a. epivalve- the older and larger of the two valves
b. hypovalve- the younger and smaller of the two valves
valve mantle- the edge of the valve that bends down perpendicular to
the valve face
connecting bands- bands which overlap each other and the valve mantles
to connect the two valves
girdle- the sum of the connecting bands
Most fall into one of two categories:
Pennate-one long axis and two short axes with the surface marking at
right angles to the long axis
Centric- circular, triangular, or oblong. Surface markings radiate
fro a central area
IV. Evolution
Earliest diatoms are from the Lower Cretaceous where their diversity
suggests an earlier origin
Extremely diverse and abundant in Cenozoic sediment
Pennate species became more abundant in the Neogene
V. Stratigraphy
Greatest stratigraphic application is for the Upper Eocene and younger
sediments
Older diatomaceous sediments often have undergone diagenesis with biogenic
opal converted to chert
Eocene and Oligocene assmeblages are fairly cosmopolitan with zones
and individual species datums having world-wide significance
Younger assemblages, particularly those of the Pliocene and Pleistocene
vary regionally. Regional zonal schemes have been established for the younger
portion of the record.
VI. Paleoenvironmental Applications (Class discussion)
interpretation of sea-ice extent
interpretation of surface water-mass migrations
productivity indicators
salinity indicators
RADIOLARIANS
I. What are Radiolarians?
Radiolarians belong to the Phylum Protozoa
Radiolarians differ from all other protozoans by a division of the
cell interior into an inner zone which is separtaed from an outer zone
by a membrane from the remaining outer zone.
II. Where do they live?
surface and deep waters
can travel and disperse via deep water-masses
all latitudes
pelagic environments, although found in fjords and near shore they
are not a significant contributing factor to shelf fauna.
marine only
III. Morphology
two major groups (orders) contribute to the sedimentary record, the
Spumellaria and Nassellaria.
Nassellarians:
axial symmetry
often with an apical horn
cephalus
thorax
abdomen- may be multi-segmented
Spumellarians:
radial symmetry
usually spherical or discoidal
clearly seen inner medullary shell an outer cortical shell
Wall structure
latticed
spongy
perforate
IV. Evolution
earliest radiolarians are documented from the Ordovician.
preservation of subsequent Paleozoic radiolarians is rare
diversity limited until the Jurassic
diversity increased greatly in the Jurassic and have remained an important
component of marine plankton since.
V. Stratigraphy
Paleozoic radiolarians are of little stratigraphic utility
During the last decade, Mesozoic radiolarians have been studied in
detail from alpine sequences in Europe. Although often poorly preserved
they many times provide the best stratigraphy in indurated and partially
metamorposed sedimentary sequences.
Greatest utility within the Cenozoic is for Eocene to Recent.
Frequency fluctuations of species abundances as a surrogate means of
identifying Late Quaternary oxygen isotopic stages (in class discussion).
Quantitative analysis of assemblages to reconstrust paleoenvironmental
conditions (in class discussion)
SILICOFLAGELLATES
I. What are Silicoflagellates?
unicellular, marine flagellates (single flagella)
autotrophs
skeleton encloses protoplasm
generally 20-50 microns, some >100 microns
II. Where do they live?
exclusively marine
most abundant in pelagic environment
may tolerate lower near-shore salinities, e.g. found in Florida bays
minor component of shelf assemblage
planktic
all latitudes
III. Morphology
internal skeleton comprised of hollow rods
descriptive terms:
basal ring
basal accessory spines
basal spines
apical ring
apical rods
apical spines
apical and basal windows
apical plate
most common genera in fossil record:
Dictyocha- usually quadrate with an apical apparatus of rods
Distephanus- usually quadrate or hexagonal basal ring with an
apical ring which may have one or more windows
Naviculopsis- two-sided basal ring with an apical bar(s) or
hyaline region, two basal spines aligned along long axis, and with or without
spines on apical bar
Corbisema- variable genus but generally three-sided basal ring
with an apical process of bars, basal accessory spines located at junction
of apical rods with basal ring, with or without basal spines
Bachmannocena- simple basal ring (circular, square, ovate, pentagonal,
etc.), no apical structure, with or without basal spines (usually small)
IV. Evolution
first occurrence in the Lower Cretaceous
diversificationin the Paleocene and Eocene
only two living genera, Dictyocha and Distephanus
V. Stratigraphy
only a few Cretaceous occurrences, so of little value in the Mesozoic
very diverse in the Paleocene and Eocene with many cosmopolitan species
good for long range correlation
diversity declined in the Early Miocene and species became more provincial