The glaciogenic origin of the Pleistocene calcareous dust in Argentina on the basis of field, mineralogical, textural, and geochemical analyses

Abstract

Calcareous dust occurs in Argentina as layers and pockets closely associated with Pleistocene deposits and periglacial features from southernmost Patagonia to at least the Mendoza Precordillera and has been traditionally interpreted as a soil horizon resulting from postdepositional pedogenesis during interglacials. Detailed field and microscopic observations and sedimentological and geochemical analyses of more than 100 samples collected from lower to upper Pleistocene deposits between 51°S and 33°S and from near sea level to 2800 m asl allow us to interpret the dust as synchronous with the host sediment. All observations and analyses lead us to conclude that: (1) the cryogenic morphology and the chemical signatures of the calcite component show that the dust is glaciogenic, (2) the dust was carried by southeasterly Antarctic winds, and (3) it was deposited over most of southern and central Argentina. Field observations, geomorphic evidence, and radiocarbon dates suggest that the dust was deposited during several Pleistocene glacial episodes.

Evidence for Pleistocene periglaciation in the lowlands of central Argentina (36–39°S)

“…The CaCO 3 carbonate is calcite, which appears under the SEM as loose idiomorphic rhombohedral and scalenohedral crystals, predominantly of micrite (<5 μm across). Techer et al (2014) and Vogt et al (2018) showed from analyses of the strontium, carbon, and oxygen isotope compositions, and of the rare-earth element distributions, that this calcite is not of marine origin but continental-not pedogenic but glaciogenic. The carbonate was transported in glacial meltwater and deposited on the emerged continental shelf where it crystallized.…”

“…The result is a set of at least five stepped levels, the highest of which is ~400 m above sea level and the lowest at 230 m above sea level (Vogt et al, 2010). The deposits contain no organic remains that can be dated by 14 C radiometry, but their age and ages of the levels may be inferred from the following: (1) presence of basalt debris in the deposits implies that they are no older than the basalt flows (i.e., no older than Plio-Pleistocene); (2) whereas the siltites are free of carbonate, all the overlying deposits contain glaciogenic calcareous dust, as do most periglacial Pleistocene deposits in Argentina (Techer et al, 2014; Vogt et al, 2018); and (3) all deposits ascribed to the Upper Pleistocene in the region by Tapia (1935), Casadío and Schulz (1986), and Calmels et al (1996) crop out at the bottoms of valleys and consist only of local material, mostly reworked siltites, which confirms the end of the connection between the Plateau and the piedmont. It follows that the stepped levels formed before subsidence of the Chadileuvú plain and before the late Pleistocene, and that they are most likely of early to middle Pleistocene age (Vogt et al, 2010).…”

“…The effect of glaciation extended throughout all of Patagonia, as well as the Pampas (Rabassa et al, 2011). The glacial activity generated calcareous dust (20–70% CaCO 3 ) found with Pleistocene deposits in Argentina from southernmost Patagonia to at least the Mendoza Precordillera (Techer et al, 2014; Vogt et al, 2018).…”