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Bioerosion traces are a powerful tool for reconstructing benthic paleo-communities through the geological record. The late Quaternary marine deposits of Patagonia (Argentina) are elongated ridges parallel to the present coast, rich in sand, gravel and shells, the latter being the main substrate for bioerosion traces. However, the ichnological studies in the Quaternary are scarce in high latitudes of the Southern Hemisphere. This work describes for the first time the bioerosion traces recorded in shells belonging to diverse taxa of mollusc from Quaternary deposits in Puerto Lobos, Southern of San Matias Gulf (Patagonia, Argentina). This study complements the scarce information on bioerosion traces in the Southern Hemisphere. A total of 710 mollusc shells were obtained from four Quaternary beach ridges at Puerto Lobos. As a result, 15 ichnotaxa were recorded for the first time in the site, 13 of them for the first time in the Holocene of San Matías Gulf. Through qualitative analysis, bioerosion patterns were observed in the late Quaternary of Puerto Lobos. The abundance of worm and sponge borings in the Pleistocene could be related to warm and sediment-free waters. On the contrary, the results of the bioerosion study in the Holocene and recent samples were very similar. This could indicate that the same environmental factor controlled both bioerosion patterns. For the Holocene, it was observed that the bioerosion pattern is mainly represented by trace produced by suspension and filter-feeding organisms, such as bryozoans, among others. Together with the increase in ichnodiversity, this could indicate an increase in nutrient availability in the San Matías Gulf associated with upwelling events. Therefore, our results reinforce the hypothesis proposed by previous authors that the upwelling events currently observed in the study area began during the mid-Holocene. [ABSTRACT FROM AUTHOR]

During the Early Cretaceous important changes occurred in South-western Gondwana related to its fragmentation, and South Atlantic Ocean opening. Then, two basins developed in southernmost Patagonia: the Austral-Magallanes Basin and the Rocas Verdes-Magallanes Basin. The Río Mayer Formation corresponds to the initial sedimentary stages of the Austral Basin including black shales, marls and fine-grained sandstones deposited in an outer shelf environment. We studied and sampled three detailed sedimentary logs at Río Guanaco Locality (S 49° 57′ 11"; W 72° 04′ 56″), dividing this unit into three informal sections (lower, middle and upper). Whole rock geochemical analyses were carried out over the three sections with the focus on trace elements, in particular, rare earth elements (REE). While, the lower section of the unit shows an affinity to acid volcanic source areas, the middle and upper sections show an affinity to intermediate source areas. These changes through the Río Mayer Formation can be correlated with the initial magmatic activity hosted in the Southern Patagonian Batholith during the Neocomian. Considering the REE patterns, the lower section of the Río Mayer Formation shows an affinity to the felsic compositions of the Tobífera Formation, while the upper section would be related to the erosion of the Punta Barrosa/Cerro Toro formations of the Rocas Verdes-Magallanes Basin. The clear distinction between the REE patterns of the Río Mayer and Zapata formations is considered evidence of the compartmentalization of these basins during the Early Cretaceous. Finally, the absence of correlation between the geochemistry of the studied unit and the Jurassic volcanic rocks of the Deseado Massif indicates that the north-eastern sector of the basin was not a source area for the Austral Basin, at least during the deposition of the Río Mayer Formation in the study area. • Geochemistry of the Río Mayer Formation reveals a clear trend for its provenance analysis. • During the Early Cretaceous the Rio Chico High was not a source area for the Austral Basin. • Austral and Rocas Verdes basins should have had different source areas during the Neocomian. [ABSTRACT FROM AUTHOR]

Hardgrounds are important surfaces for basin analysis and oil exploration, representing in some cases significant markers of the sedimentary basin fill. In the Neuquén Basin, bioerosion structures are common on the shell surfaces of benthic organisms, but bioeroded hardgrounds are comparatively uncommon. In the Pilmatué Member of the Lower Cretaceous Agrio Formation (Valanginian-Hauterivian) two examples of bioeroded hardgrounds are described in detail, allowing to recognize contrasting palaeoenvironmental and sequence-stratigraphic contexts, and in turn, discussing the potential major controlling factors in each example. In both cases Trypanites isp. and Gastrochaenolites isp. are described, interpreted as belonging to a Trypanites ichnofacies. The two cases are developed in different environmental conditions: one in non-depositional offshore conditions at the top of a parasequence (i.e., transgressive surface); and the other in offshore erosional settings with the omission surface located in an intra-parasequence position, with no obvious sequence-stratigraphic connotation. These marked differences in the palaeonvironmental conditions (non-depositional vs erosive) and sequence-stratigraphic context (inter vs intra-parasequence occurrence) interpreted for these example allowed us to propose different controlling factors related to the generation of the hardgrounds. Despite these differences, namely long periods of non deposition and low-energy conditions vs shorter time and high-energy (erosive) conditions, in both cases a Trypanites ichnofacies is developed, representing an important aspect to be considered in the characterization of the basin evolution based on omission surfaces. • The hardgrounds presented respond to non-depositional and erosional conditions. • These hardgrounds represent major stratigraphic surfaces or minor breaks in sedimentation. • Diverse environmental settings correspond to similar expressions of Trypanites ichnofacies. • Their use in basin fill characterization should be carefully evaluated in each case study. [ABSTRACT FROM AUTHOR]

Ichnological investigations were carried out on late Quaternary shells of the intertidal deep infaunal bivalve Tagelus plebeius ( Lightfoot, 1786 ) found along the southwestern Atlantic, between Uruguay and the southernmost Buenos Aires Province in Argentina. Analyses reveal distinctive marks that are spread on the outer shell surface only. The marks are regular-unbranched-elongate, perpendicular to the outer shell growth lines, with deflections on the margins, never interconnected, without bifurcations, conforming bottom-up constructions. They occur in hundreds of specimens from many samples taken from sediments ranging in age from the late Pleistocene to the Recent. These marks have never been reported or described for this species and their origin and formation remain elusive. We describe these traces thoroughly and we propose an explanation for their preservation on about half the shells examined. Potential destructive boring structures (excavated from outside-in) or bioerosion activities by other macro- or micro-organisms are dismissed. These antimarginal asymmetric traces point instead to a process of constructive bioclaustrations (grown from the bottom-up) produced in situ during the life of the bivalve by unknown symbiont organisms. Additionally, the regular pattern observed for the marks exclude host growth as a consequence of abiotic/extrinsic causes. From a palaeoecological perspective, these structures suggest a biotic interaction that was hitherto undescribed neither for bivalves nor for the late Quaternary of the southwestern Atlantic. [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]

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]

The Río Mayer Formation (Berriasian–Albian) is part of the basal infill of the Austral Basin, southwestern Gondwana. In the Los Glaciares National Park (Santa Cruz Province) seven sections were sedimentologically studied in detail. The investigated interval is mainly composed of black mudstones and shales interbedded with marls and fine-grained sandstones. The vertical distribution of these lithologies provided the basis to distinguish three major units (lower, middle and upper). In general, within the Río Mayer Formation, two different developments of the Zoophycos ichnofacies were recognized. First, in the middle unit (Valanginian–Hauterivian), this ichnofacies shows a high degree of bioturbation having a bioturbation index (BI) between 3 and 4; Zoophycos specimens are of large size, the spreiten are nearly 1 cm in height and more than 1 m in width. This ichnogenus is associated with Chondrites and Bergaueria perata . Environmentally this ichnofacies formed during a transgression, the sedimentation rates were very low and promoted the accumulation of benthic food in the outer shelf. Second, the Zoophycos ichnofacies in the upper unit (Albian) exhibits a less intense degree of bioturbation (BI between 0 and 1) and; Zoophycos is of relatively small size, the spreiten are 0.3 cm high and short. Typically are associated Ophiomorpha , Chondrites , Palaeophycus and Teredolites . When this ichnofacies formed, the prodelta margin prograded across the outer shelf and led to enhanced sedimentation rates further offshore resulting in the dilution of the nutrients. [ABSTRACT FROM AUTHOR]

The importance of the Río Mayer Formation (Lower Cretaceous, prodelta to marine outer shelf) in the hydrocarbon development of the Austral Basin (Patagonia, Argentina) has been recognized by several authors. This unit plays a key-role as source rock and caprock in the “Inoceramus inferior-Springhill” petroleum system, the most important in the basin. In this work we demonstrate that the composition of the Río Mayer Formation highly matches with the requirements to be considered for shale-oil/gas exploitation. The unit studied mainly consists of laminated black siliciclastic mudtones and shales with interbedded marlstones and sandstone levels, and in subsurface shows TOC values up to 3% and kerogen types between II and III. Compositional studies from outcrops of this unit are almost absent and constitute the main focus of this contribution. A total of ten detailed sedimentological logs were measured from the field and X-ray diffraction analysis (XRD), standard petrography, scanning electron microscopy (SEM) and determination of major elements in clay minerals by EDAX were carried out in order to characterize the composition of the Río Mayer Formation. XRD analyses (in fine-grained sediments) indicate a composition dominated by quartz and calcite, with minor proportions of feldspars and clays. Marine sediments are dominated by illite and chlorite, and commonly accompanied by mixed layered illite-smectite (IS), while the prodelta is smectite-dominated with more than 90% of this clay. Both, authigenic and detrital clays were identified using SEM-EDAX. Sandstones of the Río Mayer Formation are generally lithic and feldspar graywackes. Provenance analyses in sandstones make possible the discrimination of four groups of samples differentiated by their ages and palaeoenvironments. In comparison with other important shale-reservoirs from North America (Barnett, Marcellus, Woodford, Haynesville and Doig), the composition of the unit studied have more quartzitic composition, reflecting in a high brittleness index (BI) that result in a clear brittle pattern. [ABSTRACT FROM AUTHOR]

The reconstruction of palaeo-oxygenation levels in marine deposits from the Cretaceous has obtained a huge interest all around the world in recent years. This fascinating topic is here pointed out for the first time in the Austral Basin using the information provided by the black shales of the Río Mayer Formation, Patagonia, Argentina. The combination of sedimentology, ichnology and geochemistry (TOC, Ce anomaly and MnO content) allow the identification of three major intervals respecting the oxygen content. During the Berriasian and early Valanginian anoxic conditions prevail in the outer shelf. After that, between the late Valanginian and Hauterivian dysoxic palaeoenvironments were developed. Finally, a more oxygenated palaeoenvironment occurred since Aptian associated with a progradation of a proximal deltaic system. The identification of anoxic conditions is of much interest for the hydrocarbon research in this stratigraphical unit, which represents the most significant source rock of the Austral Basin. [ABSTRACT FROM AUTHOR]

Abstract: Results of the systematic review and regional palaeobiogeographical context of Tegula atra, including morphometric, multivariate and cladistic analyses, show that it is a keystone species in the marine Quaternary of Argentina that can be used as Pleistocene biostratigraphical tool and paleoclimate-palaeoceanographical signal. While it was absent in warmer than present high sea-level episodes during the Miocene (“Entrerriense” transgression, ca. 10 Ma) and Pleistocene (MIS11), it exhibits an excellent and abundant fossil record within dominantly cool coastal settings exclusively during the Late Pleistocene (MIS9, 7 and 5) between Río Negro and southern Santa Cruz provinces (Patagonia). It first appeared in the SEP during the late Pliocene (cooling trend), dispersed during the Late Pleistocene into the SWA presumably by rafting on macroalgae along the Cabo de Hornos and Malvinas (Falkland) currents, but became extinct in the Mar Argentino (Magellan Malacological province) during the Holocene (amelioration trend). Its absence at present represents a climate change-driven range shift and independent evidence of palaeoceanographical changes after the LGM and at the Pleistocene/Holocene transition: changes in SST (ca. 2 °C higher), wind velocities (less), light (less), nutrient availability (less), extension and intensity of cold (less) and warm (increased) shallow water currents altering water masses and biogeographical boundaries. Altogether, these changes and the Holocene scenario were disadvantageous, causing direct effects on its physiology and survival, in turn preventing the occurrence of the associated macroalgae (Durvillaea antarctica) and its successful dispersal in the SWA or retraction to the cold Humboldt System waters. This study reinforces the importance of dispersalist models to explain the origin of key taxa, adding for a better understanding of molluscan taxonomic differences along the SWA and SEP margins of South America, with implications for future coastal scenarios. The distribution of T. atra across time is a new example of the strong linkage between earth history-climatic cycles-atmospheric and oceanic circulation and the late Quaternary biotic responses, showing a possible consequence of future climate change on nearshore communities. [Copyright &y& Elsevier]

Abstract: The molluscan content from three “marine terraces” (TM) preserved along 250 km of the Santa Cruz province provided 49 molluscan taxa (33 Gastropoda and 16 Bivalvia) and the first Quaternary records for Ataxocerithium pullum, Crepidula protea, C. aculeata, Adelomelon ferrusacii, Brachidontes rodriguezi, Aequipecten tehuelchus, Ostrea tehuelcha, and Solen tehuelchus. The mollusca assemblages suggest typical marine nearshore conditions similar to the adjacent modern littoral (Southwestern Atlantic), with mostly hard substrates, shallow and cold waters. The TMVI (+5–15 m a.s.l., ca. 8–1.2 ka A.P.) is mainly characterized by dominance of Brachidontes spp., Nacella spp. and Mytilus edulis, associated with Siphonaria lessoni. No evidence has been found for the TMVI of clear biotic responses or strong palaeobiogeographic effects during the time span of the Climatic Optimum (“Hypsithermal”, mid-Holocene) which has been documented for other coastal areas northward in Argentina, down to ca. 44–45° S. Scarce differences distinguish the TMV (+15–30 m a.s.l., ca. 108–137 ka A.P., MIS5?) and TMIV (+20–30 m a.s.l., ca. 242 ka A.P.) regarding the Holocene and the modern littoral. Within the TMV, Clausinella, Eurhomalea, Solen tehuelchus and Brachidontes cf. darwinianus (typically in warmer waters) are exclusive; in the TMIV, Trophon, Buccinanops, Brachidontes and Pectinidae are characteristic. Predominance of Trophon spp. (typically in cold Magallanic waters) in modern samples vs. scarcity or absence in the TM suggest slightly lower modern SST. Several taxonomic similitudes with the Pacific Sudamerican coast (e.g., Fissurella, Nacella, Tegula, Crepidula, Trochita, and Acanthina) could respond to cold currents helping cold-water immigrants to join southern Southamerican Atlantic after the opening of the Drake Passage. [Copyright &y& Elsevier]

An integrated study combining sedimentological and ichnological data has been conducted in the lower wave-dominated deposits of the Calafate Formation. The study aimed to assess the variation in fair-weather and storm processes, tidal flux, and the coast configuration to correctly constrain sedimentary dynamics in complex depositional systems. The wave-dominated deposits comprise foreshore to upper shoreface (FA1), middle to lower shoreface (FA2) and offshore-transition deposits (FA3) moderately affected by storms. In FA1, the most proximal strata contain Macaronichnus isp. and occur within the foreshore, while the upper shoreface shows an increased ichnodiversity associated with the occurrence of the archetypal Skolithos ichnofacies evidencing heightened energies of the upper shoreface. FA2 display a fair-weather community assigned to the proximal Cruziana ichnofacies that shows a wider range and variability of living strategies, and a storm-related community represented by opportunistic colonizers which produced burrows assigned to Ophiomorpha nodosa. The monospecific occurrence of Thalassinoides isp. at the top of FA2 in CC02P section is assigned to the Glossifungites ichnofacies, developed on a firmground and autogenic surface. The ichnoassemblage in FA3 is attributable to the transitional Skolithos-Cruziana ichnofacies, that exhibits a slightly reduced diversity of the fair-weather community and a sparse bioturbation. The distribution and the general characteristics of the ichnological assemblages are consistent with deposition in fully marine conditions. The bioturbation intensity, trace-fossil diversity, maximum penetration, and burrow size distributions indicate fully oxygenated and clear waters, normal-marine salinity conditions, abundance and accessibility of food, and continuous and moderate sedimentation. Nevertheless, the ichnological signature in FA3 is related to minor physico-chemical stress produced by strong tidal currents originated during the southward expansion of the Magallanes embayment. • Integration of sedimentological and ichnological data allowed the differentiation between fair-weather and storms processes • The ichnological vertical trend shows a continuous of fully marine conditions along the shoreface depositional profile. • Tidal currents originated physico-chemical stress in FA3 deposits and later the tide-dominated deposits of the unit. [ABSTRACT FROM AUTHOR]

Depositional processes operating in deltaic shorelines create a variety of physico-chemical stressful conditions that impact directly on benthic fauna. The ichnological signatures of deltaic successions reflect these physico-chemical stresses, such as rapid sediment influx, elevated water turbidity, periodically reduced oxygenation, salinity fluctuations, and wave- and tidal-energy. In the Campanian La Anita Formation of the Austral-Magallanes Basin, two examples of deltaic successions, each showing different relative dominance of wave and fluvial processes, are described in detail, allowing the recognition of contrasting stresses that acted differentially in a wave-dominated, fluvial-influenced delta and a fluvial-dominated delta. Variations in the burrowing intensity and ichnodiversity allowed us to discriminate the different physico-chemical stresses. In the wave-dominated, fluvial-influenced deltaic deposits, the alternation between fair-weather waves and storm events acted as the main controlling factor on benthic fauna in the facies of the prodelta and distal delta front, displaying facies-crossing and horizontal elements attributable to the Skolithos and Cruziana Ichnofacies, such as Arenicolites isp., Chondrites isp., Cylindrichnus isp., Diplocraterion isp., Gyrochorte isp., Ophiomorpha isp., Palaeophycus isp., Planolites isp., Rhizocorallium isp., Rossellia isp., Schaubcylindrichnus isp. and Skolithos isp. Water turbidity and periodically reduced bottom water oxygenation conditions also played an important but subordinate role. The proximal delta front, and distributary and terminal distributary channel deposits show low burrowing intensities and ichnodiversities with structures attributable to the depauperate Skolithos Ichnofacies with few Diplocraterion isp., Gordia isp., Lockeia isp., Macaronichnus isp., Ophiomorpha isp., Schaubcylindrichnus coronus and Siphonichnus isp., showing stress conditions associated with rapid sediment influx, high energy and reduced salinity conditions related to fluvial discharges as the most important controlling factors. Periodically, fluctuations in salinity conditions due to river discharges and channel avulsion may have also played important roles. The fluvial-dominated deltaic deposits show that the controlling factors were associated with fluvial discharge and river-sediment influx with no clear influence of wave or tidal action. The facies of the distal delta front were controlled by episodic sedimentation, elevated water turbidity, periodically reduced oxygenation and salinity fluctuations, the associated trace fossil suite consists of a monospecific assemblage of Ophiomorpha isp. and sparse Palaeophycus isp. The proximal delta front and the distributary channel deposits are mostly unburrowed, locally displaying a few Arenicolites isp., Lockeia isp., Ophiomorpha isp., Psilonichnus isp. and Teredolites isp. The development of these suites was controlled mainly by heightened sedimentation rates influx triggered by high fluvial discharges, elevated water turbidity due to heightened suspended load and buoyant plumes, periodic fluctuations in salinity conditions caused by river discharges and channel avulsion. Interdistributary areas are characterized by facies preserving evidence that reduced oxygenation was the most important controlling factor in this subenvironment. Fluvial processes generate the most extreme stressful conditions for benthic colonization by tracemakers. Wave processes tend to buffer the stresses produced by river discharge. The effect of waves on fluvial stress is reflected in the higher bioturbation intensities and ichnodiversities that the wave-dominated deltaic deposits of the La Anita Formation delta show in relation to the fluvial-dominated ones. • Documentation of trace-fossils in wave- and fluvio-dominated deltas. • Physico-chemical stresses on animal-substrate interactions in deltas. • Interpretation of physic-chemical stressful conditions in deltaic systems. • Discussion of controlling factors on the activity of the benthic fauna in deltaic shorelines. [ABSTRACT FROM AUTHOR]

The exposed calcareous rocky area of the Abu Qir Headland, east of Alexandria, Egypt which range from coarse grains, through pebbles, cobbles, and boulders to rocky platforms, was significantly colonized by sclerobionts (epibionts and endobionts). The epibiont species diversity was comparatively higher than that of endobionts. Epibiont communities included bryozoans (the anascan-grade cheilostome Biflustra savartii), serpulid (Hydroides elegans, Spirobranchus cf. tetraceros, Vermiliopsis striaticeps and Protula or Apomatus) and spirorbid (Spirorbis) wormtubes, and balanoid barnacles (Amphibalanus amphitrite, Balanus trigonus, and Perforatus perforatus). The cheilostome bryozoan colonies, which developed extensive sheets, proliferated on the study rocky shore either encrusting the bioeroded basement directly, or encrusting other epilithic taxa, particularly balanoid barnacles and serpulid worms. Encrusters displayed a remarkable marginal competitive interaction (overgrowth and stand-off) for space on the study rocky shore. On the other hand, endobionts were not well represented on the studied rocky shore exposure. It was possible to identify three ichnotaxa: Gastrochaenolites, Maeandropolydora, and Finichnus. The findings documented represent a significant contribution to our knowledge of sclerobionts composition, sequence of their colonization and/or bioerosion, and their mutual relationships on the intertidal rocky shore of the Abu Qir Headland. [ABSTRACT FROM AUTHOR]

The Patagonian Sea in the SW Atlantic is one of the most productive marine ecosystems worldwide. Besides its economic relevance, this shelf sea serves as a major sink for atmospheric CO 2 and thus plays a major role in global climate. Despite that, the marine climate dynamics in that region remain barely known. Instrumental records only cover the last 30 years or so and high-resolution climate archives are currently not available. Here, we explore the possibility to obtain seasonally to inter-annually resolved paleotemperature data from shells of the bivalve mollusk, Leukoma antiqua collected alive from the shallow subtidal zone of the San Jorge Gulf. Results demonstrate that this species grows during summer and – at least at slow rate – during winter at this locality and records nearly the full seasonal temperature amplitude (monthly averages) in the form of δ 18 O shell . Furthermore, isotope-based climate reconstructions will be limited to the first 15 years of life, because growth rates are sharply reduced afterward which aggravates sampling. The oldest studied specimen attained an age of 34 years. Annual, fortnightly and lunar daily increments can potentially be used to determine the timing and rate of seasonal shell growth and help placing the shell record into precise temporal context. However, due to interferences with the shell microstructure, sub-annual growth patterns were only occasionally well developed. In this study, the temporal alignment of the growth record was therefore largely achieved by forcing T δ18O to match the shape of the instrumental temperature curve. In some years it was possible to validate such temporal alignments with fortnight increments. Shell growth rate is strongly linked to primary production which attains a maximum in spring. For yet unexplained reasons, shell formation occurs with an offset of almost −1‰ (−0.9 ± 0.3‰) from expected oxygen isotopic equilibrium with the ambient water. When this offset is adjusted for, δ 18 O shell can be used to compute past water temperature. Given the individual variability regarding δ 18 O shell , it is advised to study a sufficient number coeval specimens to obtain more reliable information on the seasonal temperature range. Presumably, the overall life history and the isotopic offset is similar for L. antiqua specimens at other localities in southern South America. Since L. antiqua not only dominates modern nearshore benthic assemblages, but also occurs abundantly in Quaternary deposits along the Argentine Patagonian coast, this species can significantly contribute to a better understanding of natural baseline conditions and past climate dynamics in southern South America. [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]

Although there is general consensus that a global greenhouse climate characterized the mid-Cretaceous, details of the climate state of the mid-Cretaceous Southern Hemisphere are less clearly understood. In particular, continental paleoclimate reconstructions are scarce and exclusively derived from paleontological records. Using paleosol-derived climofunction studies of the mid- to Upper Cretaceous Mata Amarilla Formation, southern Patagonia, Argentina, we present a reconstruction of the mid-Cretaceous climate of southern South America. Our results indicate that at ~ 60° south paleolatitude during the Cenomanian–Santonian stages, the climate was subtropical temperate–warm (12 °C ± 2.1 °C) and humid (1404 ± 108 mm/yr) with marked rainfall seasonality. These results are consistent with both previous estimations from the fossil floras of the Mata Amarilla Formation and other units of the Southern Hemisphere, and with the previous observations of the displacement of tropical and subtropical floras towards the poles in both hemispheres. The data presented here show a more marked seasonality and slightly lower mean annual precipitation and mean annual temperature values than those recorded at the same paleolatitudes in the Northern Hemisphere. [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-HCO3 to Na-HCO3. 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. [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‐HCO3 to Na‐HCO3. 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.The different processes that determine the hydrochemical facies in each sector of the freshwater lenses as a result of the interaction of the water with the different lithologies in which the lenses are stored. [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]

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]

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]

• A drastic shift in environmental conditions is recorded in Villa Mónica Fm. • Basal section represents a shoreface-offshore transition system. • Upper section evidence stromatolite reef in a tidal carbonate platform. • Phosphorous input controlled kilometer-scale biostromes and bioherms development. • Distal glacimarine and interglacial evidence remains hidden in the complete unit. The Cryogenian Period (720–635 Ma) is wide known by the occurrence of two global glaciations, Sturtian and Marinoan, responsible of dramatic climate and sea level changes as well as seawater oxygenation events. Constrained 87Sr/86Sr ratios from 0.7064 to 0.7071 and δ13C excursion are consistent with Cryogenian cap carbonates as documented in the upper Villa Mónica Formation. This unit constitutes the basal sedimentary cover of the Río de La Plata Craton in Central Argentina which begins its deposition in a shallow marine siliciclastic shelf, turning to a carbonate succession with exceptionally well-preserved stromatolites. The detailed facies analysis added to stromatolite morphologies included in paleoenvironmental models of deposition remain unknown. The later are considered necessary to establish the stratigraphic framework and the regional correlation of the unit across the basin as a piece for the Cryogenian assembly. The entire Villa Mónica Formation in the Tandilia Basin was deposited on a shelf with sedimentary facies variations observed from the shallow margins to the offshore transition zone. The transition from the lower to the upper sections implies the conquer of microbial communities to paleogeographically controlled chemocline fluctuations where the stromatolites evidence the development from a post-glaciation phosphorus-rich ocean. This drastic shift in paleoenvironments represented on the two distinctive marker sections was influenced by changes in climatic and oxygenation conditions. In this context, presumed glacial influence is predictable in a partially ice-covered Cryogenian Earth surface. [ABSTRACT FROM AUTHOR]

Abstract: Variations in the composition, distribution, and diversity of molluscan assemblages from Patagonian marine terraces (MT) formed during the late Quaternary sea-level highstands and neotectonic events—between the late Pleistocene, mid-Holocene, and present—are discussed. Molluscs and associated macrofauna (balanids, brachiopods, polychaetes, bryozoans) from nine fossiliferous localities and three modern sites suggest paleoecological, paleobiogeographical, and paleoenvironmental implications for paleoclimatic interpretations of the coastal area of Bahia Bustamante–Caleta Malaspina (∼44.9 and 45.3°S) since marine oxygen isotope stage (MOIS) 7. Crepidula protea, Buccinanops paytensis, and Brachidontes rodriguezi are first recorded for the late Pleistocene MTIV (MOIS5-7); Nacella (Patinigera) deaurata, Epitonium magellanicum, B. paytensis, Aequipecten tehuelchus, and Clausinella gayi are recorded for the mid-Holocene MTVI (MOIS1) in the area. These molluscs currently live in the SW Atlantic, but Venericardia procera represents a northward migration and Tegula atra a faunal extinction in response to climate change. Overall, they indicate hard substrates, shallow waters, and truly marine conditions, similar to the modern littoral. With respect to temperature, the qualitative, quantitative, morphological, and distributional variations suggest slightly higher SST during the mid-Holocene (MTVI, MOIS1, hypsithermal), colder for MTV (MOIS5c?, 5a?), and warmer or similar for MTIV (MOIS5e, 7?). [Copyright &y& Elsevier]

This paper describes an integrated field, petrographic and geochemical study of the Puesto del Museo Formation, a poorly known unit that evidences a Cenozoic transgression at the southernmost Golfo San Jorge Basin. The most striking features of the Puesto del Museo Formation is its occurrence as restricted ~20 m-thick-outcrops composed exclusively of friable cross-stratified grainstones. We analyzed the sedimentary facies and facies associations in order to reconstruct the depositional setting. The petrographic characterization allows assessing the composition as a very homogeneous lithological succession dominated by skeletal grainstones. Geochemistry of trace elements (Mn, Sr, Rb, rare earth elements plus yttrium = REY), and stable isotopes (C and O) were used to characterize the grainstones compositionally, and to constrain environmental and climate conditions that controlled its deposition. The diagenetic environmental comprehension helped to the interpretations of the syn- and post-depositional conditions related to the grainstones. Finally, the stratigraphic position of the Puesto del Museo grainstones into the context of the basin is discussed. This succession can be correlated with the Patagonian marine event (i.e., Golfo San Jorge and Austral basins) that took place during the late Oligocene–early Miocene, related to an elevated global sea level controlled by glacio-eustatic conditions. • Puesto del Museo Fm can represent the southernmost mid-Cenozoic carbonates at the GSJB. • These grainstones deposits flooded a rocky shore composed of the Jurassic volcanites. • The cementation begun at the seafloor followed by vadose conditions. • Trace elements supported by facies analysis reveal shallow open marine environment. • Bioclasts and C-isotope may suggest it as part of the Patagoniense transgression. [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]

The Sierras Bayas Group of the Tandilia System constitutes the Neoproterozoic sedimentary cover of the Río de La Plata Craton in Argentina that accumulated amid the breakup of the Rodinia supercontinent and subsequent assembly of Gondwanaland. Evidence for glaciation in the Villa Mónica Formation (VMF) at the base of the succession comes in the form of iron-rich laminated sediments containing dropstones composed predominantly of basement crystalline rocks and quartzites that, are sequentially overlain by a phosphatic mudstone and a ~ 40 m thick stromatolitic dolomite. Subtidal facies preserve columnar forms similar to post-glacial tubestone stromatolites seen in the Neoproterozoic records. These morphologies suggest rapid growth associated with elevated seawater alkalinity and high rates of carbonate accumulation records. The VMF dolomites in our four studied sections near Olavarría-Sierras Bayas area reveal a pronounced negative-to-positive δ 13 C up section that is similarly to these cap carbonates and others worldwide. Our sedimentological and geochemical study of the VMF sections reveal consistent carbon and oxygen isotope trends that may be useful for detailed intra-basinal correlations. Samples of the VMF fabric-retentive dolomite preserve an unusually narrow range of non-radiogenic strontium isotopic compositions (0.7068 to 0.7070) that are consistent with Cryogenian limestone facies in the potential Namibian and Brazilian equivalents. Exceptional preservation of 87 Sr/ 86 Sr compositions suggest the possibility of primary dolomite precipitation in post-glacial seawater, and furthermore that REE patterns and distributions may yield similar insights to redox conditions in the depositional basin. In particular, the VMF dolomites reveal depleted LREE abundances, a negative Ce anomaly, positive La and Gd anomalies, and low Y/Ho values. As a whole, these observations suggest oxidizing post-glacial seawater conditions associated with significant freshwater inputs into the basin. Global warming and increases in primary productivity and organic carbon burial linked to the buildup of oxygen, the positive δ 13 C trend and the increase in stromatolite biodiversity in the VMF. [ABSTRACT FROM AUTHOR]

Aggradational deltaic successions are uncommon in the stratigraphic record since deltas are progradational by nature. However, deltaic coastlines fed by multiple small distributaries rather than by a well-defined trunk fluvial distributary system might result in aggradational successions if the sediment is effectively redistributed from river mouths by active basinal processes (e.g., tides, fairweather waves, and/or storm waves). The wave-dominated deltaic succession in the lower part of the La Anita Formation accumulated during the foreland stage of the Austral-Magallanes Basin (Argentina). Through a sedimentological and ichnological study of the interval, we evaluate and discuss the potential controls on the evolution of aggradational wave-dominated deltaic successions. The studied stratigraphic interval is up to 150 m thick and includes facies deposited in wave-dominated prodelta, wave-dominated distal delta-front, wave-influenced mouth bar, terminal channel, and distributary channel settings. These facies associations stack vertically, forming clear thick aggradational sets. Fairweather wave processes largely dominate the delta-front and prodelta deposits, although discrete beds point to the periodic importance of linked storm-wave and river-flood processes. Owing to the alternation of beds generated during fairweather shoaling waves with those of coupled storm-wave and river-flood cycles, it is proposed that the overall aggradational stacking pattern of the delta is the response to the sediment balance. Clastic material supplied by the distributary channels of the delta was easily transported alongshore during fairweather conditions by longshore currents and basinward via storm-generated waves, and/or hyperpycnal currents and hypopycnal plumes generated by river floods. The alternation of these depositional processes strongly affected the benthic faunal communities, which is well expressed by the resulting ichnological suites. Storm-wave and river-flood events led to the widespread defaunation of tracemaking organisms, leading to generation of unburrowed beds. Between these events, short-lived colonization windows appeared locally, allowing sparse, facies-crossing dwelling and detritus-feeding burrows to be constructed by the recovering benthic communities. By contrast, during prolonged periods of fairweather shoaling, river-induced physico-chemical stresses were greatly reduced, and the resulting beds display elevated bioturbation intensities with greater numbers of burrows that record a wide range of behaviors. • Controls on aggradational wave-dominated deltas • Interaction between fairweather-wave, storm-wave, and river-flood processes • The development of the Rosselia and the Phycosiphon Ichnofacies is reported. • Event beds selective colonization by tracemaking organisms • Animal-substrate dynamic relationships are discussed during delta evolution. [ABSTRACT FROM AUTHOR]

Wave-, tidal-, and fluvial-dominated deltas are important hydrocarbon reservoirs worldwide, and it is well known that depositional facies types, detrital composition and diagenetic products are key aspects when evaluating potential reservoir properties. Moreover, detrital composition and diagenetic products are controlled by external forces such as tectonism, climate, and depositional conditions. The Upper Cretaceous La Anita Formation (Austral-Magallanes Basin, Argentina) is a deltaic succession that shows a clear vertical variation in the relative role of wave, tidal and fluvial processes. The formation was accumulated during the foreland stage of the basin under relatively warm climate conditions. A detailed compositional and diagenetic analysis for these deposits is provided to evaluate the role of the controlling factors on the detrital and authigenic composition, and the impact on reservoir properties. Samples were analyzed by conventional petrography, X-ray diffraction and scanning electron microscopy to obtain a full spectrum of its detrital, authigenic and diagenetic composition. The analyzed sandstones were classified as lithic arenites which come from the fold-thrust belt region and from the magmatic arc located toward the westward. The clay mineral composition is characterized by variable proportions of illite, smectite, kaolinite and mixed-layer illite-smectite with the sporadic presence of chlorite. Stratigraphic variations in the abundance of authigenic kaolinite and smectite indicate a change in the climatic conditions during the depositions of the unit evolving from tropical to more temperate conditions. Diagenetic processes affecting the porosity are considered as controlled mainly by the lithological nature of the deposits and depositional facies type. Sandstone porosity is mainly primary in origin, moderate to good in abundance and show micropore to mesopore as the main pore-sizes. This work enhances that the diagenetic products are heavily controlled by the dominant depositional process. The presence of diagenetic products as quartz overgrowth and calcite and hematite cement reduces pore spaces and affects the reservoir properties. The development of these types of cement is conditioned by the relative dominance of wave and river processes. Under wave-dominated conditions, quartz tends to develop thick overgrowths. Conversely, under river-dominated conditions quartz overgrowths are thinner and calcite and hematite cementation patches are developed. • Compositional and diagenetic analysis for wave- and river-dominated deltaic deposits are performed. • Sandstone provenance indicates supply mainly from the uplifted fold-thrust belt and magmatic arc. • Vertical variations in clay mineral composition indicate a change in paleoclimatic conditions. • The diagenetic processes recorded in the La Anita Formation conditioned the reservoir properties. • The development of different diagenetic products is controlled mainly by the dominance of the depositional processes. [ABSTRACT FROM AUTHOR]

Structure from Motion–Multi-View Stereo (SfM-MVS) is a relatively new technique that is being adopted in the analysis of sedimentary systems. The technique is especially applicable to studies which focus on the distribution, geometry and quantification of geological bodies including the analysis of sedimentary forms and tectonic structures. This photogrammetric method allows for generating virtual outcrops (VO) and high-resolution digital terrain models (DTMs). In comparison with more sophisticated and expensive techniques such as airborne LiDAR scanning or terrestrial laser scanning, SfM-MVS is a fast low-cost method which with careful use of ground control points, can produce models which are comparable to other digital survey methods for spatial accuracy. In this study, the effectiveness of SfM-MVS in a series of quantitative case studies in sedimentary and basin analyses is discussed. Focus is placed on how the research questions define the workflow strategy to know the limitations, sources of error and potential utility that the SFM-MVS technique has when a virtual sedimentary system is interpreted. Three case studies of different sedimentary environments, previously analyzed with traditional fieldwork techniques, were selected and re-analyzed. For each case study the objective was to resolve quantitative questions that were not possible to determine without the use of VO or DTMs. Questions include: (i) geometrical restoration of a growth strata succession associated with thrust systems; (ii) stacking patterns of littoral ridges during a relative sea-level fall after the Holocene climatic optimum; and (iii) quantification of lake level fall during the past 44 years of a closed lake basin. The results of the work show that the technique has significant application in the analysis of sedimentary systems. However, since geological interpretations depend on the quality of the models that are generated, planning and construction of the VO or DEMs along with their validation are essential to ensure reliable results. • The effectiveness of SfM-MVS in sedimentary and basin analyses is discussed. • Focus is on the appropriated workflow strategy to construct SfM Virtual Outcrops. • The study include analysis of growth strata, littoral ridges and lake shorelines. • Validation of SfM Virtual Outcrops is essential to ensure reliable results. [ABSTRACT FROM AUTHOR]