LAKE ZIRAHUEN (CENTRAL MEXICO): AN EXAMPLE OF LACUSTRINE SEDIMENTATION IN VOLCANIC SETTINGS

Lake Zirahuen (101° 45' W, 19° 26' N; 40 m depth) is located in a volcanically active region -the Michoacan-Guanajuato monogenetic volcanic field- (in the Transmexican Volcanic Belt), at the boundary of the two major modern climatic controls (the intertropical convergence zone and the subtropical high pressure zone) and in a region with a cultural development history of several thousand years. Its location provides the opportunity to evaluate the environmental controls (volcanic, tectonic, climatic and human impact) on lacustrine sedimentation. The initial model of lacustrine evolution of Zirahuen for the last 17,000 yr has been reconstructed by a multiproxy based analysis of vertical and lateral variations of the upper 6 m of the sedimentary secuence collected in two piston cores and seismic data. The age model is provided by 20 ¹⁴C dates and the reconnaissance of two historical tephras from Jorullo and Paricutin volcanoes. The sedimentary facies are composed of diatomaceous ooze (massive or laminated), clastic facies and volcaniclastic facies, and they have been grouped into four facies associations, which describe the sedimentary evolution of the central-north part of the lake. Lake Zirahuen was formed was formed by the damming of the La Palma river by the volcanic flows known as "La Magueyera" (LMLF). The youngest lava flow was dated by thermoluminiscence in 6560 yr. The sedimentary architecture of the lacustrine sediments has been controlled by 1) the inherited paleorelief; 2) changes in the lake morphology caused by climatic lake-level fluctuations, the emplacement of LMLF and tectonism; and 3) human activities since the last 4,000 yr.