EGU22-12770, updated on 28 Mar 2022
https://doi.org/10.5194/egusphere-egu22-12770
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Cyclic sediment deposition in the Miocene wetland of Western Amazonia is controlled by orbital forcing, uplift of the Andes and sea level change

Carina Hoorn1, Kukla Tyler2, Giovanni Bogota-Angel3, Gonzalez Arango Catalina4, Frank Wesselingh5, Pedro Val6, Hubert Vonhof7, and Robert Morley8
Carina Hoorn et al.
  • 1University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Ecosystem and Landscape Dynamics, The Hague, Netherlands (m.c.hoorn@uva.nl)
  • 2Stanford University, School of Earth, Energy & Environmental Sciences, California, USA
  • 3Facultad del Medio Ambiente y Recursos Naturales, Universidad Distrital Francisco José Caldas, Bogotá D.C., Colombia
  • 4Departamento de Ciencias Biológicas, Universidad de los Andes, Bogotá D.C., Colombia
  • 5Naturalis Biodiversity Center, P.O. Box 9517, 2300 RA Leiden, The Netherlands
  • 6Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto, DEGEO 58, Brazil
  • 7Climate Geochemistry Department, Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany
  • 8Earth Sciences Department, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK.

In the Miocene, a large wetland extended from the Andean foothills into western Amazonia. This system plays an important part in current biogeographic models and is thought to have acted as an evolutionary ‘cradle’ for aquatic species and an ‘inhibitor’ for terrestrial taxa. The generating mechanisms of this system are not fully understood, but dynamic topography, Andean uplift and eustasy are all thought to have controlled deposition. Orbital forcing is likely an additional driver that could explain the succession of shallowing upwards cycles that characterize the sedimentary record. In this study we investigated the presumed cyclicity at the Los Chorros (Colombia), a site that constitutes a representative example for the sedimentary record in the Miocene wetland system. We integrated lithological, palynological and malacological data from a sequence biostratigraphic perspective. In this approach, the Los Chorros succession is visualised to be composed of a series of flood-fill packages, with a rapid initial flood, with marine-influenced conditions at the time of maximum flood, and followed by a longer regressive infill phase. Based on the palynology we could differentiate local vegetation, such as swamps, from sources of regional origin such as terra firme vegetation (non-flooded Amazonian Forest) and montane forest (Andean), while also separating local and regional sediment sources.  Marine influences are intermittently evident in this section, based on the occurrence of short-lived maxima of mangrove pollen, foraminiferal test linings, dinoflagellate cysts, some mollusc species, and an episodic decline in terrestrial biomarkers. At the times of flooding, the lacustrine conditions in the wetland system were characterized by the presence of algae, floating ferns, and mollusc assemblages that indicate alternating oligotrophic and eutrophic conditions, while intervening subaquatic debris points to proximal submerged lowlands. The palynology also shows that the shallow lakes were fringed by a succession of Mauritiinae palm swamps, ferns, and grasses, with a diverse rainforest in the wider periphery. The sequence biostratigraphic evaluation suggests that the deposition of this sediment sequence took place prior to the 13.8 Ma global sea level fall, and most likely the period just after 14.5 Ma, towards the end of the Middle Miocene Climatic Optimum. We propose that the studied succession comprises eight 41 ka obliquity-driven depositional cycles, with rapid phases of transgression, and that mangrove elements would have colonised within the timeframe of each sea level rise.

How to cite: Hoorn, C., Tyler, K., Bogota-Angel, G., Catalina, G. A., Wesselingh, F., Val, P., Vonhof, H., and Morley, R.: Cyclic sediment deposition in the Miocene wetland of Western Amazonia is controlled by orbital forcing, uplift of the Andes and sea level change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12770, https://doi.org/10.5194/egusphere-egu22-12770, 2022.

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