Luiz César Corrêa-Gomes

Itatim Geomorphological Site: Largest Concentration of Inselbergs in Brazil

Itatim geomorphological site (IGS) in central-eastern Brazil is prominent among inselberg terrains worldwide due to the quantity and variety of shapes (castles, bornhardts , inselgebergs, castle koppies, and tors), formed from the Miocene. Factors that have played a role in the origin of Itatim inselbergs include: (i) the presence of younger intrusions within an ancient bedrock; (ii) location in shear and other tectonic contact zones where high- and low-strain areas are juxtaposed; (iii) mineralogical differences between the inselbergs and the surrounding rocks; (iv) regional uplift followed by tectonic stability in the past tens of millions of years; and (v) arid and semiarid climates exerting influence in the most recent geological past into the present.

Brazilian Estuaries: A Geomorphologic and Oceanographic Perspective

Estuaries are primarily sites where rivers meet the sea, where fresh water is mixed with sea water by the tidal flow and where salinity gradients are set up along a mixing zone. In this chapter, we consider that the estuary is an accommodation space landward of the coastline, where fluvial sediments are largely retained with no appreciable effect on the sedimentation processes of the open coast. Here we recognize 41 large estuaries along the Brazilian coast, ranging in size from 40 km2 to more than 10,000 km2, encompassing areas with different topography, climate, geology, tidal ranges, and alongshore drift. The majority of these estuaries are located along fault lines or within grabens, and although scattered, structural and stratigraphic evidences suggest that land subsidence has caused sea level to locally rise, which has been an important factor in the preservation of these coastal features. A larger number of estuaries exist in the macrotidal and humid north coastal sector where large-scale coastal subsidence occurs. The estuary sizes along the coast bear no relation with tidal ranges, but have a positive linear correlation with river discharge in the east-southeast and northeast coastal sectors. Based on the existing hydrographic data, it could be stated that the large Brazilian estuaries are hypersynchronous, ebb-dominated, and well mixed. In the deeper estuaries of the east-southeast sector, the longitudinal density gradient is an important driver for water circulation, causing vertically stratified residual flows that end up retaining suspended sediments within the estuary and promoting the accumulation of organic, muddy sediments.

Study on the gravitational flow directions of the Maracangalha Formation (Early Cretaceous), Bom Despacho, NNE area of Itaparica Island, Bahia, Brazil

The objective of the present study was to interpret the direction of gravitational sedimentary flows in the turbidite deposits of the Maracangalha Formation (Reconcavo Basin), indicating their source areas. Thus, the indicative deformational structures existing in the formation were analyzed. The structures observed ranged from brittle to highly ductile and viscous states, with a diversity of deformational styles. A total of 284 planar and linear measurements was collected in three distinct subareas, separated according to their degree of deformation. The structures found were separated into four groups according to their formation process: (i) pre-deformation structures; (ii) plastic deformation structures; (iii) intrusion structures (fluidization), related to either early or syn-sedimentation events; and finally (iv) brittle deformation structures, with late sedimentation. Some structures were observed to be good indicators of apparent mass movement direction, which yielded predominantly SSW directions, suggesting a partially confined flow, parallel to the main axes of Reconcavo Basin, towards its depocenter.

Lithogeochemistry and geochronology of the subalkaline felsic plutonism that marks the end of the Paleoproterozoic orogeny in the Salvador–Esplanada belt, São Francisco craton (Salvador, state of Bahia, Brazil)

Studies conducted over the last decade concerning the rocks that underlie the municipality of Salvador have shown a complex geological history with a great diversity of medium- to high-grade metamorphic lithotypes, deformed in several phases and frequently cut by tabular mafic dykes and irregular granitic bodies. The latter, which were the subject of this study, frequently outcrop along the coastline of Salvador and are classified petrographically as monzo-syenogranites. They are classified as subalkaline and peraluminous according to their geochemical data, and stand out for being enriched in light rare earth elements and having a strong negative Europium (Eu) anomaly. These rocks are produced from anatectic melts or through the interaction of mantle-derived magmas with crustal materials. The negative values of eNd(t) (-6.08) corroborate with the crustal character and in the diagrams of tectonic ambience, they are plotted in the field of post-tectonic granites. The Sm-Nd model age (TDM) around 2.9 Ga indicates a neoarchean source for these lithotypes, whereas their U-Pb zircon age (LA-ICPMS) of 2,064 ± 36 Ma is similar to the U-Pb (SHRIMP) and Pb-Pb (evaporation) ages for late-tectonic granites of the Itabuna–Curaca–Salvador belt. Considering the results of recent studies in the area of Salvador, the monzo- syenogranites can be interpreted as late-tectonic intrusions, since they are affected by dextral shear zones correlated with the last stage of deformation registered in the granulites of Salvador.