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700 and 1600 m, and below a depth of 1600 m the rates in core LY II-6 in the small depression west
degree of bioturbation is quite low (i.e., about IO% of Marettimo Island are similar to those in other
of the core). This low value of reworking by or- deep basin cores.
ganisms probably reflects a decrease in the amount Carbon-14 data of core Ges-12 in the small Strait
of biogenic activity concurrent with an increase in Narrows basin indicate relatively low (15 cmflOOO
the rate of sedimentation. years) sedimentation rates, but continuous deposi-
tion from the late Pleistocene until recent time
(Figure 38s).
RATES OF SEDIMENTATION
The cores examined from the Ionian margin
During the course of this study, 41 radiocarbon (LY II-3) and Balearic margin (LY II-7) slopes
dates were obtained (Table 5), and these data have provide an average sedimentation rate of 30 cm
been plotted on the core log diagrams (Figures and 15 cm per 1000 years, respectively (Figure
34, 35). These diagrams show that the top of the 38A). On the Balearic Basin plain an average rate
cores are of highly variable age, and some of them of sedimentation of 23 cmf 1000 years is reported
are very old. When ali age data are plotted against (Rupke and Stanley, 1974).
core sample depth no coherent pattern emerges, Three aspects of the sedimentation pattern in
indicating an absence of uniform trend in the rate the environments discussed earlier are considered:
of sedimentation from core to core. However, when (l) rate of deposition; (2) uniformity of these
the core data are grouped in terms of environment rates in time; and (3) the age of the sediments at
more distinct trends appear as to the rate of sedi- the top of the cores, or the degree of continuity in
mentation and the age of the sediment at the top sedimentation from the Pleistocene to the present.
of the core (Figure 38). Sedimentation rates (with some exceptions) gen-
The shallow platform environment ( cores AS erally decrease with increasing bathymetric depth,
6-7, AS 6-8) is characterized by (l) a high rate of i.e., from the shallow banks to the neritic-bathyal
sedimentation (52 cmflOO years for core AS 6-8 platform to the deep basins. With the available
in the Gulf of Hammamat) and (2) a truncation carbon-14 data, it appears that deposition in ali
(or lack of sedimentation) in some of the cores be- environments, except in the two deep basin cores
fore the end of the Pleistocene (Figure 34). The (KS 63 an d KS l 09, which ha ve higher ash an d
sedimentation rate calculated for core AS 6-8 is turbidite layers), has been relatively uniform in
the highest measured except for sections of two the late Quaternary.
cores in the deep basin environment (Figure 38). However, there is a significant difference in the
In the neritic-bathyal environments, rates of age of sediments at the tops of cores in the differ-
sedimentation range from 16 to 40 cmfiOOO years ent environments. On shallow banks, the tops of
(average of about 25 cmflOOO years), and the tops some cores are truncated in the late Pleistocene to
of a number of cores in this environment terminate early Holocene; in the neritic-bathyal environ-
in the early Holocene (Figure 38A). One core (KS ments in early Holocene; and in the deep basins,
105), unlike the above, shows a lower sedimenta- sediments have accumulated on a fairly continuous
tion rate (similar to that of the deep basins) and basis from the Pleistocene until the recent (Figures
continued deposition through much of the 34, 35). As discussed in earlier sections, sedimenta-
Holocene. tion in the shallow platform environment is closely
The rates of sedimentation in the basins ap- related to Quaternary events. It has been empha-
proximate 20 to 25 cm per l 000 years (Figure sized, for example, that the upward-coarsening and
38s). The much higher rates in two core sections upward-fining sequences in shallow environments
(lower half of KS l 09 in Malta Basin, an d in the are a direct response to eustatic oscillations.
upper half of KS 63 in Linosa Basin) are the result We have demonstrated that in the neritic-bathyal
of a greater abundance of turbidite and ash incur- environments bioturbation is an important factor
sions at these two localities. It should be noted that and that the rate of reworking by benthic orga-
in contrast to cores at shallower depths, deep basin nisms has 'continued during deposition of the en-
deposits accumulated on a more continuous basis tire core sections. Equally significant are the
until the present (Figure 38 B). Sedimentation carbon-14 dates, which indicate that oceanographic