Disorientation of Paleozoic hemispherical corals and stromatoporoids

The size distribution and orientation of massive hemispherical tabulate corals and hemispherical stromatoporoids from the Fossil Hill and Manitoulin Formations on Manitoulin Island (Niagaran and Alexandrian, Ontario), and of hemispherical stromatoporoids in the Flume and Upper Cairn Members of the Miette reef complex (Frasnian, Alberta) and the Jamesville Member of the Manlius Formation (Helderbergian, New York), was determined. In all five sample populations there is no statistically significant difference in the mean size between populations of heads in growth position and those disoriented. The process or processes responsible for disorienting heads evidently did not selectively disorient or remove specific size classes. Such disorientation, associated with little lateral transport of heads, could have been accomplished by infrequent short-lived strong wave and current action (storms), structural or soft substrate instability caused by increasing skeleton size due to growth or bioerosion, or some as yet unknown factor.Size-frequency distributions are potentially of value in separating in-place populations from those that have undergone disorientation or transport by size-selective processes. In a paleoenvironmental study this type of data, in conjunction with other information, such as sedimentological evidence or presence or absence of borers, could then be used to help determine the processes of disorientation and (or) transport.