Alluvial fan–lacustrine association in the fault tip end of a half-graben, northern Triassic Cuyo basin, western Argentina

The Triassic deposits of Cerro Puntudo in the San Juan province of western Argentina constitute the northernmost exposures of the northern portion of the nonmarine Cuyo rift basin, also known as the Las Peñas-Tamberías half-graben. The local column, with an exposed thickness of approximately 400 m, consists of abundant basal and topmost coarse alluvial fan conglomerates and breccias (facies associations I and II) and a relatively thin (approximately 50 m) intervening sequence of marginal, shallow lacustrine deposits characterized by stromatolitic (domal) limestones, tuffaceous mudstones, and fine-grained sandstones (facies association III). Subaerial exposure in the lacustrine deposits is evidenced by desiccation cracks and brecciation. A very thin (0–6 m), laterally, discontinuous succession of lacustrine deposits with similar characteristics is interbedded with the basal conglomerates. Laterally, this lacustrine interval was eroded by overlying conglomerates. The basal conglomerates commonly show crude normal grading, faint cross-bedding, and b-axis clast imbrication. The predominance of coarse deposits and paleocurrents from NW to SE, indicative of an axial flow pattern, suggest that these exposures correspond to the northern end of the Cuyo basin, which is characterized by a shallow, alluvial fan-encased, carbonate-rich lake margin. This lacustrine interval can be correlated with the thicker lacustrine section exposed to the south at Quebrada del Tigre and Ciénaga Larga along the border fault margin of a nonmarine half-graben. The correlation with these sections suggests that the Cerro Puntudo lacustrine deposits are the shallowest equivalent of more profundal, organic-rich lacustrine sediments exposed in the deepest segment of the border fault margin. These thickness and facies variations are the result of differential subsidence along the border fault margin between the low accommodation, fault tip end represented by the Cerro Puntudo section and the high accommodation, central segment located to the south.     

Speciation of dissolved copper and cadmium in the Loire estuary and over the North Biscay continental shelf in spring

Dissolved cadmium and copper species were measured in the Loire estuary and the North Biscay Bay continental shelf (France) in spring 2002. Metal behaviours along the salinity gradient, metal fluxes from the Loire system and surface distributions on the continental shelf were described and compared with the ones obtained at a period of higher discharge (i.e., winter 2001). Vertical distributions at different stations were also examined with the aim to assess whether the Loire inputs affect the Cu and Cd speciation over the continental shelf. In the Loire estuary, different metal behaviours were observed from winter. Cu and its various species mostly followed a theoretical dilution line whereas a Cd addition composed of chloro- and organic complexes was observed. According to our estimations, the Cu flux was composed, as in winter, of 40% hydrophobic organic complexes. On the other hand, Cd organic complexes accounted for less in the total dissolved metal flux than they did in winter (55 and 78% for spring and winter, respectively). On the continental shelf, a C₁₈Cu-to-TDCu ratio of 40% was observed in the stratified area under Loire influence. For Cd, the organic fraction was relatively important in the surface waters near the mouth of the estuary and decreased deeper and seaward. Thus, the Cu and Cd speciation on the North Biscay Bay continental shelf are firstly determined by the extent of the estuarine plume. Beyond the estuarine influence, biological processes appeared to be the origin of the observed variations.     

Unexpected records of ‘deep‐sea’ carnivorous sponges Asbestopluma hypogea in the shallow NE Atlantic shed light on new conservation issues

Marine cave communities have been a continued source of ecological surprises, among other things because of their close ecological and evolutionary ties with the deep sea. The discovery of cladorhizid sponges, the deepest occurring poriferan family, in shallow Mediterranean caves in the 1990s was one such surprise, leading to the generally accepted hypothesis that the whole family was carnivorous, an unprecedented feeding mode for sponges. The recent observation of the cave species Asbestopluma hypogea in the Mediterranean bathyal, confirmed the view that some shallow caves can occasionally shelter otherwise deep‐dwelling species. Here we present new distribution data of A. hypogea, from deep Mediterranean locations, and for the first time from Atlantic locations. Among the new Atlantic records, the most surprising ones are located in three different geographic areas (Ria de Arousa, Groix Island and Cherbourg) of the NW European coasts, from the Iberian Peninsula to the English Channel, where A. hypogea reaches SCUBA depths (5–50 m), while not sheltered in marine caves. The carnivorous sponge however reaches its shallowest occurrence (5 m), in a small cave at Groix Island. The ecological significance of these discoveries, particularly the very patchy distribution and peculiar dynamics, are noteworthy, and the shallow occurrence of A. hypogea, together with other deep‐water or uncommon species, constitute unique assemblages that must be considered in conservation plans.     

Boulder deposition during major tsunami events

A remarkable accumulation of marine boulders located above the present spring tide level has occurred in two coastal lowlands of the Algarve (Portugal). The size‐interval of the particles studied here is seldom reported in the literature in association with extreme events of coastal inundation, thus making this study of relevance to many other coasts worldwide. The spreads of boulders extend several hundred meters inland and well beyond the present landward limit of storm activity. The marine origin of the boulders is demonstrated by well‐developed macro‐bioerosion sculpturing and in situ skeletal remains of endolithic shallow marine bivalves. The good state preservation of the fossils within the boulders indicates that abrasion during transport and redeposition was not significant. We envisage boulder deposition as having taken place during the Lisbon tsunami of ad 1755 through the simultaneous landward entrainment of coarse particles from nearshore followed by rapid shoreward suspended‐dominated transport and non‐graded redeposition that excluded significant sorting by weight or boulder dimensions. We use numerical hydrodynamic modeling of tsunami (and storm) waves to test the observational data on boulder dimensions (density, size, distribution) on the most likely processes of sediment deposition. This work demonstrates the effectiveness of the study of boulder deposits in tsunami reconstruction. Copyright © 2011 John Wiley & Sons, Ltd.     

Non-explosive magma–water interaction in a continental setting: Miocene examples from the Eastern Cordillera (central Andes; NW Argentina)

The Middle-Upper Miocene Las Burras–Almagro-El Toro (BAT) igneous complex within the Eastern Cordillera of the central Andes (∼24°S; NW Argentina) has revealed evidence of non-explosive interaction of andesitic magma with water or wet clastic sediments in a continental setting, including peperite generation. We describe and interpret lithofacies and emplacement mechanisms in three case studies. The Las Cuevas member (11.8 Ma) comprises facies related to: (i) andesite extruded in a subaqueous setting and generating lobe-hyaloclastite lava; and (ii) marginal parts of subaerial andesite lava dome(s) in contact with surface water, comprising fluidal lava lobes, hyaloclastite, and juvenile clasts with glassy rims. The Lampazar member (7.8 Ma) is represented by a syn-volcanic andesite intrusion and related peperite that formed within unconsolidated, water-saturated, coarse-grained volcaniclastic conglomerate and breccia. The andesite intrusion is finger-shaped and grades into intrusive pillows. Pillows are up to 2 m wide, tightly packed near the intrusion fingers, and gradually become dispersed in the host sediment ≥50 m from the parent intrusion. The Almagro A member (7.2 Ma) shows evidence of mingling between water-saturated, coarse-grained, volcaniclastic alluvial breccia and intruding andesite magma. The resulting intrusive pillows are characterized by ellipsoidal and tubular shape and concentric structure. The high-level penetration of magma in this coarse sediment was unconfined and irregular. Magma was detached in apophyses and lobes with sharp contacts and fluidal shapes, and without quench fragmentation and formation of a hyaloclastite envelope. The presence of peperite and magma–water contact facies in the BAT volcanic sequence indicates the possible availability of water in the system between 11–7 Ma and suggests a depositional setting in this part of the foreland basin of the central Andes characterized by an overall topographically low coastal floodplain that included extensive wetlands.     

The importance of and need for rapid hydrologic assessments in Latin America

Long‐term observations are critical in hydrology to understand the dynamics of biological and physicochemical processes involved in and affected by the flux of water. Long‐term observations have been employed to provide basic understanding of the water cycle (e.g., infiltration, evaporation, run‐off generation, and groundwater–surface water interactions), but they are lacking in hydrologically relevant regions such as the Andes Mountains, including alpine watersheds. Although the call for long‐term data acquisition in Latin America has been made, the establishment of long‐term data collection centres remains logistically challenging. This ever‐growing scientific gap hinders our understanding of differences and similarities in hydrological processes of tropical and temperate regions. Furthermore, technological advances such as in situ optical sensors for water quantity and quality remain cost‐prohibitive for both short and long deployment at most existing research sites in Latin America, restricting researchers pursuing research funding or developing meaningful, intersite comparisons and syntheses. Here, we emphasize the importance of and need for rapid assessments (i.e., field campaigns conducted over a few days) for improved hypothesis development and mechanistic understanding of hydrological dynamics in Latin America. We report on rapid assessments conducted in the high‐elevation mountains (>3,000 m) of Colombia. Our results highlight rapidly changing dynamics in nutrient retention potential and dissolved CO₂ (pCO₂), as well as highly variable spatial distribution of water quality parameters (N, C, P, Cl) in areas with varying land use. We present an initial examination of the effects of land‐use change on stream nutrient dynamics in one of the most biodiverse and threatened ecosystems on Earth. We conclude that rapid assessments not only are necessary but also represent a cost‐effective way to develop clear, testable hypotheses to advance a hydrologic research agenda in Latin America and work towards long‐term hydrological knowledge and information for use by other scientists.