An early middle Ordovician age for collapse breccias in the east Tennessee zinc districts as indicated by compaction and porosity features

The carbonate strata of the Lower Ordovician formations in the southern Appalachian Valley were probably considerably thicker, less compacted, and more porous and permeable in early Middle Ordovician time than they are now. Analysis of selected compaction features of rocks associated with the breccias of the East Tennessee zinc districts permits quantitative estimation of the relative compaction (reduction in thickness) these sediments have undergone before and after brecciation.Total reduction in thickness of certain Lower Ordovician marker beds because of compaction during burial under younger Paleozoic sedimentary rocks and imbricate Appalachian thrust sheets appears to be at least some 40 to 50 percent. Furthermore, it is also estimated that about half of this compaction took place after brecciation in the solution-collapse structures of the zinc deposits. In comparison with laboratory compaction tests on carbonate muds it is apparent that the Lower Ordovician rocks had been buried to a depth of at least several thousand feet by the end of the Paleozoic Era. On the other hand the zones of collapse breccias probably formed at depths of generally less than a thousand feet, thus indicating an early Middle Ordovician age for their development. The general character of the rock during this time probably was similar to that of Tertiary limestone, which acts as the principal aquifer in the Coastal Plain region of southeastern United States.