ISLA Federico Ignacio
Diatom-based reconstruction of Holocene hydrological changes along the Colorado River ﬂoodplain (northern Patagonia, Argentina)
FAYO, ROCIO; ESPINOSA, M. A; VELEZ AGUDELO C; PAN J.; ISLA, F.
JOURNAL OF PALEOLIMNOLOGY
Año: 2018 vol. 60 p. 427 - 443
Diatom assemblages recovered from aColorado River delta core in northern Patagonia,Argentina were analyzed in order to assess pastenvironmental conditions. A total of 35 samples wereselected from a 172-cm core extracted 37 km from themouth One-hundredand thirty-eight taxa were recognized and groupedaccording to life forms. Two diatom zones wereidentiﬁed by cluster analysis. At the base of thesequence, the Diatom Zone I (DZI;4132 ± 35 - 2919 ± 2714C yr BP), consisted of clays, and was characterized by assemblages domi-nated by aerophilous and benthic taxa and chrysophytestomatocysts, which led to inferences of a sedimentaryenvironment corresponding to a pond experiencingdry periods. The upper section (DZII) was dominatedby ﬁne sands and silts encompassing the last * 150 yrwith abundant planktonic and tychoplanktonic dia-toms. Benthic diatoms were abruptly replaced byplanktonic forms in this zone indicating a shift todeeper waters. These results characterize the mean-dering dynamics of a deltaic system. During the Mid-Holocene, more arid periods would have favored thedeactivation of meanders and the formation of riverineand oxbow wetlands. In Late-Holocene and historicaltimes, more humid conditions and the hydrologicalsystem across the ﬂoodplain reactivated the pale-ochannel. Today, the dominant diatom species arebrackish/freshwater fragilaroids. A non-multidimen-sional scaling analysis showed a lack of analogybetween fossil and modern samples. The change indiatom ﬂoras in recent historical times was attributedto anthropogenic disturbances, a consequence of theregulation of the river ﬂow. This regulation isevidenced by less discharge, morphological modiﬁca-tions in the ﬂoodplain and increased salinity in the lastdecade.