Middle Paleogene palynology of Colombia, South America: Biostratigraphic, sequence stratigraphic, and diversity implications.

摘要

The late Paleocene-early Eocene interval is characterized by a long period of global warming that culminated with the highest temperatures of the Tertiary. This time interval is associated with plant extinctions and a subsequent increase in plant diversity in mid and high latitudes. However, data from tropical regions remain largely unknown. This time interval is also of strategic interest in northern South America because most oil reservoirs occur in Paleogene strata where detailed chronostratigraphy is necessary to develop a clear understanding of stratigraphy and structural geology.; I analyzed the palynostratigraphy of three areas in the Colombian Eastern Andes (northern Middle Magdalena, Llanos Foothills, and southern Catatumbo) with the aim of achieving three major goals: (a) to produce a time-framework using pollen, spores, and dinoflagellates; (b) to develop a sequence stratigraphic interpretation for each section using palynofacies, paleoecology, and lithofacies; and (c) to look for patterns of pollen and spores diversity through the late Paleocene-Eocene interval.; A biostratigraphic framework was built using graphic correlation. Dating sections indicate that there is not a significant time gap encompassing the early and middle Eocene in all of Colombia as previous authors had interpreted. Also, it is clear that formational boundaries of the Paleocene-Eocene formations do not correspond to epoch boundaries and cannot always be considered as chronostratigraphic surfaces. Sequence stratigraphic interpretations of each section indicate that it is not possible to establish a single sequence stratigraphic model for the three sections because they were in three different basins, isolated from each other, and with different subsidence histories, sediment sources, and stratal architecture. However, there are two events with regional significance: an earliest Eocene sequence boundary, and an early middle Eocene flooding surface.; The pollen/spores record indicates a relatively large extinction at the end of the Paleocene and a subsequent increase in diversity during the early and early middle Eocene reaching levels higher that those of the late Paleocene. This extinction and subsequent increase in diversity may be correlated with the late Paleocene Thermal Maximum and Eocene Thermal Maximum, respectively. This demonstrates that variability in tropical climate may have played an important role in the development of plant diversity in the neotropics.