Studying of outcrops and shallow bore hole at Massingir Dam area, a contribution to the knowledge art state of Massingir dam Geology

The Massingir dam is located in the Southern part of Mozambique basin, surrounded by Chicualacuala district in the North, Magude district in the South, Mabalane and Chókwe districts in the Este and Republic of South Africa in the West. In 2006, Rutten at all, by quickly field check, defined the new Formation, called Mapai Formation that is covered by the Mazamba Formation and they made a vertical log of the outcrop at deep spillway. These actor “Rutten at all” finished the research recommended, for further studies, the integration of the data of them research with shallow bore hole data to improve the knowledge state art at Massingir Dam. The main goal of this research is to understand and identify the depositional environment and their successions associated to the sea level change from tertiary to present, using the information from outcrops around the flood spillway and the bore hole data recovered in the area where was built the auxiliary spillway. The outcrops called Mass 1, Mass 2 and Mass 3, are composed mainly by carbonates sedimentary rocks, as marl, grainstone, packstone and wackstone, with conglomerate matrix support fabric as basal, representing the shallow marine entrance deposit that was covered by the carbonate ramp deposit (sea level transgression during the lower and middle Cretaceous), and sandstone with lamination, wave and current ripples and hummock, represent offshore transition related to the sea level regression and calm around the continental margin during the Paleocene. The Mass 4, is mainly composed by intercalation of claystone, sand siltstone and mud (delta front), that is covered by sandstone with current ripple (delta mouth bar), very fine sand and claystone (inner band delta channel). The bore hole described is composed mainly by siliciclastic sediments unconsolidated. The main faces found indicate the inner bend and oxbow lake that is typically of meandering or braided river. According to this data, from Mass 1 to Mass 4 and the bore hole data, applied a vertical face analysis and the faces successions, the Massingir dam area was governed by three main sedimentological environment, the marine, transitional and continental. The lithology in the area show, in general, from bottom to surface, a sea level regression.