Holocene palaeoenvironmental evolution of the Pampa coastal plain (Argentina) based on calcareous microfossils

Abstract

In the present contribution, we studied assemblages of benthic foraminifers, ostracods and charophytes in a Holocene outcrop in the southeast of the La Pampa coastal plain in Argentina. The main species recorded were Spirillina sp. A, Buccella peruviana, Ammonia parkinsoniana, A. tepida, Elphidium margaritaceum and E. gunteri among foraminifers, Limnocythere cusminskyae and Cyprideis salebrosa among ostracods. These species allowed to determine restricted environments characterized by signifi cant changes in salinity. Qualitative and quantitative studies conducted on the faunal content in the outcrop allowed to identify four environments closely linked to the sea-level changes occurred during the Holocene. In a fi rst stage, between 7500-7200 and 6300-6200 cal yr BP represent the development of a non-marine environment. Around 6300-6200 cal yr BP this environment change to brackish-estuarine with moderate energy. Sometime before c. 6000-5700 cal yr BP a clear-water lagoon, probably oligohaline, with abundant submerged vegetation is inferred. In a fi nal stage, from 2300-2000 to 2000-1700 cal yr BP, a continental environment not infl uenced by the proximity of the sea was established. The new calcareous microfossils evidences and the new chronologies provided by this work, allowed us to adjust the moment of the maximum sea level rise during the Holocene transgression and contribute to a better knowledge of the evolution of coastal paleoenvironments in relation to sea level changes.RESUMO -Na presente contribuição foram estudadas assembleias de foraminíferos bentônicos, ostracodes e carófi tas num afl oramento localizado a sudeste da planície costeira de La Pampa, Argentina. As principais espécies registradas foram Spirillina sp. A, Buccella peruviana, Ammonia parkinsoniana, A. tepida, Elphidium margaritaceum e E. gunteri entre os foraminíferos, Limnocythere cusminskyae e Cyprideis salebrosa entre os ostracodes. Estas espécies permitiram determinar ambientes restritos, caracterizados por alterações signifi cativas na salinidade. Estudos faunísticos qualitativos e quantitativos conduziram à identifi cação de quatro ambientes estreitamente relacionados às mudanças no nível do mar que ocorreram durante o Holoceno. No primeiro estágio, entre 7500-7200 e 6300-6200 cal. anos AP, foi identifi cado o desenvolvimento de um ambiente não marinho. Em torno de 6300-6200 cal. anos AP o ambiente se transforma num estuário salobro com níveis moderados de energia. Algum tempo antes c. 6000-5700 cal. anos AP desenvolveu-se um ambiente lagunar de águas claras, provavelmente oligohalino, com abundante vegetação submersa. Em um estágio fi nal, entre 2300-2000 e 2000-1700 cal. anos AP, estabeleceu-se um ambiente continental sem infl uencia marinha. Novas evidências trazidas pelos microfósseis calcários e as novas cronologias fornecidas por este estudo, permitiu ajustar o momento de máxima elevação do nível do mar durante a transgressão holocênica e contribuir para um melhor conhecimento da evolução dos paleoambientais costeiros em relaç...

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

“…Our results showed paleoenvironmental changes that would be consistent with the RSL rise during the Mid-Holocene, this inference is in agreement with the sea level highstand proposed by several authors for Bahia Samborombón and surrounding areas of the Buenos Aires province (Fucks, et al, 2010; Márquez, 2019; Márquez et al, 2016; Márquez and Ferrero, 2011; Schnack et al, 2005). After this time, it gradually declines to the current position.…”

“…This assemblage along the PM2-sequence was characterized by species of the genera Ammonia and Elphidium, along with Buccella peruviana that is mainly associated with less marine conditions such as estuarine and mash environments (Ishman et al, 1996;Sen Gupta and Barun, 1999). This association was cited for Holocene sediments from the coastal plain of Buenos Aires province, in zones located in close proximity to the study area (Laprida et al, 2007;Márquez, 2019;Márquez et al, 2016) including marsh sediments from Bahía Samborombón (Laprida, 1998;Laprida and Bertels-Psotka, 2003;Luengo et al, 2018); and in brackish sediments from Bahía Blanca estuary (Calvo-Marcilese et al, 2011, 2013.…”

“…B. peruviana has a wide range of distribution: it has been reported in coastal areas, the inner shelf, the bathyal zone and in marine-marginal environments, for example lagoons, tidal plains, muddy intertidal environments, and estuaries (Bernasconi and Cusminsky, 2007, 2009, 2015; Calvo-Marcilese et al, 2011; Laprida, 1998; Laprida and Bertels-Psotka, 2003; Márquez et al, 2016).…”

High-resolution palaeohydrological reconstruction of central Italy during the Holocene

“…Although Holocene ostracod studies (Figure 1) are available from various Mediterranean sites (Anadón et al, 1994; Belis et al, 1999; Curry et al, 2016; Marco-Barba et al, 2013; Mazzini et al, 2016; Rossi et al, 2015), our study is the first in recording high-resolution climatic changes throughout the Holocene until present days in central Italy. Ostracods are well known to be a useful proxy as their distribution, assemblage composition and abundance strongly depend on several physicochemical factors such as temperature, water depth, salinity and other abiotic and biotic parameters (Baltanás et al, 1990; Keatings et al, 2010; Marquez et al, 2016).…”

Asociaciones de ostrácodos bentónicos actuales y del Holoceno del estuario de Bahía Blanca (Buenos Aires, Argentina): interpretaciones paleoambientales

“…4.500 y 5.500 años AP. Marquez et al (2016) determinan un máximo de influencia marina en Las Brusquitas para los cal. 6.300-6.200 años AP y luego a los cal.…”