Page 29 - Maldonado_Stanley_1976

NUMBER 16 25
which includes planktonic foraminifera. in triangular plots shown in Figure 17. In one tri-
Organic ooze layers are usually associateci with angle (Figure 17 A 2 ), the end points represent the
sapropel. These two sediment types are composi- inorganic fraction (components IO to 14), plank-
tionally transitional. However, in the split cores tonic foraminifera (component 4) and the remain-
the contact between the two is very well marked by der of the biogenic fraction (components l to 9,
a sharp color change: organic oozes are pale olive except component 4).
(IO Y 6/2-5 Y 5/2), while sapropels are dark gray- The end members of the other triangle (Figure
olive (5 Y 3/2-5 Y 2j1). This contact is also noted 17 A 1 ) represent the percent of total sand fraction
on X-radiographs. A type of sediment that resem- in the bulk sample, the total biogenic fraction in
bles organic ooze is present in the Linosa Trough the sand fraction, and the total planktonic fora-
and perhaps also in the Malta and Pantelleria minifera fraction in the sand fraction; ali of these
troughs; this type also displays some petrological are recalculated to I 00%. In this representation any
affinities with the hemipelagic mud type. component could actually be as high as 100%; how-
A third type of sediment, protosapropel, is as- ever, the total planktonic foraminifera is equal to,
sociateci with this group. While genetically and or lower than, the total biogenic fraction. In this
lithologically related, the protosapropel is not con- type of representation all of the samples plotted
sidered a true sapropel because it does not display are concentrateci on the left half of the triangle.
the typical lamination of the sapropel and may be The different lines on the triangle mark the bound-
bioturbated to some extent (Maldonado and Stan- aries of different components.
ley, 1975). Core samples have been assigned a letter symbol
on Table 3 and in Figure 17; the numbers associ-
ateci with the letter key (Table 3) identify their
Sand Fraction Composition
depth (in centimeters) from the top of the core.
GENERA L
CoARSE CALCAREous SAND TYPE
The fraction larger than 63 microns was col-
lected from ali samples by wet sieving after re- The samples selected for this study are of the
moval of the organic matter with hydrogen per- shelly bioclastic sand type as defined in the pre-
oxide. The identification of grains was made using vious section. The modern, relict, or residual frac-
a binocular microscope, and relative frequencies tions generally can be distinguished on the basis of
were determined by counting 300 to 400 grains per abrasion and preservation of the skeletal material.
sample. The grain counts were made by unit area Modern biogenic components do not show signifi-
measurements as opposed to point counting. The cant evidence of transport, although tests may be
following parameters were determined: pteropods broken. Relict and residua! calcareous components
(l); molluscs (2) consisting largely of gastropods are composed of organic remains deposited during
and pelecypods; shell fragments (3); planktonic the Pleistocene and early Holocene (see core AS
foraminiferida (4); benthonic foraminifera (5); 6-8, Figure 34), or reworked from older deposits;
ostracoda (6); bryozoa (7); other invertebrates these bioclastic particles are characterized by an
(8); pian t debris (9); heavy minerals (l 0), in- iron oxide stain and the rounded, worn shape of
cluding opaque and some characteristic nonopaque the grain edges. In the Strait of Sicily the sand
2
minerals; mica (Il); pyrite and strongly pyritized fraction of relict sediments also is characterized by
tests and burrows (12); light minerals (13), in- a relatively high feldspathic content (Blanc, 1958);
cludìng carbonates and gypsum; and ash (14). The the modern biogenic sediment is generally associ-
components l to 9 represent the biogenic fraction ateci with a low feldspar content.
w h ile l O t o 14 are grouped as in organi c fraction. Other organic components of the calcareous
The results of these counts are listed in Table 3, sand type are bryozoa, echinoderma, calcareous
and the different components have been grouped algae, crustacean fragments, and plant debris. Py-
rite is not very common, and where present is usu-
2
"Pyrite" as used bere is applied to various possible fer- ally oxidÌzed, particularly in relict and residua!
rous sulfide types. sands. Glauconite is more abundant. Gypsum frag-