Tectono-Sedimentary Evolution of Southeastern Mexico's Valle De Oaxaca Graben
Facies analysis shows that Suchilquitongo/Matatlán deposition largely occurred as mud flats in a playa lake; occasional lake level rise and/o lesser terrigenous influx allowed silicified limestone to be formed. Flood plain and channel facies are scarce, suggesting that drainage was limited. Volcanism emplaced ignimbrite sheets. A sudden horst uplift induced debris flow, which formed conglomerate bodies [coalescing tallus fans]. Afterwards, Tertiary deposition ceased. K-Ar data and mammal taxa date Suchilquitongo Fm as Early Miocene [~20 Ma], and the Matatlán Formation as Middle Miocene [~15 Ma].
It is interpreted that the similarities and differences and age of the sedimentary/volcanic fill in the north and southeast, suggests that the development of the Valle de Oaxaca Graben started in the north, involving a pre-Miocene and an Early Miocene tectonic episodes, and a Middle Miocene episode, only recorded in the South. These episodes largely controlled sedimentation and volcanism in the graben.