Page 61 - Maldonado_Stanley_1976

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mud. Tbe uniform sequence prevails in tbe neritic- by individuallayers or by sequences is not reliable.
batbyal environments; bere sedimentation of bemi- Tbis does not rule out tbe possibility tbat some
pelagic muds is dominant. Tbe muds are sub- techniques, such as detailed cbemistry and petro-
sequently bioturbated; intercalations of mud logic analysis of tepbra layers (Keller et al., 1974;
turbidite sequences are also present in tbese en- F. W. McCoy, pers. comm.), may be used in tbis
vironments. Sedimentation in tbe basin environ- respect. It should be recalled, bowever, tbat turbi-
ments is similar in some respects to tbat in tbe ditic ash layers tend to bave a more limited aerial
neritic-batbyal environments. However, deep basin distribution than that of air-borne volcanic ash
deposits are recognized on tbe basis of well- layers.
stratified units including alternating layers of tur- A discussion of correlation of Strait of Sicily
biditic sequences, bemipelagic mud, and volcanic cores by carbon-14 tecbniques will be treated in a
asb layers. Gravity flow deposits sucb as slump and later section.
grain flow units also occur in tbe basin environ-
ment. Environments in or dose to tbe Strait N ar-
ENVIRONMENTAL FACTORS CONTROLLING THE STRAIT
rows are generally typified by a relatively bigber
SEDIMENTATION
proportion of coarse calcareous san·d deposits.
Certain coarse calcareous sand layers encoun- In tbe following discussion we sball consider
tered in ali of tbe sballow platform environments severa! aspects of the Strait of Sicily sedimentation
may be litbostratigrapbically correlatable. How- in terms of environmental factors. In particular
ever, tbe age of tbis litbosome need not be strictly the following will be considered: (I) the role of
isocbronous since sucb deposits are closely related Quaternary dynamics, including tbe factors related
to deptb, and tbus in turn to tbe rise or lowering to tbe cbanges of climate and eustatic sea level
of sea level and productivity as explaineèl earlier. oscillations; (2) tbe importance of deptb; and (3)
It is conceivable tbat tbe calcareous sand recovered tbe biologica! factors. Altbough latera! correlation
in different cores collected at tbe same deptb may of specific units bas not been accomplisbed, it is
be of tbe same age. However, it bas not been as- nevertbeless possible to distinguisb dominant pat-
certained tbat tbe beds are continuous laterally terns of sedimentation in eacb of tbe major en-
and they may in fact be related to severa! different vironments. As will be recalled, tbree main param-
Pleistocene eustatic oscillations. eters contro! sedimentation in any given
We were unable to correlate individuai layers or environment: pbysical, cbemical, and biologica!.
sequences between the cores collected in otber en- Witbin tbe first group are included such factors as
vironments, even within tbe small deep basins. climate, deptb, temperature, salinity, current sys-
One of tbe difficulties in tbe case of tbe neritic- tems, and boundary conditions of tbe environment
batbyal cores is tbeir uniformity and lack of dis- (geometry, bathymetry, and geology, among
tinct correlatable borizons. Furtbermore, sapropel otbers).
sequences wbicb are useful for correlation pur- The Quaternary sea level oscillations related to
poses, particularly in tbe eastern Mediterranean major climatic cbanges are tbe most important
(Ryan, 1972; Maldonado and Stanley, 1975), do factors that have determined the sedimentary proc-
not occur in the Strait proper. Even well-stratified esses in tbe sballow water platform environment.
basin cores in specific basins could not be corre- As demonstrated, the different sediment types and
lated on the basis of individuai turbiditic sequences sequences developed bere are to a large extent re-
and tephra asb layers. Cores KS 120, KS 69, and lated directly to deptb. As a consequence of deptb
KS 118 (Figure 35), and CH 61-19 (Figure 33) changes, tbere bave been alterations in current
from the Linosa Trough are particularly inter- patterns and intensity, salinity and temperatures
esting in this respect, for ali were collected at wbich inevitably affected tbe vertical evolution of
about the same deptb (witbin less tban 40-m deptb the sediment sequences in this environment. It is
difference) along a transect about 20 km in lengtb apparent that the shallow platform litbofacies
across tbe basin plain. Altbougb tbese cores are would be considerably more uniform bad tbere
similar in generai appearance, tbe radiocarbon been no Quaternary oscillations.
dates (Figure 35) indicate that correlation eitber Moreover, the sediment types in the neritic-