18. MINERALOGICAL RECORD OF CYCLIC CLIMATE CHANGES IN MEDITERRANEAN MID- PLIOCENE DEPOSITS FROM ...Frédéric Mélières, Alain Foucault, and Marie-Madeleine Blanc-ValleronABSTRACTINTRODUCTIONGEOLOGICAL SETTINGMETHODSSTRATIGRAPHICAL CORRELATIONSMINERALOGYINTERPRETATIONCONCLUSIONACKNOWLEDGMENTSREFERENCESFIGURESFigure 1. Location of Hole 964A and the Punta Piccola section.Figure 2. Abundance of D. tamalis in the Punta Piccola section and in Hole 964A.Figure 3. Lithology and mineral content of the sediment portion studied from Hole 964A. In ...Figure 4. Lithology and mineralogical content of cycles 104 to 108 (Hilgen, 1991) at Punta...TABLESTable 1. Stratigraphical equivalences between Hole 964A and the Punta Piccola section.Table 2. X-ray mineralogy data, Hole 964A.Table 2 (continued).Table 3. X-ray mineralogy data, Punta Piccola section.Table 3 (continued).Robertson, A.H.F., Emeis, K.-C., Richter, C., and Camerlenghi, A. (Eds.), 1998Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 16021918. MINERALOGICAL RECORD OF CYCLIC CLIMATE CHANGES IN MEDITERRANEAN MID-PLIOCENE DEPOSITS FROM HOLE 964A (IONIAN BASIN) AND FROM PUNTA PICCOLA (SICILY)1Frédéric Mélières,2 Alain Foucault,2 and Marie-Madeleine Blanc-Valleron2ABSTRACTMid-Pliocene sediments from Ocean Drilling Program Hole 964A (Ionian Basin) and from Punta Piccola outcrop (Sicily,Italy) consist of light-colored carbonate-rich marls (decimeter to meter thick) alternating with dark-colored, carbonate-poor,organic matter–rich beds (1–25 cm thick). These sediments show cyclic variations in their mineralogical content, especially inthe clay mineral relative percentages. Palygorskite and kaolinite are abundant in carbonated intervals, whereas smectite andchlorite dominate in dark ones. As palygorskite is known to originate from Africa, through wind transportation, we interpretthese cyclic variations to be a result of the alternation of dry periods, with dominant eolian sedimentary input from the south,and humid periods, with dominant fluvial supply.INTRODUCTIONMid-Pliocene sediments recovered from Hole 964A (Fig. 1) of theOcean Drilling Program (ODP) Leg 160 (Shipboard Scientific Party,1996) and those of the same age observed in the southern Sicily out-crops of Punta Piccola (Brolsma, 1978; Hilgen, 1987, 1991; Foucaultand Mélières, 1995) show similar facies and similar sedimentary cy-cles, which seem to be controlled by astronomically induced climaticchanges (Hilgen, 1991; Lourens et al., 1996). The aim of this study isto analyze these sediments to interpret the cycles in terms of sedimen-tary and paleoclimate processes.GEOLOGICAL SETTINGIn the Ionian basin, the studied sequence includes sediments fromSections 160-964A-9H-2 through 9H-6, from 97.585 revised meterscomposite depth (rmcd) to 102.735 rmcd. They are mainly light-colored nannofossil ooze and clayey nannofossil ooze, but dark-colored organic-rich beds (sapropels) alternate with this backgroundlithology. From top to bottom of the studied section, six sapropelswere observed, numbered from 50 to 55 (Shipboard Scientific Party,1996). A gray bed, located between sapropel 51 and sapropel 52(from 78.53 to 78.62 rmcd), may be interpreted as an oxidizedsapropel. As the sediment thickness from sapropel 50 to sapropel 55is 4.26 m, the mean cycle thickness in the studied section is 0.71 m.In Sicily, the Punta Piccola section crops out about 8 km west-southwest of Agrigento. The studied section is located in the MonteNarbone Formation and corresponds to cycles 104 to 108 (Hilgen,1991). It shows mainly light-colored carbonated marls alternatingwith gray or brown beds whose color is explained by concentrationof manganese or organic matter (Brolsma, 1978; Van Os et al., 1994).In this section, mean cycle thickness is 1.75 m, 2.5 times greater thanthe one calculated for Hole 964A.Mean sedimentation rates can be calculated using data from Lou-rens et al. (1996), assuming that the sedimentary cycles were astro-nomically controlled (2.64 cm·ka–1 at Hole 964A; 7.35 cm·ka–1 atPunta Piccola). Without higher resolution chronological data, thesedimentation rates cannot be better calculated and are therefore pos-tulated to be constant throughout the cycle duration.METHODSAt Hole 964A, 102 samples were taken at 5-cm intervals from97.585 to 102.735 rmcd. This sampling interval is sufficient to char-acterize the average 71-cm-thick cycles. At Punta Piccola,123 sam-ples were taken every 5 cm. This interval allows us a very good ac-curacy because of the larger cycles (1.75 m).Calcareous NannofossilsSmear slides for light microscope examinations were prepared us-ing standard procedures. A small amount of sediment (5 mm3) issmeared onto a glass slide using a drop of distilled water and a flattooth pick. The percentage of Discoaster tamalis within a total countof 100 discoasterids is used to correlate Hole 964A with the Punta1Robertson, A.H.F., Emeis, K.-C., Richter, C., and Camerlenghi, A. (Eds.), 1998.Proc. ODP, Sci. Results, 160: College Station, TX (Ocean Drilling Program).2Laboratoire de Géologie, Muséum National d’Histoire Naturelle, 43 rue Buffon,75005 Paris, France. URA 1761 CNRS. [email protected] 964A12° 16° 20°42°40°38°36°34°N3000m1000 m1000m14° 18° 22°ETYRRENIAN SEAIONIAN SEAPunta Piccola12° 16° 20°14° 18° 22°42°40°38°36°34°2000m1000m3000mSICILY1000mFigure 1. Location of Hole 964A and the Punta Piccola section.F. MÉLIÈRES, A. FOUCAULT, M.-M. BLANC-VALLERON220Piccola section, as it is considered as a good biostratigraphic markerin the Mediterranean (Rio et al., 1990; Channel et al., 1992; Sprovieriet al., 1994).MineralogyCarbonate content was evaluated by manocalcimetry. Quantita-tive measurements were performed by X-ray diffractometry on a Sie-mens diffractometer using copper Ni-filtered radiation. The use of ahigh-speed rotating sample holder (Mélières, 1973) and the system-atic duplication of measurements allow a relative accuracy rangingfrom 2% to 5%. Dolomite, quartz, feldspars, pyrite, and goethite con-tents were determined on powdered samples, using SiC as internalstandard and calibrated curves that take into account the lattice crys-tallinity. Calcite content is calculated using the relation % calcite = % carbonate – (1.085% dolomite). Clay mineral relative abundances were measured on carbonate-freeoriented preparations, using the weighted area of the characteristicdiffraction peaks with appropriate quantitative factors.