Page 25 - Maldonado_Stanley_1976

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NUMBER 16
layers in this core probably were introduced peri- ronments deeper than about 200 m (Figure 16).
However, detailed mapping of texture, particularly
odically into the depression by turbidity currents
and mass ftow mechanisms. The organic origin in the shallow environments, indicates that the
(shells, calcareous algae, and others) of the sedi- grain-size pattern is mosaic-like and not strictly
ment and the removal of the finest fraction by bot- depth controlled (Poizat, 1970).
The coarse bioclastic sands are interpreted as
toro currents is discussed later.
current-modified coarse lag deposits resulting from
the winnowing of the fine fractions. The bioclastic
Sediment Types in the Strait of Sicily fragments are reworked as indicated by the local
concentrations of oxidized "pralines" (=algal balls,
GENERAL DISTRIBUTION OF SEDIMENT TYPES
some with volcanic nuclei and cemented crusts;
High-resolution seismic surveys indicate that the Blanc, 1959, 1972). Oxidized organic fragments in-
unconsolidated section of Pliocene and Quaternary clude relict Pleistocene faunas, particularly on the
sediments is generally much thinner in the Strait shallow banks. These are sometimes entrained into
than in the deeper Algéro-Balearic and Ionian deeper environments by currents or slumping on
basins bounding it. A concentration of distinct re- the margins of shallow banks. Pleistocene rock sur-
ftectors defines the Miocene-Pliocene boundary faces bare ·of sediment are also present. Terrige-
(contact at top of A in Figures 5-15). Subbottom nous input at river mouths and materia! provided
profiles show that the unconsolidated units are ir- by erosion along the coast, by wind, and by vol-
regularly distributed, i.e., generally thin to absent canic eruptions account for only a small fraction
on topographic highs and thicker accumulations in of the total sediment cover of the Strait.
depressions (Finetti and Morelli, 1972a, b; Za- Cores collected at shallow to intermediate depths
rudzki, 1972). Over 300 m of gently folded, un- contain alternating mud and coarse bioclastic lay-
consolidated sediment are noted in the northwest ers (Akal, 1972; Chassefière and Monaco, 1973).
sector of the Pantelleria Basin; these may have The upper mud and sandy mud layers are oxidized
been transported from the Adventure Bank and (light yellow coloration) to a depth of l m (Blanc,
Sicily (Zarudzki, 1972). The Malta Basin has 1958; Chassefière and Monaco, 1973). Neritic-
trapped a sediment section of about l 000 m (Fi- bathyal cores are constituted entirely by mud,
netti and Morelli, 1972a), and the Linosa Basin to while deep basin cores contain alternating se-
the south comprises over l 000 m; the latter may be quences of sand, volcanic ash, and mud layers.
derived from the African craton and adjacent plat- Fines, presumably winnowed from bank areas, are
form (Zarudzki, 1972). A fourth important but transported by suspended sediment mechanisms to
shallower (about 700 m) depression, the Gela (or depths generally in excess of 50 m. Other mech-
South Sicily) Basin northwest of Malta has ponded anisms also play an important role in the erosion,
over 500 m of unconsolidated sediment according transport, and deposition of mud in the deeper en-
to the above-cited authors. A Flexotir profile trend- vironments. Bottom currents flowing across the sills
ing north northeast-south southwest across this at the margins of the Strait resuspend fine sedi-
basin (Finetti and Morelli, 1972b, fig. Sa) also ments as demonstrated by the increase of suspen-
shows a thickening of the sediment section toward sate concentrations in near-bottom waters (Pierce
Sicily and a generai southward progradation of the and Stanley, 1975). Moreover, mud turbidites are
deposits into the Basin. also important constituents of deep cores, as dis-
The grain size distribution of the Strait surficial cussed later.
sediment has been measured by Blanc (1958) and In addition to the characteristically high values
textural maps of this area compiled by the U.S. of MgC0 3 , and locally, volcanic ash and lava frag-
Naval Oceanograpliic Office (1965), Fraser et al. ments, the Strait sediment contains high values of
(1970), Poizat (1970), Emelyanov (1972), and montmorillonite (Emelyanov, 1972). The mont-
Akal (1972). Texture appears to be broadly re- morillonite content which appears to increase in
lated with morphology: coarser sediment types (silt the sector near Sicily (Chassefière and Monaco,
to sand and coarser) are concentrated on shallow 1973; Pierce and Stanley, 1975) and the island of
banks, and mud (silt and day mixtures) in envi- Pantelleria (Blanc-Vernet et al., 1975) may be