CATCH-DOWN CYCLOTHEMS FROM THE PENNSYLVANIAN OF KANSAS

Cyclothem deposition in Miami and surrounding counties of the upper Linn and Zarah subgroups was dominated by carbonate mound development produced mainly during the falling stage of each cyclothem. These mounds were composed of photosynthetic phylloid algae which acted to produce and trap carbonate mud resulting in mound aggradation during the initial onset of falling sea level as the mounds were brought further into the photic zone. This positively reinforced their growth into mounds with positive bathymetric relief that was then accentuated during later falling sea level as wave energy swept the mounded highs resulting in the progradation of phylloid intraclast and grainstone facies or occasional dislocated fine clastics or ooidal shoals. Some mounds however clearly show signs of subaerial exposure while others were never exposed and are overlain by successive transgressive or highstand units. This depositional regime is a classic example of ‘Catch-down’ cycles in which some are foreshortened ‘facies complete’ and others are truncated ‘facies incomplete’ in response to forced regression where each consecutive cycle prograded towards the southwest with mounding events occurring on top of and slightly southwest of underlying mound depocenters.