We decipher the geometry, timing, and kinematics of deformation of a region in the eastern foothills of the Eastern Cordillera of Colombia. We assess the influence of inherited structural fabrics, changes in basin geometry, erosional denudation, and the characteristics of the tectonic stress field with respect to the evolution of the structural styles of the deformation front in the Eastern Cordillera. Detailed structural and geomorphic mapping of an area of ∼5000 km², analysis of seismic-reflection profiles, cross-section balancing, tectonic stress-field indicators, and new apatite fission-track data are used to characterize the partitioning of Late Cenozoic deformation in the eastern foothills of the Eastern Cordillera of Colombia. During the late Miocene–Pliocene, in the Eastern Cordillera, deformation migrated from inverted master normal faults to low-elevation, low-amplitude structures in the foreland. However, this shift in the locus of deformation was not spatially uniform. The deformation front is wider in a northern sector of the Cordilleran foothills, where sedimentary units are thicker, and shortening is perpendicular to the structures. This shortening direction is identical to the direction of the greatest horizontal stress S_Hmax as seen in borehole breakouts. During the late Miocene–Pliocene, basement ranges are passively uplifted by younger, more frontal thrusts. The eastern foothills of the Eastern Cordillera thus reveal a complex combination of factors responsible for the structural styles and partitioning of active deformation in an inversion orogen. Over time, the most important factor changes, from the role of inherited structural fabrics to the geometries of basin fills.

Amazonia covers nearly 50% of Brazil. The history of this biome is marked by many changes in the landscape caused mainly by the Central and Northern Andes uplift. This event has influenced the palaeogeography of the Amazon and therefore its biogeography and possibly biodiversity. Herein we present palynological and lithostratigraphical results from the Solimões Formation in the well 1AS-33-AM. It was drilled in the Solimões Basin, Amazonas State, Brazil, reaching 405 m in depth. We identified 152 palynomorphs, in 32 samples, among them some biostratigraphical markers, such as Crassoretitriletes vanraadshoovenii, Fenestrites spinosus, Cichoreacidites longispinosus, Ladakhipollenites? caribbiensis and Echitricolporites mcneillyi, allowing us to recognise four biozones sensu Lorente ( 1986 Lorente MA. 1986. Palynology and palynofacies of the Upper Tertiary of Venezuela. Dissertationes Botanicae 99:1–222. [Google Scholar] ): Crassoretitriletes Interval Zone (399.10–276.70 m), Asteraceae Interval Zone (276.70–262.00 m), Psilatricolporites caribbiensis Interval Subzone (239.90–70.00 m) and Echitricolporites–Alnipollenites Interval Subzone (70–32 m). The palynological and lithostratigraphical results indicate two environmental phases. The palynomorph association presents a change marked by the sudden appearance and predominance of Grimsdalea magnaclavata from 239.90 m upwards and a general increase in the number of species. The lithostratigraphy shows from approximately the same depth greater amounts of sandstones towards the top of the well, suggesting a change from a paralic to a fluvial environment of higher energy. The first phase can be associated with the Pebas/Acre depositional systems, wetlands composed by lakes and swamps with seasonal floods that existed from 23 to 7–5 Ma. The second phase indicates a fluvial system that may be interpreted as a record of the modern Amazon transcontinental fluvial system, which was already established in the Pliocene.

In western Amazonia, palynology has been the main source of chronological information for the Neogene period. The Solimões Formation in northwestern Brazil has hundreds of meters of fine-grained rocks that have yielded rich pollen records informing on age and paleoenvironments. Here, we present new pollen data for two boreholes (1-AS-33-AM and 1-AS-37-AM) in the Solimões Basin and one outcrop (Patos) in the Acre Basin, and describe 36 new taxa (two pteridophyte spores and 34 angiosperm pollen) plus one emendation. Palynostratigraphic zonation schemes from Venezuela and Colombia were analyzed critically in order to provide relative ages for our sections. We found core 33AM to span pollen zones T14 (∼16-14.2 Ma), T15 (14.2-12.7 Ma) and T16 (12.7-7.1 Ma) sensu Jaramillo et al., (2011), while core 37AM spans zone T15? and T16. We also report the widespread occurrence of Cyatheacidites annulatus in outcrops of the Solimões Formation, implying the existence of latest Miocene (∼7 Ma) to Pliocene sedimentation and suggesting ages older than ∼7 Ma for the topmost sediments of our boreholes. Biostratigraphical relationships also indicate that Echitricolporites mcneillyi and Ladakhipollenites? caribbiensis cannot be used as Pliocene markers as previously assigned. The implications of these results to the palynostratigraphy and paleoenvironmental reconstructions of western Amazonia are discussed.