Page 40 - Maldonado_Stanley_1976

36 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

ponents of these oozes are aggregate grains, nee- shown in Figure 2lc.
dles, and irregularly shaped grains, many of which The importance of bioturbation which predomi-
are attributed to terrigenous day particles. nates on such well-oxygenated shallow platforms is
The fine fraction of sapropel (Figure 20E}F) is well documented (Sarnthein, 1972; Reineck, 1973),
characterized by an impoverishment in the number but burrowing of the sediment is not clearly ap-
of species and the amount of nannoplancton in parent on the Strait of Sicily photographs. The
the b1ack clayey laminae and a high coccolith con- absence of biogenic and current-produced struc-
tent, represented by on1y a few species, in the white tures su eh as ri pples, scour shadows, an d grooves is
lamine. Helicopostosphaera kamptneri Hay and not necessarily an indication of lack of vigorous
Mohler andfor Emiliani huxleyi may be the on1y bottom current activity. Strong bottom currents
species present in these white lamine and consti- bave been measured in this part of the Strait
tute as much as l 00% of the bulk sediment. (Molcard, 1972). Some photographs, for instance,
An association of nannop1ankton interpreted as show crinoids heeling over (Akal, 1972, fig. 8);
a warm water assemblage is reported from sapropel this and the absence of fines together reflect the
layers in the eastern Mediterranean (Miiller, effect of strong flow capable of modifying the sea
I 973). Thin laminae of diatoms, radiolarians, an d floor. An analogous set of observations has been
silicoflagellates may also be associateci with sapro- made on the banks of the Alboran Sea by Milliman
pel or organic oozes. Pyrite framboids (p) are also and others (1972), who record the heeling over of
characteristic of sapropel (Figure 20E). The sphe- organisms but find little evidence of current-
roida1 form of the framboids is an inherited char- produced structures in the coarse-textured sea floor.
acteristic provided by a preexisting template (Rick- It appears that coarse, poorly sorted sediment of
ard, 1970; Sweeney and Kaplan, 1973). They are the type observed on the shallow banks does not
attributed to the pseudomorphism processes of py- preserve such features well.
rite formation (Rickard, 1970) during early dia- The sea floor of neritic-bathyal environments
genesis of the sediment or in the water column (Figure 22) is characterized by strongly pitted and
(Ross and Dege~s, 1974: 187). Twin-gypsum crys- trailed muddy sediments. Most of the sediment sur-
tals also are common in the sapropel; they are face has been intensely disturbed and burrowed, re-
attributed to neogenesis processes (Nesteroff, 1973: flecting significantly high activity by benthic or-
719). ganisms. Broad depressions, small holes, and plow
marks or grooves are also common. The biogenic
bottom structures in these environments are well
Sea-Floor Photography
preserved, while evidence of bottom current ac-
Sea-floor photographs collected in the different tivity is not well displayed by the sediment.
Strait of Sicily environments illustrate some sur- Photographs of the deep basin environment (cf.
ficial sediment types described in the previous sec- Malta Trough, Figure 2'3) show a mud floor al-
tions. These photos are of some assistance in the most entirely reworked by benthic organisms, al-
interpretation of biogenic structures recorded in though burrowing appears to be less extensive and
the cores. less varied than in the former environment. The
The shallow platform and banks are character- most characteristic feature is the high density of
ized by a generally flat bottom with many small granular mud rods identified as large fecal pellets.
irregularities resulting from biologica! activity. Holothurians, the most common of the mud-eating
The most typical surface type is one covered by benthic organisms (Ewing and Davis, 1967; Hee-
coarse sediment with little or total absence of re- zen and Hollister, 1971), are probably the pro-
lief (Figure 2'1 ). Calcareous alga e is a common ducers of these pellets. Biogenic structures include
biogenic component. Three of the photographs small to medium-size mounds with apical holes
illustrateci in Figure 21 (A}B}D) show sand and (holothurian) and depressions, and sinuous trails
calcareous algae (algal balls) of the type described left by wandering gastropods or echinoderms. One
in the shallow platform environment by Blanc large rim crater (Figure 23n) resembles fish-
(1958); this sediment type has been termed "maerl" produced structures described elsewhere (Stanley,
(Caulet, 1972). A coarse calcareous shelly sand is 1970; Heezen and Hollister, 1971).