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

Abstract

LongNew data from 14 watersheds in the states of Santa Catarina (n = 7) and Rio de Janeiro (n = 7) show that erosion rates vary there from 13 to 90 m/My (mean = 32 m/My; median = 23 m/My) and that the difference between erosion rates of basins we sampled in the two states is not significant. Sampled basin area ranges between 3 and 14,987 km 2 , mean basin elevation between 235 and 1606 m, and mean basin slope between 11 and 29°. Basins sampled in Rio de Janeiro, including three that drain the Serra do Mar escarpment, have an average basin slope of 19°, whereas the average slope for the Santa Catarina basins is 14°. Mean basin slope (R 2 = 0.73) and annual precipitation (R 2 = 0.57) are most strongly correlated with erosion in the basins we studied. At three sites where we sampled river sand and cobbles, the 10 Be concentration in river sand was greater than in the cobbles, suggesting that these grain sizes are sourced from different parts of the landscape.Compiling all cosmogenic 10 Be-derived erosion rates previously published for southern and southeastern Brazil watersheds to date (n = 76) with our 14 sampled basins, we find that regional erosion rates (though low) are higher than those of watersheds also located on other passive margins including Namibia and the southeastern North America. Brazilian basins erode at a pace similar to escarpments in southeastern North America. Erosion rates in southern andsoutheastern Brazil are directly and positively related to mean basin slope (R 2 = 0.33) and weakly but significantly to mean annual precipitation (R 2 = 0.05). These relationships are weaker when considering all southern and southeastern Brazil samples than they are in our smaller, localized data set. We find that smaller, steeper headwater catchments (many on escarpments) erode faster than the larger, higher-order but lower slope catchments. Erosion in southern and southeastern Brazil appears to be controlled largely by mean basin slope with lesser influence by climate and lithology.

Age and evolution of diachronous erosion surfaces in the Amazon: Combining (U-Th)/He and cosmogenic 3He records

“…Independent of assumptions about the time of initiation of marine regression and possible uplift that would have triggered scarp retreat, the minimum and maximum scarp retreat rates estimated here are greater than rates of retreat of bedrock escarpment in East Australia (0.003-0.035 km.Ma -1 ; Heimsath et al, 2006), the Drakensberg in West Africa (0.05-0.095 km.Ma -1 ; Fleming et al, 1999), or the Serra do Mar escarpment in southeastern Brazil (0.013-0.09 km.Ma -1 ; Gonzalez et al, 2016), but they are comparable to rates estimated for scarp retreat on the Colorado Plateau (0.5-6.7 km.Ma -1 ; Schmidt, 1999 and references therein). If rates of scarp retreat at Carajás appear fast, it is relevant to consider that deep weathering profiles already blanketed the Carajás Surface by about 50 Ma, and that rivers and the receding scarps were eroding into deeply weathered bedrock.…”

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.…”

Corridas de detritos e as taxas de denudação a longo-termo da Serra do Mar/SP

“…Taxas mais elevadas também foram registradas por Mandal et al (2015), para o sudoeste indiano, cujas taxas variaram entre 12,2 e 114,3 m/My (média 48,6 m/My). Scharf et al (2013), por sua vez, mesuraram, para as Cape Mountains, na África do Sul, taxas entre 2,3 e 7,9 m/My (mediana 5,2 m/My), enquanto Bierman et al (2007) (SALGADO et al, 2014;GONZALEZ et al, 2016;e SALGADO et al, 2016) (FÚLFARO et al, 1976).…”

“…A Serra do Mar é um exemplo de relevo escarpado que se enquadra nesta situação, isto é, já há um número considerável de taxas de denudação mensuradas com o 10 Be (SALGADO et al, 2014;GONZALEZ et al, 2016;e SALGADO et al, 2016), mas pouco se discutiu como os processos geomorfológicos de curto-termo se relacionam com sua evolução a longotermo.…”

“…observaram valores superiores de SPI para as fontes de corridas.Zhang et al Salgado et al (2016), também para bacias que drenam a vertente oceânica da Serra da Bocaina (SP/RJ), encontraram valores ligeiramente superiores, na média de 37,1 ± 3,2 m/My. No estado do Rio de Janeiro,Gonzalez et al (2016) encontraram taxa média de 63 m/My, significativamente superior que aquelas obtidas para outras localidade da Serra do Mar.…”