Page 48 - Maldonado_Stanley_1976

44 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

28, black square symbol). In contrast, the organic
20 KS-120 ooze displays evidence of burrowing activity (Fig-
ure 28, open square). A layer of concentrated py-
~25-
o ritized tubes (b) is commonly associated with this
type of deposit. The organic ooze extends verti-
cally to the base of protosapropel deposits (par-
tially blackened square symbol). The burrowing
activity decreases sharply in the protosapropel
sediment proper and phases out in the overlying
sapropel.
185-

Definition of Sequences

GENERAL
The late Quaternary Strait of Sicily lithofacies
can be distinguished from those in the adjacent
deep basins (Balearic, Ionian) by a high degree of
bioturbation and mixing of sediment by organisms,
which results in textural uniformity, and by the
presence of relatively large amounts of coarse bio-
clastic sediment. Cores east of the Strait on the
Ioni an Basi n slope (cf. core L Y II-3) are more
highly variable both in terms of facies and se-
quences; cores on the western slope into the Algéro-
Balearic Basin comprise a large proportion of
turbiditic sequences (sand and mud turbidites).
Cores collected in the Strait proper are distinct
and generally not transitional with those of the
contiguous slopes and adjacent deep basins. We
can demonstrate that regional sedimentation pat-
terns and petrology in the Strait are closely related
with geographic setting and specific depositional
environment, including proximity to the Strait
Narrows.
The different types of sediment present in each
Strait of Sicily core can be grouped into major as-
semblages. The sediment types grouped within
each of these assemblages are termed sequences,
and these are defined on petrologic characteristics
which present distinct natura! latera! and vertical
350- trending lithological transitions. Each sequence is
Te(p)
8 defined on the basis of a succession of sediment
types that reflect deposition resulting from either a
specific sedimentary process (turbidity current,
FIGURE 27.-Selected X-radiographs (positives) showing exam- mass flow, etc.) or a regionally important, large-
ples of volcanic ash interbedded in mud from cores in
scale environmental event (cf., climatic changes
Linosa Trough: A, vertically graded ash layer (194-185 cm);
significant enough to alter water mass stratifica-
B, coarsening-upward ash layer; c, laminated type (open
triangle = ash; open circle and Te<P> = hemipelagic mud). tion and flow, eustatic oscillatory sea level patterns,
(See also Figure 35 for core logs; explanation in text.) andjor· biogenic production).