Late Paleozoic Sea Levels and Depositional Sequences

Cyclic sea level charts for the Lower Carboniferous (Mississippian), Middle and Upper Carboniferous (Pennsylvanian), and Permian show considerable variability in the duration and magnitude of third-order depositional sequences, and also in the position of general sea level as represented by second-order sea level. Transgressive and highstand system tracts are numerous on the cratonic shelves of the late Paleozoic continents. Shelf margin wedges are less well represented except at times of general lower sea levels. Most low stand wedges and all low stand fan systems are structurally deformed and make up many of the accretionary wedges and displaced terranes that lie structurally emplaced against the former Paleozoic margins of the cratons.More than seventy named third-order depositional sequences (mesothems) seem well defined in Carboniferous and Permian rocks. They may be grouped into six named second-order supercycles which in turn are parts of the Kaskaskia and Absaroka megacycles (or Sloss sequences).Most third-order sequences, wherever possible, are named for the marine limestone formation(s) or member(s) that represents the highstand facies of that particular sequence. It is also the name bearer of the associated sea level rise and fall. The second-order sequences are named for areas where the general relationships between the second-order sequences are well shown as in the Upper Mississippi River Valley, in southeastern Arizona and southwestern New Mexico, and in western Texas.Although glaciation appears to be the cause of the relatively snort term sea-level changes associated with tnese sequences, other longer term causes also are suspected in order to explain some of the phenomena. These longer term causes may relate to timing and rates of plate motions, orogenic events, and mid-oceanic ridge construction.