Valley-fill Sequence Research Articles

Transgressive Valley-Fill Sequences: Implications to Sequence Stratigraphy and Petroleum Exploration: ABSTRACT

ABSTRACT Large amounts of hydrocarbons have been discovered in association with valley fill deposits. The lateral and vertical distribution of siliciclastic rock types in transgressive valley fill deposits is governed by the stratigraphic sequence. The sequence stratigraphy is controlled primarily by the interaction of subsidence, eustacy, and volume of sediments. During periods when eustatic sea level decline exceeds the rate of subsidence, much or all of a basin may become exposed, and a lowstand surface of erosion will develop forming a stratigraphic sequence boundary. In deeper basins such as the Gulf Coast Basin, the lowstand erosion surfaces are confined to the shelves at the margins of the basin. When the sedimentation rate is less than the sum of the rate of subsidence and eustatic sea level change, a transgressive sequence develops over the lowstand surface with deeper water facies overlying shallower water and/or nonmarine facies. Reservoir potential siliciclastics accumulate in valley fill, estuarine, and wave reworked transgressive deposits. Differences in the spectrum of transgressive deposits can be attributed to variations in the rate of eustatic sea level rise, subsidence, and sediment supply. Rapid rates of subsidence and/or eustatic sea level rise relative to sediment supply result in an abrupt landward shift in facies and valleys filled primarily with estuarine muds. Examples include the Opeche formation of the Powder River Basin and the lower Wilcox and Yegua formations of the Texas Gulf Coast. The valley fill mudstones in these units trap hydrocarbons in laterally adjacent facies. Slower rates of relative sea level rise, or increased sediment supply, result in valley fill sequences with thicker basal fluvial deposits overlain by estuarine to marine sands and muds. Petroleum is produced from fluvial-estuarine reservoirs within this type of valley fill in the Morrow Formation in southeast Colorado and southwest Kansas and the Doig Formation of western Alberta. Complex valley fill sequences consisting of multiple backstepping progradational parasequences occur in association with varying rates of eustatic sea level rise or subsidence relative to sediment supply. Examples from the Muddy Sandstone of the Powder River Basin illustrate such complexities. Petroleum has been produced from fluvial, bayhead delta, and barrier island facies of the Muddy Sandstone valley fills. End_of_Record - Last_Page 303-------

A Spectrum of Transgressive Valley-Fill Sequences: Implications to Sequence Stratigraphy and Petroleum Exploration: ABSTRACT

A Spectrum of Transgressive Valley-Fill Sequences: Implications to Sequence Stratigraphy and Petroleum Exploration: ABSTRACT

Transgressive Valley-Fill Sequences in Exploration and Development: A Spectrum of Examples: ABSTRACT

Transgressive Valley-Fill Sequences in Exploration and Development: A Spectrum of Examples: ABSTRACT

Time-Stratigraphic Correlation of Lower Wilcox Valley-Fill Sequences, Colorado and Lavaca Counties, Texas: ABSTRACT

Late Paleocene and early Eocene lower Wilcox strata in southeast Texas are characterized principally by sandstone-rich deposits of fluvial and deltaic systems that prograded from a stable platform area into an unstable growth-faulted shelf margin setting. In contrast, incised valley systems, initiated during episodes of sea level lowering and filled dominantly with mud during subsequent transgressions, punctuate several lower Wilcox intervals. Further, valley-fill sequences are known to provide seals and/or reservoirs for a number of stratigraphically trapped hydrocarbon accumulations. Time-stratigraphic correlation of lower Wilcox strata provides improved differentiation of stacked valley-fill sequences and thereby more refined interpretation of depositional history and more accurate mapping for exploration purposes.

Comparison of Sandstone Reservoir Geometry in a Valley-Fill Depositional Sequence and a Deltaic Progradational Sequence, Middle Jurassic, Yorkshire, England: ABSTRACT

The geostatistic simulations elaborated by the reservoir geology group of the IFP and the Geostatistic Center of the Ecole des Mines (HERESI GROUP) are based on the interpretation of representative outcrops of littoral to deltaic deposits. The methodology includes some detailed studies of large outcrops in terms of reservoir geology, a computation of the geological and petrophysical parameters, the conditional simulation of reservoir geometry, and their internal heterogeneities by geostatistic methods. Two sites, Cloughton and Ravenscar, have been selected along the Yorkshire coast in the Middle Jurassic siliciclastic series. The Ravenscar Group series (a stratigraphic and sedimentologic equivalent of the Brent Formation in the North Sea) is well exposed in wide, extended cliffs. The two-dimensional geometry of the reservoirs is reconstructed from photomosaics and surveying. Their three-dimensional architecture is controlled by core drills located just behind the studied cliffs. The wells are full-cored wire-line log (gamma ray and dipmeter) recorded, and porosity and permeability measurements are made every 20 cm in reservoir levels.

Sea Level Control on Facies Architecture of Incised Valley-Fill Sequences: Case Study of Sabine and Trinity Valleys, Texas Continental Shelf: ABSTRACT

The rate of sea level rise likely has varied during the late Wisconsinan-Holocene transgression. The authors are investigating the sea level history of the northwest Gulf of Mexico by examining the sequence stratigraphy of incised valleys on the Texas continental shelf. Glaciologists argue that mass wasting of marine ice sheets can cause rapid and episodic relative sea level (RSL) rises on the order of 5 m/100 years. Such an event would produce a large (/approx/25 km) landward translation of the shoreline on low-gradient shelves like that of north Texas. RSL rise events are expected to be manifested as discontinuities in valley-fill sedimentation and as changes in valley shape. Nearly 1000 km of high-resolution seismic profiles collected in an area extending from Sabine Pass to Galveston and to 60 km offshore were integrated with engineering borings, vibracores, and piston cores; these data allow mapping of incised valleys and valley-fill facies associated with the ancestral Sabine and Trinity rivers. An RSL rise event is characterized by a change from slow rate of rise to rapid and back to slow. The period of rapid rise produces a major flooding surface; bayhead delta development is suppressed, and lower estuarine or marine deposits lie directlymore » on fluvial deposits. Because accommodation increases as rapidly as RSL rises, valley-fill deposition is limited to the original, deeply incised valley. In map view, the valley appears relatively straight and narrow. The valley just offshore Galveston Island represents this situation. During a period of slow rise, bayhead deltas prograde and downlap onto estuarine deposits. In this case, sediments may completely fill the original incised valley, and the river supplying this valley may meander beyond previous valley edges. In map view, such a valley will be broad and irregular in shape, much like modern Galveston Bay.« less

Sequence Stratigraphy and Onlap Relationships of a Stratigraphic Trap, Lower Cretaceous Muddy Sandstone, Hilight Field, Powder River Basin, Wyoming: ABSTRACT

In Hilight field more than 74 million bbl of oil and 244 bcf of gas have been produced from thin fluvial and shallow marine sandstones of the Lower Cretaceous Muddy Sandstone. In this area the Muddy was deposited during a late Albian sea level rise and onlaps a lowstand subaerial surface of erosion including a dendritic valley system incised into the underlying Skull Creek Shale. Transgressive valley-fill deposits of the Muddy Sandstone in the Hilight field area consist of four regionally correlative, time-bounded, back-stepping, progradational units. The retrogradational nature of these units indicates they belong in a transgressive systems tract rather than a lowstand wedge, as is often implied for valley-fill sequences. Each unit is capped by a regionally extensive marine flooding surface. The contact between units is placed at the surface representing maximum flooding or at the correlative horizon landward of the maximum transgression. Two of these contacts include thin bentonite beds which substantiate the time-stratigraphic interpretation. Petroleum is trapped in each unit by the onlap of reservoir sandstone facies against the lowstand surface of erosion on the impermeable Skull Creek Shale. Top seals are formed by mudstones at the base of overlying units or by the Shell Creekmore » Shale, which overlies the Muddy Sandstone above a regionally extensive marine flooding surface. Reservoir heterogeneity is explained by lateral facies changes within each unit. The lateral and vertical distribution of reservoir-quality sandstone in the Muddy sequence in this area can be used as a model to predict occurrences in similar sequences elsewhere.« less

Unconformities and Valley-Fill Sequences--Key to Understanding Reservoirs at Lonetree and Poncho Fields, Denver Basin, Colorado: ABSTRACT

Previous interpretations suggested that the Lower Cretaceous ''J'' sandstone in the Denver basin is divisible into three genetic units: a lower delta front (J-3), a middle delta plain (J-2), and an upper destructional marine bar (J-1). The presence of root casts and siderite cement along the upper contact of the J-3 sandstone, however, suggests that J-2 deposits are separated from the J-3 sandstone by a regional unconformity. This contact may mark the same unconformity that separates the Horsetooth and Fort Collins Members in outcrop along the western margin of the basin. J-2 deposits comprise point bar, crevasse splay, and floodplain sequences of a broad alluvial plain. Fluvial deposits at Lonetree and Poncho probably formed in a tributary to a larger order tributary that flowed southwest through the Peoria field area. These tributaries eventually drained into a major trunk stream represented by valley-fill deposits of the Kassler sandstone. Delta-front deposits (J-3) that underlie the unconformity are tightly cemented by siderite and do not produce in either field. J-2 sandstones are productive from north- and west-trending point-bar deposits in both fields and from laterally equivalent crevasse-splay deposits at Lonetree field. Secondary porosity has created a common reservoir in point-bar and crevasse-splay depositsmore » at Lonetree. Laterally equivalent deposits of major trunk streams, such as the Kassler sandstone, generally produce only over structural noses in the southern D-J basin. Overlying J-1 sandstones form northeast-trending marine bars in both field areas. Two echelon bars are present at Poncho but only the western one is productive. The eastern bar at Poncho and the single marine bar at Lonetree are wet.« less

Models for Holocene Valley-Fill Sequences from High-Resolution Seismic Facies of Galveston Bay: ABSTRACT

Reconstructions of the northern Gulf of Mexico shelf for the Holocene have relied on the dating of isolated bathymetric banks. These banks, which are interpreted as former shorelines, provide snapshots of the shelf during periods of relative sea level stillstand. A more complete sedimentary record of the Holocene transgression is likely preserved in the incised valley-fill sequences. The first step in deciphering the record of Holocene valley-fill sequences is development of high-resolution seismic facies models based on modern environments. The modern incised valley-estuarine system of Galveston Bay has been seismically surveyed. Important environments include bayhead delta (Trinity River delta), tidal inlet, flood tidal delta (Bolivar Roads), and estuarine sediments (central bay). Additionally, fluvial sediments partially infill the entrenched Trinity River valley. Seismic facies interpretation was corroborated by information obtained from sediment cores. The influence of the rate of relative sea level rise on incised valley-fill facies architecture is demonstrated in hypothetical sequence models which are applied to the interpretation of high-resolution surveys of Holocene shelf deposits.

Seismic Facies Analysis of Entrenched Valley Fill: A Case Study in Galveston Bay Area, Texas: ABSTRACT

ABSTRACT The entrenched Trinity River valley beneath Galveston Bay was studied using high resolution seismic data. The shape of the incised valley was determined on mini-sparker lines, which were obtained from the U.S. Geological Survey in Corpus Christi, Texas. Uniboom lines, shot in 1987 aboard the Rice University research vessel R/V Matagorda, provided detailed records of the sediments filling the valley. The correlation between lithofacies and high resolution seismic facies was established by integrating the uniboom data with information about sedimentary environments. Environments were interpreted from lithologic descriptions of sediment cores and tied to the seismic lines. In addition, many uniboom lines were shot directly over known modern environments (i.e., the Trinity bayhead delta, the middle estuary, and the flood tidal delta at Bolivar Roads). The good correlation between lithofacies and seismic facies warrants the use of high resolution seismic data to determine depositional environments in areas where they are unknown. Information concerning incised valley geometry and the valley-fill sequence led to conclusions concerning the evolution of the Galveston Bay estuary. Possible point bar deposits, seen overlying the Pleistocene surface on one of the uniboom lines, support the idea that the Trinity River entered a meandering phase during the Holocene transgression, prior to the flooding of the present estuary. The valley-fill sequence of fluvial sediments overlain by bayhead delta and then estuarine deposits, which is present throughout most of the estuary, seems to be interrupted in the middle of the bay. The lack of bayhead delta deposits in this area may indicate a rapid rise of sea level sometime between 6000 years B.P. and the present.

Effect and Mechanism of Episodic Sea Level Events: Record Preserved in Late Wisconsinan-Holocene Incised Valley-Fill Sequences: ABSTRACT

Effect and Mechanism of Episodic Sea Level Events: Record Preserved in Late Wisconsinan-Holocene Incised Valley-Fill Sequences: ABSTRACT

Valley-Fill Sequences and Onlap Geometries, Lower Cretaceous Muddy Sandstone, Kitty Field, Powder River Basin, Wyoming: ABSTRACT

The Muddy Sandstone at Kitty field is a valley-fill sequence that records a late Albian sea level rise and accompanying transgression. The valley was cut during a preceding sea level lowstand. Stratal geometries and facies successions within the valley fill demonstrate the history of transgression was not gradual and progressive. Rather, the valley fill comprises a series of discrete, time-bounded, depositional units which onlap the erosional surface. Five time-bounded depositional units were defined by facies successions and were used to define onlap geometries. Facies successions within individual units record progressive shoaling. Capping each succession, there may be a planar disconformity, a thin bioturbated interval, or the deepest water facies of the next depositional event. Thus, the termination of each depositional event is marked by an episode of rapid deepening. At a single geographic location, stratal successions within older depositional units represent more landward facies than those within younger units. Therefore, the onlap geometry of the valley-fill sequence consists of a landward-stepping arrangement of depositional units. The primary reservoirs within the valley-fill sequence, at Kitty field, are laterally coalesced, channel-belt sandstones at the base and barrier island sandstones at the top. Reservoir sandstones of lesser quality occur within the intermediate estuarinemore » facies. The stacking pattern, developed by onlap of the units, results in multiple pay zones within mid-valley reaches. The boundaries of each depositional unit define a high-resolution, chronostratigraphic correlation of valley-fill strata, a correlation corroborated by bentonites. This correlation method gives an accurate description of the internal geometry of valley-fill strata and, therefore, provides a basis for understanding the process of transgressive onlap.« less

Tectonics and Depositional Environments in Early Pennsylvanian of South-Central New Mexico: ABSTRACT

The Pennsylvanian Magdalena Group unconformably overlies Precambrian to Mississippian strata throughout south-central New Mexico. Regional southward tilting, warping, and erosion resulted in progressively older pre-Pennsylvanian subcrop relations from south to north. Normal marine shelf sedimentation was represented by upward shoaling cycles containing mixed siliciclastics and carbonates. Channels cut into Ordovician strata in the southern Caballo Mountain area suggest that this area was a relatively deep valley or trough during Late Mississippian-Early Pennsylvanian erosion. Marine transgression from the south backfilled the preexisting stream valleys with sequences of packstone, wackestone, shale, and coarse quartzarenite. Topographically higher areas were blanketed with thin beds of laminated bioclastic packstone, grainstone, lime mudstone, and shale. Semirestricted tidal to nearshore environments are reflected in local sections by finely laminated hematitic dolomites, oncolitic wackestones, limestone conglomerates containing reworked Mississippian chert, and terrigenous shales supporting petrified wood float. Depositional onlap farther north resulted in a thinner and younger sequence. The cyclic nature of these deposits reflects a proximity to the shoreline and suggests an abruptly shifting base level, possibly controlled by Early Pennsylvanian glacial eustasy. The time-stratigraphic position of the valley-fill depositional unit may be broadly correlated to other Late Mississippian-Early Pennsylvanian valley-fill sequences recognized in the Delaware basinmore » and Grand Canyon.« less

Sedimentary Facies in Air-Fall Pyroclastic Debris, Arikaree Group (Miocene), Northwest Nebraska, U.S.A.

ABSTRACT The Arikaree Group is an important constituent of the Tertiary sequence in the northern High Plains of the western United States. The Upper beds form a distinct formation-rank unit within the Arikaree Group. The bulk of the unit consists of air-fall pyroclastic debris; epiclastic detritus is only a subordinate part of the sediment. In the Agate Fossil Beds area, the Upper beds constitute a valley-fill sequence along the edge of a broad, shallow southeast-trending paleovalley. The valley fill has fluvial and eolian components. The fluvial component represents in-channel deposition within a sandy braided system. Large-scale trough cross-strata are the most common sedimentary structure in the fluvial deposits. The eolian component consists of unreworked ash-fall mat rial. This sediment lacks current-produced sedimentary structures. In the Agate area, the fluvial and eolian components of the Upper beds differ from those in the subjacent Harrison Formation. Parallel laminae predominate in stream-channel deposits of the Harrison Formation and are associated with stream marginal dunes. The temporal change in fluvial style and in the character of associated eolian deposits observed between the Harrison Formation and the Upper beds suggests an increase in stream discharge with the passage of time and development of an effective vegetation cover. The latter may have resulted from the establishment of prairie grasses in the region. The absence of thick vertical accretion deposits is used to assign the fluvial facies of the Upper beds a braided-stream origin. The stratification sequence contains large-scale trough cross-strata but not large-scale planar-tabular cross-strata. The absence of planar-tabular cross-strata is atypical of stratification sequences of sandy braided systems.

Depositional Facies and Uranium Occurrence, Triassic (Dockum Group), Texas Panhandle: ABSTRACT

Late Triassic (Dockum Group) rocks accumulated in relict Paleozoic basins bound by the Amarillo uplift on the north and the Glass Mountains on the south. Basins were reactivated by late Paleozoic or early Mesozoic tectonic activity that created the Gulf of Mexico. More than 2,000 ft (600 m) of terrigenous clastics, derived mostly from older sedimentary rocks, accumulated within the basin. Source areas were in Texas, Oklahoma, and New Mexico. The Dockum Group accumulated in a variety of depositional systems including (1) braided and meandering streams, (2) alluvial fans and fan deltas, (3) highly constructive lobate deltas, (4) lacustrine systems including ephemeral and relatively long-lived lakes, and (5) mud flats. Dockum sedimentation was cyclic, a reflection of alternately humid and arid climatic conditions. During humid climatic conditions lake level was relatively stable. Meandering streams supplied sediment to high-constructive lobate deltas in the central basin area; braided streams and fan deltas were dominant depositional elements within southern and northern basin areas. During arid climatic conditions base level was lowered, stream valleys evolved, and small fan deltas developed along ephemeral lake margins; evaporites, calcretes, silcretes, and soils developed on floors of ephemeral lakes and on delta platforms. Uranium occurs within about 25 depositional facies. Highest uranium values are in lacustrine facies which developed under arid climatic conditions. Channel-lag facies of meander-belt systems generally exhibit consistently higher uranium values than other depositional facies. Crevasse-channel and crevasse-splay deposits locally contain mineralized carbonized wood. Delta-front sandstones of high-constructive lobate deltas contain uranium. Radioactive minerals are present within conglomeratic parts of the valley-fill sequence. Although a relation exists between uranium occurrence and depositional facies, prediction of uranium occurrence is difficult because of a complex groundwater history. End_of_Article - Last_Page 835------------

A review of the braided-river depositional environment

Generalized sedimentation models have been developed from a review of more than sixty recent papers on modern and ancient braided-stream deposits. Braided rivers consist of a series of broad, shallow channels and bars, with elevated areas active only during floods, and dry islands. There are three main bar types; longitudinal, comprising crudely bedded gravel sheets; transverse to linguoid, consisting of sand or gravel and formed by downstream avalanche-face progradation; and point or side bars, formed by bedform coalescence and chute and swale development in areas of low energy. Important sediment-forming processes include bar formation, channel-floor dune migration, low-water accretion and overbank sedimentation. Braided-stream deposits consist of up to three gravel facies, five sand facies and two fine-grained facies. Vertical sequences recorded in modern and ancient deposits are of several types: flood-, channel fill-, valley fill-, channel re-occupation- and point bar-cycles. Some of these fine upward and could be confused with meandering-river sequences. Facies assemblages and vertical sequences fall into four main classes, which are proposed as sedimentation models for the interpretation of ancient braided-river deposits in the surface and subsurface: (1) Scott type: consists mainly of longitudinal bar gravels with sand lenses formed by infill of channels and scour hollows during low water. (2) Donjek type: may be dominated by sand or gravel; distinguished by fining-upward cycles caused by lateral point-bar accretion or vertical channel aggradation. Cycles commonly are less than 3 m thick, but cycles up to 60 m may be present, representing valley-fill sequences. Longitudinal and linguoid-bar deposits, channel-floor dune deposits, bar-top and overbank deposits all may be important. (3) Platte type: characterized by an abundance of linguoid bar and dune deposits (planar and trough crossbedding). No well-developed cyclicity, probably owing to a lack of topographic differentiation in the river (no evidence of deep, primary channels, abandoned areas or overbank areas). (4) Bijou Creek type: consists of horizontally laminated sand plus subordinate amounts of sand showing planar crossbedding and ripple marks. Formed during flash floods and may be most typical of ephemeral streams.

Soil trends in two valley fill sequences

A sequence of profiles in alluvium from the South Coast of New South Wales and another from the Southern Tablelands are described and compared. Each sequence displays profiles of essentially sedimentary nature on low, narrow alluvial benches, cumulic soils on the more general flood-plain landscapes, soils with A and minimal texture B horizons on low terraces, and soils with strongly differentiated A and texture B horizons on high alluvial terraces. Profile development for each sequence is represented as depth functions and from these data indices of profile anisotropy (IPA) are derived. The step-wise changes in biotic and mineral profile organization from stratigraphically young to old soils are similar at both locations. Comparable profile sequences on ,alluvium have been observed in many other locations in humid south-eastern Australia. Available stratigraphic information at these locations is insufficient for estimates of rate of soil development to be made.

Discriminant-function analyses of data on a valley-fill sequence in southeastern Queensland

A sedimentary sequence in which four units were morphologically distinguished was examined for 23 chemical and physical attributes and the data subjected to discriminant-function analysis. Intercorrelation between attributes was such that Cu, Mn, Ca, fine-sand content and organic carbon did not contribute to the discrimination. The elements most useful were Mg, K, Fe, and Zr, whereas a smaller contribution was made by Ti, Al, P, Mn, Zn, Na, Sr, Co, Pb, coarse-sand content and the cation exchange capacity and potassium content of the clay. The sequence of layers in the section could best be interpreted in terms of four depositional cycles whose deposits tend to become finer in an upward direction. There was no need to invoke intervening stable periods of pedogenesis to explain the formation of dark clay bands.

Use of the Vertical Profile in Environmental Reconstruction: ABSTRACT

The relation of the vertical stratigraphic succession to areal depositional patterns was first observed by Johannes Walther and is known as Walther's Law of Facies. Each depositional unit in a vertical stratigraphic succession is the result of a particular sedimentary environment. When these units are compiled vertically, they represent a sequence of environments characteristic of a specific over-all sedimentary process such as regression or transgression. These environmental successions are definite and recognizable and may be used to define over-all sedimentary processes in ancient rocks. Therefore, environmental sequences provide a reference framework for interpreting the sedimentary history of any stratigraphic section. Only a limited number of specific vertical sequences has been found in a comparative study of Recent and ancient sediments. The following sequences have been developed into models of sedimentation. Regressive Marine c. Marine shale or lagoonal deposits b. Thin-bedded sand/silt and shale a. Poorly bedded shale Lowermost units are deposited below wave base; higher units close to sea-level. Fluvial (channel or valley-fill sequence) d. Ripple cross-laminated zone c. Laminated, even-bedded sand/silt zone b. Festoon cross-bedded zone a. Basal conglomeratic bedload zone Deltaic Sequences Regressive marine sequences overlain by nearshore fluvial, bay, and marsh deposits; characterized by extensive marine deposits and variable non-marine sediment distribution patterns. Transgressive Marine b. Marine shales or fragmental limestones a. Sand or silt Widespread distribution and thinness are diagnostic; basal unit abruptly overlies shale in many instances; gradation upward into marine shale is rapid. Bathyal-Abyssal Sediments Widely distributed, thin-bedded; fauna and sedimentary structures characteristic of deeper water. Lacustrine Sediments Resembles regressive marine sequences, but is developed on a smaller scale and lacks marine fauna. End_of_Article - Last_Page 374------------