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Omission surfaces represent a gap in the sedimentary record on a particular environment, constituting an important tool for basin analyses. Nevertheless, not always these surfaces constitute key sequence-stratigraphic surfaces, and their correct interpretation is highly important for the recognition of genetically related strata. Documentation and interpretation of ichnological data from stratigraphic surface can refine the sedimentological model. The Puesto El Moro Formation (lower Upper Cretaceous) in the Austral-Magallanes Basin, southern Patagonia (Argentina), shows excellent examples of several omission surfaces stacked during a transgressive context associated with the beginning of the foreland stage. Each of these surfaces, interpreted as Tidal Ravinement Surfaces, contain Thalassinoides isp. and Sinusichnus isp., which represent opportunistic colonization by crustaceans into a predominantly firm substrate. In this case study, the vertical recurrence of substrate-controlled trace fossil suites is the result of high-frequency repeated coastal conditions during the transgression; the associated surfaces, which have limited lateral extension, have low potential for correlation at basin scale. [ABSTRACT FROM AUTHOR]

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The fossil record yields a peculiar phenomenon in different kinds of molluscan shells: bioclaustrations formed around (epi)symbionts during growth of the hosts' shell margin. Four morphologies, two of them formerly considered bioerosion traces, are here united in the parataxonomy of bioclaustration structures under the revised cecidogenus Rodocanalis. These are: (1) simple linear grooves (Rodocanalis linearis csp. nov.) formed below the periostracum in Pleistocene to Recent endobenthic bivalves; (2) series of distally ramifying grooves (Rodocanalis runicus) in Silurian orthoconic nautiloids; (3) irregular networks of grooves (Rodocanalis reticulatus) in Jurassic to Cretaceous bivalves and gastropods; and (4) regular reticulate networks (Rodocanalis geometricus csp. nov.) in Jurassic to Cretaceous gastropods. The linear grooves might be associated with commensal worms, while multiple lines of reasoning point towards hydrozoan symbionts in the case of the branched and anastomosing grooves. After the hydrozoan larva settles and the first polyp becomes fixed on the calcareous ostracum at the shell margin, the process of bioclaustration commences when the periostracum surrounds the base of the polyp, which moves towards the external shell surface, while the hydrorhizae develop in the only possible direction: towards the shell growth margin. This enables new polyps to originate at the shell edge by budding, while the bioclaustration of the stolonial hydrorhizae advances. We consider the nature of this symbiotic relationship as mutualism, with the hydrozoan symbiont taking advantage of the host's feeding current or food debris, and the molluscan host profiting from the defensive capability of the hydrozoan's cnidocysts. [ABSTRACT FROM AUTHOR]

This article analyses the Line of Sight (LOS) surface velocity for the 2016-2020 period, in Bahía Blanca city using DInSAR technique. The results show significant LOS velocities in determinate sectors of the city, presenting values of up to -20 mm/year. Based on the results, we divide the city into three different sectors as a function of LOS velocity, the urban growth factor, and the topographic slope. Sector A, where the subsidence is being induced by loads of new buildings, soil compaction and waterproofing, and residential groundwater pumping. Sector B, where the highest displacement rates are triggered by a combination between groundwater pumping and soil creep process. Sector C has the lowest velocities, low urban growth factor, and absence of groundwater pumping. In all cases, the surface displacement indicates that a review of the urban planning should be carried out as well as increasing control over the groundwater exploitation. [ABSTRACT FROM AUTHOR]

This study integrates ichnological and sedimentological data to interpret depositional environments in the carbonate sediments of the Mobarak Fm. (Lower Carboniferous) in the Alborz Mountains of northern Iran. Seven ichnofabrics including Thalassinoides (Th), Zoophycos‒Phycosiphon (Zo-Ph), Skolithos‒Thalassinoides (Sk-Th), Zoophycos‒Diplocraterion (Zo-Di), Thalassinoides‒Rhizocorallium (Th-Rh), Zoophycos‒Arenicolites (Zo-Ar) and Chondrites‒Phycosiphon (Ch-Ph) have been identified in the studied succession. Th ichnofabric is characterised by the dominance of the deposit-feeding trace fossils, revealing low sedimentation rate and activity of the organisms in a loose substrate. Vertical succession of the Zo-Ph, Sk-Th and Zo-Di ichnofabrics indicates change in the firmness of the substrate. Th-Rh and Zo-Ar ichnofabrics reveal two different energy phases including a lower energy condition with the activity of deposit-feeders and a higher energy phase identified by the activity of suspension-feeders. Ch-Ph ichnofabric is characterised by low diversity and low abundance of trace fossils that were identified in black, limy shale, displaying a long lasting outer ramp setting with low energy, low sedimentation rate, and dysoxic-anoxic conditions of the substrate. Ichnological features of the Mobarak Fm. are controlled by subsidence-inducing changes in the accommodation space of the depositional system dictating variations in paleoenvironmental conditions such as oxygen levels and hydrodynamic energy. [ABSTRACT FROM AUTHOR]

Late Quaternary marine molluscan skeletal concentrations from Argentina constitute a remarkable record of variations in palaeoceanographical conditions during interglacial times (mainly ca. 125 ka to present). Particularly, the Golfo San Jorge coastal area represents an extraordinary geographical zone to target from different points of view, mainly due to its linkage between northern and southern Patagonia, characterized by particular and contrasting physico-chemical conditions with direct consequences for littoral marine communities, determining their composition and structure. Among varied biological activities controlled by different environmental factors (i.e., substrate nature, sedimentation rates, water depth, sea surface temperature, salinity, nutrients-productivity), bioerosion traces can provide palaeoenvironmental evidence with important implications for palaeoclimate interpretations. In addition, the application of bioerosion patterns regionally and through time is a recent valuable worthy palaeoenvironmental tool not as yet developed for Patagonia. We attempted to characterize, qualitatively/semiquantitatively, the ichnotaxonomic composition of the coastal area of northern Golfo San Jorge since the Late Pleistocene; to compare results with those obtained for other geographical areas along Patagonia and the Bonaerensian coastal sectors; lastly, to evaluate its palaeoenvironmental/palaeoclimatic significance in a clue area in terms of circulation patterns near the Southern Ocean climatic pump. At Bustamante (Northern Patagonia Frontal System) Domichnia traces were dominant during the Late Pleistocene while Praedichnia in the mid-Holocene. Bustamante exhibits the highest ichnodiversity for the whole Argentinean coastal area. Ichnodiversity is not strongly different between Late Pleistocene and mid-Holocene interglacials and compared to present; however, the relative abundance of some ichnotaxa (e.g., Oichnus, Iramena, Pennatichnus , at Camarones; Oichnus , Iramena, Pinaceocladichnus, at Bustamante) differs across time. These variations, particularly the highest abundance in the Late Pleistocene (mainly Last Interglacial) of traces made by bryozoans- associated at present with modern enhanced productivity levels and coastal fronts in the Argentine continental shelf- point to higher productivity and more intensified northern Patagonia Front, as a result of a different palaeocirculation pattern, reinforcing previous independent sources of evidence based on molluscan palaeobiogeographical analyses. [ABSTRACT FROM AUTHOR]

Freshwater lenses associated to shell ridges and sand sheets exist on the coastal wetland of Samborombón Bay. As they constitute one of the most vulnerable aquifer systems, it is the aim of this study to determine the hydrogeochemical processes that condition the chemical quality of its groundwater and to assess their present and future capability as sustenance of native woods and local villagers. To achieve this, hydrogeomorphological field surveys were made and groundwater samples were taken. Results show that lenses have a mean thickness of 12 m and its chemical quality depends on the dissolution of CO 2(g) and carbonates, weathering of silicates and ion exchange. Lenses can be affected by long-term climatic variability and mining. The study of morphology and geochemistry of the freshwater lenses bring lights into important information about the management of water resources and conservation of the environment. [ABSTRACT FROM AUTHOR]

In the Lago San Martín region (Santa Cruz Province, Argentina), the Springhill Formation (50-100 m thick) overlies the syn-rift El Quemado Complex, showing outcrops with wedge geometry. Four sedimentological sections were measured in the field, and three depositional palaeoenvironments were interpreted. The Springhill Formation starts with fluvial deposits, characterized by channel-fills and floodplains with palaeosol development, passing transitionally to a coastal plain and, finally, to marine sedimentation. The initial sandy transgressive deposits (Facies Association 9) are the main focus of this study, in which 10 ichnogenera ( Arenicolites, Bergaueria, Cylindrichnus, Diplocraterion, Macaronichnus, Palaeophycus, Planolites, Ophiomorpha, Rosselia and Skolithos) are described. Two ichnoassociations (foreshore and shoreface) were defined, and their distribution was controlled by the local palaeoenvironmental conditions, mainly energy, bathymetry and grain size of sediments. A highly bioturbated surface ( BI = 4) was recognized in Section 1 showing a limited occurrence and disappearing over short distances perpendicular to the palaeoshoreline. This surface shows a sharp sub-horizontal gently undulating top contact with a bioturbation thickness between 15 and 25 cm. This type of surface has limited usefulness as a key correlative surface, because it is spatially restricted in rift basins due to the tectonic activity, which creates high accommodation space rates. A more accurate characterization of the initial transgressive deposits of the Springhill Formation - which is the most important reservoir in southern Patagonia - could provide new ideas to solve problems in sub-surface studies. [ABSTRACT FROM AUTHOR]

Most research on bivalves from the south-western Atlantic used morphological (shell) characters for taxonomic discriminations. Dominant Veneroids from Argentinian Quaternary coastal deposits exhibit wide morphological variation – often making objective discriminations difficult/impossible, which could be objectively described and compared through geometric morphometrics techniques. This work focuses on comparison of geometric morphometrics methods applied to fossil and modern shells, to assess inter- and intra-generic variations. Three approaches were considered: landmarks (L), semi-landmarks (SL) and outlines. Shell shape analyses for different time spans (Pleistocene, fossil Holocene and modern) and areas (Patagonia and Bonaerensian) showed that Elliptic Fourier analysis (EFA), Landmarks and Landmarks plus Semilandmarks (L+SL) can discriminate at generic levels:Mactra, Mulinia(Mactridae) vs.Pitar, Protothaca, Eurhomalea, Clausinella(Veneridae). L and L+SL are powerful for inter/intraspecific distinctions ofMactra. Variability ofMactra isabelleanaincludes the remaining nominal ‘species’ (transitional morphs). Causal environmental factors of (phenotype) variation could be addressed for modern environments (substrate, salinity and energy). Subtrigonal-inflated shells predominate in muddy, quieter, shallow mixo-polyhaline waters; ovate-elongate-compressed in sandy, poly-euhaline, deeper habitats. Differential spatial distribution (and abundance) across time responds to Late Quaternary high sea-level stands: transgressive maxima allowed higher salinity in marginal-marine areas and optimal conditions forMactra isabelleanacontrasting with scarcer records in the Mar Argentino today. [ABSTRACT FROM AUTHOR]

Salinity is one the major stress factors that controls the biotic activities in marine environments. In general, the mixture with fresh-water has been mention as a great stress factor, but the opposite, i.e. high-salinity conditions, is less developed in the ichnological literature. Along the Al-Khafji coastline, Saudi Arabia, hard substrates (constituted by gastropods, bivalves and coral skeletons) contain diverse and abundant bioerosion traces and associated encrusters. Field and laboratory observations allowed the recognition of eight ichnospecies belong to the ichnogenera Gastrochaenolites , Entobia , Oichnus, Caulostrepsis and Trypanites , which can be attributed to various activities produced by bivalves, sponges, gastropods and annelids. The borings demonstrate two notable ichnological boring assemblages, namely, Entobia -dominated and Gastrochaenolites- dominated assemblages. The highly diversified bioerosion and encrustation in the studied hard organic substrate indicate a long exposition period of organic substrate with slow to moderate rate of deposition in a restricted (high-salinity) marine environment. This bioerosion study shows that high-salinity, at least for the study area, is not an important controlling factor for ichnology. [ABSTRACT FROM AUTHOR]

Abstract: Our analysis of palaeobiodiversity and palaeobiogeography of Quaternary molluscan assemblages provide information on the last coastal scenarios in the SW Atlantic. We present patterns of species richness, areas of endemism and between areas relationships based on records (721 taxa) from Argentina and northwards in South America (Surinam, Brazil, Uruguay), including Pleistocene, Holocene and modern sites (48 localities). In Argentina, our data since the Mid-Late Pleistocene (MIS11-1; ca. 400ka B.P. to present) suggest environmental changes linked to sea-level and climatic fluctuations, large enough to alter benthic associations (compositional, geographical variations, including a few extinctions). The southwards decreasing diversity trend for modern bivalves (mostly infaunal taxa) and gastropods (mostly epifaunal taxa), from Surinam to Tierra del Fuego, responds mainly to latitudinal SST, salinity barriers, hydrodynamic forces (rivers and shallow currents): minima peaks fit with local estuarine and marginal marine sites influenced by the Río de la Plata plume; highest peaks with fully marine, warmer waters influenced by the Brazilian Current (Bonaerensian sector); a similar trend applies for the Holocene; Pleistocene maxima peaks in Patagonia belong to MIS11 and MIS5 highstands (warmer than today). Multivariate (Cluster Analysis, CA; Minimum Spanning Trees superimposed to Principal Coordinates Analysis, PCO) and cladistic (Parsimony Analysis of Endemicity, PAE) methods showed congruent relationships between localities, discriminating marginal from open marine environments, but PCO combined with PAE was most advantageous for our area and dataset (382 gastropods, 339 bivalves; 29 Pleistocene, 28 Holocene and 35 modern sites) allowing objective, quick comparisons. Shifts of areas of endemism during the Holocene and Pleistocene relate with SST and salinity changes; a more homogeneous Mid-Holocene (ca. 7–5ka B.P.) scenario, of regionally increased salinity and higher (ca. 2°C) SST, defined the Bonaerensian and northern Patagonian sectors, facilitating southwards shifts of bivalve and gastropod taxa; for Patagonia a colder Pleistocene scenario south of SAO is documented by Tegula atra (exclusive Pleistocene cold water species extinct in the SWA), probably a signal of post-LGM palaeoceanographical changes in the Mar Argentino. [Copyright &y& Elsevier]

The Austral-Magallanes Basin covers the southernmost region of Patagonia, South America. South of Lago Argentino, the Calafate Formation documents part of the foreland stage of the evolution of this basin. Here, sandstones from the Calafate Formation were characterized using petrographical, X-ray diffraction (XRD) and geochemical data in order to establish their tectonic setting and sediment source areas. Based on our results, three intervals (lower, middle, and upper) were distinguished according to their composition. The lower and upper intervals are composed of felsic volcanic lithics, abundant quartz and orthoclase. A shift in the composition was observed in the middle interval, with an increase in the modal abundance of plagioclase as well as other accessory minerals such as pyroxene. In addition, XRD data reveal that the middle interval is dominated by smectite in the clay-fraction, whereas the lower and upper intervals present mixed-layer chlorite-smectite and chlorite assemblages. Similar differences are observed using major and trace elements: data from the lower and upper intervals point to source rocks of intermediate to acid composition, while the middle interval had source rocks of intermediate composition and a lower degree of weathering. With regard to the provenance studies, the three intervals have a strong affinity to intermediate compositions of the Tobífera Formation (El Quemado Complex) and with the diorite/andesite of the Patagonian Batholith, which implies an exclusive contribution from the western edge of the basin. However, the shift in the composition towards the middle interval indicates a sediment supply from the juvenile Andean arc, suggesting contemporaneous magmatic activity during the deposition of the Calafate Formation sandstones. This peak of magmatic activity may have been caused by an eastward migration of the arc, driven by a switch in the tectonic setting south of 48°S. • Petrographic and XRD analyses show changing compositional signatures throughout the unit. • Al 2 O 3 -(Na 2 O+CaO)–K 2 O diagram and CIA values indicate initial-moderately weathered sources. • Samples have Zr/Sc ratios of ~3 meaning that they are depleted compared to typical UCC. • In the Th/Sc–Zr/Sc and Co/Th–La/Sc diagram samples plot between the andesitic and granitic field. • Nb <20ppm and Zr <350ppm values indicate a tectonic affinity of a subduction-related volcanic arc. [ABSTRACT FROM AUTHOR]

The Ediacaran Loma Negra Formation may be deposited in a platform environment related to the Clymene Ocean. This unit is exposed in the Olavarría and Barker areas within the Tandilia Basin, and composed entirely of lime mudstones (∼40 m thick). The age of the Loma Negra Formation (LNF), the uppermost unit of the Sierras Bayas Group, has been debated, but it should be older than 560 Ma (age of the overlying succession) and younger than 600 Ma (age of the underlying iron-rich mudstone of the Colombo Formation) . This extended carbonate platform (>100 km) is divided into two sedimentary facies: one related to the basal section, in which lime mud originated by suspension fall-out in an open-marine ramp (reddish or greenish limestones), and the other facies represented by black to dark grey limestones from the middle and upper sections. The LNF limestones studied, obtained from five sections near the Olavarría and Barker areas, reveal constant curves of positive δ 13 C values (∼+2 to +4%), similar to those recorded in other middle-Ediacaran marine proxies worldwide. Our sedimentological and geochemical study of the LNF sections shows extraordinarily consistent carbon and oxygen isotope trends that may be useful for detailed intrabasinal correlations. Samples of the LNF fabric-retentive micrite preserve an unusually narrow range of oxygen isotope compositions, which is consistent with potential climatic variation, considering the multi-proxies retained. A subsequent decrease in carbonate primary productivity and an increase in siliciclastic supply are associated with the negative δ 13 C trend in the overlying unit, at the base of the La Providencia Group. This negative excursion in δ 13 C from +2.8 to −3.6% is also regarded as a response to the cooling and sea-level fall probably linked to the Gaskiers glaciation. Furthermore, such data are consistent with late-Ediacaran carbonates from other Neoproterozoic successions. Strontium isotope ratios in limestones (0.7060–0.7070) should reflect the near-primary strontium isotope composition of the original seawater, particularly regarding the strontium content (∼300 ppm) and the Rb/Sr ratios (≤0.001) of primary micrite, consistent with a seawater origin. Strontium isotope data reaches 0.7082 with an Rb/Sr ratio of 0.001–0.006. [ABSTRACT FROM AUTHOR]

Freshwater lenses are groundwater sources of limited dimensions that can be usually found in a variety of climates worldwide. These aquifers' quality is important for socioeconomic development, being cation exchange one of the most important geochemical processes that can change the water geochemistry. This study aims to assess the cation exchange processes that determine the chemistry of freshwater lenses in a multilayer aquifer type, considering the center-east of the Pampean Region (Argentina) as a case study. Water samples were taken from the freshwater lenses at different depths to analyze major ions in the laboratory. In addition, geological profiles were made along with the extraction of sediment samples for X-ray diffractometry (XRD) and laboratory tests to analyze the cation exchange capacity. The results show that water stored in the lenses has a vertical facies variation from Ca-HCO 3 to Na-HCO 3 . According to the laboratory results, the change of water facies mainly occurs in the clayey sediments that divide the carbonate bioclastic material above and the loessic sediment below, being cation exchange the most important process. PRACTITIONER POINTS: Cation exchange is the main geochemical process regulating groundwater chemistry. Hydrochemical changes determine the quality of freshwater lenses. Na/Ca exchange is mainly regulated by the groundwater flow into the bioturbated clay. Batch exchange tests were also carried out to quantify the Na/Ca exchange processes., (© 2023 Water Environment Federation.)