Late Pleistocene-Holocene evolution of the Doce River delta, southeastern Brazil: Implications for the understanding of wave-influenced deltas

Brazil's coast displays many wave-influenced deltas that are still incompletely understood, despite their significance for reconstructing the history of Late Pleistocene-Holocene sea-level changes in this region and the potential to advance in the knowledge of wave-influenced deltas. Among them, the Doce River delta is the most expressive, given its larger geographic extension. The present work shows that this is a wave-influenced delta that evolved within the context of Late Pleistocene-Holocene sea-level fluctuations, rather than a mid-Holocene lagoonal delta as proposed elsewhere. The delta had an initial progradation at an OSL age of 132.7 (+/- 9.1) ka after the Marine Isotope Stage (MIS) 5e, which was followed by major progradation between 45,775-49,391 and 29,678-29,226 cal yr BP. Beach ridges/spits formed during these phases were in part destroyed during an ensuing transgression between 8161-7933 and 4974-4850 cal yr BP. The central delta remained dominated by fluvial processes, which kept pace with the rising sea level due to relatively high rainfall in the Doce River drainage basin. The Doce River delta started to grow again after the late-Holocene transgression, a process still on-going at the present time. During this evolution, the Doce River was deflected northward and then southward, a process that did not result in any significant facies change when the updrift and downdrift sides of the river's mouth are compared. Such a pattern is in disagreement with previously proposed asymmetry index models for wave-influenced deltas, which predict an uneven distribution of sandy- or muddy-rich deposits in the updrift and downdrift sides of the river's mouth, respectively. Several other deltas along the Brazilian coast also display facies configuration similar to the Doce River delta or have patterns opposed to those proposed by the asymmetry index models. Based on these analogs, it can be stated that the geometries and fades patterns of wave-dominated deltas are not determined simply by the interplay of fluvial and marine processes. Instead, they can be strongly influenced by the fluvial influx, sea-level changes and/or tectonic reactivations, as it appears to be the case of Brazilian wave-influenced deltas, including the Doce River delta. Such a conclusion calls for a word of caution when applying processes-based facies models to reconstruct wave-influenced deltas in the sedimentary record. (C) 2015 Elsevier B.V. All rights reserved.