EVOLVING PROVENANCE SIGNATURES IN PLIOCENE-PLEISTOCENE LOESS DEPOSITS ALONG THE ATLANTIC MARGIN OF ARGENTINA

Wind-blown dust from southern South America provides critical nutrients for autotrophic marine biota in the South Atlantic Ocean which impacts the carbon cycle. Argentina contains expansive loessic deposits that record eolian sedimentation over million-year time scales, although the specific sediment sources and transport pathways are unresolved. Cliffs along the east coast of Argentina expose upper Pliocene and lower Pleistocene loess units that provide insight into dust transport over the past 4 million years. We collected nine samples for detrital zircon U-Pb provenance analysis in locations near Mar del Plata, Argentina. The samples contain several age populations with major probability peaks at ca. 10 Ma, 100 Ma, 180 Ma, 260 Ma, 380 Ma, 460 Ma, and 540 Ma. These ages are consistent with upper Pleistocene and Holocene loess in Argentina and can be correlated to sediment source areas located in the Central and Southern Andes. Using existing detrital zircon data from Argentina, we can distinguish several age populations that correspond to specific latitudes within the Andes, improving our understanding of proto-sources and transport pathways. Vertically, there is a general trend of increased sediment input from northern Patagonian sources within the Pliocene-Pleistocene loess units. The exact cause of this trend is unknown; however, it could be related to Pleistocene sea-level fluctuations, which would have exposed large areas of the continental shelf south of Mar del Plata to southerly winds and eolian entrainment. It is also possible that the expansion of alpine glaciers in north Patagonia during the Pleistocene resulted in higher sediment fluxes, with the detritus transported to eastern Argentina by river systems like the Río Colorado. These data indicate that the sediment source areas and transport pathways during the Late Pleistocene-Holocene in central Argentina were also important during the Pliocene and Early Pleistocene. Additionally, these units indicate that dust delivery from central Argentina to the South Atlantic Ocean was active as far back as the Late Pliocene.