Heterolithic Deposits Research Articles

Architecture of a tide‐influenced river delta in the Frontier Formation of central Wyoming, USA

The Frewens sandstone is composed of two elongate tide‐influenced sandstone bodies that are positioned directly above and slightly landward of a more wave‐influenced lobate sandstone. The 20‐km‐long, 3‐km‐wide Frewens sandstone bodies coarsen upwards and fine away from their axes, have gradational bases and margins and have eroded tops abruptly overlain by marine shales. These sandstones are superbly exposed in large cliffs on the banks of the South Fork of the Powder River in central Wyoming, USA. The deposits change upwards from thinly interbedded sandstones and mudstones to metre‐thick heterolithic cross‐strata and, finally, to metres‐thick sandstone‐dominated cross‐strata. There is abundant evidence for tidal modulation of depositional flows; however, palaeocurrents were strongly ebb‐dominated and nearly parallel the trend of sandstone‐body elongation. Detailed mapping of stratal geometry and facies across these exposures shows a complex internal architecture. Large‐scale bedding units within sandstone bodies are defined by alternations in facies, bed thickness and the abundance of shales. Such bedsets are inclined (5°–15°) in walls oriented parallel to palaeoflow and gradually decrease in dip over hundreds of metres as they extend from the sandstone‐dominated deposits higher in a sandstone body to muddier deposits lower in the body. Where viewed perpendicular to palaeoflow, bedsets are 100‐metre‐wide lenses that shingle off the sandstone‐body axis towards its margins. The sandstone bodies are interpreted as sand ridge deposits formed on the shoreface of a tide‐influenced river delta. Metres‐thick cross‐strata in the upper parts of sandstone bodies resemble deposits of bars (sandwaves) formed where tidal currents moved across shallows and the tops of tidal ridges. Heterolithic deposits lower in sandstone bodies record fluctuating currents caused by ebb and flood tides and varying river discharge. Erosion surfaces capping sandstone bodies record tidal ravinement. The tidal ridges were abandoned following transgression and covered with marine mud as waters deepened.

Depositional environment of the Vejle Fjord Formation of the Upper Oligocene-Lower Miocene of Denmark: a barrier island/barrier-protected depositional complex

The Vejle Fjord Formation was deposited in the coastal area at the eastern margin of the Upper Oligocene to Lower Miocene North Sea. Detailed studies of lithology and depositional structures demonstrate that coarsening-upwards successions resulted from landwards migration of barrier complexes as a response to relative sea-level rise. The formation of barriers, their migration and construction of new barriers was controlled by a varying balance between sediment supply and sea-level rise. The exposed sediments are mainly back-barrier deposits and represent deposition on the lagoon-facing barrier beach, wash-over fans, tidal flood deltas, tidal flats and the lagoonal floor. The barriers themselves are only sparsely represented in the studied exposures. Their influence on the depositional pattern is revealed by the formation of storm wash-over deposits and tidal inlet/tidal delta deposits. The destructional pattern of the barriers (storm erosion or tidal inlet widening) was apparently controlled by the orientation of barrier sections relative to the prevailing storm direction. A back-barrier beach deposit was developed with landwards-dipping heavy-mineral lamination. It forms part of a shallowing-upwards succession and represents a transgressive phase. Wash-over sands are up to 50 cm thick massive sand beds which pinch out laterally and interdigitate with lagoonal mud. Tidal inlet/tidal delta deposits are sandy intercalations in the lagoonal mud. The thickness is highly variable and marginal parts are strongly bioturbated. The tidal flat facies is dominated by small-scale channel fills of heterolithic deposits with a distinctive tidal rhythmicity, both on a single-tide scale and a neap—spring scale. The Vejle Fjord Formation is constructed of transgressive coarsening-upwards successions, which represent the growth and migration of barriers over their fine-grained back-barrier deposits. A large supply of clastic material forced new barriers to form further seawards than older ones, resulting in an overall regressive trend.

Reservoir Characterization of Thinly Laminated Heterolithic Facies Within Shallow-Marine Sand Bodies: ABSTRACT

Shallow marine sandstones typically form high quality reservoirs but they can contain a significant proportion of extremely heterogeneous facies. Particularly significant are heterolithic (mixed interlaminated sand-mud) deposits which are common in estuarine/incised valley-fill reservoirs and other tidally-influenced depositional environments. The complex mm/cm-scale interfingering of sands and clays in these reservoirs is below the resolution of most logging tools, which poses major problems for the petrophysical evaluation, quantitative reservoir modelling and reservoir performance prediction. This study outlines an integrated geological/petrophysical framework for the reservoir characterization of heterolithic facies from the Jurassic of the North Sea Basin which utilizes well logs, cores, minipermeameter and analog outcrop data. The calibration of wireline logs (GR, LDT/CNL, EPT and dipmeter) with cores helps in establishing the relationship between the architecture of sand-shale laminations and their wireline log response/electrofacies. The routine sampling procedure for porosity/permeability measurement from cores will not accurately determine the average reservoir properties for these heterolithic intervals. The selection of measurement points is of vital importance for determining average reservoir properties. The minipermeameter measurements are especially useful for these thin bedded reservoirs and serve as a useful guide for reservoir zonation and evaluation of petrophysical properties from wireline logs. The incorporation of analog more » outcrop data helps further in establishing vertical and lateral communication relationships at field scale. « less

Depositional Environment of the Downdip Queen City (Eocene) Sandstone, Mestena Grande Field Area, Jim Hogg and Duval Counties, Texas: ABSTRACT

ABSTRACT The downdip Queen City sandstone interval in the Mestena Grande field area of the south Texas Gulf Coast Basin comprises two sandstone depositional units, referred to herein as A Lobe and B Lobe. A total of 583 ft (179 m) of conventional core from 11 wells containing predominantly B Lobe deposits was examined macroscopically. The A Lobe is a thin (6-34 ft; 1.8-10.4 m) fine- to very fine grained, mostly bioturbated, well-sorted sandstone. The B Lobe is composed of fine to very fine, well-sorted sandstone interbedded with siltstone and mudstone. The trace fossil assemblage of the B Lobe indicates that sediments were deposited in the Cruziana ichnofacies. Trace fossils and authigenic minerals also suggest oxygen stratification during deposition. The B Lobe contains five subunits, each as much as 13.5 ft (4 m) in net sandstone thickness. These units were deposited as part of a highstand systems tract during the early Lutetian Stage (early middle Eocene). The B Lobe is a primarily aggradational unit composed of storm-generated sandstone and heterolithic deposits of the lower shoreface to inner shelf environment. The A Lobe is an upward-coarsening unit that represents progradation of the shoreface during late highstand systems tract development. An interlobal mudstone, which separates the units, marks the transition from early to late highstand systems tract development. End_of_Record - Last_Page 767-------

Tectonic Influence on Deposition and Erosion in a Ramp Setting: Upper Cretaceous Cardium Formation, Alberta Foreland Basin

This paper presents the results of a combined outcrop and subsurface investigation of the Upper Cretaceous Cardium Formation in northwestern Alberta and adjacent British Columbia, Canada. More than 100 measured core and outcrop sections combined with more than 1100 well logs were used to examine stratigraphic relationships in an area of over 45,000 km2. The Cardium consists of stacked regressive-transgressive cycles deposited during shoreline progradation along the western margin of a foreland basin occupied by the Western Interior seaway. In general, these cycles consist of shoaling upward successions (highstand systems tracts composed of shoreface sandstones and conglomerates and heterolithic offshore deposits) capped by transgressive erosion surfaces. Linear incised lowstand coarse-grained shoreface deposits are present at some stratigraphic levels. A single, thick (locally more than 20 m thick in the study area) nonmarine wedge that overlies shoreface sandstones is interpreted to represent deposition during rising sea level rather than accumulation behind a prograding strandline. Preservation of the incised lowstand shoreface deposits is associated with topographic breaks. In places, trends of isopachs, facies transitions, erosional bevels on transgressive erosion surfaces, synsedimentary faults, and modern production trends can be directly superimposed and closely correspond to basement structural trends. This suggests that basement structures were being remobilized during Cardium deposition, possibly in response to thrusting in the orogen c belt.

Lower Bahariya Formation in the Khalda Field--Sedimentation, Diagenesis, and Reservoir Properties: ABSTRACT

Khalda field is located in the northern portion of the Khalda west concession in the western desert of Egypt. Production is from the upper Cenomanian lower Bahariya Formation. The trap is established by a north-south-trending, oval, domal anticline dissected by east-west faulting. A major northeast-southwest-trending fault zone bounds the feature to the east. The lower Behariya comprises a sequence of tidal flats at the base, which pass upward through mixed flats and terminate in mud-rich flats. These are overlain by shallow marine sands and capped by the marine shales and limestones of the upper Bahariya. The whole sequence represents the action of a progressive, yet punctuated, marine transgression across a tidal flat. Facies associations, recognized from core and wireline-log data include inner shelf and mud-rich tidal-flat claystones, tidal heterolithic deposits, rippled sand-sheet/shoal complexes, cross-bedded sands, bioturbated shoal/bar complexes, lag deposits, tidal and storm channel fills, and shallow marine-shelf sheet-sand deposits. From facies correlations, an 11 zone reservoir modeling scheme has been defined. Reservoir quality, dependent on facies type, grain size, and distribution of authigenic cements, is best where rippled sand-sheet/shoal complexes and shallow-marine sheet-sands are abundant. Diagenetic modeling indicates that much of the observed porosity is secondary following carbonate dissolutionmore » and that quartz cement is the only major factor causing porosity reduction. Authigenic glauconite, found in large concentrations, together with fine laminations, controls effective permeability.« less

Sandstone mounds and associated facies sequences in some Late Precambrian and Cambro‐Ordovician inshore tidal flat/lagoonal deposits

ABSTRACTSandstone mounds occur in some shallow marine heterolithic deposits from the Late Precambrian Stangenes Formation (N. Norway) and the Cambro‐Ordovician Crozon Formation (N. W. France) and Cabos Series (N.W. Spain). The sediments displaying the mounds accumulated in partially protected tidal flat/ lagoonal environments immediately before and during major transgressions.The mounds are erosional features typically occurring on the tops of sheet sandstones (ca. 50–500 mm thick) some of which may have a storm washover origin. Mound genesis related to periodic emergence and late stage run‐off is supported by their intimate association with mudcracks and other very shallow water features (e.g. bidirectional current‐formed structures, wave ripples, ladder and interference patterns, mudflakes, etc.). Variation in mound morphology suggests that post‐depositional dissection began as elongate ridge‐gully couplets with secondary erosion of the ridge flanks leading to the development of more characteristic hemispherical geometries. Emergence may have been a function of tidal fluctuations and/or subsidence of storm surge events.Facies sequences point to the repeated filling of these inshore environments by storm washovers superimposed on ambient tidal conditions which possibly resulted from the progressive decay of beach barriers during transgression.