Reconstruction of paleoenvironments and paleoclimate during the last and present interglacials over the Patagonian coast (Argentina), with particular reference to the shell geochemistry

The present study aims a better understating of the paleoceanographic, paleoclimatic and paleoenvironmental conditions of the Patagonia Atlantic coast in the in the vicinity of San Jorge Gulf (Chubut and Santa Cruz Provinces, Argentina) through the study of the geochemistry (stable isotopes and trace elements) of molluscs collected in the late Quaternary marine deposits. On the basis of XRD powder analysis, petrographic and trace element screening tests (comparison between marine shells and paleosols), a large dataset of unaltered bivalves with aragonite (Ameghinomya antiqua species) or mixed aragonite-calcite (Mytilus edulis and Aualcomya atra species) composition of the shells was identified. Analytical data definitively demonstrate the suitability of Ameghinomya antiqua and Mytilidae family specimens as potential proxies for paleoclimatic studies. Oxygen isotopic composition of modern Mytilus edulis in the study area is progressively more positive moving southward. The isotopic composition on modern mussels along the Atlantc coast of Patagonia seems to reflect the changes in seawater temperature. Stable isotope (13C/12C and 18O/16O ratios) and trace elements (Ba/Ca, Sr/Ca, Mg/Ca, Mn/Ca, Fe/Ca) data indicate large variability of modern condition in the gulf, but in the past too systematic differences between old beach ridges sets existed and can be interpreted as substantial different paleoceanographic conditions, partly related also to local mixing with freshwater. Paleontological and geochemical data indicate that the Holocene and the previous interglacial appear consistently different from the present. In particular they seem to contain molluscs indicating a stronger influence of the warm and saltier Brazil current in the area and, then, fluctuations in the relative position between the two surface currents (Brazilian and Malvinas) over the time

Geomorphologic Map of Northeastern Sector of San Jorge Gulf (Chubut, Argentina)

This paper presents a 1:100,000 scale geomorphologic map of the Northeastern sector of San Jorge Gulf (Chubut Province) in Patagonia, Argentina, covering more than 1,000 km 2. Derived from remote sensing data and validated by three field surveys, it has been compiled in order to understand the past and recent evolution of the area with particular reference to sea-level oscillation studies, for which this map is the basic tool. The very low human impact and rates of dynamic landscape change allow the preservation of extensive palaeo deposits and landforms, including those indicative of sea-level variations. The relative change of sea level dominates landscape evolution, allowing the formation of widespread marine and lagoon deposits often interfingering with fluvial deposits and reworked by aeolian process in the framework of consequent beach progradation.Facultad de Ciencias Naturales y Muse

Stable oxygen and carbon isotope composition of holocene mytilidae from the camarones coast (Chubut, argentina): Palaeoceanographic implications

The stable isotope composition of living and of Holocene Mytilidae shells was measured in the area of Camarones (Chubut, Argentina). The most striking results were the high δ18 O values measured in samples older than ca. 6.1 cal ka BP. In the younger samples, the δ18 O values remained substantially stable and similar to those of living specimens. Analysis of the data revealed the possibility for this isotopic shift to be driven mainly by changes in temperature probably accompanied by minor changes in salinity, suggesting cooler seawater before 6.1 cal ka BP, with a maximum possible temperature shift of ca. 5◦ C. A possible explanation of this change can be related to a northward position of the confluence zone of the Falkland and Brazilian currents. This is consistent with the data obtained in marine cores, which indicate a northerly position of the confluence in the first half of the Holocene. Our data are also in line with the changes in wind strength and position of the Southern Westerlies Wind, as reconstructed in terrestrial proxies from the Southernmost Patagonia region.Fil: Boretto, Gabriella Margherita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Zanchetta, Giovanni. Università degli Studi di Pisa; Italia. Istituto di Geologia Ambientale e Geoingegneria; Italia. Consiglio Nazionale delle Ricerche; ItaliaFil: Consoloni, Ilaria. Università degli Studi di Pisa; ItaliaFil: Baneschi, Ilaria. Istituto di Geoscienze e Georisorse; Italia. Consiglio Nazionale delle Ricerche; ItaliaFil: Guidi, Massimo. Istituto di Geoscienze e Georisorse; Italia. Consiglio Nazionale delle Ricerche; ItaliaFil: Isola, Ilaria. Istituto Nazione di Geofisica e Vulcanologia; ItaliaFil: Bini, Monica. Consiglio Nazionale delle Ricerche; Italia. Università degli Studi di Pisa; ItaliaFil: Ragaini, Luca. Università degli Studi di Pisa; ItaliaFil: Terrasi, Filippo. Seconda Universita Degli Studi Di Napoli; ItaliaFil: Regattieri, Eleonora. Istituto di Geoscienze e Georisorse; ItaliaFil: Dallai, Luigi. Istituto di Geoscienze e Georisorse; Italia. Istituto Nazione di Geofisica e Vulcanologia; Italia. Università degli studi di Roma "La Sapienza"; Itali

Oxygen stable isotope analyses on ameghinomya antiqua shells: A promising tool for palaeoenvironmental reconstruction along the quaternary patagonian Argentina coast?

There are only a few data concerning the Quaternary climate fluctuations in the marine environments of the Atlantic Patagonian coast. In this regard, the aragonitic shell of the Ameghinomya antiqua bivalve offers the possibility to study the climate variability and the seasonal cycles of sea water temperature in the region at different geological times. We compared oxygen isotopic profiles along the shell-growth axis on four well-preserved A. antiqua bivalves collected from marine coastal deposits of Marine Isotope Stage (MIS) 7, MIS 5, Holocene (7.284 ±140 yr cal BP), and from the present-day active beach of Bahia Bustamante (Patagonia Argentina). Shell ontogeny was determined through the annual growth lines recorded along the external region of the shell, and was also verified by cross-section analyses. The fossil bivalves were around 15 years old, while the Present day shell was 10 years old. When the modern climatic data available are compared, the higher δ18Oshell values represent the cold season, while the lower δ18Oshell values indicate the warm season. The δ18Oshell ranges indicate different environmental conditions and seasonal temperature variations between specimens. By assuming, a constant δ18Ow calculated with the limited environmental data available, superficial seawater temperatures are estimated from the specimens. These paleotemperatures may overestimate water temperatures, and shell formation seems to occur with an offset from expected oxygen isotopic equilibrium with the water in which they lived. Meanwhile, A. antiqua shells are suitable bioarchives for the comparison of seasonal patterns throughout the Quaternary, thus constituting another proxy for the evaluation of paleoclimatic and paleoenvironmental changes in the Patagonia region.Fil: Boretto, Gabriella Margherita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Consoloni, Ilaria. Università degli Studi di Pisa; ItaliaFil: Morán, Ariana Gisela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Regattieri, Eleonora. Consiglio Nazionale delle Ricerche; ItaliaFil: Gordillo, Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Fucks, Enrique Eduardo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; ArgentinaFil: Zanchetta, Giovanni. Università degli Studi di Pisa; ItaliaFil: Dallai, Luigi. Istituto di Geoscienze e Georisorse; Itali

Geomorphologic Map of Northeastern Sector of San Jorge Gulf (Chubut, Argentina)

This paper presents a 1:100,000 scale geomorphologic map of the Northeastern sector of San Jorge Gulf (Chubut Province) in Patagonia, Argentina, covering more than 1,000 km 2. Derived from remote sensing data and validated by three field surveys, it has been compiled in order to understand the past and recent evolution of the area with particular reference to sea-level oscillation studies, for which this map is the basic tool. The very low human impact and rates of dynamic landscape change allow the preservation of extensive palaeo deposits and landforms, including those indicative of sea-level variations. The relative change of sea level dominates landscape evolution, allowing the formation of widespread marine and lagoon deposits often interfingering with fluvial deposits and reworked by aeolian process in the framework of consequent beach progradation.Facultad de Ciencias Naturales y Muse

RILEVAMENTO GEOLOGICO E ANALISI DI FACIES DEI DEPOSITI PLEISTOCENICI DELLA ZONA COMPRESA TRA IL FIUME CECINA E CASALE MARITTIMO (TOSCANA, PISA)

L’obiettivo di questa tesi è stato il rilevamento e l’analisi di facies dei depositi che affiorano nella zona della bassa Val di Cecina, al confine tra le province di Pisa e di Livorno, allo scopo di ricostruire l’ambiente di sedimentazione e quindi l’evoluzione paleogeografica dell’area suddetta. L’area studiata è compresa all’interno della Sezione n°294080 (Guardistallo) in scala 1:10.000 della Carta Tecnica Regionale della Regione Toscana, di cui è stato effettuato un rilevamento, e comprende i comuni di Montescudaio, Guardistallo e Casale Marittimo. Il rilevamento si è svolto nell’ambito del progetto C.A.R.G. di cartografia geologica della Regione Toscana. I sedimenti affioranti in quest’area sono compresi tra il Giurassico medio-superiore (complesso del Dominio Ligure) e l’Olocene. I depositi considerati in questa tesi sono quelli compresi tra il Pleistocene inferiore e medio. Nella prima parte viene fornito un inquadramento geologico dell’area studiata dal punto di vista strutturale e stratigrafico ed un’analisi delle precedenti conoscenze sulla stratigrafia e la tettonica della zona. Successivamente sono state descritte le unità litostratigrafiche del Pleistocene inferiore e medio, individuate nel rilevamento, dal punto di vista sedimentologico e micropaleontologico, che ha permesso di individuare, attraverso l’analisi di facies, i diversi ambienti deposizionali susseguitisi nelle unità individuate durante il rilevamento. E’ stata inoltre effettuata un’analisi composizionale sui conglomerati affioranti nella zona, che ha permesso una trattazione statistica dei dati ed un confronto fra le varie formazioni. Infine è stata proposta una discussione incentrata sulle ipotesi di ricostruzione paleogeografica dedotta dall’analisi di dettaglio delle successioni stratigrafiche e sulle possibili correlazioni con i depositi coevi del margine a nord del fiume Cecina. Dall’analisi dei dati è emersa una nuova suddivisione delle unità litostratigrafiche ed una maggiore definizione degli ambienti deposizionali rispetto ai precedenti lavori. Le analisi sui conglomerati evidenziano delle forti novità per quanto concerne l’area di alimentazione di alcune formazioni pleistoceniche, in quanto si notano dei cambiamenti nella composizione che indicano variazioni di alimentazione

Holocene Beach Ridges and Coastal Evolution in the Cabo Raso Bay (Atlantic Patagonian Coast, Argentina)

The Holocene evolution of the Cabo Raso bay (Atlantic Patagonian coast) was reconstructed by means of geomorphological, stratigraphic, and palaeontological analyses, assisted by radiocarbon dating. Six beach ridges were individuated and mapped in the field, as well as some rocky erosional landforms,e.g.,inner margins of marine terraces. Thanks to quarry sections, the internal structure of beach ridges, their relationship with continental deposits, and the fossil contents were determined. Two specimens ofAulacomya atraandBrachidontes purpuratuswere radiocarbon dated at 6055 and 4500 ± 20 YBP, respectively. The bedrock outcrops at the base of an analysed section allowed us to associate the age of the samples collected to the elevation of the marine transgression surface upon which the entire deposit rests. Because a beach ridge is a regressive form, the elevation of the base of the dated deposit was assumed to be equivalent to or slightly lower than the maximum sea-level stationing, represented by the inner margin of the coheval marine terrace. The altimetric correlation between the base of the beach ridge dated at 6055 ± 20 YBP and the inner margin of the corresponding marine terraces allowed us to constrain the maximum Holocene marine transgression to about 3 to 2m above sea level. This elevation for the maximum Holocene transgression is lower than that shown by most of the previous data for Patagonian coast, but it shows a crude agreement with recent estimates coming from geophysical models that report, for this area, a departure from the eustatic value of sea level, mainly caused by glacioisostatic process. This means that the employment of marine erosional landforms, associated with other multisource field data, proved to be determinant for reconstructing the sea-level variation in the Patagonian coast

Geomorphologic Map of Northeastern Sector of San Jorge Gulf (Chubut, Argentina)

This paper presents a 1:100,000 scale geomorphologic map of the Northeastern sector of San Jorge Gulf (Chubut Province) in Patagonia, Argentina, covering more than 1,000 km2 . Derived from remote sensing data and validated by three field surveys, it has been compiled in order to understand the past and recent evolution of the area with particular reference to sea-level oscillation studies, for which this map is the basic tool. The very low human impact and rates of dynamic landscape change allow the preservation of extensive palaeo deposits and landforms, including those indicative of sea-level variations. The relative change of sea level dominates landscape evolution, allowing the formation of widespread marine and lagoon deposits often interfingering with fluvial deposits and reworked by aeolian process in the framework of consequent beach progradation

Coastal landscape evolution and sea-level change: a case study from Central Patagonia (Argentina)

The coastal fringe of Central Patagonia preserves a unique and spectacular succession of landforms discontinuously formed since MIS 11 up to the Holocene. The study area, stretching from 44° 34′ to 44° 54′ S of latitude, is crucial to analyze the complexity of multitemporal shorelines formation and preservation along the Atlantic coast of South America. We used depositional and erosional landforms to get reliable and well chronologically constrained sea level markers. In particular, multistoried swale infillings, produced by a complex relationship between river discharge and marine activity, were considered the most accurate sea level markers. Palaeo sea level elevation was assessed cross checking evidence obtained from different marker types and considering the original position of each of the measured features with respect to its contemporary sea level. A dedicated field measurement of the markers current elevation was necessary, considering the macrotidal regime that currently affects this coastal area. Literature and new data provide an excellent set of dating, useful to chronologically constrain all the palaeo shorelines that have been identified. On the whole five sea level highstands have confidently been referred to Holocene (maximum transgression peak), MIS 5, 7, 9 and 11. Sea level elevation for each of them was stated respectively at 2.5, 7.5, 10.5, 22.5 and 32.5 m a.s.l., but different error bars and levels of accuracy are assigned to each of these estimates, based on innovative criterions that are widely discussed in the text. Our work enabled us to obtain new, self-consistent values of the last 400 ka uplift rates for this coastal tract and to compare them with those calculated by other authors, suggesting for the investigated time span a moderate coastal uplift