Relative Sea-level Lowstand Research Articles

Controls on Eolian Facies Architecture, Middle Jurassic Page Sandstone, Colorado Plateau

Eolian systems to not fit simply into basin sedimentation models developed for marine/coastal sequences. Therefore a new conceptual framework was developed linking eolian basin-scale sedimentation patterns to conditions and events within and external to the eolian environment. Controlling factors at this scale are eolian sediment budget, sand supply, water-table fluctuation, and subsidence. These parameters and their relative rates predict eolian system type, genetic stratigraphy, mode of preservation, and resulting facies architecture. This conceptual model allows interpretation of the genetic or event stratigraphy of an eolian sandstone and inference of basinal conditions during its formation. The Page Sandstone, an erg system adjacent to the Middle Jurassic Carmel interior seaway, consists of two laterally continuous accumulations of dry eolian systems, relatively uninterrupted by super surfaces (Harris Wash and upper Thousand Pockets); these are separated by a contrasting eolian condensed zone, which consists of lenses of dry dunefield accumulations truncated by multiple wet super surfaces. The Harris Wash and upper Thousand Pockets represent times of high sand supply and positive sediment budget, with water table well below the sediment surface during a relative lowstand of the Carmel sea. The condensed zone indicates a time of low sand supply, a high but fluctuating watermore » table, and a sediment budget fluctuating from positive to negative. It corresponds to a relative Carmel sea-level rise. In the Page Sandstone single or multiple super surfaces in the eolian system correspond to maximum flood surfaces in the marine system. In contrast, relative sea-level lowstands are represented by erg accumulations uninterrupted by hiatal surfaces.« less

A Depositional Model in the Arabian Intrashelf Basin: The Upper Jurassic Hanifa Reservoir of Abqaiq Field, Saudi Arabia

Abqaiq field is a northeast-trending anticline approximately 60 km long and 12 km wide and contains several reservoirs. The 100 m thick Hanifa Reservoir interval consists of interlayered peloidal packstone and wackestone with subordinate dolomite and anhydrite. During an Upper Jurassic relative sea level lowstand, paleotopography within the Arabian Intrashelf basin localized fine-grained packstone into isolated mounds over the Abqaiq South Dome area, while muddier facies were being deposited over the North Nose. The Abqaiq Hanifa carbonate mound was zoned using sequence stratigraphy as a conceptual framework to ensure that chronostratigraphic relationships were honored, and that the subsequent computer model would therefore accurately reflect spatial porosity continuity within the reservoir. The Hanifa Reservoir was subdivided into five widely correlative zones that approximate separate parasequences, each beginning with tight mudstone-wackestone and grading upward into porous wackestone-packstone. Sequence stratigraphy interpretations are based on regional wireline log correlations combined with core descriptions and show the Abqaiq Hanifa to be time equivalent to only the upper few meters of the Hanifa Reservoir in fields to the north. In addition to reservoir modeling utility, these two general intrashelf basin settings have potential for stratigraphic traps. Wherever reservoir-quality rock can be found, proximity to the Hanifa/Hadriyamore » source rocks-the source for much of Saudi Arabia's vast reserves-makes the Hanifa a favorable exploration target.« less

Late Quaternary sedimentation in St. George's Bay, southwest Newfoundland: acoustic stratigraphy and seabed deposits

Shallow seismic reflection data collected in St. George's Bay, southwest Newfoundland, reveal a complex pattern of subsurface topography and acoustic facies. Two basins in the inner bay are underlain by glacially overdeepened valleys that extend to depths in excess of 180 m. Within the thick Quaternary sequence in the inner bay we recognize eight acoustic units. Units 1 (ice contact), 2 (subaqueous outwash), and 3 (draped glaciomarine) record the presence and retreat of a major Late Wisconsinan ice margin. Unit 4 (postglacial mud) has resulted from reworking of glaciogenic sediments in response to changes in relative sea level. Unit 5 (postglacial sand) is a shoreface deposit on the seaward front of the former moraine. Unit 6 (postglacial delta) was formed by fluvial reworking of glaciogenic sediments during the postglacial lowstand of relative sea level. Unit 7 (postglacial barrier–platform) comprises seaward-fining clinoform prisms that have prograded into the basins, and underlie gravel beach-ridge plains at Stephenville and Flat Island. Unit 8 (postglacial spillover) results from entrainment of coarse sediment on the shallow sill and subsequent progradation into the basins of the inner bay.Seabed sediment in the basins is mud where sampled. The submarine platforms associated with the barriers at Stephenville and Flat Island are largely sandy. The sill is covered by a gravel veneer, with irregular patches of sand that coalesce and thicken seawards. Extensive areas of gravel ripples testify to the continued mobility of much of the coarse sediment on the sill.A major ice front in the inner bay was present prior to 13.7 ka BP. The draped glaciomarine sediments, dated at 13.7–11.2 ka BP in nearby Port au Port Bay, were deposited after withdrawal of the ice front to the vicinity of the present coast, during a readvance, and subsequently. During the postglacial lowstand of relative sea level much of the present sill area was emergent.

Viking Formation (Albian) at Eureka, Saskatchewan: A Transgressed and Degraded Shelf Sand Ridge (1)

The Viking oil field at Eureka is part of the long (80 km), narrow (10 km) east-west-trending Dodsland-Hoosier offshore sand ridge in west-central Saskatchewan. The various facies of the ridge are encased in marine mudstones, and the ridge has formerly been interpreted as a tidal current deposit. However, core examination shows that the facies are burrowed and bioturbated and very few primary sedimentary structures are preserved. The sandstone facies are extensively bioturbated by Teichichnus, and contain no medium-scale cross-bedding, and no other tidal features such as reactivation surfaces, spring-neap cycles and tidal bundles. Cross sections constructed from well logs and cores demonstrate that the ridge overlies an erosion surface, and that at least three other erosi n surfaces occur within the sand body. These surfaces strike east-west, and dip very gently southward. Pebble veneers occur in patches on the erosion surfaces. We interpret the ridge as having formed from a plume of sand in a shallow sea, with its western end close to a deltaic distributary channel (similar to the plume east of the modern Nile delta). The regional Viking shoreline moved north or northeastward into the basin during a lowstand of relative sea level. During subsequent transgression, the delta was eroded and displaced an unknown distance southwestward. The ridge also shifted southward, and was finally detached from the distributary and abandoned on the shelf. Original slopes of the southern ridge margin were flattened to gradients of 0.0006-0.0009 by storm-generated currents. The internal erosion surfaces were probably formed during the overall transgression. Rates of sediment movement were relatively slow, resulting in almost c mplete bioturbation and, hence, destruction of primary sedimentary structures.

Sequence Stratigraphic Architecture of Slope Fan Deposits: Miocene Puente Formation, Los Angeles Basin: ABSTRACT

Outcrops of the Miocene Puente Formation in the eastern Los Angeles basin represent deposits of a slope and base of slope apron along the margin of a rapidly subsiding basin. In contrast to a traditional canyon-fed submarine fan, coarse-grained sediments of the Puente Formation were transported down the slope through shallow gullies fed from fan deltas prograding across the narrow shelf. Sandstone and conglomerate of the Soquel Member of the Puente accumulated in multiple lobes forming a coalescing base-of-slope apron. The principal depositional components of this system include sheet-like sands and associated shallow channels. The Sycamore Canyon Member consists of a series of overlapping, prograding wedges identifiable from aerial photo mosaics. The internal architecture of these prograding wedges is complex, consisting of stacked sand- and gravel-filled channels associated with finer grained levee and interchannel deposits. The Soquel and Sycamore Canyon members of the Puente Formation are interpreted as having been deposited during times of relative sea level lowstand, and the finer grained La Vida and Yorba members represent deposits of relative sea level highstands. Sequence and facies architecture of Puente Formation deposits correspond to reservoir quality and heterogeneity of potential reservoir units. Lowstand channel-fill deposits typically represent the best reservoirmore » facies due to their higher porosities and permeabilities and low clay contents, although slope gullies of the Soquel Member are often carbonate cemented. Interchannel and overbank facies of the Sycamore Canyon Member are clay rich resulting in lower permeabilities. Sheet sands of the Soquel Member slope-apron system have intermediate porosities, permeabilities. and clay contents.« less

Sedimentary Architecture of Marginal and Shallow Marine Depositional Systems Tracts in Upper Cretaceous Series of San Juan Basin: ABSTRACT

The Upper Cretaceous series of the San Juan basin consists of five (or more ) depositional sequences bounded partially by subaerial unconformities and partially by correlative, basinward conformities. Three depositional systems tracts account for nearly all the preserved strata: highstand, lowstand, and transgressive. At relative sea level highstand, sediments are accommodated at the most landward sites within the basin (e.g., early Gallup Sandstone tongues). This systems tract is characterized by prograding bay-head deltas and successive open-marine deltas. During the ensuing sea level fall, much of the highstand system is removed by subaerial erosion. At relative sea level lowstand, sediments accumulate at the most basinal sites in the form of prograding strand plains, associated shelf sand sheets and plumes, and a minor amount of fluvial channel and overbank deposits. During transgression the coastal plain is aggrading and hence traps most terrigenous clastics before they reach the open coast. The attendant erosional retreat of the shoreface, however, releases coarse sediment (sand) to the shelf, where it accumulates in large-scale shelf sand ridges. These ridges are the principal petroleum reservoirs in the Cretaceous rocks of the basin (Tocito Sandstone Lentil, parts of the Twowells Tongue of the Dakota Sandstone, etc.). During the transgressionmore » a carbonate-dominated condensed section encroaches landward, stratigraphically above the transgressive depositional systems. This surface attains its maximum landward extent some time between peak rate of sea level rise and highstand. The three principal surfaces of the depositional sequence - the sequence boundary, the transgressive ravinement surface, and the condensed section - all have clearly defined sedimentological characteristics.« less

Carbonate Sequence Stratigraphy and Controls on Carbonate Platform Development--Case Study from Permian of West Texas-New Mexico: ABSTRACT

Integration of seismic stratigraphic concepts with detailed field studies and geohistory analysis provides powerful interpretation leverage for deciphering the complex geologic history of carbonate platform-basin areas. Changes in carbonate productivity as well as platform growth and the resultant facies distribution are controlled most importantly by changes in relative sea level. The structural history of the Permian basin during the Permian shows two subsidence cycles of 10-20 m.y. duration. These subsidence cycles were major factors in the long-term (106 - 107 m.y.) development of the Permian carbonate platforms. During periods of relatively rapid subsidence, aggradation was dominant; during periods of slow subsidence, major platform progradation occurred. Superimposed on the long-term tectonic cycles is a series of third-order eustatic cycles (0.5-3 m.y.), which controlled development of 27 depositional sequences. Each sequence is composed of three depositional systems tracts: (1) a lower basin-restricted wedge interpreted to have been deposited during a relative fall and lowstand of sea level, (2) a transgressive systems tract of variable thickness, and (3) an upper, relatively thick, aggradational-to-progradational carbonate platform system, which includes significant allochthonous deposition in the basin and is interpreted to have been deposited during a relative highstand in sea level. The lowstand systems tracts are composed dominantly of quartz sandstone, commonly intercalated with carbonate debris beds at the toe of the slope. S quence boundaries display erosional truncation (subaerial on platform or at platform margin, subaqueous on slope) and/or subaerial exposure. Erosion and debris deposition occurs both within and outside submarine-canyon feeder systems. Two highstand depositional styles are differentiated here: (1) a keep-up system, which represents a relatively rapid rate of accumulation able to keep pace with periodic rises in sea level and displays a mounded-oblique stratal geometry at the platform margin, and (2) a catch-up system, which represents a relatively slow rate of accumulation and displays a sigmoid profile at the platform margin. Individual strata units of the platform margin and slope area of the catch-up carbonate system have a much longer sea-floor residence time and display significantly greater amounts of early submarine cement. The underlying transgressive systems tract tends to have a keep-up or give-up (i.e., thin, drowned) depositional style. End_of_Article - Last_Page 1522------------

Evolution of the Cape Fear Terrace: A complex interaction between the Gulf Stream and a paleo-shelf edge delta

A high-resolution seismic stratigraphic study of the Cape Fear Terrace (outer continental shelf off Cape Fear, North Carolina) combined with bio-lithostratigraphic data have yielded a complex chronostratigraphic framework of the Quaternary sequences that comprise this portion of the North American continental margin. The Cape Fear Terrace is one of six terraces/protuberances that form significant topographic irregularities along the South Carolina and North Carolina shelf-slope break. The Cape Fear Terrace is situated upon an anomalous, point-source, prograding, shelf margin feature which has protruded out onto the upper slope throughout much of the Quaternary. This upbuilding/outbuilding followed a period of active submarine erosion in which the ancestral Gulf Stream and/or associated meanders cut an erosional path beneath the present shelf margin during the early Pliocene. The protuberance was originally constructed during a relative lowstand of sea level as a shelf-edge delta. Severe modification of this deltaic lobe occurred during a relative highstand of sea level as Gulf Stream activities began to more effectively modify the margin. The anomalous thick accumulation of shelf-edge sediments acted as a barrier to flow inducing complex flow patterns of the Gulf Stream causing preferential erosion on its downstream side. Subsequent deposition may have resulted during more elevated highstands of sea level, as evidenced by the presence of active sand waves in the terrace protuberance region today. Once this shelf-edge bathymetric irregularity had been established, the Gulf Stream acted as a dynamic force inducing cellular flow structures within the shelf environment and enabling sediments to be transported seaward along the paleo-shoals complex.

Tectono-Eustatic Controls on Carbonate Platform Development, Permian Basin Outcrop-Subsurface: ABSTRACT

Integration of seismic stratigraphic concepts, detailed field studies, and geohistory analysis provides powerful interpretation leverage for deciphering the geologic history of the Permian carbonate platform complexes. The structural history of the Permian basin during the Permian shows two subsidence cycles of 10 to 20 m.y. duration. These subsidence cycles played a major role in the long-term (millions to tens of millions of years) development of the Permian carbonate platforms. During periods of relatively rapid subsidence, aggradation was dominant; during times of slow subsidence, major basinward platform progradation occurred. Superimposed on the long-term tectonic cycles are a series of third-order eustatic cycles (0.5-3 m.y.) which controlled development of 23 depositional sequences. Each sequence is composed of three depositional systems tracts: (1) a lower basin-restricted wedge interpreted to have been deposited during a relative fall and lowstand of sea level; (2) a transgressive systems tract of variable thickness; and (3) an upper aggradational to progradational carbonate platform system interpreted to have been deposited during a relative highstand in sea level. The lowstand systems tracts are composed dominantly of quartz sandstone, commonly intercalated with carbonate debris beds at the toe-of-slope. Two highstand depositional styles are differentiated here: (1) a keep-up system which maintainsmore » pace with periodic rises in relative sea level and displays a mounded-oblique stratal geometry at the platform margin and (2) a catch-up system which represents a relatively slow rate of accumulation and displays a sigmoid profile at the platform margin. Sequence boundaries display erosional truncation (subaerial on shelf or at shelf edge; subaqueous on slope) and/or subaerial exposure.« less

Sequence Architecture and Lithofacies Assemblages of Submarine Fan Deposits in Los Molles Formation (Jurassic), Neuquen Basin, Argentina: ABSTRACT

The Neuquen basin is a remnant of the Mesozoic back-arc basin trend that developed along the western margin of South America. It contains a thick, diverse sequence of Jurassic sedimentary strata, whose facies distribution was strongly influenced by syndepositional tectonism. The predominantly dark, laminated shales and siltstones of the Los Molles Formation range from Pliensbachian to Callovian in age and record the progradation of the outer shelf, slope, and basin-plain sediments deposited during the shoaling phase of the lowermost, or Cuyan, Jurassic cycle. Based on outcrop, well, and seismic data, several thick packages of sandstone and conglomerate within the Los Molles are interpreted to represent submarine fan deposits that developed during periods of relative sea level lowstand. Sea level falls were probably related to local synchronous tectonic pulses rather than true eustatic fluctuations. The distribution of coarse-grained fan deposits was apparently strongly controlled by the location of major Jurassic fault trends that stabilized the position of the shelf-slope break through time. Based on the geometry and sequence architecture, two distinct styles of fan development are recognized in the Los Molles sandstones. The most common style (type A) is characterized by sequences that have poorly defined, sand-poor lobes with well-developed channel-leveemore » complexes. Some channels exhibit large-scale accretion surfaces, probably resulting from lateral migration. Thick-bedded arenite facies are limited to amalgamated channel fills, whereas thin-bedded classical turbidites are present as overbank deposits. Type A fans were built by turbidity and fluxoturbidity currents from submarine canyon point sources. The less common fan sequences (type B) lack channeling; they are dominated by thick, massive beds of internally featureless sandstone that are bounded by chaotic slump deposits.« less

Tectonic and eustatic controls of late quaternary shelf sedimentation along the Central California (Santa Cruz) continental margin: high-resolution seismic stratigraphic evidence

A high-resolution “uniboom”, seismic stratigraphic investigation of a portion of the central California continental shelf has demonstrated that depositional patterns and sequences are controlled largely by an interplay of glacioeustatic sea-level fluctuations superimposed on local tectonics. Wrench tectonics, associated with active right-lateral shear along the San Gregorio fault zone, and the Pigeon Point Basement High control the location, distribution and overall geometry of depositional sequences via en echelon folding and differential subsidence. Areas of relatively thick and thin late Quaternary sediments conform in large part with structures produced during wrenching. Glacioeustatic sea-level oscillations have also shaped depositional patterns and sequences. Correlation of our seismic stratigraphic data with a southern California continental margin sea-level curve, suggests that during the last glacial maximum, approximately 18,000 yrs ago, a relative lowstand resulted in the erosion of a distinct unconformity upon which late Quaternary sediments have accumulated. A rapid rise of sea level to a relative stillstand, approximately 12,000 yrs ago, produced a concave-up, marine terrace profile across the mid-shelf, that has since been infilled with as much as 22 m of Holocene clastic sediments. A relative drop of sea level, approximately 11,000 yrs ago, allowed sediments to build seaward as a series of prograding clinoforms that form the basal sequences of the late Quaternary sediment fill. The succeeding Holocene transgression partially eroded the top of this earlier regressive sequence, and has now established a typical, wave-graded shelf along which sediments fine in a seaward direction to water depths of 90–100 m. At greater shelf water depths, surface sediments coarsen and appear to be relicts of previous relative sea-level lowstands. The presence of now submerged and buried marine terraces along both the central and southern California continental margins, at elevations lower than modern terraces actively forming today, suggests that flights of raised marine terraces may not always decrease in age with decreasing elevation, as is commonly assumed for relative dating. Because sea-level fluctuations during at least the past 700,000 yrs, have been both numerous and of unequal magnitudes, it is likely that age inversions will occur within any given flight of raised Quaternary marine terraces along tectonically active continental margins.

High-Resolution Seismic Stratigraphy of North Carolina Continental Margin, Cape Fear Terrace: Sea Level Cyclicity, Paleobathymetry, and Gulf Stream Dynamics: ABSTRACT

A high-resolution seismic stratigraphic study of the Cape Fear Terrace (outer continental shelf off North Carolina) combined with biolithostratigraphic data has yielded a chronostratigraphic framework of the Quaternary sequences that comprise this portion of the North American continental margin. The Cape Fear Terrace is an anomalous, point-source, prograding, shelf-margin feature that has experienced positive relief through much of the Quaternary. This upbuilding or outbuilding followed a period of active, early Pliocene, submarine erosion in which the ancestral Gulf Stream cut an erosional path beneath the present shelf margin. The terrace was originally built up during a relative lowstand of sea level with the construction of a shelf-edge deltaic feature. Severe modification of this delta front occurred during a relative highstand of sea level as the Gulf Stream began to impinge upon the margin. The anomalously thick accumulation of shelf-edge sediments acted as a barrier to flow, inducing complex flow patterns of the Gulf Stream. Excavation of these sediments yielded a ter ace feature with preferential erosion on the upstream side. Subsequent deposition in the terrace region may have resulted during fairly highstands of sea level, as evidenced by the presence of active seaward-prograding sand waves in the terrace region today. Once this shelf-edge bathymetric irregularity (the terrace) had been established, the Gulf Stream acted as a dynamic force inducing cellular flow structures within the shelf environment, which enabled sediments to be transported seaward along the paleo-shoals complex. End_of_Article - Last_Page 284------------