stands.
Goat Seep - Precursor to the Capitan
Authors: Crawford G. Allan
Published: November 2010

The Goat Seep Dolomite, which immediately underlies the Capitan Limestone, constitutes the lower third of the Guadalupian shelf-margin interval and formed the first large, high-angle, reef-like carbonate unit in the Permian Reef Complex of West Texas and New Mexico. The Goat Seep Dolomite and the Capitan Limestone are similar in that both consist predominantly of inclined strata deposited on a high-relief shelf margin with a steep edge of 25° to 30°, and both can be divided into three similar facies: a shelf-edge or reef facies, a high-angle foreslope, and a low-angle toe-of-slope facies. Shelf-to-basin relief ranged from about 250 m at the beginning of Goat Seep time to 600 m at the end of Capitan time (Fig. 1). The dominant fossils in both are sponges. However, the Goat Seep is not simply an older Capitan, but differs significantly in aspects of morphology, mineralogy, fossils, and cements. Compared to the Capitan, the Goat Seep (1) is largely dolomite; whereas, the Capitan is primarily limestone; (2) has a much thinner to absent shelf-edge or "massive" facies; (3) contains little or no skeletal boundstone, algae, or the problematic organism Tubiphytes, which are common in much of the Capitan (particularly the Upper Capitan); and (4) contains less coarse-fibrous and interparticle cement, interpreted to have an early marine origin.

The major similarities and differences between the Goat Seep and the Capitan formations are discussed below and are summarized in Figure 2. Most of the information on the Capitan comes from the work of Babcock (1974, 1977) and Yurewicz (1976, 1977). Data on the Goat Seep are largely from Crawford (1981).
Diagenesis of the Capitan Limestone, Upper Permian, Mckittrick Canyon, West Texas
Authors: Mruk Denise H.
Published: November 2010

This paper is a summary of a diagenetic study of calcite cements in the Capitan Limestone, McKittrick Canyon, West Texas (Mruk, 1985). This study deciphers the diagenetic history of the Capitan Limestone using basic field observations, detailed cathodoluminescence petrography, and carbon and oxygen isotopes.
Dolomitization Model for the Forereef Facies of the Permian Capitan Formation, Guadalupe Mountains, Texas-New Mexico
Authors: Melim Leslie A. , Scholle Peter A.
Published: November 2010

The Capitan Formation includes the massive "reef" and the bedded forereef slope facies of the Permian Reef Complex (Fig. 1). The ongoing controversy over the nature of the reef has not substantially affected interpretation of the bedded forereef slope portion of the Capitan. Whether the "reef" was a major wave-resistant barrier or not, it shed massive volumes of debris into the 600 m deep Delaware Basin allowing as much as 7 km of lateral progradation during Late Guadalupian time. The forereef talus facies contains allochthonous fragments of both reef and near-back-reef material; much of this detritus dips steeply into the basin (with primary dips of up to 35°) and interfingers at the base of the slope with siltstones of the Bell Canyon Formation. Material was transported downslope by rockfall, debris flow, turbidity current, and other processes, yielding complex large- and small-scale fabrics. In general, sorting is poor and individual beds thin rapidly and get finer-grained in a basinward direction. Locally, small channels filled with sand- to silt-sized siliciclastic material cut through the carbonate strata. These slope channels (carbonate and noncarbonate) and variably sorted sediment packages exerted a strong influence on the early hydrology of the forereef zone.
Carbonate Sedimentology of the Manzanita Member of the Cherry Canyon Formation
Authors: Hampton Bret D.
Published: November 2010

The Manzanita, the uppermost member of the Cherry Canyon Formation, is one of three carbonate units that extend from the toe of the Goat Seep Dolomite far out across the Delaware Basin. It is one of eight named carbonate units that serve to subdivide the 1000 m-thick siliciclastics of the Delaware Mountain Group. The Manzanita Member is unique among these Delaware Basin carbonates (Table 1). Instead of thickening into the toe-of-slope reef carbonates, the Manzanita appears to pinchout at the top of slope (King, 1948; Newell et al., 1953). The Manzanita has uniform thickness (approximately 15 to 20 m) far into the basin and contains no channels or coarse shelf debris; it is dolomitized much farther into the basin than the other tongues and has numerous evaporite molds. The continuity across the basin and paucity of coarse fossil grains also distinguish the Manzanita from most other tongues.

The Manzanita crops out in three major areas. Two of these, approximately perpendicular to depositional strike, are along the Western Escarpment of the Guadalupe Mountains and the top of a cuesta extending some 25 km into the Delaware Basin (see Fig. 1). More isolated outcrops occur in the third area, which extends about parallel to depositional strike for some 12 km eastward along the base of the Capitan Reef Escarpment from the southwestern tip of the Guadalupe Mountains. A representative section (Fig. 1) in this vicinity, 3 km east of the type section at Nipple Hill, is shown graphically on Figure 2.
Shallow-Water Gypsum in the Castile Formation - Significance and Implications
Authors: Kendall Alan C. , Harwood Gill M.
Published: November 2010

The predominantly anhydritic Castile Formation (Lower Ochoan, Permian) of the Delaware Basin (Fig. 1) is commonly used to illustrate the necessity for surface-reflux in marine evaporite basins and as a textbook example of deep-water evaporite sedimentation in a barred basin. The occurrence of basin-wide, mm-calcite/anhydrite laminae and of salinity cycles (laminar anhydrite at the base, passing upward gradationally into 'nodular' anhydrite and laminar halite) have generated depositional models involving a brine-filled basin (up to 600 m deep) that exhibited periodic fluctuations in salinity. Such models have been widely applied to other evaporite-filled basins.

Pseudomorphs of bottom-grown gypsum crystals have been found in 'nodular' anhydrite intervals within the lower parts of the Castile Formation in the Union University "37" No. 4 well (Anhydrite I Member) and the much visited New Mexico roadside outcrop (the "State Line Outcrop") along U.S. 62, 1.2 km north of the Texas-New Mexico boundary (which Anderson and Kirkland, 1987, attribute to the uppermost Anhydrite II Member) (Figs. 2 and 3). Complete gradation between well-preserved pseudomorphs and nodular anhydrite layers in the Union core suggest that nodular anhydrite intervals throughout the Castile Formation were also originally composed of bottom-grown gypsum crystals. This would better explain their lateral persistence and their stratigraphic restriction to certain horizons than their being a recrystallization of anhydrite laminae, as has previously been suggested.
Inside Auk—the Anatomy of an Eolian Oil Reservoir
Authors: Heward Alan P.
Published: November 2010

Auk field is located in the central North Sea and produces oil from Permian Zechstein carbonates and the underlying Rotliegend sandstones. The Rotliegend is 150 to 500 m thick and can be divided into five discrete episodes of desert sedimentation. Deposits of the upper three episodes are oil bearing, with eolian slipface sands forming the main producing intervals. The earliest deposits (unit 5) are localized waterlain conglomerates, which possibly infill topography on the unconformity with the Devonian. They are overlain by a large wedge-shaped mass of eolian slipface sands (unit 4) that onlaps the Devonian. Unit 3 represents a change in eolian deposition with a marked increase in wind-ripple laminated strata. Their abundance probably indicates more variable winds, and thin conglomerates of interdunal dolomite clasts suggest periodically wet conditions. This depositional unit varies in thickness by about 100%, with thick areas corresponding to the stacked deposits of slipfaceless draa and thin areas to stacked interdunes. Dune slipface sands within the draa accumulations are orientated toward the east and cannot be correlated over hundreds of meters between wells in a cross-wind direction. Unit 2 contains a still greater proportion of wind-ripple laminated sands and waterlain deposits. Its geometry is dominated by a large depositional mound -7 km across wind, 87 m thick, and thinning to 10 m in its adjacent interdunes. The mound is located above an interdunal thin of unit 3. Several intervals of dune and probably draa slipface sands occur where the mound is thickest, and a distinctive body of fine-grained eolian sands mantles its northern flank. The uppermost unit (1; Weissliegend) comprises waterlain mass-flow sands that partially infill interdunal lows and appear to represent reworking of a largely abandoned erg by rain water. Intercalated organic-rich shales and dolomites contain indications of evaporitic conditions, desiccation, and deflation and yield no evidence of marine faunas. The succeeding marine Zechstein gently inundated remaining topography.
Subsurface Characterization of Mesaverde Reservoirs in Colorado
Authors: Lorenz John C. , Warpinski Norman R. , Branagan Paul T.
Published: November 2010

The geometries of nonmarine-sandstone reservoirs of the subsurface Mesaverde Group in northwestern Colorado were estimated on the basis of sedimentologic studies. The accuracy of the estimates was subsequently assessed by geophysical tests and reservoir-engineering studies, such as vertical seismic profiles, hydraulic-fracture diagnostics, pressure tests (drawdown/buildup, production, and interference tests), and tracer tests. After the effects of natural fractures on these subsurface tests are accounted for, the tests provide indications of reservoir boundaries, internal heterogeneity, and continuity that are compatible with sedimentologic predictions.
Variations in Fluvial Style as Revealed by Architectural Elements, Kayenta Formation, Mesa Creek, Coloralk), USA
Authors: Bromley Michael H.
Published: November 2010

Architectural studies in the Kayenta Formation (Lower Jurassic) of the Colorado Plateau reveal the characteristics of two types of sandstone body, that reflect both ephemeral and perennial fluvial processes. The first type is composed of high-regime horizontally-laminated sandstone, forming multiple-event Storys up to 8 m thick, deposited by flash floods. The second type is composed of planar cross-beds, deformed parabolic cross-beds and massive sandstone formed under low-regime flow from a perennial river during high stage.

The style of deposition is dependent upon the degree of confinement within the boundaries of the channel system in question. Where confinement was dominant, sedimentary fill often reflects the geometry of the containing channel. Paleocurrent distribution reflects the depositing flow conditions in confined bodies. Horizontally-laminated units show strongly unimodal currents, whereas the heterolithic confined units show a wider scatter.

Where flow was unconfined (during high stage, when thalwegs were inundated), the resulting deposits are broad sheets interfingering with underlying confined sandbodies. A zone of interdigitation displays sharp changes in paleoflow direction within the same stratigraphic horizon, resulting from the simultaneous action of confined and unconfined depositional processes. The interdigitation records the incremental abandonment of channels, as large unconfined barforms encroached on them during high stage.

Discharge variability is inferred from lithofacies composition; variable but perennial discharge shows a wide range of lithofacies, including clay drapes resulting from minimum, sluggish flow. Flashy discharge shows only two lithofacies types, those representing low-regime waxing and waning flow and those representing high-regime peak flow. Clay drapes are absent
Facies Architecture of a Devonian Soft-Sediment-Deformed Alluvial Sequence, Broken River Province, Northeastern Australia
Authors: Lang Simon C. , Fielding Christopher R.
Published: November 2010

The Late Devonian Rockfields Member of the Bulgeri Formation in northeast Queensland, Australia, was deposited in a tectonically active alluvial basin. The source area was an uplifted igneous and metamorphic terrain to the south of a major oblique-slip fault zone, forming the basin margin. The member is characterized by relatively uniform, very fine- to medium-grained, soft-sediment-deformed sandstones, interbedded predominantly with slightly reddened siltstones. Detailed mapping of sediment body geometries and internal structures has resulted in the recognition of eight architectural elements. Channel-fill elements include laminated sand sheets, dune complexes, scour fills, laterally-and downstream-accreting macroforms, and linguoid barforms. Floodplain elements include levees, crevasse splays, and overbank fines.

The abundant soft-sediment deformation structures (mainly convolute lamination) were produced by liquefaction of sandy bedforms, during or immediately after rapid deposition. Larger scale structures, however, deform multiple erosion surfaces. These may be due to liquefaction of saturated unconsolidated sands during earthquakes of magnitude >5, with inferred epicenters along the fault zone 20 km to the south.

The proposed depositional model comprises a broad, sandy braidplain with marked discharge variation, resulting in widespread seasonal flooding. Channel-avulsion events, combined with a relatively high subsidence rate associated with tectonic activity, resulted in the accumulation of laterally extensive, sheet-like, channel sandbodies and fine-grained floodplain deposits. A modem analog is the seasonally inundated low-sinuosity channel system of the alluvial plains and fans surrounding the Gulf of Carpentaria, north Queensland. This model bears some resemblance to published models for low-sinuosity streams, but sufficient differences warrant recognition as a distinct fluvial style.

The unit represents an example of a strongly layered sequence with laterally extensive (>1,500 m) channel sandstone bodies 3-10 m thick, separated by floodplain deposits 0.3-2 m thick of comparable lateral extent (1,500 to >4,000 m). Hydrocarbon reservoirs with similar architecture, uniform grain size, and a general lack of internal fine partings could be considered to behave isotropically with respect to fluid flow within individual bodies.
Cenozoic Fluvial-Facies Architecture and Aquifer Heterogeneity, Oroville, California, Superfund Site and Vicinity
Authors: Blair Terence C. , Baker Fred G. , Turner Joseph B.
Published: November 2010

A three-dimensional facies analysis of Cenozoic fluvial deposits in the vicinity of a federal Superfund site near Oroville, California, was conducted to characterize aquifer heterogeneity and to provide a basis for accurate modeling of the complex groundwater system. A network of 29 boreholes in the 6.5-km2 study area penetrated four distinctive fluvial units, including the Laguna Formation (upper Pliocene-Holocene), Nomlaki Tuff (upper Pliocene), Mehrten Formation (Miocene-upper Pliocene), and lone Formation (Eocene). All four formations consist of pebble-cobble gravel, sand, and clay deposited by the Feather and ancestral Feather River systems at the margin of the Sacramento Basin near the western Sierra Nevada mountain front. Sediment gravity flows and waterlain andesitic and pumice-rich volcaniclastic facies derived from the southernmost Cascade volcanic centers episodically choked the ancestral Feather River system during late Pliocene upper Mehrten and Nomlaki Tuff deposition. Cenozoic fluvial aggradation was interrupted by three periods of valley cutting, which occurred 1) during the Oligocene, between deposition of the lone and Mehrten Formations; 2) during the late Pliocene, between deposition of the Nomlaki Tuff and Laguna Formation; and 3) during the middle Pleistocene, after most Laguna deposition was completed. The Oligocene and late Pliocene paleovalleys, 24 to 61 m deep, are filled with vertically and laterally interconnected channel pebble-cobble gravel of the Mehrten and Laguna sequences.

The principal aquifer zones in the study area are >30-m-thick units of hydraulically continuous channel gravel and sand of the Laguna, Mehrten, and lone Formations. These aquifer zones are continuous across Oligocene and late Pliocene paleovalley margins through channel-fill gravel and sand of the various formations. Floodplain clay and volcaniclastic debris-flow units act as aquitards, which locally limit the interaction between permeable zones. A dissolved pentachlorophenol plume in local ground water originates at the Superfund site (a wood treatment plant) in the northern end of the study area, where it initially moves within the Laguna Formation. The plume has migrated into hydraulically continuous Mehrten and lone gravels that are in contact -425 m south of the plant site. The plume has also passed into juxtaposed Mehrten and Laguna gravels 1,400 m south of the plant site. Pumping-test data demonstrate that no marked changes in hydraulic conductivity occur across the paleo v alley- fu11 boundaries. Local changes in the hydraulic-gradient vector are caused by changes in the permeability of the aquifer material or in the thickness of the aquifer zones, both of which are associated with lateral changes in formations and facies.
Fluvial-Sandstone Reservoirs of The Travis Peak Formation, East Texas Basin
Authors: Tye Robert S.
Published: November 2010

Gas production (7.2 Bcf) from low-permeability sandstones in the Early Cretaceous Travis Peak Formation, North Appleby field, Nacogdoches County, Texas, is enhanced through hydraulic fracturing of stacked, blocky to upward-fining sandstones encased in impermeable mudstone interbeds. Pervasive quartz cement in the sandstones decreases porosity and permeability and contributes to formation of the reservoir seal.

Subsurface data indicate that much of this 615-m-thick section represents aggradation of alluvial-valley deposits. Multiple channel belts form a network of overlapping, broad, tabular sandstones having thickness-to-width ratios of 1:850 (2.4 to 13.2 m thick; widths exceed 6.4 to 8 km). Six to eight channel belts, each containing 80 to 90% medium- to fine-grained sandstone, locally occupy a 61 -m-thick interval. In a vertical sequence through one channelbelt sandstone, basal planar cross-bedding grades upward into thinly interbedded sets of planar cross-beds and ripple cross-lamination. Clay-clast conglomerates line scoured channel bases. Adjacent to the channels, fine-grained sediments accumulated in well-drained swamps and lakes. Poorly sorted sandstones represent overbank deposition. During Travis Peak deposition, alluvial styles evolved from dominantly bed-load deposition near the base of the formation to more mud-rich, mixed-load systems at the top.

Sandstone geometry, continuity, and internal heterogeneity influence reservoir performance and well-to-well communication. Small-scale bedforms, biogenic structures, and scour surfaces create fluid-flow barriers and segment reservoirs. Within the channel belts, best-quality reservoir sandstone (high porosity and low-water saturation) exists in narrow bands that are oriented subparallel to depositional dip. Reservoir quality decreases at channelbelt margins (levees) and tops (abandoned channel) and in fine-grained interchannel areas (shadow zones behind longitudinal bars).
Sand Bank and Dune Facies Architecture of a Wide Intracratonic Seaway
Authors: Surlyk Finn , Noe-Nygaard Nanna
Published: November 2010

The 200- to 300-m-thick Raukelv Formation was deposited in an intracratonic seaway between East Greenland and Norway during the Late Jurassic-earliest Cretaceous (Volgian-Valanginian), a period of considerable tectonic unrest in the region. The formation is three-dimensionally exposed over 900 km2. Four basic architectural elements are recognized: 1. The sandbank (SB) element is composed of single, tabular mega-cross-beds 15-50 m thick, which extend over the whole outcrop area (900 km2). 2. the sand-dune (SD) element consists of a large-scale tabular cross-bedded coset, 2-8 m thick, which extends over the whole outcrop area (900 km2). 3. the sandsheet (SS) element comprises a burrowed and glauconitized, mainly trough cross-bedded coset, 2-10 m thick, with sheet geometry, which extends over most or all of the outcrop area; and 4. the siltstone (SI) element is 2-20 m thick, has sheet geometry, and extends over at least 100 km2.

The SB, SD and SS elements are topped by planar, glauconitized commonly pebble-sttewn omission surfaces with U-shaped burrows. Most sand banks of the SB element migrated eastward from the western coastline, whereas the linear dunes of the SD element migrated southward, parallel to the basin axis and to the coast. Sedimentation seems to have been governed mainly by coast-parallel or offshore-directed currents set up by storms and tides. The low-amplitude 3-D dunes of the SS element migrated toward the south or, rarely, toward the north.

Rates of subsidence and sediment influx can be considered as relatively constant for the time interval in question. The succession consists of stacked SB, SD, SS and SI elements. A clear, systematic, sequential stacking order has not been observed, although there is a tendency for development of an SB, SS, SD cycle. A total of four SB, three SD, three SS and two SI elements has been recorded. Deposition is interpreted as controlled mainly by fluctuations in regional sea level during a period of lowstand. The individual elements reflect fairly rapid regional sea-level fluctuations on a background of the overall lowstand. The main transport of sand in the basin took place in extensive fields of linear sand dunes (SD element). Sand banks (SB element) were initiated at times of high rate of sea-level rise, and the main growth by eastward progradation took place during highstands. Some bank tops were eroded during sea-level fall, whereas others were drowned during rise. In both cases the tops became glauconitized and burrowed during the succeeding rise. The omission surface was slowly covered by bioturbated siltstone (SI element) during high rate of sea-level rise. In case of slower rate of rise a reworked, transgressive sheet sand (SS element) was formed. Sea level is estimated to have fluctuated between 30 and 50 m during deposition of the SB elements. These oscillations had a duration of about 1 m.y. and were superimposed on a lowstand following the Kimmeridgian highstand. The lowstand had a duration of about 10 m.y.
Contrasting Styles of Late Neogene Deep-Water Sandstone Deposition, Offshore Texas
Authors: Morton Robert A.
Published: November 2010

Middle Miocene and middle Pliocene deep-water sandstone reservoirs of the western Gulf Coast Basin are associated with failed shelf margins and subregional unconformities referred to as submarine pediments. The submarine pediments formed broad, convex-landward arcs along nondeltaic slopes and on the southwestern flanks of subjacent delta systems. They were created by retrogressive failure and were later enlarged by erosion during periods of lowered sea level. At times of lowered sea level, the deep embayments that carved into the continental platform funneled nearshore sands downslope to basin-floor fans.

The pediments were first backfilled by deep-water mudstones deposited by mass-transport processes. These slump blocks and high-energy turbidites exhibit mounded to chaotic seismic reflections that dip landward. Later, sand-rich channel-levee complexes were deposited above the basal mudstones and near the seismic-facies transition from chaotic reflections to overlying horizontal or wavy reflections. The pre-entrenchment morphology of the shelf margin was finally restored by coalescence of small, prograding deltas that are recorded as clinoform reflections.

Unconfined lower-slope and basin-floor fans associated with the submarine pediments are generally sand poor. The sand-rich lowstand-fan deposits are restricted to highly elongate, dip-oriented leveed channels that mark the principal pathways of sediment transport.

Sandstones confined to leveed channels of the upper-fan and pediment fill are the most prolific hydrocarbon reservoirs within each stratigraphic sequence. These channel sandstones exhibit high vertical continuity but low lateral continuity because interbedded turbidite mudstones increase away from the channel axes. Thin sandstones of the lower fan may exhibit high lateral continuity, but they typically have poor-reservoir properties because of high concentrations of original muddy matrix.
Modern Shelf Sand Ridges
Authors: Snedden John W. , Dalrymple Robert W.
Published: November 2010

Shelf sand ridges are common features on many modern continental shelves but have not been widely cited as analogs for ancient sand bodies. Modern shelf sand ridges are elongate, coastal- to shelf-sand bodies that are larger than subaqueous dunes, with lengths of the order of 10 km and heights that are more than 20% of the water depth. These ridges are also longer-lived than smaller bedforms, persisting for thousands to tens of thousands of years. Progress in understanding these features has gone from early studies of their morphology and surficial-sediment characteristics to recent investigations of current and wave dynamics and establishment of their internal stratigraphy through vibracoring. From these studies, it is clear that once formed, most ridges are maintained and even enlarged by present-day shelf-flow dynamics. Ridges existing in tide- and storm-dominated shelf regimes share many similarities, which suggests that both are formed by the same fundamental interaction between flow and an initial bathymetric irregularity. The Huthnance (1982) hydrodynamic model appears to offer an adequate description of that interaction. Synthesis of previous work indicates that storm- and tide-dominated ridges pass through three stages of development: 1) an initial irregularity (the ridge nucleus) forms due to coastal or shelf processes; 2) nearshore and/or shelf currents (either storm- or tide-driven) interact with the irregularity in the manner described by the Huthnance model; and 3) the ridge evolves as a result of continued current action. These processes and events are most likely to occur during transgressions, because sandy coastal deposits, the most common ridge nuclei, are reworked on the shelf as relative sea level rises. Thus, most ridges are expected to overlie the transgressive ravinement surface.

Understanding the nature of the initial irregularity and the amount of subsequent migration is the key to explaining the diversity of ridge characteristics. Based on the degree of ridge evolution, we categorize shelf ridges into three classes: Class I-juvenile or stationary ridges that retain their initial nucleus; Class II- ridges that have migrated somewhat but retain part of their nucleus; and Class III- "fully evolved" ridges that have migrated sufficiently that they contain no trace of their origin. The degree of ridge evolution greatly affects the economic potential of ancient subsurface analogs, as ridge reworking/remolding during migration results in cleaner sand and increased sand-body volume. Transgressive conditions are most favorable for ridge development (e.g., Transgressive Systems Tracts), given the presence of widened shelf areas, drowned bathymetric irregularities that act as ridge nuclei, and loose sand derived from ravinement.
Genetic Characteristics of Glauconite and Siderite: Implications
for the Origin of Ambiguous Isolated Marine Sandbodies
Authors: Stonecipher Sharon A.
Published: November 2010

Authigenic glauconite and siderite form under a limited range of well-documented geological and geochemical conditions. Because glauconite precursors need to remain at or near the sediment water surface for long periods of time in a setting where they can be repeatedly exhumed and shallowly buried, glauconite typically develops on the outer margins of continental shelves in areas of low sediment input. Based on these requirements, glauconite has traditionally been used as an indicator for transgressive sequences because transgressions tend to trap sediment on the continents. However, from a sequence stratigraphic standpoint, glaucony may be present in virtually any part of a depositional sequence due to remobilization. Glaucony can provide useful information for sequence stratigraphy only if variations in its abundance, physicochemical properties, and spatial/temporal characteristics are carefully documented.

Siderite typically forms in one of two distinct environments: one characterized by strongly reducing conditions (methanogenic zone), and one under slightly reducing conditions (post-oxic zone). Methanogenic siderite is more common in continental and fresh-water lacustrine than marine deposits. Post-oxic conditions are commonly associated with marine environments exhibiting moderately low concentrations of organic matter and low sedimentation rates. Siderite is also frequently found in association with sequence boundaries where it occurs as a secondary cement below the lowstand surface of erosion (LSE).

These restrictions on environment of origin provide information on the hydrologic regime and, by inference, the depositional and sequence stratigraphic setting of the host sediment in which these minerals are found. By examining the genetic significance of minerals such as glauconite and siderite, the origin of ambiguous, controversial, isolated marine sand bodies such as those discussed elsewhere in this volume may be clarified. This paper summarizes what is currently known about the chemical characteristics of these minerals and discusses generalized models of their distribution in a variety of sequence stratigraphic settings.
Marine and Marginal Marine Mudstone Deposition
Authors: Maceachern James A. , Stelck Charles R. , Pemberton S. George
Published: November 2010

This study integrates ichnological, palynological and foraminiferal assemblages of selected mudstones, principally from the late Albian Viking Formation of central Alberta, to characterize their paleoecology. Ichnological assemblages have been based on the analysis of more than 300 cored intervals. Twenty-two palynological samples were analyzed from 9 wells, and 14 foraminiferal samples were analyzed from 7 wells. The selected samples comprise 5 depositional "types", namely: 1) transgressive systems tract shelf deposits; 2) highstand systems tract lower offshore deposits; 3) transgressive systems tract upper offshore deposits; 4) transgressive systems tract embayment/lagoon deposits; and 5) transgressive systems tract estuarine incised valley central basin deposits.

The palynological assemblages were most useful in separating fully marine from strongly brackish-water (estuarine) environments within the Viking Formation. Peridinioid dinoflagellate concentrations are anomalously high in samples from the central basin mudstone of estuarine incised valley complexes. Foraminiferal assemblages were sufficient to differentiate most of the subenvironments, based on changes in the diversity and abundance of genera and species, as well as the presence of environmentally tolerant forms. The paucity of foraminifera within the estuarine incised valley mudstone limited their paleoecologic utility in these deposits.

Ichnological analysis was able to differentiate between shelf, lower offshore, upper offshore, embayment/lagoon and estuarine incised valley central basin mudstones. In addition, this data can be collected during initial facies descriptions without the need for laboratory analysis, making it an essential paleontologiC discipline in facies analysis.
The Origin of the Tocito Sandstone and its Sequence Stratigraphic
Lessons
Authors: Nummedal Dag , Riley Gregory W.
Published: November 2010

A detailed and comprehensive study of all Tocito outcrops along the margins of the San Juan basin, New Mexico, combined with an equally comprehensive study of the subsurface Tocito by David Jennette and clive Jones oil-rich, shale-encased sand bodies. The Tocito Sandstone is entirely Coniacian in age. It is separated from the underlying Gallup Sandstone on the Four Corners Platform by a major unconformity that locally is associated with a lacuna up to 3 million years. In the southeast San Juan basin, however, there is no demonstrable biostratigraphic gap.

The formation of the Tocito is intimately connected with an episode of Coniacian tectonism that triggered the uplift of the Waterflow Antic Line that trends northwest-southeast across the Four Corners platform and adjacent regions of the San Juan basin. Uplift of this anticline commenced immediately after Gallup Sandstone deposition and gave rise to an elevated seafloor region across which shallow marine tidal (and storm?) currents eroded several hundred feet of Mancos Shale. Concurrently, the stream system that previously had fed the wave-dominated shorelines of the Gallup, the Torrivio system, began delivering its load into the embayment (or strait?) formed behind the uplifted anticline. In that setting of strongly enhanced tides and reduced wave action, the lower Tocito formed as a tide-dominated delta complex. In late Coniacian time regional subsidence set in, probably by reversal of movement on the inferred fault below the flank of the anticline. The ensuing marine transgression truncated much of the tidal delta facies of the lower Tocito, as well as some of the fluvial Torrivio, and formed a set of shelf sand ridges across much of the Four Corners platform

Studieson modern continental shelves have revealed that such juxtaposition of transgressive shelf sand ridges directly above anearly Holocene ravinement surface that has truncated underlying regressive deltaics is quite common. Therefore, an accurate documentation of the differences in distribution, geometry, vertical textural trends, and component facies between the lower, regressive member and the upper, transgressive member of the Tocito Sandstone may provide a useful template for a better understanding of the many similar delta/cstuary/shclf sand-stone complexes in the rock record. The Tocito Sandstone has excellent porosity and is the major oil reservoir rock in the San Juan basin. Documentation of the Tocito sand body and shale body geometries, therefore, will help us better understand fluid flow in such reservoirs, of which there probably are many more than currently recognized.