The Cleveland Basin in North East England is one of the best and well known examples of an exhumed potential petroleum system, associated with the North Sea. The stratigraphy is composed of Lower to Upper Jurassic siliciclastic rocks and Cretaceous carbonates. The area is made up of varying units deposited in different environments displaying an array of sedimentary structures related to petroleum geology.
Alum Shale Member - Dark mudrock (indication or organic content and deep deposition environment), rich in Ammonites, Brachiopods and Belemnites. Potential source rock.
Scarborough Formation - Fine grained terrestrial fluvial sands with interbedded organic rich layers in the form of lenticular coal beds. The erosive sharpe contact between the previous Alum Shale Member and the Scarborough is displayed in the photo and represents an overall regressive cycle.
The Saltwick Formation - Medium grained terrestrial fluvial sands of a meandering river system with muddy over-bank deposits. The sequence shows an erosive contact controlled by the energy of the river system creating an erosive contact between the mud and sand layers. The reservoir quality of this unit is increased when individual sand bodies erode into each other and become well connected. This unit is also vertically thick and laterally extensive making it an excellent potential reservoir.
The Saltwick Formation - Drag folds created by a higher energy environment of originally deposited cross beds being deformed.
Cretaceous Chalks (well cemented) with large calcite recrystallisation and veins. This rock has the potential to be both a seal and reservoir for the petroleum system. Porosity is created by dissolution of the rock by fluids passing through. Cavities and fractures are created by large scale tectonic deformation.
Base of Cleveland Ironstone Formation - areas of intense bioturbation were prolific throughout the stratigraphy. This bioturbation is able to mix mud and sands, reducing permeability and increasing seal potential.
Stylolites in Cretaceous chalk- indicates fluids moving through during tectonic compressive regime.
Cretaceous Chalk - slickenlines and down-stepping indicating movement of fault.