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    ABSTRACT: This study focuses of sedimentary structures formed by microbial consortia, in a particular coastal setting, an ancient tidal channel, separated from the ocean by a sandy spit and connected by a blind tidal channel at the opposite end. Most studies in modern and ancient environments consider water movement as the triggering mechanism acting in the formation and deformation of sedimentary structures. As such, the paper documents the presence of several microbial structures such as shrinkage cracks, flip-over mats, microbial chips and multidirectional ripples which are related to tidal processes, while bulges and gas domes structures are formed after occasional inundation events. However, the more conspicuous structures covering a great area at the study site are folds and roll-ups, the product of deformation of microbially-induced structures by the action of sporadic spring-tidal currents due to strong winds. Therefore, the objective of this research is to document modern sedimentary structures in a coastal area and to provide a mechanistic explanation for their formation, based on the interplaying effects of the moisture variation and high shear-stress. Also, several microbial sedimentary structures are distinguished throughout vertical sediment cores, such as microbial chips, detached mat, sponge fabrics, tears and concentric structures, which are identified in a sedimentary profile. Through the recognition and interpretation of modern sedimentary deformation structures, this study contributes empirical tools for the reconstruction of analogous paleoenvironments in fossil studies.
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    ABSTRACT: The aim of this work is to assess the physicochemical conditions of the supratidal sediments colonized by microbial mats at two sites from Rosales Harbor (Bahía Blanca Estuary, Argentina) close to sewage discharge. Both sites differed in the size grain. No differences in pH, Eh and temperature were observed. Moisture retention and chlorophyll a concentration were significantly different between sites and sediment layers. Heavy metals and organic matter content were significantly higher in SII. No statistical differences were found in porewater nutrients concentration, being higher in SI (except DSi). The presence of Escherichia coli in water and sediment (1000 CFU/100 mL – uncountable and 35–40 CFU g−1 dw, respectively) evidenced microbial contamination in the study area. The relationships between the physicochemical parameters evaluated and the influence of the sewage discharge allow defining two different areas in the Rosales Harbor despite the proximity and the presence of microbial mats.
    Marine Pollution Bulletin 02/2015; 91(2). DOI:10.1016/j.marpolbul.2014.10.008 · 2.79 Impact Factor
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    ABSTRACT: Microbial mats in coastal environments play an important role in both stabilizing the sediment and preserving sedimentary structures. They represent the first biological systems that appeared on Earth, even forming large fossils in carbonate settings known as stromatolites. However, microbial mats have also been recognized for siliciclastic environments as sandy mat structures. In particular, mats are the primary element of the so-called Microbially-Induced Sedimentary Structures (MISS) and their various types represent very useful proxies for the interpretation of the environmental conditions in which they were formed. The objectives of this paper are twofold. The first is to provide a general background review of microbial mats in tidal flats, including their evolution, structure, and morphology. The second objective is to provide a modern case study in which we examine the role of storms relative to day-to-day tidal currents. Although tidal currents could be an important eroding factor, we demonstrate that waves, no matter their magnitude, play a significant role in developing different types of MISS such as wrinkle structures and eroding mats into flipped-over fragments. Furthermore, we also show the significance of wave-induced pressure onto groundwater in forming other types of MISS as Kinneya structures and petee ridges. Knowing the environmental conditions to which present-day microbial mats are subject and how they evolve upon drastic changes in those conditions (i.e., storm events), represent an important basis for the interpretation of fossil MISS.
    Marine Geology 06/2014; 352:367–380. DOI:10.1016/j.margeo.2013.10.002 · 2.20 Impact Factor
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    ABSTRACT: RESUMEN El estudio de matas microbianas en ambientes marinos costeros silicoclásticos actuales constituye una importante fuente de información para el análisis de análogos fósiles. En el estuario de Bahía Blanca se estudiaron planicies de marea cubiertas por matas desde un enfoque geobiológico, con el objetivo de identificar y describir estructuras inducidas por actividad microbiana (ESIAM), y distinguir rasgos presentes en los sistemas actuales que permitan reconocer estas comunidades de microorganis-mos en depósitos fósiles. Se realizaron muestreos biológicos y sedimentológicos, y se implementaron técnicas de microscopía óptica y electrónica para la determinación de microorganismos y la identificación de texturas características y minerales auti-génicos. Las matas microbianas resultaron estar dominadas por cianobacterias y, en menor proporción, diatomeas; microorga-nismos que generan sustancias exopoliméricas que bioestabilizan la superficie sedimentaria. Se reconocieron texturas típicas de matas epibentónicas, tales como granos orientados y granos pequeños unidos por la mata, pirita framboidal y ceolitas. En la zona intermareal-supramareal se identificaron domos de gas, fábrica porosa esponjosa y superficies tipo colador. Además se observaron grietas de contracción, dobleces, fragmentos de mata, depresiones y remanentes erosivos, pliegues y arrugas, así como también ondulitas multidireccionales. Las estructuras halladas están relacionadas con condiciones de calma/latencia, exposición prolongada (desecación) y eventos de tormenta con alta energía erosiva sobre la planicie (olas y corrientes fuertes). En este sentido, las ESIAM resultan importantes indicadoras de condiciones ambientales particulares que presentan un elevado potencial de preservación. Su reconocimiento en el registro fósil, a través de rasgos macro y microscópicos, permiten refinar las interpretaciones paleoambientales en sucesiones marino-costeras. ABSTRACT Microbially-induced sedimentary structures (MISS) in the Puerto Rosales tidal flat, Bahía Blanca estuary The study of microbial mats in modern siliciclastic coastal marine settings represents an important analogue for the analysis of fossil deposits in similar paleoenvironments. In the Bahía Blanca estuary, mat-covered tidal flats were studied from a geobiological perspective with the aims of identifying and describing microbially-induced sedimentary structures (MISS), and to distinguish features in modern systems that allow the recognition of such microbial communities in fossil deposits. Systematic biological and sedimentological samplings were carried out, and the identification of microorganisms and the recognition and characterization of typical textures and authigenic minerals were performed through light and electronic microscopy techniques. Microbial mats were dominated by cyanobateria, followed by diatoms; both groups of microorganisms are known to secrete extracellular polymeric substances (EPS) and biostabilize the sedimentary surface. Characteristic textures of epibenthic mats, such as oriented grains and mat-bound small grains, framboidal pyrite and zeolites were recognized. In the intertidal-supratidal zone, MISS termed gas domes, sponge pore fabric, and sieve-like surfaces were identified. Moreover, shrinkage cracks, flip-overs, mat chips, erosional remnants and pockets, folds, as well as multidirected ripple marks were observed. These structures are related to calm conditions/latencies, prolonged subaerial exposure (desiccation), and storm events with high hydrodynamic energy (erosive) acting over the tidal flat (e.g. waves and currents). In this sense, MISS constitute important indicators of specific environmental conditions and thus their recognition in the rock record allows a refined interpretation of the paleoenvironment in coastal marine successions.
    Revista de la Asociacion Geologica Argentina 01/2014; 71(3):331-344.
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    ABSTRACT: One of the aims of tidal sedimentology in recent years is to find signatures in the stratigraphic record that help in recognizing basic ancient tidal processes. The present study was carried out on the supratidal zone of the middle Bahía Blanca estuary which is colonized by extensive microbial mats. The purpose of the study was to relate the tidal and wave energy with the microbially-induced sedimentary structures (MISS) present in the tidal flat. The energy reaching the area was quantified by tidal and wave records, while MISS were simultaneously recognized and described after a strong storm event. The MISS and the microsequences of sediments in vertical cross-sections of the tidal flat were considered as tidal signatures over a supratidal zone, when high-tide in severe energy conditions can reach the zone. This paper contributes to the understanding of physical sedimentary parameters that control the modification of microbial structures in modern siliciclastic regimes and that, in turn, can aid in the reconstruction of ancient hydraulic settings.
    Sedimentary Geology 10/2013; 296:1–8. DOI:10.1016/j.sedgeo.2013.07.006 · 2.13 Impact Factor
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    ABSTRACT: Biofilms and microbial mats cover the tidal flats of the central zone of the Bahía Blanca estuary (Argentina), creating extensive layers. The objective of this study was to characterize the microphytobenthic communities in these biofilms and mats from sediment cores taken in March, June, September and December 2010. Microorganisms were identified and enumerated by microscopy, and their biomass (chlorophyll a, biovolume) quantified at two different stations in the lower supratidal zone, located ∼210 m apart from each other (namely S1 and S2). Additionally, the colloidal carbohydrates produced by these microbial communities were quantified, together with physical parameters such as temperature, granulometry, moisture and organic matter content of the sediment layers that comprise a typical epibenthic mat. On the other hand, changes in biomass and colloidal carbohydrate content were studied through a half-tidal cycle (7 h). There were significant seasonal differences in microphytobenthic biovolume (P Microcoleus chthonoplastes) was dominant on all dates at both stations, followed by pennate diatoms. Chlorophyll a and colloidal carbohydrate contents in sediment presented a similar pattern to that of microalgal biovolume; with a 5-fold variation in chlorophyll a for S1 between consecutive sampling events on September and December. There were significant differences between sampling dates in colloidal carbohydrates (P a contents did not show significant differences throughout a half-tidal cycle, likely the product of vertical migration along the section sampled. Conversely, the content of colloidal carbohydrates varied 5-fold, showing a significant (P Keywords: biofilms; cyanobacteria; diatoms; microbial mats; microphytobenthos; tidal flat Document Type: Research Article DOI: http://dx.doi.org/10.1080/01490451.2012.757998 Affiliations: 1: Estación Costera “J. J. Nágera, ” Depto. de Ciencias Marinas, Universidad Nacional de Mar del Plata, Buenos Aires, Argentina 2: Instituto Argentino de Oceanografía (IADO). CONICET, Bahia Blanca, Buenos Aires, Argentina 3: Instituto de Investigación en Paleobiología y Geología, Universidad Nacional de Río Negro/CONICET, General Roca, Río Negro, Argentina Publication date: September 14, 2013 More about this publication? Information for Authors Subscribe to this Title ingentaconnect is not responsible for the content or availability of external websites $(document).ready(function() { var shortdescription = $(".originaldescription").text().replace(/\\&/g, '&').replace(/\\, '<').replace(/\\>/g, '>').replace(/\\t/g, ' ').replace(/\\n/g, ''); if (shortdescription.length > 350){ shortdescription = "" + shortdescription.substring(0,250) + "... more"; } $(".descriptionitem").prepend(shortdescription); $(".shortdescription a").click(function() { $(".shortdescription").hide(); $(".originaldescription").slideDown(); return false; }); }); Related content In this: publication By this: publisher In this Subject: Microbiology By this author: Pan, Jerónimo ; Bournod, Constanza N. ; Pizani, Natalia V. ; Cuadrado, Diana G. ; Carmona, Noelia B. GA_googleFillSlot("Horizontal_banner_bottom");
    Geomicrobiology 09/2013; 30(8). DOI:10.1080/01490451.2012.757998 · 1.80 Impact Factor
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    Diana G. Cuadrado
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    ABSTRACT: The goal of this study was to analyze microbial mats and biofilms from the lower supratidal area of the Bahía Blanca estuary (Argentina), and explore their relationship with sediments and other physical forcings. Thirteen monthly sediment samples (uppermost 10 mm) were taken and their composition and abundance in microorganisms was determined by microscopy. Physical parameters (solar radiation and sediment temperature at −5 cm) were recorded with a frequency of 5 minutes by a coastal environmental monitoring station. Additionally, sediment grain size and moisture content were determined for distinct layers in the uppermost 20 mm, and the rate of inundation of the supratidal area was estimated from tidal gauge measurements. There were significant seasonal differences in the biomass of the microphytobenthic groups considered (filamentous cyanobacteria and epipelic diatoms), with the former consistently making up >70% of the total biomass. The relationships between microphytobenthos and sediment temperature and solar radiation fitted to linear regressions, and consistently showed an inverse relationship between microphytobenthic abundance and either one of the physical parameters. The granulometric analysis revealed a unimodal composition of muddy sediments, which were vertically and spatially homogeneous; additionally, there were significant seasonal differences in water content loss with drying conditions prevailing in the summer. Several Microbially-Induced Sedimentary Structures (MISS) were identified in the supratidal zone such as shrinkage cracks, erosional pockets, gas domes, photosynthetic domes, mat chips and sieve-like surfaces. In contrast to studies from analogous environments in the Northern Hemisphere, we found reduced microphytobenthic biomass in summer, which were explained by increased evaporation/desiccation rates as a consequence of increased radiation, despite frequent tidal inundation. In conclusion, the observed density shifts in the benthic microbial communities are attributable to physical forcings dependent upon seasonal variations in interplaying factors such as sediment temperature, solar radiation and tidal inundation.
    International Journal of Geosciences 01/2013; 4:352-361. · 0.26 Impact Factor
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    ABSTRACT: The preservation and cementation of sedimentary structures under the influence of microorganisms in siliciclastic environments have been poorly studied in contrast to carbonatic settings, where they have been extensively investigated. Whereas in carbonatic environments, microbial mat-induced precipitation of calcium carbonate results in a cementation process producing a quick lithification, in siliciclastic environments other minerals would act as cement. The focus of this paper is to document the presence of authigenic minerals within a biosedimentary fabrics and the possible link of these minerals with the extensive microbial mats that colonize the tidal flat of the temperate Bahía Blanca estuary. “Anoxic” minerals (e.g. pyrite) and authigenic zeolites such as analcime, clinoptilolite, mordenite, phillipsite and chabazite were recognized through SEM and EDX analyses. These minerals were most likely formed by alteration of volcanic ash, which is present in this tidal flat and also silica may result from dissolution of frustules of benthic diatoms. Minerals precipitated in this setting are significant as they would act as early cement in the eogenesis, enhancing the preservation of sedimentary and biogenic structures.
    Sedimentary Geology 10/2012; s 271–272:58–66. DOI:10.1016/j.sedgeo.2012.06.005 · 2.13 Impact Factor
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    ABSTRACT: Microbially induced sedimentary structures (MISS) result from the interaction between benthic microorganisms and sediments; MISS preferably form in upper intertidal to supratidal settings from the Archean to the modern. The identification of MISS in Neogene deposits of the Rio Negro Formation (Late Miocene to Pliocene), Rio Negro Province, Argentina, covering the transition from continental to marine facies (and vice versa), provides the base to refine the paleoenvironmental interpretation. The overall clastic paleocoast was differentiated into high-energy erosional domains and protected areas where MISS became preserved. However, during peak transgression also the initially protected areas experienced high energy sediment reworking. Because of the extent erosion in the high-energy coastal setting, the localized occurrence of tidal-flat deposits was difficult to recognize. The thin tidal flat deposits exhibit macroscopic and microscopic features that can be attributed to the interaction between microorganisms and sediment, such as cracks with upturned margins, sponge pore fabric, wrinkle structures, multidirected ripple marks, floating sand grains and so on. In addition, the biostabilization processes typical of substrates housing microbial mats led to the excellent preservation of vertebrate footprints that characterize these deposits.
    Palaeogeography Palaeoclimatology Palaeoecology 10/2012; s 353–355:1–9. DOI:10.1016/j.palaeo.2012.06.021 · 2.75 Impact Factor
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    Diana G Cuadrado, Eduardo A Gómez
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    ABSTRACT: RESUMEN. Se estudió la morfología de un campo de dunas submarinas desarrollado en una entrada de marea que conecta la plataforma continental argentina con bahía Anegada (sur de la provincia de Buenos Aires). Se infiere la circulación sedimentaria a partir del desplazamiento diferencial de las geoformas medido en relevamientos consecutivos. Como parte de la metodología se utilizó un ecosonda y un sistema batimétrico por medición de fase (SBMF) denominado GeoSwath que permitieron obtener la morfología submarina en detalle. Se observaron dunas grandes sobre el límite sur del campo de dunas con altura entre 4,5 y 5,0 m y espaciamiento entre 100 y 120 m, a profundidades de 24 m, que se desplazan hacia el exterior del canal a una rapidez entre 18 y 75 m año -1 . Hacia el límite norte del campo, a 21 m de profundidad las dunas eran de menor magnitud, entre 2,0 y 2,5 m de altura y espaciamiento entre 40 y 80 m, y se desplazaron a una rapidez entre 18 y 36 m año -1 hacia el interior de bahía Anegada. Se obtuvo la distribución del flujo de agua en toda la columna, en un perfil perpendicular al canal relevado, mediante ADCP. Los valores máximos de rapidez de corriente fueron durante la marea creciente, alcanzando 2,0 m s -1 . Los resultados obtenidos permiten definir un modelo circulatorio de transporte de sedimentos arenosos, con la formación de un delta de marea de flujo en la cabecera de la entrada de marea y un delta de reflujo en el límite del dominio oceánico, unidos por una garganta de marea profunda, exenta de sedimentos inconsolidados. Palabras clave: campo de dunas, velocidad de migración, transporte de sedimentos, GeoSwath, ADCP, Argentina.
    Latin American Journal of Aquatic Research 03/2012; 40(1):42-52. DOI:10.3856/vol40-issue1-fulltext-5 · 0.42 Impact Factor
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    Diana G. Cuadrado, Eduardo A. Gómez
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    ABSTRACT: A tidal inlet on the Argentinean coast is studied. An integrated approach of combining detailed bathymetry survey, seabed sampling and tidal current measurements was used to characterize the tidal inlet morphodynamics. A Phase Measuring Bathymetric System (PMBS) "GeoSwath Plus" from GeoAcoustics Ltd. with centimetric precision and a mean swath coverage of 160 m, was used to recognize bedform morphologies and to determine bedform dynamics by comparison of successive surveys . Tidal velocities were recorded during a complete tidal cycle using an ADCP mounted on a ship operating at a frequency of 650 kHz. Maximum tidal currents, of the order of 2 m s- 1, exhibit different patterns across the channel. While maximum ebb currents dominate in the central and southern area of the channel, flood maximum currents dominate on the northern flank. The complex morphology of a dune field in an inlet and the resulting 3-D dune movement mechanism are also presented. In the middle of San Blas channel, a field with symmetrical large dunes (10-100 m in spacing) and very large dunes (> 100 m in spacing) 4.5 to 5 m in height was found. Dune migration rates were measured by comparing two successive morphological maps of the field, reaching a rate up to 21 m year- 1 toward the ocean. In contrast, the smaller dunes present on the northern border of the field migrate in an inward direction at a rate of 15.7 m year- 1.
    Geomorphology 12/2011; 135:203-211. DOI:10.1016/j.geomorph.2011.06.038 · 2.79 Impact Factor
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    Débora Beigt, Diana G. Cuadrado, María C. Piccolo
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    ABSTRACT: This paper deals with the application of satellite images to study turbidity and water circulation patterns in San Blas channel during a theoretical tidal cycle. Eight Landsat TM and ETM images acquired under clear-sky conditions and representing different tidal stages were selected from a pool of Landsat images provided by the argentinean National Commission of Space Activities (CONAE) and the US Geological Survey. Standard digital image processing techniques were used to perform geometric and radiometric corrections on the visible and near-infrared bands. An image-based atmospheric correction (COST method by CHAVEZ, 1996) was applied. An ISODATA unsupervised classification was performed in order to identify different turbidity levels throughout the channel and adjacent areas. The results suggest that suspended sediment transport towards the channel mouth by ebb currents occurs along both flanks. These currents carry suspended sediment into the open sea, generating an ebb tidal delta which tends to rotate in a clockwise direction. Flood currents trigger turbidity mostly over the southern flank of the channel, generating a flood tidal delta with elongated banks extending in the direction of the tidal currents. From the elongated shape of the turbidity plumes, general tidal circulation patterns were identified. R E S U M O Este trabalho analisa a turbidez e a circulação da agua no canal San Blas durante um ciclo de maré teórico através de imagens satelitais. Foram utilizadas 8 imagens Landsat TM e ETM adquiridas em condições de céu claro e ao longo de diferentes momentos da maré. As imagens foram proporcionadas pela Comisión Nacional de Actividades Espaciales (CONAE) y pelo Serviço Geológico dos Estados Unidos (USGS). As correções geométricas e radiométricas foram realizadas nas bandas do espectro visível e do infravermelho próximo, utilizando técnicas padrões de processamento digital. Foi aplicada a correção atmosférica COST (CHAVEZ, 1996). Foi realizada uma classificação ISODATA não supervisionada para identificar diferentes níveis de turbidez al longo do canal e zonas adjacentes. Os resultados sugerem que o transporte de sedimento em suspensão para a boca do canal se da ao longo de ambos flancos, pela ação das correntes de refluxo. Estas correntes geram um delta de refluxo com uma tendência de rotação para a direção sul. As correntes de fluxo provocam turbidez principalmente sobre a costa sul do canal, gerando um delta de fluxo com bancos alargados na direção das correntes de maré. As plumas de turbidez permitiram identificar padrões gerais de circulação da maré.
    Brazilian Journal of Oceanography 09/2011; 59(3):241-252. DOI:10.1590/S1679-87592011000300004 · 0.53 Impact Factor
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    08/2011; 46(2):199-206. DOI:10.4067/S0718-19572011000200009
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    Diana G. Cuadrado, Noelia B. Carmona, Constanza Bournod
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    ABSTRACT: Extensive microbial mats have been found in the siliciclastic tidal flats of the temperate Bahía Blanca estuary in the Atlantic coast of Buenos Aires province, Argentina. Several microbially induced sedimentary structures (MISS) occur especially in the upper intertidal and lower supratidal flats, among which the most conspicuous are erosional pockets, gas domes, microbial mat chips, and polygonal oscillation cracks. Biostabilization processes by epibenthic and endobenthic mats are also analyzed. Endobenthic mats occur in the upper intertidal area stabilizing ripples that despite the occurrence of severe storms persist in a fixed position for at least 2 months. Epibenthic mats occurring in the lower supratidal area also protect the substrate forming a thick microbial cover through the studied period. This thick cover was only affected by a strong storm that formed areas with erosional pockets and mat pieces. Nevertheless, the loose sediment within the erosional pockets was quickly colonized by microorganisms that developed a thin biofilm layer after a week. Changes in sediment accumulation were also recorded all over the upper tidal flat during a year, showing an important increase due to bioturbation activities of crabs. This situation also affected microbial mat growth, which evolved from a thin microbial biofilm into a thick, stratified microbial mat community in almost 2 years, mainly in the lower supratidal areas. The results of this study not only help us to better characterize the complex interactions between the microorganisms forming microbial mats, the tidal-flat sediment and the physical parameters that control this setting, but also have important implications for the understanding of analogous fossil sedimentary successions.
    Sedimentary Geology 05/2011; 237:95-101. DOI:10.1016/j.sedgeo.2011.02.008 · 2.13 Impact Factor
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    ABSTRACT: The geochemistry, mineralogy, and grain size distribution of several estuarine cohesive sediment samples from potentially human-influenced areas without such an influence were analyzed to determine the natural heavy metal content and evaluate its impact on the Bahía Blanca estuarine environment. The data were compared with different ranges of concentrations for heavy metals in marine sediments established by the NOAA Screening Quick Reference Tables in which values range from background levels to those considered toxic to the marine environment. Our total heavy metal contents were below the established hazardous levels in all the analyzed samples, even though the potentially human-influenced areas (harbors, industry, urban spread) showed the highest total concentration values as well as greater percentages of bioavailable compounds. This would imply a low and not extensive anthropogenic input into the environment. The relatively high proportions in which Cd, Pb, and Cr appear as bioavailable compounds at some sites not influenced by human activity suggest the presence of a natural source for these elements. This could be attributed to the weathering of naturally occurring volcanic minerals, indicating that special care must be taken when monitoring of sediment for anthropogenic activity is carried out within this environment. According to the results obtained, and in order to minimize the environmental impact caused by periodic water injection dredging, relocation of sewage outfalls from vessel mooring areas into open waters is strongly recommended.
    Ocean Dynamics 01/2011; 61(2):285-293. DOI:10.1007/s10236-010-0354-7 · 1.68 Impact Factor
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    ABSTRACT: Field studies in a siliciclastic mesotidal flat in Bahia Blanca Estuary, Argentina, reveal the presence of extensive areas with microbial mats, covering the upper intertidal and lower supratidal areas. Study of recent environments with microbial mats has increased considerably in recent years, not only because of their unique sedimentologic and ecologic characteristics but also because they provide important implications for the understanding of fossil environments. The main purpose of this research was to evaluate the role of microbial mats in the preservation of biogenic structures.We recorded the distribution of recent biogenic structures all over the siliciclastic tidal flat, focusing the analysis on the preservation of bird tracks. Several footprints were selected and photographed; we recorded the morphologic modifications they experienced over the course of 10 months. This study revealed that most of the footprints showed resistance to tide and wind erosion and also to the heavy rains and storms that affected the tidal flat. This resistance is clearly associated with the presence of the microbial mats, which are known to biostabilize the sediment. In addition, microscopic analysis of the tidal-flat sediment revealed the presence of zeolites, indicating early cementation, which may have favored the consolidation of the footprints. Mat thickness also affected the morphology of the footprints; in areas with thick microbial mats overlying water-saturated sands, the tracks were deeply impressed and did not show fine details. On the contrary, in zones with thin microbial mats overlying relatively stiff muds, the traces were shallowand preserved details such as skin impressions and skid marks. Both types of footprints were affected by mat growth, although in the shallow traces the modification was faster and the fine details were progressively obliterated. This study yields valuable insight into the relationship between microbial mats and the morphology of the footprints and provides key information for the analysis of fossil tracks in equivalent paleoenvironments.
    SEPM Special Publication No. 101 01/2011; Society for Sedimentary Geology., ISBN: 978-1-56576-314-2
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    Eduardo A. Gómez, Diana G. Cuadrado, Jorge O. Pierini
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    ABSTRACT: By means of surveys carried out with a Phase Measuring Bathymetric System and current profiles obtained through an ADCP of the internal area of the Bahía Blanca estuary, a field of large dunes was analysed. There are two different and well-defined zones characterized by particular dune morphology and differing hydrodynamics. The reduction in the channel cross-section by a geological control leads to the increase in tidal current velocity, which together with the available sediment leads to the formation of Very Large Dunes (H > 4 m and L > 100 m) with the typical morphology of a limited amount of sediment overlying a rigid substrate. The migration rate of these dunes, between 65 and 130 m year− 1, decreases as the bedform height increases. Differing sediment transport rates across the channel result in a non-uniform migration rate, which is responsible for the formation of dunes with linear crests oblique to the tidal current direction. This fact indicates that determination of the sediment transport direction by using only large bedform orientation may be subject to a significant error.
    Geomorphology 09/2010; DOI:10.1016/j.geomorph.2010.04.022 · 2.79 Impact Factor
  • Diana G. Cuadrado, Eduardo A. Gómez
    07/2010; 17(1):3-16.
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    ABSTRACT: In order to reach a navigational depth of 45 feet during the entire tidal cycle, the most internal section of the Access Channel to the Bahía Blanca harbour complex will be shortly dredged. At the outer end of this section, an unusual field of large dunes occurs. Within this field, results show two different and well defined zones characterized by particular dunes morphology each and a differing hydrodynamic profile, with lateral and vertical variations in tidal currents velocity and direction. Dunes migration also shows differential migration rate depending on the bed form size. Differences in speed and direction of tidal currents between both channel sides are responsible for the dunes field formation. Such asymmetry is caused by the occurrence of hard to erode materials cropping out at both channel flanks which generate a narrowing of the channel southward and by the presence of a submarine bank northwards.
    01/2010;
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    Diana G. Cuadrado, Eduardo Alberto Gómez
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    ABSTRACT: The morphology of a submarine dune field developed in a tidal inlet that connects the Argentinean continental shelf with Anegada Bay (southern Buenos Aires province) was studied. The sediment circulation was inferred from the differential displacements of the bedforms evaluated by comparing consecutive surveys. An echosounder and a Phase Measuring Bathymetric System (PMBS) called GeoSwath were used to obtain a detailed submarine morphology. Large dunes, with heights between 4.5 and 5.0 m and from 100 to 120 m separating them, were present near the southern limit of the dune field at 24 m depth. These dunes move towards the outer part of the channel at a speed of 18 to 75 m year-1. At the northern end of the dune field, at 21 m depth, the dunes are smaller, being 2.0 to 2.5 m in height and separated by 40 to 80 m. The smaller dunes move towards the interior of Anegada Bay at 18 to 36 m year-1. The distribution of the water flow in the entire water column was obtained through a perpendicular profile of the channel by means of an ADCP. Maximum current speeds were 2 m s-1, and were found during flood tide. The results obtained indicate a circulatory transport model of sedimentary sands, with the formation of ebb and flood deltas at both ends of the deep inlet throat, which lacks of unconsolidated sediments.

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