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

Southern South American dust provides critical nutrients for autotrophic marine biota in the South Atlantic Ocean, ultimately affecting the global carbon cycle via wind-blown sediment. Argentina is home to expansive loessic deposits that record eolian sedimentation over millions of years, however, the exact source and transport pathways of these deposits remains unclear. Pliocene and lower Pleistocene loess units are exposed along the east coast of Argentina and provide insight into sediment transport over the past 4 million years. Detrital zircon U-Pb analyses were conducted on nine samples from these coastal deposits collected near Mar del Plata, Argentina. Several age populations were present within the samples with the most notable modes at ca. 10 Ma, 100, Ma, 180 Ma, 260 Ma, 380 Ma, 460 Ma, and 540 Ma. Similar ages are present in Upper Pleistocene and Holocene loess in other locations in Argentina and can be attributed to sources in the Central and Southern Andes. The correlation between detrital zircon data from recent sediments on the Argentine Pampas with our samples indicates these coastal deposits are part of the same eolian system. There is a general vertical trend throughout the samples suggesting an increased input of sediment from northern Patagonia during the late Pliocene to the mid Pleistocene. The cause of this trend remains unknown, however, changing climatic conditions were a likely driving force behind the change in source contributions. Several hypotheses can explain the change in detrital zircon populations including increased glaciation in northern Patagonia, which may have increased sediment flux in the region, and fluctuations in sea level that would have exposed the continental shelf south of Mar del Plata to southerly winds and eolian entrainment. Regardless of the cause, these data indicate that the Late Pleistocene-Holocene dust delivery system in Argentina was active as far back as the Late Pliocene.