Mapping Neogene and Quaternary sedimentary deposits in northeastern Brazil by integrating geophysics, remote sensing and geological field data Cl  odis de Oliveira Andrades-Filho a, b, * , Dilce de F  atima Rossetti c , Francisco Hilario Rego Bezerra d , Walter Eug ^ enio Medeiros d , M  arcio de Morisson Valeriano c ,  Edipo Henrique Cremon c , Roberto Gusm ~ ao de Oliveira e a Instituto de Geoci^ encias, Universidade de S~ ao Paulo e USP, Rua do Lago, 562, CEP 05508-080 S~ ao Paulo, SP, Brazil b Universidade Estadual do Rio Grande do Sul, Rua Assis Brasil, 842, CEP 95400-000 S~ ao Francisco de Paula, RS, Brazil c Instituto Nacional de Pesquisas Espaciais e INPE, Avenida dos Astronautas,1758, Caixa Postal 515, CEP 12227-010 S~ ao Jos e dos Campos, SP, Brazil d Universidade Federal do Rio Grande do Norte e UFRN, Avenida Senador Salgado Filho, 3000, CEP 59072-970 Natal, RN, Brazil e Serviço Geol ogico do Brasil (CPRM), Avenida Sul, 2291, 50770-011 Recife, PE, Brazil article info Article history: Received 24 June 2014 Accepted 23 September 2014 Available online 2 October 2014 Keywords: Barreiras Formation Post-Barreiras sediments Gamma-ray Morphometry abstract Neogene and late Quaternary sedimentary deposits corresponding respectively to the Barreiras Forma- tion and Post-Barreiras Sediments are abundant along the Brazilian coast. Such deposits are valuable for reconstructing sea level fluctuations and recording tectonic reactivation along the passive margin of South America. Despite this relevance, much effort remains to be invested in discriminating these units in their various areas of occurrence. The main objective of this work is to develop and test a new methodology for semi-automated mapping of Neogene and late Quaternary sedimentary deposits in northeastern Brazil integrating geophysical and remote sensing data. The central onshore Paraíba Basin was selected due to the recent availability of a detailed map based on the integration of surface and subsurface geological data. We used airborne gamma-ray spectrometry (i.e., potassium-K and thorium- Th concentration) and morphometric data (i.e., reliefedissection, slope and elevation) extracted from the digital elevation model (DEM) generated by the Shuttle Radar Topography Mission (SRTM). The pro- cedures included: (a) data integration using geographic information systems (GIS); (b) exploratory sta- tistical analyses, including the definition of parameters and thresholds for class discrimination for a set of sample plots; and (c) development and application of a decision-tree classification. Data validation was based on: (i) statistical analysis of geochemical and airborne gamma-ray spectrometry data consisting of K and Th concentrations; and (ii) map validation with the support of a confusion matrix, overall accuracy, as well as quantity disagreement and allocation disagreement for accuracy assessment based on field points. The concentration of K successfully separated the sedimentary units of the basin from Precam- brian basement rocks. The reliefedissection morphometric variable allowed the discrimination between the Barreiras Formation and the Post-Barreiras Sediments. In addition, two units of the latter (i.e., PB1 and PB2) previously mapped in the field were promptly separated based on Th concentration. A regression analysis indicated that the relationship between geophysical and geochemical values obtained for the PB1, PB2 and Barreiras Formation is significant (R-squared ¼ 0.91; p-value <0.05). Map validation presented a high overall accuracy of 84%, with a coefficient of quantity disagreement of 12% and a co- efficient of allocation disagreement of 8%. These results indicate that the methodology applied in the central onshore Paraíba Basin can be successfully used for mapping the Barreiras Formation and Post- Barreiras Sediments in other areas of the Brazilian coast. The ability to rapidly and precisely map these units using such methodology could reveal their geographic distribution along the northeastern coast of Brazil. © 2014 Elsevier Ltd. All rights reserved. * Corresponding author. Universidade Estadual do Rio Grande do Sul e UERGS, S~ ao Francisco de Paula, RS, Rua Assis Brasil, 842, 95400-000, Brazil. Tel.: þ55 54 32442912. E-mail addresses: clodisfilho@gmail.com, andradesfilho@usp.br, clodis-filho@uergs.edu.br (C.O. Andrades-Filho), rossetti@dsr.inpe.br (D.F. Rossetti), bezerrafh@geologia. ufrn.br (F.H.R. Bezerra), walter@geofisica.ufrn.br (W.E. Medeiros), valerian@dsr.inpe.br (M.M. Valeriano), cremon@dsr.inpe.br (  E.H. Cremon), roberto.gusmao@cprm.gov.br (R.G. Oliveira). Contents lists available at ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames http://dx.doi.org/10.1016/j.jsames.2014.09.018 0895-9811/© 2014 Elsevier Ltd. All rights reserved. Journal of South American Earth Sciences 56 (2014) 316e327