# Susceptibility and Remanent Magnetization Estimates from Orientation Tools in Borehole Imaging Logs
## 3 Results
### Campos Basin Geologic Settings  
The Campos Basin, located at the South Atlantic continental margin along the southeastern coast of Brazil, is part of the Central Segment of the South Atlantic Ocean. The development of Campos Basin was initiated during the Late-Jurassic/Early-Cretaceous break-up of Gondwana super continent, followed by the opening of the South Atlantic Ocean. Early mechanical subsidence was accomplished by episodic events that reactivated the Proterozoic basement fabric under regional E-W extension. Its stratigraphy includes Early Cretaceous to recent sediments. According to [23], the stratigraphic record of the Campos Basin may be divided into three tectonost stratigraphic mega-sequences: Non Marine Rift, Transitional Post-Rift, and Marine Drift, as shown in Figure 5. The Non-Marine Rift is associated with synthetic and antithetic faults forming several half-grabens filled with fluvial-delta sediments. The Transitional Post-Rift is characterized by evaporite deposi  
Figure 4: Geographic location of well 1-RJS-755-RJ at 2950 m water depth in the Campos Basin, Brazil. Contour lines represent the bathymetry (modified from [22]).  
tion, where salt movements play important role by controlling stratigraphic and structural features responsible for several exploratory plays. The Marine Drift may be subdivided into a carbonate Restricted Marine sequence (Albian to Turonian) and a siliciclastic Open Marine sequence (Late Cretaceous to Quaternary).  
The overall structural style in Campos Basin, exhibited in Figure 6, is controlled by a detachment surface at the base of Aptian salt as proposed by [24]. Above the Aptian detachment the thin-skinned salt tectonics with extensional-proximal and compressional-distal domains have been active during divergent margin phase since the Albian, and is characterized by Nitric fault-rollover systems, turtle-back structures, raft tectonics, down building diapirs, salt walls, and compressional salt tongues [25; 26]. Bellow the detachment, the basement is characterized by a system of horsts and grabens limited by steep normal faults that were active during the rift phase in the Early Cretaceous [27]. As suggested by [24] the basement structure controls the salt tectonic domains, with extensional structures to the West, and diapirs, salt walls, and compressional structures to the East of the main internal basement high.  
In a recent paper, [28] has proposed that the Pre-Salt units bellow the detachment are constituted by four depositional sequences that nearly corresponds to the tectonic stages  
Figure 5: Schematic dip-oriented geological section in the Campos showing the tectonost stratigraphic mega-sequences (modified from [23]).  
Figure 6: Structural section through central Campos Basin showing the dominant detached structural style (modified from [24]).  
of the rifting: rift initiation, rift climax, transition and post-rift, as shown in Figure 7a. The rift initiation stage is represented by intense tholeiitic volcanic activity. According to [24], the rift climax stage is defined by the development, in the basement, of an extensive NE-SW and NNW-SSE system of horsts and grabens limited by steep normal faults. The rift transition stage is characterized by a carbonate section whose basal portions is associated to the rift climax stage. Carbonate deposits including argillaceous, laminates and spherulitic facies represent the post rift stage as mentioned by [28]. This stage is of great exploratory importance because the entire carbonate section constitutes the main hydrocarbon reservoirs of the Pre-Salt sequence and will be the focus of our magnetic susceptibility and remanence estimates.