TECTONIC CONTROL AND PETROLEUM GEOLOGY OF THE PALEOZOIC CLASTICS OF THE MARANHÃTO BASIN, BRAZIL

• Published in: Journal of Petroleum Geology
• Main Author: Carozzi, Albert V.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1980
• Subjects: Ice Sheet
• Online Access: http://dx.doi.org/10.1111/j.1747-5457.1980.tb00968.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1747-5457.1980.tb00968.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1747-5457.1980.tb00968.x

Selected paleoenvironmental maps of the Maranhão Basin from Silurian to Eo‐Carboniferous are analyzed in tercs of their source rock and reservoir potentials. These maps combine petrographic data with the distribution of clay mineral assemblages, palynofacies, trace‐metals, organic carbon and boron. Two depositional models are recognized. The first one, which lasted from Silurian to Eo‐Carboniferous, is model of coalescent deltas in which delta systems (with seven subenvironments) are separated by interdeltaic aras (with five subenvironments). The second model, limited to the Late Devonian, shows a continental ice sheet interfering with a system of coalescent deltas and generating mixed glacio‐deltaic sediments. The evolution of clastic supplies from Silurian to Eo‐Carboniferous consists of three major episodes of delta progradation strongly influenced by a synsedimentary tectonic control through lineaments of the Precambrian basement. This control concentrated the potential reservoirs in the SE portion of the basin. However, among the three major sandstone systems, the first two (Jaicos and Itaim Formations), which are the coarsest, had their reservoir properties strongly decreased by diagenetic cementation. This leaves the third one (Cabeças Formation) as the best potential target for exploration, particularly since its sandstones under lower deltaic distributaries to delta front facies interfinger with the shales of the Pimenteiras Formation, which at that level display their best developmetn as source‐beds. Further enhancement of these reservoirs is provided where their progradation extends sufficiently westward to be involved in structures along that side of the basin.