488 SEDIMENTARY ENVIRONMENTS/Depositional Systems and Facies Figure A large scale coarsening up unit generated by the progradation of a major delta The unit ends abruptly at a flooding surface (arrowed), above which are stacked smaller scale coarsening up units (parasequences) Namurian, County Clare, Ireland cycles may lead to inferences about the variability of the delta front and delta plain and hence allow a more refined characterization of delta type The validity of such an approach depends, of course, on the successively prograding deltas having been of broadly similar character In successions where no cyclicity is apparent and no patterns of vertical facies change can be identified, mathematical investigation such as Markhov chain analysis may help to detect an underlying pattern beneath the random noise However, the demonstration of statistical significance may be limited by insufficient data Architectural Elements and Bounding Surfaces Where sedimentary successions are very well exposed in extensive desert or coastal cliffs, it is clearly not sensible to rely solely on the vertical sequence of facies to reconstruct the depositional environment Lateral facies relationships, where they can be Figure The facies succession of an idealized model cyclothem compared with the observed facies successions upon which it is based