Page 14 - Maldonado_Stanley_1976

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Miocene is identified and correlated with sequence zone defined by Burollet (1967) and Finetti and
A of Finetti and Morelli (1972a, b). Morelli (1972a).
Broad Uplift (Environment 3): This zone in-
cludes those areas occupying positive structural
ENVIRONMENTS
axes (Burollet, 1967); e.g., the South-Sicily Medina
SLoPE (Environment l).-The slopes considered Uplift, Jeffara-Malta axis (km 110-160, Figure
here are those that flank the Strait of Sicily on the 6c), and the northeastern extension of the Galite
east (Ionian) màrgin and the west (Algéro- Archipelago (km 908-983, Figure 6B 1 , B 2 ). The
Balearic) margin, and steep slopes which bound the latter is deeply cut by a canyon. These areas are
major deep basins of the Strait. A transect from characterized by a broad, convex-up topography
Pantelleria Trough to the Adventure Bank (km (probably gentle anticlinal-like folds) and small
590 to 615, on Figure 3) crossing a slope of the distinct valleys. Faulting is not as prominent a
type discussed here is shown in Figure 5. This feature in this zone as in the other outer margin
highly irregular slope appears on 3.5 kHz records environments of the Strait. The reduced sediment
as a series of single or multiple hyperbolic pat- cover on the convex-up topography suggests a slow,
terns. Poor definition of stratification or sediment uniform rate of sediment accumulation, or erosion
ponding is in part an acoustic artifact (roughness by bottom currents (Pierce and Stanley, 1975), or
and steepness of the slope); poor penetration also both.
may be due to a reduction of the unconsolidated Neritic-Bathyal Platform (Environment 4): The
sediment cover. neritic-bathyal platform includes essentially flat,
Outcrops of older Tertiary deposits have been depressed areas al though the sea floor in this zone
repm ted from slopes bounding the major basins of is not completely confined as are the basins. De-
the Strait (Colantoni and Borsetti, 1973). Such positional processes dominate here. Two platform
slopes average about 2.5°, but attain much higher sectors are traversed: the Pelagian Shelf, km 160-
values locally; they commonly display a steplike 365 (Figures 7, 8), and the Galite Platform, km
configuration as a result of fault offsets (Figure 5). 850-908 (Figure 9).
Two cores retrieved from this environment show The platform environment is characterized by
rather distinct lithofacies: core LY II-7 on the thick sequences of deposits which pinch out locally
Algéro-Balearic margin includes an alternating se- on topographic highs (cf. symbol on Figure 3, km
quence of turbidites and hemipelagic mud, while 160, km 908) and less frequently on the platform
core LY II-3 on the Ionian Basin margin com- proper (Figure 7, a~ km 305; km 780). Thinning
prises distinctive gray to black organic-rich sapro- of strata is the result of simultaneous deposition
pel layers as well as turbidites and hemipelagic and vertical fault offset, which may also result in
mud. the development of an offlap sequence (Figure 8,
NERITIC-BATHYAL BoRDERLAND (Environments 2, a~ km 325) or truncation. Growth-faults (Figure 7)
3, 4, 5).-Somewhat more than half of the Strait with thickening of sediment layers on the down-
area lies within a depth range of 200 to 700 m. thrown block are observed; similar phenomena are
This zone is morphologically complex and the described by Hardin and Hardin (1961) in the
sparker profiles reveal the importance of vertical Gulf of Mexico.
structural displacement that has broken the sea The fault offsets observed in seismic records are
floor into a complex net of horsts and grabens. associated with tilted blocks, small grabens and
Four subzones are recognized. horsts (Figure 7), and small mounts (Figure 9, km
Outer Margin~ Faulted (Environment 2): An 880). The ratio of height to width of these tectoni-
outer margin, faulted zone, distinguished at the cally displaced blocks is approximately l to 100;
eastern end of the Strait (km 68-115, Figures 3, the maximum throw of these faults observed in our
6A), comprises the transitional area between the records is about 200 m (Figure 7); and the maxi-
Strait proper and the margin slopes. The sea floor mum topographic relief is about 170 m. Displaced
on the 3.5 kHz records presents an irregular, (slumped) Quaternary deposits (Figure 8, b~ km
rugged topography with a reduced sediment cover. 365; Figure 9, a~ km 870), and gentle anticlinal
This area corresponds to the faulted and flexured (km 220) and synclinal (km 180, km 200) struc-