科研之友
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摘要
We present first results about an Archaic (9000-4000 BP) site, El Tebernal, in the eastern part of Mexico. At El Tebernal, a set of lithic artifacts was found associated with a paleosol (lower paleosol) and buried by an upper paleosol and a modern soil. The artifacts are made from local limestone and chert. Selected paleosol properties were evaluated (total organic carbon, grain size distribution, carbon stable isotope composition, magnetic susceptibility, and micromorphology) that provide information about paleoenvironmental conditions. The lower paleosol is composed of the following horizons: 3E, 3EB, 3BE, 3Btg1, 3Btg2, 3C while the upper paleosol only has a 2A horizon. The lower paleosol is very well developed, with in situ clay coatings, moderate weathering of primary minerals, and a matrix free of carbonates, although the alluvium in the lowermost part of the profile contains a mixture of limestone and volcanic materials. The entire sequence is covered by the modern soil mantle which is formed by an A horizon. Radiocarbon ages determined on soil organic matter from the 3Btg1 and 2A horizons were 5580 to 5320 Cal BP and 2350 to 2320 Cal BP, respectively. We interpret the age of 3Btg1 as close to the final stage of soil formation, because the organic matter content in this horizon is illuviated. Pedogenesis likely began sometime prior to the reported age in the Early Holocene. The paleosol properties indicate a long period of landscape stability (n x 10(3)-10(4) years) under humid and temperate conditions. It is probable that volcanic events from Pico de Orizaba, located several kilometers from El Tebernal, affected this stability. One of the last eruptions produced a block-and-ash flow of dacitic composition dated at 4100 BP that contributed to the end of pedogenesis. The upper paleosol (2A horizon) as well as the modern soil contain ceramics from the Post-classic period (AD 900-1521). The profile is cut by a channel and infilled by a dark material that dates to 1140 to 970 Cal BP (AD 810-980). In consequence, the area has been strongly affected by human occupations during the Holocene. We suggest these ceramic societies caused erosion and activation of geomorphic processes.
- 出版日期2014-8-25
