The Sagari-Kinteroni Anticline: an example of an out-of-sequence tectonic wedge in the Camisea area, Peru
The Sagari-Kinteroni Anticline lies within the Camisea subbasin of southeastern Peru and is, along with the Mipaya and San Martin structures to the south, the leading/frontal anticline of the sub-Andean foreland fold-and-thrust belt in this area. In this study, we integrated surface (geologic map and strike/dip) with subsurface (well and 2D and 3D seismic) data to characterize the geometric and kinematic evolution of the Sagari-Kinteroni Anticline. At the Sagari well location, the Sagari-Kinteroni Anticline developed due to movement along an underlying flat-ramp-flat style thrust fault. However, unlike in a classical fault-bend fold where the backlimb dip of the fold equals the dip of the ramp, the Sagari-Kinteroni Anticline has a backlimb dip that is less than the dip of the ramp. This geometry is characteristic of a shear fault-bend fold. At the Kinteroni well location, the Sagari-Kinteroni Anticline exhibits a similar fold geometry and is related to the same underlying flat-ramp-flat style thrust fault. However, unlike at the Sagari well location, the Sagari-Kinteroni Anticline at this location is cut by a significant thrust fault that splays off the main flat-ramp-flat style thrust fault. It is also cut by a steeply dipping listric backthrust. Based on geometrical relationships, we interpret that the significant thrust fault splay terminates upwards into the backthrust, forming a tectonic wedge/triangle zone that postdates the earlier formed shear fault-bend fold. Therefore, this tectonic wedge would be considered “out-of-sequence” with respect to the evolution of the sub-Andean fold-and-thrust belt in this area.