Early-to-Middle Holocene environmental reconstruction in the southern Puna (26° S, Argentina) from camelid coprolite records

Abstract

Paleoenvironmental records in the eastern Andes (16–26° S), broadly indicate a gradual trend towards aridity from the Early to the Middle Holocene with certain chronological discrepancies. Even under this adverse climatic scenario, the archaeological record suggests the presence of hunter-gatherers in the southern Argentinian Puna associated with the availability of resources for their subsistence, even during drier than present periods. Herbivore coprolites contain multiple proxies that provide independent records of paleovegetation and paleoenvironments. Among them, plant tissue fragments and pollen grains, offer a powerful and complementary insight on past vegetation changes and their relationship with climatic conditions during the Holocene, particularly in the southern Argentine Puna. Thus, in this work camelid coprolites recovered from the archaeological site Quebrada Seca 3 (QS3) were analyzed using microhistological and palynological techniques to reconstruct the diet of these herbivores but also to infer vegetation and environmental changes from the Early to Middle Holocene (ca. 9600–6100 cal yrs BP) in the southern Argentine Puna (26°S). Results of both records show similar patterns in the percentages and species richness (especially those growing in wetlands) within and between coprolites dating to the Early Holocene (9600-8000 cal yrs BP) which suggest an environmental stability during this period. Around 8000 cal yrs BP, an increased variability in the richness of grasses, shrubs, dwarf shrubs, annual herbs and sedges species shows the gradual establishment of dry conditions, peaking around 6100 cal yrs BP. By this time, variability in the plant content of coprolites reflects seasonality in the assemblages due to the presence/absence of annual herbs either in the pollen or microfragment records. Therefore, it is likely that coprolites were from different animals that were hunted at different times of the year, supporting the evidence that QS3 has been occupied for short intervals of time after 7200 cal yrs BP when environmental conditions were extremely arid. The complementary analysis of the microfragments and pollen records preserved in coprolites provide valuable, complementary and alternative archive for herbivorous diet and for vegetation and environmental reconstructions, reinforcing that multiproxy approaches are necessary to obtain maximum information from coprolite studies.