CHRONOLOGY OF THE PALEOGENE CONTINENTAL SUCCESSION IN COLOMBIA; PALYNOLOGICAL DATA COMPARED WITH U/PB DETRITAL ZIRCON DEPOSITIONAL AGES

Palynological analyses have improved the chronology of Paleogene continental strata recorded westward of the Cordillera Central of Colombia. U/Pb detrital Zircon analyses in those continental strata have yielded ages that could improve the calibration of the palynological biozonation; however, detrital Zircon ages need to be evaluated under sedimentology and sandstone composition criteria to define whether the age given by the Zircon corresponds to the age of deposition. U/Pb detrital zircon analyses have yielded Paleogene ages in 8 areas, and they are grouped into three groups. Zircons isolated from volcaniclastic rocks and lithoarenites with volcanic rock fragments have a population of 53-56 Ma; these rocks are interbedded with a thick succession of mudstones dated palynologically near the Paleocene-Eocene boundary. A second population (58-62 Ma) has been documented in Upper Paleocene strata from 3 localities, where sublitharenites, litharenites and mudstones accumulated in high subsidence regime. These ages agree with palynological dating. The third population (51-48 Ma) has been reported in quartzose sandstones that accumulated in low subsidence regimes (amalgamated channels); palynology from overlying mudstone beds indicated a younger late Middle Eocene (~40 Ma). However, an age of 50 Ma is reported in an undated unit that consists of litharenites. Overall, ages given by detrital zircons in units accumulated in high subsidence regimes agreed with biostratigraphic dating, and could be considered as depositional ages. In contrast, detrital zircons from quartzarenites accumulated in amalgamated channels in low subsidence regimes produced much older ages than expected from biostratigraphy. Synorogenic volcanic zircons define an Upper Paleocene-Early Eocene magmatic activity located to the west, and spatial distribution of the magmatic arc influenced the availability of synorogenic zircons (i.e., Central Cordillera of Colombia).