Clay Mineralogy

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especially detailed X-ray and SEM study by Bernoulli and Melieres {this volume), an intense dolomitization causcd by interstitial water extremely rich in magnesium has completely replaced the calcitic biogenic material {McDuffand Gieskes, this volume). The calcium content of the dolomite ranges from CaiW to Ca35, and the mineral exhibits a very unusual morphology consisting of pseudohcxagonal flakes, up to 40 ¿tm across, with well-developed (001) crystal faccs. On the X-ray diffractograms, the {001) reflections are considerably enhanced (the ¡006] peak intensity is similar to that of the (104) peak). The amount of dolomite (plus some calcite remains at the top of the core) is very constant all along the core and similar to the amount of calcite (plus minor amounts of dolomite) in all the overlying Pliocene section. This, together with the nature of the clay mineral assemblage characterized by attapulgite, indicates that Core 11 belongs lithologically to the Pliocene. The sidewall Core 25, taken 3 meters above Core 11, displays essentially the same mineralogy, in contrast, in sidewall Core 26, taken 4 meters above sidewall Core 25, the mineralogy is identical to that of the overlying nannofossil marls (calcite 70%). Therefore the "front of dolomitization" can be located between the two sidewall cores {371-375 m below the sea floor).

The mineralogy of the Pliocene section (Cores 11 to 5) indicates that the deposition of the highly calcareous nannofossil marls resulted from the establishment of "normal marine" conditions in the basin, following the stressed environment existing during the upper Messin-ian (dark gray dolomitic muds). The appearance of attapulgite indicates that the Pliocene sea was able to carry a terrigenous material from North Africa. The fact that this material is almost devoid of a "coarse fraction" (quartz + feldspar content ranges from 5% to 10%) suggests either that the surrounding landmasses did not generate such a "coarse" material, or more likely that this "coarse" material could not reach the area {Site 374) because of the rather gentle character of the slopes of the basin. In this latter hypothesis the basin would have been relatively shallow with regard to the present physiography. The infilling of the area by seawater is tentatively understood as the result of a moderate raising of the water level, allowing the shoreline to reach the African "coast."

On the basis of the variations of the clay mineral assemblage in the less than 2 nm fraction, the Pliocene section can be divided into two parts. In the lower part (Core 11 to Core 9, Section 4), attapulgite is largely dominant (50% to 55%), suggesting that the terrigenous input is mainly derived from North Africa. This is in good agreement with the fact that, during the early Pliocene, Sicily, Calabria, and Pelopenese were only partially emerged (in Sicily and Calabria, the marine calcareous facies of the early Pliocene — "Trubi" — is well developed). Therefore these areas could not have acted as notable terrigenous sources. In the upper part {Core 9, Section 3 to Core 5), attapulgite is still present {average 30%), but smectite (chiefly from Sicily) and chlorite (chiefly from Greece) increases significantly.

This change, occurring within the MPL-2 zone (about 4.5 m.y, B.P.) may be related to the compressional tectonic episode in the early Pliocene in the Peloponese (southwestern Greece) and Apulie (southeastern Italy) (Mercier, et al., 1976), and to uplifting phases in Sicily at the same time (Mascle, 1974).

The 300-meter-thick Quaternary sequence, only documented by four cores (Cores 4 to 1), shows very significant differences in mineralogy, to the Pliocene: (a) an increase in quartz + feldspar content (average 15%, reaching 40% in Core 1); (b) a marked increase in clay mineral content (average 70%, except in Core 1: 20%); (c) a notable decrease in carbonate content (average 15%, reaching 40% in Core 1 due to aragonite contribution); (d) a disappearance of attapulgite, and (e) an increase in smectite which becomes the dominant mineral in the less than 2 ^m fraction. The disappearance of the North African contribution (attapulgite) to the terrigenous input can be explained in terms of dilution by the Sicilian and Calabrian detrital supply (smectite), the importance of which is probably related to two differential vertical movements: lowering of the Ionian Basin, accentuated in the northern part, and uplift of the Sicily and the Calabrian Arc, causing a tipping oveT towards the south and southeast. These relative moven ents are probably a consequence of the underthrusting of the European plate by the African plate, in this area (Ryan et al., 1971). A compressional tectonism, active in the early Quaternary, has been demonstrated in the external Aegean Arc (Mercier et al., 1976). As a result of these movements, the northwestern continental slope in the Ionian Basin became steeper allowing important downslopc transportation of terrigenous material. At Site 374, the mineralogy of Core 1, characterized by quartz, feldspar, aragonite (produced on the shelf), and very well-crystallized illite (mica), illustrates remarkably well this type of sedimentation, the accumulation rate of rate of which is high (averaging 150 mm/1000 yr).

Resume a) Late Messinian: after deposition of evaporites in shallow ponds episodically submerged, dark dolomitic muds arc deposited in a calm environment under unfavorable conditions for the biota.

  1. Early Plioccne: infilling of the basin by rising of the water level until shoreline reached North African platform; basin was probably not very deep, as suggested by the low and very fine terrigenous input; establishment of "normal marine" conditions with well-oxygenated environment; bloom of planktonic life, acting as source of high calcareous nannofossil marls, the base of which was later dolomitized.
  2. Middle and upper Pliocene: within the MPL-2 Zone (about 4.5 m.y.B.P.), partial emergence of Sicily, Calabria and Peloponese; persistence of the early Pliocene physiography.
  3. Quaternary: fast infilling of rapidly subsiding Ionian Basin with detrital material derived from uplifted landmasses.

Sites 375 and 376

Sites 375 and 376 are located on the Florence Rise, about 40 km west of Cyprus. They complement one another and their results have been combined. Site 375 is a deep hole with spot coring, drilled near the top of the rise, on its southern flank, in 1900 meters of water. In order to investigate the pre-Messinian sediments, this hole was located in that part of the rise where these sediments subcrop beneath a veneer of Plio-Quaternary sediments. The hole penetrated 135 meters of Plio-Quaternary sediments which were not cored, about 50 meters of Messinian evaporites (Cores 1 and 2), then a 400-meter-thick sequence of Tortonian (Cores 4 to 7), Serravallian (Cores 8 and 9), Langhian (Cores 10 and II) age. It was terminated at 821.5 meters subbottom in the Burdigalian sediments (Cores 12 and 13). Fifty-one samples were submitted for X-ray analysis (Figure 6). Site 376 is located about 12 km north of Site 375. It is on the northern flank of the Florence Rise, near the pinch-out of the salt layer of the southern margin of the Antalya Basin, in 2101 meters of water. The hole, which was cored almost continuously for 216.5 meters subbottom, penetrated about 55 meters of Plio-Quater-nary nannofossil marls {Cores 1 to 6), 80 meters of upper Messinian turbidites (Cores 7 to 15) consisting of nannofossil maristones dolomitic in the upper part (Cores 7 to 11), and 80 meters into the upper Mediterranean evaporite formation (Cores 16 to 23) consisting mainly of gypsum and green dolomitic maristones (Cores 16 to 20) and anhydrite and halite in the lowermost pan (Cores 22 and 23). Thirty-six samples were submitted for X-ray analysis (Figure 7).

Before discussing the mineraiogical data, it is necessary to briefly outline the structural framework of the western part of Cyprus, with emphasis on petrology and mineralogy of the outcropping rocks and their detrital products. The southwestern part of Cyprus, which is the largest part of the island, is chiefly made up of the Troodos Massif. It consists (Desprairies and Lapierre, 1973) of a core of peridotites and gabbros surrounded by a complex of doleritic and ophitic intrusions; a thick volcanogenic sequence (pillow-lavas, sills, dykes and pyroclastics) belts the system, and the whole displays numerous features of ophiolites. All these rocks have been extensively altered, mostly by early hydrothermal processes, and their detrital products have been accumulated and reworked around the Troodos Massif. The mineralogy of these deposits, mainly Upper Cretaceous in age, is everywhere strikingly dominated by smectites, constituting at times up to 100% of the clay minerals. Smectites are often associated with ciinoptiiolite. Attapulgite has been found in significant amounts. On the southwestern edge of Troodos, some sediments consist almost exclusively of regular mixed-layer types such as corrensite (65%) and allevardite (20%). It is obviously beyond the scope of the present work to give more detailed information on the mineralogy of West Cyprus, Nevertheless, the brief mineraiogical data outlined here are very important, because Sites 375 and 376 are located in the immediate vicinity of Cyprus. South Turkey, although more distant from the Florence Rise than Cyprus is, may have acted as source of terrigenous material. In this area, ophiolites are well developed too, and display similar mineralogy to that of Cyprus ophiolites.

The mineralogy of the pre-Messinian sediments {Site 375) is rather uniform suggesting that, on the whole, the conditions of sedimentation did not change very much {Figure 6).

The Burdigalian maristones, documented by only one sample (Core 13) are characterized by a high clay mineral content (63% of the hulk), dominated by smectite (30%) and well-crystallized kaolinite (20%), calcite (24%), and quartz (12%). No feldspar is detectable in the bulk. This suggests that the maristones were derived from a terrigenous material highly weathered under a rather warm and humid climate.

The Langhian sediments (Cores 11 and 10) display various lithologies. Nevertheless they are characterized by a high carbonate content (average 60%) and a very low quartz content (3%). Plagioclase feldspar occurs as traces. Carbonates consist mainly of calcite reaching 96% in white foraminifer limestone. Calcium-rich dolomite (CAM) is present in significant amounts (up to 19%) together with attapulgite (up to 11%) in the reddish and greenish maristones, suggesting that some diagenesis occurred in this facies. Smectite dominates the clay mineralogy, sometimes accompanied by kaolinite, which could indicate the influence of a warm climate during this period. The reddish and greenish maristones were deposited in a very calm marine environment, receiving at times a biogenic detrital input.

The Serravallian maristones (Cores 9 and 8) are characterized by a higher terrigenous content than those of the Langhian. Feldspar occurs significantly, being sometimes as abundant as quartz (up to 8%). The ciay mineral content increases markedly, due to illite and chlorite contribution; nevertheless smectite remains dominant. The less than 2 ¿nn fraction, dominated by smectite (70%), does not display marked change, suggesting the persistence of terrigenous sources. The importance of smectite and the presence of serpentine (up to 2%) leave little doubt as to the ophiolite origin of the terrigenous input which is probably derived from Cyprus. The increase in quartz, illite, and chlorite (the coarsest clay particles), indicates more active transportation of terrigenous material. The extreme variations in calcite content (0% to 78%) can only be understood if the sediments devoid of calcite were sampled in turbidites consisting of very fine terrigenous material. Sediments very rich in calcite indicate that, between the periods of turbidity current activity, the deposiiional conditions were calm, allowing the settling of calcareous biogenic production. The fact that these turbidites consist of very fine particles (in Sample 8-5, 69-72 cm calcite content is 1% and clay content is 85%) can be explained either by the weakness of turbidity currents, or more likely by the location of Site 375 on the flank of Florence Rise, which meant that only the finest particles reached the site. The

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MINERALOGY

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