New Perspectives on the Quaternary Paleogeography of Coastal Ecuador and Its Relationships with Climate Change

Abstract

Well-preserved Quaternary sedimentary sequences in the central coast of Ecuador have provided sufficient relevant information for paleogeographic reconstruction and climatic evolution, from stratigraphic, geochemical, and biological analysis. The Jaramijo canton site is one of the most remarkable results in the stratigraphic correlation of lithological units with delineation of a paleo sea-cliff of age 14C 43,245 ± 460 B.P. (belonging to the MIS-3). This MIS-3 is associated with a period of glaciation, but the data obtained, such as δ 18O, indicate paleo-temperature values of −1 to −1.5, which are interpreted in this study, indicate that the central coast of Ecuador has an interstadial phase (warm years in a glacial stage). Two more paleo-coastal cliffs have been mapped from orthophoto analysis, but these are younger. The sedimentary levels analyzed in this study include deposits that occurred in MIS 3 to MIS 1. Holocene transgression has modified the central coast of Ecuador and increased the level of coastal climate hazard by sea level rise. Indeed, paleo-coastlines have been evidenced from bathymetric data in the depth contours of −5.5 m and −7.6 m, at 440 and 650 m distances from the up-to-date coastline. For the Jaramijó site, the rate of cliff-erosion and wave-cut platforms are in the order of 1.1 to 2.4 m/yr. These cliff-erosion rates, with a moderate to high coastal vulnerability index, can be increased if we consider mathematical models with an estimated sea-level rise scenario to be, in 2100, about +1 to +1.4 m.