Denudation and retreat of the Serra do Mar escarpment in southern Brazil derived from in situ‐produced ¹⁰Be concentration in river sediment

Abstract

The Serra do Mar escarpment, located along the southeastern coast of Brazil, is a high-elevation passive margin escarpment. This escarpment evolved from the denudation of granites, migmatites and gneisses. The granites outcrop in the form of a ridge along the escarpment crest, due to its differential erosion ('sugarloaf' hills) from the surrounding lithologies. Several studies suggest that the passive margin escarpments are actively retreating toward the interior of the continent. However, no prior study has calculated the long-term denudation rates of Serra do Mar to test this hypothesis. In this study, we measured the in situ-produced 10 Be concentration in fluvial sediments to quantify the catchment-wide long-term denudation rates of the Serra do Mar escarpment in southern Brazil. We sampled the fluvial sediments from ten watersheds that drain both sides of the escarpment. The average long-term denudation rate of the oceanic side is between 2.1-and 2.6-fold higher than the rate of the continental side: 26.04 ± 1.88 mm ka -1 (integrating over between 15.8 ka -1 and 46.6 ka -1 ) and 11.10 ± 0.37 mm ka -1 (integrating over between 52.9 ka -1 and 85.4 ka -1 ), respectively. These rates indicate that the coastal base level is controlling the escarpment retreat toward the continental high lands, which is consistent with observations made at other high-elevation passive margins around the globe. The results also demonstrate the differential erosion along the Serra do Mar escarpment in southern Brazil during the Quaternary, where drainages over granites had lower average denudation rates in comparison with those over migmatites and gneisses.Moreover, the results demonstrate that the ocean-facing catchments have been eroded more intensely than those facing the continent. The results also reveal that drainage over the granites decreases the average denudation rates of the ocean-facing catchments and the 'sugarloaf' hills therefore are natural barriers that slowly retreat once they are exhumed.

Spatial variability of 10 Be-derived erosion rates across the southern Peninsular Indian escarpment: A key to landscape evolution across passive margins

“…The study area experiences most rainfall during the summer monsoon, from June to September (Sarker, 1966;Grossman and Durran, 1984). The WGM is a barrier to southwest winds and results in deep convection that leads to intense orographic rainfall on the coastal plains and over the foothill region (Grossman and Durran, 1984;Gunnell, 1997).…”

Long-term background denudation rates of southern and southeastern Brazilian watersheds estimated with cosmogenic 10Be

“…DR1. Watersheds sampled for Salgado et al 2006Salgado et al , 2007Salgado et al , 2008Salgado et al and 2013 publications. Watersheds are shown imposed over a Digital Elevation Model (DEM) background.…”

Morfogênese Da Chapada Das Mesas (Maranhão-Tocantins): Paisagem Cárstica E Poligenética

“…Essa variação foi extrema, visto que foram mensuradas taxas medianas -na faixa de 12 metros por milhão de anos -paralelamente a outras muito mais elevadas e que superaram os 60 metros por milhão de anos (Tabela 2). Sendo assim, as maiores taxas erosivas mensuradas na área superam, inclusive, a maior parte das taxas já registradas nas faces mais escarpadas da Serra do Mar (Salgado et al, 2013;Gonzalez et al, 2016), área onde foram, até ao presente momento, mensuradas as mais altas taxas erosivas do Brasil via Rev. Bras.…”