Neotectonics in Marajó Island, State of Pará (Brazil) revealed by vertical electric sounding integrated with remote sensing and geological data

Abstract

Studies suggest that the Marajó Island has experienced neotectonic activity during its latest evolution. However, there are no data demonstrating the presence of tectonic structures in its shallow subsurface. This work integrates vertical electric sounding, morphostructural lineaments, and geological data aiming to show fault control on the Late Pleistocene-Holocene sedimentation of this area. Resistivity values were related to mud (< 90 Ωm), clayey sand (90 and 200 Ωm), sand (200 and 500 Ωm), as well as Fe-bearing sand and laterite (> 500 Ωm). The latest values were related to the unconformity with lateritic paleosol at the top of the Barreiras Formation. Despite the values ≤ 500 Ωm of both the Barreiras Formation and the Late Pleistocene-Holocene unit, the latter was distinguished along four electric sections due to the presence of this unconformity, combined with the integration of available 14 C, and luminescence ages of Quaternary sediments. The electric sections recorded several places with lateral interruptions of resistivity values within short distances, which were related to faults. The Miocene strata were vertically displaced by normal faults, giving rise to new accommodation space where Late Pleistocene-Holocene sediments were deposited. Fault reactivation was crucial to renew sedimentation in eastern Marajó Island during its latest evolutionary stage.

Um Lixão sob o Ponto de Vista da Geofísica Rasa, município de Caracaraí, Roraima, Brasil

“…Segundo Parasnis (1971) e Kearey et al (2009) valores de resistividade elevados podem ser atribuídos a materiais arenosos e valores de resistividade baixos geralmente são atribuídos a materiais argilosos. Entretanto, a presença de concreções lateríticas porosas podem acarretar aos valores de ρa aumentos acentuados em relação as camadas arenosas (Souza e Carvalho, 2017;Souza et al 2013;Souza, 2010;Laureano, 2007).…”