Abstract:
Palynomorph preservation in sedimentary rocks is strongly affected by various taphonomic
factors related to transport, deposition, diagenesis and preservation potential. The
palynological record may contribute to distinguish different taphonomic factors and also
displays changes in paleoenvironment, especially in volcanic settings where a very complex
interaction of eruptive, gravitational and fluvial processes in time and space can be observed.
Herein, we report on new palynological data from the Miocene Tepoztlán Formation. The 800
m thick formation mainly consists of pyroclastic rocks, mass flow units (lahars) and fluvial
deposits. It is part of the southern Transmexican Volcanic Belt, cropping out south of the
Valley of Mexico and within the two states of Morelos and Mexico State. The volcaniclastic
succession records various stages of recovery of vegetation related to a wide variety of
disturbance factors and mechanisms. During the entire period of deposition, mixed
mesophytic forests appear to have been widespread in the lowlands along streams and midaltitude
uplands surrounding the valley. Pollen assemblages were repeatedly reset by volcanic
eruptions or their secondary effects (lahars) to more limited assemblages with gradual recoveries to the initial stages before the eruption. A clear distinction can be made between
samples taken from different transport regimes (fluvial, lahar and pyroclastic flow transport).
The highest percentages of well-preserved, amorphous, and crumpled palynomorphs can be
found in fluvial sediments while the highest percentage of fragmented palynomorphs is
characteristic of lahar deposits. In contrast, the highest percentage of corroded palynomorphs
can be found in deposits originating from pyroclastic flows.
