No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
The flooding of the San Matías Gulf: The Northern Patagonia sea-level curve
Abstract
Northern Patagonia is characterised by tectonic depressions below
present sea level. Some of them are today flooded by the sea; others
remain emerged although they are at altitudes of - 50 m (Bajo del
Gualicho), - 35 m (Salinas Grandes) and - 7 m (Salina La
Piedra). San Matías Gulf also was such an emerged depression
below contemporary mean sea level during the Late Pleistocene. It
flooded between 11,500 and 11,000 years ago, when the sea level
surpassed the sill of the gulf (today 50 m below mean sea level) during
postglacial sea-level rise. In those days, shrublands extended on the
slopes of the tectonic depression. In-situ pieces of woods dredged from
the bottom of the gulf at depths of 70 m gave a conventional age of
11,310 ± 150 years BP. We used the wood, together with dated
shells from the continental shelf, and shells and organic matter dated
from the San Blas, Negro and Chubut coastal plains to construct a
sea-level curve. Sea level rise surpassed the present level somewhat
before 6000 years BP, reaching a maximum stand of + 6 m. It has since
gently diminished towards present sea level.
... Also shown is the post-LGM potential position of the coastline on the Argentine Continental Shelf during the apparent stabilization of sea level from the paleogeographical model developed by Ponce et al. (2011). Cavallotto et al. (1995), Guilderson et al. (2000) and Isla (2013). Modified from Violante and Parker (2004). ...
... Unfortunately, the relative sea-level curve generated by Violante and Parker (2004), compiled after the results of Guilderson et al. (2000) and Cavallotto et al. (1995) and presented in this article, does not have sufficient resolution to highlight MWP-1A and MWP-1B (Figs. 2 and 10). Isla et al. (2013) suggest that the San Matías Gulf, located~350 km north of the GSJ and characterized by a sill at a depth of 60 m, should have been flooded during MWP-1B. In the GSJ, the slight transition of depositional conditions separating L3 and L4 and estimated to between 11.9 and 11.6 cal ka BP (records from a shell-rich bed; 11.1 cal ka BP in 006PC) could be correlated to the sea-level jump related to MWP-1B. ...
... Since the first Atlantic to Pacific drainage reversal event, which occurred at~15.3 cal ka BP (Thorndycraft et al., 2019), 12.8 cal ka BP (Turner et al., 2005) or 10.5 ka BP (Glasser et al., 2016), and especially since the capture of the Deseado River meltwater drainage by the Baker River watershed flowing into the Pacific Ocean (Fig. 1a), the discharge of the Deseado River has drastically decreased, with potential effects on sedimentation in the GSJ (Isla et al., 2013). However, the increase in log(Ti/Ca) ratios from the early Holocene displays an opposite trend to the potential diminution of fluvio-glacial outflows through the Atlantic coast, which is consistent with the eustatic and relative sea-level curves (Fig. 10). ...
This study presents the first detailed description of the upper sedimentary succession of the late Pleistocene and Holocene deposits in the Gulf of San Jorge (Patagonia) based on several hundred kilometers of high‐resolution seismic (sparker) profiles and numerous sediment cores. High‐resolution seismic stratigraphy confirms the existence of a paleo‐fluvial network formed during sea‐level lowstands and buried by central basin estuarine deposits during the last marine transgression. Analyses of lithostratigraphy and radiocarbon ages indicate the onset of subtidal sedimentation at ~14 cal ka bp . Before the onset of subtidal conditions, the first steps of marine incursion seem to have led to the development of lagoonal/wind–tidal flat environments, advocating for a sea‐level stillstand. An abrupt increase in the log(Ti/Ca) ratio in a distinct multi‐centimeter‐thick layer and the identification of a wave‐ravinement surface suggest rapid sea‐level rise in the gulf prior to ~14 cal ka bp , consistent with Meltwater Pulse 1A. Overall, this study highlights the significant impact of sea‐level rise on sedimentation in the gulf from the onset of marine incursions to the mid‐Holocene, as well as the reduced contribution, as currently observed, of riverine inputs due to the progressive diminution and withdrawal of glacial drainage starting before the Holocene.
... The geological and morphological evolution of the Colorado River delta plain has been mainly explained as a result of eustatic and climatic changes (Codignotto & Weiler 1980, Weiler 2000, Spalletti & Isla 2003, Melo et al. 2003, 2013, Martínez et al. 2019. Today, the Colorado River delta is the remnant of a deltaic system with greater extension during the Pleistocene-Early Holocene (Spalleti & Isla 2003, Melo et al. 2003, 2013. ...
... The geological and morphological evolution of the Colorado River delta plain has been mainly explained as a result of eustatic and climatic changes (Codignotto & Weiler 1980, Weiler 2000, Spalletti & Isla 2003, Melo et al. 2003, 2013, Martínez et al. 2019. Today, the Colorado River delta is the remnant of a deltaic system with greater extension during the Pleistocene-Early Holocene (Spalleti & Isla 2003, Melo et al. 2003, 2013. Most of these studies inicially outlined the influence of Holocene stages in the delta evolution, using the paleontological information as a complementary biochronological tool (Charó et al. 2015). ...
... The abundance and persistence of marinecoastal tychoplanktonic in LCH core indicates that the marine influence prevailed at the site during the last 11,000 years, with important bedload and resuspension processes. According to the Holocene sea-level fluctuations recorded in Argentina (Isla 1989, Isla & Espinosa 1998, Cavallotto et al. 2004, Spagnuolo 2005, Isla 2013, Prieto et al. 2017, evolutionary phase I and II (DZI-II, early and middle Holocene, respectively) occurred during sea level rise, while the most recent phase (DZ III) occurred under regressive conditions (Late Holocene). ...
Diatom assemblages and coastal sedimentary facies succession in the deltaic plain of the Colorado River (Argentina) were studied in order to reconstruct the environment conditions in response to Holocene eustatic sea-level changes and delta progradation. Samples were selected from a 200-cm core (39°35'52" S, 62°6'43" W). Chronology was based on radiocarbon datings in bulk samples and mollusk shells. Nine lithological units were recognized where fine and very fine sand predominate. The core sediments were dominated by tychoplanktonic coastal-marine diatoms. The accompanying flora included stable marine-coastal taxa and allochthonous fluvial fresh-brackish species. Three diatom zones (DZ) were established based on cluster analyses. The LCH site was significantly affected by Late Pleistocene and Holocene sea-level fluctuations, and the progradation of the deltaic lobe during the last ca. 7,000 14C yr. BP. Ancient tidal channels were flooded in the early Holocene postglacial transgression. Erosive and re-working processes associated with the formation of estuarine channels, affected valves preservation, yielding with barren sections. Tidal flats and marshes have developed in the area during the late Holocene regression phase. The comparison of the sedimentary sequence with deltaic facies evolution models, confirm the presence of a hiatus, which masks the Holocene Maximum and highstand.
... The genesis of the North-Patagonian gulfs (Golfo San Matías, Golfo Nuevo, and Golfo San José) has been linked to tectonic activity (Bouza et al., 2017;Isla, 2013;Kostadinoff, 1992;Roveretto, 1921;Windhausen, 1921) and to multiple exogenous processes (including wind, fluvial action, and mass wasting; Fucks, Schnack, and Charó, 2012;González Díaz and Di Tomasso, 2011;Mouzo and Garza, 1979;Paterlini and Mouzo, 2013;Zambrano, 1973). The time of the flooding of the Golfo San Matías depression was attributed to the Last Interglacial (marine isotopic stage [MIS] 5e; Mouzo, 2014). ...
... Recently, Mouzo and Paterlini (2017) proposed that this submergence occurred during the Last Interglacial Transgression (Late Pleistocene) as a consequence of coastal retreat and subaerial depression flooding. For Golfo San Matías flooding, Isla (2013) proposed a sea level between 50-60 m below present msl, whereas Mouzo and Paterlini (2017) suggested a sea level of 75 below msl. In the case of Golfo Nuevo, Mouzo and Garza (1979) postulated that its origin and development took place because of multiple processes such as wind and fluvial erosion and mass wasting. ...
... Finally, regarding Holocene deposits, broad consensus was achieved among different authors because of the precision of the method and the continuity and well preservation of the records. Hence, common agreement can be observed when defining the last transgression during the Holocene (MIS 1; Fucks, Schanck, and Charó, 2012;Isla, 2013;Mouzo, 2014;Mouzo and Paterlini, 2017;Sander et al., 2018). ...
Bunicontro, M.P. and Marcomini, S.C., 2021. Geomorphological evolution of the Patagonian coast surrounding the Golfo Nuevo (Chubut, Argentina) during Late Quaternary: Overview and new proposal. Journal of Coastal Research, 37(3), 528–543. Coconut Creek (Florida), ISSN 0749-0208.
The main contribution of this paper is a new interpretation of the geomorphological evolution of the North Patagonian coast surrounding the Golfo Nuevo from Mid-to-Late Pleistocene until present. The proposed model shows how continental and marine landforms evolved during the Late Quaternary. According to this, the Golfo Nuevo depression formed during the Middle Pleistocene (>130 ka) above previous fluvial terraces, which are attributed to different stages of the Chubut river. Several pediment types and levels were also identified: (1) flanking pediment (level 1) associated with an ancient fluvial valley; (2) convergent pediment related to a previous depression of Golfo Nuevo (level 2), both assigned to Middle Pleistocene; and (3) a littoral pediment (level 3) linked to a Holocene highstand level. The height and position of accretion marine terraces are discussed, in addition to their previous dating. It can be assumed that Golfo San Matías was flooded twice as a consequence of marine transgressions (marine isotopic stage [MIS] 5 and MIS 1). Likewise, Golfo Nuevo and Golfo San José were affected only once, during the maximum Holocene transgression (MIS 1). This paper highlights the importance of reconstructing the geomorphological evolution of a coastal area of the Patagonia as a result of a combination of changes linked to sea-level variations (mainly associated with glacio-eustasy) and climate, paleo-shorelines records, and continental landforms through Late Quaternary. The proposed geomorphological model can be considered a novelty because of the complex integration of continental and marine landforms and the study of their relative relation.
... The SMG ( Fig. 1) is located at the northeastern coast of Patagonia and features several different Quaternary mollusc deposits. Throughout the late Quaternary, regional climate at SMG, as well as sea levels, were subject to various changes (Codignotto et al., 1992;Ponce et al., 2011;Fucks et al., 2012;Isla, 2013). The origin of the gulf itself is related to ancient continental depressions, which were flooded by the ocean (Mouzo et al., 1978;Cavallotto and Violante, 2003;Isla, 2013), date back to at least 12,000 years (Ponce et al., 2011;Isla, 2013). ...
... Throughout the late Quaternary, regional climate at SMG, as well as sea levels, were subject to various changes (Codignotto et al., 1992;Ponce et al., 2011;Fucks et al., 2012;Isla, 2013). The origin of the gulf itself is related to ancient continental depressions, which were flooded by the ocean (Mouzo et al., 1978;Cavallotto and Violante, 2003;Isla, 2013), date back to at least 12,000 years (Ponce et al., 2011;Isla, 2013). The SMG, especially San Antonio Bay, provides a rich molluscan fossil record of Pleistocene and Holocene deposits (Feruglio, 1950;Fucks et al., 2005;Gordillo et al., 2014) with the aragonitic shells of the bivalve Amiantis purpurata being the most abundant and best-preserved fossil specimens in both deposits (Bayer and Gordillo, 2013;Bayer et al., 2014). ...
... Throughout the late Quaternary, regional climate at SMG, as well as sea levels, were subject to various changes (Codignotto et al., 1992;Ponce et al., 2011;Fucks et al., 2012;Isla, 2013). The origin of the gulf itself is related to ancient continental depressions, which were flooded by the ocean (Mouzo et al., 1978;Cavallotto and Violante, 2003;Isla, 2013), date back to at least 12,000 years (Ponce et al., 2011;Isla, 2013). The SMG, especially San Antonio Bay, provides a rich molluscan fossil record of Pleistocene and Holocene deposits (Feruglio, 1950;Fucks et al., 2005;Gordillo et al., 2014) with the aragonitic shells of the bivalve Amiantis purpurata being the most abundant and best-preserved fossil specimens in both deposits (Bayer and Gordillo, 2013;Bayer et al., 2014). ...
Amiantis purpurata is a common warm-temperate water bivalve species distributed from southern Brazil to northern Patagonia, Argentina, which has a rich and well preserved fossil record in the San Matías Gulf (SMG) dating back to the late Quaternary. This study aims to establish A. purpurata shells as a new palaeoarchive of past marine conditions in South America. We compared the stable oxygen and carbon profiles (δ 18 O shell ; δ 13 C shell) of eleven specimens of A. purpurata from different geological times (modern, Late Holocene and interglacial Late Pleistocene), and additionally present in situ oxygen isotope values of seawater within SMG (δ 18 O water). Using both sets of information, we calculated and reconstructed palaeowater temperatures for the Late Holocene and compared them to modern water temperatures. Our findings indicate that A. purpurata records past environmental parameters such as water temperatures on a seasonal scale and can therefore be considered a suitable candidate for future palaeoenvironmental reconstructions in Northern Patagonia. This study is the first step towards further stable isotope analyses on fossil A. purpurata shells, which will show whether and if so, to what extent, important global climate events such as the Neoglacial (Early Holocene), the Hypsithermal (Middle Holocene) and the Little Ice Age (Late Holocene) occurred in South America.
... Gathering radiocarbon datings from cores taken by the Lamont-Doherty Geological Observatory (Guilderson et al., 2000) and those collected at the coast, a sea-level curve was performed timing the flooding of San Matías Gulf (Isla, 2013). ...
... During the Upper Pleistocene (about 11,500 yrs BP) the depressions of the San Matías Gulf are assumed to be emerged, dry and below sea level. The coast during those days was 70 m below present MSL (Isla, 2013) and there was a significant northward longshore transport of gravel (Fig. 8). At the boundary between Pleistocene and Holocene (10,000 yrs BP) the seal level raised to -60 m. ...
La morfodinámica de playas fue enunciada como dependiendo del clima de olas, el rango de mareas y el tamaño de grano. La disponibilidad de sedimento es un factor condicionante heredado. Siete playas naturales del norte de Patagonia: 4 de la Provincia de Buenos Aires y 3 de Río Negro fueron relevadas durante 7 años. La playa de La Chiquita se caracteriza por la abundancia de arena fina aportada por el delta del Río Colorado. La Playa Pocitos es relativamente estable aunque está cambiando debido a la colonización por la ostra formadora de arrecifes Crassostrea virginica. Faro Segunda Barranca es una playa abierta muy afectada por tormentas extratropicales del SE. La playa de la Villa Siete de Marzo tiene una dinámica activa afectada por los embancamientos de la desembocadura del Río Negro y tormentas episódicas. La playa del Balneario El Cóndor es muy ancha con una caudalosa deriva litoral de oeste a este. La playa frente al Faro San Matías (Península Villarino) está controlada por una plataforma de abrasión cercana al límite de la bajamar. La playa Las Grutas está también controlada por una plataforma de abrasión aunque la abundancia de arena está relacionada al delta de reflujo de la Bahía de San Antonio. Las playas abiertas de la Provincia de Buenos Aires son muy afectadas por una deriva litoral hacia el norte inducida por olas del Atlántico Sur. Por el contrario, las playas de Río Negro son afectadas por fuertes vientos del oeste que fluyen paralelos a la costa.
... años AP (Isla, 1989;Cavalotto et al., 2004). Con posterioridad al máximo transgresivo holoceno, el nivel relativo del mar disminuyó y continúa haciéndolo en el hemisferio sur, de manera que la fase regresiva resultante dio lugar a las morfologías costeras actuales (Isla, 2013). Se han propuesto distintas curvas de cambios relativos del nivel del mar en diferentes regiones costeras de Argentina (Isla, 1989;Aguirre & Whatley, 1995;Gómez & Perillo, 1995;Isla & Espinosa, 1998;Cavallotto et al., 2004;Spagnuolo, 2005;Isla, 2013;Prieto et al., 2017). ...
... Con posterioridad al máximo transgresivo holoceno, el nivel relativo del mar disminuyó y continúa haciéndolo en el hemisferio sur, de manera que la fase regresiva resultante dio lugar a las morfologías costeras actuales (Isla, 2013). Se han propuesto distintas curvas de cambios relativos del nivel del mar en diferentes regiones costeras de Argentina (Isla, 1989;Aguirre & Whatley, 1995;Gómez & Perillo, 1995;Isla & Espinosa, 1998;Cavallotto et al., 2004;Spagnuolo, 2005;Isla, 2013;Prieto et al., 2017). Estas curvas coinciden en la tendencia general de los cambios, sin embargo, poseen particularidades en respuesta a la variabilidad regional y local como por ejemplo la cota máxima del nivel del mar (Schnack et al., 2005). ...
Holocene diatoms of the Colorado River Delta, Argentina. A paleoenvironmental approach from the study of “small fragilarioids”. Diatom assemblages of a sedimentary succession in the deltaic plain of the Colorado River (Argentina) were studied in order to reconstruct the paleoenvironmental conditions of the delta in response to Holocene sea-level changes. A 191 cm depth core was extracted by vibracoring from Las Isletas (LI), located 22 km from the coast (39°43’5.7”S, 62°20’49.7”W). A cluster analysis – CONISS of 35 subsamples defined three diatom zones (DZ). The sedimentary succession is dominated by small fragilarioids, being Punctastriata glubokoensis Williams, Chudaev & Gololobova the most abundant species; the accompanying flora included fresh-brackish and allochthonousmarine-coastal taxa. At the base, subzone DZIA (191–163 cm, 7,315±64 14C yr BP) included sandy lithological units and presented abundant marine-coastal species. The overlying subzone DZIB (163–96 cm) has low abundance of allochthonous marine species. The uppermost zone, DZII (96 cm from the top) integrate the silt-sandy lithological units, and it was deposited ca. 2,218±29 14C yr BP. DZII lacked marine species. The LI sequence represents the infilling of a river-estuarine channel with tidal influence ca. 7,300 14C yr BP that gradually evolved into a fresh-brackish river channel, similar to the current river, ca. 2,200 14C yr BP. During the Middle Holocene transgression, the greatest marine influence would have transported coastal marine species upstream to the LI site; the increase of fluvial influence associated with the progradation of the delta lobe would have favored the ubiquity and persistence of the small fragilarioids in the fluvial-delta assemblages of the Colorado River during the last ca. 7,000 14C yr BP. Keywords: Fragilariaceae, delta, sea level, Holocene, Patagonia. As associações de diatomáceas, de uma sucessão sedimentar da planície deltaica do Rio Colorado (Argentina), foram estudadas com o objetivo de reconstruir as condições paleoambientais do delta, em resposta às flutuações do nível do mar no Holoceno. Um testemunho de 191 cm de profundidade foi extraído usando um vibracoring no sitio Las Isletas (LI), localizado a 22 km da costa atual (39°43’5,7”S, 62°20’49,7”O). A análise diatomológica de 35 sub-amostras permitiu definir três zonas de diatomáceas (DZ) por meio de uma análise de agrupamento – CONISS. O testemunho foi dominado por pequenos fragilarioides, sendo Punctastriata glubokoensis Williams, Chudaev & Gololobova a espécie mais abundante. A flora acompanhante apresentou espécies de água salobra-duciaquícolas e táxons marinho-costeiros alóctones. A subzona basal DZIA (191–163 cm, 7.315 ± 64 anos 14C AP) incluiu unidades litológicas arenosas e apresentou abundantes diatomáceas marinhas costeiras alóctone. A subzona sobrejacente (DZIB: 163–96 cm) exibiu poucos táxons marinhos. A zona DZII (96 cm no topo) integrou unidades litológicas de areia-siltosa, formadas ca. 2.218 ± 29 anos 14C AP. DZII e não apresentou espécies marinhas costeiras. A sequência LI representa o assoreamento de um canal fluvial-estuarino com influência de marés ca. 7.300 anos 14C AP que evoluiu gradualmente para um canal fluvial de águas salobra-dulciaquícolas, semelhante ao rio atual ca. 2.200 anos 14C AP. Durante a transgressão do Meso-holoceno, o aumento da influência marinha teria transportado espécies costeiras-marinhas a montante do sítio LI. O aumento da influência fluvial associada à progradação do lobo deltaico teria favorecido a onipresença e a persistência de pequenos fragilarioides nas associações fluvio-deltaica do Rio Colorado durante os últimos ca. 7.000 anos 14C AP. Palavras-chave: Fragilariaceae, delta, nível do mar, Holoceno, Patagônia.
... marine bathymetry dataset to reflect relative sea level (Table 5). We use published data from the Argentinian Atlantic coast (Guilderson et al., 2000;Peltier and Drummond, 2002; Schellmann and Radtke, 2010;Isla, 2013). There is a dearth of data for the Pacific margin during the LGM, Late Glacial and Holocene, and sea level change in the northern part of the study area may be overestimated in our reconstruction. ...
... Further north, at San Matías Gulf (41°S, 62°W; Argentinian continental shelf), in situ pieces of wood from 70 m below sea level yielded radiocarbon ages of 11.3 ± 0.15 cal. ka BP (Isla, 2013). The mid-Holocene highstand of +6 m was reached at 6 ka BP. ...
We present PATICE, a GIS database of Patagonian glacial geomorphology and recalibrated chronological data. PATICE includes 58,823 landforms and 1,669 geochronological ages, and extends from 38°S to 55°S in southern South America. We use these data to generate new empirical reconstructions of the Patagonian Ice Sheet (PIS) and subsequent ice masses and ice-dammed palaeolakes at 35 ka, 30 ka, 25 ka, 20 ka, 15 ka, 13 ka (synchronous with the Antarctic Cold Reversal), 10 ka, 5 ka, 0.2 ka and 2011 AD. At 35 ka, the PIS covered of 492.6 x10³ km², had a sea level equivalent of ~1,496 mm, was 350 km wide and 2090 km long, and was grounded on the Pacific continental shelf edge. Outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams. The PIS reached its maximum extent by 33 – 28 ka from 38°S to 48°S, and earlier, around 47 ka from 48°S southwards. Net retreat from maximum positions began by 25 ka, with ice-marginal stabilisation then at 21 – 18 ka, which was then followed by rapid irreversible deglaciation. By 15 ka, the PIS had separated into disparate ice masses, draining into large ice-dammed lakes along the eastern margin, which strongly influenced rates of recession. Glacial readvances or stabilisations occurred at least at 14 – 13 ka, 11 ka, 6 – 5 ka, 2 – 1 ka, and 0.5 – 0.2 ka. We suggest that 20th century glacial recession (% a⁻¹) is occurring faster than at any time documented during the Holocene.
... In either case, Tegula atra in conjunction with the two northern Patagonian species (Chama iudicai and Glycymeris sanmatiensis) lived during Pleistocene times before the formation of the San Matías Gulf Isla 2013). This gulf is a semicircular basin separated from the open sea by areas that have developed a threshold of lesser depth than the central part of the basin (Cavallotto 2008). ...
... On the basis of the analysis of this palaeogeographical evolutionary model, concluded that the San Matías and San José gulfs would have been formed at around 12,000 calibrated years BP. A radiocarbon dating performed on Late Pleistocene wood fragments extracted from the bottom confirmed an age of between 11,500 and 11,000 years, when the sea level surpassed the sill of the gulf (today 50 m below mean sea level) during postglacial sea-level rise (Isla 2013). ...
As mollusks grow, their shells become biogeochemical records of the environmental and climatic conditions experienced throughout their lifetime. Following the ideas developed in Chap. 8, in this chapter stable isotopes are treated in conjunction with individual growth in the selected fossil specimens of different bivalves.
... In either case, Tegula atra in conjunction with the two northern Patagonian species (Chama iudicai and Glycymeris sanmatiensis) lived during Pleistocene times before the formation of the San Matías Gulf Isla 2013). This gulf is a semicircular basin separated from the open sea by areas that have developed a threshold of lesser depth than the central part of the basin (Cavallotto 2008). ...
... On the basis of the analysis of this palaeogeographical evolutionary model, concluded that the San Matías and San José gulfs would have been formed at around 12,000 calibrated years BP. A radiocarbon dating performed on Late Pleistocene wood fragments extracted from the bottom confirmed an age of between 11,500 and 11,000 years, when the sea level surpassed the sill of the gulf (today 50 m below mean sea level) during postglacial sea-level rise (Isla 2013). ...
Molluscan death assemblages are useful for reconstructing paleocommunities and can also provide signals for evaluating predation and other interactions. This chapter gives examples of biotic interactions that can be recorded in mollusk shells. We will provide data on the interaction between drilling predators and their shelled prey, and will also refer to preserved shell encrusters and organisms which settle on live hosts or dead shells.
... In either case, Tegula atra in conjunction with the two northern Patagonian species (Chama iudicai and Glycymeris sanmatiensis) lived during Pleistocene times before the formation of the San Matías Gulf Isla 2013). This gulf is a semicircular basin separated from the open sea by areas that have developed a threshold of lesser depth than the central part of the basin (Cavallotto 2008). ...
... On the basis of the analysis of this palaeogeographical evolutionary model, concluded that the San Matías and San José gulfs would have been formed at around 12,000 calibrated years BP. A radiocarbon dating performed on Late Pleistocene wood fragments extracted from the bottom confirmed an age of between 11,500 and 11,000 years, when the sea level surpassed the sill of the gulf (today 50 m below mean sea level) during postglacial sea-level rise (Isla 2013). ...
This chapter is focused on the analysis of the shell microstructure of different taxa and on how this information can be used for paleoenvironmental interpretations. A physic-chemical analysis on Modern, Holocene and Pleistocene shells of the purple clam Amiantis purpurata helps discern the structural changes during early diagenesis. In addition, the analyses of the microstructure of two other bivalves (Glycymeris longior and Ameghinomya antiqua) from the same region explain the differences in the degree of fragmentation in both species as a result of different structural features. Finally, cathodoluminiscence applied to Tawera gayi provides information on the skeletal growth cycles that is useful for evaluating changes.
... In either case, Tegula atra in conjunction with the two northern Patagonian species (Chama iudicai and Glycymeris sanmatiensis) lived during Pleistocene times before the formation of the San Matías Gulf Isla 2013). This gulf is a semicircular basin separated from the open sea by areas that have developed a threshold of lesser depth than the central part of the basin (Cavallotto 2008). ...
... On the basis of the analysis of this palaeogeographical evolutionary model, concluded that the San Matías and San José gulfs would have been formed at around 12,000 calibrated years BP. A radiocarbon dating performed on Late Pleistocene wood fragments extracted from the bottom confirmed an age of between 11,500 and 11,000 years, when the sea level surpassed the sill of the gulf (today 50 m below mean sea level) during postglacial sea-level rise (Isla 2013). ...
Carbonate shells have long been used as a proxy for paleoenvironmental conditions. In particular, oxygen and carbon stable isotopes from carbonate mollusk shells have been used for reconstructing water temperatures, the timing of upwelling events and changes in salinity. In this chapter, isotopic analysis was performed on shells of one particular species at different radiocarbon ages. It is also uses an example to show how to calculate paleotemperatures.
... In either case, Tegula atra in conjunction with the two northern Patagonian species (Chama iudicai and Glycymeris sanmatiensis) lived during Pleistocene times before the formation of the San Matías Gulf Isla 2013). This gulf is a semicircular basin separated from the open sea by areas that have developed a threshold of lesser depth than the central part of the basin (Cavallotto 2008). ...
... On the basis of the analysis of this palaeogeographical evolutionary model, concluded that the San Matías and San José gulfs would have been formed at around 12,000 calibrated years BP. A radiocarbon dating performed on Late Pleistocene wood fragments extracted from the bottom confirmed an age of between 11,500 and 11,000 years, when the sea level surpassed the sill of the gulf (today 50 m below mean sea level) during postglacial sea-level rise (Isla 2013). ...
Taphonomy is the “science of the laws of burial” (Efremov 1940); it involves the transition of animal remains from the biosphere to the lithosphere. In this chapter we refer to various taphonomic attributes (e.g., fragmentation and abrasion, among others) by looking at examples in different environments and different taxa; and we explain the advances made in taphonomy by the working group.
... In either case, Tegula atra in conjunction with the two northern Patagonian species (Chama iudicai and Glycymeris sanmatiensis) lived during Pleistocene times before the formation of the San Matías Gulf Isla 2013). This gulf is a semicircular basin separated from the open sea by areas that have developed a threshold of lesser depth than the central part of the basin (Cavallotto 2008). ...
... On the basis of the analysis of this palaeogeographical evolutionary model, concluded that the San Matías and San José gulfs would have been formed at around 12,000 calibrated years BP. A radiocarbon dating performed on Late Pleistocene wood fragments extracted from the bottom confirmed an age of between 11,500 and 11,000 years, when the sea level surpassed the sill of the gulf (today 50 m below mean sea level) during postglacial sea-level rise (Isla 2013). ...
The study area in southern South America comprises a very extensive geographic area covering more than 2,000 km and involving two distinct biogeographic areas. This chapter focuses on faunistic changes within and between provinces, faunistic shifts and the extinction of particular species during the Quaternary.
... Regarding the causes and trigger mechanisms involved in the closed basin formation, there are many controversies. Whereas, wind erosion was proposed to explain the close basins formation (Mouzo et al. 1978;González Díaz and Di Tommaso 2011); tectonics was also proposed (Roveretto 1921;Kostadinoff 1992;Isla 2013) and a combination of both processes was also suggested (Kostadinoff 1992;Haller et al. 2000). In this chapter, we arrive to the conclusion that while wind erosion could have been important, tectonic activity related to fault blocks was probably the trigger mechanism for the formation of the great closed basins. ...
... Topographic/bathymetric data of the Golfo San Matías and Golfo Nuevo indicate depression borders much deeper than the topographic borders of the Golfo San José (−55, −35 and −20 m a.s.l., respectively). Thus, Golfo San Matías and Golfo Nuevo would have been flooded before the Golfo San José (Fig. 6c, d), as previous studies suggested (i.e., 10-19 ka BP; Codignotto 2008;Ponce et al. 2011;Isla 2013). Finally, during the last millennium, sand dunes formation in the upland and plain system and present beach/marsh formation in the coastal zone system took place, resulting in the current landscape of The Península Valdés (Fig. 6e). ...
The present landscape of the Península Valdés is the result of a complex interrelation between climatic (aeolian deposition, windblown processes, glacial and interglacial cycles, pluvial and fluvial processes), tectonic, and eustatic controls that had work in the Andean foreland during the late Cenozoic. Based on a geomorphological approach, which includes new descriptions, interpretations, and hierarchically classification of the main landforms of this region, together with previous geomorphological surveys, the Península Valdés area was grouped in three major geomorphologic systems: Uplands and Plains, Great Endorheic Basins, and Coastal Zone. Based on the interrelationship among these three geomorphological systems the landscape evolution of the late Cenozoic of Península Valdés could be summarized in five main stages: (1) development of fluvial and alluvial systems during the Pliocene early Pleistocene; (2) closed basin formation associated to tectonic processes during the early middle Plesitocene; (3) first marine transgressions during the late Pleistocene; (4) flooding of the gulfs and construction of the peninsula in the late Plesitocene–Holocene; (5) final flooding in the region during the middle Holocene.
... These significant changes have influenced the patterns of faunal abundance and they might also have affected dispersal, migration and displacement processes Charó et al., 2014;Prevosti et al., 2015; among others). Several papers dealing with analyses of the fossil fauna together with geological studies along the Argentinean Patagonian coast have been published (Codignotto et al., 1992;Ponce et al., 2011;Fucks et al., 2012;Isla, 2013). ...
... Towards the end of the Pleistocene, the formation of the modern configuration of the SMG (12,000 years B.P. ;Ponce et al. 2011;Isla 2013) would have resulted in geomorphological changes that probably produced the environmental differences evidenced by the studied assemblages. These environmental changes resulted in substrate variations and modifications in the paleocirculation of the gulf which therefore modified nutrient supplies. ...
The aim of this study is to describe and interpret the paleoenvironmental history of the San Matiás Gulf (SMG), in northern Patagonia, Argentina, which is associated with possible biotic and abiotic changes that occurred during the late Quaternary. In this regard, a taphonomic (disarticulation, right/left valve ratio, fragmentation, abrasion, teeth preservation) and paleoecologic (alpha diversity, species abundance, life habit, substrate preference, feeding mode) analysis of Amiantis purputata (the target species) and its accompanying faunal remains (the non-target species) in modern, Holocene and Pleistocene shell assemblages, was performed. The general trend of the SMG throughout the late Quaternary was that of a low energy environment with varying water energy intensity depending on the study area. Additionally, each study site contains different substrates marked by patches of sand and rock which would have also determined the presence of certain species and, in turn, the proportion of sandy and rocky patches may have changed over time thus leading to the development of different local paleocommunities. Therefore, this gulf presents a dynamic mosaic of environments over time. Its waters would have been sufficiently rich in nutrients to allow the development of the filter feeding fauna which dominated the late Quaternary, especially A. purpurata. Crepidula species, which feed in two distinct ways (herbivore and filter feeding), increased in proportion throughout the Holocene. These changes, among others, coincided with the Last Glacial Maximum, the final configuration of the SMG, the Climatic Optimum of the Holocene and the impact of humans in the area.
... Similar situations were reported from the coasts of Peru and Chile where three tidal gauges indicate land emergence, whereas four suggest submergence. For the Atlantic coast, most of the tidal-gauge records indicate submergence between 0.7 and 4.2 mm/y (Emery and Aubrey, 1991), although uplifting trends were assumed for the Atlantic continental shelf of Patagonia (Guilderson et al., 2000;Isla, 2013). ...
... However, caution should be considered in relation to regional uplifting trends. In the Argentine continental shelf a long-term uplifting rate of 0.08 mm/y (Guilderson et al., 2000) has been estimated and considered to explain the Holocene sea-level rise at the Argentine trailing-edge margin (Isla, 2013). ...
Isla, F.I., and Angulo, R., 0000. Tectonic processes along the South America coastline derived from Quaternary marine terraces.
South America is overriding the Nazca, Antarctic, and Cocos plates, and at the same time is moving along the Caribbean and Scotia plates. Quaternary sea-level highstands are ideal benchmarks to estimate tectonic uplifts considering altitude differences along the coast. The Sangamonian highstand, corresponding to the Marine Isotopic Stage 5, is the most helpful indicator for these purposes as it is more easily preserved and spanning a record of 120,000 years. The Mid-Holocene highstand leads to errors assigned to tidal-range variations, estuarine floods, and meteorological effects; however, its maximum altitudes could confirm faster uplifting rates. The major uplifting trends were estimated in relation to the subduction of seismic or aseismic ridges along the Pacific Ocean coast. The Quaternary uplifted terraces of the Atlantic coast at Patagonia were explained by the decreasing uplift induced by the subduction of the Chile Ridge, and related to a very modern volcanic field.
... The formation of this gulf has been debated. Different hypotheses have been proposed for many years (Rovereto, 1921;Windhausen, 1931;Feruglio, 1950;Ponce et al., 2011;Isla, 2013;Mouzo, 2014). Since the beginning of the 20th century, when Windhausen (1918) mentioned that its origin was related to tectonic causes and not to the regression of the Eocene sea and the associated erosion, as suggested by Ameghino (1906). ...
... In this sense, the altitudes of the deposits should be interpreted in relation to recent local effects, either uplifting or subsiding (Villalobos Silva 2005;Garrett et al. 2020;Quezada et al. 2020). Notwithstanding these behaviors between the eastern and western coast, sea level curves were proposed for the Magellan strait region (Porter et al. 1984;Bujalesky et al. 2013;Björck et al. 2021), the Atlantic southern coast (Schellmann and Radtke 2003), the northern coast (Isla 2013;Fig. 2), and the Chilean coast . ...
The Patagonian coast evolved in relation to different issues. An arid climate dominates to the north, while very humid conditions prevail to the south of the Pacific coast and at the Fuegian archipelago. Tidal effects increase from north to south at the Atlantic coast, while the Pacific coast is dominantly microtidal. Patagonia has been uplifting in relation to the Andes mountains; at the Atlantic coast, the uplift increases toward the south. Marine terraces originated by the Quaternary sea-level fluctuations that developed in response to the sediment availability. The cliffy Atlantic coast is receding at a rate between 0.3 and 1.4 m yr.−1. Reversals in the direction of river discharges changed the supply of sediment to the coast; dams constructed at the piedmonts also caused these sediment shortages. Gravel availability contributed to the armoring of beaches and the longshore growing of spits. In many places, these barriers are protecting marshes and tidal flats against the sea level rise.
... Fjord ingression basins store sediment archives that have the potential to record changing climate and the complete cycle of fjord development from the LGM to present day. Sediment cores recovered from these basins can also be used to determine the timing of post-glacial sea-level rise by dating the transition between lacustrine and marine sediment, as has been done for fjord records collected in the Fiordland, New Zealand (Dlabola et al., 2015) and southern South America (Isla, 2013). The sill depth, after adjustment for tectonic and glacial isostatic elevation changes, sedimentary cover, and modern tidal variations, is used as measure of paleo sea-level height and the age of sediment deposited in the basin can provide chronological constraint (Dlabola et al., 2015). ...
Subantarctic islands are located at a critical latitude for reconstructing past changes in ocean-atmosphere interactions. Currently, there is a lack of high-resolution records from the Pacific sector of the Southern Ocean that can be used to reconstruct climate since the Last Glacial Maximum (LGM). Here, we present a reconstruction of environmental change from a fjord ingression basin at New Zealand’s subantarctic Auckland Islands (50.5°S) over the last ∼19 ka cal BP. Using sedimentological and geochemical analysis of cores collected along a depth transect in Norman Inlet we find evidence for four different stages of environmental history: deglacial, lacustrine, marine transgression, and marine. Glaciers retreated from their maximum extent before 19.4 ka cal BP during a period of ice retreat that appears synchronous across the Pacific basin, likely due to southward migration of the Subtropical Front. However, in contrast to other glaciated regions, we see no evidence for ice re-advance, and a proglacial lake was present in the basin until 15.7 ka cal BP. Following deglaciation, organic-rich sedimentation dominated the lacustrine environment until post-glacial sea-level rise flooded the depositional basin at 8.8 ka cal BP. Deposition of organic-rich sediment continued during the Antarctic Cold Reversal and we find no evidence for a glacial re-advance. Mixing of terrestrial and marine organic matter during the marine transgression (8.8–6.7 ka cal BP) indicates significant erosion and re-working of sediment in the catchment as seawater overtopped the sill. Modern fjord circulation commenced ∼6.7 ka cal BP when sea level reached its maximum in the early Holocene. This well-dated, high-resolution record constrains the timing of deglaciation, sea-level rise, and subantarctic environmental change following the LGM that expands our understanding of the key drives of climate change in the middle to high southern latitudes.
... There are many controversies about the geomorphologic processes that originated these landforms. Whereas wind erosion was proposed to explain the formation of the endorheic basins, for example, in the Península Valdés region (Mouzo et al. 1978;González Díaz and Di Tommaso 2011), tectonics was also proposed (Roveretto 1921;Kostadinoff 1992;Isla 2013) and a combination of both processes was also suggested (Kostadinoff 1992;Haller et al. 2000). Although wind erosion could have been important, tectonic activity related to fault blocks probably triggered the formation of the great endorheic basins (Bouza et al. 2017b). ...
The reproductive cycle of Galapagos giant tortoises has primarily been studied in captive individuals via noninvasive methodologies, including hormonal studies, radiographs, and ultrasound. During the annual reproductive cycle, mating peaks occur during the hot season months (December–June), followed by nesting during the cool season (June–December). Females dig flask-shaped holes in the soil typically in flat areas at lower elevations where soil suitable for digging accumulates. Females deposit 1–26 eggs and close nests with a mixture of urine, feces, and soil, which then dries into a hard cap, which seals in moisture and provides a protective layer for developing embryos. Rate of development and sex of the embryos depend on the temperature of the nest: when incubation temperatures are high (above 29.5°C) embryos become female and when temperatures are low (below 28°C) male. Eggs hatch after between 90 and 270 days of incubation. Young remain in the nest for up to 1 month until all eggs have hatched and consumed their yolk reserves. Hatchlings then dig an exit hole and emerge from the nest.
... The great endorheic basins are characterized by a typical centripetal drainage network (Fig. 4.9c, d) There are many controversies about the geomorphologic processes that originated these landforms. Whereas wind erosion was proposed to explain the formation of the endorheic basins, for example, in the Península Valdés region (Mouzo et al. 1978;González Díaz and Di Tommaso 2011), tectonics was also proposed (Roveretto 1921;Kostadinoff 1992;Isla 2013) and a combination of both processes was also suggested (Kostadinoff 1992;Haller et al. 2000). Although wind erosion could have been important, tectonic activity related to fault blocks probably triggered the formation of the great endorheic basins (Bouza et al. 2017b). ...
The purpose of this chapter is to summarize the geological-geomorphological regions of Patagonia with a general characterization of the main geomorphological units. A review of studies on geology, stratigraphic, main geologic landmarks, geological history, and geological resources will be briefly described. This review was performed on the base of geological province concept, including a stratigraphic-morphostructural criteria and a description of major endogenous and exogenous processes responsible for the formation of landscape units. In this chapter these geological-geomorphological regions include Chile and Argentina and were grouped as: (1) Coastal Cordillera and Central Valley (Chile), (2) Southern Andes Cordillera, (3) Mountain Sector of the Neuquén Embayment, (4) Northern Patagonian Tablelands, (5) The North Patagonian Broken Foreland and Somún Curá Massif, (6) Central Patagonian Tablelands, (7) Deseado Massif, (8) Southern Patagonian Tableland, and (9) Islas Malvinas Plateau.
... There are many controversies about the geomorphologic processes that originated these landforms. Whereas wind erosion was proposed to explain the formation of the endorheic basins, for example, in the Península Valdés region (Mouzo et al. 1978;González Díaz and Di Tommaso 2011), tectonics was also proposed (Roveretto 1921;Kostadinoff 1992;Isla 2013) and a combination of both processes was also suggested (Kostadinoff 1992;Haller et al. 2000). Although wind erosion could have been important, tectonic activity related to fault blocks probably triggered the formation of the great endorheic basins (Bouza et al. 2017b). ...
Understanding how human beings perceive and interact with the local herpetofauna is fundamental for its conservation. In this chapter, we propose looking forward to the local ecological knowledge (LEK) of the Patagonian lizards, especially the “matuasto”. The preliminary analysis of ethnohistorical sources points out the relevant role of “matuastos” in the cosmologies of the original people from Patagonia, often considered as immortal, selfish and harmful beings. Field reports agree on the warning not to disturb these territorial lizards; otherwise, they would react aggressively with bites. The recorded stories account for frequent biting events on sheep. The local perception on “matuastos” as harmful beings would provoke an attitude of caution and rejection towards them. This work provides a first overview on the relationship of lizards and the people from Patagonia while constituting an initial step for future research.
... The SMG is a relatively young seascape; its basin was flooded approximately 11 000 yr ago during the post-glacial sea-level rise (Isla 2013). It is located between 40°47' and 42°13' S on the Atlantic coasts of South America, covering a total area of approximately 18 000 km 2 (Gagliardini & Rivas 2004;Fig. ...
With the unprecedented rate of biodiversity change in the world today, understanding how diversity gradients are maintained at mesoscales is a key challenge. Drawing on information provided by 3 comprehensive fishery surveys (conducted in different years but in the same season and with the same sampling design), we used boosted regression tree (BRT) models in order to relate spatial patterns of α-diversity in a demersal fish assemblage to environmental variables
in the San Matias Gulf (Patagonia, Argentina). We found that, over a 4 yr period, persistent diversity gradients of species richness and probability of an interspecific encounter (PIE) were
shaped by 3 main environmental gradients: bottom depth, connectivity with the open ocean, and proximity to a thermal front. The 2 main patterns we observed were: a monotonic increase in PIE with proximity to fronts, which had a stronger effect at greater depths; and an increase in PIEwhen closer to the open ocean (a ‘bay effect’ pattern). The originality of this work resides on the identification of high resolution gradients in local, demersal assemblages driven by static and dynamic environmental gradients in a mesoscale seascape. The maintenance of environmental gradients, specifically those associated with shared resources and connectivity with an open system, may be key to understanding community stability.
... The SJG was originated as a tectonic depression flooded by the sea during the last deglaciation (Isla, 2013) when the sea level surpassed the −30 m depth (Paterlini and Mouzo, 2013). The flooding is assumed to have generated turbidity currents that eroded a submarine canyon with levees and a complex submarine fan (Paterlini and Mouzo, 2013). ...
The goal of this work was to infer the spatio-temporal patterns of bottom circulation of San José Gulf (SJG), Patagonia, Argentina. The SJG is mainly affected by tidal circulation and presents two hydrographic domains. The Western Hydrographic Domain (WHD) presents vertically mixed waters year-round contrary to the seasonal stratified Eastern Hydrographic Domain (EHD), resulting in the formation of a thermal front between domains. Samples of sediments were collected in spring 2016 and summer 2017 at several locations to analyze the grain-size composition by means of laser diffractometry. A conceptual model of bottom hydrodynamics was inferred based on sediment's grain-size trends. Asymmetric dominant tidal currents affect bottom sediment distribution. A general northward sediment transport is dominant at the WHD, while at the EHD there is a seasonal shift in the transport direction. There, a net northward transport with a counterclockwise gyre dominates bottom hydrodynamics at the end of the thermal front formation, conditioned by residual currents. In contrast, a net southward circulation likely driven by strong westerly winds throughout autumn and winter prevails at the beginning of the water column stratification. The inferred sediment transport suggests a net loss of material that has to be recovered by tidal currents entering through the mouth and coastal sources as runoff, mudslides, and/or aeolian dust.
... The origin and the friable character of the deposits determine the high availability of sand-to gravel-sized material in the area (Gélos et al., 1992;Martínez and Kutschker, 2011). San Matías Gulf itself is a more than 200 m deep basin separated from the open Atlantic Ocean by a sill (Isla, 2013;Moreira et al., 2011;Perillo et al., 2006). ...
Geomorphological and sedimentary records of Holocene coastal deposits may serve as archives for the local reconstruction of trends in coastal evolution and of the key forcing parameters controlling long-term change. We here present new observations on the sedimentology, chronology, and surface properties of a coupled beach ridge and coastal lagoon system located on the northern shore of San Matías Gulf, NE Patagonia, Argentina. The study is based on remotely sensed data, sediment cores, and a large number of samples dated using optically stimulated luminescence (OSL). The field site is located in a topographical depression within a cliffed shoreline composed of friable sand and gravel stones. The oldest preserved lagoonal deposits formed in the protected inner part of the system c. 2300 years ago. An up to 4-km-wide strandplain prograded rapidly between c. 1000 and 500 years in the more exposed western part of the system. Lagoonal deposition occurred primarily during the last 500 years. The chronology and spatial arrangement of landforms appear to result from a switch-over in sediment delivery probably caused by local implications of major shifts in climate regime. Even though we were not able to identify or benchmark the precise triggers of geomorphological change at Caleta de los Loros, our study presents an example of the potential importance of environmental changes on the rapid and non-linear development of coastal sedimentary systems.
... The San Matías Gulf is relatively young (approximately 11000 years old; Isla, 2013) and constitutes a semi-enclosed ecosystem, with an interesting demersal community that remains relatively isolated from the Argentine Continental Shelf. Its community has a well-known history supporting direct impacts and externalities from hunting, fishery development and conservation strategies of single species, among others. ...
The understanding of how active aeolian coastal dunes transform into fully vegetated forms, and the specific dune configurations that emerge, particularly within coastal dune systems, is limited. This study examines the changes in dune morphology associated with vegetation growth within transgressive dunefields in NE Patagonia, Argentina. The dunefields are located along the northern coast of the San Matías Gulf, ranging from relatively small to large, and dominantly active in the past ~80 years. Satellite and aerial images were analyzed using GIS procedures to calculate vegetation cover changes and dune migration rates and identify different dune types and their evolutionary stages of fixation. Five stages were defined in relation to vegetation cover and dune shapes and patterns, from bare sand to fully vegetated dunes. Transverse or barchanoid ridges (sometimes with akle [fish scale], or chaotic patterns) convert to partially vegetated sub-parabolic dunes and finish as parabolic dunes. In other cases, the dunes may convert to reticulate, akle, or chaotic patterns, completely vegetated. Various stages span a continuous range from unvegetated to fully vegetated dunes across a wide array of timeframes. In some cases, it was possible to recognize changes from stage one to five in ~20 years. Where the initial transverse dune is largely maintained during the stabilization process a distinctive pattern named “gusanos” (worms) was identified. The vegetated surface measured in some areas changed from 11 % to 51 % vegetation cover between 1961 and 2022, with migration rates decreasing from 9.53 m/year to zero between 1991 and 2020. The increase in vegetation growth also coincides with higher temperatures, weaker winds and decreasing grazing livestock within this Patagonia area. The recorded processes are similar to coastal dune and vegetation changes in some semiarid regions from the Southern Hemisphere between 30 and 60◦ S, especially in South Australia.
Patagonia is a key place to analyze the climatic trends (waves and winds) of the Southern Hemisphere. The northern coast of the San Matías Gulf (“Bahía Sin fondo” for the original Spanish descriptions) is characterized by an attached sand barrier developed on top of former cliffs. Morphological features are indicating changes in the regional slope when the sea level drowned the depression of the gulf. An original eastern slope was progressively replaced by slopes towards the south. The availability of sand during the transgression and maximum sea level was directed to the east due to the dominant westerly winds. Sand dunes accumulated on top of former cliffs and today –due to coastal erosion-, remain as cliff-top dunes. A conceptual model for the formation of these cliff-top barriers is described in relation to the fluctuation of the sea level and the sand migration, which was studied through mineralogical analysis comparing the different environments: cliff, beach, and dunes. Their composition explains the sediment transport shift and is locally associated to the Río Negro Formation deposits and regionally to Andean Cordillera volcanic sources.
Estuaries and deltas are common along modern coasts and are well represented in the geologic record because of the high preservation of their deposits. Worldwide, estuaries are more abundant than deltas because of the relatively short time available for Holocene coastal sedimentation due to sea level variations. The evolution of estuaries and deltas during the recent geological past can be reliably reconstructed. Among others, paleostudies in estuaries aim to reconstruct sea level and freshwater input variations, and the timing and frequency of extreme events (e.g., tsunamis). A significant number of studies have been published in the past 20 years, which used preserved remains of microorganisms accumulated during long intervals in sediments. The preserved record of fossil remains evidences the response of microorganisms to environmental changes at the time of their deposition. Among the proxies preserved in sediments, diatoms are one of the most reliable bioindicators to trace environmental changes. Due to rapid reproduction rate under favourable conditions and their siliceous frustule, they are abundant in recent and older sediments from estuaries and deltas. In this manuscript, results from previous studies were reviewed, integrated and statistically analyzed with the aim to reconstruct Holocene coastal changes in relation to sea level curves. These studies were conducted along a latitudinal transect on four estuarine mesotidal systems from Northern Patagonia, Argentina: Colorado River delta (39°40′S; 62°08′W), San Blas Bay (40°33′S; 62°13′W), Negro River (40°57′S; 62°49′W) and Chubut River estuaries (43°22′S; 65°03′W). The focus is on the preserved diatom assemblages and the paleoecological information they represent. Seven coastal sedimentary cores were correlated. Based on multivariate analysis (NMDS), fossil and modern diatom assemblages were integrated and compared. These estuary systems are dominated by littoral drift, where the plains became flooded by the sea about 7000 ¹⁴C years BP ago. When the sea transgression occupied the area, Colorado delta and San Blas Bay evolved from tidal channels flooded to tidal flats, sand flats and marshes during the late Holocene regression. At Colorado River, the gradually increase of the fluvial influence is associated with the eastward progradation of the deltaic lobe during the last ca. 7000 ¹⁴C years BP. At the Negro River estuary, a shallow vegetated brackish/freshwater environment evolved into marine conditions, tidal channels and marshes during the last 2000 ¹⁴C years BP. A marine coastal environment (estuary) at ca. 4400 ¹⁴C years BP that evolved into a salt marsh was inferred at the inlet of the Chubut River. Diatom salinity-preferences showed how connections between the wetland and the sea varied over time with sea level changes and gradual infilling. Diatom-inferred paleoenvironments and radiocarbon dates allowed reconstruction of the coastline position to the east in the Early Holocene and to the west during transgressive-regressive events.
Marine Isotopic Stage 3 (MIS 3) was a period of rapid climatic changes and sea level
fluctuations. Regarding these fluctuations some doubts were based on the limit of the radiocarbon dating method (about 50,000 years B.P.). However, the modelling of the isotopic oxygen ratios is also indicating sea level fluctuations. In this sense, only at certain depths it is possible to accept these ages at stable coasts, and taking note about the taphonomic conditions within the sequence. Shells located at depths higher than 60 m on stable and wide continental shelves as that of the Northern Patagonia have been analyzed here in that sense.
The coasts of southern Buenos Aires, Patagonia and Tierra del Fuego are dominated by cliff erosion. Mean rates of cliff retreat are estimated to be about 0.5-0.6 m/year by comparing old photographs with modern satellite images. Considering the height of the Patagonian and Fueguian cliffs (70 to 120 m), the volume of sediment eroded from these cliffs exceeded the volumes provided by the erosion of the cliffs of Buenos Aires (10 to 20 m height). These erosion rates support an estimated delivery of 217 million tons of sediment per year to the continental shelf, exceeding significantly the 22 millions of tons/year transported by the larger Patagonian rivers Negro and Colorado. However, the contribution of these rivers has decreased since the Late Pleistocene changes in the direction of transport of some watersheds. The Chubut and Chico de Santa Cruz rivers suffered reductions of 21-24% in their watershed areas, resulting in reductions of about 33-34% in the volume of water transported to the Atlantic Ocean per year. As the amount of sediment delivered to the Argentine continental shelf by cliff erosion is higher than the fluvial transport, it should be also considered in the balance of beaches fed by longshore transport.
The Chubut River flows from the Andes to the Atlantic Ocean, and is interrupted by a single dam built at the middle valley. The lower valley is dominated by the aggradation of an alluvial plain induced by a complex of spits that enclosed the inlet in the last 5000 years. The river has reduced its flow because the blocking of the upper basin by terminal moraines during the Upper Pleistocene. At least the last two marine transgressions have flooded this estuary, and contributed to the aggradation during regressions. The area is of particular interest in regard to irrigation channels practiced since the XIX century. Today, the mean monthly flow is less than 10 m3/s although peaks of 95 m3/s have been recorded in Gaiman in July 2001. The dynamics of the estuary is dominated by waves (wave-dominated estuary) as tidal effects attenuate in less than 5 km. Three vibracores were collected within this floodplain: (a) at Gaiman, an area without any effect of the sea (35 km from the coast); (b) at Trelew, at the former avulsion plain of the river (18 km from the coast); and (c) at Playa Magagna, a saltmarsh located 0.4 km from the beach.
The purple clam Amiantis purpurata (Lamarck) is a warm-temperate species which inhabits the shallow waters from Espiritu Santo (Brazil) to northern Patagonia. It is understood to be one of the few survivors of the middle–late Miocene faunal turnover which was characterized by the appearance of new taxa, most of them living today along the Argentinean coast. In order to study the biogeographical history of A. purpurata, a detailed review of its records was carried out. The oldest record of A. purpurata comes from the late Miocene of Uruguay, and it appears that A. purpurata survived because its wide thermal tolerance range allowed larvae to migrate from Uruguay to the south, where they settled on the southern coast of the province of Buenos Aires and the San Matías Gulf. In addition, the characteristics of this gulf would have fostered the development and settlement of the larvae, thus giving rise to the most abundant southern population during the Pleistocene. At the end of the Pleistocene, A. purpurata also survived the Last Glacial Maximum and, once in the Holocene, the A. purpurata population at the San Matías Gulf became isolated, also representing the most abundant southern population of this species. In its brief Neogene geological history, Amiantis purpurata followed main global, regional and local events; thus it can be considered as an environmental indicator for this period.
La integración de los depósitos neógenos en un marco regional pone de manifiesto la gran extensión areal que tienen estas unidades en el área extrandina. Mediante la caracterización de las unidades neógenas de la región central de Argentina, se propone un esquema de correlación de las unidades para enmarcarlas en un modelo evolutivo geológico regional. Surge de este análisis la existencia de dos grandes ciclos de depositación continental, producidos con posterioridad al retiro del mar paranense, uno en el Mioceno tardío y otro en el Plioceno. Ambos ciclos están separados por un importante hiatus depositacional y erosivo, y sus cuencas respectivas no coinciden en su extensión areal. De esta manera se propone que la cuenca de antepaís pliocena se restringe arealmente hacia el sur con respecto a la miocena tardía.
The aim of this paper is to give the general outlines of a SOAR project
named "Saltpan surface variations analysis with RADARSAT-2 data". The
main goal of this project is to study the potential of polarimetric
RADARSAT-2 data for landscape and environmental analysis of quaternary
salt bodies located in the southern part of Buenos Aires province,
Argentina. Most of these deposits are traditionally exploited to mining
"salt" for industrial and domestic use. However, their exploitation is
conditioned by a number of factors related to environmental and weather
conditions as well as on hydrologic regimes. The geomorphologic,
hydrological and environmental settings of recognized salt pan deposits
of this area are presented, as well as the general properties of their
evaporite minerals, resulting from field and laboratory studies. Also,
the methodological approach proposed to take advantage of RADARSAT-2
data is discussed.
Resumen Se analizaron los foraminíferos bentónicos de un testigo correspondiente al Holoceno reciente del Golfo Nuevo. La fauna recuperada fue bentónica y las especies predominantes fueron Buccella peruviana f. campsi (Boltovskoy), Buliminella elegantissima (d'Orbigny) y Bulimina patagonica d'Orbigny. Los análisis cualitativos y cuantitativos confirman condiciones marinas marginales con menor oxi-genación que las actuales. Ello sería la consecuencia de un desmejoramiento climático que por su magnitud y persistencia habría lle-gado a invertir el sentido de la actual circulación termohalina del golfo, representando entonces una probable consecuencia de la denominada Pequeña Edad de Hielo. Abstract [Benthic Foraminifera of the Holocene from Golfo Nuevo, Argentine: paleoclimatical inferences]. Benthic Foraminifera from a recent Holocene core from Golfo Nuevo were analyzed. The fauna recovered was benthonic, and the predominant species were Buccella peruviana f. campsi (Boltovskoy), Buliminella elegantissima (d'Orbigny) and Bulimina patagonica d'Orbigny. Qualitative and quanti-tative analyses confirmed marginal marine conditions with lower oxygenation levels than under present-day conditions. This may have been a consequence of deterioration in climate which, due to its magnitude and persistence could have inverted the direction of the gulf's current thermohaline circulation, in which case it would represent a probable consequence of the so-called Little Ice Age.
The European Space Agency (ESA) funded two projects in 1991 and 1994 concerning the observation of the Argentine coastal environment with synthetic aperture radar (SAR). Studies were carried out for the periods 1992-1994 and 1994-1997. Several ERS-1/2 satellite SAR images were acquired over the San Matias Gulf in the Patagonian coast during these two periods. SAR is a side-looking imaging radar that operates from either a satellite or an aircraft. The instrument emits a series microwave pulses toward the earth in a direction perpendicular to the flight path. Imagery is constructed from the strength and time delay of the returned signals, which depend primarily on the roughness and dielectric properties of the surface under observation and the distance from the radar. Ocean surface roughness wave-like patterns, imaged as a series of bright and dark linear features by SAR, are persistently observed over the San Matias Gulf mouth region. A total of thirty-three (33) ERS-1/2 SAR images (100 km X 100 km) from 15 different orbits from 1992 to 2000 were analyzed. This series of observations has allowed for a detailed examination of the location, persistence, and the conditions involved in the imaging of the observed wavelike patterns. Very strong tidal currents of the order of 2 m/s characterize the gulf region. The characteristics of recurrent surface patterns in the SAR images indicate that they are caused by the interaction of the tidal currents with bed forms in the bottom topography of the gulf. The location of these bed forms is poorly documented in the available bathymetric charts of the region. The SAR images show the significant potential that satellite radar observations have as a tool for detecting unmapped coastal ocean bottom features, particularly, where bathymetric mapping activities can be extremely difficult, dangerous, or costly.
This chapter focuses on the neotectonics of Argentine–Chilean Patagonia and overviews the active tectonics of the southernmost region of South America, which constitutes a field of relatively recent development on a national standard. The presence of remarkable morphotectonic features associated with active faulting fronts in several of the defined seismotectonic regions indicates modern tectonic activity for this region of Patagonia. From the point of view of seismic risk studies, these regions have been subjected to various seismic effects and can be considered as units of potential risk. Once the different aspects of tectonics, large morphological features, seismic activity, and active volcanism have been analyzed individually, it is important to consider in combination because their occurrence indicates those regions where the earth's crust is being exposed to greater stresses and the resulting tension release. To properly estimate seismic risk in the Patagonian region, it is necessary to delimit these regions in such a way that they can be identified as independent units called “seismotectonic regions.” The four identified Patagonian seismotectonic regions are (1) Liquiñe–Ofqui–Fagnano, (2) Somuncurá (3) Agnia, and (4) Deseado.
This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan, sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,
Diatom and sedimentological analyses of two cores from San Bias Bay and the analysis of historical charts provide information about the environmental evolution of this estuarine complex during the last 5000 yr BR The Holocene sea-level regression is recorded in San Bias Bay by infilling of a tidal channel. Two sediment cores were drilled at Arroyo Jabaliaccute; (San Bias Bridge) and at the former inlet of Arroyo Walker and Arroyo Jabalí (Paso Seco). The diatom record of the San Bias Bridge sequence is dominated by marine and brackish/freshwater plankton and tychoplankton and composed by fine to very fine sand and mud characterizing the infilling of a tidal channel. The Paso Seco sequence is more abundant in sand. Textural and diatom facies are interpreted as the infilling of a tidal channel very similar to the one at San Bias Bridge, that evolved towards the top into a sandflat characterized by the dominance of marine and marine-brackish epipsammon accompanied by marine tychoplankton. Arroyo Walker and Arroyo Jabalí were flowing eastward across a tidal channel during the Holocene. Because of obstruction of the channel, the tidal channel assemblages were replaced by sandflat assemblages. According to historical charts, as late as 1833 a tidal inlet still existed in this sector, which was later obstructed completely according to Twentieth Century charts. At this timescale, eustasy is considered to be a minor environmental control on the dynamics of the system. Instead, control is forced by other factors, such as inlet instability due to morphological changes of the sand barrier whether emergent or submerged.
This chapter focuses on the physical geography of Late Cenozoic of Patagonia and Tierra del Fuego. This chapter discusses a junction of natural elements in the southern end of South America. Bedrock substratum and structure, climate, distribution of the superficial runoff, soils, and vegetation, all act together in a systematic, cause–effect relationship and form a group of homogeneous geographical spaces that are joined under first-order geological and atmospheric elements, such as tectonic plates and the general atmospheric circulation. The interaction of the wetter Pacific winds and the Andean Cordillera is the basic natural condition that determines the geographical aspects of the natural, physical environment of the southernmost end of South America. The pluvial and snow régime of the streams, the allochtonous character of the tableland streams, the development of contrasting biomes, such as jungle-like forests and rainshadow deserts, with a modest thermal régime are a consequence of the orographic barrier interaction with the air masses of the Southern Pacific anticyclonic centers and the polar front.
This chapter focuses on the existing pollen datasets from Patagonia, between 37o and 52o S covering the Late Quaternary and a comparison with selected pollen data from Chile. A continuous pollen record does not exist in Patagonia that link the Last Glacial Maximum (LGM) with previous interglacial–glacial periods. The only pollen record that probably represents interglacial conditions about 430 ka (MIS 11) is that from Cañadón El Mosquito, in southern Patagonia. During the Mid Holocene, the westerlies brought higher humidity to both the Andean zone and the southern extreme of Patagonia. Semiarid conditions in extra-Andean region suggest that the westerlies were less intense than present. An increase of aridity and temperature at the northeast Patagonia led to an arid climate and to the establishment of the Arid Diagonal during this time. In Patagonia, postglacial times were characterized by high fire frequency. Human impact, volcanism, and climate have been proposed to explain spatial and temporal variations of this fire frequency throughout different intervals.
Fundamental characteristics of the climate system during the most recent precessional cycle of the Earth's orbit around the Sun consist of the final expansion of land ice to its maximum extent, the subsequent episode of deglaciation, and the variations of global sea level that accompanied these events. In order to address the important issue of the variation of continental ice volume and related changes in global sea level through the late glacial period, we employ an extended set of observations of the pre-glacial and postglacial history of sea-level rise at the island of Barbados, together with a refined model of continental deglaciation and an accurate methodology for the prediction of postglacial sea-level change. Although our results provide unambiguous evidence that the post LGM rise of eustatic sea-level was very close to the widely supported estimate of 120 m, the data also provide evidence that LGM must have occurred 26,000 years ago, approximately 5000 yr earlier than the usually assumed age.
During his journey on the Beagle, Darwin observed the uniformity in the elevation of coastal Eastern Patagonia along more than 2000 km. More than one century later, the sequences of Quaternary shorelines of eastern Patagonia have been described and their deposits dated but not yet interpreted in terms of geodynamics. Consequently, we i) mapped the repartition of the Quaternary coastal sequences in Argentinean Patagonia, ii) secured accurate altitudes of shoreline angles associated with erosional morphologies (i.e. marine terraces and notches), iii) took into account previous chrono-stratigraphical interpretations in order to calculate mean uplift rates since ~ 440 ka (MIS 11) and proposed age ranges for the higher and older features (up to ~ 180 m), and iv) focused on the Last Interglacial Maximum terrace (MIS 5e) as the best constrained marine terrace (in terms of age and altitude) in order to use it as a tectonic benchmark to quantify uplift rates along the entire passive margin of Eastern South America. Our results show that the eastern Patagonia uplift is constant through time and twice the uplift of the rest of the South American margin. We suggest that the enhanced uplift along the eastern Patagonian coast that interested Darwin during his journey around South America on the Beagle could originate from the subduction of the Chile ridge and the associated dynamic uplift.
We present, for the first time, an optical spectroscopic data cube of the
giant star-forming region 30 Doradus, obtained with the GIRAFFE on the VLT at
Paranal Observatory. The main emission lines present in this data cube
correspond to H{\alpha}, [NII] 6548 {\AA} and [NII] 6584 {\AA}. By using this
data set, we found that H{\alpha} presents from simple to multiple profiles,
which suggests that different physical mechanisms act in different ways on the
excited gas in 30 Doradus. We found, at least, three unclassified large
expanding structures. These structures correlate with peaks in the X-ray
distribution. Given the excellent signal-to-noise ratio and the large spatial
coverage of this data cube, we have studied in detail the kinematics of 30
Doradus, showing the importance of the small scale phenomena on the integrated
properties of 30 Doradus.
Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 19 (2004): PA1024, doi:10.1029/2003PA000903. We apply a shock-capturing numerical model based on the single-layer shallow water equations to an idealized geometry of the Black Sea and the Sea of Marmara in order to test the implications of a suggested sudden Black Sea infill 8400 years ago. The model resolves the two-dimensional flow upstream and downstream of the hydraulic jump provoked by the cascade of water from the Sea of Marmara into the Black Sea, which would occur during a sudden Black Sea infill. The modeled flow downstream of the hydraulic jump in the Black Sea would consist of a jet that is in part constrained by bathymetric contours. Guided by the Bosporus Canyon, the modeled jet reaches depths of up to 2000 m and could explain the origin of the sediment waves observed at this depth. At a late stage of the infill the modeled jet is attached to the coast and might account for the course of a submerged channel at the mouth of the Bosporus. The preservation of continuous barrier-washover-lagoonal fill systems occurring on the Black Sea shelf is, however, not easily reconcilable with the large flows over the southwest Black Sea shelf predicted by the model. Intensified flow in the upstream basin (Sea of Marmara) is restricted to the immediate vicinity of the Bosporus, suggesting that a sudden reconnection need not have disturbed sediments in the wider Sea of Marmara. L. Pratt and K. Helfrich were supported under O.N.R. grant N00014-010100167 and N.S.F. grant OCE-0132903. L. Giosan was supported by a postdoctoral scholarship grant from CICOR (a Joint Institute of Woods Hole Oceanographic Institution and NOAA).
The timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets and their effects on the Earth's surface. Moreover, the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans, which probably disturbed the ocean's thermohaline circulation and, hence, global climate. Sea-level increase bear witness to the melting of continental ice sheets, but only two such records - from Barbados and New Guinea corals - have been accurately dated. But these corals overlie active subduction zones, where tectonic movements are large and often discontinuous (especially in New Guinea), so the apparent sea-level records may be contamined by a complex tectonic component. Here we date fossil corals from Tahiti, which is far from plate boundaries (and thus is likely to be tectonically relatively stable) and remote from the locations of large former ice sheets. The resulting record indicates a large sea-level jump shortly before 13,800 calendar years BP, which correponds to meltwater pulse 1 A in the Barbados coral records. The timing of this event is more accurately constrained in the Tahiti record, revealing that the meltwater pulse coincides with a short and intense climate cooling event that followed the initiation of the Bolling-Allerod warm period, but preceded the Younger Dryas cold event by about 1 000 years. (Résumé d'auteur)
La zona costera del noreste de la Patagonia se caracteriza por importantes acantilados que contienen excelentes afloramientos de la Formación Río Negro (Mio-Plioceno). Dentro de una sucesión
principalmente continental se intercala un nivel marino asignado al Mioceno Tardío que presenta espesores máximos de hasta 10 metros y una geometría lenticular a gran escala. Está constituido por
pelitas y areniscas finas bioturbadas con asociaciones de megafósiles que incluyen moluscos, principalmente bivalvos, corales, cirripedos y erizos. El nivel marino integra una secuencia deposicional caracterizada por un ciclo marino completo transgresivo-regresivo. El contexto geotectónico del área de estudio sugiere un control mayormente eustático durante la época en que se formaron estas
asociaciones de megafósiles, las cuales fueron analizadas desde el punto de vista tafonómico y paleoecológico. Las asociaciones fosilíferas relacionadas con el cortejo transgresivo (TST) se
caracterizan por su riqueza en bivalvos (ostreidos y pectínidos). Las asociaciones relacionadas al cortejo de alto nivel (HST) constituyen acumulaciones monoespecíficas de ostreas donde se manifiestan
muy importantes los procesos de bioerosión que indican que los organismos han estado expuestos un tiempo suficientemente largo durante el cual la sedimentación fue mínima. Hacia el techo de la
secuencia se evidencia una rápida somerización relacionada con una regresión forzada (FR) debido a una rçapida caída del nivel del mar. El proceso de somerización en sentido vertical se pone de manifiesto
por la presencia de especies de menor batimetría, procesos de incrustación y la superposición abrupta de asociaciones costeras sobre otras de mayor profundidad.
The first absolute ages and the general accretion features of coastal deposits in bahía Engaño are presented. The accretion deposits correspond to vast accumulations of littoral gravel ridges, which constitute the major morphological units, such as marine terraces and palaeospits. Areas of semirestricted environments corresponding to inactive lagoons, are delimited by different groups of beach ridges. Results of 14C dating indicate that most of coastal deposits in bahía Engaño were accumulated during Holocene marine regressive phases. The progradation pattern is characterized by three major cycles of accretion limited by two pulses of erosion or no deposition. The most recent pulse of erosion occurred between 3900 and 3200 years BP.
This paper analyzes littoral deposits of the Holocene transgression in Anegada Bay, Argentine Republic (39°50'S to 40°00'S and 62°15'W). At least five transgressive episodes were identified as Transgresive Stages (TS 0 to V) being marked by barrier island and lagoon development. Their Probable Geological Age (PGA = the minimum 14C age) and Approximate Ages (AA = with 14C ages obtained from mollusk-shells in life position), are: TS-0 = 6560 ± 130; TS-I = 6190; TS-II = 5570; TS-III = 5200; TS-IV = 4350 and TS-V = 3600 BP. The TS-I represents the maximum Holocene Transgression and the TS-0 corresponds to a previous event. Both could be related to maximum solar activity peaks (thermoeustatic transgression). The younger TS (TS-II to V) show minor transgressive episodes which could be related to exceptionally high tides (coincident with the Progressive Cycle of the Lunar Perigee) and to high wave-energy episodes (exceptional storms). The storm episodes could be coupled to episodic events of great magnitude such as the ENSO (past ENSO-like = El Nino Southern Oscillations events). These kind of events might have caused massive sediment pulses and changes in the direction of the littoral drift.
Diatom assemblages from a sediment core and a sequence outcropping 6 km from the Río Negro mesotidal inlet were studied in order to reconstruct salinity and depth changes. The sequence comprises the interval between 2027±34 14C years BP to the present. Diatom data from 44 samples were analyzed according to ecological characteristics of each taxon. The basal section was dominated by the oligohalobous indifferent taxa: Navicula viridula var. germainii Kütz. (benthos), Epithemia adnata (Ehrenb.) Kütz. (epiphyte) and Surirella brebissonii Kramm. and L.-Bert. (oligohalobous halophilous and benthos). From 2027 yr BP a tidal channel characterized by the dominance of the marine plankton and tychoplankton Thalassionema nitzschioides Grun., Delphineis surirella (Ehrenb.) Andrews, Delphineis minutissima Hustedt. Simonsen and Rhaphoneis amphiceros Ehrenb. was installed. Paralia sulcata (Ehrenb.) Cleve and Cymatosira belgica Grun. were present to the top of the sequence, where brackish-freshwater aerophilous taxa, such as Diploneis ovalis (Hilse) Cleve and Pinnularia viridis (Nitz.) Her., were dominant. The shallow and vegetated brackish-freshwater environment from the bottom of the core, evolved towards a tidal channel, declining gradually in depth and salinity, to a marsh subject to tides and floods at the top of the sequence.
For the first time radiocarbon dates with corresponding altimetry over present mean sea level are correlated for the Holocene of Argentina. Relative rates of continental uplift for 15 localities distributed over 3500 km of the Argentina coast are determined, and a model of coastal evolution is described. Maximum transgressive levels were reached between 4000 and 6500 yr BP. The relative uplift rates for the Holocene varied between 0.12 and 1.63 m/1000 years. The neotectonism along the Argentina coast is clearly evident as the minimum uplift rates are associated with sedimentary basins while maximum ones correspond to interbasin zones. -Authors
Falta traduccion del título. The integration of Neogene deposits in a regional framework evidences their large areal distribution in the extra Andean fo-reland region of Central Argentina. A correlation scheme is proposed for placing the different lithostratigraphic units identi-fied within a regional geological evolutionary model. The stratigraphic and sedimentological analyses suggest that after the marine regression of the Paranense Sea, two major cycles of continental deposition, separated by a regional unconformity, occurred in the late Miocene and the Pliocene respectively. The areal extension of the Late Miocene and the Pliocene sedi-mentary basins does not coincide; the Pliocene basin with more restricted areal extension, dominantly developed southward.
El estudio de los ensambles de diatomeas en sedimentos holocenos de los
estuarios del río Negro y del río Chubut, en el norte de la Patagonia Argentina,
permitió inferir la evolución paleoambiental de esos ambientes mesomareales en
relación a los cambios del nivel del mar durante el Cuaternario. Se analizaron cuatro
secuencias sedimentarias, dos en el río Negro (a 1,5 km y a 10 km de la
desembocadura) y dos en el río Chubut (a 0,40 km y a 36 km de la desembocadura).
Se realizaron análisis cualitativos y semi-cuantitativos de las muestras obtenidas a fin
de interpretar los cambios ambientales, en relación a la salinidad y la profundidad. El
estudio de los ensambles de diatomeas del río Negro permitió reconstruir la evolución
del estuario durante los últimos 2000 14 C años AP que habría comenzado con un
ambiente salobre/dulceacuícola con vegetación asociada que evolucionó
gradualmente hacia un ambiente marino, un canal de mareas, y a una marisma en
tiempos recientes. En el río Chubut, la secuencia ubicada a 36 km de la
desembocadura corresponde al relleno de un cuerpo de agua dulce/salobre con
vegetación desde los 8020±110 14 C años AP hasta el presente, mientras que en la
desembocadura se infiere un ambiente costero/marino (estuario) a partir de los
4376±69 14 C AP que evolucionó hacia una marisma instalada entre los 672±39 14 C
años AP y la actualidad. Dada la fuerte influencia de los cambios de salinidad en los
ensambles diatómicos, los efectos de las mareas son el principal factor que controla la
composición y distribución de las comunidades en la región.
Seventeen playa lakes in Patagonia between 39° and 47° S were cored with the aim of reconstructing the vegetational, climatic and geomorphological history by means of sedimentological and palynological analysis. The paper discusses the initial results from two salt lakes, Salina Anzoátegui (39°00′23′S, 63°46′30”W) and Salina Piedra (40°34′59”S, 62°40′26”W), lying in closed depressions at the northeastern margin of the arid diagonal of Patagonia. Both the sedimentological and the palynological results of the analyzed sediment cores from these playa lakes suggest prevailing arid climatic conditions with mainly aeolian morphodynamic processes during the mid-Holocene. In late Holocene times the climate changed to more semi-arid conditions, with a higher rainfall frequency and more frequent fluvial input into the lake, possibly reflecting greater influence from the Atlantic high pressure cell leading to more distinct seasonality.
As in other parts of the world, the northern coast of the San Matías Gulf (Northern Patagonia, Argentina) has undergone remarkable changes after the Middle Holocene sea level maximum. By means of an interdisciplinary work, the geomorphologic evolution of Bajo de la Quinta coastal hollow was reconstructed since ca. 600014CBP, when the oldest human occupation of the area was detected. Main recorded changes in coastal configuration seem to have had a noticeable influence in both the use of marine resources along time by native hunter-gatherer groups, and the preservation of the archaeological evidence. With respect to the first issue, changes in human paleodiets and fishing practices could be related with the sedimentary filling and rectification of this littoral after the high marine level scenario. This study highlights the importance of reconstructing past scenarios of human activities for archaeological interpretation, in particular when studying high dynamic environments such as the coastal landscape.
The San Matías Gulf, located between 40 47' S and 42 13' S on the Atlantic coast of South America, with an area of approximately 18 000 km², is the second largest in Argentina. This gulf has been studied by means of historical data obtained in oceanographic campaigns carried out before 1990 and with satellite images of low-resolution (1000 m) NOAA-AVHRR obtained from 1985. The analysis of this information permitted to infer some environmental characteristics related to temperature, salinity, productivity and circulation. The objective of the present work is to analyze LANDSAT-TM and ETM+ data from 1997-2003. Approximately 30 free of clouds images, obtained in different times of the year, were processed. The thermal channel allowed to obtain a detailed distribution of surface temperature, to identify thermal fronts and to analyze its variability along the year. Also, this channel and channel 1 permit to observe the influence, in the southern part of the gulf, of the water coming from the continental shelf and San José Gulf. The results obtained did not only contributed to corroborate the environmental characteristics already inferred previously from cruise data, but also, to identify others, so far unknown
Extract
Plate XL.
1. Boulder Formation in the Valley of the Santa Cruz. During the survey of the shores of South America, southward of the Rio Plato, by Capt. FitzRoy in H.M.S. Beagle, I did not meet with any boulders on the eastern plains of the continent until we arrived on the banks of the river Santa Cruz, in lat. 50° 10′ S. Nor did they occur there near the coast, but were first noticed in ascending the river at the distance of about 100 geographical miles from the Atlantic, and 67 from the nearest slope of the Cordillera. Twelve miles further west, in lon. 70° 50′ W., that is, fifty-five miles from the mountains, they were extraordinarily numerous; consisting of compact clay-slate, feldspathic rock, a quartzose chloritic schist, and basaltic lava; and they were generally of an angular form, and many of them resembled fragments of rock at the foot of a precipice. The size of some was immense: I measured a square one of chloritic schist, which was five yards on each side and projected five feet above the ground; a second, which was more rounded, was sixty feet in circumference, and stood six feet above the ground; how much of each was buried beneath the surface I could not ascertain. There were innumerable other fragments from two to four feet square. The vast open plain on which they lay scattered, is 1400 feet above the level of the sea; its surface is somewhat but not greatly irregular, and
Neritic-littoral marine sedimentary deposits from the Argentine Shelf
provide a record of late Pleistocene sea level variation. Sediments
interpreted to reflect the last glacial maximum low-stand are ˜150
m below present. Using a simple Airy isostatic model for hydroisostatic
compensation and correcting for a minor tectonic component yields a
local eustatic sea level lowering of ˜105 m at the last glacial
maximum. The deglacial sea level curve records two rapid sea level rises
consistent with MWP1-A and 1-B as documented by the Barbados coral-based
sea level curve. Comparison with relative sea level variations predicted
by the ICE4G VM2 viscoelastic model have highlighted a deficiency in the
model's predicted sea level history for this region. Detailed data-model
comparisons of late Pleistocene sea level variations are necessary in
the face of climate change induced sea level perturbations to determine
regional and or systematic biases in the treatment of lithosphere
viscosity and accurate predictions of future sea level.
This chapter focuses on the Late Cenozoic fluvial deposits of Argentine Patagonia. The study of the Patagonian fluvial deposits comprises the analysis of a very extensive group of units that have historically been known as “Rodados Patagónicos” or “Patagonian gravels.” The chapter discusses the present stage of knowledge and proposes a classification based upon genetic, spatial, and chronological criteria. The gravel mantles that extend almost parallel to the present drainage lines may be genetically related to fluvial valley processes, whereas the rest of the units must be associated with climatic fluctuations, the glacial and interglacial periods, and to modifications in base levels because of tectonic, epirogenic, eustatic, and glacioisostatic movements during the Late Cenozoic. The approach adopted in this chapter is basically genetic, allowing the differentiation of (1) fluvial valley units, (2) glaciofluvial units, and (3) piedmont units. Additionally, the use of other criteria of spatial, geomorphological, and temporal nature has permitted a better characterization of the identified morphostructural units. The marked climatic, tectonic, and geological differences existing throughout Patagonia do not encourage the use of a single genetic scheme for all these units. Evidence seems to indicate that it is necessary to develop specific models that would explain the origin and occurrence of these gravel sheets.
San Jose Gulf is a small semienclosed bay connected by a narrow mouth to a much larger basin, the San Matias Gulf. Intriguingly, this comparatively small water body, characterized by high biological productivity, has contributed most of the historical shellfish production in the region. A remote sensing approach allowed us to advance a composite conjecture aimed at explaining that phenomenon. A combination of circulation, strong tidal currents, and coastal topography leads to the formation of a frontal system inside San Jose Gulf and to the development of turbulent fluxes that drive the hydrographic regime. The front divides the San Jose Gulf in two domains (west and east). The origin of water flowing into the west domain was tracked to the Valdes Frontal System, on the continental shelf. The west domain is highly turbulent due to the formation of vortexes and dipoles during the tidal cycle. Detachable dipoles formed at the edge of jets outflowing from San Jose Gulf can reach the central part of San Matias Gulf, constituting a possible larval transport mechanism between the two gulfs. Our results led us to postulate that (1) nutrients from the continental shelf are “trapped in” and larvae are retained in the east domain of San Jose Gulf, resulting in persistently high biomass of secondary producers, and (2) asymmetrical exchange, in the form of vorticial flows, “pumps out” waterborne material from the San Jose Gulf into San Matias Gulf, affecting the connectivity between the two basins.
This chapter focuses on the coastal geology and morphology of Patagonia and the Fuegian Archipelago. Patagonia and Tierra del Fuego show a wide and varied record of coastal evolution for the Quaternary period, comprising the complicated relationships among glacial deposits, interglacial highstands, and different uplift trends. The sea-level highstands that occurred during the Middle Pleistocene are difficult to distinguish because it is necessary to consider the precision of the dating method and if the uplifting rate permitted a vertical displacement between two consecutive highstands. In northern Patagonia, Holocene beach plains originated because of gravel abundance, between capes or related to river inlets. On the Atlantic coast of Tierra del Fuego there are regressive-like sequences of beach ridge plains in protected areas, and transgressive-like beach plains developed at exposed areas are subjected to fluctuations in gravel availability.
Geomorphologic and chronostratigraphic investigations in various coastal localities along the middle and south Patagonian Atlantic coast, from Bahía Vera (44°S) in the north to San Julián (49°S) in the south, confirm a rich sequence of Holocene beach ridge systems and littoral and valley-mouth terraces. Beach ridges are present up to 10 m above current highest tide level (hTw) and date to the early mid-Holocene transgression maximum. Beach-ridge deposits represent high-energy, wave dominated coastal environments, whereas valley-mouth terraces and littoral terraces (elevations of 5.5–6.5 m above hTw) developed in wave-protected coastal environments.The surface elevation of these littoral forms suggest that the middle and south Patagonian Atlantic coast is likely undergoing a slow glacio-isostatic uplift on the order of 0.3–0.4 mm/a since the mid-Holocene. The early Holocene sea-level rise reached the modern coastline by 8100 14C years ago (c. 8600 cal BP) at the latest. Sea level at that time was most likely near its present position. The Holocene transgression maximum lasted from 6900 to at least 6200 14C BP (c. 7400 to 6600 cal BP), raising relative sea level to about 2 m to a maximum of 3 m above the present level, after which sea level declined to the present level. Two significant sea-level falls of at most 1 m occurred: a) between 6200 and 6000 14C BP (c. 6600 to 6400 cal BP), and b) between 2600 and 2400 14C BP (c. 2300 to 2050 cal BP).We assume, that both significant sea-level falls were predominantly driven by eustatic changes of ocean volume, whereas both thermo-steric changes and changes of tides may also have contributed to these relatively strong sea-level drops. Gravitational changes driven by Greenland ice growth (sensu Mitrovica et al., 2001) may also have amplified any eustatic portion of sea-level fall. The trend of a general sea-level decline since the mid-Holocene transgression maximum seems to be predominantly glacio-isostatically driven.
Six areas of the Patagonian coast, Argentina, were investigated in order to determine the number, characteristics, geomorphology and development of Quaternary littoral zones. It became apparent that utilizing ratios of aspartic acid and leucine of various molluscan species would be the most useful in correlation, relative age dating and estimating the ages of these zones. The oldest littoral zone is found at elevations between 24 and 41 m above mean sea level and is judged to be older than Oxygen Isotope Substage 5e in age based on relatively high amino acid ratios and extrapolated from non-linear kinetic models. An intermediate aged littoral zone may be present at some locations based upon beach ridges or platforms varying in elevation between 16 and 28 m above mean sea level. ratios are generally lower than those for the oldest zone but show a greater variation. This zone may represent the Substage 5e sea level stand. Well defined young beach ridges 8–12 m above mean sea level are found in most locations and have been 14C dated, and verified by amino acid ratios, as being Holocene. The presence of Quaternary aged emerged littoral zones at roughly the same elevation suggest that the glacio-eustatic contribution is the primary cause of the high sea level stands whereas secondary variations are attributed to other factors.
Raised beaches developed during Holocene times along the northern Beagle Channel coast. These deposits contain a rich marine fauna, especially shelled organisms such as mollusks.Four Holocene marine sites along the northern coast of the Beagle Channel have been analysed; from west to east they are: Bahía Ensenada, Playa Larga, Bahía Brown and Cutalátaca airfield. They were studied in relation to relative altitude, sediment type, faunal composition and radiocarbon dates.The area is characterized by several discontinuous terraces with elevations varying from about 1.5 to 10 m above sea level. Their possible origin (1) due to tectonic uplifting, in comparison with raised beaches of the northern part of Tierra del Fuego, and (2) resulting from glacio-isostatic recovery, taking into account the ice retreat, is discussed.Seventeen species of mollusks (eight bivalves, nine gastropods) were collected from the study sites. All of them are living species from the Beagle Channel and have been interpreted as representative of Holocene paleocommunities in this channel. These species show no evidence of substantial climatic changes during the Holocene, although minor temperature fluctuations cannot be ruled out yet.
San Sebastian Bay is a large, semicircular coastal embayment situated on the Atlantic coast of Tierra del Fuego, Argentina. It is a high-energy, subantarctic environment with a tidal range of 10.4 m, influenced by large waves of Atlantic and local origin and swept by constant, strong westerly winds. A 17 km long gravel spit protects the Northern part of the Bay giving rise to a gradient in sedimentary processes. From south to north, are seven distinct sedimentary environments. Coastal sedimentation started at least 5200 years before present (BP) and a rapid progradation related to a relative sea-level drop has infilled about 6 kilometres of the Bay with a sedimentary sequence 10–11 m thick. 14-C dating of unabraded shells in the Chenier ridges of the relict part of the complex allows for a precise reconstruction of the stages of the progradation, that has slowed from 2.35 m/year at 5000 years BP to 0.6 m/year at present. The possible causes of the sea-level drop are discussed.
Evolución de los depósitos litorales en bahía Anegada
- N E Weiler
Weiler, N.E., 2000. Evolución de los depósitos litorales en bahía Anegada, Provincia de Buenos Aires durante el Cuaternario Tardío. Unpublished PhD thesis, University of Buenos Aires, Buenos Aires, 184 pp.
Edades 14 C y ciclicidad de la acreción en depósitos costeros elevados
- A J A Monti
Monti, A.J.A., 2000. Edades 14 C y ciclicidad de la acreción en depósitos costeros elevados, Bahía Engaño, Chubut. Revista de la Asociación Geológica Argentina 55, 403–406.