Volcanic stratigraphy of a high-altitude Mammuthus columbi (Tlacotenco, Sierra Chichinautzin), Central México

Abstract

The discovery of a near complete skeleton of Mammuthus columbi in a cornfield located on the northern slopes of the Sierra Chichinautzin volcanic field south of Mexico City sparked the interest of the scientific and public community. Although remains of this species of mammoth are frequently discovered in central Mexico, this new find is at the southernmost and highest (ca. 2770 m asl) location yet within the Mexico Basin. In addition, the bones were found embedded in dark volcanic ash, raising the possibility of a relationship between the death of the animal and explosive activity at a neighboring scoria cone, as the site is located <10 km from several young volcanoes. Stratigraphic, sedimentological, geochemical, and geochronological studies were conducted at the discovery site and within a 5-km radius to determine the tephra stratigraphy in the area and constrain the source of the “mammoth ash” and the age and taphonomy of the fossil remains. Results show that the mammoth was buried after death by stream-flows (dilute lahars) that were triggered by torrential rain that remobilized loose scoriaceous ash ejected by the San Miguel cone some time after its eruption ca. 17,000 BP.