Mio-Pliocene Foraminiferal Biostratigraphy and Stratochronology of central and northeastern Tunisia

• Stephen K. Wiman ^{[1] [2]}
  1. [1] University of Colorado Boulder

     University of Colorado Boulder

     Estados Unidos

     
  2. [2] Cities Service Company, Exploration and Production. Research Laboratory, Tulsa, Oklahoma
• Localización: Revista española de micropaleontología, ISSN 0556-655X, Vol. 10, Nº. 1, 1978, págs. 87-143
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • During Middle Miocene to early Late Pliocene time, sedimentary basins of central and northeastern Tunisia were intermittently connected with the Mediterranean. As a result of tectonic activity which began in the Middle Miocene and persisted through the Pleistocene, Mio-Pliocene marine and continental deposits are exposed along the southern flanks of the Tunisian Dorsale.

    The purpose of this investigation is to place the Mio-Pliocene sedimentary sequence of central and northeastern Tunisia in a stratochronologic framework which facilitates local and regional correlation, to zone the marine units of this interval using planktic foraminiferal biostratigraphy and to make paleoecologic inferences from assemblages of benthic foraminifera. Sixteen surface outcrops between the Algerian frontier and the Cap Bon peninsula (including the Island of Zembra) were measured and trench-sampled for microfossils. Foraminifera recovered in this investigation are illustrated using scanning electron microscopy.

    The Miocene marine units investigated here (the Mahmoud and Saouaf Formations) accumulated at middle continental shelf or shallower depths as determined from benthic foraminiferal assemblages recovered from exposures on Cap Bon. Southwest of Cap Bon the Miocene benthic foraminiferal record is dominated by indicators of restricted to inner continental shelf environments, and planktic foraminifera are absent or rare, poorly preserved and unsuitable for age zonation. Regional correlation of the Miocene sequence is difficult because the key planktic foraminiferal species utilized in Mediterranean Miocene zonation are rare in the Tunisian samples studied.

    The rich foraminiferal assemblages recovered from the Pliocene Raf-Raf Formation marls exposed in the Nabeul-Hammamet area accumulated under significantly deeper paleoenvironmental conditions than prevailed at any time throughout the Miocene in Tunisia. During Early Pliocene (Zanclean) and early Late Pliocene (Piacenzian) time, foraminiferal marls were deposited in a relatively deep (outer continental shelf to upper slope) basin on the Cap Bon peninsula. The diverse and well preserved Raf-Raf Formation foraminiferal assemblages are useful in age zonation, paleobathymetric interpretation and regional correlation.

    The Tunisian Miocene sedimentary sequence is unique among Mediterranean basins of similar age in that persistent deep-water connections with the Mediterranean were not maintained and that the stratigraphic record is lacking in diagnostic planktic foraminiferal species. In contrast with the Miocene, the Pliocene sedimentary sequence exposed on Cap Bon is rather typically Mediterranean in character. Although the Late Miocene (Messinian) Mediterranean salinity crisis has not been documented within the study area, the Pliocene geologic history of the Nabeul-Hammamet area can be interpreted from the foraminiferal assemblages of the Raf-Raf Formation exposed there.

    This investigation differs from previous efforts in that currently valid and acceptable stage designations used in global correlation are applied to the Tunisian Mio-Pliocene sedimentary sequence for the first time, systematic paleontology in current usage among specialists in Mediterranean Neogene foraminifera is employed, the time-transgressive nature of rock formations and the importance of facies changes are emphasized, and the geologic history of the study area is compared with those of other Mediterranean Mio-Pliocene basins and related to regional events whenever possible.