Page 35 - Maldonado_Stanley_1976

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0RGANIC OozE TYPE SEM Analysis of the Lutite Fraction
The organic ooze and protosapropel types are A scanning electron microscopic analysis serves
transitional between the hemipelagic mud and the to determine the composition of the lutite fraction
sapropel types in terms of sand-fraction composi- and provides a rough quantitative approximation
tion, texture, and structure. Thus, a small amount of the different components. In order to prepare
of clastic sand fraction is present as well as a less the samples for electron microscopy, the organic
uniform biogenic fraction in contrast to the sapro- matter is first destroyed with 30CJ hydrogen per-
0
pel type. Organic ooze is characterized by the fre- oxide. Then the sample is wet sieved to separate
quent occurrence of pyritized worm tubes; these the fraction coarser than 63 microns. The residue
are concentrated at the top of the organic ooze is then placed in suspension. A drop of this sus-
layer and are well displayed in the core X- pension is pippeted immediately after mixing and
radiographs (Figure 28). placed on a standard metal specimen plug. The
sample is then dried at room temperature and
coated with gold. No sticking tape was used. In the
BRYozoAN CoNTENT
case of some coarser grained sam ples, grains w ere
The sand fraction of 44 samples from different glued (Elmer's glue) to the plug to avoid discharge.
environments (cores LY II and AS) were exam- The plug was examined with a Cambridge In-
ined for bryozoan content (Salvador Reguant, Uni- strument Stereoscan. Photographs were made of
versity of Barcelona, Spain, pers. comm.). The each sample using SEM low magnification (100-
bryozoan content is low except in shallow platform 500 magnification), which reveals details of sedi-
cores. Bryozoan fragments may be transported in ment texture and a rapid inventory of the fossil,
the various environments in the same fashion as authigenic, and detrital assemblages in the silt
are the planktonic foraminiferal tests associated fraction. Individuai grains and the fine silt and
with them; fragments of cellariiform zooarial tubes day fraction have been examined systematically
and, locally, of catenicelliform species (in LY using high (X 2000) magnification.
II-6, g) disintegrate when animals die and can be The identification of the different particles is
transported in suspension prior to deposition. based on a comparison with previous works and, in
Rapid burial in fine sediment is necessary for the particular, those of Stieglitz (1972) and Milliman
preservation of these delicate fragments. (1974) for the calcareous fraction. The distinc-
Sample AS 6-8, a, is of interest because it con- tion between the calcareous biogenic and the in-
tains an assemblage of species indicative of a some- organic clastic particles is often subtle, especially
what low energy environment although the core in the finest fractions.
was collected at a depth of 93 m. An examination The common components of the lutite fraction
of 97 fragments reveals the following zoaria: mem- are clay-size particles and aggregates, calcareous
braniporiform (3); celleporiform (2); adeoniform fragments of tests, siliceous grains, aggregate
(12); vinculariiform (30); reteporiform (8); cel- grains, calcareous inorganic grains, calcareous nan-
lariiform (42). This zoarial assemblage is closely noplankton, spicules, foraminifera, and volcanic
related to that reported from slope environment ash fragments. Pollen, dinoflagellate cysts, pyrite
(cf., Caulet, 1972:239, 243). It is difficult to ex- framboids, diatoms, plant fragments, and silico-
plain in terms of the sea-floor depth where this flagellates are abundant in some samples.
core was collected an d the age of this sam p le The composition of the lutite fraction of the
(17,000 to 20,000 years BP, Table 5). One possible sand-silt sediment type (Figures 18, 19A-c) is the
interpretation is that this sample consists of re- most variable of all the. sediment types studied.
sidua! materia! (i.e., a thanatocoenosis) from a Calcareous biogenic and bioclastic particles and
different environment. The possibility of reworking terrigenous feldspathic grains are predominant in
of older materia! appears corroborated by the the coarse silt fraction (c and f in Figure 18A,B).
abundance of gypsum grains in the same sample, The biogenic calcareous grains, mostly calcareous
also believed to have been eroded from outcrops of algae and foraminiferal test fragments (c), are the
the shelf. dominant components (Figure 18B). Well-