Chemical weathering rate, denudation rate, and atmospheric and soil CO 2 consumption of Paraná flood basalts in São Paulo State, Brazil Fabiano Tomazini da Conceição a, ⁎, Carolina Mathias dos Santos a , Diego de Souza Sardinha b , Guillermo Rafael Beltran Navarro a , Letícia Hirata Godoy a a UNESP – Universidade Estadual Paulista, Instituto de Geociências e Ciências Exatas, Rio Claro, São Paulo, Brazil b UNIFAL – Universidade Federal de Alfenas, Instituto de Ciência e Tecnologia, Rio Claro, São Paulo, Brazil abstract article info Article history: Received 13 January 2014 Received in revised form 15 October 2014 Accepted 23 October 2014 Available online xxxx Keywords: Landscape evolution Chemical weathering rate Anthropogenic influence Atmospheric/soil CO 2 Watershed Denudation rate The chemical weathering rate and atmospheric/soil CO 2 consumption of Paraná flood basalts in the Preto Stream basin, São Paulo State, Brazil, were evaluated using major elements as natural tracers. Surface and rain water samples were collected in 2006, and analyses were performed to assess pH, temperature, dissolved oxygen (DO), electrical conductivity (EC) and total dissolved solids (TDS), including SO 4 2- , NO 3 - , PO 4 3- , HCO 3 - , Cl - , SiO 2 , Ca 2+ , Mg 2+ , Na + and K + . Fresh rocks and C horizon samples were also collected, taking into account their geological context, abundance and spatial distribution, to analyze major elements and mineralogy. The Preto Stream, downstream from the city of Ribeirão Preto, receives several elements/compounds as a result of anthropogenic activities, with only sulfate yielding negative flux values. The negative flux of SO 4 2- can be attrib- uted to atmospheric loading that is mainly related to anthropogenic inputs. After corrections were made for atmospheric inputs, the riverine transport of dissolved material was found to be 30 t km -2 y -1 , with the majority of the dissolved material transported during the summer (wet) months. The chemical weathering rate and atmo- spheric/soil CO 2 consumption were 6 m/Ma and 0.4 · 10 6 mol km -2 y -1 , respectively. The chemical weathering rate falls within the lower range of Paraná flood basalt denudation rates between 135 and 35 Ma previously in- ferred from chronological studies. This comparison suggests that rates of basalt weathering in Brazil’s present- day tropical climate differ by at most one order of magnitude from those prevalent at the time of hothouse Earth. The main weathering process is the monosiallitization of anorthoclase, augite, anorthite and microcline. Magnetite is not weathered and thus remains in the soil profile. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The balance between chemical and physical erosion contributes to the geomorphological modeling of the Earth's surface. Chemical erosion or chemical weathering, resulting in the deposition of Ca and Mg carbonates (and smaller amounts of Fe and Mn) in the oceans, is the main mechanism of CO 2 consumption from the atmosphere and has the basic function of moderating the climate. At the same time, the physical erosion acts on the weathered surface by removing the cover and carrying the particulate matter through rivers to the oceans. Interest in the evaluation of weathering rates has increased in recent years, mainly in the northern hemisphere, through the use of the PROFILE model (Hodson et al., 1996; Koptsik et al., 1999; Langan et al., 1996; Sverdrup and Warfvinge, 1993) and models using the sodium, calcium, potassium, magnesium and total dissolved load concentra- tions, where inputs from rainfall require corrections to obtain fractions that are from dissolved rocks (Bain et al., 2001; Boeglin and Probst, 1998; Clow and Drever, 1996; Dessert et al., 2001, 2003; Gibbs, 1970; Grasby and Hutcheon, 2000; Jonhson et al., 1968; Land et al., 1999; Louvat, 1997; Louvat and Allègre, 1997, 1998; Louvat et al., 2008; Millot et al., 2002; Paces, 1986; Semhi et al., 2000; White and Blum, 1995). Some studies in South America have focused on the chemical weathering rates of silicate rocks (Bonotto et al., 2007; Conceição and Bonotto, 2003, 2004; Moreira-Nordemann, 1980, 1984; Mortatti and Probst, 2003; Sardinha et al., 2010). The continental flood basalt provinces (CFB provinces) play an important role in the global consumption of CO 2 due to their areal extent and the strong susceptibility to weathering of this kind of volca- nic rock, as suggested in several studies elsewhere (Dessert et al., 2001; Louvat, 1997; Louvat and Allègre, 1997, 1998; Louvat et al., 2008). How- ever, there have been no studies so far on chemical weathering rates and CO 2 consumption in the Paraná CFB province, which covers 917,000 km 2 and 61% of the Paraná Sedimentary Basin (Fig. 1). Thiede and Vasconcelos (2010) indicated an age of 134.6 ± 0.6 Ma for Paraná CFB province, with a duration of this volcanism corresponding to b 1.2 Ma, revealing a minimum average magma eruption rate of ca. Geomorphology xxx (2014) xxx–xxx ⁎ Corresponding author at: 1 – Avenida 24-A, no. 1515, C. P. 178, CEP 13506-900, Bela Vista, Rio Claro, São Paulo, Brazil. Tel.: +55 19 3526 9358. E-mail address: ftomazini@rc.unesp.br (F.T. da Conceição). GEOMOR-05003; No of Pages 11 http://dx.doi.org/10.1016/j.geomorph.2014.10.040 0169-555X/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph Please cite this article as: da Conceição, F.T., et al., Chemical weathering rate, denudation rate, and atmospheric and soil CO 2 consumption of Paraná flood basalts in São Paulo State, Brazil, Geomorphology (2014), http://dx.doi.org/10.1016/j.geomorph.2014.10.040