Footprints of shod humans from a mid-20th century beachrock (Getxo, Basque Country): a modern “Laetoli” ichnosite in the “Anthropocene”?

DÍAZ-MARTÍNEZ IGNACIO; LÓPEZ-HORGUE MIKEL A.; HEREDIA ARTURO M.; PERALES-GONGENOLA LEIRE ; ISASMENDI ERIK ; GÓMEZ OLIVENCIA ASIER ; BADIOLA AINARA; BERRETEAGA ANA ; ARLEGI MIKEL ; PEREDA-SUEBERBIOLA XABIER ; ASTIBIA HUMBERTO

Khon Kaen

Congreso; 6th International Palaeontological Congress; 2022

International Palaeontological Association

At the end of the 19th and for much of the 20th century, the Nervión-Ibaizabal River estuary (Bay of Biscay, northern Iberian Peninsula) was involved in an industrial revolution. Steel companies benefited from the iron ores exploited in the mountains near Bilbao and Encartaciones region. Wastes generated after blast furnace iron production was dumped in the nearby coast and Abra estuary approximately between 1902 and 1966, with a quantity up to 30 million tons of wastes (Pujalte et al., 2015). Anthropogenic sediment input exceeded substantially the natural sediment balance of these beaches -Tunelboka, Arrigunaga and Gorrondatxe (Getxo municipality, Biscay)-, resulting in a rapid prograding beach geometry, finely preserved after early cementation processes (Astibia, 2012). Here, a singular human ichnological record found in the Gorrondatxe beachrock is presented. This beachrock is divided into two units formed mainly in a foreshore environment (sensu Pujalte et al., 2015): the lower one is conglomeratic with decimeter-sized fragments of slag, refractory bricks, and clasts of the Eocene substrate; and the upper unit is mainly composed of sandstones with mm-sized fragments of slag as well as bullets, plastics or even nylon stockings. Coeval to this last unit are backshore deposits, composed of cm-thick sandstones alternating with clay drapes, which preserve hundreds of footprints of shod humans. The footprints, of 12 cm to 29 cm in length, are preserved as both concave and convex epirrelief in two almost consecutive track-bearing surfaces. Following the social conventionalisms of this epoch, the large bootprints were produced by men, the impressions of heels by women and small footprints by children. This accumulation of footprints has an approximate age between the 30s to the 60s of the 20th century based on chronological information extracted from the artifacts and historical documents. Just as the Laetoli footprints open a window to the life of the first bipedal hominins of the Pliocene, these footprints show us the uses and customs of modern society in the midst of the "Anthropocene".