Swaley Cross-stratified Sandstones Research Articles

Sedimentary Architecture of Storm-Influenced Tidal Flat Deposits of the Upper Mulichinco Formation, Neuquén Basin, Argentina

This study reports on the Lower Cretaceous upper Mulichinco Formation in the Neuquén Basin, west-central Argentina. The studied succession comprises shallow marine strata, deposited in a mixed wave and tidal flat environment where ebb-tidal currents dominated. We describe mixed storm- and tide-influenced deposits within progradationally stacked high-frequency sequences, and discuss process interaction, sediment dispersal and preservation potential. These storm and tidal deposits mix spatially on bed-, bedset- and sequence scales, suggesting multiscale process interaction. The study investigates a 12 km long continuous outcrop, oriented sub-parallel to the paleocoastline. The succession comprises subtidal flat and meandering tidal channel complexes, with interbedding and interfingering of storm and tidal deposits. The tidal deposits are widespread and comprise moderately sorted sandstones with bimodal paleocurrent directions, single and double mud drapes, reactivation surfaces, and inclined heterolithic stratification. Varying bimodal paleocurrent directions suggest that the paleocoastline was irregular, consisting of both protrusions and bays. Storm deposits are mainly found erosively interbedded with subtidal flat sandstones, and exhibit dm-thick well sorted hummocky and swaley cross-stratified sandstones. These storm deposits show systematic lateral variations in abundance, from dominant to absent, which is linked to subtle variations in water depth along the irregular paleocoastline. As the tidal deposits are widespread across the study area, and with no significant facies change, the varying dispersal of storm-influenced deposits is considered a product of wave refraction, with converging and diverging wave energy at interpreted positions of coastal protrusions and embayments, respectively. Consequently, the irregular paleocoastline morphology caused spatial variability in wave impact and controlled preservation of interbedded storm and tidal deposits at the coastal protrusions, while facilitating complete tidal remobilization of sediments in the embayments. With no evidence for fluvial influence, ebb-tidal currents are considered as the main drivers for sediment dispersal onto the subtidal flat, through the meandering tidal channels.

WAVE-DOMINATED SHORELINE DEPOSITS IN THE LATE MIOCENE SEDIMENTARY SEQUENCE IN THE MIRI FORMATION NORTH SARAWAK, MALAYSIA

The research area is located in Miri region, north Sarawak. Observation was focused on selected outcrops along road cuts and beach. The distribution of outcrops is widely distributed at a few localities in Miri region such as Tanjong Lobang, Airport road, Hospital road and Oil Well road. Sedimentary sequences can be traced by facies variations as shoreline environment based on the sedimentary structures. Four facies were identified and characterised successfully in the study area based on their sedimentary structures, namely facies 1: planar cross stratified (PcS), facies 2: swaley cross stratified (ScS), facies 3: swaley-Hummocky cross stratified (SHcS), facies 4: Hummocky cross stratified (HcS) and heterollithic facies (He). Facies evaluation deduced that the sedimentation settings resulted as foreshore, upper shoreface, middle shoreface, lower shoreface and tidal (minor occurrence). Wave-dominated in the upward coarsening interval is unambiguous that representing by abundance of hummocky cross stratification and other storm deposits in the sandstone dominated portions, well-defined swaley cross stratified sandstone interval, and up to several meters thick sets of planar cross beds interval interpreted to have been formed by swash waves. Heterolithic units in this wave dominated sequences are as minor occurrence of tidal influence during fair weather .

High-Resolution Stratigraphy of the lower portion of the Green River Formation at Raven Ridge and Red Wash Field, NE Uinta Basin, Utah, Colorado, USA: Facies and Stratigraphic Patterns in a High-Gradient, High-Energy Lacustrine System

Lacustrine strata of a portion of the Green River Formation studied in outcrops along Raven Ridge and in the subsurface around Red Wash Field in the northeastern Uinta Basin represent cyclic storm-dominated shoreface to deep lake deposition within a syntectonic embayment on the margin of Eocene Lake Uinta. The study interval consists of the lower Green River Formation, including the Douglas Creek, Garden Gulch, and lower Parachute Creek members, from the top of the underlying Wasatch to the Mahogany Zone of the Parachute Creek Member. Data consists of 11,900 ft (3627 m) of section measured at 23 locations across Raven Ridge, including 7,800 ft (2377 m) of hand-held gamma-ray scintillometer measurements, and over 500 wells in the greater Red Wash Field area, including pay zone analysis correlated to stratigraphy in the field. Facies analysis, as the basis for an integrated stratigraphic approach, reveals a seven-fold hierarchy of stratigraphic cycles ranging from two orders of large-scale cycles to five orders of progressively higher-frequency (smaller scale) shoreface-lake cycles across an 18-mile (29 km) long and 1900-ft (579 m) thick dip-oriented stratigraphic transect. This study recognized twenty-two facies grouped into eight facies tracts using Walther’s Law for two composite shoreface successions: one for a siliciclastic storm-graded shoreface profile that was dominant during times of regression and one for a carbonate profile that dominated in times of transgression. Two important regional facies trends across Raven Ridge include: 1) greater proportions of mudstone facies present in the southern, upper portion of the Green River Formation; and 2) significantly higher proportion of bioturbated sandstone in the northern, lower portion of the formation. The long-term 2nd-order transgression of Lake Uinta from base to top of the study interval results in an evolution from a low-gradient shoreline with marshes, ponds, and sand/mud flats to a high-gradient high-energy profile composed of spits and shorefaces that grew southward away from the emergent highlands. A composite storm-graded shelf profile shows how trough, hummocky, and swaley cross stratification type and amalgamation style change offshore proportionally to contain mud-dominated tempestites, erosional storm furrows, and oil shale. In the most offshore positions, diastasis cracks caused by differential loading are common. The lacustrine shoreface profile is compressed in the Green River Fm. in the study area with narrow facies tracts and large local gradient changes as a result of different responses to sediment supply. As a lake grows and shorelines migrate, the increase in accommodation is balanced, or in-phase, by a corresponding increase in sediment supply resulting in shoreface progradation keeping up with lake-level rise. As the shoreface stacks vertically during the rise, over steepening and failure of the profile generates gravity-flow sandstone facies. Little reworking of hummocky cross stratification high on the profile was observed, probably because wave power was limited by a shallow fair-weather wave-base. These differences also result in more symmetrical lacustrine shoreface cycles, with a large proportion of sediment partitioned into rise hemicycles, as opposed to the classical fall-asymmetric marine para-sequence which tends to have little to no strata preserved in the rise hemicycle along most of the shoreface profile. Landward-stepping lacustrine shoreface cycles are more common during the early rise portions of larger-scale 3rd-order megacycles for similar reasons. Strata at Raven Ridge support the concept that Eocene Lake Uinta was chemically stratified, or meromictic, at least during certain periods. The equable subtropical Eocene paleoclimate is interpreted to be the most important control on meromixis. Chemical stratification played a critical role in the development and preservation of organic matter, as evidenced by oil shale facies. The equable climate, however, might also have made the lake prone to thermal stratification. A paradox exists in the storm dominance of the lacustrine shorefaces and the coeval lake stratification: wave energy apparently was insufficient to break through the strong chemocline. Red Wash Field, directly downdip from the Raven Ridge outcrop belt, is an example of an oil field in a setting where the lake margin is not coincident with a structural feature: a “non-coincident” margin. Reservoirs mostly are present in the 6th-order aggradational shoreface cycles that are interpreted to have accumulated in the rise portions of 3rd-order megacycles. The best reservoir facies are trough, hummocky, and swaley cross-stratified sandstone deposited by storm processes and structureless sandstone probably derived from over steepening and failure of the shoreface during transgression. A petroleum accumulation model encompassing the Red Wash-Raven Ridge area proposes that lacustrine-sourced petroleum originated from an over-pressured mature cell in the Altamont-Bluebell field region. Oil migrated updip through leaky seals and became trapped in reservoirs within the non-coincident lake margin strata. An irregular shoreline configuration and compaction folds at Red Wash Field trapped petroleum. After reaching spill point at Red Wash Field, oil migrated farther updip to Raven Ridge and Asphalt Ridge, forming tar sand accumulations.

Allostratigraphy of the Peace River Formation (Albian) in north-western Alberta and adjacent British Columbia

Abstract The middle to upper Albian Peace River Formation was deposited at the southern end of the ‘Hulcross Sea’, an embayment of the Boreal Ocean that occupied the foredeep of the Western Canada foreland basin. The Peace River Formation can be allostratigraphically divided by numerous, regionally-mappable erosion surfaces, recognizable both in wireline logs, core, and outcrop. We propose recognition of the informal Harmon, Cadotte and Paddy alloformations, bounded by four regionally-mappable marine transgressive surfaces, HE0, CE0, PE0 and VE3 in ascending order. The Harmon alloformation consists predominantly of marine mudstone, and is divided into five allomembers bounded by marine flooding surfaces and/or thick bentonites. The Harmon forms a wedge thinning from >145 m in the SW to 5 m in the NE over approximately 300 km. There is no geometric evidence of a sigmoidal geometry, or that allomembers downlap onto a single, distinct surface. Deposition took place on a very low-gradient and low-relief marine ramp, strongly influenced by storms. The Cadotte alloformation consists of well-sorted swaley cross-stratified sandstone and was deposited on a wave-dominated strandplain shoreface. Ravinement surfaces divide the Cadotte into three, sheet-like allomembers, each typically about 10 m thick. Allomembers CA and CB are mainly fine-grained sandstone whereas allomember CC is dominantly medium-grained sandstone with abundant pebble conglomerate. Towards the north, sandstone grades laterally into heterolithic facies indicative of an offshore setting. The Paddy alloformation lies unconformably on the Cadotte, and comprises an array of facies, with alluvial and lagoonal deposits predominant in the south. Further north, sandstone indicative of a wave-influenced strandplain shoreline forms a belt trending WSW-ENE across the middle of the area; heterolithic offshore marine deposits lie to the north. The Paddy alloformation comprises nine allomembers, PA to PI, that onlap progressively onto the basal unconformity PE0 from SW to NE. The pronounced wedge shape and muddy lithology of the Harmon implies rapid flexural subsidence and largely vertical aggradation whereas the sheet shape of the Cadotte suggests a lower rate of subsidence when high-frequency eustatic change may have driven rapid regressions and transgressions. The lower Paddy allomembers PA to PF are strongly wedge-shaped, suggestive of renewed tectonically-driven subsidence whereas upper allomembers PG to PI are more sheet-like, suggesting that a tectonic load exerted a less important influence and instead, more uniform regional isostatic subsidence took place, driven by the load of the eastward-encroaching sediment body. Sandstone-rich Paddy strata are abruptly overlain, at the VE3 unconformity, by a blanket of dark marine mudstone that forms the basal part of the lithostratigraphic Shaftesbury Formation; the mudstone between the VE3 and VE4 surfaces is of upper Viking age, and has a pronounced wedge geometry which implies a major new pulse of flexural subsidence in the west.

Recognition of wave-dominated, tide-influenced shoreline systems in the rock record: Variations from a microtidal shoreline model

Existing wave-dominated facies models are based on microtidal coastlines and do not adequately address wave-dominated environments influenced by significant tidal ranges. Observations from modern environments show that such systems are abundant along tide-influenced shorelines facing wide shelves and large embayments, such as much of the northern Australia coast; yet equivalent deposits have been rarely recognized from the ancient record. Geomorphological literature shows that tidal influence on wave-dominated shorelines has the effect of shifting the shoaling, breaking, and swash wave zones up and down the beach profile; when the tidal range is appreciable, sedimentation is affected significantly. Many macrotidal, wave-dominated systems (tidal range >4m), for example, are non-barred and are characterized by poor development of dune-scale bedforms in the subtidal zone and along the beach profile. Other systems do develop cross stratification, but this occurs in the intertidal zone rather than the subtidal zone as is implied in existing wave-dominated facies models. The association of many wave-dominated, tide-influenced environments with shallow shelves also suggests that major storms may be capable of reworking sediment significant distances from the shoreline.We present an ancient example of a wave-dominated, tide-influenced, fluvial-affected system (Wtf) from the Campanian Bearpaw to Horseshoe Canyon Formation transition near Drumheller, Alberta, Canada, which has been described in closely spaced outcrop exposures and core. Wave domination in the coarsening-upward interval is unambiguous and is represented by abundance of micro-hummocky cross stratification and other storm beds in the mudstone-dominated portions, a well-defined swaley cross stratified sandstone interval, and an up to four meter thick, horizontal planar stratified interval interpreted to have been formed by swash waves. Tide influence is suggested by common double carbonaceous and mud drapes and well-developed tidal rhythmites. The anomalously thick horizontal planar interval described above is interpreted also to be related to tides that shift the zones of wave reworking up and down the beach profile. Fluvial influence is suggested by the presence of fluid mud beds in the lower portion of the succession and the abundance of carbonaceous debris through the entire interval. The boundary between the mudstone-dominated and sandstone-dominated portions of the succession is sharp and scoured, and is interpreted as the boundary between a subaqueous delta front or mudstone belt below and a wave-dominated, tide-influenced shoreline above. Observations in this study and a survey of geomorphologic literature lead to a new proposed model of facies distributions for a wave-dominated, tide-influenced system. Additional ancient case studies are needed in order to generate robust facies models capable of dealing with the full variability of such systems.

Comparative analysis of facies and reservoir characteristics of Miri Formation (Miri) and Nyalau Formation (Bintulu), Sarawak

This study on the sedimentological and reservoir petrophysical properties (porosity, permeability, density, sonic velocity) of sandstones were conducted on the sedimentary rocks belonging to the Miri Formation (Middle Miocene) from Miri and Nyalau Formation (Middle Miocene) from Bintulu in Sarawak. The objectives are i) to investigate and determine the facies characteristics and reservoir properties of the different types of sandstones, and ii) to establish the relationships between the facies characteristics and petrophysical properties. Two lithofacies have been sampled from the outcrops of Nyalau Formation and four lithofacies from the outcrops of Miri Formation based on lithology, sedimentary structures, fossil traces and bed geometry. These are grouped into four major lithofacies: (i) hummocky cross-stratified sandstones (HCS); (ii) trough cross-bedding sandstones (TCB); (iii) bioturbated sandstones; and (iv) swaley cross-stratified sandstones (SCS). Hummocky and swaley cross-stratified sandstones, trough cross-bedded sandstones and some bioturbated sandstones of Miri formation recorded the highest poro-perm values, with relatively lower density values (as compared Bintulu samples). The TCB sandstones are well sorted sandstones, with minimal mud content. This has contributed to the high poro-perm values. The bioturbated swaley cross-stratified sandstone (MF4) shows high permeabilities in some samples and low permeabilities in others. This reflects the heterogeneity in facies characteristics and poro-perm distribution of bioturbated samples. Bioturbated HCS, the HCS and TCB sandstones of Bintulu show moderate poro-perm values. The Nyalau Formation rocks are older, and thus are expected to have undergone greater compaction than the younger Miri Formation. This is also reflected in the higher density values recorded for all the Bintulu samples. INtrodu Ct Io N In general, facies characteristics determine the overall reservoir properties of sandstones, while diagenetic changes impose a secondary control on their poro-perm characteristics. The purpose of studying the reservoir sedimentological characteristics and petrophysical properties of Tertiary sandstones from Sarawak is to investigate and determine the facies characteristics, and reservoir properties of the different types of sandstones, and to establish the relationships between the facies characteristics and petrophysical properties. This study on the sedimentological and reservoir petrophysical properties (porosity, permeability, density, sonic velocity) of sandstones were conducted on the sedimentary rocks belonging to the Miri Formation (Middle Miocene) from Miri and Nyalau Formation (Middle Miocene) from Bintulu in Sarawak.

Depositional controls on petrophysical properties and reservoir characteristics of Middle Miocene Miri Formation sandstones, Sarawak

Rock exposures around the town of Miri, Sarawak, belonging to the Miri Formation (Middle Miocene strata), represent the uplifted part of the subsurface sedimentary strata of the Miri oilfield. Data derived from outcrop studies concerning facies and sand body characteristics, and petrophysical properties are crucial for subsurface reservoir characterization and modeling of hydrocarbon reservoirs deposited in similar settings. The aim of this paper is to integrate lithofacies and petrophysical properties of Miri sandstones, in order to characterize and quantify the Miri reservoirs. The Miri Formation consists of a wide range of siliciclastic, tide-generated and storm-and wave- generated facies. Twelve lithofacies have been identified and grouped into two major facies associations: (i) the estuarine, tide-dominated, and (ii) the shoreface-offshore transition, storm-and wave-dorninated facies associations. The estuarine lithofacies are characterized by distinct and diagnostic tidal signatures; tidal dune cross-bedding with mud draped cosets and foresets including mud couplets, bidirectional (herringbone) cross-bedding, rhythmic stratifications, flaser bedding, wave bedding and lenticular bedding. Shoreface-offshore transition, storm-and-wave facies association is represented by sandstone bodies with evidences of storm and wave generated sedimentary structures; swaley cross-stratified sandstones, amalgamated hummocky cross-stratified sandstones, bioturbated sandstones and mudstone inter-bedding with parallel stratified to hummocky cross-stratified sandstone. Petrophysical properties were determined for six sandstone lithofacies: (i) Lithofacies A (multiple stacked trough cross-bedded sandstone, tidal channels and bars, estuary mouth), (ii) Lithofacies B (parallel-bedded sandstone of estuary upper flow sand flat), (iii) Lithofacies F (homogeneous coarse sandstone, outer estuarine tempestites), (iv) Lithofacies G (swaley cross­ stratified, upper-to-middle shoreface sandstone), (v) Lithofacies I (fine-grained bioturbated sandstone of the lower shoreface) and (vi) Lithofacies L (fine-grained, hummocky cross stratified sandstone, offshore transition). These lithofacies are characterized by a wide range of permeability values, which vary by several orders of magnitude (0.35 to 287 md), while porosity vary by only a few percent. Lithofacies A and F recorded the best reservoir properties; porosities are 23.3-29.7% and permeabilities are 9.64-287 md. Lithofacies G shows a wide range of porosity and permeability values that range from high to low reservoir properties; porosities are 23.5-27.5% and permeabilities are 3.4-45 md Lower shoreface and offshore transition (lithofacies I and L respectively) display the lowest reservoir properties; porosities are 13.5-24.5 % and permeabilities are 035-3.4 md In general, high reservoir quality of Miri sandstones is associated with coarser grain size, low clay contain and better sorted grains. Extensive clay drapes, bioturbation, and increasing proportion of very fine grains content result in significant decrease in permeability in both tide-generated and wave-generated lithofacies.

Ripple cross-stratification in swaley cross-stratified sandstones of the Chungo Member, Mount Yamnuska, Alberta

Swaley cross-stratified sandstones are exposed in the Late Cretaceous Chungo Member of the Wapiabi Formation at Mount Yamnuska, Alberta. At this site, many of the individual flaggy-weathering, thin beds of sandstones that make up the swaley cross-stratified structure are internally ripple cross-stratified. The association of swaley and ripple cross-stratification has not previously been described and is interpreted to indicate compound cross-stratification generated under combined flow condi tions. Furthermore, this association brings into question the possible genetic relationship between swaley cross-stratification and hummocky cross stratification, a sedimentary structure generated under purely oscillatory conditions.

Lateral and vertical facies sequences in the Upper Cretaceous Chungo Member, Wapiabi Formation, southern Alberta

The Chungo Member of the Wapiabi Formation (Campanian) shales out northward and (or) eastward from Lundbreck to the Bow Valley, southern Alberta. At Lundbreck, basinal mudstones are overlain by turbidite and hummocky cross-stratified sandstones in an overall coarsening-upward sequence. The marine part of the sequence is capped by dominantly swaley cross-stratified sandstones, interpreted as storm-dominated shoreface deposits. Nonmarine fluvial deposits overlie the shoreface. Essentially the same sequence persists northward to the area of the Highwood River, but in the Highwood River – Sheep River – Longview area, the swaley cross-stratified shoreface sandstones are progressively cut out by a north- and (or) east-ward-dipping erosion surface with up to 40 m of relief. The erosion surface is overlain by a lag of chert pebbles and then by a marine coarsening-upward sequence of offshore to shoreface deposits (the lower tongue of the Nomad Member). Nonmarine Chungo deposits then prograded north- and (or) eastward to overlie this marine tongue in the Highwood area. They are in turn abruptly overlain by a gravel-coated transgressive surface marking the upper marine tongue of the Nomad Member. Finally, marine shales of the Nomad Member are abruptly overlain by dominantly fluvial rocks of the Belly River Formation.We suggest that the main Chungo shoreface, stratigraphically equivalent to the Milk River sandstone of southeastern Alberta, prograded north- and (or) eastward to at least the Highwood River area. A rapid relative lowering of sea level followed by stillstand resulted in the formation of the erosion surface and the supply of gravel to the basin. The overlying coarsening-upward sequence indicates the resumption of shoreline progradation, but this appears to have been relatively short-lived; it was terminated by the transgression of the upper Nomad tongue.

Depositional environments and paleogeography in the Albian Moosebar Formation and adjacent fluvial Gladstone and Beaver Mines formations, Alberta

The marine Moosebar Formation (Albian) has a currently accepted southerly limit at Fall Creek (Ram River area). It consists of marine mudstones with some hummocky and swaley cross-stratified sandstones indicating a storm-dominated Moosebar (Clearwater) sea. We have traced a tongue of the Moosebar southward to the Elbow River area (150 km southeast of Fall Creek), where there is a brackish-water ostracod fauna. Paleoflow directions are essentially northwestward (vector mean 318°), roughly agreeing with turbidite sole marks (329°) in the Moosebar of northeastern British Columbia.The Moosebar sea transgressed southward over fluvial deposits of the Gladstone Formation. In the Gladstone, thick channel sands (4–8 m) are commonly multistorey (up to about 15 m), with well developed lateral accretion surfaces. The strike of the lateral accretion surfaces and the orientation of the walls of channels and scours indicate northwestward flow (various vector means in the range 307–339°). The Moosebar transgression was terminated by construction of the Beaver Mines floodplain, with thick, multistorey sand bodies up to about 35 m thick. Flow directions are variable, but various vector means roughly cluster in the north to northeast segment. This indicates a major change in dispersal direction from the Gladstone and Moosebar formations.A review of many Late Jurassic and Cretaceous units shows a dominant dispersal of sand parallel to regional strike. This flow is mostly north-northwestward (Passage beds, Cadomin, Gladstone, Moosebar, Gates, Chungo), with the southeasterly dispersal of the Cardium being the major exception. Only at times of maximum thickness of clastic input (Belly River and higher units, and possibly Kootenay but there are no published paleocurrent data) does the sediment disperse directly eastward or northeastward from the Cordillera toward the Plains.