Abstracts Earth and Environmental Sciences

Stratigraphy of Neogene deposits in the Rethymnon Province, Crete, with special reference to the phylogeny of uniserial Uvigerina from the Mediterranean region

by J.E. Meulenkamp

Stratigraphical and micropaleontological investigations were performed on Neogene deposits of the Rethymnon Province, Western Crete. The Neogene succession includes marine as well as brackish and fresh-water sediments. Eight formations are recognized, several of which have to be regarded as lateral equivalents. From the sediment types and their distribution along the north coast it is concluded that to-day's topography still reflects the paleogeographic conditions existing during the Neogene. The micropaleontological part of the paper deals with the phylogeny of two groups of Uvigerinids, the U. melitensis group and the U. cretensis group, both showing a main trend to uniserial chamber arrangement. Apart from our Cretan material samples are studied from localities elsewhere in the Mediterranean region. These samples are derived from Italy, Spain, France and Malta, and are partly taken from the stratotypes of the Late Neogene stages. The representatives of the U. melitensis and the U. cretensis groups can be distinguished by external characters such as the presence or absence of a distinct, regular, biserial stage in between the triserial and uniserial parts of the test, the more or less recurved character of the sutures, and the regular or irregular arrangement of the early uniserial chambers. The U. cretensis group corresponds to the U. gaudryinoides group in the literature, whose phylogeny was first emphasized by PAPP(1963). Representatives of this group are common in younger Neogene deposits throughout the Mediterranean region. So far the U. melitensis group is restricted to the Maltese Neogene and to the basal part of the Cretan Neogene succession. The evolutionary trend is the same in both lineages and comprises among other things an increase in the average number of uniserial chambers, an increase in the relative length of the uniserial part of the test, and the development toward an arrangement of the uniserial chambers in more regular series. Besides, a general trend is observed to relatively more slender tests. No development is found in the length or in the breadth of the test. The striate ornamentation appears to be strongly environment controlled; specimens from deposits close to evaporites show an aberrant ornamentation. Since a typological approach of the observed features proves to give unsatisfactory results, counts and measurements are made on a number of parameters. The latter are based on the number of uniseral chambers, the character of the uniserial chambers, the length of the uniserial part of the test, and the length and the breadth of the test. The uniserial chambers can be divided into primitive uniserial chambers and fully developed ones, depending on the angle between the upper and lower sutural planes. In fully developed uniserial chambers these planes are more or less parallel, whereas they form an angle of 20° and more in primitive uniserial chambers. In ontogeny, the fully developed uniserial chambers are the younger ones. In the course of time…