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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The Micropaleontology Project, Inc. is collaborating with JSTOR to digitize, preserve and extend access to Micropaleontology.ABSTRACT: Sediment grab samples from a series of depth transects were collected at 112 locations on the continental margin of Portugal. The benthic microfauna is rich and diverse; 248 species in 107 genera were observed. Distributions of the more frequent benthic species were further examined. Twenty-four species of planktonic foraminifera were identified. All the data have been treated by a descriptive multivariate analysis (correspondence analysis).The major oceanographic feature is seasonal upwelling, which decreases the planktonic-benthic ratio and permits the introduction of cold water species, both benthic and planktonic. The distribution of benthic and planktonic species depends on the depth and more exactly on factors related to it: temperature and its seasonal variations, salinity and sediment facies. Three benthic distributional patterns have been related to the grain size of the sediment. We can distinguish sand-dwellers, species tolerant towards muddy sediment, species tolerant towards muddy sand and species living indifferently in sand and mud.

The cross -sections of the river El Akarit are of considerable importance because they explain the geomorphological and palae-climatical evolution of south-Tunisia for 40.000 years. The present study has permitted us to distinguish the succession of two sedimentary sequences separated by an unconformity formed by the channeling action of running waters and already observed by W.D. Page (1972). Thanks to a multidisciplinary collaboration successive environments of these two sequences have been studied in detail. The first, at the end of late Pleistocene begins with a wet period whose age is uncertain in spite of carbon 14 dating tests and the presence of «mounsterian» levels. The microfauna especially the Foraminifera indicate variable salted ponds with relation to probable transgression of the sea (about 27.000 BP ?). The second sedimentary sequence also begins with hydromorphic deposits, more typical of euryhaline environments with thalassoid affinities according to the microfauna, the Molluscs and probably the microflora. This period is between 8700 and 7400 BP. Here also the pollens indicate a dominant steppe-like vegetation with a slight increase of trees at about 6500-6000 BP, just before the general deposits of gypsum-dusts and the beginning of a sebkha period. The resumption of stream waters and the deposit of loess indicate the end of the extreme dry period and the return to a steppe-like vegetation nearly 3500 years ago. For 2 or 3 millennial even when the marine level remained high, we noted a very speedy gullying of about 8 to 10 m, along this valley. In addition to this paleoclimatic reconstitution this study calls into question the interpretation and the datation of glacis 2-the major shape of south-Tunisian piedmonts-and chiefly the assumption of the tectonic stability of the Oudref threshold between the chotts and the gulf of Gabès.

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