Lacustrine record in a volcanic intra-arc setting: the evolution of the Late Neogene Cuitzeo basin system (central-western Mexico, Michoacán)

Late Miocene to Quaternary lacustrine and alluvial–lacustrine sequences were deposited in the Charo–Morelia sub-basin, to the south of the recent Cuitzeo lacustrine depocentre (central-western Mexico), where deposition was largely controlled by widespread faulting and block tilting. Moreover, pyroclastic and epiclastic deposits occur throughout the terrigenous and biogenic sequence, which indicates intense synchronous volcanic activity, directly linked to the faulting. The Charo alluvial–lacustrine sequences crop out extensively to the south of the present Cuitzeo Lake and their exposures record the development and spreading of Late Miocene and Pliocene alluvial–lacustrine zones. The resulting sequences are up to 40 m thick and record four major evolutionary stages related with specific tectonic and volcanic events, which caused changes in the basin morphometry and the palaeodrainage conditions. The first of these stages (Late Miocene) caused the generation of small, NE–SW-oriented shallow lacustrine and swampy zones, which resulted from the activity of strike-slip faults with the same orientation. Alluvial deposits and shallow lacustrine diatomaceous horizons were deposited during this stage. The second stage (Early Pliocene) gave rise to the formation of NE–SW-trending basins related to the extensional reactivation of the earlier NE–SW strike-slip faults. Within this second stage the Charo–Morelia lacustrine depocentre became a larger, deeper tropical lake. The planktonic and planktonic-facultative lacustrine diatom floral assemblages record the development during this stage of a major lake transgression, which could be caused both by wetter climate and tectonic watershed and drainage rearrangement. The third and fourth stages (Quaternary) were related to widespread block tilting processes, which were linked to the generation of E–W-oriented extensional faults and which resulted in the shifting and restriction of the larger, perennial, steadier lacustrine zones to the present Cuitzeo Lake. To the south of this lake the sedimentary record of this stage started with widespread fluvial sequences, which erosively overlaid the diatomitic deposits. The lacustrine zones developed during this alluvial-dominated stage were restricted to small depressions and consisted of small lakes and pond-related environments, which were fed by ephemeral fluvial currents. These minor water bodies were infilled and overlain by acidic pyroclastic fall deposits developed during a