Bensallah, Mustapha2013-02-172013-02-172012https://dspace.univ-tlemcen.dz/handle/112/1419the terrestrial record is notorious for being patchy and highly endemic in several regions and timeperiods .however ,the continous effort of various scientists has led to well -established regional biostratigraphies for different foffil groups.between different depositional environnement.and this in higher resolution than before