Submarine Fan Deposits Research Articles

Paleogene Sedimentation and Deformation Along Svalbard's Sheared Margin: ABSTRACT

The northern part of the Svalbard-Barents margin was a shear margin from 58 Ma to 36 Ma. The strike-slip effects on Spitsbergen are evident in (a) the Central Basin, (b) the fold-and-thrust belt of western Spitsbergen, and (c) Forlandsundet Graben. An early mid-Paleocene transtensional regime is suggested by about End_Page 480------------------------------ 500 m (1,640 ft) of deltaic deposits dispersed westward into the Central basin. These onlapped the basin margins in response to initial high rates of subsidence along the flank of the shear zone. Late Paleocene uplift and increasing transpression along the shear zone is recorded by a drainage reversal and about 2 km (1 mi) of easterly offlapping deltaic deposits. In western Spitsbergen, deformation of late Paleocene through Eocene age represents the culmination of transpression and is characterized by thrusts, asymmetric folds, and steeply-dipping reverse faults producing approximately 10-15 km (6-9 mi) of crustal shortening. Farther west, the Eocene to early Oligocene Forlandsundet Graben, and probably other smaller basins, originated after the climax of transpression, possibly during collapse of the uplifted axis of the orogenic belt. Although the Forlandsundet Graben contains a true vertical thickness less than 3 km (2 mi) of fan-delta to submarine fan deposits, its apparent thickness greater than 5 km (3 mi) suggests basin migration during increasing transtensional conditions. Extensional deformation of the graben sequence heralded the transition of the Svalbard margin from a sheared to a rifted regime. From 36 Ma, Spitsbergen was uplifted, and deep (> 5 km, 3 mi) rift basins developed along the new continental margin. End_of_Article - Last_Page 481------------

Cenozoic Basin Development in Hispaniola: ABSTRACT

Four distinct generations of Cenozoic basins have developed in Hispaniola (Haiti and Dominican Republic) as a result of collisional or strikeslip interactions between the North America and Caribbean plates. First generation basins formed when the north-facing Hispaniola arc collided with the Bahama platform in the middle Eocene; because of large post-Eocene vertical movements, these basins are preserved locally in widely separated areas but contain several kilometers of arc and ophiolite-derived clastic marine sediments, probably deposited in thrust-loaded, flexure-type basins. Second generation basins, of which only one is exposed at the surface, formed during west-northwesterly strike-slip displacement of southern Cuba and northern Hispaniola relative to central Hispani la during the middle to late Oligocene; deposition occurred along a 5-km (3-mi) wide fault-angle depression and consisted of about 2 km (1 mi) of submarine fan deposits. Third generation basins developed during post-Oligocene convergent strike-slip displacement across a restraining bend formed in central Hispaniola; the southern 2 basins are fairly symmetrical, thrust-bounded ramp valleys, and the third is an asymmetrical fault-angle basin. Fourth generation basins are pull-aparts formed during post-Miocene divergent strike-slip motion along a fault zone across southern Hispaniola. As in other Caribbean areas, good source rocks are present in all generations of basins, but suitable reservoir rocks are scarce. Proven reservoirs are late Neogene shallow marine and fluvial sandstones in thi d generation basins. End_of_Article - Last_Page 503------------

Seismic Facies and Reservoir Distribution in a Prograding Shelf-Slope-Basin Plain System: Chandler and Torok Formations, North Slope, Alaska: ABSTRACT

The Chandler-Torok sequence is one of several Cretaceous-Tertiary clastic wedges shed north and east from the ancestral Brooks Range hinterland into a rapidly subsiding foredeep trough. Each wedge consists of a End_Page 935------------------------------ lower sequence of hemipelagic shales and submarine-fan deposits succeeded by slope-deposited silty shales and culminating in shelf and fluvio-deltaic sandstones, shale, and coal. Basinal facies are expressed seismically as convergent bottomset reflectors of moderate to high amplitude and continuity, grading updip into mounded and channelized events of poor continuity and variable amplitude that onlap the base of the slope. This hummocky facies represents a combination of overlapping submarine fan lobes and gravity-failure deposits. The overlying slope sequences are expressed as complex sigmoid-oblique clinoform bundles of low amplitude bracketed by discrete continuous events of high amplitude. Clinoform bundles downlap over mounded facies onto bottomset events except where removed by eeply incised submarine canyons. Mounded submarine fans generally onlap the base of toplapped foresets, documenting their development during periods of low stand and shelf bypass. They were blanketed by high-amplitude foresets during transgressive periods of relative sea level rise. Shelf and nonmarine facies are seismically expressed as prograding and aggrading topset reflectors that respond to fluctuating sea level and sediment supply. Amplitude and continuity are high in the eastern wave-dominated shelf setting, low in the western river-dominated setting, and uniformly variable in the alluvial-plain setting owing to discontinuous channels and coal measures. Maximum reservoir development parallels the wave-dominated shelf setting. End_of_Article - Last_Page 936------------

Paleogene evolution of the Kodiak Islands, Alaska: Consequences of ridge‐trench interaction in a more southerly latitude

The Kodiak Islands of Alaska are principally composed of a Late Cretaceous and Paleogene complex of accreted deep‐sea rocks. An early Paleocene magmatic event invaded the accretionary complex with mid‐ocean ridge basalt (MORB), andesite, and granodiorite. Geochemical evidence suggests both the andesite and granodiorite are mixtures of MORB and sediment. The volcanic rocks are interlayered with coarse clastic sediments and deformed with the latter; the granodioritic intrusions, with K‐Ar ages as old as 62 Ma postdate emplacement of the early Paleocene sedimentary and volcanic rocks. Interaction of the subduction complex with the Kula‐Farallon ridge most simply explains this early Paleocene magmatic episode. Paleomagnetic studies of the volcanic rocks indicate this interaction occurred at 40.3±6° north latitude, which is 25.3±9° south of the expected position of the Kodiak Islands relative to North America. The magmatic arc presently northwest of the Kodiak accretionary complex was active during the Late Cretaceous and early Paleocene, diminished after the ridge‐trench interaction, and resurged from late Eocene into Miocene time. The magmatic resurgence is coeval with the obductive offscraping of Eocene to Oligocene(?) submarine fan deposits in the Kodiak Islands. The petrology of these fan deposits indicates they are the most likely proximal equivalent for the Zodiac fan, thereby limiting its relative motion with respect to the Kodiak Islands. Possible models accounting for the northward motion of the Kodiak accretionary complex include (1) coupling the accretionary complex and possibly related arc to the northward‐moving Kula Plate and closing an ocean basin north of the arc in Paleogene time, (2) emplacing the Kodiak accretionary complex at the northward limit of the paleomagnetic data, with subsequent northward motion accomplished by closure of a small back arc basin and/or intracontinental shortening, and (3) transcurrent faulting and northward motion of the Kodiak accretionary complex without the presently adjacent arc.

Sedimentary, tectonic, and sea-level controls on submarine fan and slope-apron turbidite systems

To help understand factors that influence submarine fan deposition, we outline some of the principal sedimentary, tectonic, and sea-level controls involved in deep-water sedimentation, give some data on the rates at which they operate, and evaluate their probable effects. Three depositional end-member systems, two submarine fan types (elongate and radial), and a third nonfan, slope-apron system result primarily from variations in sediment type and supply. Tectonic setting and local and global sea-level changes further modify the nature of fan growth, the distribution of facies, and the resulting vertical stratigraphic sequences.

The Cengio submarine turbidite system of the Tertiary Piedmont Basin, Northwestern Italy

The Cengio sandstone member of the Tertiary Piedmont Basin in northwestern Italy has a conservatively estimated volume of 2.5 to 3 km3 (length: 6.4 km; width: 4.8 km; thickness: 170 m). It is interpreted as a sandstone-rich submarine fan deposit. The Cengio member consists of eight tabular depositional sandstone lobes that are 5- to 25-m thick. These lobes filled a submarine structural depression and onlap and/or pinch-out against bounding slope mudstones. The stacking of the lobe units was related to synsedimentary tectonism.

A Delta-Slope-Submarine Fan Model for Maestrichtian Part of Great Valley Sequence, Sacramento and San Joaquin Basins, California

Shoaling of the Great Valley fore-arc basin, which began in the northern Sacramento basin during the Campanian Stage, shifted southward in the Maestrichtian to the southern Sacramento and northern San Joaquin basins, where a regressive sequence of submarine fan, slope, and deltaic deposits aggregates 6,500 ft (2 km) in thickness. Water depth decreased to sea level as ponded submarine fans aggraded the basin floor, and slope and deltaic systems prograded basinward over them. The central part of the fore-arc basin was filled by the end of the Cretaceous; the southern part was not filled until the middle Eocene. Deltas prograded westward and southwestward from the Sierran magmatic arc. The Starkey delta system evolved from cuspate/lobate wave-dominated deltas with extensive upward-coarsening delta-front sand beds to highly lobate fluvial-dominated deltas with moderately developed delta-plain facies. This system was succeeded by elongate fluvial-dominated deltas with thick delta-plain/fluvial sequences in the Bethel Island fluvial-deltaic system. Thin, fine-grained, black, glauconitic shale beds were deposited during intervals of regional transgression and deltaic abandonment. Several progradational-transgressive cycles are recorded. The Roberts Island slope system comprises several thick shale sections deposited during progradational events. Benthic foraminifera grade upward from abundant, varied, lower bathyal species to sparse upper bathyal or neritic species. Clinoform beds that offlap from east to west are evident in electric-log cross sections and seismic profiles. Lenticular, channeled sand beds, transverse to the slope, appear to be incised slope channels that funneled sand from the delta front to submarine fans on the basin floor. Shelf-edge slumps can locally be recognized by flow folds, mudstone blocks, and anomalous thicknesses and bedding attitudes, particularly near growth faults. The Union Island submarine fan system consists of several fans; most are elongate parallel to the southeasterly trend of the basin. Fans consist of upper, middle, and lower segments. Thick-bedded, channelized, upward-fining, coarse-grained sand beds characterize the upper fan. Medium to thick-bedded, channelized, massive fine to medium-grained sand beds predominate on the midfan. Lower fan deposits are not extensive but consist of symmetrical or upward-coarsening sequences of shale and thin to medium-bedded fine to very fine sand. Channeling is less common on the lower fan. Most fans have multiple lobes, each lobe having been fed by a different delta. Gas is produced from deltaic and submarine fan deposits. Delta-front sand beds form very small reservoirs where growth faults provide subtle structural traps. Distributary-channel sand beds are highly productive, owing mainly to stratigraphic pinch-outs but locally perhaps to structural traps. Submarine fan traps have so far been located mainly in midfan deposits, either in the structurally high suprafan mounds or along lateral fan margins near the base of the slope where fan deposits onlap and pinch out against slope shale. Exploration in lower and upper fan deposits has barely begun.

Stratigraphy, Depositional History, and Reservoir Potential of Cretaceous and Early Tertiary Rocks of Lower Cook Inlet, Alaska: ABSTRACT

Depositional relations within strata of Cretaceous age in the lower Cook Inlet area have been clarified by recent drilling and high quality seismic data. Lower Cretaceous (Neocomian) strata are preserved along the Cook Inlet basin axis and are correlated with the Herendeen Formation of Port Moeller and the Nelchina beds in the Matanuska Valley. The Kaguyak Formation of Cape Douglas is expanded to include strata which range in age from Albian through Maestrichtian. Three members are proposed, which are (in ascending order) the Unnamed Albian-Cenomanian, the Middle Member, and the Saddle Mountain Member. Depositional relations within the Kaguyak Formation were strongly controlled by tectonic events and resultant basin configuration. The Unnamed Albian-Cenomanian Member (up to 1,400 ft [425 m] thick) is composed of carbonaceous sandstone and shale. It is correlated with similar-age deposits in the Matanuska Valley and the Mt. Katmai area, and represents shallow to marginal marine deposition. The Middle Member is up to 4,400 ft (1,350 m) thick and consists of a southeastward-thickening wedge which is predominantly marine siltstone and claystone. Sandstone is significant only at Kaguyak Bay where proprietary studies indicate submarine fan deposition, and in the Socal Anchor Point well where a similar environment is likely. Middle Member strata lap-up on and over-top a topographic shelf, which began to develop at about Turonian time and was a prominent feature in the area east of the Iniskin Peninsula by Campanian ti e. Significant shallowing at the beginning of Maestrichtian time was accompanied by an outpouring of coarse clastics of the Saddle Mountain Member. Up to 2,000 ft (600 m) of mostly nonmarine sandstone, siltstone, and conglomerate extends seaward (southeastward) to the shelf edge. We suggest that this shelf edge was the paleolimit of Saddle Mountain Member deposition and that marine reworking and washing fluvially supplied sand along this shelf edge provided the only Cretaceous sandstone with reservoir potential in this area. Overlying and possibly continuous with the Saddle Mountain Member is a Paleocene sequence of sandstone and conglomerate, about 600 ft (185 m) thick in the COST well. This interval is seismically and lithologically distinct from the underlying Cretaceous and overlying West Foreland Formation rocks and is named the Silver Salmon Formation. This formation showed the best reservoir properties of the Tertiary rocks in lower Cook Inlet. End_of_Article - Last_Page 480------------

History of Sedimentologic Concepts Applied to Northern Appalachian Piedmont Metasediments

The northern Appalachian Piedmont is underlain by metamorphosed sedimentary and igneous rocks. The sedimentary origin of many of these rocks was established during the late 1800's. Other rocks, particularly the massive inclusion-bearing metasediments (diamictites), were considered to be xenolithic granites until the 1940's or later. Relict sedimentary textures and structures are preserved in some Piedmonst metasediments despite sillimanite-grade metamorphism. Few sedimentary structures, other than bedding, were reported until the early 1960's, when graded bedding and sequences of sedimentary structures resembling the Bouma Cycle, characteristic of turbidity current deposits, were reported front metagraywackes in the Maryland Piedmont. The metagraywackes are now interpreted as submarine fan deposits. Few of the metasediments have been studied from a sedimentologic viewpoint. Most of our knowledge of the sedimentary structures and depositional environments has been contributed by igneous and metamorphic petrologists, primarily George W. Fisher and Clifford A. Hopson. Sedimentologists (Juergen Reinhardt and Gregory S. Gohn) working in the Piedmont have dealt primarily with lower metamorphic grade carbonate rocks in the western and northwestern Piedmont.

Submarine Fan Sedimentation, Ouachita Mountains, Arkansas and Oklahoma: ABSTRACT

More than 10,000 m (33,000 ft) of interbedded sandstones and shales comprise the Upper Mississippian and Lower Pennsylvanian flysch succession (Stanley, Jackford, Johns Valley, Atoka) in the Ouachita Mountains of Arkansas and Oklahoma. Deposited primarily by turbidity current and hemipelagic processes in bathyal and abyssal water depths, these strata form major submarine fan complexes that prograded in a westerly direction along the axis of an elongate remnant ocean basin that was associated with the collision and suturing of the North American and African plates. A longitudinal fan system is visualized as the depositional framework for these strata which were deposited in a setting analagous to the modern Bengal fan of the Indian Ocean. Facies analysis of the Jackfork Sandstone indicates that inner fan deposits are present in the vicinity of Little Rock, Arkansas; middle fan distributary channel and crevasse splay deposits occur at DeGray Dam, Arkansas; and outer fan depositional lobe deposits are present in southeastern Oklahoma. Basin plain equivalents are postulated to exist as far away as the Marathon region in west Texas. Boulder-bearing units (olistostromes) with exotic clasts were shed laterally into the Ouachita basin, primarily from its northern margin. These olistostromes occur throughout the fan succession in all facies (i.e., inner, middle, and outer fan). This relationship may serve as a useful criterion for recognizing similar fan systems in the rock record. End_of_Article - Last_Page 517------------

Hydrocarbon Accumulations in Turbidite and Contourite Sands of Upper Cretaceous Forbes Formation, Bounde Creek Gas Field, California: ABSTRACT

Upper Cretaceous marine strata of the Forbes Formation in the northern Sacramento Valley are composed of terrigenous clastic detritus deposited in westward-prograding shelf to basinal sedimentary environments that existed in a south-trending fore-arc basin. Subsurface stratigraphic investigations in the Bounde Creek gas field indicate that upper, middle, and lower informal divisions of the Forbes Formation are composed of submarine fan and slope sediments deposited in the northern extension of the fore-arc basin. The upper Forbes contains deposits of inner slope sub-association. Predominantly very fine to fine-grained contourite and feeder channel sands are present within this upper section. These inner slope deposits are underlain by, and are interpreted to pass westwardly into, outer slope and inner fan deposits that comprise the middle part of the Forbes. Sands within this middle part are generally coarser (very fine to coarse-grained), thicker bedded, and have greater stratigraphic irregularity than vertically adjacent deposits within the formation. The lower Forbes consists of middle and outer submarine fan deposits. Sand bodies in this interval were deposited in channels and as suprafan lobes. Ongoing analysis indicates that channel configurations were, in some places, influenced by synd positional faulting that created steep channel margins and abrupt route alterations and/or abandonments. Sand lobe deposits exhibit areal continuity and lateral lithologic gradations. In the Bounde Creek gas field, distinct hydrocarbon accumulations occur in sand packages that are interpreted to represent: (1) feeder channels and contourites of slope associations; (2) channel lag or mouth bars of middle to inner fan sub-associations; and (3) suprafan lobes of middle to outer submarine fan sub-associations. Paleogeographic reconstructions of depositional horizons within the Forbes reveal a scenario of development and progradation of these inner slope to outer fan associations, and allow geometric projections of hydrocarbon-bearing sand bodies within the system. End_of_Article - Last_Page 468------------

Seismic Stratigraphy and Sea Level Changes in Active Margin Settings: An Example from Luzon, Philippines: ABSTRACT

Controversy arises when attempting to relate unconformities on a tectonically active margin to global changes in sea level. Seismic stratigraphy studies on active margins generally concentrate on defining large seismic packets and do not directly relate unconformities and their correlative conformities to global sea level changes. In the Central Valley of Luzon, we determined sequence boundaries in the basin and developed an age model that strongly suggests that sea level change is the major factor affecting shorter term (less than 5 m.y.) changes in sedimentation on this active margin. The Central Valley is a Cenozoic fore-arc basin bounded by an arc complex and the left-lateral strike-slip Philippine fault on the east and by an east-dipping subduction zone adjacent to the Manila Trench on the west. Multichannel seismic reflection, well, and outcrop data were used to determine the depositional history of the basin. Because much of the 13 km (8 mi) thick basin fill consists of deep-water marine sediments, conventional criteria such as coastal onlap and erosional truncation could not always be used. Instead, evidence for pulses of submarine fan deposition during lowstands of sea level (suggested by Vail and Hardenbol in 1979, and by Shanmugan and Moiola in 1982) was used to identify some of the sequence boundaries. The ages of the major boundaries, predicted from comp risons with Cenozoic Sea level curves, agreed very well with established ages from well and outcrop data. The supposed difficulty in determining sea level changes in active margins is that tectonic effects override and cloud the effects of global sea level changes. We agree that major regional tectonic events such as the initiation of subduction or strike-slip movement that creates or destroys basin morphologies clearly are the dominant factors in the overall stratigraphy of the basin. However, episodic tectonic events during continued basin evolution result in discrete changes in local basin morphology and sediment source areas which may lead to local unconformities or local increase or decrease in sediment influx. These effects are probably small compared to the basin-wide effects of global sea level changes. Such is the case in the Luzon Central Valley where the effects of global sea l vel changes can be seen throughout the basin. End_of_Article - Last_Page 502------------

Structural Controls on Submarine-Fan Geometry and Internal Architecture: Upper La Jolla Fan System, Offshore Southern California

La Jolla fan, offshore of San Diego, California, is a well-studied example of submarine-fan sedimentation, yet the internal architecture of the fan has remained poorly known. High-resolution seismic data, recorded in a 1 by 2 mi (1.6 by 3.3 km) grid, over much of the fan, allow better understanding of upper and middle fan features and processes, and of structural controls on fan sedimentation. Three bathymetrically prominent conduits supply sediment to the upper La Jolla fan system from stream and nearshore littoral drift-cell sources. La Jolla canyon (and contiguous La Jolla fan valley) is the main feeder to the fan. Seismic profiling data confirm the previously reported erosional character of the channel and constructional nature of flanking levees. These data also reveal that the position of the channel is controlled by the geometry of a buried, hard-rock structure. Newport canyon-channel, northerly feeder to the upper La Jolla fan system, is a single well-defined channel with flanking constructional levees where it lies in a structurally controlled trough. In contrast, the channel splays into multiple broad, poorly defined channels where sedimentation is unconstrained. A buried Pliocene-Pleistocene ancestral version of Newport channel displays the same structural control. The position of Loma sea valley, southern feeder to La Jolla fan system, is tightly controlled by the structure of the steep flank of Coronado Bank. Thus, Loma sea valley trends parallel with the shore and is fed by an orthogonal set of tributary channels which drains the San Diego shelf to the east. At intersections with these tributaries, abnormal thicknesses of sediment partially clog Loma sea valley. These channel fills may be analogous to those occurring in terrestrial trunk stream-intermittent tributary systems like the Colorado River in the Grand Canyon. Seismic data demonstrate that the La Jolla fan system comprises a complex interleaved set of sediment wedges derived from multiple sources and woven around the wrench tectonic fabric of uplifts and basins of the southern California borderland. Thus, La Jolla fan system presents an expansion from the simple radial growth pattern of fan sedimentation to a complex fan system built of a number of smaller interwoven radial growth components. Despite these complexities, lithofacies patterns are in part predictable for the La Jolla fan system. Fault-bounded uplifts form long-lived barriers to sediment dispersal and enhance channel development along their flanks. Multistory channel complexes, detectable seismically, commonly occur in these structurally controlled positions adjacent to wrench elated uplifts.

Simulation and Design of Steam Drive in a Vertical Reservoir

Summary A three-dimensional (3D) simulation model was used to design steam drive in a steeply dipping (53 deg.) heavy-oil reservoir in California and to select the optimal well pattern from eight alternatives. Sensitivity runs were made to study selected reservoir and operating parameters. The results show that upstructure injection with a modified staggered pattern results in increased recovery. Injection rate, steam quality, and formation dip are important parameters. Permeability normal to the bedding plane has little effect. Grid orientation affects oil recovery efficiency but does not change the optimal well pattern that was selected. Introduction The Webster sand sequence in the Midway-Sunset field is an attractive candidate for steam drive. The sands are unique because of their steep dip (53 deg.). It was recognized that placement of injection would be critical. Initial planning addressed the question, "What would be the optimal well pattern for this steeply dipping reservoir?" A three-dimensional, finite-difference, steam-injection simulator was used to assist in answering this question. This paper describes the reservoir and its geology, the brief production history under primary depletion and cyclic steam injection, and the results of the simulation study. Based on this study, a steam-drive project has been designed. A drilling and completion program for the project is under way, and steam injection is scheduled for mid- 1982. Reservoir Characteristics Geology The section 2F Monarch lease (220 acres) is situated in the southern portion of the Midway-Sunset field near the town of Maricopa, CA. The main productive horizon is the Webster sand sequence at an average depth of 1,200 ft. The Monarch sand has limited development and is separated from the Webster sand by a fault. The Webster sand series (Upper Miocene) consists of turbidites and submarine fan deposits separated by numerous thin and discontinuous diatomaceous shale beds. The sands are divided into five main units (A, B, C, D, and E) and are thickest near the center of the property. The average stratigraphic thickness of each unit is 100 ft. The beds dip an average of 53 deg. northeast and are truncated updip by a gently dipping Pliocene unconformity. Fig. 1 shows a typical induction-electric log. Rock and Fluid Properties The Webster sand is unconsolidated, poorly sorted with fine to coarse grains, and conglomeratic in part. Core analysis showed that porosity is 21 to 28% and air permeability is 1,200 md under reservoir conditions. The sand is saturated with a 14 deg. API oil, whose viscosity is a strong function of temperature. Table 1 is a summary of rock and fluid properties used in the simulation. Water/oil and gas/oil relative permeabilities of Webster sand cores at reservoir temperature were measured and plotted in Figs. 2 and 3, respectively. Temperature-dependent endpoints of the relative permeability curves given in Table 2 were either measured or estimated from published data. Production History The Midway-Sunset field was discovered in the early 1890's. The initial development of Section 2F began in 1917. Primary production continued until about 1960 when it became uneconomical. By that time, cumulative production from the Webster sands was 2.3 MMSTB, and the production rate was 120 BOPD. Cyclic steaming on Section 2F started in 1965 with good response. JPT P. 1546^

A Precambrian upper basin-slope and prodelta in Northeast Finnmark, North Northway; a possible ancient upper continental slope

ABSTRACT The 60-m- to 540-m-thick lower Naeringselva Member of the Basnaering Formation crops out on Varanger Peninsula, North Norway, and is part of the 9-km-thick late Precambrian Barents Sea Group. It is underlain by at least 3.2 km of submarine fan deposits and is the oldest part of a 2.5-km- to 3.5-km-thick fluvio-deltaic succession (Basnaering Formation). The upper part of the member is delta front deposits. The lower Naeringselva Member mainly comprises fine-grained, thin-bedded deposits, divided into four facies: 1) Facies I, parallel-laminated mudstone; 2) Facies II, current-rippled siltstone, interpreted with Facies I as low density, low velocity turbidity current deposits; 3) Facies III, structureless mudstone, interpreted as possible hemipelagic deposits; and 4) Facies IV, wave-rippled fine/very fine-grained sandstone, interpreted as due to wave action. Soft-sediment deformation is abundant as various styles of slide, slump, and in situ disturbed layers up to tens of meters thick. Erosional-depositional discordances are evident between packets of beds. The stratigraphic position and sedimentology of the lower Naeringselva Member suggest that it is part of an ancient upper basin-slope and prodelta, with submarine fan deposits on the lower basin-slope. Paleocurrent data, with a limited number of slide fold readings, imply that deposits from downs-lope flowing sediment-laden currents prograded the slope towards the east-north-east. Apart from sporadic storm events, the slope was below wave base. Modern analogues for the lower Naeringselva Member appear to be the upper part of continental slopes separating submarine fan from delta deposits as in the Mississippi Delta-Slope-Fan system.

Stratigraphy and Sedimentology of Upper Miocene Williams Sand, San Joaquin Valley, California: ABSTRACT

The upper Miocene, late Mohnian age, Williams Sand crops out in the southeastern Temblor Range along the southwest margin of the southern San Joaquin Valley, California. The Williams is composed of lenses of generally coarse material within the siliceous Antelope Shale Member of the Monterey Formation and is stratigraphically equivalent to the Stevens Sand. The sands and shales were deposited in paleontologically defined waters as much as 4,000 ft (1,219 m) deep. Based on field and laboratory studies, the Williams is interpreted as a End_Page 1689------------------------------ submarine fan deposit. Continuous grain-size plots of the outcropping sands were drafted and distinct turbidite facies were identified using Mutti and Ricci-Lucchi's classification. At the surface, the Williams dips northeast into the valley and contains many rather thin-bedded, usually graded, sandstones and conglomerates, with high porosity and permeability, which are interbedded with siltstone and shale. Thick deposits of shale, commonly cherty, separate large bundles of turbidites that pinch out along strike. The sandstone bundles often form coarsening- and thickening- upward sequences typical of deposition on the smooth suprafan lobes of the midfan. Other sandstones form fining- and thinning-upward sequences diagnostic of deposition on the channelized suprafan, although lack coarse pebbly material. App rently, the Williams fan continued to prograde until at least midway through its depositional history, when significant lateral shifting of coarse-grained sandstone bodies occurred. According to petrographic modal analyses, the sands are arkosic, having a clay matrix and occasional carbonate and opal cements. Lithologic descriptions plus petrographic and paleocurrent data suggest the source terrane was only a few miles west-southwest, and most likely was the northern Gabilan Range. The northern Gabilan Range is composed of granitic and metamorphic rock, and is now located 150 mi (240 km) northwest of the outcropping Williams owing to Miocene and post-Miocene strike-slip displacement along the San Andreas fault. In the subsurface, the Williams is composed primarily of fine to medium-grained sands, which are rather thinly bedded, poorly sorted, and interbedded with thick shales and siltstones characteristic of a lower fan facies. Oil is produced from Williams sands less than 2 mi (3.2 km) north of the study area from the Spellacy and Midway anticlines of the Midway Sunset field. Shales, and occasionally bentonites, separate the producing Williams into different reservoirs. End_of_Article - Last_Page 1690------------

Lithic Wackes of Early-Middle Eocene Lookingglass Formation, Southwest Oregon: ABSTRACT

The early to middle Eocene Lookingglass Formation is exposed over a wide area in southwestern Oregon. The formation contains a thick sequence of turbidite deposits consisting dominantly of very coarse to fine-grained lithic wackes, with minor amounts of pebbly sandstone, siltstone, mudstone, or shale. Sediments, mainly from the Klamath region on the south, and partly from a volcanic arc on the east, were deposited in a north-trending fore-arc basin approximately 125 by 155 mi (200 by 250 km) in size. Within the lower part of the sequence, the lithic wackes are mainly thick-bedded, normally graded, pebbly sandstones and very coarse to coarse sandstones that contain a shallow-water marine fauna. Channel-fill conglomerate lenses occur within some of the thick beds of sandstone. This part of the sequence is interpreted as a proximal submarine-fan deposit. The lithic wackes of the upper part of the sequence, however, generally form sheets of thinner bedded, medium to fine-grained sandstone with more matrix. They contain deeper water marine fauna and are devoid of channel-fill conglomerate lenses. This part of the sequence is interpreted as a distal submarine-fan deposit. Sedimentation took place at a high rate and was accompanied by rapid subsidence of the basin. The lithic wackes have undergone fairly intense diagenetic alteration, which includes cementation by calcite, silica, chlorite, and clay minerals; the replacement of feldspar grains, lithic fragments, and matrix materials by calcite and chert; and the recrystallization of chlorite. Cementation and compaction have considerably reduced the porosity of these sandstones. End_of_Article - Last_Page 1683------------

Minnehaha Member of Upper Devonian Brallier and Scherr Formations of Central Appalachians: ABSTRACT

The Minnehaha member of the Upper Devonian Brallier and Scherr formations has been informally named, and its use as a time band within the marine strata of the Devonian Catskill delta complex of the central Appalachians is suggested. The coarse clastic bundle of the Minnehaha member can be identified in both outcrop and subsurface for approximately 150 mi (235 km) along the Allegheney Front from Bedford County, Pennsylvania, to Greenbrier County, West Virginia. The Minnehaha member is 20.9 to 98.4 ft (6.37 to 30.0 m) thick, consisting of interbedded very thinly to thickly bedded medium-gray siltstones and olive gray shales, with some grayish-red siltstones and shales. The Minnehaha member was deposited by turbidity currents in generally unchanneled suprafan environments during the earliest Cohocton Stage. Three major, time persistent, depositional systems are recognized as having contributed to the Minnehaha member. End_Page 1171------------------------------ They are in order, from northeast to southwest, the Fulton, Mouth of Seneca, and Augusta depositional systems. The relatively brief time interval of Minnehaha deposition by three separate depositional systems strongly suggests a sea-level drop in the Appalachian basin as a causal factor. The overlapping of submarine fan deposits from three depositional systems could enhance the hydrocarbon reservoir potential of the Minnehaha member. The Minnehaha member may be the shoreward correlative of the gas productive Sycamore siltstone of north-central West Virginia. End_of_Article - Last_Page 1172------------

Sedimentation Associated with Cirque Barite-Zinc-Lead Deposit: ABSTRACT

The barite-zinc-lead Cirque Deposit and other major showings in the Gataga district are part of an Upper Devonian to Mississippian sequence of basinal shales and submarine fan deposits of chert pebble conglomerate which were derived from the northwest. This sequence is preserved in the Akie, Pesika, and Gataga troughs, and unconformably overlies Ordovician to Silurian slope and basinal facies of the Kechika trough. The Akie trough is host to all known potentially economic barite-zinc-lead deposits in the district. Both regional and detailed linear elements of the Cirque Deposit trend northwesterly and are asymmetric normal to the strike line. The background depositional unit is a soft gray aluminous shale which grades into black and carbonaceous shale to the southwest. An envelope consisting of diagenetically silicified fine carbonaceous clastic units was formed about the deposit. The outermost part of the diagenetic envelope consists of ribbon-bedded porcellanite with blebby and laminated massive barite on the northeast. Silicified platy poker chip shales with calcareous siltstone laminae are between the ribbon porcellanites and ore. The core of the cycle consists of up to 70 m of barite and sulfides on the axis of the deposit. Laterally, the ore section interfingers to the northeast with an e ual thickness of flaggy to blocky bedded silicified black shale containing abundant finely laminated pyrite. Pb:Zn ratios increase northeasterly, and ore isopachs are asymmetric toward the northeast with the thickest zone being on the southwest edge of the deposit. End_Page 585------------------------------ Genetically the barite-sulfide accumulations are considered to result from exhalative activity restricted to regionally developed basement faults. Accumulation occurred within a minor trough with resultant facies asymmetries being related to different topographic and paleochemical conditions during sedimentation and diagenesis. End_of_Article - Last_Page 586------------

Geometry and Internal Characteristics of Archaean Submarine Channel Deposits, Pilbara Block, Western Australia

ABSTRACT Well-preserved submarine fan deposits of early Archaean age (ca 3.3 Ga) occur in the Pilbara Block of Western Australia. Channel, interchannel, lobe, and basin-plain deposits are recognizable in two facies associations termed, respectively: conglomerate-sandstone-shale and sandstone-shale. Unitary upper-fan channel deposits are recognizable in the conglomerate-sandstone-shale facies association. The channel deposits consist of inverse-to-normal graded, and graded-stratified resedimented conglomerates and sandstones. These facies accumulated respectively in the thalweg and on the adjacent terrace of the upper fan channel and grade laterally into thin-bedded cde turbidites of levee origin. The coarse channel facies are enclosed within interchannel shales, iron-formations, and carbonates. The morphology of midfan channel deposits is strongly influenced by grain-size reflecting different provenances. Where conglomeratic in the west, these deposits are laterally continuous tabular bodies consisting of scour-based, graded-stratified conglomerate-sandstone couplets. Grading predominates but associated horizontal and cross stratification indicates periodic late-stage traction reworking. These midfan sediments are considered to have accumulated in shallow, laterally switching channels on a braided suprafan. Arenaceous midfan channel deposits occur in the southeast and comprise narrow lenses of amalgamated Bouma a or ab sandstones displaying an upward decrease in bed thickness. Sedimentation took place in laterally confined channels within cohesive argillaceous banks. he enclosing interchannel shales contain abundant overbank sandstones often with complete Bouma sequences. Both midfan channel types grade basinwards into upward-coarsening basin plain to lobe deposits. Basin-plain shales and iron-formations are considered to be analogues of Holocene hemipelagic and pelagic sediments.