Foreshore Deposits Research Articles

Tectonic control on the palaeogeographic evolution of thrust‐top basins at the active margin of the Guadalquivir Basin (central Betic Cordillera, S Spain)

AbstractThe Guadalquivir Basin is the foreland basin of the Betic Cordillera (S Spain). Closest to the orogen, several thrust‐top basins evolved during the Late Miocene in the central part of the cordillera. Here, we study the Upper Miocene deposits in five of these satellite basins: Montefrío, Iznájar‐Cuevas de San Marcos, Antequera, Bobadilla Estación and Teba, in order to (1) update the stratigraphic framework, (2) infer a depositional model, (3) establish the relationship between sedimentary record and tectonic context and (4) reconstruct the palaeogeography of the area during the Late Miocene. Upper Miocene sediments mostly consist of mixed carbonate‐terrigenous deposits. Facies characterization allows inferring a sedimentary model corresponding to a ramp with foreshore deposits changing to a shoal belt offshore in the inner ramp. Swaley and hummocky cross‐stratified deposits formed in the transition to the middle ramp, and plane parallel carbonate beds in the distal middle‐outer ramp. Factory facies, dominated by rhodoliths and bryozoans, also occur in the middle‐outer ramp environments. Silts and marls formed in the deepest outer ramp and basin settings respectively. Breccias accumulated at the toe of palaeocliffs and conglomerates and massive coarse sands were deposited in fluvio‐deltaic systems. Conglomerates and sands were also reworked as gravity flows and redeposited offshore. Local facies include rudstones‐grainstones displaying large‐scale trough‐cross bedding formed in a strait in Montefrío, and marls with chalky carbonates deposited in a shallow marine, sheltered lagoon with hydromorphic soils in Bobadilla Estación. The study basins evolved in an N‐S compressive tectonic context responsible of the emersion of the main Betic reliefs. Concomitantly, E‐W and ESE‐WNW extension originated the main depocentres. The influence of the tectonic activity on the sedimentary infills is indicated by the presence of synsedimentary deformations and several diachronic unconformities, which are younger westward. Tectonism, in turn, also controlled the palaeogeographic evolution during the late Tortonian‐early Messinian interval.

Late holocene progradation in a mixed siliciclastic-carbonate beach ridges system, Northeast Brazil

A morpho-sedimentary analysis based on grain size, texture, composition, luminescence ages, and morphologic pattern was performed in a beach ridge system located on the Brazilian semiarid coast to understand the siliciclastic and bioclastic mixtures during a progradation of strandplain. Moreover, the rhodolith beds were adopted as a new sea-level proxy to analyze the coastline displacement trajectory of the mixed siliciclastic-carbonate sedimentary environment. The beach ridges system shows a succession of ridges and swales interrupted in the central part by a lagoon plain, the western sector exhibits the crest relief related to the ancient foredune on top and underlying foreshore deposits, and the eastern sector shows a great presence of transgressive dunes overlying beach ridges. Foredune/aeolian facies and the foreshore facies (with rhodolith beds associated) show siliciclastic and bioclastic mixture related to the late Holocene coastal progradation with a progressive increase in carbonate influence, mainly calcareous algae, foraminifera, and molluscs. Moreover, comparing the modern counterpart of the older beach ridges, finer and better-sorted sediments were found in the ancient deposits than in the modern ones. Thus, the progradation was marked by an eminently dissipative beach system. This coeval sedimentation is controlled by key local settings, such as the semi-arid climate, the absence of local fluvial input, the shallow shelf, and the carbonate factory for bioclastic supply. The presence of rhodolith beds in the foreshore facies with an elevation lowering trend towards the modern coastline reinforces the hypothesis that the mixed progradational pattern was accompanied by a small fall in sea level, which corroborates with late Holocene regional curves and provides pioneering preliminary contributions for the studied area.

Deposition of sandstone (early Cambrian) above the Great Unconformity in the Sino-Korean Block, Gondwana: Control of antecedent topography

The global transition between the Precambrian and Phanerozoic eons in concert with rise in eustatic sea-level caused an important change in paleoenvironments, represented by sedimentary records above the Great Unconformity. In the Sino-Korean Block, Gondwana, the unconformity has been recognized by a boundary between various basement rocks and the overlying distinctive suite of sandstone (including conglomerate, conglomeratic sandstone, and mudstone) of the early Cambrian age. A plate tectonic reconstruction of the Cambrian-Ordovician succession in the northeast Asian continent reveals that the sandstone deposited largely in the eastern part of the platform (North China Platform), including the Taebaeksan and Pyeongnam basins. In the western part of the platform, the basal sandstone is correlated to basal carbonate rocks of middle Cambrian age, forming a time-transgressive or diachronous unconformity. The disparity in sedimentary facies of the basal deposits overlying the Great Unconformity was primarily due to antecedent topography of the bounding continent: in the eastern platform, the drainage area comprised high-relief Precambrian massifs, whereas in the western part, it comprised low-relief massifs. During the initial stage of sea-level rise, the eastern part of the platform formed progressively open shoreface and foreshore environments with localized embayments in which relatively coarse-grained gravelly sandstone deposited in fan-delta and tide-dominated environments. In the western platform, however, the supply of siliciclastic sediments was limited and the sandstone formed a relatively narrow linear belt of delta and distributary mouth bars and foreshore deposits. In the rest of the platform farther west, accommodation created by subsequent sea-level rise was filled with carbonate sediments. This study demonstrates that antecedent topography of the unsubmerged drainage area played a major role for the deposition of sandstone in the initial transgression stage, forming the Great Unconformity.

Possible Pleistocene Pinniped Ichnofossils on South Africa's Cape South Coast

Helm, C.W.; Carr, A.S.; Cawthra, H.C.; De Vynck, J.C.; Dixon, M.; Stear, W.; Stuart, C.; Stuart, M., and Venter, J.A., 2022. Possible Pleistocene pinniped ichnofossils on South Africa's Cape south coast. Journal of Coastal Research, 38(4), 735–749. Coconut Creek (Florida), ISSN 0749-0208. Exposed surfaces of cemented foreshore deposits and aeolianites on the Cape south coast of South Africa have been demonstrated to contain numerous Pleistocene vertebrate tracksites. Two ichnosites have recently been identified that appear to demonstrate traces made by seals. These would be the first seal trace fossils thus far described in the global fossil record. The sites are situated 560 m apart in the Goukamma Nature Reserve. One site exhibits apparent flipper traces and a furrow, and the other site exhibits impressions consistent with moulds of juvenile seals. In conjunction with new luminescence dating of the associated sediments, these findings suggest a seal presence on Cape south coast beaches ∼75,000 years ago in the mild glacial period of Marine Isotope Stage 5a.

Terrace Morpho-Sedimentary Sequences on the Sibari Plain (Calabria, Southern Italy): Implication for Sea Level and Tectonic Controls

The Sibari Plain (northeastern Calabria) shows a well-developed stair of late Quaternary marine/coastal terraces resulting from the interaction between sea level fluctuations and tectonic uplift. This paper (i) provides a stratigraphic description of terraced deposits between the Raganello and Coscile rivers, (ii) assesses the relative controls of eustacy and uplift on the staircase formation, and (iii) unravels the Quaternary morphosedimentary evolution of the study area. A geomorphological approach was coupled with stratigraphic field surveys. Photo interpretation, topographic map analyses, and field surveys allowed us to map ten orders of terraces forming telescopically incised valley-fills. Based on the uppermost position of foreshore deposits on inner margins and an average uplift rate of ~1 mm/y, inferred from the Marine Isotope Stage (MIS) 5.5, terraces were correlated with highstands. Sedimentological and stratigraphic analyses allowed us to recognize four assemblages of genetically associated sedimentary facies related to superimposed and juxtaposed coastal and alluvial systems, showing a seaward-stepping architecture. Based on stratal geometry and facies association, we argue that alluvial/fluvial sediments and coastal depositional systems formed contemporaneously along the same terrace. Terrace arrangement resulted from repeated cycles of valley incision (sea level fall) and aggradational to progradational stacking pattern (sea level rise and highstands) in a framework of sustained uplift.

Morphology of Pleistocene elephant tracks on South Africa's Cape south coast and probable elephant trunk-drag impressions

AbstractAeolianites and cemented foreshore deposits on South Africa's Cape south coast have the capacity to record and preserve events that transpired on them when they were composed of unconsolidated sand. Thirty-five Pleistocene elephant tracksites have been identified along this coastline. This abundance of sites along what was the margin of the vast Palaeo-Agulhas Plain allows for an appreciation of the forms that elephant tracks and traces can take in the context of the global proboscidean track record. They point to a significant regional elephant presence from Marine Isotope Stage (MIS) 11 (~400 ka) through MIS 5 (~130–80 ka) to MIS 3 (~35 ka) and also indicate repeated use of certain dune areas. They buttress Holocene and historical evidence that elephants made use of open areas in the region, and that the remaining “Knysna elephants” retreated into dense afrotemperate forest for protection in recent centuries. Analogies can be drawn between Pleistocene elephant tracks and Mesozoic dinosaur tracks, and some of the Cape south coast elephant tracks are among the largest Cenozoic (and hence, Quaternary) tracks ever to be described. A newly identified tracksite in this area may provide the first reported evidence of elephant trunk-drag impressions.

Pleistocene golden mole and sand-swimming trace fossils from the Cape coast of South Africa

AbstractMore than 250 Pleistocene vertebrate trace fossil sites have been identified on the Cape south coast of South Africa in aeolianites and cemented foreshore deposits. These discoveries, representing the epifaunal tracks of animals that moved over these sand substrates, complement traditional body fossil studies, and contribute to palaeo-environmental reconstruction. Not described in detail until now, but also important faunal components, are the infaunal traces of animals that moved within these sandy substrates. Six golden mole burrow trace sites (Family Chrysochloridae) have been identified on the Cape south coast. In addition, three sites, including one on the Cape southeast coast, have been identified that show evidence of sand-swimming, probably by a golden mole with a means of locomotion similar to that of the extantEremitalpagenus. Such traces have not been described in detail in the global ichnology record, and merit the erection of a new ichnogenusNatatorichnus, with two ichnospecies,N. subarenosaichnosp. nov andN. sulcatusichnosp. nov. Care is required in the identification of such traces, and the orientation of the trace fossil surface needs to be determined, to avoid confusion with hatchling turtle tracks. Substantial regional Pleistocene dune environments are inferred from these sand-swimming traces.

Integrated reservoir characterization of the Paleozoic and Mesozoic sandstones of the El Ouar field, Algeria

This study presents the interpretation of depositional environment and petrophysical properties of Mesozoic and Paleozoic reservoirs from the south-eastern Berkine Basin, Algeria by integrating core analyses and geophysical logs. Sedimentary structures and ichnofossils identified from 100 m of recovered cores have been interpreted to characterize the depositional settings of the studied reservoirs. During the mid-late Triassic, fluvial to marginal marine processes deposited the TAGS and TAGI reservoirs, while the Palaeozoic megasequences are characterized by shallow marine reservoirs (tidal bars and foreshore deposits) interbedded with thin marine shales. Porosity and water saturation have been estimated from geophysical logs and calibrated with core-based laboratory measurements. An empirical relationship between core porosity and permeability has been established for the El Ouar area and the same has been employed to generate a continuous and confident permeability profile against the target reservoir formations. Petrophysical characterization indicates a higher porosity and permeability in Triassic and Carboniferous sandstones than the Devonian F6 members. Triassic TAGS and TAGI sandstones possess the highest reservoir qualities in the El Ouar field. The Thorium and Potassium content available from spectral gamma-ray data have been utilized to identify the clay types associated with various sandstone reservoirs (Illite in Triassic sandstone, Kaolinite in Carboniferous units, mixed clay and Th bearing heavy mineral dominance in Devonian units). The study will be helpful for understanding of hydrocarbon resource potential and subsequent production planning in the study area.

Depositional architecture of a wave-dominated clastic shoreline (Pilmatué Member, Argentina): Linking dynamics and stratigraphic record of bar-trough systems

Bar-trough morphologies are a dominant feature of modern wave-dominated clastic shorelines. Despite these barred configurations being widely described from modern systems there is still some uncertainties associated with their interpretation in the ancient record. There is a lack of detailed outcrop-based studies describing the facies distribution and architecture within bar trough systems which causes a disparity between observations of modern processes and the subsequent preserved rock record.This work presents a detailed characterization and interpretation of the sedimentary record of a bar-trough setting. This was achieved through the analysis of nearshore (i.e. upper shoreface and foreshore) deposits within a parasequence in the Lower Cretaceous, Pilmatué Member of the Agrio Formation (Neuquén Basin, Argentina). A high-resolution facies and architectural analysis was developed, combining detailed sedimentary logs with the mapping of bounding and internal surfaces within the nearshore deposits. The facies analysis suggests that trough and planar cross-bedded facies are remnants of dunes in the upper shoreface due to a strong influence of longshore currents, while planar laminated facies would be the result of swash processes in the foreshore. Additionally, the presence of a well-defined surf diastem, the persistent low-angle obliquity of palaeocurrents and the preservation of concave-upward stratigraphic surfaces led to the interpretation of those deposits as representing the production of a bar-trough configuration with longshore currents distributing large amounts of sediment along the shore. This analysis allowed us to reconstruct the dominant processes for sediment transport and deposition within these barred nearshore settings and to identify different key architectural surfaces for the upper-shoreface and foreshore deposits. The architectural analysis of such surfaces led to define four different orders of hierarchy, which respond to depositional and erosional processes operating at different scales. The comparison between different resulting architectures of wave-dominated barred shoreline offers the possibility to improve in the palaeoenvironmental reconstructions for ancient or recent successions. The proposed model for bar-trough clastic shoreline successions relates an absence of bar-related deposits to major storms and shoreline erosional processes. This conceptual model offers a new interpretation for explaining the mid-scale evolution of bar-trough settings and the relationship between the modern and ancient record.

Pleistocene large reptile tracks and probable swim traces on South Africa’s Cape south coast

The Cape south coast of South Africa contains a wealth of Pleistocene vertebrate trace fossil sites in aeolianites and cemented foreshore deposits. Published studies have described mammal and avian tracksites identified along this coastline. We report here on a number of Pleistocene palaeosurfaces within the Garden Route National Park that exhibit tracks of large reptiles, including probable swim traces. The tracks were probably made by more than one species, and may include a crocodylian. There are no extant reptiles in this coastal region capable of making such tracks and traces, which probably represent an indication of a previously more extensive range for the Nile crocodile and a monitor lizard. These findings demonstrate the potential for ichnology to complement the traditional body fossil record. Two Middle Stone Age stone artifacts were found embedded in one palaeosurface containing multiple reptile trackways. These discoveries have implications for the understanding of Pleistocene palaeoenvironment and palaeoclimate – in an area which is important in the study of modern human origins.
 Significance:
 
 Large reptile Pleistocene fossil tracksites have recently been discovered on the Cape south coast of South Africa where there are no previous such records, and no reptiles of this size are currently found in the region.
 These sites include the first reported probable reptile swim traces in Africa and one tracksite also contained two Middle Stone Age artifacts.
 These discoveries have implications for Pleistocene environments and climate on the Cape south coast.

Elephant Tracks: A Biogenic Cause of Potholes in Pleistocene South African Coastal Rocks

Helm, C.W.; Cawthra, H.C.; De Vynck, J.C.; Dixon, M., and Stear, W., 2021. Elephant tracks: A biogenic cause of potholes in Pleistocene South African coastal rocks. Journal of Coastal Research, 37(1), 59–74. Coconut Creek (Florida), ISSN 0749-0208.The Cape south coast of South Africa contains extensive outcrops of Pleistocene aeolianite and cemented foreshore deposits. More than 250 vertebrate tracksites have been identified in these deposits, including 35 elephant tracksites. In places, where large palaeosurfaces are occasionally exposed, numerous potholes are evident on the remains of what is most likely a palaeo-coastline. Features suggestive of elephant tracks are apparent on such surfaces and in overlying layers. In order to develop, potholes require a disturbance or depression in the surface to act as a “pothole-precursor” on which erosive forces can act. While elephant tracks or similar biogenic origins for potholes have not previously been described, such an explanation appears plausible for at least some pothole features in areas known to have harboured elephants or other large vertebrate trackmakers when these surfaces were composed of unconsolidated sand. Four sites on the Cape south coast are examined and described. Evidence for use of beaches as travel corridors for elephants is described, and candidate Pleistocene trackmaker species are considered. The age of these palaeo-surfaces is considered to range from Marine Isotope Stage 11 to Marine Isotope Stage 5. It is concluded that depressions formed by elephant tracks should be considered as a precursor for the formation of potholes on suitable Pleistocene surfaces in littoral zones.

Rappel historique et aspects stratigraphiques et taphonomiques du gisement pléistocène supérieur d'Arenal de son Servera (Majorque, îles Baléares)

The upper Pleistocene deposit of Arenal de son Servera is reviewed using data from earlier works and new considerations based on its stratigraphy and taphonomical aspects of the fossils. In the present study, five different kinds of facies are identified: [1] palaeosols with pebbles from the Miocene basement, [2] aeolianites, [3] foreshore deposits with thermophilous molluscan fossil fauna, [4] palaeosols resulting from the pedogenesis of the beach units, and [5] bioclastic channelled deposits eroding the underlaying units. The detailed taphonomical analysis revealed that the fossils enclosed in these rocks remained on the sea bottom for a significant amount of time, but they were not bioeroded, perhaps because a submerged sand bar repeatedly buried and exhumed them. In addition, the fact that Persististrombus latus shells are in their position of maximum stability allows to infer that they were washed up on the shore during moderately energetic events, possibly comparable to present-day ordinary storms. These two last points could be of interest to the field of coastal management, as they provide insight on the scope of physical changes these systems could undergo in the present warming of the Mediterranean.

Patterns in the sand: A pleistocene hominin signature along the South African coastline?

The Cape south coast of South Africa boasts one of the richest Middle Stone Age (MSA) archaeological records in the world. Here coastal caves and rock shelters contain well-documented archives of early humans, including early evidence of human adornment and jewelry, rock engraving and rock paSabstextinting. It has been suggested that palaeoenvironmental conditions in the area were critical to the survival of the human species. Humans travelled over dune surfaces, interdune areas and beaches during this period. These are now preserved as palaeosurfaces in aeolianites and cemented foreshore deposits, through which the ancient landscapes can be interpreted. Such contemporary sand surfaces may have formed potential canvases on which foraging behaviour or the creation of patterns or symbols could have been recorded. We question whether MSA humans left evidence of their presence other than their footprints when moving over these surfaces, and if so, whether such evidence can be discerned and interpreted today, as a hominin signature preserved in exposures of aeolianite and cemented foreshore deposits. We discuss other agents that could have caused similar patterns, and we consider the merits of eight sites that we have identified on the Cape south coast. In combination they encapsulate the complexity, challenges and potential of such study. We conclude that evidence at some of these sites suggests an anthropic origin, potentially constituting a previously undocumented form of MSA hominin expression and activity.

Pleistocene vertebrate tracksites on the Cape south coast of South Africa and their potential palaeoecological implications

Body fossil remains usually provide the main palaeontological resource for palaeoecological studies. Ichnology has the capacity to independently complement such data. Fossil tracksites provide a direct record of animals whose tracks have been preserved, and with regard to the Palaeo-Agulhas Plain they have direct relevance in considering palaeoecology. While biases may be present in ichnological data, they are different from the biases inherent in traditional body fossil studies. A ground survey along a 350 km portion of the Cape south coast, between Arniston in the west and Robberg in the east, identified well over a hundred-and-thirty ichnofossil sites in Late Pleistocene coastal aeolianites and lithified foreshore deposits. Some of these tracks were made by extinct species or subspecies. In other cases these tracksites demonstrate spatial range extensions of extant species, when compared with data available from body fossils or historical records. These sites include the largest and best preserved archive of Late Pleistocene hominin tracks thus far described. The tracksites occur on the margin of the Palaeo-Agulhas Plain, which may allow for palaeoenvironmental conclusions to be drawn regarding Late Pleistocene conditions on this extinct landscape. We summarize the most important sites, discuss the limitations and challenges of ichnological studies, and provide perspectives on future work.

Facies Associations of Early Cretaceous Arumit Formation and Early to Late Cretaceous Ungar Formation in Vulmali and Ungar Islands, Tanimbar (Indonesia)

DOI:10.17014/ijog.6.2.185-208Cretaceous sediments are among the important petroleum system elements for hydrocarbon exploration in Tanimbar area. However, little is known about their facies associations and depositional environments. Facies association analyses have been carried out in fourteen surface sections. Early Cretaceous Arumit Formation comprises three facies associations: subtidal, intertidal, and supratidal deposits. A progradational open-coast tidal flat depositional environment suggests the deposition of sediments of the Arumit Formation. The presence of tidal rhythmites, mud drapes, and fluid mud in those sediments are diagnostic features of a tide domination process in deposition of this unit. Early to Late Cretaceous Ungar Formation in the studied area consists of four facies associations: intertidal, marine offshore to lower shoreface, upper shoreface, and foreshore deposits. An open-coast wave dominated depositional environment is proposed for deposition of sediments of the Ungar Formation. Wave dominated environments in the coarsening upward interval is represented by hummocky cross stratification, cross-bedded sand and gravel, planar parallel stratification, and low-angle stratified beds.

An interpretation of wave refraction and its influence on foreshore sediment distribution

To analyze the grain size and depositional environment of the foreshore sediments, a study was undertaken on wave refraction along the wide sandy beaches of central Tamil Nadu coast. The nearshore waves approach the coast at 45° during the northeast (NE) monsoon, at 135° during the southwest (SW) monsoon and at 90° during the non-monsoon or fair-weather period with a predominant wave period of 8 and 10 s. A computer based wave refraction pattern is constructed to evaluate the trajectories of shoreward propagating waves along the coast in different seasons. The convergent wave rays during NE monsoon, leads to high energy wave condition which conveys a continuous erosion at foreshore region while divergent and inept condition of rays during the SW and non-monsoon, leads to moderate and less energy waves that clearly demarcates the rebuilt beach sediments through littoral sediment transport. The role of wave refraction in foreshore deposits was understood by grain size and depositional environment analysis. The presence of fine grains with the mixed population, during the NE monsoon reveals that the high energy wave condition and sediments were derived from beach and river environment. Conversely, the presence of medium grains with uniform population, during SW and non-monsoon attested less turbulence and sediments were derived from prolong propagation of onshore-offshore wave process. These upshots are apparently correlated with the in situ beach condition. On the whole, from this study it is understood that beaches underwent erosion during the NE monsoon and restored its original condition during the SW and non-monsoon seasons that exposed the stability of the beach and nearshore condition.

Mid and Late Holocene evolution of Brateș Lake region (Danube floodplain) based on the multiproxy analysis

This study proposes a local paleo–landscape reconstruction of the Danube floodplain based on a stratigraphic sequence retrieved from Brateș Lake which, by its emplacement near the confluence of Danube – Prut rivers, was fully receptive to changes associated to hydrological, geomorphological or anthropogenic driven events. Due to its intermediate position within the Lower Danube valley Brateș Lake is a proxy for the evolution of Cotul Dunării area (the region of Danube valley turning from S–N to W–E direction) and provide valuable information about the timing of Danube river advancement to the Black Sea after its reconnection to World Ocean. The sediments were analysed to get the history of their deposition by means of accelerator mass spectrometry (AMS) 14C dating, grain–size parameters, organic matter and carbonate content, magnetic susceptibility together with paleo–fauna and pollen content which altogether led to the identification of main stages: i) delta front advance into Danube estuary (before 8000 BP), ii) shoreline foreshore deposits which describe shoreline position (8000–7900 yrs BP), iii) river floodplain development (7900–5300/5000 yrs BP), iv) lake formation (5300/5000 yrs BP – present).

Palaeoecology of Macaronichnus segregatis degiberti: Reconstructing the infaunal lives of the travisiid polychaetes

Macaronichnus segregatis degiberti, a relatively large ichnosubspecies of Macaronichnus segregatis, is an almost straight to gently curved, cylindrical, fossilized burrow, oriented horizontal to oblique to the bedding plane. It is interpreted as a pascichnial trace fossil formed through selective sand feeding and excretion of a free-living polychaete, such as a relatively large travisiid (formerly classified as opheliid or scalibregmatid) polychaete Travisia. While the other ichnosubspecies, i.e., M. s. segregatis, M. s. lineiformins, M. s. meandriformis, and M. s. spiriformis, are commonly 2–5 mm in diameter and occur exclusively in foreshore deposits, M. s. degiberti attains a diameter of up to 15 mm and shows wide environmental distribution, ranging from tidal channels, tidal sand bars, tidal sandridges, tidal flats, upper to lower shorefaces, bioturbated sandy shelves, shelf storm-sheets, to shelf sand ridges. The core of M. s. degiberti, consisting mainly of light mineral-rich sand grains, is composed of alternating lamellae of light mineral-rich and heavy mineral-rich sands, arranged oblique to the bedding plane. On the other hand, the mantle, composed mainly of heavy mineral-rich sands, has a smooth outline, or evenly spaced lobes flanked on both sides. The morphology of the mantle lobes and core lamellae suggests repeated pulses of sediment probing and excreting behaviour of the tracemaker. Two or more burrows of this ichnosubspecies tend to occur adjacently, sometimes intertwining. As Travisia develops directly, lacking any planktic larval stages, aggregations of the burrows can be interpreted to reflect the burrowers' interindividual exploratory behaviour with the aim of copulation. Travisia, also known as a “stink worm”, secretes volatile chemical substances that might act as sex pheromones to attract other individuals for reproduction within the substrate. Therefore, a new category of ethological classification of trace fossils “sequorichnia” (sequor, follow; and ichnia, traces), for exploration of other individuals, is proposed here. This is the first record of interindividual exploratory behaviour of infaunae.

The evolution of Chabahar beach ridge system in SE Iran in response to Holocene relative sea level changes

The Chabahar Strandplain (CHS) stretches along the Chabahar bay at a width of more than 5 km along the northern coast of the Gulf of Oman and SE Iran; an area that has been subjected to tectonic uplift as a part of the Makran accretionary prism. The CHS comprises of beach ridges, inter-ridge swales, sand dunes, tidal channels and fluvial deposits. We present the first documentation of the spatial distribution and the internal architecture of the CHS based on topographic surveys, sediment percussive coring, trenching and ground penetrating radar (GPR) transects. Radiocarbon dating on marine shells from foreshore deposits of 8 representative beach ridges yielded ages between 4800 and 270 cal. years BP at respective distances of 4800 to 670 m from the present shoreline. We interpret the boundary between the foreshore (beach) and the foredune deposits as indicator of past sea levels by analogy to present shore processes. This boundary is readily recognizable in sediment profiles from cores and trenches as well as GPR reflectors. Based on the age model and depositional features, we estimate relative sea level fall of up to 15 m over the past 4800 years. Considering that the eustatic sea level changes for this period are negligible for the Makran coast, this relative sea level fall is related to tectonic uplift across the coastal Makran. The elevation of palaeo-shorelines with similar ages decrease from east to west of the CHS, which suggest that alongshore variations in uplift rates are likely related to different movements of coastal fault blocks.

Sequence architecture and depositional evolution in Lufeng Depression, Pearl River Mouth Basin, South China Sea Part B: The shore deposits of Zhuhai Formation

The Zhuhai Formation in Lufeng Depression is mainly deposited during a depression stage. In this paper, we employ cores, wireline logs, and seismic reflections to reveal sequence architecture and depositional evolution in target intervals. The results indicated that one second‐order sequence and two third‐order sequences were identified and sequence stratigraphic framework was established. The second‐order sequence was developed in response to base‐level falling, while third‐order sequences were mainly formed during base‐level rising. In addition, each third‐order sequence did not change too much in thickness. Then the shore deposits (shoreface and foreshore) were delineated, and the depositional characteristics were described within the framework with the help of related data. The shoreface and foreshore deposits within the sequence stratigraphic framework varied significantly in stacking patterns of wireline logs and cores. Based on comprehensive analysis, it can be concluded that base‐level changes played an important role in controlling sequence architecture. And lacustrine fluctuations derived from accommodation space changes exerted an essential effect on depositional evolution. This study provides significant insights into revealing the sequence architecture and depositional evolution and discussing hydrocarbon potential in the transition stage in the Zhuhai Formation.