Stromatoporoid shape and burial ratio changes during growth history and their methodological consequences in morphometrical analyses



Eight Devonian stromatoporoids with clearly exposed arrangements of latilaminae were subjected to detailed morphometrical analyses. Distinctive sets of latilaminae were marked on photographs taken from polished specimens, which allowed reconstruction of their individual growth histories by presenting consecutive stages of their growth. The growth forms measured above the sediment surface and the overall shapes of the skeleton at a given time have proved to differ distinctly between each other throughout the growth history of these stromatoporoids. The morphometrical features of individual specimens (both of their growth forms and of their whole skeletons) distinctly changed throughout their development. Changing environmental factors directly influenced the growth form above the sea floor, and each specimen shows its own specific history of growth form changes. Instead, overall shapes of the skeleton of most of the studied specimens changed in a similar general manner resulting from growth during sediment accumulation. Basing the palaeoenvironmental considerations only on the stromatoporoids’ final shapes may thus be very misleading. It is therefore suggested that the ascription of a specimen to a particular morphometrical category should be based on the mode of its growth history represented by a curve recording the V/B changes (vertical height versus basal length) during consecutive growth stages. Certain sedimentary processes have their direct reflection in the mode of stromatoporoid growth, and are recorded by the attributes of the shape profile (V/B), and burial ratio (BR) curves, which allows deciphering such features as, for example, periodicity of sediment supply, substrate consistency and tempo of sediment cementation. This is particularly valuable when the deposits are recrystallized and the sedimentary structures are not visible. The paper also tests the applicability of the new definitions of the parameters describing the stromatoporoid shape introduced recently by the author.