Infralittoral Prograding Wedge Research Articles

Seismic stratigraphy of the north-westernmost area of the Malta Plateau (Sicily Channel): The Middle Pleistocene-Holocene sedimentation in a tidally influenced shelf

In this study we present the results of a seismic-stratigraphic analysis of sub-bottom profiles in the north-westernmost area of the Malta Plateau in order to define the depositional mechanisms for the upper Quaternary sequences. During this interval the morphology of the Malta Plateau was characterized by a ramp and bathymetries not exceeding 200 m. Two major unconformities, related to MIS 6 and MIS 2 (the latter corresponding to the Last Glacial Maximum, LGM), characterize the upper Quaternary sequences. The geometries of the recognized seismic units indicate as depositional mechanisms were controlled by subsidence and sea-level fluctuations. In detail, deposits related to the last glacial event were recognized through their seismic pattern and have been interpreted as formed by the interaction between tide and wave dynamics. Contrary to the northern Sicilian continental margin, in the Malta Plateau ramp no LGM-related lowstand prograding wedge was recognized due to the absence of an effective shelf edge. It is considered as a consequence of the morphology and the dominant deposition processes in the Malta Plateau. Afterwards the ramp morphology allowed a rapid drowning of the Malta Plateau instead with the formation and preservation of transgressive deposits revealed as bedforms. The highstand deposits appear as prograding bodies and have been classified as infralittoral prograding wedge.

High‐frequency cycles of brachiopod shell beds on subaqueous delta‐scale clinoforms (early Pliocene, south‐east Spain)

AbstractDuring the early Pliocene, subaqueous delta‐scale clinoforms developed in the Águilas Basin, in a mixed temperate carbonate–siliciclastic system. The facies distribution is consistent with the infralittoral prograding wedge model. Stacking patterns and bounding surfaces indicate that the clinoforms formed during the highstand and falling sea‐level stages of a high rank cycle. Twenty‐two prograding clinothems were recognized over a distance of ≥1 km. Biostratigraphic data indicate a time span shorter than 700 kyr for the whole unit (MPl3 biozone of the Mediterranean Pliocene). Cyclic skeletal concentrations and occasional biostromes of suspension feeders (terebratulid brachiopods, modiolid bivalves and adeoniform bryozoan colonies), slightly evolved glauconite and occasionalGlossifungitesichnofacies formed on the clinoforms during high‐frequency pulses of relative sea‐level rise. During such stages, increased accommodation space in the topsets of the clinoforms caused a strong reduction of terrigenous input into the foresets and bottomsets. This provided favourable conditions for the development of these suspension feeder palaeocommunities. During stillstand stages, however, reduced accommodation space in the topsets eventually resumed progradation in the foresets. There, the abundance ofDitrupatubes indicates frequent siltation events that extirpated the terebratulid populations and other epifaunal suspension feeders in the foreset and bottomset subenvironments. The occurrence of shell beds on the clinoforms suggests that this case study represents lower progradation rates than standard examples where shell beds bound the clinobedded units at their base and top only. Importantly, the distributions of biofacies and ichnoassemblage associations contribute significantly to the understanding of the effects of relative sea‐level fluctuations on the evolution of subaqueous delta‐scale clinoform systems.

Sedimentary architecture of a prograding oolitic-siliciclastic wedge: Response to changes in wave-base oscillation (Kimmeridgian, Iberian Basin)

Abstract A detailed facies and sequential architectural analysis has been carried out along the wedge-shaped shallow marine cross-bedded oolitic-siliciclastic Ricla Member (Kimmeridgian, Northern Iberian Basin). The obtained results are based on fieldwork along the 4 × 1 km continuous outcrops with the use of high-resolution photomosaics and drone-made videos, which have led to a precise and extensive facies reconstruction. Three main facies that are laterally related (A to B to C) in down-dip direction have been differentiated, which correspond to the topset, foreset and bottomset parts of a sloping depositional surface. Sedimentation was controlled by sweeping drift and downwelling storm-induced currents causing avalanching processes, with the deep action of oscillatory currents. The sedimentary architecture consists in 5 successive units composed by several sub-units, arranged according to different stacking patterns, which reflect the sedimentary response to wave-base oscillations superimposed to the regressive part of a third-order transgressive-regressive cycle. The sedimentological features indicate that this unit, which has been previously interpreted as a dune complex fit with an infralittoral prograding wedge model, as it is observed in geographically close and stratigraphically similar units. The Ricla Member is therefore regarded as an example of a well-exposed grain-supported unit with broad potential application to other prograding grain-dominated lithosomes that do not conform to the traditional sand shoal model.

Submarine canyon-head morphologies and inferred sediment transport processes in the Alías-Almanzora canyon system (SW Mediterranean): On the role of the sediment supply

Canyon head regions are key areas for understanding the shelf-to-canyon sedimentary dynamics and assessing the predominant hydrodynamic and sedimentary processes shaping their morphology. High-resolution multibeam bathymetry surveys conducted on the shelf, upper slope and along the main thalwegs of the Alías-Almanzora submarine canyon system were used to recognize the specific morphological features of the various canyon heads and infer the main sediment transport mechanism operating through them. Off the Almanzora River, different canyon head morphologies were observed at 65–90m water depth, incising the outer prodeltaic deposits. A direct connection from the river supply is evidenced by the presence of a large radial field of sediment waves on the prodelta, presumably related to hyperpycnal flows during flash flood events, and their continuation towards trains of cyclic steps that merge into the Almanzora canyon head. Processes linked to seepage and groundwater sapping also seems apparent in the prodeltaic deposits, which results in pockmark alignments and formation of elongated narrow canyon heads. At the southern limit of the Almanzora prodelta, another type of canyon head results from the formation and merging of linear gullies. These have been interpreted as the morphological expression of the distal off-shelf transport of flood-related hyperycnal flows. However, most of the canyon heads of the main tributaries of this canyon system (i.e., Garrucha, Cabrera and Alías) are found at much shallower water depths (7–20m). They generally show a continuation in land with rivers or intermittent creeks (known as “ramblas”) that also experience flash flood events, but some of them are disconnected from any river source. These canyon heads cut into the infralittoral prograding wedge, displaying feeder channels that tend to oriented against the direction of the prevalent long-shore current. Some canyon head tributaries show sediment waves along their axis interpreted as the result of hyperpycnal flood events or storm-induced turbidity flows. This study focusses on the diversity of sediment transport processes that can co-exist in the various canyon tributaries of a given submarine canyon system, stressing on the importance of the canyon heads location with respect to the principal sedimentary source, which ultimately determines their main geomorphological traits.

Depositional model for a prograding oolitic wedge, Upper Jurassic, Iberian basin

Facies architecture and bedding patterns of the Kimmeridgian Pozuel Formation (Iberian Basin) evidence that this 50–70-m thick oolitic-grainstone unit conforms to the Infralittoral Prograding Wedge (ILPW) model instead of the classic models used for interpreting oolitic grainstones sandbodies on carbonate ramps or platforms (i.e., bank-margin shoal complexes, beaches and beach ridges).Ten lithofacies have been distinguished in the Pozuel Formation: 5–10° dipping clinobedded oolitic grainstone foresets passing to tabular oolitic packstones-grainstones, which interfinger the muddy basinal bottomsets. Landwards, the clinobeds pass into subhorizontal topsets composed of trough cross-bedded to structureless oolitic grainstones; oolitic-skeletal grainstones with stromatoporoids and coral-stromatoporoid-microbial mounds. Siliciclastic lithofacies and oncolitic/peloidal packstones occur at the innermost position. These lithofacies stack in strike elongated, 5–20-m thick, 0,5–2 km dip-oriented wide, aggradational-progradational packages with complex sigmoid-oblique geometries.Lithofacies, depositional geometries and stacking pattern permit to summarize the main characteristic of such Upper Jurassic oolitic infralittoral prograding wedge potentially to be applied in other oolitic sandbodies both in outcrops and subsurface: 1) sediment production within the wave action zone, 2) grainstone-dominated textures, 3) prograding basinward onto basinal muds, 4) laterally (strike) extensive, paralleling the shoreline, 5) variable thickness, commonly of few tens of meters, 6) broadly sigmoidal to oblique internal architecture, with topsets, foresets and bottomsets, 7) dip of foresets close to the angle of repose, 8) topsets deposited in shallow-water, extending through the shoreface, from the shoreline down to the wave base, 9) mounds, either microbial or skeletal, may occur in the topsets.The coated-grains factory was along the high-energy, wave-dominated outer platform (topset beds), from where the mud was winnowed and the grains transported both landward to the platform interior, and seaward to the platform edge, from were the grains cascaded down the slopes as grain flows and mass flows, forming clinobeds. This genetic model can be applied to other grain-dominated lithosomes, some of them forming hydrocarbon reservoirs, e.g., the Jurassic Hanifa Formation and some Arab-D (e.g., Qatif Field) in Arabia, the Smackover Formation in northern Louisiana and south Arkansas, the Aptian Shuaiba Formation (e.g., Bu Hasa Field) and the Cenomanian Mishrif Formation (e.g., Umm Adalkh Field) of the Arabian Gulf.

The Neapolitan Yellow Tuff caldera offshore the Campi Flegrei: Stratal architecture and kinematic reconstruction during the last 15ky

Abstract In this study we integrate high-resolution swath bathymetry, single channel reflection seismic data and gravity core data, to provide new insights into the shallow structure and latest Quaternary to Holocene evolution of the submerged sector of the Neapolitan Yellow Tuff (NYT) caldera (Campi Flegrei) in the Pozzuoli Bay. The new data allow for a reconstruction of the offshore geometry of the NYT caldera collapse–ring fault system, along with the style and timing of deformation of the inner caldera resurgence. Our interpretation shows that the NYT eruption (~ 15 ka BP) was associated with a caldera collapse bounded by an inward-dipping ring fault system. The ring fault system consists in a 1–2 km wide fault zone that encircles an inner caldera region ~ 5 km in diameter and is often marked by the occurrence of pore fluids ascending through the fault zone, up to the seafloor, particularly in the western sector of the bay. A shallow magmatic intrusion along the ring fault zone was also detected offshore Bagnoli in the eastern part of the Pozzuoli Bay. Following the NYT eruption, the inner caldera region underwent significant deformation and resurgence with a maximum cumulative uplift of the offshore structure in the order of 180 m. The net uplift rate of the caldera resurgent dome was ~ 9–12 mm/year during the period 15.0–6.6 ka BP. The style of deformation of the resurgent structure can be described in terms of a broad doming, accompanied by subordinate brittle deformation, mostly concentrated in a small apical graben at the summit of the resurgent dome. Chronostratigraphic calibration of seismic profiles obtained by three tephra layers cored in the Pozzuoli Bay indicates 5 to 25 m of post-Roman differential subsidence and tilting towards ESE of the inner caldera resurgence, as recorded by the drowning of the infralittoral prograding wedge below the present-day storm wave base.

The influence of shelf-indenting canyons and infralittoral prograding wedges on coastal morphology: The Carchuna system in Southern Spain

Abstract Submarine canyons and progradational sedimentary bodies are common features of continental margins worldwide. Few studies have analyzed the relationship between the coastal morphology and the morphology and sedimentary characteristics of the adjacent shelf in wave-dominated coasts; or the potential role played by shelf-indenting canyons as inducers of sediment deposition in shallow waters. This work presents a study that correlates the coastal morphology with the characteristics of the adjacent offshore shallow shelf in an area with a complex inner bathymetry: the Carchuna system, Spain. The study area is characterized by large-scale non-rhythmic cuspate features in the coastline, whereas the inner bathymetry exhibits a shallow-water infralittoral prograding wedge (IPW) and a shelf-indenting canyon that has tributaries located a short distance from the coastline. Using detailed bathymetric measurements, observational data and wave propagation modeling, the influence of the different bathymetric elements was quantified, and a mechanism proposed for the generation of the Carchuna IPW. The wave propagation results show that the canyon is the main source of the alongshore modulation of nearshore waves and that it plays a major role in the generation of the large-scale cuspate features in the shoreline. Additionally, these results suggest that the long-term coastal erosion associated with extreme storms yielded sufficient sediment which when subsequently transported eastward, the dominant littoral drift direction, formed the IPW. Once formed the IPW modified the wave propagation patterns and contributed to the development and reinforcement of the shoreline features.

Holocene highstand deposits in the Gulf of Cadiz, SW Iberian Peninsula: A high-resolution record of hierarchical environmental changes

A comparison of the internal structure of Holocene highstand shallow-marine deposits with emerged spit-bar systems in the Gulf of Cadiz margin (SW Iberian Peninsula) is presented, in order to increase the knowledge about the patterns of environmental fluctuations of sub-Milankovitch periodicity during the recent highstand period. A high-resolution seismic database of boomer profiles was interpreted, focusing on shallow-marine deposits of the Gulf of Cadiz shelf, such as the Guadalquivir River prodelta, the Guadiana River depositional system and the Faro–Tavira infralittoral prograding wedge. The results indicate that the internal architecture of recent highstand shelf deposits is complex, as the recognition of three main types of seismic unit motifs suggests the existence of a hierarchical pattern of environmental fluctuations: (a) Major-scale motifs: the most significant feature observed in the seismic records is the pervasive occurrence of two major-scale motifs (lower and upper) within the Holocene highstand systems tract. (b) Intermediate-scale motifs: each major-scale motif is composed of two intermediate-scale motifs, defining four intermediate-scale motifs (H 1 to H 4). (c) Minor-scale motifs: the internal structure of major- and intermediate-scale motifs reveals a high degree of environmental variability during the recent highstand, probably led by climatic cyclicities of submillenial scale. The lower major-scale motif is characterised by alternating progradational–aggradational minor-scale motifs, whereas the upper major-scale motif presents a more uniform internal structure dominated by progradational units. The influence of two distinct trends or asymmetric cycles of sea-level change seems to have been significant in the generation of the major-scale architecture. The transition between both major phases was probably related with a major sea-level rise. Other factors, such as changes in the magnitude and/or direction of storm events and climatically induced changes of sediment supply, are proposed to have controlled the generation of intermediate- and minor-scale architectures.

Contrasting styles of the Holocene highstand sedimentation and sediment dispersal systems in the northern shelf of the Gulf of Cadiz

An approach to the interpretation of the Holocene highstand depositional systems and the influence of shelf circulation patterns on sediment dispersal in the northern Gulf of Cadiz shelf (SW Iberian Peninsula) is reported. The study area comprises the transition from the southern Portuguese shelf, lacking major fluvial input, to the Guadiana and Guadalquivir shelves, receiving sediments from fluvial sources. An integrated study using high-resolution seismic profiles and meteorological and physical oceanography data was undertaken to reach the proposed goals. A lateral transition of shelf environments is evidenced during the most recent sea-level highstand period. The Portuguese shelf can be considered as a moderate to high-energy environment, where the dominance of storm events led to the construction of a significant infralittoral prograding wedge, as a consequence of normal incidence of storm waves and steep shelf profile. The Guadiana shelf shows a distinct partition of depositional systems, as a result of a moderate fluvial supply and significant reworking wave and current activity over morpho-structural highs. Proximal facies are attributed to poorly developed prodeltas, whereas distal facies are interpreted as muddy belts. The Guadalquivir shelf is a fluvially dominated environment, as the most prominent feature is a thick, widespread prodelta whose formation has been controlled by significant fluvial supply, moderate hydrodynamic regime and smooth shelf topography. The comparison between sediment transport patterns evidenced in geophysical records and shelf circulation patterns enables us to propose a model for the sediment dispersal during the Holocene highstand period. Sediment dispersal is controlled by an intermittent counter current system, which seems to be intimately linked with the wind regime. Eastward dispersal on the middle to outer shelf is led by the general anticyclonic circulation, dominant under the influence of westerly winds. Westward dispersal occurs in the inshore zones, mainly led by the entrance of warm water tongues on the shelf under the action of easterly winds. These two opposing patterns of sediment dispersal are bounded by zones of current shear (Huelva Front and Strafford Shear).

The infralittoral prograding wedge: a new large-scale progradational sedimentary body in shallow marine environments

A progradational sedimentary body, the infralittoral prograding wedge (IPW), has been developing from the mean fair-weather wave-base level to the storm wave-base level between the onshore (beach) and the offshore (inner continental shelf) depositional zones along the Spanish coast during the Late Holocene. The main sedimentary body is composed of large inclined master beds which prograde seawards parallel to the shoreline, formed by sediments swept offshore by waves from shallow-water littoral environments. The inclined beds downlap onto finer-grained offshore sediments and, in turn, are overlain by shoreface deposits. The IPW is generated by downwelling storm currents and associated seaward transport of sediment. It represents a new depositional model for clastic wave-dominated coasts, and its identification requires a new subdivision of the nearshore environment.