Exploring geophysical and palynological proxies for paleoenvironmental reconstructions in the Miocene of western Amazonia (Solimões Formation, Brazil)

Abstract Western Amazonia underwent important landscape changes during the Miocene due to the Andean uplift. Vast wetlands developed during this period and prevailed until the late Miocene. The evolution of this environment has been studied on the basis of sedimentology and paleontology. Here, we explore geophysical proxies (Gamma Ray, Electric Resistivity and Spontaneous Potential) from cores of the Solimoes Formation (Brazil) to support paleoenvironmental reconstructions and potentially validate pollen taxa as environmental indicators. We show a general tendency from geophysical profiles to increasing energies in the depositional settings in agreement with lithologies during the accumulation history of the Solimoes Formation. Moreover, ACME zone of the fossil palm Mauritia ( Mauritiidites franciscoi ) is associated with low energy environments, ACME of the extinct palm Grimsdalea magnaclavata is associated with similar environments but of a transitional nature, oscillating between high and low energies, and ACMEs of fossil Poaceae ( Monoporopollenites annulatus ) are mostly associated with high-energy environments of more active fluvial dynamics. These three phases appear in order from early, early/middle and middle/late Miocene in the cores, which we believe reflects the climax development and subsequent demise of the wetland system. Additionally, marine surfaces are detectable in the geophysical logging what could help sampling strategies for future studies on cores aiming to detecte these marine events.