Beach-ridge Plain Research Articles

Morphostratigraphy and facies architecture of sandy barriers along the Eastern Shore of Nova Scotia

Linear southeast trending valleys along the Eastern Shore of Nova Scotia were initially formed by fluvial incision and subsequently scoured during Pleistocene glaciations. Estuarine and barrier sedimentation was initiated when the valleys were drowned during the marine transgression of the early- to mid-Holocene. This coast continues to experience transgression, due to relative sea-level rise of 35–40 cm per century. Eastern Shore barriers have formed under a wave-dominated regime. The modal wave is highly energetic, with a height of 1.5–2 m and a 9–10 s period. Tidal range is low mesotidal with maximum spring range of 2.1 m. Fluvial sediment supply to Eastern Shore estuaries is negligible. Four sandy barriers from the Eastern Shore exhibit erosional and progradational morphologies that result from differences in the balance between relative sea-level rise, sediment supply and depositional processes within coastal compartments. Morphological contrasts represent the cyclic nature of barrier and estuarine evolution along the Eastern Shore. During transgression, sedimentation commences with a unit of fine grained central basin deposits overlain by a bed of fine to medium, massive and cross-bedded flood-tidal delta sands. An erosional surface lies at the contact between the flood-tidal delta facies and the overlying nearshore facies of tabular and cross-bedded gravelly sands. In some cases, the nearshore unit may grade upward into a second, younger flood-tidal delta deposit that is in turn incised, and then filled by sandy channel fill facies. The tidal delta facies is overlain by beach sands at the seaward side and washover deposits on the landward side of the barrier. The uppermost facies in the sequence includes a composite unit of upper beach and dune sands. Where sediment supply is sufficient, a beach ridge plain will form, producing a composite barrier stratigraphy with transgressive and regressive elements.

Heightened North Pacific Storminess during Synchronous Late Holocene Erosion of Northwest Alaska Beach Ridges

A progradational regime of falling sea level and/or high sediment input has produced extensive beach ridge plains in northwest Alaska during the last 4000 yr. Eleven Chukchi Sea beach ridge complexes, oriented at various angles to wind fetch, provide a cumulative history of longshore transport and erosion. Archaeological and geological upper limiting radiocarbon ages ( n = 59) allow correlations between depositional units on seven beach ridge complexes. Progradation started 4000 yr B.P. at nearly all complexes, as eustatic sea level stabilized. Two disconformities or truncations are found on most of the complexes, providing time-parallel storm horizons, dated at 3300-1700 and 1200-900 14C yr B.P. Between 1700 and 1200 14C yr B.P. most of the complexes prograded, indicating the predominance of less-stormy conditions. Modern synoptic patterns that produce Chukchi beach ridge erosion are linked to northerly shifts in North Pacific storm tracks. The regionwide beach ridge erosional truncations correlate with records of glacier expansion, heightened precipitation evident in tree-rings, stream flooding, and shelf deposits reworked by storm surges.

Andisol formation in a Holocene beach ridge plain under the humid tropical climate of the Atlantic coast of Costa Rica

Soil formation has been studied in relation with time in a 5000-year old chronosequence on volcaniclastic beach ridges of the perhumid tropical Atlantic coast of Costa Rica. All soils are under tropical rainforest. Drainage conditions change by subsidence from excessively drained in the two youngest soils to imperfectly drained in the two oldest soils. Parent material is rather homogeneous andesitic sand with a volcanic glass component of less than 10%. It has been found that under these conditions Andisols form within 2000 years. Imperfect drainage caused mottling and accumulation of iron-coatings, as well as the formation of a thin O-horizon in the oldest profiles. Sand content of the soils decreases regularly with soil age, while the amount of fine material increases concurrently. The increase in fine material and the accumulation of organic matter cause an increase of CEC and andic properties, and a decrease in bulk density and pH with soil age. Depth of biological influence increases with soil age, but soil faunal activity is hampered in the oldest three profiles, probably by imperfect drainage. Due to the extreme leaching conditions, the sum of exchangeable cations is less than 2 cmol + kg −1 in the B-horizons of the older soils, notwithstanding the presence of a considerable amount of weatherable primary minerals.

Variation of coastal dynamics during the last 7000 years recorded in beach-ridge plains associated with river mouths: example from the central Brazilian coast

The reconstruction of relative sea-level changes, during the last 7000 years, has shown that the central Brazilian coast was been subjected to submergence until approximately 5100 yr. B.P. However, the emergence after 5100 yr. B.P. was interrupted by two important fluctuations with an amplitude of approximately 2–3 m and a duration of 200–300 yr. This evolutionary history, which is quite different from that of several other regions in the world, played an essential role in the development of the central Brazilian coastal plains, whether or not they are associated with important river mouths. The periods of submergence, characterized by erosional phases, introduced noticeable changes in the geometry of the coastal deposits. The periods of emergence gave rise to sandy terraces covered by beach-ridges whose orientation is determined by the longshore drift. Elsewhere on a low sandy coast, the direction of longshore sand transport depends on the orientation of the swell. In a coast subjected to various swell patterns the efficient swells are defined as those which determine the resulting longshore transport direction. Such swells are not necessarily the most prevalent. For instance, along the central Brazilian coast the southern sector waves, in spite of their infrequent occurrences, are much more powerful than the northern sector waves and therefore generate a longshore sand transport from south to north. When fossil beach-ridges are present, as is the case on the central Brazilian coast, their geometry reflects the past directions of longshore sand transport. This makes it possible to determine the provenance of past efficient swells and to establish the past wind patterns. A detailed study of the beach-ridge geometry of some sections of the central Brazilian coast, showed a sequence of reversals of the longshore drift during the last 5100 yr, with a duration ranging from 10 to 100 yr. These reversals represent changes in the direction of effective waves, which determine the longshore transportation of sediments, and, consequently, indicate changes in the wind pattern.

Controls on Quaternary coastal evolution of the east-northeastern coast of Brazil: roles of sea-level history, trade winds and climate

East-northeastern Brazil has a wave-dominated, micro- to meso-tidal coast, lying entirely within the southern Atlantic trade wind belt. Integration of geologic mapping, radiocarbon dating and vibracoring data shows that the Quaternary coastal evolution of this area was controlled by three major factors: (1) sea-level history; (2) trade winds; and (3) climate change. Sea-level history. Along the east-northeastern coast of Brazil, relative sea level has fallen approximately 5 m during the last 5000 y. Correlation of this sea-level history with the evolution of beach-ridge, lagoonal and coastal plain deposits shows that: (1) sea-level rise favours the formation of barrier island—lagoonal systems and the construction of intralagoonal deltas; (2) sea-level lowering is not conductive to barrier island formation. Rather, lagoons and bays become emergent and beach-ridge plains rapidly prograde. Trade winds. Sediment dispersal systems along the coastal zone of east-northeastern Brazil have been highly persistent since Pleistocene time, as deduced from beach-ridge orientation. This persistence results from the fact that sediment dispersal in wave-dominated settings is ultimately controlled by atmospheric circulation which, for the east-northeastern coast of Brazil is associated with the South Atlantic high-pressure cell. The remarkable stability of this cell through time, has allowed the accumulation of extensive beach-ridge plains at the longshore drift sinks located along the coast. Climate change. Effects of Quaternary climate changes on coastal sedimentation are twofold. Climate changes may affect rainfall patterns, thus exerting an important control on coastal dune development. Along the coast of northeastern Brazil, active coastal dunes are only present in those areas in which at least four consecutive dry months occur during the year. Mapping of these areas has shown that dune development during the Holocene has been episodic, these episodes being probably controlled by variations in rainfall patterns associated with climate changes. Secondly, despite its overall stability, the position of the high-pressure cell has experienced small shifts in position during the Holocene in response to climate changes. Changes in wind direction associated with these shifts have induced modifications in the coastal dispersion system, which are recorded in the strandplains as small truncations in the beach-ridge alignments. These results have important implications in understanding accumulation of ancient sandstone shoreline sequences.

Late Holocene sea-level changes from grain-size data: evidence from the Gulf of Mexico

Grain-size kurtosis of sand in the beach ridge plain of St. Vincent Island, Florida, is numerically reasonably uniform within any one ridge set, but changes at important set boundaries. Where these changes are found, there are also differences in air photo and field appearance and in measured ridge-set heights. Sets with low kurtosis (∼3.0) stand topographically high, and sets with higher values (∼3.6) stand low. Study of wave energy levels and beach sand grain-size kurtosis along modem Gulf of Mexico beaches shows that kurtosis is an inverse function of surf-zone energy density. Storms and storminess (for the study area) can be evaluated in the framework of the selective- transport model of May (1973); the actual data sequence is greatly different from what is required by the model, and therefore storms and storminess cannot be invoked to explain the history of the area. Instead, the data sequence matches results predicted by the model for small sea-level changes. Storms and tectonism do not have appropriate durations and rates of operation, hence did not cause changes in kurtosis across St. Vincent Island. Slow land elevation changes (warping, isostatic adjustment) do not take place repeatedly up and down like the granulometric parameters. Tidal effects, in the study area, are both much too small and too frequent to have been important. The changes in kurtosis therefore indicate water level changes, and provide a sea-level history, including three sea level drops and four rises, of 1-3 m each, since about 3000 BP. Similar results have been obtained elsewhere, so these results are not local.

Oolitic sandbody depositional models and geometries, Mississippian of southwest Britain: implications for petroleum exploration in carbonate ramp settings

A 1000 m thick early Mississippian carbonate supersequence, the “Carboniferous Limestone” of southwest Britain, consists of three third-order depositional sequences. These comprise parasequences in various configurations, and the whole forms a carbonate ramp stack. Within this framework five major oolitic carbonate sandbodies developed: (a) Castell Coch Limestone, (b) Stowe Oolite, (c) Brofiscin Oolite, (d) Gully Oolite, and (e) High Tor Limestone. The depositional regime was storm- and wave-dominated throughout and the major sandbodies represent a range of progradational carbonate beaches, barriers and detached subtidal shoals. Analysis of the three-dimensional shapes and distribution of these five examples shows that they evolved to produce three major carbonate sandbody geometries: (a) strings, (b) sheets, and (c) wedges. These geometries are characterised using the five field examples and offered as a template which may assist in the exploration and reservoir modelling of petroleum-rich high-energy ramp systems. Progradation, for up to 40 km, of barrier islands (Stowe Oolite) and beach-ridge plains (Gully Oolite Formation) generated strings, and “thick” sheets individually up to 10–20 m thick. “Thin” shoreface-retreat carbonate packstone/grainstone sheets up to 5 m thick (High Tor limestone) developed during transgressions as veneers across flooding surfaces. These are comparable with sheet sands developed in siliciclastic shelf depositional systems. Progradation, for up to 30 km, and vertical aggradation of shoreline-detached oolite shoals (Castell Coch limestone, Brofiscin Oolite), generated basinwards-expanding or thinning wedges up to 30 m thick. Tectonically controlled stacking of strandplain sheets produced a composite carbonate sandbody up to 80 m thick (Gully Oolite). The intrinsic (sedimentary) and extrinsic (eustacy, tectonism, climate) factors which controlled these sandbody geometries are addressed. Establishing the positions of the sandbodies accurately within depositional sequences allows them to be located within inferred seismic sequence geometries and provides one possible solution to the difficult problem of predicting carbonate facies distribution in subtle stratigraphic plays. In this ramp system, the most homogeneous sandbodies (up to 30 m grainstones), with greatest reservoir facies potential, are represented by shoal-belt wedges. Potential grainstone reservoir facies in the prograding shorelines are limited to the upper parts of individual shoreface sequences (max. 10 m grainstones). For shoreline carbonate sandbodies, the greatest reservoir and stratigraphic trapping potential exists in the earliest ramp parasequences where enveloping offshore sediments are siliciclastic mudstones. In later stages, potential seals are likely to be less reliable, low-porosity outer ramp carbonates.

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.

Resurrecting beach ridge archaeology: Parallel depositional records from St. Lawrence Island and Cape Krusenstern, Western Alaska

AbstractArchaeological sites on gravel beach ridge plains offer a treacherously facile method of reconstructing cultural chronology based on the assumption that settlements were preferentially situated nearest the sea. the initial phase of beach ridge methodology in Alaska dates from its 1930s use by Henry Collins at St. Lawrence Island and its 1950s use by Louis Giddings in Kotzebue Sound. Numerous questions of cultural and depositional chronology remain unresolved. At Gambell, on St. Lawrence Island, three sets of ridges span the period since about 2000 B.P., with a prominent disconformity after Punuk culture times at ca. 1100 B.P. Reviewing the 14C dates (n = 83) we find that the Gambell sequence (n = 50) broadly parallels that of Kotzebue Sound, especially in the similar erosional disconformity at 1200‐1000 B.P., related to increased storminess in the North Pacific. the Cape Krusenstern sequence is only loosely constrained by 14C dates (n = 33) disproportionately concentrated on 7 of the 114 ridge fragments. the dating of early Choris culture is especially problematic, which seems to occur both before and after the Old Whaling culture, well‐dated at 2900‐2800 B.P. on the 53rd ridge. However, reanalyzing the depositional sequence, we find that some of the more easterly Choris ridges probably represent erosional events after the Old Whaling occupation.

Podzol development in a holocene chronosequence .1. Moruya Heads, New South-Wales

Calcareous sands (Fluvisols/Regosols) and Podzol soils of at least seven different ages (0, 2500, 3000, 5000, 5800, 6200 and 6500 calendar years) form a soil chronosequence in the prograded beach-ridge plain near Moruya Heads, on the south coast of New South Wales. Ages of the soils were determined by radiocarbon dating of marine shell deposited with the sediment. The soils range from undifferentiated quartz sand mixed with marine shell debris at the youngest site, to well developed podzols with pronounced AI, A2 and iron-humus B horizons at the oldest sites. Age trends are evident in a range of physical and chemical soil properties, the most significant of which are: an increase in the thickness of the A2 and B horizons with a concomitant decrease in C horizon thickness; a decrease in Munsell colour chroma in the A1 and A2 horizons and an increase in B horizon chroma; a fall in the pH of all horizons (particularly in the younger soils); an increase in depth to the leaching front of marine shell carbonate; the progressive leaching of HC1-extractable manganese, calcium, magnesium and sodium from the soil profiles; and the progressive development of the A2 and B horizons in terms of HC1-extractable iron and aluminium.

Hauts niveaux marins Pleistocenes du littoral bresilien

The high sea-level, corresponding to the last Pleistocene interglacial stade, left the most important records represented by extensive beach-ridge plains along the central and southern coasts of Brazil. During the maximum level, which was dated at 123,000 yr B.P. by coral samples, the relative sea-level was situated 8 ± 2 m above present level. Four generations of Quaternary marine sandy deposits have been described in southern Brazil (State of Rio Grande do Sul), where they are known as Barrier I, II, III and IV. The Barrier IV, about 4 m high, corresponds to the last great transgressive-regressive phase, whose maximum occurred about 5100 yr B.P. The Barrier III, with a height of about 8–10 m, corresponds to the penultimate transgressive-regressive period, whose maximum was produced about 123,000 yr B.P. The Barrier II, about 13–15 m high, and the Barrier I, about 20–25 m high, situated at inner positions in relation to the previous ones, have been formed during high sea-levels older than 123,000 years. Along the coastal plains of the States of Sergipe and Bahia, the high sea-level older than 123,000 years is represented only by one phase through cliffs carved within the Barreiras Formation. On the other side, along the coastalp plains of São Paulo, Paraná and Santa Catarina, there are marine terraces with a minimum height of 13 m above present sea-level, which are certainly older than the Barrier III, and are probably recording the transgressive-regressive period of the Barrier II (middle Pleistocene?).

Oil Recovery in a Low-Permeability, Wave-Dominated, Cretaceous, Deltaic Reservoir, Big Wells (San Miguel) Field, South Texas

The Upper Cretaceous Big Wells (San Miguel) reservoir in Dimmit and Zavala Counties, south Texas, produces from a broadly lenticular, wave-dominated deltaic sandstone encased in prodelta and shelf mudstones. An updip porosity pinch-out coincides with a gentle undulation on a uniformly gulfward-dipping monocline and forms a structurally modified stratigraphic trap. The reservoir is relatively tight and has an average porosity of 21% and average permeability of 6 md; wells require fracturing to stimulate production. Ultimate recovery, based on current production trends and technology, is projected to be 57 million bbl, or 29% of the 198 million bbl field. The reservoir is subdivided into an upper, nonproductive, transgressive shelf sandstone and a lower, productive, but intensely bioturbated, deltaic sandstone. The tight, nonproductive upper sandstone seals the reservoir, which consists of four major internal facies. A dip-oriented distributary system carried sediment into the basin. Sediment was then transported along strike (dominantly to the southwest) by longshore drift. Wave action reworked the sands into a beach-ridge plain. The resultant distributary and beach-ridge plain complex exhibits an asymmetric cuspate geometry elongated to the southwest. Landward of the delta system lay a muddy coastal plain. Prodelta and lower shoreface silts and shelf muds were deposited seaward of the deltaic and shore-zone system. The northward transition from thicker and cleaner sandstones of the beach-ridge plain to argillaceous sandstones within and adjacent to the distributary system strongly affects oil recovery from the field. Reservoir permeability and induced-fracture half-lengths (the distance from the well bore to the fracture terminus or half the total length of induced fracture, calculated from pressure transient analysis) decrease dramatically to the north. Consequently, well performance peaks in the beach-plain sediments and decreases northward and updip and downdip into adjacent muddier sediments. Recovery efficiencies of the original oil in place average 50% in the southern half of the pool and drop to 20-30% in the north. However, recovery of movable (nonresidual) oil is highly efficient. About 88% of the nonresidual oil in the pool will be produced. Wave-dominated deltaic reservoirs are characterized by minimal well-to-well variability, excellent internal continuity, and, consequently, maximum efficiency of mobile-oil recovery.

The morphodynamics of beach-ridge formation: Magilligan, Northern Ireland

Magilligan foreland is a Holocene beach-ridge plain comprising three principal sets of sand ridges. Sets I and II are related to the mid-Holocene progradation of the plain, while Set III represents recent deposition at the distal margin. At present, two types of beach ridge are being formed, in both cases as part of the general recovery sequence following storm erosion of the dune cliffs. Mode I beach-ridge development is associated with shore-normal sediment transport under dissipative wave conditions. These ridges form around the High Water Mark of Spring Tides through the migration of coalescence of swash bars within 30 to 55 days of a storm. Mode II formation is more complex; sediment initially stored in nearshore bars is moved alongshore, causing bar elongation. The bar moves into the intermediate and even reflective wave domains. Eventually narrowing of the bar leads to severance of a downdrift portion, usually at or near the major drift pulse to the north west of the foreland. Normally this sediment-starved remnant welds progressively onto the beach face in the direction of the dominant process gradient (east to west) but occasionally locally generated, counteractive seas move sediment onshore employing the bar as a traverse conduit. Mode II beach ridges “emerge” onto the upper beach around 90–150 days after a storm. The beach ridges have distinctive structures, depending on their mode of formation, and both constitute important sources for dune-building sand.

Nature and palaeoenvironmental significance of a buried soil sequence from Magilligan Foreland, Northern Ireland

Soil horizons delimit three periods of sand deposition and subsequent topographic stability at Magilligan Foreland, Co. Londonderry. All the deposits are composed of texturally and mineralogically similar material. The earliest topography is a beach ridge plain; podzols cap the ridges and peats occur in the inter‐ridge depressions, together comprising a buried palaeocatena. The podzols are visually distinct but chemically and mineralogically immature. Peat and podzol genesis probably began between 3,000 and 2,500 years B.P., and were terminated between c. 1,100 years B.P. and c. 600 years B.P. by burial under an extensive layer of aeolian sand. This sand was eroded to a planar surface before developing a sand‐pararendzina, which represents a second period of surface stability. The third deposit, a discontinuous dune sand, is presently also developing a sand‐pararendzina. Difficulties of using 14C dates to erect absolute chronologies are discussed.

Facies Architecture and Production Characteristics of Strand-Plain Reservoirs in North Markham-North Bay City Field, Frio Formation, Texas

The North Markham-North Bay City field, Matagorda County, Texas, produces oil and gas from multiple barrier and strand-plain sandstones of Oligocene age stacked over a rollover anticline in the Frio fault zone. Three principal oil reservoirs--the Cayce, Cornelius, and Carlson--account for 83% of the 49 million bbl produced from the field. All three were deposited in strand-plain systems and display considerable heterogeneity. The Cayce reservoir is composed of beach-ridge plain, distributary, and deltaic facies. Reservoir heterogeneity results in anisotropic fluid behavior. Water influx in the beach-plain deposits follows broad fronts, whereas water invasion in channel deposits is more restricted and erratic. The Cornelius reservoir was deposited in a system intermediate etween sand-rich beach plains and mud-rich chenier plains. Sandy beach ridges, separated by muddy swales, compose the productive framework of this class of strand-plain reservoir and act as conduits for early water influx. Sandstones, possibly of washover origin, in the intervening swales produce oil but are more rapidly drained than are beach-ridge sandstones. The Carlson reservoir produces from transgressed strand-plain deposits. The Carlson had a complex and episodic depositional history, yet water-influx and oil-production maps suggest isotropic fluid behavior. Modern sand-rich transgressive shore-zone deposits are characteristically sheetlike, as is the transgressive component of the Carlson reservoir. This distinctive morphology appears to have fostered reservoir productivity. Oil recovery follows predictable trends. Recovery efficiency is highest from the transgressive sheet sands of the Carlson, intermediate from the composite Cayce, and lowest from the depositionally complex and mud-rich Cornelius. Reservoir efficiency of strand-plain sandstones exceeds that of barrier and back-barrier deposits productive elsewhere in the Frio Formation of the central Texas Gulf Coast.

Stratigraphy of Transgressive Barrier Island Arc: ABSTRACT

Isles Dernieres, a Holocene transgressive barrier island arc on the Louisiana coast formed as a result of dominant marine processes reworking deposits of the abandoned Caillou distributaries of the early Lafourche delta lobe. The island system exhibits a variable transgressive and regressive stratigraphy throughout its framework, which is discriminate from comparable Atlantic coast transgressive barrier sequences. Continuous subsidence and storm breaching divide the island system into 3 major island segments: Western, Central, and Eastern Isles Dernieres, each of which is separated by locally interjacent tidal inlets. Vibracore data reveal that Western Isles Dernieres represents a series of accreting sand spits that resulted from the erosion and longshore transport of the abandoned distributary channel deposits from the central deltaic headland. This 3 to 4-m (10 to 13-ft) thick sequence of sand spits and associated marsh deposits overlies interdistributary silts and clays. Central Isles Dernieres is a fluvial-deltaic complex that exhibits marsh and tidal-flat deposits capping a relatively thick sequence of levee and interdistributary bay sediments. A relatively thin beach-ridge plain lies locally submerged beneath sand spit and marsh deposits of Eastern Isles Dernieres. This beach-ridge plain formed during a regressive phase of island evolution. Erosion of the beach-ridge plain above the effective wave base presently provides an active sand source for the downdrift accreting sand spit at the eastern end of Isles Dernieres. A high preservation potential of the western and eastern transgressive sequences of Isles Dernieres is probably due to rapid subsidence and the consequent in-place drowning of the island segments. In contrast, Atlantic coast barrier counterparts often exhibit incomplete transgressive sequences owing to continued shoreface erosion. End_of_Article - Last_Page 511------------

Sedimentation in a Transgressed Interdistributary Bay on Mississippi-Lafourche Delta Lobe: ABSTRACT

Caminada Bay is a shallow south Louisiana bay, located between the distributary levees and beach-ridge plain of the late Lafourche Mississippi delta (900-500 y.B.P.) on the west and the Bayou Des Families levees (3,000-2,000 y.B.P.) on the east. Small distributaries traversed the region of the present-day bay, probably during both early and late Lafourche time. The Lafourche delta actively prograded until about 500 y.B.P. when it was abandoned by the Mississippi River; the area of the present bay then entered its transgressive phase. Grand Isle, which separates Caminada Bay from the Gulf of Mexico, was subsequently built by sand derived from local distributary-mouth bars and erosion of the Lafourche beach-ridge plain to the west. As a consequence of the cutoff in fluvial ediment supply and continued subsidence, the lower delta plain of the Lafourche lobe is currently being transformed into the rapidly expanding Caminada Bay. Visual description, x-ray radiography, and resin peels of 23 vibracores (4 to 8 m, 13 to 26 ft, in depth) reveal the following vertical succession of sedimentary units beneath the bay: (1) basal paleobay deposits, (2) an intermediate unit representing Lafourche delta lobe progradation, and (3) upper transgressive bay deposits. The deepest unit penetrated (paleobay deposits) consists of mottled or bioturbated very fine sand and clay and shell beds. The intermediate unit (delta lobe) consists of intricately interlaminated very fine to fine sand, silt, and clay. It features lenticular, wavy, and flaser bedding. The upper transgressive unit consists of banded organic-rich clay with in-situ and detrital peat. Expansion of the bay by wave erosion of the many marsh islands removes most of the organic-rich upper unit. A thin unit of bioturbated muds is currently being emplaced on the bay floor. End_of_Article - Last_Page 475------------

Regressive and Transgressive Sand Bodies Associated with Lafourche Delta in South Louisiana: ABSTRACT

The beach ridge plains and coastal barrier systems along the seaward margin of the wave-dominated Lafourche delta represent regressive and transgressive events associated with multiple delta lobe progradations and abandonments over the last 1,500 years. Two major delta lobes, the Early Lafourche and the Late Lafourche, can be recognized by the subaerial expression of the abandoned deltaic plain. Associated with each delta lobe is a regressive beach ridge plain deposited during distributary progradation and coastal barrier system deposited during distributary transgression. The Cheniere Caminada beach ridge plain is associated with the Late Lafourche delta lobe. It consists of more than 70 subparallel beach ridges in an arcuate fan-shaped configuration which flare seaward along the eastern levees of Bayous Lafourche and Moreau. Radiocarbon dates indicate beach ridge building began approximately 600 years ago when Bayou Lafourche built seaward of the older Bayou Blue shoreline and started intercepting westward longshore sediment transport, resulting in the formation of Cheniere Caminada. Near the fan apex, beach ridges are 7 to 8 m (23 to 26 ft) thick and thin westward to 2 to 3 m (6.5 to 10 ft) thick. A typical beach ridge stratigraphic sequence coarsens upward with shoreface silty sands overlain by a cap of washover and aeolian sands. Beach ridge growth ceased approximately 300 years ago when Bayou Lafourche was abandoned. Distributary abandonment initiated the transgression at Bayou Lafourche and the development of an erosional deltaic headland, the Caminada-Moreau coast, with a set of symmetrical, flanking barriers, the Timbalier Islands to the west and the Caminada Pass spit and Grand Isle to the east. Reworking of distributary and beach ridge sand bodies by shoreface retreat supplies the sand source required for coastal barrier generation. Shore-parallel transport distributes sand from the headland source into downdrift marginal spits, tidal deltas, and flanking barrier islands. Cores show that the flanking barriers (Timbalier Island and Grand Isle) increase in thickness from 2 to 3 m (6.5 to 10 ft) near the headland to 5 to 6 m (16 to 20 ft) at their downdrift ends. A typical flanking barrier strat graphic sequence shows a coarse-grained tidal inlet fill overlying a finer grained interdistributary bay fill and underlying a thin cap of washover and aeolian sands. In the Early Lafourche delta, only remnants of an older regressive beach ridge plain, Chenier Caillou, can be recognized owing to its advanced stage of transgression. A series of relict, partially submerged beach ridges associated with the Caillou headland can be seen spreading seaward on their western margin in the central Isles Dernieres indicating the dominant longshore transport direction was westward. Cores show a regressive sequence 7 to 8 m (23 to 26 ft) thick, similar to Cheniere Caminada, where shoreface silty sands underlie washover and aeolian deposits. The Isles Dernieres represent the transgressive barrier system of the Early Lafourche delta lobe. Abandonment of the Caillou distributaries occurred approximately 600 to 800 years ago. Due to long-term subsidence, the Caillou headland is now submerged below sea level and the Early Lafourche barrier system has evolved into a transgressive barrier island arc separated from the mainland by an intradeltaic lagoon. Sediment dispersal consists of seaward transport into an inner-shelf sand sheet, landward transport into washover deposits, and shore-parallel transport into tidal deltas and marginal recurved spits. Cores show the central Isles Dernieres consist of a thin washover sand sheet 1 to 2 m (3 to 6.5 ft) thick transgressing over delta plain and beach ridge deposits. The downdrift ends of the Isles Dernieres islands are thicker, up to 4 to 5 m (13 to 16 ft), and overlie fine-grained interdistributary bay fills. In the subsurface of Grand Isle and Cheniere Caminada, lies the transgressive barrier system of the Bayou Blue distributary abandoned 1,200 years ago. The sand source for barrier generation is two Bayou Blue distributaries which lie - 10 m (-33 ft) below sea level adjacent to Barataria Pass. The transgressive sand body strikes northwest and is overlain by a sequence of regressive interdistributary clays and silts, regressive beach ridge sands (Cheniere Caminada), and a transgressive flanking barrier sand (Grand Isle). Radiocarbon dates indicate Bayou Blue Barrier was actively transgressing landward 920 years ago. The identification of regressive beach ridge plains along the Lafourche delta suggests that these wave-dominated delta plain components may be stratigraphically more significant in the Mississippi delta than recognized before. Sequential delta lobe abandonments have led to the development of imbricating regressive End_Page 530------------------------------ and transgressive sand bodies in the Lafourche delta complex. End_of_Article - Last_Page 531------------

Seismic Stratigraphy of Barrier-Island Arc Retreat Paths in Mississippi River Delta: ABSTRACT

The stratigraphic record preserved in the retreat path of Mississippi delta barrier-island arcs is controlled by erosional shoreface retreat processes, relative sea level rise, and sediment supply. Marine reworking combined with subsidence of the abandoned delta generate a characteristic sequence of facies from flanking barrier islands, barrier-island arcs to inner-shelf shoals depending on age. The preservation of any part of these sequences is a function of the rate of relative sea level rise and the depth at which individual barrier environments accumulate below the base of the advancing shoreface. More than 500 km (300 mi) of high resolution shallow seismic profiles correlated with vibracores from retreat paths fronting the Isles Dernieres and Chandeleur barrier-islan arcs, show contrasting stratigraphic sequences preserved on the inner continental shelf (Mississippi delta). The Isles Dernieres barrier-island arc developed as a consequence of the Caillou Headland abandonment in the early Lafourche delta approximately 800 years B.P. The base of the advancing shoreface lies 3 to 4 m (10 to 13 ft) below sea level and truncates the entire Isles Denieres barrier-lagoonal sequence and the upper part of the Caillou delta plain. On the lower shoreface, channels can be seen projecting seaward under the central part of the island arc; associated with it is a beach-ridge plain extending eastward. On the inner shelf, a sand sheet up to 60 cm (2 ft) thick marks the retreat path of the Isles Dernieres. The Chandeleur barrier-island arc was generated by abandonment of the St. Bernard delta complex 1,500 years ago. The base of shoreface erosion lies 6 to 8 m (20 to 26 ft) below sea level, and truncates the entire barrier-lagoonal sequence in the central part of the system. On the downdrift flanks only the upper portion of tidal inlet and recurved spit complexes are truncated. Scattered outcrops of shell reefs and lagoonal deposits occur on the lower shoreface. Beyond the shoreface, a 1 to 5 m (3 to 16 ft) thick sand sheet, with gently seaward dipping interval reflectors, caps tidal inlet scars up to 10 m (33 ft) thick, as well as the basal portions of migrating barrier-island sequences associated with earlier shoreline positions. Differences seen in the two stratigraphic sequences are a function of distributary size and depositional history of each barrier-island arc. The Isles Dernieres developed from a series of small sand-deficient distributaries in the Lafourche delta complex, whereas the Chandeleur Islands developed from large sand-rich distributaries of the St. Bernard delta complex. End_of_Article - Last_Page 1470------------

Coastal progradation as a by-product of human activity: an example from Hoed, Denmark

Bird, Eric C. F. and Christian Christiansen: Coastal progradation as a by-product of human activity: an example from Hoed, Denmark. Geografisk Tidsskrift 82: 1–4. Copenhagen, June 1. 1982. Quarry waste (gravel and sand) dumped on the shore at Hoed, Denmark, has been re-worked by wave action and formed into a beach-ridge plain. Progradation of up to 220 metres has occurred on a 9.5 km sector of coastline, extending 5.5 km north and 4 km south from the dumping area. Historical evidence, supplemented by a modern survey, indicates the pattern of coastline progradation, which was most rapid between 1954 and 1971, when waste dumping was at its maximum.