Reassessment of the Cerro Toro (Chile) Sandstones in View of Channel-Levee-Overbank Reservoir Continuity Issues
Outcrops of the Cretaceous Cerro Toro sandstones within Parque Nacional Torres del Paine (southern Chile) have been described in a submarine channel-levee-overbank context; the adjacent, thin, levee-overbank beds genetically are associated with the main channel bodies, which are present as post-erosional fill. Examination of key outcrops indicates that a more complex association exists between the thick- to massively bedded channel-fill sandstones and the laterally adjacent thin-bedded sandstones.
The Cerro Toro sandstones are composed of three primary rock types: (1) gravely sandstone containing clasts ranging from coarse sandstone to small boulders; (2) fine-to medium-(at times coarse-) grained quartzo-feldspathic sandstones and siltstones in sheet sandstones possessing few or no sedimentary structures, probably deposited in lobe or distal overbank facies; and (3) fine- to medium-grained quartzo-feldspathic sandstones and siltstones in sheet sandstones, possessing abundant sedimentary structures, indicative of the levee-overbank facies.
The gravely sandstones occupy multi-storied, channel-fill positions and rest on erosional surfaces cut into sandstones, siltstones, and/or shales. The gravels rest only in erosional contact with the lobe sandstones and not the overbank sandstones. No thick-to massively bedded gravely sandstones have been found to be genetically related to the overbank sandstones.
A reservoir model based on the Cerro Toro sandstones of the Torres del Paine area would be composed of a laterally extensive, thin-bedded lobe sheet sand having a high degree of lateral continuity and punctuated by channel-fill sandstones having a highly variable internal lithologic and potential fluid flow character.