Modern Beach Research Articles

A new method for calculating the primary porosity of unconsolidated sands based on packing texture: Application to modern beach sand

Abstract The primary porosity is one of the fundamental parameters for quantitatively predicting reservoir quality and studying diagenetic evolution. Primary porosity is usually estimated by empirical approaches or empirical formula, through using a single parameter, such as sorting or grain size. However, these methods have some disadvantages which lead to obvious errors. Primary porosity can be affected by multiple factors, such as particle size, sorting, grain shape and packing texture, therefor, one empirical formula is not practical for different type of sands. A new mathematical model is proposed in this paper for calculating the primary porosity of unconsolidated sands based on the concept of packing texture. The grain size, grain size distribution curve and packing texture are considered in this mathematical model. This paper tests the practicability of the mathematical model through using 40 modern beach sands sample collected from eastern China and 37 samples from literature. These modern beach sands in the study area can be divided into three types based on the particle size distribution curve. Each type sample is further divided into several units according to the particle size ratio. The mathematical model firstly calculates the primary porosity of two adjacent units by using the binary packing model, and then the primary porosity of the entire sand sample. The error of model-predicted primary porosity ranges between −2% and 2%, and the correlation coefficients are all above 0.9. As a comparison, the errors of empirical formula-predicted results range between −6% and 6%, and the correlation coefficient is 0.63. The newly-proposed mathematical model for the primary porosity based on grain size distribution and packing texture is more reliable compared to the traditional empirical formula.

Heavy minerals distribution and provenance in modern beach sands of Campania, Italy

The Campania region (southern Italy) is an excellent area to determine the effects of multiple source lithology (volcanic+sedimentary), climate, weathering, transport anddepositional environment on heavy minerals enrichments in the sandy beaches of the coastline between Pozzuoli and Bacoli, and at the Volturno river-mouth. The heavy mineral (HM) assemblage should reflect the clastic supply from the potassic to ultrapotassic lavas and pyroclastic rocks of the Campania and of the Roman Magmatic provinces (Phlegrean Fields, Roccamonfina volcano), and from the recycling of sedimentary - both carbonate and siliciclastic - terranes of the Apennine thrust belt. Opaque oxides, pyroxene and amphibole assemblage dominates in the beach placers of the Campania shoreline - from Bacoli to Pozzuoli - as well as in the Volturno river mouth sands to the north. Modern heavy minerals assemblages reflect clastic contribution from magmatic source rocks whereas contributionfrom sedimentary terranes - exposed extensively in the Volturno river drainage - provide no recycled heavy minerals to the river-mouth sand. Thus, heavy minerals linked to a provenance from the Apennine thrust belt source rocks result diluted and/or unrecognizable using the only HM approach with respect to the minerals provenance sourced by the potassic volcanic fields of Latium and Campania. Thediverse detrital heavy minerals have been characterized describing major stages of progressive chemical weathering, from unweathered to corroded to etched morphologies, a process - in this case-history - playing a minor role in reducing HM diversity through dissolution of moderately stable mineral species.

Heavy minerals distribution and provenance in modern beach sands of Campania, Italy

This work focuses on the textural characterization of modern sand supplied from a volcanic island in the Aeolian Archipelago, with particular attention given to the factors that control grain rounding. Twelve beach sands were collected from hightide berms spaced along Lipari’s accessible coastal perimeter. Point-count data were collected using a petrographic microscope with an automated stepper stage. Changes in grain roundness were assessed to evaluate grain resistance to transport(currents and wave abrasion). A numerical value was assigned to very angular (1), angular (2), sub-angular (3), sub-rounded (4), rounded (5) and well-rounded (6) categories. Analyzed particles are monocrystalline grains of plagioclase (Plag) and pyroxene (Py) and volcanic lithic fragments of Lvl (volcanic lithic with lathwork texture), Lvmi (volcanic lithic with microlitic texture), Lvv (volcanic lithic with vitric texture) and Lvf (volcanic lithic with felsitic texture). The most common roundness category among all the grains from the sampled coastal stretches of Lipari island is 3 (sub-angular, 36,1%), immediately followed by 2 (angular, 28,5%), 4 (sub-rounded, 20,0%), 1 (very angular, 10,1%), 5 (rounded, 4,2%) and lower occurrence of 6 (well rounded, 1,1%). We have also determined that some grain types tend to round more quickly in beach environments, such as plagioclase among the monocrystalline grains and Lvmi among the lithic grains population. Lipari’s beach sands are all better rounded on the eastern side which is the more protected part of the island. Alternatively, the sand grains on the east side of the island have alonger residence time on the beach.

Provenance inferred through modern beach sands from the Gulf of Tehuantepec, Mexico

Different parent rocks, climate, and relief control the provenance of beach sands on the coast of Mexico. This is the first paper to address the provenance problem of beach sands in south‐eastern Mexico considering a homogeneous climate and relative similarity in parental rocks but different relief. Two coastal areas are confined in this study: (a) the Western Gulf of Tehuantepec (WGT) and (b) the Eastern Gulf of Tehuantepec (EGT). The WGT beach sands are probably controlled by the denudation of orthogneisses, Eocene–Miocene basaltic–andesites–dacites–rhyolites from the Volcanic Belt of the Sierra Madre del Sur (VBSMS), and granites to diorites from the Coastal Plutonic Belt (CPB). The rocks exposed in the EGT are represented by orthogneisses and tonalite, granodiorite, and gabbro suites from the Palaeozoic–Mesozoic Chiapas Coastal Plutonic Belt (CHCPB). Quaternary andesites and dacites from the Tacaná Volcano are located in the eastern coastal area. The Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration (PIA) values indicate that the less weathered beach sands are in the WGT compared to the EGT coastal area. Plagioclase transport is preserved in a narrow coastal plain that contributes to a lower a weathering rate compared to the EGT sands deposited in a wider coastal plain. Geochemical analyses show that the WGT and EGT beach sands are admixtures of felsic, intermediate, metamorphic, and volcanic sources in their sands composition. Relief seems to play a major role in the composition of beach sand in both coastlines, since parental rocks are mostly similar in composition and climate remains homogeneous along the coast.

Macrobioerosion and Microbioerosion in Marine Molluscan Shells from Holocene and Modern Beaches (39°–40°S, South of Buenos Aires Province, Argentina)

AbstractThe marine sediments of the area of Verde Peninsula – Jabali Island (39°28′S/62°19′W–40°28′S/62°11′W) Holocene in age (3–2 ky), and modern beaches contain a significant amount of bioeroded mollusc shells. Fifteen sites were analyzed, in which 20.11% of the mollusc shells (2168 valves) presented bioerosion traces, in 54 species (30 bivalves and 24 gastropods). Fourteen ichnogenera were reported: Entobia, Maeandropolydora, Iramena, Caulostrepsis, Pennatichnus, Pinaceocladichnus, Trypanites, and Gastrochaenolites (Domichnia), Gnathichnus and Radulichnus (Pascichnia), Finichnus and Centrichnus (Fixichnia), Oichnus (Praedicnia) (macrobioerosion), y Semidendrina (microbioerosion), the latter is first reported in mollusc shells in Argentina. Eleven ichnospecies were identified Finichnus peristroma, Maeandropolydora sulcans, Gnathichnus pentax, Pinaceocladichnus onubensis, Caulostrepsis taeniola, Centrichnus eccentricus, Radulichnus inopinatus, Oichnus simplex, Oichnus paraboloides, Oichnus gradatus, and Gastrochaenolites torpedo (lithic remains). The dominant ichnogenera in the Holocene deposits are Iramena, Entobia and Oichnus. The same ichnogenera are constant with different abundance in the modern beaches, and increasing representation of Pinaceocladichnus and Pennatichnus. The dominant ichnofacies in the Holocene deposits is Trypanites, revealing a benthonic marine community composed of cheilostome bryzoans, clionaid sponges, predator gastropods, regular echinoids, polychaete annelids, bivalves, thallophytas and fungi. Generally, the area was described as a sublittoral, low‐energy, stable environment with high rate of oxygenation, and sandy bottoms, with rocky bottoms at Villalonga locality.

Integrating millennial and interdecadal shoreline changes: Morpho-sedimentary investigation of two prograded barriers in southeastern Australia

Prograded barriers are distinctive coastal landforms preserving the position of past shorelines as low relief, shore-parallel ridges composed of beach sediments and commonly adorned with variable amounts of dune sand. Prograded barriers have been valued as coastal archives which contain palaeoenvironmental information, however integrating the millennial timescale geological history of barriers with observed inter-decadal modern beach processes has proved difficult. Technologies such as airborne LiDAR, ground penetrating radar (GPR) and optically stimulated luminescence dating (OSL) were utilised at Boydtown and Wonboyn, in southeastern Australia, and combined with previously reported radiocarbon dates and offshore seismic and sedimentological data to reconstruct the morpho-sedimentary history of prograded barrier systems. These technologies enabled reconstruction of geological timescale processes integrated with an inter-decadal model of ridge formation explaining the GPR-imaged subsurface character of the barriers. Both the Boydtown and Wonboyn barriers began prograding ~7500–8000years ago when sea level attained at or near present height along this coastline and continued prograding until the present-day with an initially slower rate of shoreline advancement. Sources of sediment for progradation appear to be the inner shelf and shoreface with a large shelf sand body likely contributing to progradation at Wonboyn. The Towamba River seems to have delivered sediment to Twofold Bay during flood events after transitioning to a mature estuarine system sometime after ~4000cal. yr BP. Some of this material appears to have been reworked onto the Boydtown barrier, increasing the rate of progradation in the seaward 50% of the barrier deposited over the past ~1500years. The GPR imaged beachfaces are shown to have similar geometry to beach profiles following recent storm events and a model of ridge formation involving cut and fill of the beachface, and dune building in the backshore, explains the character of the preserved beachface record and the morphology of the ridges. This model is applicable to future management of individual beaches where such beaches are subject to ongoing cut and fill, dune building processes and inherited sediment budget conditions.

A quantitative sedimentary model for the modern lacustrine beach bar (Qinghai Lake, Northwest China)

Lake beach bar sandstone has been regarded as an important oil and gas reservoir in China. However, types and depositional mechanisms of the sandstone have not yet been fully studied. In this study, we analyzed modern beach bars in Qinghai Lake, the largest modern lake in China. The key factors controlling beach bar development in the lake were found to be wave length and height, lakeshore terrain, and material supply. Sedimentary models were established based on modern coastal dynamic theory. Beach bars were divided into breaking and surf bars. Breaking bars develop near the breaking zone where water depth is a function of wave height and length. Maximum breaking bar thickness is calculated from the difference between breaking point depth and breaking wave height. Surf bars develop in the surf zone where surf water depth equals breaking wave height. Maximum surf bar thickness is given by the breaking wave height. Wind waves play an important role in the location and construction of Qinghai Lake beach bars.

The Lake Krasnoe obsidian source in Chukotka (Northeastern Siberia): geological and geochemical frameworks for provenance studies in Beringia

Basic data on the geology and geochemistry of obsidian from the Lake Krasnoe source in Chukotka (Northeastern Siberia) are reported for the first time. The data are based on 2009 fieldwork and analytical studies of igneous rock samples. The lake shore and surrounding parts of the Rarytkin Range were thoroughly examined. Two geochemical types of rhyolitic obsidian were recognized for the first time: (1) metaluminous obsidian related to the fine-grained crystalline rocks and (2) peralkaline obsidian corresponding to ignimbrite ash-flows or lapilli-tuffs composition. Both types are related to the final phase of acidic volcanism in the Western Kamchatkan-Koryak Volcanic Belt. Based on the results obtained, we conclude that accumulation of obsidian pebbles in the lake’s modern beach deposits is related to silicic melts that erupted during the late Eocene-early Oligocene in the form of extrusive domes or pyroclastic flows, which are now either covered by Quaternary sediments or located below the water level. The Lake Krasnoe obsidian was intensively used by the ancient populations of Chukotka as a raw material for making stone tools. It was also occasionally transported to Alaska across the Bering Strait in later prehistory. The distances between source and utilization sites are up to 700–1100 km. Geochemical data for Lake Krasnoe obsidian, based on neutron activation analysis and X-ray fluorescence that are presented here, can now be used for provenance studies in the Northeastern Siberia and adjacent regions of northern North America.

Recent Rhodolith Deposits Stranded on the Windward Shores of Maio (Cape Verde Islands): Historical Resource for the Local Economy

ABSTRACT Johnson, M.E.; Baarli, B.G.; da Silva, C.M.; Cachao, M.; Ramalho, R.S.; Santos, A., and Mayoral, E.J., 2016. Recent rhodolith deposits stranded on the windward shores of Maio (Cape Verde Islands): Historical resource for the local economy. Maio is a volcanic island with an area of 269 km2 in the Cape Verde archipelago off the west coast of Africa. Although considered a leeward island, it absorbs NE trade winds that typically register 5 to 6 on the Beaufort Scale (moderate to fresh breeze). The trade winds produce ocean swells commonly 3.5 m in height that scour the island's north coast but also generate eastern longshore currents. Outcrops with Pleistocene rhodoliths occur on the SE and south shores and include lithified dunes mainly composed of crushed rhodolith debris. In contrast, the modern beaches and Pleistocene dunes on the more sheltered west coast are practically devoid of rhodoliths. Present-day rhodolith banks off the north coast would seem to be precluded by intense wave action. This ...

Petrographic analyses of sand temper/inclusions in ceramics of Kikiniu, Kikori River and modern sand samples from the Gulf Province (Papua New Guinea)

ABSTRACTThe archaeological site of Kikiniu (a.k.a. Kulupuari) in the mid‐reaches of the Kikori River, Gulf Province (Papua New Guinea) contains a rich assemblage of ceramic sherds dating to 1550–1000 calBP. This is a region for which there is no ethnographic and no prior archaeological evidence of ceramic manufacture, but for which during the ethnographic period premade pottery vessels are well known to have been imported en masse from long‐distance seafarers from Yule Island and Port Moresby. Here we present initial petrographic analyses of sand temper/inclusions from 20 excavated sherds from Kikiniu, and 14 samples of modern beach and river sand collected across the area, to determine whether the Kikiniu ceramics could have been locally manufactured, and if not, from where they were imported. Our preliminary results confirm that the majority of the sherds, and possibly all, are from ceramics that were probably imported from manufacturing sites to the south‐east. Given that the Kikiniu region was then a rainforest, sago‐rich region, ceramics probably arrived at Kikiniu as part of the sago trade as far back as c.1550–1000 calBP.

Provenance of volcaniclastic beach sand in a magmatic-arc setting: an example from Lipari island (Aeolian archipelago, Tyrrhenian Sea)

AbstractLipari, an active volcanic island in the Aeolian magmatic arc, is an excellent area to determine the effects of multiple source lithology, climate, weathering, transport and depositional environment on epiclastic sand composition. Volcaniclastic sand samples from 12 modern beaches were petrographically characterized using the Gazzi–Dickinson method, and the proportions of source rocks in combination with topography in associated coastal drainage basins were quantified using GIS. Several types of bedrock in the 12 drainage basins that are the likely prominent sources for sand at each sampled beach were recognized, and divided into two categories of provenance lithotypes: lavas and pyroclastic rocks ranging in composition from basaltic andesitic, to andesitic, to rhyolitic. Volcanic lithic fragments from Lipari beach sand consist of colourless and black glassy volcanic fragments with lathwork, felsitic, vitric and microlitic textures. Moreover, high amounts of detrital less durable minerals, such as pyroxene, olivine and Fe oxides, illustrate how the analysed sands preserve the source rock(s) provenance signals. Applying the concept of Sand Generation Index we see that these lithotypes have different propensities to create detritus, in terms of both grain-size and composition. Clastic contribution from pyroclastic rock outcrops such as pumice is not found in the size ranges studied, suggesting that these pumiceous source rocks probably only produce gravel or very fine sand and silt. This finding has implications for the stratigraphic record because pumice clasts, ranging from medium to fine grain-size, could be underrepresented in older volcaniclastic deposits and overrepresented in other size fractions.

Distinguishing offshore bird hunting from beach scavenging in archaeological contexts: The value of modern beach surveys

Determining whether seabirds recovered from coastal shell middens were obtained via active hunting or scavenging of beached carcasses is a challenge for archaeologists. Traditional methods have included analyzing skeletal part frequencies, abundance, age profiles, and contextual evidence. The assumption has been made, based on limited biological data, that an assemblage of carcasses scavenged from the beach will have more wing elements, and fewer legs and heads. Few studies, however, have embraced modern beaching data to verify this assumption and assess the potential faunal resources available for scavenging. We analyze the skeletal part representation of modern beached birds observed by the Coastal Observation and Seabird Survey Team (COASST), comparing the COASST dataset to two idealized hypotheses used by archaeologists: the human scavenging hypothesis (wings only are recovered, while heads and legs are absent) and the human hunting hypothesis (all body parts are found in equal proportions). Finally, we apply these results to analysis of the bird remains from the Minard site (45-GH-15), a late Holocene coastal site in Grays Harbor, Washington. We find that contemporary beached bird data are closer to replicating the human hunting hypothesis as compared to the human scavenging hypothesis, as >75% of the 19,599 carcasses in the COASST dataset had a combination of head, wings and legs. This result, and the similarity in taxonomic distribution between our contemporary beached bird data and Minard assemblage, suggests that indigenous peoples may have used scavenging as a viable means of resource acquisition in the past. Use of contemporaneous beached bird data may provide zooarchaeology with a statistically defensible baseline of information on the phenology, abundance and condition of bird carcasses.

Prey selection, size, and breakage differences in Turbo undulatus opercula found within Pacific Gull (Larus pacificus) middens compared to Aboriginal middens and natural beach deposits, southeast Australia

Qualitative discrimination criteria are employed commonly to distinguish cultural shell middens from natural shell deposits. Quantitative discrimination criteria remain less developed beyond an assumption that natural shell beds tend to contain a wider range of shell sizes compared to cultural shell middens. This study further tests this assumption and provides the first comparative quantitative analysis of shell sizes from cultural middens, bird middens, and beach shell beds. Size distributions of opercula of the marine gastropod Turbo undulatus within two modern Pacific Gull (Larus pacificus) middens are compared with two Aboriginal middens (early and late Holocene) and two modern beach deposits from southeast Australia. Results reveal statistically significant differences between bird middens and other types of shell deposits, and that opercula size distributions are useful to distinguish Aboriginal middens from bird middens but not from beach deposits. Supplementary qualitative analysis of taphonomic alteration of opercula reveal similar opercula breakage patterns in human and bird middens, and further support previously recognised criteria to distinguished beach deposits (water rolling and bioerosion) and human middens (burning). Although Pacific Gulls are geographically restricted to southern Australia, the known capacity of gulls (Larus spp.) in other coastal contexts around the world to accumulate shell deposits indicates the broader methodological relevance of our study.

Geological records of western Pacific tsunamis in northern Taiwan: AD 1867 and earlier event deposits

Located in the western circum-Pacific seismic zone, Taiwan is an ideal area for recording tsunamis that originate in the tectonically and volcanically active systems of the Ryukyu Arc, Okinawa Trough, and Luzon Arc. However, because of Taiwan's short historical record, there is only credible evidence for one disastrous tsunami, which occurred in northern Taiwan in AD 1867. To better understand the western Pacific tsunamis, an Upper Holocene deposit of a coastal plain inundated by the AD 1867 tsunami was investigated to search for geological evidence of tsunamis.Based on facies characteristics and sediment composition, we identified two sharp-based, decimetre-thick marine quartzose sandy layers that fine upward and landward, intercalated with floodplain marsh sand and mud. The fluvium are rusty red, rich in volcanic clasts and Fe, and comparable to modern riverine sediments of local andesitic provenance. Extending 0.8km inland, the marine quartzose sandy layers are light-coloured and rich in quartz and Si, have high Ca/Ti values, and are comparable to the modern beach–dune sediments of regional siliciclastic provenance.Radiocarbon dating indicates that the marine sandy layers are correlated with the AD 1867 tsunami and an older event at the boundary between the 17th and 18th centuries. Both events were probably associated with reported earthquakes involving normal faulting. In addition, the distribution patterns of the two marine sandy layers are similar, suggesting that the inundation distances, run-ups, and flow heights of the two events are comparable. This indicates that the disastrous tsunamis were frequent in the area between northern Taiwan and the Okinawa Trough of the western circum-Pacific seismic zone.

The approval of modern beach resort in Fukuoka City and the environs

The approval of modern beach resort in Fukuoka City and the environs

Ground penetrating radar examination of thin tsunami beds — A case study from Phra Thong Island, Thailand

Coastal overwash deposits from tsunamis and storms have been identified and characterised from many coastal environments. To date, these investigations have utilised ad-hoc time, energy and cost intensive invasive techniques, such as, pits and trenches or taking core samples. Here, we present the application of high-frequency ground penetrating radar (GPR) to identify and characterise the 2004 Indian Ocean Tsunami (IOT) and palaeotsunami deposits from Phra Thong Island, Thailand. This site is one of the most intensively studied palaeotsunami sites globally and preserves a series of late-Holocene stacked sandy tsunami deposits within an organic, muddy low-energy backbeach environment.Using 100, 500 and 1000MHz GPR antennas, 29 reflection profiles were collected from two swales (X and Y) inland of the modern beach, and two common mid-point (CMP) profiles using the 200MHz antennas were collected from Swale Y. Detailed examination of the CMPs allowed accurate velocity estimates to be applied to each profile. The reflection profiles included across-swale profiles and a high-resolution grid in Swale X, and were collected to investigate the feasibility of GPR to image the palaeotsunami deposits, and two profiles from Swale Y where the tsunami deposits are poorly known. The 500MHz antennas provided the best stratigraphic resolution which was independently validated from the stratigraphy and sedimentology recovered from 17 auger cores collected along the profiles. It is clear from the augers and GPR data, that the different dielectric properties of the individual layers allow the identification of the IOT and earlier tsunami deposits on Phra Thong Island. Although applied in a coastal setting here, this technique can be applied to other environments where thin sand beds are preserved, in order to prioritise sites for detailed examination.

Paleoecology of a marine endobenthic organism in response to beach morphodynamics: Trace fossil Macaronichnus segregatis in Holocene and Pleistocene sandy beach deposits

Trace fossils made by ancient animals provide information on the ecology of their producers. Insights from their modern analogues also help us to understand the paleoecology of trace fossils. The arrangement of the trace fossil Macaronichnus segregatis, a probable feeding trace of an opheliid polychaete occurring in ancient beach deposits, was investigated to verify whether findings from modern beaches can be used to interpret geological records. The mode of occurrence of this trace fossil on horizontal sections of sediment was analyzed in Holocene and Pleistocene beach deposits. Two modes of the trace fossil arrangement were identified, as in a modern example. One mode shows a weak preferred orientation, whereas the other shows a strong preferred orientation. According to data from modern beaches, the weak preferred arrangement of the trace fossil corresponds to the pattern of subsurface burrowing under fair weather conditions. In contrast, the preferred orientation of the trace fossil indicates that it was formed under storm conditions. These interpretations are also supported by sedimentological evidence of the trace-fossil-bearing strata. The preferred orientation mode occurs just below an erosional surface, which was possibly created by a strong storm event. The results indicate that the trace fossil M. segregatis represents the behavior of its producer in response to beach morphodynamics, or the dynamic migration of a beach face on an ancient sandy beach.

Mixed assemblages of drilling predators and the problem of identity in the fossil record: A case study using the muricid gastropodEcphora

AbstractDrillholes made by naticid and muricid gastropods are frequently used in evolutionary and ecological studies because they provide direct, preservable evidence of predation. The muricidEcphorais common in many Neogene Atlantic Coastal Plain assemblages in the United States, but is frequently ignored in studies of naticid predation. We used a combination of Pliocene fossil, modern beach, and experimentally derived samples to evaluate the hypothesis thatEcphorawas an important source of drillholes in infaunal bivalve prey shared with naticids. We focused on the large, thick-shelled venerid,Mercenaria,which is commonly drilled by naticids today. Laboratory experiments, modern beach samples, and the published literature confirm that naticids preferentially drill near the umbo (significant clumping of holes), show a significant correlation between prey size and predator size (estimated by outer borehole diameter), and preferMercenaria<50 mm antero-posterior width when other prey are present. Fossil samples containingEcphora(with or without other large muricids) show no drillhole site stereotypy (no significant clumping, greater variability in placement), no significant predator: prey size correlation, drilled prey shells larger than the largest modern naticids could produce in an experimental setting, and drillholes larger in diameter than those estimated for the largest Pliocene naticids, thus supporting our hypothesis. Substantial overlap in the placement of holes drilled by naticids and muricids, however, made identifying predators from drillhole position problematic. The lack of overlapping ranges of prey shell thickness between fossil and other samples precluded the use of drillhole morphology to establish predator identity (e.g., ratio of inner borehole diameter to outer borehole diameter, drillhole angle). Whereas the difficulty in determining predator identity from drillholes limits the types of analyses that can be reliably performed in mixed-predator assemblages, recognizingEcphoraas a prominent drilling predator creates the opportunity to investigate previously unrecognized questions.

Form changes inAmiantis purpurata(Bivalvia, Veneridae) shells over the past 100,000 years in North Patagonia (Argentina)

Amiantis purpuratashells from the San Matías Gulf (SMG) were analysed in order to compare both morphology and size throughout the late Quaternary in relation to environmental changes. Shells from modern beaches, Holocene marine assemblages (late Holocene, 3630 ± 100 yearsbp) and interglacial Pleistocene marine assemblages (MIS 5, 100 ka yearsbp) were studied by measuring the height and length, and using the elliptic Fourier analysis (EFA) to take an outline contour. The Pleistocene shells were smaller, more elliptical and with a deeper lunule than the Holocene and modern ones. No significant differences were recorded in the allometry index throughout the late Quaternary. The variation in size and shape of theA. purpuratashells could be related to the phenotypic plasticity of this species as a response to the environmental changes registered in the SMG during the Quaternary. These changes include variations in sea surface temperatures, salinities and substrates, and also water circulation changes, which would have modified nutrient availability. Morphological changes imply burrowing activity, mechanical stability, nutrient uptake and defence response to predation.

Geochemical evolution of groundwater in the Western Delta region of River Godavari, Andhra Pradesh, India

The present study on geochemical evolution of groundwater is taken up to assess the controlling processes of water chemistry in the Western Delta region of the River Godavari (Andhra Pradesh), which is one of the major rice-producing centers in India. The study region is underlain by coarse sand with black clay (buried channels), black silty clay of recent origin (floodplain) and gray/white fine sand of modern beach sediment of marine source (coastal zone), including brown silty clay with fine sand (paleo-beach ridges). Groundwater is mostly brackish and very hard. It is characterized by Na+ > Mg2+ > Ca2+:HCO3− > Cl− > SO42− > NO3−, Na+ > Mg2+ > Ca2+:Cl− > HCO3− > SO42−, and Mg2+ > Na+ > Ca2+ > or < K+:HCO3− > Cl− > or > SO42− facies. The ionic relations (Ca2+ + Mg2+:HCO3−, Ca2+ + Mg2+:SO42− + HCO3−, Na+ + K+:TC, Na+ + K+:Cl− + SO42−, HCO3−:TC, HCO3−:Ca2+ + Mg2+, Na+:Cl− and Na+:Ca2+) indicate that the rock weathering, mineral dissolution, evaporation and ion exchange are the processes to control the aquifer chemistry. Anthropogenic and marine sources are also the supplementary factors for brackish water quality. These observations are further supported by Gibbs mechanisms that control the water chemistry. Thus, the study suggests that the initial quality of groundwater of geogenic origin has been subsequently modified by the influences of anthropogenic and marine sources.