Diatom-inferred palaeoenvironmental changes of a Pliocene lake disturbed by volcanic activity

Author： Vilaclara G. Martinez-Mekler G. Cuna E. Ugalde E.

ISSN： 0921-2728

Source： Journal of Paleolimnology, Vol.44, Iss.1, 2010-06, pp. : 203-215

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Abstract

Lake development in geologically active basins is a complex phenomenon as shown by the bed of the Pliocene Tlaxcala paleolake disturbed by volcanic eruptions in central Mexico. A 5-m layered freshwater diatomite outcrop section shows volcanic ashes throughout a bottom Stephanodiscus zone up to a more recent Aulacoseira zone. A 0.5-m transition region begins with an abrupt decrease in volcanic inputs and ends with a shift to Aulacoseira solida (Eulenstein) Krammer. Sediment analysis points to a shallow eutrophic lake in the bottom zone undergoing a transition to higher water volume leading to a threshold depth for the species shift. The lake was apparently deeper and mesotrophic thereafter. A common interpretation is to attribute such a volume change to a moisture increase. However, evidence of geological activity, mainly volcanism and faulting, suggests that it could have also been rooted in geomorphological changes of the lake basin.