3-D seismic-based morphometric analysis of Silurian pinnacle reefs, southern Ontario, Canada

ABSTRACT This paper presents the first 3-D seismic-based statistical analyses of Silurian pinnacle reef morphology from the Michigan Basin. Using a patchwork of small 3-D seismic surveys from southwestern Ontario, 35 such reefs were mapped. Pinnacle outlines were mapped by defining onlap of younger strata onto the steeply dipping reef margin. Most morphometric data presented herein, including reef length, width, area, orientation, and other parameters, were derived from a GIS-based workflow. These pinnacles are quite small (almost all pinnacles are < 0.5 km2 in areal extent) compared to global datasets of reef morphology. The most areally extensive reefs tend to be the tallest, and reefs tend to get larger towards the basin center. Most are somewhat oval shaped, and the axes of the most elongated reefs tend to strike parallel to the paleobathymetry. 3-D seismic-based analyses are supplemented herein with data from reefs mapped using 2-D seismic, logs, and/or gravity data to show that the spacing between all reefs in the study area (n = 128) is generally 1–2 km, but some reefs are 4 km or more from the nearest other buildup. These morphometric data, combined with other analyses, were used to refute an alternative interpretation of pinnacle origin. Although the analyses presented herein provide a unique descriptive dataset for analyzing Silurian pinnacle reefs, interpreting the genetic significance of our results would require additional work that integrates them with sedimentologic and seismic stratigraphic analyses.