MICROMORPHOLOGY OF EL FIN DEL MUNDO CLOVIS SITE, SONORA, MEXICO

El Fin del Mundo Clovis site is located in northern Sonora, Mexico. Two localities within the site preserve sedimentological records of the ancient environment. Locality 1 is characterized by a diatomaceous deposit (Stratum 4) containing Late Pleistocene animal bones. Locality 3 is a nearby series of cemented carbonate deposits. In 2008, Localities 1 and 3 were sampled for micromorphological and geochemical investigation. Stratum 4 at Locality 1 consists of a sequence of siliceous diatomaceous layers sandwiched by carbonaceous deposits. Diatoms are present throughout Stratum 4, but are most numerous and best-preserved in a layer of diatomite at the base of Stratum 4 that covers a bed of mastodon bones of likely Clovis age and rests on top of Stratum 3. Coarse materials are dominated by sand-sized grains of quartz and feldspar at the base of the sequence and fragments of reworked micritic algal carbonate features at the top of the sequence. Syndepositional modifications to the sediment include the formation and infilling of burrows and development of a vermicular microstructure. Despite evidence of bioturbation, laminations in the diatomite are locally preserved. Post-depositional modifications include the formation of root channels and cementation of the deposits by secondary minerals. The carbonate in Locality 3 is divided into three cemented layers that vary in coarse material content as well as microstructure. The lower and middle carbonate layers date to ~15,000-14,000 ¹⁴C yrs BP. The upper carbonate is undated. Locality 3 exhibits a fining upward sequence and contains diatoms as well as fragments of shell. Iron oxide mottles suggest past fluctuations in oxygen content of the ground and surface waters. The micromorphology of these sediments is consistent with precipitation in standing water, or a marl-like deposit. The Locality 1 and 3 sediments may thus represent different facies of a local pond or marsh system in the Terminal Pleistocene. The micromorphology of El Fin del Mundo sediments suggests that the Paleoindian inhabitants of the site were exploiting a semi-arid wetland environment that is significantly different from the habitat of the region today.