radiolaria - Marum

Radiolaria 14 Bibliography - 1990
Anderson, R.Y., Linsley, B.K. & Gardner, J.V.
1990. Expression of seasonal and ENSO forcing in climatic
variability at lower than ENSO frequencies: evidence from
Pleistocene marine varves off California. Palaeogeogr.
Palaeoclimatol. Palaeoecol., 78/3-4, 287-300.
Upper Pleistocene marine sediments along the upper
continental slope off northern and central California contain
alternations of varved and bioturbated sediments and associated
changes in biota and sediment composition. These alternations can
be related to conditions that accompany El Niño and anti-EI Niño
(ENSO) circulation. Anti-EI Niño conditions are characterized by
increased upwelling and productivity and by low concentrations of
dissolved oxygen in the oxygen minimum zone that resulted in varve
preservation. El Niño conditions are characterized by little or no
upwelling, low productivity, and higher concentrations of dissolved
oxygen that resulted in zones of bioturbation.
Alternations of varves and zones of bioturbation, that range
from decades to millennia, occur through the upper Pleistocene
section. The inferred long-term alternations in El Niño and anti-EI
Niño conditions appear to be a re-expression of ENSO's primary 3-7year
cycle. Decadal to millennial cycles of productivity associated
with El Niño and anti-EI Niño conditions may have served as a
"carbon pump" and transferred atmospheric CO2 to the marine
reservoir.
Changes in sediment composition and organisms associated
with El Niño or anti-EI Niño conditions can be related to both
seasonal and ENSO phenomena. Expression of these changes at
lower-than-ENSO frequencies may be partly explained by adding the
effects of seasonal variability to effects produced by a selfoscillating
ENSO system. However, deterministic mechanisms,
including solar modulation of ENSO, may also contribute to long-term
alternations of El Niño and anti-EI Niño conditions.
Baumgartner, P.O. 1990. Genesis of Jurassic Tethyan
radiolarites - The example of Monte Nerone (Umbria-Marche
Apennines). In: Atti del II convegno internazionale Fossili
Evoluzione Ambiente, Pergola 1987. (Pallini, G., Cecca, F.,
Cresta, F. & Santantonio, M., Eds.). pp. 19-32.
Recent advances in Mesozoic radiolarian biostratigraphy have
allowed to obtain detailed age data on the start and the duration of
radiolarite sedimentation in four selected sections of the Monte
Nerone and adjacent areas. These data, together with the rich and
detailed ammonite data provided by Cecca et al. (1987a, b) Cresta
et al.. (1988) etc. from the basis for a detailed sedimentation
history explaining the distribution pattern of siliceous and
calcareous facies on the Monte Nerone Seamount and in the adjacent
basin. General conclusions on the genesis of Tethyan Jurassic
radiolarites can be drawn from this well documented example. The
Lower Bajocian to Lower Kimmeridgian hiatus observed on Monte
Nerone is explained by vigorous periodically changing currents
effectively preventing the net accumulation of sediment on the
structural high. As sedimentation starts again on the high, a
concomitant decrease of sedimentation rates can be observed in the
adjacent basin.
The local (intrabasinal) facies distribution of calcareous vs.
siliceous sediments cannot be explained by regional
paleoceanographic concepts. General productivity and local
dispersal of calcareous and siliceous pelagic sediment at any time
as well as diagenetic processes must be discussed to reasonably
explain the small scale facies pattern.
In Western Tethys basinal Middle Jurassic radiolarites are
coeval with condensed pelagic limestones on swells. This facies
contrast is not a function of the presence of a CCD. While the CCD
model is consistent with the observed carbonate distribution, it does
not explain occurrence and distribution of radiolarites. The absence
of silica on the swell can obviously not be explained by the
dissolution of carbonate at depth. Moreover, basinal facies are not
solution residues of less deep swell facies, because radiolarites
have much higher sedimentation rates than coeval condensed
limestones on swells.
It is mainly the intrabasinal dispersal of radiolarians which
determined the local occurrence and age span of radiolarites: During
the late Middle Jurassic, persistent bottom currents prevented
radiolarians, characterized by a very low bulk density, from
accumulation on the swells and carried them into the basins. The
general scarcity of calcareous plankton is responsable for the
formation of condensed limestones on swells and for a low carbonate
input, as compared to silica, to the basins. Low concentration of
calcareous plankton together with a vigorous circulation also
explains shallow, irregular and sharply defined ACD and CCD.
During the late Oxfordian, calcareous plankton production
slowly increased and/or current activity decreased leading to an
overall better carbonate preservation (= beginning of fall of ACD and
CCD). Because of diminished current activity, radiolarites started to
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accumulate also on the swells. This tendency continued through the
Kimmeridgian and early Tithonian with a successive increase in
carbonate, gradually displacing radiolarites first on the swells and
then in the basins.
Bechennec, F., Le Métour, J., Rabu, D.,
Bourdillon de Grissac, C., De Wever, P.,
Beurrier, M. & Villey, M. 1990. The Hawasina Nappes:
stratigraphy, palaeogeography and structural evolution of a
fragment of the south-Tethyan passive continental margin.
In: The Geology and Tectonics of the Oman region.
(Robertson, A.H.F., Searle, M.P. & Ries, A.C., Eds.), vol.
49. Special Publications of the Geological Society of
London, pp. 213-223.
Lithostratigraphic and biostratigraphic revision of the Hawasina
Nappes in the eastern and central Oman Mountains, including the
redefinition of the Hamrat Duru Group and the definition of the three
new groups, the Al Aridh, Kawr and Umar Groups, has led to a new
interpretation of the palaeogeographic and structural evolution of
the south-Tethyan continental margin. Margin history began in the
Late Permian with a phase of extension and rifting, accompanied by
considerable magmatic activity, and led to the development of the
Hamrat Duru Basin separating the Arabian Platform to the south
from the Baid Platform to the north. In the Middle to Late Triassic
renewed extension led to rifting, again accompanied by important
magmatic activity, with the break-up of the Baid Platform, and the
development of the Al Aridh Trough, the Misfah Horst and the Umar
Basin. These Permian and Triassic tectonic units together
constituted the Hawasina Basin. A third phase of extension during
the Late Tithonian-Berriasian caused a general foundering of the
continental margin. The development of the Hawasina Basin
terminated in the Santonian, when compression initiated the first
fase of obduction that closed the basin. Ongoing obduction, during
the Campanian, led thrusting of the Hawasina and the Samail
ophiolite nappes onto the Arabian Platforn by gravitational
mechanisms.
Berdnikov, V.A. 1990. Quaternary stratigraphy of the
Central Basin of the indian Ocean as indicated by Radiolaria.
Oceanology, 29/4, 469-473.
Detailed analysis of radiolarian complexes in cores from the
Central basin of the Indian Ocean distinguishes four layers,
corresponding to the radiolarian zones in the Nigrini zonal scale
(1971). Some 136 species of radiolarian were determined and
counted in 320 sediment samples. The age of the core sediments is
determined. Two intervals representing periods of cooling are
identified in each of the cores.
Bernstein, R.E., Betzer, P.R. & Takahashi, K.
1990. Radiolarians from the western North Pacific Ocean: a
latitudinal study of their distribution and fluxes. Deep-Sea
Res. Part A, oceanogr. Res. Pap., 37/11, 1677-1696.
Free-drifting sediment traps were deployed individually to make
day-long collections of settling particulates at seven stations in the
western North Pacific Ocean. Samples were taken between 70 and
2200 m along a longitudinal section between 16 and 50°N latitude.
Radiolarian skeletons were mechanically isolated under a reflected
light microscope. Subsequent gravimetrically determined radiolarian
silica fluxes range from 0 to 4.43 mg m -2 day -1 and show
significant and consistent increases at all depths with increasing
latitude. Radiolarians also were counted and categorized into each of
their three suborders: Nassellaria, Spumellaria and Phaeodaria. An
inverse relationship is evident between the proportions of
phaeodarians and polycystines (nassellarians plus spumellarians),
with the phaeodarians increasing relative to the polycystines with
increasing latitude.
Although the absolute numbers of phaeodarians in the northern
samples may not exceed the numbers of their polycystine
counterparts in the south, the comparatively large and heavy
phaeodarian skeletons contribute significantly to the increased
silica fluxes noted in the north. This contribution, combined with a
high susceptibility to dissolution, may signify that phaeodarians are
important for the recycling of silica in the northern North Pacific.
Spectrophotometric analyses of seven phaeodarian species and
one species of colonial spumellarian show that silica constituted
between 86 and 99% of the phaeodarians' skeletons and 75% of the
spumellarians' skeletons. Non-radiolarian amorphous silica was
mobilized by a selective chemical leach and quantified
spectrophotometrically. Significant and consistent increases in the
flux of this diatomaceous silica fraction (ranging from 0.14 to 47.0
mg m -2 day -1 ) are noted with increasing latitude. In almost all cases,
diatomaceous silica fluxes are greater than those of the
radiolarians. With the exception of some anomalously high
percentages, radiolarian-derived silica ranges from 0 (only one
sample) to 24% of the total amorphous silica flux.