Lower Shoreface Research Articles

Modelling of annual sand transports at the Dutch lower shoreface

Dutch coastal policy aims for a safe, economically strong and attractive coast. This is achieved by maintaining the part of the coast that support these functions; the coastal foundation. The coastal foundation is maintained by means of sand nourishments. Up to now, it has been assumed that net transports across the coastal foundation’s offshore boundary at the 20 m depth contour are negligibly small. In the framework of the Coastal Genesis 2.0 program we investigated sand transports across this boundary and across other depth contours at the lower shoreface.This paper presents a computationally efficient approach to compute the annual sand transport rates at the Dutch lower shoreface. It is based on the 3D Dutch Continental Shelf Model with Flexible Mesh (3D DCSM-FM), a wave transformation tool and a 1DV sand transport module. We validate the hydrodynamic input against field measurements and present flow, wave and sand transport computations for the years 2013–2017.Our computations show that the net annual sand transport rates along the Dutch coast are determined by peak tidal velocities (and asymmetry thereof), density driven residual flows, wind driven residual flows and waves.The annual mean alongshore transports vary along the continuous 20 m depth contour. The computed total cross-shore transports are onshore directed over the continuous 20 m, 18 m and 16 m depth contours and increase with decreasing water depth.The effect of density difference and wind on the 3D structure of the flow and on the sand transports cannot be neglected along the Dutch lower shoreface. Our computations show that excluding the effect of density results in a significant decrease of the onshore directed transports. Also switching off wind largely counteracts this effect.The net cross-shore transport is determined by a delicate balance between gross onshore and offshore transports, where wave conditions are important. We show an example for Scheveningen where the net cross-shore transport is onshore directed when including all wave conditions but would be offshore directed when excluding waves higher than 3.5 m. In contrast, at Callantsoog the highest waves contribute more to the offshore directed transports. These results suggest that storm conditions play an important role in the magnitude and direction of the net annual transport rates at the lower shoreface.

Palaeosols in an Upper Pliocene fluvial to shallow marine succession (Valdelsa Basin, Central Italy): A sequence-stratigraphic perspective

The present study provides an example of how palaeopedology and facies analysis may be integrated for the interpretation of a cyclothemic succession in the Upper Pliocene (Piacenzian) of the Valdelsa Basin (central Italy). The stacking of facies and intervening bounding surfaces, including palaeosols, outline a hierarchy of elementary (EDS) and composite (CDS) depositional sequences within the unconformity-bounded stratigraphic units (S4-S6 synthems) which compose the succession. The focus of the study is on synthem S4 and the transition to synthem S5. Synthem S4 records the development of a distal alluvial plain dominated by floodbasin mudstone with subordinated channelized sandstone (S4 1 ), followed by the incision of a fluvial valley aggraded by the cyclical stacking of braided and low sinuosity channelized conglomerate and sandstone (S4 2 ). Synthem S5 includes lower shoreface sandstone and inner shelf mudstone related to a major transgression which affected the study area during the late Piacenzian. Evidence of soil-forming processes is well preserved within sub-unit S4 1 where five palaeosols (PS4a-e) are stacked within the facies architecture of EDS1 c-d , both being defined as transgressive to high stand tracts. Increasing palaeosol development was observed within both EDSs, while palaeosols were generally thicker and more closely stacked within EDS1 d . Palaeosols were interpreted as marking minor cycles of accommodation space creation within EDS1 c , while marking a better defined high stand tract in EDS1 d . Increasing upward soil development was observed within each EDS, with generally better developed soils in EDS S41d. The unconformable transition from S4 to S5 is marked by a thin veneer of slope deposits, bearing pedogenic carbonates reworked from a missing PS4f palaeosol, formed during the shaping of the erosional surface separating sub-units S4 1 and S4 2 . The results of this study indicate that: 1) the sedimentary and pedogenic processes recorded in the channelized facies and palaeosols in the floodbasin facies of sub-unit S4 1 , are coherent with a palaeoenvironmental setting dominated by seasonal climate; 2) the facies-palaeosol architecture of S4 synthem corresponds to those described in sequence-stratigraphic models applied to continental successions. The pedo-sedimentary signature of the major sea-level fluctuation recorded in the transition between S4 and S5 synthem differs from these models. In this case a well-developed and drained palaeosol, expected to record the maximum regressive surface shaped during the falling stage of sea level, is missing. This difference is related to a rapid fall and subsequent rise of relative sea level which marked the transition between S4 and S5 synthems. • Palaeosol and facies analysis coherently restore a Piacenzian fluvial system. • A seasonal climate controlled sediment dispersal and weathering. • Palaeosols are key-surfaces in the cyclical fluvial facies architecture. • Cyclothemic stack of palaeosols partially fits sequence-stratigraphic models. • Major sequence boundary lacks a well developed palaeosol.

Diagenesis and the Conditions of Deposition of the Middle Jurassic Siderite Rocks from the Northern Margin of the Holy Cross Mountains (Poland)

The aim of the present study is to reconstruct sedimentary conditions of Middle Jurassic rocks that contain siderites to identify the mineral composition of the inserbeds and to recognize the origin of the siderite. Thin inserbeds of siderite rocks occur most frequently within Bajocian siliciclastic deposits and, more rarely, Aalenian and Bathonian. The research material comes from 11 boreholes located in the north and northeastern margins of the Holy Cross Mountains. The research methods included sedimentological analyses, and studies in polarizing and scanning electron microscopes, staining of carbonates, cathodoluminescence, X-ray structural analysis, and stable carbon and oxygen isotopic determinations were used. Middle Jurassic sideritic rocks are most often represented by clayey siderites, which also include muddy and sandy varieties and siderite sandstones. There are also local occurrences of coquinas, claystones, mudstones, and siderite conglomerates. The main component of sideritic rocks is sideroplesite. Berthierine, pistomesite, calcite, and ankerite are important components, too. The action of diagenetic processes of cementation, compaction, replacement, and alteration within the Middle Jurassic deposits was most intense during the eo- and mesodiagenesis. The sedimentological analysis showed that most of the studied siderites were formed in a low-oxygenated marine environment, mainly in the transition zone between the normal and storm wave bases and in the lower and middle shoreface zones. The results of the petrographic, mineralogical, and geochemical studies indicated the origin of the sideritic rocks mainly in the marine environment, with the participation of meteoric water. There were slight differences in the chemical composition of sideroplesite depending on the environment it crystallized in. There was no correlation between the values of the carbon isotope determinations in the sideroplesite and the environmental conditions of its crystallization. Slight differences were visible in the case of the average values of δ18O in the sideroplesite.

The Lower Cretaceous “Continental Intercalaire” around Tidikelt (Central Sahara, Algeria): Sedimentology, palaeontology and ichnology

The Lower Cretaceous strata are exposed over a large surface in the northern part of the Ahnet basin. They consist of transgressive, horizontal formations overlying the folded Palaeozoic formations by angular unconformity across the Tidikelt region. The present study addresses the respective lithostratigraphical units of the “Continental Intercalaire” succession and their subsequent palaeo-environment in the Tidikelt area using a trace fossil analysis combined with sedimentological and palaeontologic data. The lithological and sedimentological features of the study sections recognised eleven sub-units organised within four lithological units: the Lower Clay Unit of Barremian-Neocomian age consisting of three Sub-units (Akablie Sandstone, Sidi Mahmoud Clays and Pebbly Sands); the Quartzite Sandstones Unit referred to a Late Barremian-Early Aptian age; the Middle Clay-Sandstone Unit consisting of a thick deposit of Early Aptian-Albian age, divided into five Sub-units (Tit Sandstones, In Salah Sand-Clay, In Salah Sandstone, Foum El Bouib Sandstone, and Sandstone-Clay); and the Upper Clay Unit comprising the Oued Taleh Sand and the El-Golea Clays Sub-units. Vertebrate remains all evidence a Late Albian-Early Cenomanian age for the top part of the Continental Intercalary. Ichnologic data analysis documents lower diversity of the invertebrate trace fossils: only ten ichnotaxa are recorded so far and grouped in five ichnoassemblages. Fuvial-lacustrine ichnoassemblage represents a continental ichnofacies of a fluvial-lacustrine environment: Mermia, Scoyenia and Skolithos ichnofacies. Fluvial Ichnoassemblage of the Quartzite Sandstone Unit is represented by insect trace fossils typical of the Coprinisphaera ichnofacies. Fluvio-marginal ichnoassemblage corresponds to a tidal-influenced, fluvial deposit transgressive on Unit B, represented by Skolithos and Psilonichnus ichnofacies. Lower shoreface ichnoassemblage shows the upper part of Unit C, documented by horizontal trace fossils such as Thalassinoides and vertical root traces, all supporting a lower shoreface environment in a semi-arid climate interlined by well-oxygenated episode with nutrient-rich conditions and vegetation dominance. Near to shoreface ichnoassemblage coincides with the upper unit D of coastal deposits with fluvial-tidal influence at the base (Oued Taleh Sands) associated with Scoyenia and Skolithos trace fossils and lagoon deposit of the El-Golea Clays Sub-units.

Empirical depths of closure along the US East coast

Depth of closure (DOC) is a commonly-used parameterization of the seaward limit in significant elevation change along a beach profile. Engineers, scientists, and resource managers use this parameter to make decisions and formulate designs for activities ranging from ecological restorations to beach nourishment and harbor construction. We present empirically measured DOC values from eight sites along the U.S. East Coast from Long Island NY to Georgia. The sites represent a spectrum of settings between fully wave-dominant and mixed-energy barriers and beaches, and five of the eight surveys extend back at least one decade. There are multiple DOC formulations based on wave conditions that tend to over-estimate DOC values compared to empirical observations. Our results show a similar pattern, with modeled DOC averaging 2.5 m (m) deeper than surveyed values but yielding reasonable results in wave-dominant environments. Along mixed-energy sites, modeled DOC values range from 1.0 to 5.7 m deeper than empirical observations. Alongshore comparison of observed DOC values within individual sites also suggests the movement of shoals on the lower shoreface near inlets may further complicate DOC estimates compared to strand-type shorelines with relatively featureless nearshore slopes.

Timing of Bellerophontoid (Gastropoda) Demise in the Early Triassic of South Primorye, Russian Far East

The stratigraphic distribution and modes of occurrence of Early Triassic Bellerophontoidea (Gastropoda) are studied at seven sections in South Primorye, Russian Far East, where depositional environments ranging from nonmarine, shoreface, to distal basin plain settings are recorded. Warthia zakharovi and Dicellonema abrekensis are abundant in Induan (Griesbachian and Dienerian) fine- to medium-grained, hummocky cross-stratified (HCS) sandstone beds occasionally intercalated with wavy-mudstone layers, whereas they are absent in coarser-grained cross-stratified successions. This observation suggests that bellerophontoids inhabited a lower shoreface environment above the storm wave base and possibly an inner shelf environment as well during this particular stage. Olenekian (Smithian and Spathian) bellerophontoids have not been found in the storm-induced sandstone beds, but W. zakharovi occurs in the lower Smithian sandstone beds of distal turbidites intercalated in the laminated mudstone. This mode of occurrence strongly suggests that W. zakharovi inhabited a deeper environment than lower shoreface, most probably an inner shelf environment, and after death, its shells were transported from their habitat to the basin-floor by sediment gravity flow. Bellerophontoids have not been found in middle Smithian and younger strata in South Primorye, and the timing of this disappearance is synchronous with other areas of the world. Bellerophontoids were distributed over wide-ranging areas from the equator to the high latitudes during Induan time, but they disappeared from the lower latitude areas and the shallower marine environments of middle latitude South Primorye during the early Smithian, before eventually becoming extinct during middle Smithian time. Such a step-by-step demise strongly implies that the severe global warming and related harmful events that occurred during the Smithian may have had a serious effect on bellerophontoids. The extinction of Bellerophontoidea before the beginning of the late Smithian suggests that the group may have been more sensitive to global warming and related harmful events than other organisms.

Small-scale bedforms and associated sediment transport in a macro-tidal lower shoreface

Ripples and small-scale bedforms are ubiquitous in shallow water environments under the combined action of currents and waves. Small scale processes linked to their formation and migration are interconnected with sediment transport at larger scales (e.g. tens of metres to kilometres), both resulting in and being affected by large scale sediment transport and geomorphological evolution. The lower shoreface provides a key link between coasts and continental shelves, but the contribution of ripples and small-scale bedforms to sediment transport in this region has yet to be fully addressed. This work presents a study of sediment dynamic processes on the lower shoreface in the presence of small-scale bedforms. Observations were made during the winter of 2017 on the lower shoreface of Perranporth Beach, which is in the south west of the UK and exposed to Atlantic waves. The analysis of morphological expressions and the variability of ripples under waves, currents and wave-current conditions are assessed. Ripple morphology and associated dynamics are analysed for their potential contribution to the exchange of sediment between the lower and the upper shoreface. In the present study it was observed that even though ripples were evolving depending on the wave-current forcing, little ripple migration was observed due to low wave skewness. The implication is that ripple migration and bedload transport are only a small contribution to onshore sediment transport under low to moderate energy conditions. However, during more energetic conditions, ripples were washed out and the wave skewness increased, resulting in onshore sediment transport under a sheet flow regime. This suggests that ripple formation and migration can have little impact on the cross-shore supply of sediment from the lower shoreface to the upper shoreface and that more energetic wave conditions are required to significantly transport sediment towards the beach.

The iron oolitic deposits of the lower Devonian Yangmaba formation in the Longmenshan area, Sichuan Basin

Oolitic ironstones are widely distributed in South China, particularly in Middle and Upper Devonian strata, and are referred to as Ningxiang-type iron deposits. The hybrid siliciclastic-carbonate deposits of the Lower Devonian Yangmaba Formation iron-enriched interval (dominated by hematite ooids and chamosite ooids) are recognized in the Shigouli section of the Longmenshan area, Sichuan Basin. The Yangmaba Formation ironstones differ from other Devonian Ningxiang-type oolitic ironstones: The Ninxiang-type ironstone deposits are commonly interpreted to have been deposited in a narrow coastal zone or inland restricted bays and lagoons with clastic and carbonate sedimentary sequences; by contrast, the studied oolitic ironstones are interpreted to have been deposited in a shoreface zone to inner shelf based upon field and petrographic investigations. Our study shows that this oolitic ironstone consists of dominantly hematite ooids and chamosite ooids. Major element and trace element discrimination diagrams, PAAS (Post-Archaean average Australian sedimentary rock) normalized REE (Rear earth element) patterns, and positive Ce/Ce* anomalies show evidence of a hydrogenous origin. The weathering of adjacent terrestrial rocks from the formation of the palaeo-land surface is interpreted to be the main Fe source for the oolitic ironstones.Environmental energy and redox conditions are the important factors controlling ironstone formation and distribution of the hybrid deposits of the Yangmaba Formation in the Shigouli section of the Longmenshan area. Oolitic ironstones formed in oxidizing conditions of the upper shoreface zone include the carbonate concentric ooids with slightly hematite ooids occurring in higher energy upper oxidizing shoreface subzone, moderately hematite concentric ooids deposited in middle oxidizing shoreface subzone of fluctuant environmental energy, and hematite ooids present in lower oxidizing shoreface subzone of lower-energy conditions or weakly agitated environment. The chamosite concentric ooids and superficial ooids formed in reducing conditions of the lower shoreface and upper offshore transition. The former occurred in upper reducing shoreface subzone near the fair weather wave base, and the chamosite superficial ooids were deposited in lower reducing shoreface subzone and upper offshore transition that was affected by episodic high energy events.

Late Pleistocene baldcypress (Taxodium distichum) forest deposit on the continental shelf of the northern Gulf of Mexico

Approximately 13 km south of Gulf Shores, Alabama (United States), divers found in situ baldcypress (Taxodium distichum) stumps 18 m below the ocean surface. These trees could have only lived when sea level fell during the Pleistocene subaerially exposing the tectonically stable continental shelf. Here we investigate the geophysical properties along with microfossil and stratigraphical analyses of sediment cores to understand the factors that lead to this wood’s preservation. The stumps are exposed in an elongated depression (~100 m long, ~1 m deep) nested in a trough of the northwest–southeast trending Holocene sand ridges and troughs with 2–5 m vertical relief and ~0.5 km wavelength. Radiocarbon ages of the wood were infinite thus optically stimulated luminescence (OSL) dating was used to constrain the site’s age. Below the Holocene sands (~0.1–4 m thick), separated by a regional erosional unconformity, are Late Pleistocene mud‐peat (72±8 ka OSL), mud‐sand (63±5, 73±6 ka OSL), and palaeosol (56±5 ka OSL) facies that grade laterally from west to east, respectively. Foraminiferal analysis reveals the location of the terrestrial‐marine transitional layer above the Pleistocene facies in an interbedded sand and mud facies (3940±30 (1σ) 14C a BP), which is part of a lower shoreface or marine‐dominated estuarine environment. The occurrence of palaeosol and swamp facies of broadly similar ages and elevation suggests the glacial landscape possessed topographic relief that allowed wood, mud and peats to be preserved for ~50 ka of subaerial exposure before transitioning to the modern marine environment. We hypothesize that rapid sea‐level rise occurring ~60 or ~40 ka ago provided opportunities for local flood‐plain aggradation to bury the swamp thus preserving the stumps and that other sites may exist in the northern Gulf of Mexico shelf.

The shell-armoured trace fossil Ereipichnus pickerillensis from the Pliocene Moruga Formation, Trinidad: morphology and palaeoenvironment

A new ichnospecies, Ereipichnus pickerillensis, is described from lower shoreface deposits of the Pliocene Casa Cruz Sandstone Member of the Moruga Formation on Trinidad. E. pickerillensis comprises horizontal and sub-horizontal tubular burrows that are lined with radially orientated, poorly imbricated bivalve and other small shell fragments. In the studied strata, E. pickerillensis is found in association with Zoophycos, Asterosoma, Thalassinoides, and other elements of the Cruziana ichnofacies.

Dominant updriftward sediment transport on the updrift-side of a modern deflected delta, Ishikari coast, Hokkaido, Japan

The Ishikari coast of Hokkaido, Japan is a wave-dominated semi-enclosed coast, the sediments of which are primarily sourced from a single river (the Ishikari River), forming a northeast deflected delta. Asymmetric and deflected deltas are generally considered to be formed under net longshore sediment transport downdriftward; however, through sedimentological and grain-size trend analysis (GSTA) of seafloor sediments, along with some other observational data, we recognised dominant updriftward sediment transport on the updrift-side of the deflected delta system. GSTA showed that the most important trend in the coast is coarser, better-sorted, and more positively skewed (CB+). CB+ trends around the river mouth converge from the lower shoreface zone to the river mouth spit on the updrift side. The trends reflect the combined effects of shore-normal wave action and river sediment discharge. Wave-driven surface currents crossing over the delta lobe converge at the southwestern side of the river mouth. In the deeper zone (lower shoreface), southwest (updriftward) oriented CB+ trends prevail. These trends reflect successive re-deposition of delta front sands, with progressive mud winnowing, driven by the strong south-westerly bottom currents observed in the bay during winter storms. Although GSTA did not show any apparent trend field in the nearshore zone, gradual fining of sand fractions to the southwest, along with the chronological transition of the coastline after the construction of a large port (trap of drifted sands on the downdriftside of the port and regression of coastline on the updriftside of the port), suggest a dominant longshore sediment transport updriftward on the updrift-side of the delta. Because the growth of deflected deltas depends on dominant sediment accretion on the updrift-side, these results can be rationalised in the case of internally sourced deflected deltas. Uncertainties remain regarding the net alongshore sediment transport of the entire Ishikari coast; however, the deflected planform is controlled by deflected mouth bars and river mouth jets due to the waves approaching the river mouth at slightly oblique angle in winter, and is likely independent on the direction of dominant sediment transport.

Architecture of a tide-influenced, wave dominated shallow-marine deposit from a Paleoproterozoic rift setting: Example from the Badalgarh Formation, Bayana basin, Rajasthan, northwest India

A ~125 m thick shallowing-upward arenaceous succession from the Badalgarh Formation, Bayana basin, India provided the opportunity to document shelf to foreshore transition from a paleoproterozoic rift set-up. Process-based facies analysis allowed identification of 12 different shallow-marine facies types, grouped under four different facies associations namely (i) lower offshore or open shelf, (ii) upper offshore to distal lower shoreface, (iii) lower to middle shoreface and (iv) upper shoreface to foreshore. From unequivocal dominance of wave- and storm-generated features and fortuitous documentation of tide-generated structures in upper offshore, lower and middle shoreface settings, we infer a tide-influenced, wave-dominated coast at the Badalgarh Sea. From measurement of different vector attributes through the studied succession, we infer (i) near east–west orientation for the Badalgarh shoreline, (ii) storm deposits as products of shore-perpendicular return flow, and (iii) tidal peak flow at a high angle with the shoreline and confined in the upper offshore, lower and middle shoreface settings. A gradational transition from offshore to lower shoreface and, in turn, to middle and upper shoreface suggests accretionary character for the Badalgarh shoreface in a high-gradient rift setting. Overlying deep water (distal offshore) argillaceous marine strata, the arenaceous shallowing-upward Badalgarh succession is interpreted as a product of highstand systems tract (HST) constituted of stacked tens- to hundreds of meter-thick shallowing-upward depositional cycles. Since the abrupt shift in facies type (shallow to deep water) across the upper boundaries of depositional cycles is not unambiguous, we intend to assign these cycles as genetic stratigraphic cycles or T-R cycles over ‘parasequence’.

Hutchison Medallist 1. Wave-Dominated to Tide-Dominated Coastal Systems: A Unifying Model for Tidal Shorefaces and Refinement of the Coastal- Environments Classification Scheme

Coastal depositional systems are normally classified based on the relative input of wave, tide, and river processes. While wave- through to river-dominated environments are well characterized, environments along the wave-to-tide continuum are relatively poorly understood and this limits the reliability and utility of coastal classification schemes. Two tidal shoreface models, open-coast tidal flats (OCTF) and tidally modulated shorefaces (TMS), have been introduced for mixed wave-tide coastal settings. Following nearly two decades of research on tidal shorefaces, a number of significant insights have been derived, and these data are used here to develop a unified model for such systems. First, OCTFs are components of larger depositional environments, and in multiple published examples, OCTFs overlie offshore to lower shoreface successions that are similar to TMS. Consequently, we combine OCTFs and TMSs into a single tidal shoreface model where TMS (as originally described) and TMS-OCTF successions are considered as variants along the wave-tide continuum. Second, tidal shoreface successions are preferentially preserved in low- to moderate-wave energy environments and in progradational to aggradational systems. It is probably difficult to distinguish tidal shorefaces from their storm-dominated counterparts. Third, tidal shorefaces, including both TMSs and OCTFs, should exhibit tidally modulated storm deposits, reflecting variation in storm-wave energy at the sea floor resulting from the rising and falling tide. They may also exhibit interbedding of tidally generated structures (e.g. double mud drapes or bidirectional current ripples), deposited under fairweather conditions, and storm deposits (e.g. hummocky cross-stratification) through the lower shoreface and possibly into the upper shoreface.The development of the tidal shoreface model sheds light on the limitations of the presently accepted wave-tide-river classification scheme of coastal environments and a revised scheme is presented. In particular, tidal flats are components of larger depositional systems and can be identified in the rock record only in settings where intertidal and supratidal deposits are preserved; consequently, they should not represent the tide-dominated end-member of coastal systems. Instead, we suggest that tide-dominated embayments should occupy this apex. Tide-dominated embayments exhibit limited wave and river influence and include a wide range of geomorphological features typically associated with tidal processes, including tidal channels, bars and flats.

A rules-based shoreface translation and sediment budgeting tool for estimating coastal change: ShoreTrans

Predicting change to shorelines globally presents an increasing challenge as sea level rise (SLR) accelerates. Many shoreline prediction models use the simplistic ‘Bruun rule’ for dealing with SLR profile translation, in-part due to alternative approaches being too complex and time-consuming to implement. To address this, we introduce ShoreTrans: a simple, rules-based, user-input driven, shoreface translation and sediment budgeting model, that applies the surveyed 2D-profile (not a parameterization), for estimating change to realistic coastlines, resulting from SLR and variations in sediment supply, while accounting for armouring, hard-rock cliffs and outcropping rocks. The tool can be applied to sand, gravel, rock and engineered coasts at a temporal scale of 10–100 years, accounting for shoreline trends as well as variability. The method accounts for: (1) dune encroachment/accretion; (2) barrier rollback; (3) non-erodible layers; (4) seawalls; (5) lower shoreface transport; (6) alongshore rotation; and (7) other sources and sinks. Uncertainty is accounted for using a probabilistic distribution for inputs and Monte Carlo simulations. We provide a first-pass assessment of two macrotidal UK embayments: Perranporth (sandy, dissipative, cross-shore dominant transport) and Start Bay (gravel, reflective, bi-directional alongshore dominant), then use idealised profiles to investigate the relative importance of forcing controls on shoreline recession and beach width. For the dissipative sandy site, the primary modes of coastal change are predicted to be short-term storm erosion and SLR translation while long-term trends may be important but are highly uncertain. For the reflective gravel site, the primary mode is multi-decadal longshore sediment flux, while short-term alongshore rotation and SLR translation are secondary. Relative to the ShoreTrans approach, the Bruun rule under-predicts shoreline recession in front of cliffs, seawalls and for low barriers that rollback, and over-predicts where large erodible dunes are present. ShoreTrans directly addresses change in beach width, with beaches in front of seawalls and cliffs predicted to shrink, such that narrow beaches (<50 m width) may disappear under 1-m SLR. As a standalone tool, ShoreTrans is transferable to many coast types and will provide coastal practitioners with a simple first-pass estimate of how the 2D appearance of a complex profile may change under SLR. A future benefit will be to combine this approach with existing hybrid modelling techniques to augment SLR translation predictions.

Lithological Parameters Controlling Rock Strength and Elastic Properties of Peritidal and Deep Marine Carbonate Mudrocks, Lower to Upper Jurassic Succession, Central Saudi Arabia

The study integrated lithofacies analysis and measurement of total organic carbon "TOC," porosity, and mechanical properties to evaluate the main factors controlling rock strength and elastic properties of three carbonate mudrocks units within the Jurassic succession of Central Saudi Arabia. Textural and microstructural analyses revealed that the former two units (Hanifa Formation Hawtah Member and Tuwaiq Formation) have five lithofacies interpreted as a lower shoreface intra-shelf basin deposition, respectively. Two mudrock lithofacies within the Upper Marrat Formation were recognized, both deposited under peritidal low ramp setting. Weak to moderate correlations between mechanical properties and porosity in all studied formations were observed; coefficient of determination R2 values range between 0. 1 and 0.7. Tensile strength has the strongest correlation with porosity and mineral composition. Hard phase mineral (quartz, feldspar, and pyrite) abundance has a more robust correlation with elastic moduli compared to the other minerals. Relatively higher R2 values were observed for the correlations between rock strength and clay + TOC content in Tuwaiq and Hanifa compared with Marrat mudrocks. Marrat and Tuwaiq mudrocks lithofacies have a stronger correlation between particle size and unconfined compressive strength, whereas particle size is weakly correlated with elastic moduli. Sedimentary layering and associated anisotropy significantly control these correlations. Deep lower shoreface deposits of Hanifa mudrock are mechanically stiffer than intra-shelf basin outer ramp deposits of Tuwaiq mudrock lithofacies. Peritidal Upper Marrat mudrock lithofacies have slightly higher stiffness than Tuwaiq mudrock and lower stiffness than Hanifa mudrock. The results are useful to predict the rock brittleness of these Jurassic intervals and their worldwide equivalent.

Transition from alluvial to wave-tide-dominated Meso-Neoarchean shelf sedimentation in the Mankarchua Quartzite, Singhbhum craton, eastern India

The Mankarchua Quartzite is a 300 m thick arenite-dominated succession developed on the southwestern margin of the Singhbhum craton, eastern India. Detrital zircon dates available from the succession suggest the age of the youngest population at 2.9 Ga. The arenite dominant succession with very low degree of deformation or metamorphic overprint preserves the depositional primary sedimentary structures and petrography for reconstruction of depositional setting and tectonic setting with considerable clarity. We classified the Mankarchua Quartzite into three members, namely, in the ascending order, the Rajabasa Member, the Timi Member and the Gurusanga Member. Facies analysis on the succession identifies eleven sedimentary facies that can be related to basin margin alluvial fan, wave-/tide-dominated lower shoreface to shelf transitional environments. The entire succession represents a lower order transgressive sequence presumably controlled by tectono-eustatic base level rise and drowning of a continental shelf. Three members can be related to higher order cycles that are likely to have resulted from local scale basin margin tectonics. Paleocurrent patterns corroborate to the alluvial fan/braided stream and wave-/tide-dominated depositional settings. The succession records transition in a narrow interval from coarse-grained conglomerate-pebbly sandstone to sandstone-siltstone-mudstone dominated facies associations in a Meso-Neoarchean drowning shelf.

Zoophycos and related trace fossils from the Chefar El Ahmar Formation, Upper Emsian-Frasnian Ia-Ib (Ougarta, SW Algeria)

The Upper Emsian to Frasnian Ia-Ib strata of the Marhouma area (or “km 30” outcrop), exposed in the Ougarta Range (SW Algeria) belong to the Chefar El Ahmar Formation. On the basis of distinct lithological and palaeontological features, this formation is subdivided into three members (Lower Marly Limestones Member, Middle Marly Limestones Member, and Upper Marly Limestones Member). The studied beds show low to moderate diversity of trace fossil assemblage which contains thirteen ichnotaxa: Chondrites intricatus, Chondrites isp., Chondrites cf. targionii, Circulichnis cf. montanus, Cochlichnus isp., Neonereites biserialis, Neonereites multiserialis, Nereites isp., Palaeophycus isp., Planolites isp., Thalassinoides isp., Zoophycos aff. cauda-galli, and Zoophycos isp. A. The two latter ichnotaxa are the most common trace fossils in the assemblage and occur at three different levels showing different bioturbation intensities. The first Zoophycos-bearing level (Zl 1) is characterised by an overall high bioturbation intensity reflecting a very high oxygenation rate and nutrient supply, allowing the development of large and dense Zoophycos specimens. The second Zoophycos-bearing level (Zl 2) has a considerable reduction of bioturbation intensity as compared to the previous level, with an abundance of Chondrites, which is probably due to radical palaeoecological changes that suggests dysoxic and stressful conditions. The third Zoophycos-bearing level (Zl 3) is characterised by an overall moderate bioturbation intensity. The distribution of trace fossils was influenced by lithology, sedimentation rate, energy level (storm events), bottom oxygenation, and nutrient supply. The lithofacies and trace fossils of the Chefar El Ahmar Formation both indicate a depositional environment fluctuating from the lower shoreface to lower offshore zone.

Tafofácies e Correlação Estratigráfica de Afloramentos Devonianos na Região Nordeste do Estado do Paraná, Brasil

The northeastern region of the state of Paraná, Brazil, is still little known in its paleontological and stratigraphic aspects. This work focused on Devonian outcrops located in Arapoti and Piraí do Sul and aimed at the recognition of sedimentary facies and the definition of taphofacies, with the intention of paleoenvironmental interpretation and stratigraphic correlation. Three different facies were identified, representing shoreface to offshore environments, and also three taphofacies were defined: T1 characterizes the most proximal and destructive environments, T2 represents lower shoreface environments and T3, originated offshore. The base of the section is correlated to the early Devonian, Ponta Grossa Formation, Siluro-Devonian Sequence (Neopraguian-Eoemsian) due to the visible contact with sandstones of the Furnas Formation, and the top, due to the presence of microfossils, is positioned in the São Domingos Formation, Devonian Sequence I (Neoemsian-Eoeifelian).

MORPHOLOGICAL HYSTERESIS OF ARTIFICIAL BEACH UNDER LARGE WAVE CONDITION: AN EXPERIMENTAL INVESTIGATION

Submerged Artificial sandBars (SAB) are usually implemented on the lower shoreface to protect berms or dunes during storm surges. The lee-effect of SAB is due to its ability in triggering large wave breaking, so that sediment concentration in water column and sediment transport capacity will decrease in the covered areas. Previous studies analyzed the lee-effect and topography evolution of SAB, however the morphological coupling of SAB and natural profiles is seldom referred. In this study, the morphological coupling between SAB located on the lower shoreface and the berm in upper beach is investigated in a well-controlled physical experiment.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/KsOK30StZZQ

Holocene progradation and retrogradation of the Central Texas Coast regulated by alongshore and cross‐shore sediment flux variability

AbstractFifteen transects of sediment cores located off the central Texas coast between Matagorda Peninsula and North Padre Island were investigated to examine the offshore record of Holocene evolution of the central Texas coast. The transects extend from near the modern shoreline to beyond the toe of the shoreface. Lithology, grain size and fossil content were used to identify upper shoreface, lower shoreface, ebb‐tidal delta and marine mud lithofacies. Interpretations of these core transects show a general stratigraphic pattern across the study area that indicates three major episodes of shoreface displacement. First, there was an episode of shoreface progradation that extended up to 5 km seaward. Second, an episode of landward shoreline displacement is indicated by 3–4 km of marine mud onlap. Third, the marine muds are overlain by shoreface sands, which indicates another episode of shoreface progradation of up to 5 km seaward. Radiocarbon ages constrain the onset of the first episode of progradation to ca 6.5 ka, ending at ca 5.0 ka when the rate of sea‐level rise slowed from an average rate of 1.6–0.5 mm/yr. Results from sediment budget calculations and sediment transport modelling based on reasonable estimates of an ancient shoreline shape and wave climate indicate that the first progradation was a result of sand supplied from erosion of the offshore Colorado and Rio Grande deltas. The transgressive phase occurred between ca 4.9 ka and ca 1.6 ka and coincided with a major expansion of the Texas Mud Blanket, which resulted in burial of offshore sand sources and the shoreface being inundated with mud. The second, more recent episode of shoreface progradation began ca 500 years ago with a maximum rate of ca 6 m/yr. This most recent change signals a healing phase of coastal evolution from the late Holocene transgressive event. Currently, the shoreline along the central Texas coast is retreating landward at an average rate of 0.30 m/yr, indicating that the second progradation event has ended.