Marta Pappalardo

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

Abstract 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 of Aulacomya atra and Brachidontes purpuratus were 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 2 m 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)

Abstract Please click here to download the map associated with this article. 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. 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.

A New Approach for the Study of the Coast Indentation Index

Abstract The indentation index, which is the ratio between the real length of a coast and its Euclidean length, is a parameter applied to characterize rock coasts and to study their evolution. Rather than subjectively selecting two or more sectors of a rock coast, the method proposed in this paper considers analyzing the indentation index on the same coastline previously split into several adjacent tracts with equal Euclidean length. By digitizing the coastline in a GIS environment, it becomes possible to test several Euclidean length values on the same coastline, obtaining a different spatial variability of the indentation index with each trial. The best length values that maximize the spatial variability of the indentation index are those that determine an indentation index pattern characterized by high variance and low spatial autocorrelation. The spatial distribution of the indentation index can eventually be analyzed considering known littoral forces acting on the studied coast. When more than one Euclidean length value is found to maximize the variability of indentation index within the same coast, it is likely that there are one or more littoral forces acting or interacting differently at different scales.

GLACIER RETREAT IN THE MARITIME ALPS AREA

Abstract. In the southernmost tract of the Alps (Italian‐French Maritime Alps), extensively covered by glaciers during the Last Glacial Maximum, about 30 small glaciers were present by the end of the Little Ice Age. The aim of this paper is to document the progressive decrease towards exhaustion of these glaciers, located at the latitude of 44° N, highlighting the factors affecting their retreat. All available data sources were investigated for this work including: the annual glaciers fluctuations record, comparative analyses of historical maps and multi‐temporal oblique photographs and direct surveys in the field. The history of the Maritime Alps glaciers fluctuations was thoroughly reconstructed. Stationary conditions were observed from 1896 up to the beginning of the 1930s; since then they underwent phases of withdrawal with variable intensity. In the early 1990s, only six glaciers were still present, the extent of which were all was dramatically reduced. In the past two decades, the Maritime Alps glacier fronts experienced a global retreat of about 100 m, with a sharp acceleration after 2002. Currently ice patches along cirque walls and/or semi‐buried lenses of ice are still present; morphological evidence of permafrost creeping in the glacier forefield accounts for the incipient transition to periglacial landforms (i.e. rock glaciers). The main factors controlling glaciers retreat seem to have been their original extent at the beginning of the current regressive phase and their distance from the main chain divide. From a climatic point of view unfavourable factors for glaciers persistence have been in the last decades a remarkable and sharp temperature increase, a decrease in winter snowfall and a shift of the rainfall peak from autumn to spring.

New insights on the Holocene marine transgression in the Bahía Camarones (Chubut, Argentina)

The stratigraphic reconstruction of the northern sector of the Bahia Camarones (Chubut, Argentina) allowed to improve our understanding of the Holocene marine transgression in the area.The first phase of the maximum of the transgression, is interpreted as dominated by the high rate of eustatic rise of sea level until ca. 6-7 ka BP possibly associated to sedimentary starvation as suggested by fossil accumulation. After this first phase, the general trend indicates a progressive fall of the relative sea level after the Middle Holocene high stand as documented in other parts of south America Atlantic coast. Our data, coupled with the robust radiocarbondata set available for the area from literature, indicate three main local steps of coastal aggradation between ca. 6600 and 5400 yr BP (ca. 7000-5600 yr cal BP), ca. 3300 and 2000 yr BP (ca. 3100-1700 yr cal BP), and ca. 1300-500 yr BP (ca. 1000-300 yr cal BP). A significant age gap in coastal aggradation is present between ca. 5300 and 4400 yr BP (ca. 5600-4500 yr cal BP), and perhaps between ca 2000 and 1300 yr BP (ca. 1700-1000 yr cal BP). These can be linked to phases of local sea level fall and/or phases of sedimentary starvation and/or changes in drift transport which can have produced local coastal cannibalization. However, no conclusive data can be advanced. Data obtained from careful measurements of sea level markers represented by the top of marsh and fluvial terraces indicate lower values for the sea level estimation compared with the data set previously proposed for the area. This stigmatizes the fact that field-oriented works are still the priority in the Patagonia coast along with accurate age measurement, especially for obtaining the fundamental information we need for predicting the environmental impact, in these coastal areas, from accelerate sea level rise as effect of global warming.

Middle- to late-Holocene relative sea-level changes at Puerto Deseado (Patagonia, Argentina)

Stratigraphic, morphologic and radiocarbon data from Puerto Deseado coastal area (Santa Cruz Province, Argentina) indicate that the Holocene coastline formed in response to the discontinuous aggradation of coarse gravely beaches since c. 6300 cal. yr BP related to a progressive falling of relative sea level. Beach ridge crests crudely approximate to the sea level showing at least three steps of aggradation and relative sea-level lowering. Two inactive abrasive notches at c. 7.9 and 3.4 m a.s.l. have recorded this sea-level trend, suggesting two important phases when sea level was stationary. This allows the estimation of a rate of relative sea-level fall in the last c. 3500 years of c. 1.8 mm/yr. Moreover, notches and morphological data indicate that the crest of the beach ridges exceeded the sea-level height by c. 2 ± 0.5 m. This value provides a reasonable regional estimate to be applied to produce comparable relative sea-level curve for Atlantic Patagonia coast.

Late-pleistocene wedge structures along the patagonian coast (argentina): Chronological constraints and palaeo-environmental implications

Abstract This paper investigates several wedge structures formed in continental deposits covering marine sediments deposited during 5 along the central Patagonian coast of rgentina. The size and surface microtexture characteristics of the infilling sediments are consistent with a depositional environment dominated by aeolian transport. Fragments of Andean volcanic rocks (glass shards) in the wedge‐fill suggest long‐distance transport via a westerly component of wind direction. The wedges are interpreted as products of deep seasonal frost action in frozen ground, which produced open cracks that filled rapidly with partially non‐local aeolian sediments. Many wedges cross cut carbonate crusts that formed under permafrost conditions in coastal Patagonia. The radiocarbon dating of carbonate crusts yielded an age of 25–27 kyr bp, while wedge‐fill sediments are OSL dated to 14-670 ± 750 yr bp. This indicates that ground wedge formation occurred during a cold event (the Antarctic Cold Reversal period) that interrupted the permafrost degradation following the Last Glacial Maximum.

First finding of a terrace with preserved marine deposit along the coast of Eastern Liguria (Italy)

Remnants of a loose coarse deposit were found on a rock terrace 28 m above the present day sea level, along the coast of Eastern Liguria. A general geomorphological analysis of the site was carried out. The deposit sedimentological characteristics were detailed and a morphometric analysis of the coarse fraction was carried out. This enabled us to infer the marine genesis of the deposit; it is the first time that a Quaternary marine deposit is found along the coast of Eastern Liguria. Details regarding the nature of the deep weathering processes (in particular oxidation and decarbonatation) that affected it were collected by means of thin section. The age of an old sea level can be inferred, due to the absence of absolute dating, only relating it to similar surfaces present throughout the coastline of the region and linking them to the sea level curves obtained from oxygen isotope records. On the basis of the collected data we propose the chronological attribution of the studied terrace to theδ18O stage 11, considering that the area might have been affected by tectonic uplift.RiassuntoSu un terrazzo in roccia, a 28 m sul livello del mare attuale lungo la costa della Liguria orientale sono stati rinvenuti i resti di un deposito sciolto e grossolano. È stata condotta un’analisi geomorfologica del sito, sono state descritte in dettaglio le sue caratteristiche sedimentologiche ed è stata compiuta un’analisi morfometrica dei clasti che ha permesso di provare l’origine marina del deposito; è la prima segnalazione di un deposito marino quaternario lungo la costa della Liguria orientale. Dall’osservazione del deposito in sezione sottile sono stati dedotti elementi sulla natura degli intensi processi di alterazione, in particolare ossidazione e decarbonatazione, che lo hanno interessato. Questo terrazzo marca un alto livello di stazionamento marino. L’attribuzione cronologica, in mancanza di datazioni radiometriche, è compiuta in maniera indiretta, rapportando questa superficie ad altre simili che sono presenti lungo la costa ligure e mettendole in relazione con le curve di fluttuazione del livello marino ottenute dalle serie isotopiche dell’ossigeno. Si propone, sulla base delle osservazioni effettuate, per il terrazzo in questione un’attribuzione allo stadioδ18O 11, non escludendo che esso possa avere subito un sollevamento per cause tettoniche.

Assessing tectonic subsidence from estimates of Holocene relative sea-level change: An example from the NW Mediterranean (Magra Plain, Italy)

New sedimentological sea-level indicators are presented from the River Magra coastal plain, in NW Italy. Chronologically well-constrained paralic peats and organic sediments which had been deposited in a defined relationship with sea level were recovered in four of the seven boreholes considered in this work. Their evolution scatters in the time span of the past 6000 years. Since the cores are located within a single sedimentary basin, it was possible to correct the elevation of marker horizons for the effect of sediment compaction by means of both a field and a geotechnical method. Thus, seven reliable index points for the mid- to late-Holocene sea-level rise were obtained. The age–depth model derived from them was compared with that of sea-level predictions from two different Glacial Isostatic Adjustment (GIA) models available for the area. In both cases, the modelled sea-level estimates overlie the index points, suggesting lower relative sea-level elevation than the one predicted considering the combined eustatic and hydro-isostatic components. Based on the general tectonic setting of the area, this finding was interpreted as the effect of a tectonic subsidence of the basin, the rate of which can be quantified on average as 0.5 mm/yr since the middle Holocene, with a sharp increase after 2500 yr BP. By providing a reliable estimate of the rate of tectonic subsidence in a coastal area of NW Italy, this research contributes to refining the geodynamic model of this part of the Mediterranean basin.

Evolution of an Upper Pleistocene aeolianite in the northern Mediterranean (Liguria, NW Italy)

Based on a 19th century scientific report, a recent geological survey has highlighted the presence of a complex, mostly Aeolian deposit along the coast of Liguria (Laigueglia, Savona Province, NW Italy). This finding was recognized to be a relevant palaeoclimatic marker, being the northernmost aeolianite outcrop ever reported from the Mediterranean Basin. The investigated deposit is spread along a steep sea-facing slope from 2-3 m up to almost 60 m a.s.l.; it is strongly reworked due to recent urbanization of the area. Its stratigraphic features were recognized thanks to its exposure in different sections and analysed in order to obtain reliable indications on the sedimentary environments. Facies analysis suggests that the sedimentary body is a relict cliff-top dune evolved on top of a foreshore deposit in temperate-cold and moist climate conditions. Two samples from the upper, strictly aeolian part of the sequence were subjected to OSL (Optically Stimulated Luminescence) dating and yielded an age consistent with its deposition during the Marine Isotopic Stage (MIS) 5.2 and 5.1 substages (88-83 and 83-71 ka). This paper contributes to the increase of the number of Upper Pleistocene coastal aeolianites accounted for in literature. Being located at the northern border of the occurrence of aeolianites in the northern Mediterranean, it helps to outline climatic and environmental boundary conditions for the formation of this type of deposit.