Ravinement Surface Research Articles

Architecture and formation of transgressive–regressive cycles in marginal marine strata of the John Henry Member, Straight Cliffs Formation, Upper Cretaceous of Southern Utah, USA

AbstractMarginal marine deposits of the John Henry Member, Upper Cretaceous Straight Cliffs Formation, were deposited within a moderately high accommodation and high sediment supply setting that facilitated preservation of both transgressive and regressive marginal marine deposits. Complete transgressive–regressive cycles, comprising barrier island lagoonal transgressive deposits interfingered with regressive shoreface facies, are distinguished based on their internal facies architecture and bounding surfaces. Two main types of boundaries occur between the transgressive and regressive portions of each cycle: (i) surfaces that record the maximum regression and onset of transgression (bounding surface A); and (ii) surfaces that place deeper facies on top of shallower facies (bounding surface B). The base of a transgressive facies (bounding surface A) is defined by a process change from wave‐dominated to tide‐dominated facies, or a coaly/shelly interval indicating a shift from a regressive to a transgressive regime. The surface recording such a process change can be erosional or non‐erosive and conformable. A shift to deeper facies occurs at the base of regressive shoreface deposits along both flooding surfaces and wave ravinement surfaces (bounding surface B). These two main bounding surfaces and their subtypes generate three distinct transgressive–regressive cycle architectures: (i) tabular, shoaling‐upward marine parasequences that are bounded by flooding surfaces; (ii) transgressive and regressive unit wedges that thin basinward and landward, respectively; and (iii) tabular, transgressive lagoonal shales with intervening regressive coaly intervals. The preservation of transgressive facies under moderately high accommodation and sediment supply conditions greatly affects stratigraphic architecture of transgressive–regressive cycles. Acknowledging variation in transgressive–regressive cycles, and recognizing transgressive successions that correlate to flooding surfaces basinward, are both critical to achieving an accurate sequence stratigraphic interpretation of high‐frequency cycles.

The sand ridge field of the South Yellow Sea: Origin by river–sea interaction

The origin of a large field of sand ridges offshore from the north Jiangsu coast in the South Yellow Sea has been investigated on the basis of bathymetry, seabed samples, high-resolution seismic profiles and 31 to 71m deep boreholes. Sediment composition including heavy minerals and clay minerals sampled from surface sediments shows that most of the sand was derived from the Changjiang (Yangtze) River, but in the northern part of the field particularly the clay came from the Huanghe (Yellow) River. Seismic profiles show late Pleistocene distributary channels of the ancient Changjiang River underlying much of the southern part of the sand ridge field. The Holocene transgression cut a widespread ravinement surface reworking abundant late Pleistocene sandy sediment. The available sand was reworked by tidal currents into large ridges. The location of the ridges is strongly influenced by relict channels in the southern part of the field and by tidal currents in the northern, and especially the northeastern part of the field, resulting in a radiating ridge pattern. These ridges provide an example of the evolution of a large scale geomorphic feature resulting from river–sea interaction, in which climatic and sea level changes played an important role.

Tidally influenced clastic epeiric sea at a Mesoproterozoic continental margin, Rjukan Rift Basin, southern Norway

Precambrian epeiric sea paleoenvironments record information about ancient tidal conditions and nearshore sedimentation patterns. The Mesoproterozoic Brattefjell Formation, part of the Rjukan Rift Basin in southern Norway, presents diagnostic criteria of an ancient tidal influence in a shallow clastic epeiric sea environment during the post-rift stage of the sedimentary basin. Eight different sedimentary lithofacies/subfacies and two genetically related lithofacies associations were recognized from the formation. The conglomerate lithofacies records a transgressive ravinement surface due to wave scouring. The sandstone lithofacies consists of six subfacies: ripple-marked, planar cross-bedded, trough cross-bedded, low-angle cross-bedded, and horizontal laminated sandstones. The sandstone lithofacies records sedimentation by shallow current flows or oscillatory waves of lateral migrating straight- or slightly sinuous-crested sandbars and channel-fill deposits. The associated bi-polar cross-bedding, slump-folds, ladder-back type ripples, shrinkage cracks, double-mud drapes, iron ooids, load casts, and flame structures indicate variation of the flood-ebb cycles in tidal sandbars, rapid sedimentation, and sediment compaction. Tidal bundle measurements suggest that 16–18 bundles were formed during the neap-spring cycle, indicating mixed semidiurnal tides. A mudstone lithofacies (two subfacies) records waning current strength deposits, channel abandonment, and either vertical aggradation of the channels or coastal plain deposits. The lithofacies associations reflect fluctuating energy conditions in a shallow clastic shoreline influenced by tides and waves. At least 23 shallowing upward cycles caused by autocyclic tidal water level changes were recognized from the lower part of the formation.Based on the lithofacies assemblages, the Brattefjell Formation can be subdivided into sandy subtidal, lagoon-estuary, and shallow marine shoreface-offshore environments deposited above the fairwater wave base. The Brattefjell Formation records millions of years of fluctuating water levels with an overall transgressive trend, indicating allocyclic patterns caused by regional subsidence. The formation is interpreted to represent a tidally influenced epeiric sea in which shallow water levels extended over part of a continent and it was associated with marine transgression. The shoreface was fed sediment by alongshore and coastal current drifts during shoreface transgressive erosion, in a low shoreline gradient with reduced sediment input and lack of major braided-fluvial channel(s).

Delta development and channel incision during marine isotope stages 3 and 2 in the western South Yellow Sea

Approximately 4100 km of high-resolution seismic profiles recently obtained from the western South Yellow Sea were subdivided into seven seismic units by six major seismic surfaces. Three sediment cores between 60 and 71 m in length, obtained from localities on the seismic profile lines, were analyzed for sedimentary characteristics, clay mineral components, and benthic foraminiferal and ostracod assemblages and were also dated by AMS 14C and optically stimulated luminescence to document the environmental history of the region. Stratigraphic units in the cores were confidently correlated with seismic units in the profiles. Stratigraphic correlation among these three cores and the previous well-studied core QC 2 was facilitated by the cold-water deposits in marine isotope stage (MIS) 5. The three cores document the sedimentary sequence during the period from MIS 6 up to MIS 1. Strata formation and sedimentary environment changes since MIS 5 are strongly controlled by sea-level fluctuations. Most of the successions were formed in MIS 5, MIS 3, and MIS 1 with major erosions in MIS 4 and MIS 2. Particularly our data revealed the presence of a large delta active during MIS 3 (likely from the early stage of MIS 3 to about 40 cal kyr BP) that was subsequently affected by channel incision. The delta succession and incised-channel fills have a high concentration of smectite in their clay mineral components, suggesting that the paleo-Yellow River was the main contributor to the delta development and channel incision. The delta sequence has a coarsening-upward trend and consists of two seismic facies. The upper facies shows lateral alternations of chaotic and oblique or very low-angle reflectors, which correspond to sandy (proximal) delta-front and delta-plain facies, and the lower facies is characterized by seaward-dipping clinoforms, which correspond to muddy (distal) delta-front and prodelta facies. The top surface of the delta inclines very gently seaward, consistent with a deltaic development associated with the sea-level fall in MIS 3. The incised-channel system consists of two main channels with multiple tributaries in a dendritic pattern. The incised-channel fills begin with fluvial and then estuarine sediments, which are truncated by a transgressive ravinement surface and capped by transgressive deposits. The main incision channels have a terraced cross-sectional morphology, which is interpreted to reflect multiple episodes of sea-level fall during incision, presumably from the late MIS 3 to the Last Glacial Maximum.

Sequence stratigraphy in the context of rapid regional uplift and high‐amplitude glacio‐eustatic changes: the Pleistocene Cutro Terrace (Calabria, southern Italy)

AbstractThe Cutro Terrace is a mixed marine to continental terrace, where deposits up to 15 m thick discontinuously crop out in an area extending for ca 360 km2 near Crotone (southern Italy). The terrace represents the oldest and highest terrace of the Crotone area, and it has been ascribed to marine isotope stage 7 (ca 200 kyr bp). Detailed facies and sequence‐stratigraphic analyses of the terrace deposits allow the recognition of a suite of depositional environments ranging from middle shelf to fluvial, and of two stacked transgressive–regressive cycles (Cutro 1 and Cutro 2) bounded by ravinement surfaces and by surfaces of sub‐aerial exposure. In particular, carbonate sedimentation, consisting of algal build‐ups and biocalcarenites, characterizes the Cutro 1 cycle in the southern sector of the terrace, and passes into shoreface and foreshore sandstones and calcarenites towards the north‐west. The Cutro 2 cycle is mostly siliciclastic and consists of shoreface, lagoon‐estuarine, fluvial channel fill, floodplain and lacustrine deposits. The Cutro 1 cycle is characterized by very thin transgressive marine strata, represented by lags and shell beds upon a ravinement surface, and thicker regressive deposits. Moreover, the cycle appears foreshortened basinwards, which suggests that the accumulation of its distal and upper part occurred during forced regressive conditions. The Cutro 2 cycle displays a marked aggradational component of transgressive to highstand paralic and continental deposits, in places strongly influenced by local physiography, whereas forced regressive sediments are absent and probably accumulated further basinwards. The maximum flooding shoreline of the second cycle is translated ca 15 km basinward with respect to that of the first cycle, and this reflects a long‐term regressive trend mostly driven by regional uplift. The stratigraphic architecture of the Cutro Terrace deposits is the result of the interplay between regional uplift and high amplitude, Late Quaternary glacio‐eustatic changes. In particular, rapid transgressions, linked to glacio‐eustatic rises that outpaced regional uplift, favoured the accumulation of thin transgressive marine strata at the base of the two cycles. In contrast, the combined effect of glacio‐eustatic falls and regional uplift led to high‐magnitude forced regressions. The superposition of the two cycles was favoured by a relatively flat topography, which allowed relatively complete preservation of stratal geometries that record large shoreline displacements during transgression and regression. The absence of a palaeo‐coastal cliff at the inner margin of the terrace supports this interpretation. The Cutro Terrace provides a case study of sequence architecture developed in uplifting settings and controlled by high‐amplitude glacio‐eustatic changes. This case study also demonstrates how the interplay of relative sea‐level change, sediment supply and physiography may determine either the superposition of cycles forming a single terrace or the formation of a staircase of terraces each recording an individual eustatic pulse.

The Furnas/Ponta Grossa contact and the age of the lowermost Ponta Grossa Formation in the Apucarana Sub-Basin (Paraná Basin, Brazil): integrated palynological age determination

The Furnas/Ponta Grossa Formation contact was until recently considered gradational or abrupt and of a Lochkovian to Pragian age in the Apucarana Sub-basin (Parana Basin, south Brazil). Based on sedimentology and palynomorph evidence a hiatus has been revealed between the Furnas Formation and the overlying Ponta Grossa Formation. The boundary between the topmost Furnas sandstones and the lowermost Ponta Grossa fine-grained sandstones constitutes a transgressive ravinement surface generated during a latest Pragian - early Emsian transgression. The hiatus corresponds to a maximum of ca. 4 Ma. A similar gap is also present in the Alto Garcas Sub-basin.

Paleoenvironments and sequential stratigraphy of Ordovician marginal marine deposits of Sierra de Zapla (Sierras Subandinas, northwestern Argentina) and their relation with the Central Andean Basin

The best and most complete palynologically constrained Ordovician section across the Sierras Subandinas crops out in the southern part of the Sierra de Zapla along the Capillas River (Subandean Ranges, Jujuy Province). The dominantly marginal marine setting explains the scarcity of invertebrates throughout the section. Palynomorphs are the main tool in stratigraphic studies of the area and trace fossils are important aids in paleoenvironmental analysis. Based on a detailed facies analysis, geometry and paleocurrent analysis, and recognition of key surfaces, four depositional sequences (S1-S4) with different internal arrangements and compatible with 3rd order cycles were identified. The Zanjón Formation (upper part of Global Stage 2 and Global Stage 3) with unexposed base, initiates the stratigraphic section and it is characterized by a heterolithic facies association with subordinate storm layers, thin-bedded phosphate-rich micro-conglomerates and inarticulate-rich shell beds. Common subaerial exposure features like truncated ripple tops and mud cracks suggest tidal flat environments. This interval yields a mixed Skolithos-Cruziana ichnofacies. Towards the top, an increase in mottling and a gradual change into dominant purplish-red colors (Laja Morada Member of the Labrado Formation) indicate a protracted subaerial emergence during a Darriwilian (Global Stage 4) relative sea-level drop, and a fluctuating water table in interfluves. This unit is covered in sharp erosive boundary by the Lagunilla Member of the Labrado Formation, suggesting development of composite fluvial incisions. Sandy fluvial to tide-dominated estuarine fills and thoroughly-bioturbated subtidal hetherolithic beds overlie the sequence boundary representing a typical transgressive systems tract. Development of surfaces with dominant Skolithos forms are interpreted as representing Glossifungites ichnofacies typically indicating by-pass erosion and firm-ground development previous to reworking of interfluves by advancing ravinement surface. The Capillas Formation (upper Darriwilian and lower part of Global Stage 5), sharply levels the previous estuarine complexes and represents a fine-grained wedge that gradually coarsens up. This unit contains the only truly marine shelly fauna concentrated in few storm beds above the fine-grained interval that characterizes a maximum flooding stage. This is the only interval that can be positively correlated with sections in the Cordillera Oriental to the west and Bolivia. A gradual coarsening to silty sandstones and the replacement of Cruziana by Skolithos dominated ichnofacies suggest a shallowing-upward section, capped by the thick-bedded, high energy quartz sandstones with pipe-rock structures of the Centinela Formation (middle and upper part of Global Stage 5). A shallowing-upward trend indicates the progradation of deltaic complexes, which in turn were erosively truncated by the waxing stage of the Gondwanan Hirnantian (uppermost Ordovician) ice-cap represented by the Zapla Formation (Global Stage 6) along the Central Andes. Above the diamictite-rich Zapla Formation the Lipeón Formation (Silurian) is interpreted as related to repeated transgressive ravinement surfaces that truncated Fe+2 saturated estuaries after a waning glacial stage and isostatic rebound, favouring the deposition of oolitic ironstones and succeeded by the development of a Zoophycos dominated muddy shelf.

Storm deposited pebble and cobble-sized particles in the early Emsian of the Ponta Grossa Formation, Paraná Basin (state of Paraná, Brazil)

Quartzite pebble and cobble-sized particles from an arenaceous siltstone with fine sandstone lenses have been found at two localities in the Campos Gerais region, Apucarana Sub-Basin (Paraná Basin), south Brazil. These particles were first interpreted as glacial diamictites, but their smooth surfaces and surrounding sediments indicate another origin. Two of the pebbles are associated with a small scale hummocky cross stratification in the top layer, and with fine sandstone layers below, which is indicative of currents formed by oscillatory flow. None of the particles show any traces of encrustation, and their morphology suggests they have been formed in a fluviatle environment. The surrounding siltstone is affected by bioturbation and contain brachiopods (Australospirifer). Palynomorphs indicate that these storm deposits were formed during an early Emsian maximum inundation on a transgressive ravinement surface.

Sedimentary architecture of the Loire River drowned valleys of the French Atlantic shelf

AbstractThe analysis of a dense grid of high resolution seismic profiles collected offshore the present day Loire River estuary indicates the presence of a thick and complex Pleistocene coastal wedge between the coast and 50 meters water depth. Most of this coastal wedge is preserved in a fossil valley network starting 10 km off the coast on the “Precontinent Breton” topographies and wedging out progressively 50 km in the offshore where the shelf flattens. This system is comprised of three main valleys 30 km long, 40–60 m deep and 0.7 to 4 km wide each, in average, with a northern valley incompletely filled by sediment. These valleys are incised into Eocene (Ypresian-Bartonian) sedimentary rocks lying unconformably on the metamorphic and magmatic rocks of the South Armorican Massif basement. The coastal wedge is comprised of six seismic units. From the base of the valleys to the seafloor, these units are successively interpreted as (1) colluvial (U1) and braided river deposits (U2), overlain by restricted marine to estuarine sediments (U3), and (2) straight to meandering fluvial deposits (U4) giving rise vertically to floodout marine sediments (U5). The whole sediment pile is capped by open marine bioturbated mudstones (U6).This succession of seismic units is organised in two depositional sequences bounded by an unconformity of regional extent, which corresponds to a drastic change in the paleovalley fill architecture. The lower sequence fills up the southern and central valleys when the upper sequence fills up the northern valley network. Both sequences are sharply truncated by a ravinement surface at the base of the offshore shales formed during the Holocene marine transgression. The correlation of the observed depth of the incisions and transgression surfaces with the global sea-level curve provides an indirect estimate of the ages of the depositional sequences. The lower sequence is probably Saalian (130–200 Ka, MIS 6) and the upper one Weischelian (110–12 Ka, MIS 2–4 and 5a–d). The ages and the infill of these valleys are very close to the ones observed in the largest paleovalleys of the inner French Atlantic shelf (Gironde, English Channel) and consistent with the sedimentary record of the continental Loire River (stepped terraces). In the later case, the Saalian period corresponds to a sharp increase on the incision of the river that shaped the morphology and determined the location of the present-day Loire valley.

Comparison of wave-and tide-dominated incised valleys: specific processes controlling systems tract architecture and reservoir geometry

Abstract This paper presents a comparison between the system tract architecture and the reservoir geometries of the Gironde and Leyre (Arcachon) incised-valley fills, both located within the Bay of Biscay 100 km apart. This study, based on high resolution seismic lines acquired by Ifremer on the continental shelf and onshore core and well data, illustrates that some features of the Gironde and Leyre valleys fills are similar while some others are not. The architecture of both valley fills is characterized by fifth order depositional sequences (corresponding to an interval from 120000 yr B.P. to present day). Both valleys are filled predominantly with transgressive systems tract, with associated poorly developed lowstand and highstand systems tracts. Key stratigraphic surfaces punctuate the valley-fill architecture and comprise deeply eroding tidal ravinement surfaces merged with and enhancing, earlier formed, fluvial-related erosive sequence boundaries. These tidal ravinement surfaces can be undulatory in form and in most places mark the basal boundary of the incised valleys. In contrast, nearly horizontal wave ravinement surfaces cap the incised-valley fills, extending over the adjacent interfluves. The Gironde and Leyre (Arcachon) valley fills exhibit two main stratigraphic differences: 1) transgressive systems tract sand bodies are ribbon shaped within the Gironde and tabular shaped within the Leyre; 2) lowstand systems tract deposits, represented by fluvial sediments, are preserved within the Gironde but absent within the Leyre. In a wave- and tide-dominated environment, the geometry of the sandbodies within the transgressive systems tract is a function of the tidal ravinement processes, which characterizes the estuary inlet. Two categories of tidal ravinement processes can be distinguished here: “anchored tidal ravinement” and “sweeping tidal ravinement”. The Gironde estuary is characterized by an “anchored tidal ravinement”. The tidal inlet has remained largely in a fixed location; littoral drift has not shifted the tidal inlet to the south because it is constrained by resistive Eocene carbonates that define the margins of the Gironde incised valley. In contrast, the Leyre estuary is characterized by a “sweeping tidal ravinement”. The inlet has been shifted approximately 30 km to the south by the formation of a littoral drift associated spit. This extensive lateral shifting was made possible by the fact that the incised valley was cut into unconsolidated, easily eroded Pleistocene sands. Within a wave- and tide-dominated environment, the preservation potential of the lowstand systems tract is a function of the size of the fluvial drainage basin. During lowstand time, the erosive power of the fluvial discharge was much greater within the much larger Gironde valley, consequently the fluvial sequence boundary was cut much deeper in the Gironde valley than within the Leyre valley and, correspondingly, the thickness of the associated fluvial deposits was commensurately greater. In response, the lowstand systems tract was not preserved within the Leyre valley fill because the depth of tidal ravinement erosion formed during the sea-level rise and associated transgression was greater than that associated with fluvial incision generated during the sea-level fall.

The Holocene transgression as recorded by incised-valley infilling in a rocky coast context with low sediment supply (southern Brittany, western France)

Abstract A combination of morphobathymetric studies, very high-resolution seismics, core sampling and radiocarbon age data is used to investigate the latest stage of the sedimentary infilling of incised valleys in southern Brittany, related to the Holocene transgression. Owing to the bedrock morphology of this highly irregular rocky coast, two main types of valleys are defined by topographic rocky highs parallel to the coastline: 1) wide and rather shallow incised valleys offshore from a topographic sill, 2) narrow and relatively deep valleys between the sill and the coast (ria-type valley). The sedimentary infilling in both types of valleys becomes highly differentiated as the transgression advances onto the coastal area. In the wide valley seaward of the topographic sill, the infilling consists mainly of offshore heterolithic facies while, in the ria-type valley, most of the infill is composed of brackish mudflat deposits and estuarine tidal muddy sands. As the transgression proceeds, the rocky highs are flooded and the whole area is finally covered by the offshore facies. Radiocarbon dating indicates that: 1) the marine ravinement surface is highly diachronous (a few thousand years cross-shore); 2) the top of the offshore facies, coarser and very shelly, represents an episode of condensed sedimentation from about 3000 to 4000 years ago, amalgamating the maximum flooding surface (MFS) and the highstand systems tract (HST). However, we observe a muddy drape, strongly bioturbated in places, in the most proximal areas, overlying the offshore facies. It is thought to represent the modern and most recent stage of sedimentary infilling. This mud cover is made of fine-grained sediments of fluvial and biological origin, and is interpreted as a prograding HST. It reflects an increased influx, partly due to human activities. Finally, the main features of incised valley sedimentary infilling in a rocky coast context with low sediment supply can be characterized by (i) the very strong control of bedrock morphology, (ii) the diachronous character of the transgression, (iii) the late position of the MFS, and (iv), the highly reduced volume of the HST.

Rippled scour depressions on continental shelf bank slopes off Nordland and Troms, Northern Norway

Multibeam bathymetry acquired under the MAREANO programme from the continental shelf off Nordland and Troms, northern Norway, show bedforms that we have interpreted as rippled scour depressions. They occur in three areas offshore on bank slopes facing southeast, more than 15 km from land. They are generally found where the slope gradient is low, in water depths of 70–160 m. Individual depressions are up to 3 km long, 1 m deep and up to 300 m wide. They occur in areas where sediments evolve quickly from glacial deposits on the banks to post-glacial muddy sediments on the glacial troughs. Multibeam backscatter and underwater video data show that depression floors are covered by rippled, gravelly, shelly sand. Ripple crests are parallel or slightly oblique to the depression axis orientation. Sand without bedforms is observed between the depressions. TOPAS seismic lines show that the uppermost seismic unit consists of the sand between the depressions. The base of this unit may be the last transgressive/tidal/wave ravinement surface. Physical oceanographic modelling indicates that maximum current velocities are up to 0.6 m/s in the rippled scour depression areas. Stronger currents appear to inhibit the building of these features. Tidal currents play an important role as they trend parallel to the southeast banks slopes and are likely responsible of the gravelly ripples formation inside the depressions as well as the persistence of these depressions which are not covered by finer sediments. On Malangsgrunnen bank, some of the rippled scour depressions are in the extension of NW–SE furrows located on the bank. Simulated bottom currents indicate currents mainly perpendicular to these furrows, as for the rippled scour depressions on the bank slopes. Nevertheless, these features could also highlight currents coming from the northwest which reach the bank margin and continue down to the areas of the rippled scour depressions. These currents could be responsible for the formation of some of the bedforms, together with tidal currents.

Composition, age, and depositional rates of shoreface deposits under barriers and beach plains of the Columbia River littoral cell, USA

The Columbia River littoral cell (CRLC) consists of four subcells (totaling 160 km in length) that are unique in the West Coast of the United States, in that they contain prograded barriers and beach plains, reaching 0.5–3 km in width (Fig. 1). The prograded beach deposits (1–5 ka in age) overlie shoreface deposits (1–8 ka in age), as identified in 18 ground penetrating radar profiles, and sampled from 24 boreholes. Two competing hypotheses were initially proposed to account for the origins of these unique, progradative shorelines: (1) cross-shore feeding by onshore wave transport of pre-Holocene sand from the submerged shelf, and (2) longshore dispersal of nearshore sand that was supplied to the littoral system by bedload sediment discharge from the Columbia River during the Holocene. The CRLC sand forming the shoreface deposits is fine (diameter 0.2 ± 0.02 mm) and rich in lithic fragments (20–40% by volume). Gravel and shell lag layers are uncommon in most of the CRLC shoreface deposits, but they show greater abundance locally near ravinement surfaces, tidal inlets, and in the Clatsop subcell, located south of the Columbia River mouth. Gravel and granule layers increase upsection in barriers south of the Columbia River and downsection in barriers at the northern end of the littoral system. These trends suggest different mechanisms of shoreface sediment feeding within the four subcells. However, borehole samples from all four subcells show the same sand provenance, i.e., post-glacial Columbia River sand, which is identified by high ratios of hypersthene:augite in heavy-mineral fractions. Selected shoreface sections were dated (0.5–8 ka) by AMS radiocarbon analysis of articulated-shell and wood fragments recovered from auger flights (3–22 m depth subsurface). Relatively young shoreface deposition (2.5 ka at − 6.5 m elevation NGVD88) in the Clatsop subcell south of the Columbia River shows a net-southward beach transport that fed shoreface and beachface progradation into deeper water. Older and deeper shoreface deposition (4.4 ka at − 7.1 m elevation) in the Long Beach subcell north of the Columbia River was a result of the filling of innermost-shelf accommodation space prior to beachface progradation. The total volume of shoreface sand deposited under the barrier spits and beach plains of the CRLC is estimated to be 6–7 km 3 deposited since 6–8 ka. There was a net-northward transport of littoral sand (∼ 1 × 10 6 m 3 year− 1) along the nearshore and inner-shelf; subsequently some of this sand was transported onshore to feed beaches of the northernmost subcells. Columbia River sand was also the source for the formation of the offshore shelf wedge above the transgressive ravinement surface, and for the filling of major tidal basins located north of the Columbia River. In summary, the unique progradational history of the CRLC barriers and beach plains derives from the combination of (1) longshore dispersal of fine sand discharged from the Columbia River during Holocene time, and (2) across-shore feeding of beaches at the northern end of the littoral system from fine sand carried north along the nearshore and the inner-shelf.

Transgressive and regressive deposits forming the barriers and beachplains of the Columbia River Littoral Cell, USA

Holocene transgression of the Columbia River Littoral Cell (CRLC) led to ravinement of the lowstand topography and the subsequent formation of a transgressive sequence of deposits. During the late Holocene, sea-level rise slowed and then stabilized, leading to the deposition of a regressive sequence that was expressed geomorphically as beachplains and barrier spits. The major focus of this study was to describe the architecture of the transgressive and regressive deposits of the CRLC; this was facilitated by the use of drill core, radiocarbon dates, and geomorphic information. A generalized stratigraphic sequence for the CRLC sand bodies consists of a ravinement overlain by a coarse transgressive lag, which is overlain by transgressive and regressive beachface and shoreface deposits that are covered, in places, by aeolian sand. Throughout the Holocene, sediment discharge from the Columbia River was so high that accommodation space was rapidly occupied and beach progradation occurred as sea level was still rising. Today, even as areas close to the Columbia River are experiencing highstand regressive conditions, in the most northerly part of the littoral cell transgressive conditions still exist and a ravinement is being cut due to insufficient sediment input to fill available accommodation space. Ravinement under the oldest CRLC barrier spit, near the southern end of Long Beach Peninsula, began at about 7–8 ka, while ravinement of the northern portion of the Clatsop Plains was initiated at approximately 5 ka. The ravinement surface was formed at about 4 ka in the Grayland Plains sub-cell and < 1 ka in the North Beaches sub-cell. The diachronous nature of the ravinement surface is reflected in the generally younger radiocarbon ages toward the northern sub-cells.

Sedimentary development of the Pearl River Estuary based on seismic stratigraphy

The Pearl River Estuary in the Southern China was studied both by applying concepts of seismic stratigraphy to the interpretation of high resolution seismic profiles and by correlating with borehole records. The correlation between seismic facies and borehole stratigraphy of the estuary enables to propose a seismic stratigraphy model of the estuarine infill. The stratigraphy and evolution of the Holocene succession of the estuary were reconstructed. The history of estuarine sedimentary development consists of five stages represented by 5 seismic units bounded by laterally sub-continuous seismic interfaces and being consistent with the 5 borehole subdivisions: (i) The basal stage deposits, represented by BU and the borehole section P, might represent the paleo Pearl River alluvial deposits in the Late Quaternary. (ii) The stage I deposits, represented by SU1 and the borehole section A, might be late glacial prodeltaic deposits that occurred during Marine Isotope Stage 3 highstand. (iii) The stage II deposits, represented by SU2 and the borehole section B, consist of relatively coarse-grained sediments deposited during the post glacial transgression about 20–10 ka BP. (iv) The stage III deposits (SU3 and the borehole section C) were generated when the rate of sea level rise decreased in ∼ 20–10 kz BP, which forced sediments to be deposited inside the estuary, where a tidal ravinement surface was characterized by strong erosions and channel formations in the outer zone of the estuary. (v) The stage IV deposits (SU4 and the borehole section D) are the infillings of the estuarine highstand progradation during the last 6000 yrs when the sea surface almost reached the present level.

Internal architecture of the soft sediment cover of the South-Aquitaine shelf (Bay of Biscay): A record of high frequency sea level variations?

Very high-resolution seismic profiles highlighted three main depositional sequences of several hundred meters thick on the South-Aquitaine shelf. The youngest one, the soft sedimentary cover (U1), is presented in this article. It is composed of six seismic units deposited during the Late Quaternary and corresponds to a repetition of a sequence type. The sequence type is formed in four phases: an erosional unconformity (S), a sub-unit “a”, an internal erosional unconformity (St) and a sub-unit “b”. The first phase begins with the erosional unconformity (S), which could be formed during the sea level fall. The second phase is the deposition of the sub-unit “a”, likely during the sea level lowstand and the early sea level rise. Its acoustic facies is generally chaotic with small channels and could be filled by coarse or heterogeneous sediments. The third phase is the formation of a plane and high amplitude unconformity (St) which could be correlated with a transgressive or a wave ravinement surface. The fourth phase corresponds to the deposition, probably during the sea level rise, of the sub-unit “b” which is characterized by subparallel reflections.

Stratigraphic evolution from shoreface to shelf-indenting channel depositional systems during transgression: Insights from the lower Pliocene Súa Member of the basal Upper Onzole Formation, Borbón Basin, northwest Ecuador

Shelf-indenting canyons and their tributary systems are fairly common constituents of Quaternary shelves of active continental margins, but they have been rarely reported from older successions. Recognition of these prominent geomorphologic features in the ancient record has important implications not only for a proper understanding of shoreface-to-shelf depositional systems, but also from a petroleum exploration standpoint as they represent efficient conduits for moving coarse-grained river- and nearshore-borne sediments to the adjacent slope even during periods of relative rise in sea level. Coastal exposures of the lower Pliocene Súa Member in the surroundings of Súa (northwest Ecuador), preserve the unusual juxtaposition of incising submarine channels onto nearshore deposits. This succession accumulated along a narrow, active continental margin during tectonically induced transgression and affords a rare opportunity to evaluate the stratigraphic evolution of such systems from an outcrop perspective. A comprehensive facies characterization combined with application of sequence stratigraphic concepts has led to definition of the following physical surfaces and stratal units in ascending order. (i) A polygenetic, regionally extensive erosional surface resulting from the superposition of the wave ravinement surface onto the previous subaerial sequence boundary (SB/wRS). (ii) A nearshore, sand-prone lithofacies succession comprising a condensed basal shellbed deepening upwards through lower-shoreface bioturbated silty sandstones, into inner shelf sandy mudstones. (iii) Two steep, U-shaped erosional features (turbidite shelf-entrenchment surfaces), interpreted as shelf channels, deeply incised into the subjacent nearshore sediments and marking an abrupt deepening of facies. (iv) A thick, fining-upward sedimentary succession laid down within the confines of the channels by high- and low-density turbidity currents and including both bed-load (traction) and suspended-load deposits; the overall fining- and thinning-upward character exhibited by the infill of these channels is thought to reflect decreasing flow energies and is consistent with the gradual cut-off of clastic influx to their upper reaches in response to progressive detachment from an adjacent coastal source during relative rise in sea level. Based on detailed analysis of facies and a sequence stratigraphic interpretation of outcrop data, this study contributes to extend the existing sequence stratigraphic schemes, further attesting that shelf-sediment bypass and deep-water sedimentation can take place at sea levels other than lowstand.

Early Miocene shell concentration in the mixed carbonate-siliciclastic system of Kutch and their distribution in sequence stratigraphic framework

The Early Miocene succession of Kutch represents a mixed carbonate-siliciclastic depositional system. The carbonate part of the succession, characterized by high abundance of shallow marine benthic fauna, hosts typical shell concentrations (also referred as shell beds). The thickness of shell concentrations vary in scale from 5 cm to 100 cm and are separated by poorly fossiliferous to barren silty shales/siltstones. Based on taphonomic and sedimentological observations, shell concentrations are classified as lag, event, composite/multi-event and hiatal types. The occurrence of different types of shell concentrations in the background of sequence stratigraphic framework is the main theme for the present study. Overall, the shell concentrations occupy the middle part of the sequence i.e. upper part of the transgressive systems tract and lower part of the highstand systems tract. Lag concentrations are found in the lower part of the sequence while composite concentrations, the major contributors in the sequence, occur in upper part of the transgressive systems tract and in the lower part of the highstand systems tract. The hiatal concentrations are associated with maximum flooding surface while the position of event concentrations is independent of sequence stratigraphic framework. The shell concentrations occupy marine flooding surface or marine ravinement surface, thus mark parasequence boundaries.

Late Quaternary evolution of the Çanakkale Strait region (Dardanelles, NW Turkey): implications of a major erosional event for the postglacial Mediterranean-Marmara Sea connection

Seismic and bathymetric data from the Canakkale Strait and its extensions onto the shelves of the Marmara and Aegean seas indicate that the strait was formed mainly by an erosional event. Four seismic units are observed on seismic profiles. The lower two of these (units 4 and 3) constitute the basement of a regionally widespread erosional unconformity (ravinement), which developed during marine isotope stage 2 (MIS 2). The two upper units (units 2 and 1), which overlie the ravinement surface, form a higher-order sequence. Sequence stratigraphic analysis indicates that units 2 and 1 deposited as lowstand and highstand systems tracts respectively, since the end of MIS 2. The transgressive systems tract is represented by a major erosional event which occurred throughout the Canakkale sill area when the Mediterranean-Marmara Sea connection and, hence, the Canakkale Strait was formed. The existence of the erosive Şarkoy Canyon along the shelf edge of the southern Marmara Sea demonstrates that the flow direction causing the erosion was from south to north, thus proving that it was produced by Mediterranean water flowing over the sill into the Marmara Sea basin.

Sedimentary environments and depositional characteristics of the Middle to Upper Eocene whale-bearing succession in the Fayum Depression, Egypt

The discovery of whale fossils from Eocene strata in the Fayum Depression has provoked interest in the life and lifestyle of early whales. Excellent outcrop exposure also affords the dataset to develop sedimentological and stratigraphic models within the Eocene strata. Previous work generally asserts that the thick, sand-rich deposits of the Fayum Depression represent shoreface and barrier island successions with fine-grained lagoonal and fluvial associations capping progradational successions. However, a complete absence of wave-generated sedimentary structures, a preponderance of thoroughly bioturbated strata and increasingly proximal sedimentary successions upwards are contrary to accepted models of the local sedimentological and stratigraphic development. This study considers data collected from two Middle to Upper Eocene successions exposed in outcrop in the Wadi El-Hitan and Qasr El-Sagha areas of the Fayum Depression to determine the depositional affinities of Fayum strata. Based on sedimentological and ichnological data, five facies associations (Facies Association 1 to Facies Association 5) are identified. The biological and sedimentological characteristics of the reported facies associations indicate that the whale-bearing sandstones (Facies Association 1) record distal positions in a large, open, quiescent marine bay that is abruptly succeeded by a bay-margin environment (Facies Association 2). Upwards, marginal-marine lagoonal and shallow-bay parasequences (Facies Association 3) are overlain by thick deltaic distributary channel deposits (Facies Association 4). The capping unit (Facies Association 5) represents a transgressive estuarine depositional environment. The general stratigraphic evolution resulted from a regional, tectonically controlled second-order cycle, associated with northward regression of the Tethys. Subordinate cycles (i.e. third-order and fourth-order cycles) are evidenced by several Glossifungites-ichnofacies demarcated discontinuities, which were emplaced at the base of flooding surfaces. The proposed depositional models recognize the importance of identifying and linking ichnological data with physical–sedimentological observations. As such – with the exception of wave-generated ravinement surfaces – earlier assertions of wave-dominated sedimentation can be discarded. Moreover, this study provides important data for the recognition of (rarely reported) completely bioturbated sand-dominated offshore to nearshore sediments (Facies Association 1) and affords excellent characterization of bioturbated inclined heterolithic stratification of deltaic deposits. Another outcome of the study is the recognition that the whales of the Fayum Depression are restricted to the highstand systems tracts, and lived under conditions of low depositional energy, low to moderate sedimentation rates, and (not surprisingly) in fully marine waters characterized by a high biomass.