The mystery of the shells at the river bank

Hi, nice to meet you! My name is Magnita. A few days ago, I was taking a walk along Samborombón Bay. It’s a beautiful place in Argentina (Fig. 1), there are many canals and rivers that empty into the Atlantic Ocean. When I was walking, I looked at the river bank, and something surprised me. In the sediment, I could see a line of marine shells. Wow! That was surprising because I wasn’t anywhere near the sea! I wondered: how did these shells get here? Do you know what could have happened? I had no idea.Fil: Ballesteros Prada, Angélica María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentin

Evolución paleoambiental de la zona central de la Bahía Samborombón en el Holoceno a partir del análisis de foraminíferos bentónicos

La Bahía Samborombón está ubicada sobre el sector oriental de la cuenca sedimentaria de la depresión del Salado, provincia de Buenos Aires. Esta zona se caracteriza por el afloramiento de secuencias sedimentarias de origen continental, con intercalación de depósitos de origen marino de edades pleistocenas y holocenas, las cuales se relacionan con eventos transgresivos y regresivos generados por las variaciones eustáticas del nivel del mar. Con el objetivo de reconstruir con mayor detalle los cambios paleoambientales ocurridos en la zona central de la Bahía Samborombón, específicamente entre los 57°O y los 35°S, se realizó un análisis micropaleontológico a partir de la composición de foraminíferos bentónicos en tres perfiles localizados en una transecta perpendicular al margen costero de la bahía Samborombón.Centro de Estudios Integrales de la Dinámica Exógen

FIGURE 5 in Study of marsh foraminifera from the coastal plain of Buenos Aires (Argentina) and its ecological implications

FIGURE 5. Proportions of specimens from taphonomic analysis categorized according to one of three preservation groups for each station: A) well preserved shells, lacking at the most the last chambers; B) "black" shells with chamber fillings and/or with a polished coating in shades of black and dark brown and C) broken and fractured shells; elevation and type of sediment (% sand and clay).Published as part of Prada, Angélica Ballesteros & Bernasconi, Emiliana, 2019, Study of marsh foraminifera from the coastal plain of Buenos Aires (Argentina) and its ecological implications, pp. 522-540 in Zootaxa 4560 (3) on page 532, DOI: 10.11646/zootaxa.4560.3.5, http://zenodo.org/record/399347

Study of marsh foraminifera from the coastal plain of Buenos Aires (Argentina) and its ecological implications

The objective of this work was determinate the diversity and abundance of benthic foraminifers from recent sediments of Channel 15, Samborombón Bay (35º57´–35º58´S and 57º25´–57º22´W). From this analysis, we identified 31 species grouped within 17 genera. The assemblages were composed mainly of hyaline and agglutinated forms characterized by Elphidium aff. poeyanum, Elphidium gunteri, Ammonia parkinsoniana, Arenoparella mexicana and Trochammina inflata, reflecting an environment of marsh or floodplain. The foraminifer’s tests were generally well preserved, with morphologies that indicate predominantly epifauna and epifauna-infauna. The present work shows that despite having a general fauna characteristic of these environments, there are small microenvironments that are characterized by the state of preservation, diversity and abundance of the found specimens. In that context, three associations were recognized; A, dominated by Astrononion sp.1 that was registered in the central part of the channel; association B, characterized mainly by E. aff. poeyanum that was founded in the internal and external areas of the channel and association C, characterized by a considerable increase of mentioned agglutinated species (close to 50%) registered in the center of the channel. This study represents one of the first contributions on the distribution of foraminifera and their ecological characteristics from recent sediments in Samborombón Bay.Fil: Ballesteros Prada, Angélica María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Bernasconi, Emiliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentin

Foraminiferal paleodiversity and paleoenvironments at the NE coastal plain of Buenos Aires province (Argentina) during the Mid-Holocene sea level highstand

In this investigation, we carried out a Mid-Holocene paleoenvironmental reconstruction based on fossilized benthic foraminifera, retrieved from sedimentary deposits located in Bahía Samborombón coastal plain. A total of 38 species, grouped into 19 genera, were identified. The assemblage, constituted mainly by Buccella peruviana (d’Orbigny), Cribroelphidium poeyanum (d’Orbigny), Ammonia parkinsoniana (d’Orbigny) and Ammonia tepida (Cushman), indicate predominantly abnormal marine conditions, characterized by low oxygen levels between ca. 6880–6640 and 5600–5430 yrs cal. BP. During this interval, a quantitative analysis carried out on the assemblages as well as indexes suggest found three different paleoenvironments. The first one, occurring ca. 6880–6640 yrs cal. BP, was a brackish environment with low oxygenation levels and low bottom energy. Then, ca. 6500–6250 yrs cal. BP, an environment with more marine influence, increased oxygen levels and higher energy prevailed. This higher oxygenation could be related to the flow of seawater into the area during the Mid-Holocene sea-level highstand. The third paleoenvironment developed ca. 5590–5430 yrs cal. BP, was under a gradual transition back to a brackish environment with low oxygen levels as well as low energy.Fil: Ballesteros Prada, Angélica María. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Patagonia Norte. Instituto de Investigaciones En Biodiversidad y Medioambiente. Subsede San Martín de Los Andes-inibioma | Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Instituto de Investigaciones En Biodiversidad y Medioambiente. Subsede San Martín de Los Andes-inibioma.; ArgentinaFil: Luengo, Mariel Samanta. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Geología Aplicada; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Vilanova, Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Fucks, Enrique Eduardo. Universidad Nacional de La Plata; ArgentinaFil: Bernasconi, Emiliana. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Patagonia Norte. Instituto de Investigaciones En Biodiversidad y Medioambiente. Subsede San Martín de Los Andes-inibioma | Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Instituto de Investigaciones En Biodiversidad y Medioambiente. Subsede San Martín de Los Andes-inibioma.; Argentin

Environmental changes related to the Holocene sea-level transgression and successive highstand (7–5.5 Kyr) at the NE coastal plain of Buenos Aires (Argentina)

We present a high resolution multi-proxy study about environmental changes that occurred during the Holocene sea-level transgression and successive highstand (7–5.5 Kyr) in the central zone of Bahía Samborombón (∼35.6° S), Argentina. This study, one of the first in the area that integrates geomorphological and paleontological proxy data (pollen, non-pollen palynomorphs, foraminifera and mollusk shells), and focusing on a short time interval, offers the advantage of recognizing environmental and vegetation changes in a more comprehensive way. The aim of this work is to reconstruct the salt marsh vegetation history and paleoenvironmental changes; and to develop a model of the geomorphological evolution during the mid-Holocene sea-level transgressive phase. Between 6700 cal yr BP and 6500 cal yr BP, several rapid environmental changes took place. Those changes affected vegetation and microfauna, as well as the geomorphological features. During this period, middle to high salt marsh vegetation developed in an extensive and open tidal plain, where wide and long paleo tidal channels were flowing. Between 6500 and 6220 cal yr BP, the salt marsh transitioned into low salt marsh one as a response to a continued rise in sea level, resulting in the landward transgression of the coastline. The relative sea level reached the highstand between 6220 and 5500 cal yr BP and, consequently, extensive inundation of the coastal plain took place, except for the elevated areas such lunettes and ridges. After 5500 cal yr BP, seaward prograding beach and sand ridges formed in response to the onset of a regressive phase. Since then, the ancient tidal plain, extending ∼10 km from the present coastline, has been subjected to aeolian and pedogenetic processes.Fil: Luengo, Mariel Samanta. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios Integrales de la Dinámica Exógeno; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Ballesteros Prada, Angélica María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Vilanova, Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Bernasconi, Emiliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Fucks, Enrique Eduardo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios Integrales de la Dinámica Exógeno; Argentin