Initial time of two high altitude crater lakes (nevado de toluca, central mexico) recorded in subfossil cladocera

The ob jec tive of this study was the rec og ni tion and re con struc tion of the or i gin of two high al ti tude lakes and the ecolog i cal con di tions of their early ex is tence based on subfossil Cladocera and chem i cal anal y ses. The study fo cused on the old est lac us trine sed i ments from Lake Sol and Lake Luna, lo cated in the crater of Vol cano Nevado de Toluca (Cen tral Mex ico). The Nevado de Toluca crater de vel oped ap prox i mately 12 ka yr BP. Ac cord ing to the lit er a ture, the vol cano was last ac tive ap prox i mately 3.3 ka yr BP, and the lakes de vel oped af ter that erup tion. The re mains of nine Cladocera spe cies were found in the bot tom sed i ments of both lakes. The most dom i nant taxa were two en demic lit toral spe cies: Alona manueli and Iliocryptus nevadensis. The to tal fre quency of Cladocera spec i mens in both of the sed iment cores was very low. No Cladocera re mains were re corded in the sed i ment layer at depths be tween 123–103 m from Lake Luna. The re sults of the lithological and geo chem i cal anal y ses showed that this sed i ment layer was com posed of allochthonous ma te rial, prob a bly orig i nat ing from slid down from the vol ca nic cone. This was sug gested by the con - tent of sil ica (up to 13%), iron (up to 12%), and ti ta nium (up to 4%). The Cladocera re mains re corded in the bot tom sed i - ments sug gested that both res er voirs de vel oped as fresh wa ter lakes at the be gin ning of the sed i men ta tion. The cal i brated ra dio car bon dates ob tained for the bot tom sam ples were 4040 to 3990 yr BP for Lake Luna (129 cm) and 4485 to 4485 yr BP for Lake Sol (89 cm). The ob tained ages were older than the dates of the last erup tion, which oc curred ap prox i mately 3300 yr BP. This re sult was likely re lated to the type of ra dio car bon dated ma te ri als (charcoals).