Page 74 - Maldonado_Stanley_1976

NUMBER 16 67

1.000

t.OOO

....
~
'.000- l
~ l
::'! ~
::::! -.J
bl ~
~. -----r---.;---.,......_
4,000 l
10°W 10° 15°
currents -. D [[[]] ~

less dense ventilated partly stagnant (H2S-rich)
surface water water unvent i l a t ed deep water
water
FIGURE 39.-Schematic showing possible early Holocene water mass changes in the Mediterranean.
The model depicts stratification and reversal of currents during the warming phase of the
climatic curve. The present study indicates that deep Strait basins remained ventilated at the
time that sapropel layers accumulated in the eastern Mediterranean. (Topographic base after
Wiist, 1961.)

position, (b) SEM investigation of the lutite frac- quences, latera! distribution, and depth is demon-
tion, (c) sedimentary structures observed in X- strated. The coarse calcareous deposits on banks,
radiographs and split cores, and (d) examination comparable to those on shallow shelves and plat-
of the sea floor by underwater photography. forms elsewhere in the Mediterranean, are typified
6. The sediment types are grouped into se- by upward-fining and upward-coarsening se-
quences, each of which is defined on the basis of a quences. Sediment facies in the shallow platform
succession of sediment types. A sequence represents environments are directly related to Quaternary
deposition resulting from a specific sedimentary sea level oscillations. The sediments in the some-
accident (turbidity current, mass flow, etc.) or from what deeper neritic-bathyal environments are typi-
a regionally important, large-scale environmental cally uniform muds devoid of marked stratification,
event. An example of the latter: the Quaternary while the more variable and well-stratified deep
climatic changes which were significant enough to basin sediment sections include turbidites, volcanic
alter water mass stratification and movement, eu- ash layers, and hemipelagic mud sequences.
static oscillatory patterns, and biogenic production. 8. Two types of layers containing volcanic sedi-
The four major sequences distinguished are (l) ment are distinguished: (l) air-borne tephra
upward-coarsening and upward-fining; (2) uni- layers, and (2) turbiditic ash-rich layers. The
form; (3) turbiditic (includes mud and sand-silt former dis,play a vertical gradation in grain size
turbidites); and (4) sapropel sequences. (fining or coarsening upward), parallel lamina-
7. The dose relation between sediment type, se- tion, or in some cases are structureless. The latter