Sedimentary Responses to OAE2 across a Spectrum of Carbonate Depositional Settings: A Case Study from Examples in Central and Southern Italy
R. Forkner, G. Frijia, M. Mutti, and D. Minisini
Investigations into the deposition and maturation of high-TOC source rocks associated with environmental perturbations spanning the Cenomanian-Turonian boundary (CTB / OAE2) have led to the development of several unconventional resource plays around the world. Imperative to the development of plays targeting tight, high-TOC beds is the ability to either stimulate the interval through hydraulic fracturing, or instead be able to produce from vertically adjacent intervals that may preserve a measure of matrix permeability. It is therefore clear that an understanding of both the occurrence of high TOC source rocks and their adjacent carrier beds is required for successful development of unconventional resources.
In order to better constrain the sedimentary response of carbonate systems to OAE2, a case study was undertaken to describe Cenomanian-Turonian deposits occurring across a spectrum of carbonate depositional settings cropping out in central and southern Italy. Depositional settings include basinal pelagic deposits around Gubbio (predominantly chalks with interbedded black cherts and black shales); slope deposits in Gran Sasso d’Italia (including stacked calciturbidies and mass transport deposits interbedded with black cherts and black shales); platform interior lagoon deposits from the Majella massif in central Italy(skeletal and peloidal packstones interbedded with bituminous marly mudstones); and lagoonal to peritidal deposits from the Appenine carbonate platform in Southern Italy.
In each setting, the repetitive successions of facies making up the majority of the section were interrupted in distinct stratigraphic intervals across the CTB by black shales or laminated marls. This indicates that whatever environmental perturbation affected the area in the late Cenomanian, it was pronounced enough to temporarily suppress local carbonate production in both pelagic and neritic settings and, instead, preserve higher-TOC rocks in their place. This is important information to be considered when developing resource plays that may target depositional environments other than deep pelagic basins, as encasing rock may be better able to contribute to overall matrix permeability.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013