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66 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

cupies a zone of particularly strong current regime sins from nonsapropel basins in the west, is clearly
(Molcard, 1972). Currents accelerate in the con- one of the key sites in which to investigate this
stricted narrows and decelerate as the Strait widens, problem.
with a probable increase in deposition away from
Summary
the N arrows. Thus we would expect that cores
collected in the vicinity of the N arrows would pro- l. This marine sedimentological study defines
vide the best record of water mass-bottom current the major Quaternary lithofacies observed in cores
fluctuations during the recent geologica! past. collected in the different sectors of the Strait of
It is probably not accidental that there is an ap- Sicily and establishes the relationship between
parent correlation between the time of truncation sedimentary facies, depositional environment,
of core tops in the Strait neritic-bathyal environ- structural displacement, transport processes, and
ments and that of the most recent protosapropel late Quaternary events which affected the centrai
and sapropel formation (dated at about 9000 to Mediterranean region.
7500 years BP) in the eastern and centrai Mediter- 2. The major depositional environments in, and
ranean. Independently, other workers (Colantoni immediately adjacent to, the Strait of Sicily are as
and Borsetti, 1973) record microfauna1 changes in follows: slope; neritic-bathyal borderland; basin
the Linosa and Malta basins at about this period. (intermediate and deep); shallow platform;
One possible explanation for these early Holocene marked topographic high (submarine mounts, vol-
depositional and faunal changes is a temporary canoes, diapirs); canyon; and the Strait Narrows
short-term reversa1 of surface and deeper water between Cape Bon, Tunisia, and Marsala, Sicily.
flow (Olausson, 1961; Mars, 1963; Huang et al., These environments are broadly defined on the
1972; Nesteroff, 1973; Huang and Stanley, 1974; basis of morphology, structural configuration, and
and others). At present, less dense water flows thickness and attitude of the sedimentary cover as
(> 30 cmjsec) southeastward above northwestward measured in seismic records. The shallow platform,
flowing (32 cmfsec) Levantine water (Molcard, neritic-bathyal borderland, and basins are the most
1972). We propose a contrasting early Holocene characteristic environments in the Strait.
short-term cur:rent reversal model in which less 3. The lithologic uniformity of core sections,
dense surface water flowed to the northwest in the high degree of bioturbation, and the impor-
response to the early Holocene climatic evolution tance of coarse calcareous sediments serve to dis-
(Figure 39). Surface water salinity and tempera- tinguish the late Quaternary Strait of Sicily litho-
ture conditions (Farrand, 1971; Fairbridge, 1972) facies from those of the adjacent deep Ionian and
undoubtedly were modified in the Mediterranean Balearic basins.
during the warming phase of the climatic curve, 4. Three major Strait lithofacies assemblages are
but the degree of stratification resulting from this recognized: (l) coarse calcareous sand layers inter-
remains a point of conjecture (Letolle and bedded with mud and sandy lutite deposits prevail
Vergnaud-Grazzini, 1973). on shallow banks; (2) homogeneous, bioturbated
Our core analysis shows (l) that the sea floor of light olive gray to dusty yellow muddy sequences
the Strait of Sicily remained ventilated and swept predominate in the neritic-bathyal environments
by currents at a time when anaerobic conditions and are also found in some basins; (3) mod,erate-
prevailed in the Ionian-Levantine basins east of to well-stratified sand (including gravity sediment
the Strait, and (2) that the Strait although a broad flow units and ash) alternating with hemipelagic
sill apparently did not completely block circula- and turbiditic mud are generally present in deep
tion between the eastern and western Mediterra- basi n an d Stra i t N arrows cores.
nean basins. We conclude that the regional litho- 5. Five major sediment types are distinguished:
facies distribution observed is best explained in (l) coarse calcareous sand; (2) sand- to silt-size
terms of early Holocene paleooceanographic sediments; (3) ash; (4) mud; and (5) sapropel
changes including possible reversal of currents. and organic ooze (the latter type is retrieved only
The latter concept requires further testing and we in cores on the Ionian margin east of the Strait).
suggest that the Strait of Sicily, the major sill The sediment types are defined on the basis of the
separating sapropel-rich eastern Mediterranean ba- (a) sand fraction (> 63 microns) content and com-