Abstract: Many carbonate reservoirs are located on top, or down the flanks, of extant structural highs or syndepositional palaeo-highs. This study examines diagenesis in Pennsylvanian oolitic reservoirs close to the crest and down the flank of a long-lived anticline. It illustrates that the position of the best reservoir quality shifted back and forth during successive diagenetic events. Cement stratigraphy shows that early diagenesis did not enhance reservoir character significantly. Most oomoldic porosity formed penecontemporaneously with compaction. Fluid-inclusion and stable isotope data indicate that late cements precipitated during burial conditions by refluxing brines and later hydrothermal fluids. After initial burial, greater permeability existed downdip, where smaller amounts of early meteoric cement allowed for compaction. Subsequent reflux cementation initially degraded downdip reservoirs preferentially and then progressed updip, resulting in relatively uniform reservoir porosity. Later hydrothermal events are most important in affecting the distribution of the highest quality present-day reservoir. Highest porosity is preserved in wells down the flanks of the structure, where hydrothermal cements are not as prevalent. Understanding the effect of diagenesis on location of the best reservoir in relation to palaeotopographical and structural highs allows for the prediction of reservoir quality using seismic and mapping data typically available in the subsurface.

Abstract Spatial self-organization, the process where coherent spatial patterns emerge through internal interactions, is widely observed in modern natural systems. Compelling examples range from ripple and dune formation in aquatic and terrestrial systems to formation of patterned coral reefs and vegetation in arid regions. Despite this wide range of contemporary cases, the concept of self-organization and its potential effects on geological patterns have not yet been widely discussed by the geological community, especially in carbonate depositional systems. We present four case studies from modern bivalve beds, coral reefs, microbial carbonates, and tidal channels, and one from the rock record considering carbonate cyclicity, where spatial self-organization could explain regularity in preserved strata. Only two of these five case studies, bivalve beds and tidal channel systems, are accompanied by a firm understanding of the mechanisms that generate emergent patterning. Three types of ecosystem spatial self-organization—scale-dependent feedback creating regular patterns, criticality behavior causing scale-free patterns, and oscillating consumer resource interactions causing consumer waves—are well documented. The first two of those appear to hold most relevance for carbonate depositional environments. Considerable work remains to understand the processes and products of spatial self-organization in carbonate deposystems.