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8~ at 166m (Figure 33), collected near the center of bation structures. Poorly stratified mud layers are
the Strait at intermediate depths (350 m), shows noted in a few cases. Typical examples of such
a Iithology transitional with the types described uniform cores include, among others, LY II-4 and
above: i.e., a vague upward-fining sequence with 6A (Figure 34), and KS 7.8 and 105 (Figure 35).
intercalations of coarse bioclastic sand layers and Another distinction is the Iow sand content (2%-
muds toward the upper portion of the sequence. 7%) in the mud; this fraction consists mostly of
The coarsening- and fining-upward sequences planktonic foraminifera, pteropods, and a minor
are similar to those cored in deltaic environments but diverse assemblage of faunal remains.
(Oomkens, 1970; Maldonado, 1975). The upward- The uniform sequence includes hemipelagic
fining type may be analogous to transgressive del- and, less frequently, turbiditic muds which have
taic sequences while the upward-coarsening se- been intensively homogenized by biogenic sedi-
quences correspond to deltaic offlap sequences. mentary structures (Figure 26). These sequences
However, the assemblage of sedimentary structures are most prominent in neritic-bathyal p1atform
present in the Strait cores are not closely similar and depression environments (4, 5). The most
to those of deltaic origin, and the source and com- common structure is subtle mott1ing visible in
position of detrital materia! is also different. The X-radiographs (Figure 26E). Bioturbation is ver-
upward-fining sequences in the Strait and deltas in tically developed and not of the "layer-by-Iayer"
generai essentially are produced by the same type type characteristic in some areas of the Mediter-
of sedimentary event, i.e., the postglacial eustatic ranean such as the Strait of Otranto (cf. Hesse and
rise of sea leve!. On the other hand, the upward- von Rad, I 972). T h ere are various types of dis-
coarsening sequences in deltas are the result of tinct burrows in addition to mottled structures.
progradation as reflected by a high detrital influx; The finest deposits display tiny light-colored
in the Strait this vertical progression is related to threadlike shafts (Frey, 1973); these are straight or
eustatic changes of the sea level across the Strait slightly curved, sometimes sharply bent, and are
surface. These oscillations altered productivity usually less than 0.5 mm thick and severa! deci-
and current activity and thus controlled the sub- meters in length (Figure 26F). This structure is
sequent deposition of coarse biogenic deposits. similar to the fine stringlike feature called mycel-
On some banks, fine grained sediments have ac- lia (Bouma, 1964; Reineck and Singh, 1973:406),
cumulated since the last rise of sea level, thus de- also noted elsewhere in the Mediterranean
veloping an upward-fining sequence. On others, (Huang and Stanley, 1972). Burrow systems of
truncation and continued nondeposition have pre- small fucoid-like or chondrite-like tubes are similar
·vailed since the last eustatic low stand. to the above; these are a few millimeters long and
Radiocarbon dating (Milliman et al., 1972, dis- branch dendritically (Figure 26c). The burrow
cussion in later section) substantiates the theory casts of both types include either carbonate or
that the coarse calcareous sand is best developed pyritized materia!. According to Hesse and von
during the rising stages of sea 1evel rather than Rad (1972), the chondrite-like burrows and bur-
during the Iowering or lowest sea level stage. In row casts are possibly the hyphae of marine fungi.
any case, there can be Iittle doubt that these se- Nevertheless, Howard and Frey (1973) describe
quences are closely associated with dynamic sea the burrows of capitellid polychaetes in estuarine
level changes. During periods of stabilized sea level muds, which are similar to both mycellia and
(such as at present) the rate of sedimentation has chondrite-Iike types. The Iaterally stopping struc-
been notably reduced, at Ieast in the deeper sectors tures (H esse an d von Rad, I 972), or press struc-
of the shelf. tures of Reineck and Singh (1973:141), are also
abundant, and these are interpreted as sea-urchin
tracks (Howard et al., 1974). Other burrows in-
UNIFORM SEQUENCE
clude tunnels, shafts, and spiral-shaped coils that
The most diagnostic features of cores from the are between 2· to 20 mm wide and a few centimeters
neritic-bathyal environments are (I) their ex- or decimèters long (Figure 26B). These burrows
tremely uniform, homogeneous aspect, even in are attributed to acorn worms. The simple, bifur-
X-radiographs, and (2) the abundance of biotur- ·cated burrow perpendicular, or inclined, to bed-