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Ocean Drilling Program Scientific Results Volume Kastens, K. A., Mascle, J., et al., 1990 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 107 24. PLIOCENE-PLEISTOCENE STABLE ISOTOPE RECORD FOR OCEAN DRILLING PROGRAM SITE 653, TYRRHENIAN BASIN: IMPLICATIONS FOR THE PALEOENVIRONMENTAL HISTORY OF THE MEDITERRANEAN SEA1 Robert Thunell,2 Douglas Williams,2 Eric Tappa,2 Domenico Rio,3 and Isabella Raffi3 ABSTRACT Planktonic foraminiferal oxygen and carbon isotope analyses from Tyrrhenian Sea Ocean Drilling Program (ODP) Site 653 provide a continuous record of the Pliocene-Pleistocene paleoceanographic history of the Mediterranean. Long-term trends in oxygen isotopes primarily reflect changes in global climatic conditions, with a more local or re• gional signal superimposed on this record. For example, significant enrichments in 180 due to decreases in surface water temperature and/or increases in continental ice volume occurred at 3.1, 2.7, 2.1, 1.6, and 0.4 Ma. In contrast to most open-ocean results, the early Pliocene 6lsO record of Site 653 exhibits high-amplitude fluctua• tions indicative of very unstable climatic conditions in this region. Another unique aspect of this Mediterranean 6180 record is the pronounced cooling at the Pliocene/Pleistocene boundary. The carbon isotope record for Site 653 also ex• hibits high-amplitude variability throughout the Pliocene-Pleistocene. This variability most probably reflects changes in the carbon isotopic composition of the source of Mediterranean surface waters. INTRODUCTION Capo Rossello region of southern Sicily. These latter two studies were significant in that they demonstrated the potential of such Despite two previous Deep Sea Drilling Project (DSDP) legs land-based sections for paleoenvironmental reconstructions. in the Mediterranean Sea (Legs 13 and 42A), only a very general In this paper we present Pliocene-Pleistocene oxygen and picture exists regarding the post-Messinian paleoenvironmental carbon stable isotopic records for ODP Site 653 from the Tyr• history of this region. This is due largely to poor core recovery rhenian Sea, and use these records to evaluate the paleoceano• and sediment mixing caused by rotary drilling. Ocean Drilling graphic evolution of the Mediterranean during the last 5 m.y. Program (ODP) Site 653 in the Tyrrhenian Sea was hydraulically The semi-isolated nature of the Mediterranean Sea combined piston cored in an attempt to rectify this situation. One of the with the prevailing climatic regime (evaporation exceeds precipi• primary scientific objectives of this site was to collect a continu• tation) are responsible for the present day lagoonal circulation ous Pliocene-Pleistocene pelagic sequence that would serve as a (inflow at surface and outflow at depth). It is important to un• deep-sea type section for both stratigraphic and paleoenviron• derstand how and when this hydrographic regime was estab• mental studies, and also provide a basis for correlating the deep- lished. Specifically, we will consider three important problems sea and land-based marine records of the Mediterranean region. pertaining to the paleoceanographic history of the Mediterra• Prior to ODP Leg 107, DSDP Site 132 from the Tyrrhenian nean: (1) the nature of marine conditions reestablished in the Basin represented the most complete Pliocene-Pleistocene record earliest Pliocene following the Messinian salinity crisis; (2) changes available for the Mediterranean. Micropaleontological (Ciaranfi in water exchange with the Atlantic through time; and (3) the and Cita, 1973; Thunell, 1979), sedimentological (Chamley, 1975) importance of global climatic events in regulating oceanographic and stable isotopic studies (Keigwin and Thunell, 1979; Thunell conditions within the Mediterranean. and Williams, 1983a) of this site have contributed significantly METHODS to our understanding of the paleoclimatic and paleoceanographic evolution of this region. In particular, the oxygen isotopic study ODP Site 653 is located in the western Tyrrhenian Sea (40°15'N, of Thunell and Williams (1983a) documented the response of 11°26'E; 2820 m water depth) close to DSDP Site 132. The present study is based primarily on material recovered from Hole 65 3A (Cores the Mediterranean Sea to major global climatic changes at ap• 107-653A-1H through -23X) which contained 196 m (93% recovery) of proximately 3.2 Ma and 2.4 Ma. With the exception of numer• Pliocene-Pleistocene nannofossil ooze (Mascle et al., this volume). In ous isotopic studies of upper Pleistocene piston core material addition, Core 107-653B-23X was studied in order to provide better cov• (Vergnaud-Grazzini, 1975; Vergnaud-Grazzini et al., 1977 and erage of the basal Pliocene. 1986; Thunell et al., 1977; Thunell and Williams, 1983b; Buck• Stable isotope analyses were carried out following the procedures de• ley et al., 1982), there have been relatively few isotopic studies scribed in Williams et al. (1977). All samples were analyzed using a VG of the longer term Pliocene-Pleistocene history of the Mediter• Isogas Sira 24 isotope ratio mass spectrometer and the data are pre• ranean. Vergnaud-Grazzini (1983, 1985) has reported data for sented in delta notation (5) with respect to the PDB standard. Orbulina several early Pliocene samples from Mediterranean DSDP Sites universa was selected for analysis because it was stratigraphically the most continuous species. Specimens of O. universa from the 355-425 134, 374 and 375, while Thunell et al. (1985) and Van der /*m size fraction were analyzed from all samples except those from Core Zwaan and Gudjonsson (1986) have presented oxygen isotopic 107-653A-1H. Within this core, O. universa was absent and specimens records for the Pliocene land-based marine sequence from the of Globigerina bulloides were substituted. Calcium carbonate content was determined for the earliest Pliocene interval of Site 653 (Cores 107-65 3A-23X and -653B-23X) using a gaso- metric technique similar to that described in Jones and Kaiteris (1983). 1 Kastens, K. A., Mascle, J., et al., 1990. Proc. ODP, Sci. Results, 107: Col• lege Station, TX (Ocean Drilling Program). STRATIGRAPHY AND BIOCHRONOLOGY 2 Department of Geological Sciences, University of South Carolina, Colum• bia, SC 29208. Planktonic foraminifers and calcareous nannoplankton have 3 Istituto di Geologia, Universita degli Studi di Parma, 43100 Parma, Italy. been used to subdivide biostratigraphically the sequence from 387 R. THUNELL, D. WILLIAMS, E. TAPPA, D. RIO, I. RAFFI Site 653. Several different planktonic foraminiferal (Cita, 1975; 1986; Thunell et al. 1987; Channell et al., 1988). According to Spaak, 1983) and nannofossil zonations (Martini, 1971; Raffi these studies the Miocene/Pliocene boundary is positioned and Rio, 1979; Okada and Bukry, 1980) are commonly used for within the lowermost reversed interval of the Gilbert chron, just Pliocene-Pleistocene material from the Mediterranean, provid• below the Thvera subchron. This age is considerably younger ing good stratigraphic resolution. In addition, the recent studies than the 5.3 Ma assigned to the boundary by Berggren et al. of Rio et al. (1984 and in press), Zijderveld et al. (1986), Hilgen (1985). (1987) and Channell et al. (this volume) have calibrated the vari• The calcareous plankton biostratigraphic events recognized ous biostratigraphic events used in these zonations to an abso• in Site 653, and their associated ages, are listed in Table 1. An lute time scale, thus establishing a biochronologic framework age vs. depth plot of these datum levels indicates that Site 653 for the Pliocene-Pleistocene of the Mediterranean. In the present contains a very complete Pliocene-Pleistocene sequence (Fig. 1). study we are using the recently proposed age of approximately Sedimentation rates average approximately 42 m/m.y. below the 4.84 Ma for the Miocene/Pliocene boundary (Zijderveld et al., Calcidiscus macintyrei last occurrence (1.45 Ma) and increase to an average of 60 m/m.y. above this datum. Table 1. Calcareous plankton biostratigraphic datum levels iden­ tified in Site 653. RESULTS The oxygen and carbon isotopic data for Site 653 are listed in Depth Age Datum (mbsf) (Ma) Reference Table 2 and plotted to depth in Figure 2. An examination of the 6180 record (Fig. 2) reveals a number of very distinctive features: FO E. huxleyi 15.6 0.26 Thierstein et al. (1977) FO P. lacunosa 29.12 0.46 Thierstein et al. (1977) 1. A long-term enrichment of nearly 3%o occurs from the Base of small Gephyrocapsa 64.97 1.10 Rio et al. (in press) Base of large Gephyrocapsa 73.80 1.32 Rio et al. (in press) base of the Pliocene to the top of the Pleistocene. Early Plio• 16 LO G. oceanica 85.50 1.62 Rio et al. (in press) cene 5 0 values fluctuate between 0 and - 2%o, while late Pleis• LO D. brouweri 88.70 1.89 Rio et al. (in press) tocene values vary from l%o to 3%o. FO G. inflata 98.60 1.99 Hilgen (1987) 2. The lower Pliocene (below 160 m) is characterized by LO D. pentaradiatus 111.49 2.41 Rio et al. (1984) LO D. tamalis 119.22 2.60 Rio et al. (1984) high-amplitude (2%0-3%o), long-period (200,000-300,000-year) FO G. bononiensis 138.80 3.03 Hilgen (1987) fluctuations. LO R. pseudoumbilica 156.60 3.56 Rio et al. (in press) 3. The 2%o enrichment at 140 m results in a shift to generally FO D. assymetricus 169.90 3.84 Rio et al. (in press) heavier values above this depth. FO G. puncticulata 186.20 4.15 Channell et al., 1988 FO G. margaritae 209.60 4.66 Channell et al., 1988 4. A 2%o enrichment occurs across the Pliocene-Pleistocene boundary (~ 83 m), and glacial values above this level are con• Note: FO = first occurrence and LO = last occurrence. sistently 1.0%o heavier than those below. 250 n G. margaritae f.o. G. puncticulata f.o. D. asymetricus fa R. pseudoumbilica lo. G. bononiensis fa D.
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