Growth strategies of the tabulate coral Favosites bohemicus on unstable, soft substrates: An example from the Hamar Laghdad (Lower Devonian, Anti-Atlas, Morocco)

Abstract

Coralla of the tabulate coral Favosites bohemicus coming from the famous Kess-Kess mud mound locality of the Hamar Laghdad (SE Morocco) area have been studied with respect to their growth patterns and colony development. The Emsian Kess-Kess mounds developed in a relatively deep-water, low-energy environment, below fair-weather wave-base. After the mound growth ceased, the slopes of the mounds were covered by soft, muddy sediment and colonised by tabulate corals. The morphological characteristics of F. bohemicus coralla analysed in the present study document various responses of the coral colonies to sediment creeping on the steeply inclined slopes. The coralla are massive and display a strong variability in shape and size; most of the specimens are, however, of spherical and sub-spherical shape. The striking feature of the majority of the colonies is that they are either deflected and tilted in one direction, or display indications of being continuously overturned, both features reflecting changes in growth direction of the corals. The tilted and curved direction of growth was likely caused by the slow creeping of the sediment, along with which the colonies were being slowly moved down the slope. The most important factor that controlled the intensity of the mass movements was presumably the slope inclination, which varied among both different mounds and different slopes of individual mounds. Since corals affected differently by mass movements of variable strength attained various sizes and shapes, morphological analyses of F. bohemicus provide clues on the sediment characteristics, as well as type and frequency of mass movements in the cover of the Kess-Kess mud mounds, enabling valuable insights into the initial stages of their burial.