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 Shallow-water carbonate systems encompass a spectrum of environments, from reefs to shoals to tidal flats. Although the sedimentologic characteristics of these systems have been studied for many years, new remote-sensing data provide unique, unparalleled perspectives on spatial heterogeneity in Holocene carbonate systems. The purpose of this paper is to describe the structure, content, and utility of a database of remote-sensing images that are included on a companion CD. The twenty-five focus areas include a range of depositional systems from across the globe. The image database for most areas includes three scales of remote-sensing data: one that captures the regional context (Moderate Resolution Imaging Spectroradiometer [MODIS] data, with 250 m 2 pixels), another that illustrates the local setting (Landsat data, with ~ 30 m 2 pixels), and a third that includes high-resolution details of the area (IKONOS or QuickBird data, with 4 m 2 or 2.5 m 2 pixels). These are presented in an interactive, zoomable format, and are supplemented by supporting information on the setting and published work in each area. The overall goal of the database is to provide the suite of new images to a broad audience, rather than to provide a detailed interpretation of any or all areas, or an overview of controls on carbonate depositional systems. These images can be used in several ways. For example, specific examples in the database have been applied as a learning tool in a classroom, and quantitative analysis illustrates enhanced student understanding of spatial complexity in these systems. Additionally, beyond the classroom, these images provide information on depositional models and the scales of depositional heterogeneity in carbonate systems for geologists, reservoir modelers, and geophysicists.