Carbonate Dissolution and Porosity Development in the Burial (Mesogenetic) Environment
Wright, Victor P.; Harris, Paul (Mitch)
The early paradigm for porosity formation in carbonate rocks stressed subaerial exposure and attendant shallow meteoric diagenesis. Mazzullo and Harris argued in the early 1990s that porosity formation also occurs in deep-burial, or mesogenetic, settings where brines charged with organic acids, carbon dioxide, and/or hydrogen sulfide derived from organic matter diagenesis and thermochemical sulfate reduction were likely fluids to cause significant dissolution, and suggested that the mesogenetic origin of some porosity may go unrecognized as there are similarities between mesogenetic and shallow meteoric pore types. Subsequently, numerous authors have interpreted deep-burial dissolution in carbonate reservoirs and some have proposed that significant volumes of porosity were created in this manner.
Ehrenberg and others have recently argued that the burial dissolution model violates important chemical constraints on mass transport in that the ubiquitous presence and rapid kinetics of dissolution of carbonate minerals causes the mesogenetic porewaters to be always saturated and buffered by carbonates, therefore providing little opportunity for the preservation of significantly undersaturated water chemistry during upward flow, even if the initial generation of such pore waters could occur. And they strongly argue that the burial dissolution model is unsupported by empirical data in that their review of the literature where this model has been advanced reveals a consistent lack of quantitative treatment.
The term burial dissolution (corrosion) is in itself confusing as such effects can take place at depths potentially affected by near-surface, meteoric processes, such as when ascending hydrothermal fluids cool to produce corrosion by retrograde solubility. The issue is not burial but is that the fluids causing dissolution are derived from depth and are not linked to near surface processes associated with either high order sequence boundaries or to telogenetic (low order surfaces) effects. A critical consideration is that eogenetic dissolution is commonly controlled by mineral instabilities in the carbonate sediment, however during burial stabilized minerals are dissolved. Critical flow pathways are linked to the structural grain of the limestone (faults, fractures, pressure solution effects), and are hydrologically unconnected to fluid flow from any subaerial surface.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013