Trazas radicales ferrosas en una secuencia aluvial del río Quequén Grande (Buenos Aires): implicancias estratigráficas y ambientales

Abstract

We analyse and discuss the occurrence of roots and root traces in a Late Pleistocene-Holocene alluvial sequence at La Horqueta II, Quequén Grande river (Buenos Aires Province). The working hypothesis that the ferruginous root traces present at the alluvial section are transgressive stratigraphic features in relation to their host material (older than 9,000 14Cyr BP) is considered. Census of both present vegetation and root traces were carried out along with chemical and grain-size analysis, morphological descriptions of the root traces, histological studies and a radiocarbon dating. The roots associated to the traces may belong to the Poaceae family, main component of the present vegetation, and exhibit a variable degree of preservation suggesting different relative ages. A I'C dating of a highly decomposed root yielded an age of 118.5 years ± 0.6 I'C yr BP which, together with the occurrence of roots from the present vegetation inside some of the traces, suggest that these root traces are transgressive stratigraphic features. Probably, most of the root traces were formed during the last 2,500 I'C yr BP and their formation continues today.