radiolaria - Marum

Bibliography - 1992 Radiolaria 14
submerged deeply enough to allow an intermittent "spillover" of
circumantarctic cold water into the Argo Basin, creating increased
bottom current activity. Circumantarctic cold-water radiolarians
transported into the Argo Basin upwelled along the margin and died
en masse. Concomitant winnowing by bottom currents led to their
accumulation in distinct radiolarite layers. High rates of faunal
change and the sharp increase of bottom current activity are
thought to be synchronous with the two pronounced late Berriasianearly
Valanginian lowstands in sea level. Hypothetically, both
phenomena might have been caused by a glaciation on the Antarctic-
Australian continent, which was for the first time isolated from the
rest of Gondwana by oceanic seaways as a result of Jurassic and
Early Cretaceous seafloor spreading.
The absence of typical Tethyan radiolarian species during the
late Valanginian to late Hauterivian period is interpreted as
reflecting a time of strong influx of circumantarctic cold water
following oceanization (M11) and rapid spreading between southeast
India and western Australia.
The reappearance and gradual increase in abundance and
diversity of Tethyan forms along with the still dominant
circumantarctic species are thought to result from overall more
equitable climatic conditions during the Barremian and early Aptian
and may have resulted from the establishment of an oceanic
connection with the Tethys Ocean during the early Aptian.
Baumgartner, P.O., Bown, P., Marcoux, J.,
Mutterlose, J., Kaminski, M., Haig, D. &
McMinn, A. 1992. Early Cretaceous biogeographic and
oceanographic synthesis of Leg 123 (off northern Australia).
In: Proceedings of the Ocean Drilling Program, Scientific
Results. (Gradstein, F.M., Ludden, J.N. et al., Eds.), vol.
126. College Station, TX (Ocean Drilling Program), pp.
739-758.
Biogeographic observations made by Leg 123 shipboard
paleontologists for Lower Cretaceous nannofossils, foraminifers,
radiolarians, belemnites, and inoceramids are combined in this
chapter to evaluate the paleoceanographic history of the
northwestern Australian margin and adjacent basins. Each fossil
group is characterized at specific intervals of Cretaceous time and
compared with data from Tethyan and Southern Hemisphere highlatitude
localities. Special attention is given to the biogeographic
observations made for the Falkland Plateau (DSDP Legs 36 and 71)
and the Weddell Sea (ODP Leg 113). Both areas have yielded
valuable Lower Cretaceous fossil records of the circumantarctic
high latitudes.
In general, the Neocomian fossil record from DSDP and ODP
sites off northwestern Australia has important southern highlatitude
affinities and weak Tethyan influence. The same is true for
the pelagic lithofacies: radiolarian chert and/or nannofossil
limestone, dominant in the Tethyan Lower Cretaceous, are minor
lithologies in the Exmouth-Argo sites. These observations, together
with the young age of the Argo crust and plate tectonic
considerations, suggest that the Argo Basin was not part of the
Tethys Realm.
The biogeography of the Neocomian radiolarian and nannofossil
assemblages suggests opening of a seaway during the Berriasian
that connected the circumantarctic area with the Argo Basin, which
resulted in the influx of southern high-latitude waters.
This conclusion constrains the initial fit and break-up history of
Gondwana. Our results favor the loose fit of the western Australian
margin with southeast India by Ricou et al. (1990), which accounts
for a deeper water connection with the Weddell-Mozambique basins
via drowned marginal plateaus as early as the Berriasian. In fits of
the du Toit-type (1937), India would remain attached to Antarctica,
at least until the late Valanginian, making such a connection
impossible.
After the Barremian, increasing Tethyan influence is evident in
all fossil groups, although southern high-latitude taxa are still
present. Biogeographic domains, such as the southern extension of
Nannoconus and Ticinella suggest paleolatitudes of about 50°S for
the Exmouth-Argo area. Alternatively, if paleolatitudes of about 35°
are accepted, these biogeographic limits were displaced northward
at least 15° along Australia in comparison to the southern Atlantic.
In this case, the proto-circumantarctic current was deflected
northward into an eastern boundary current off Australia and carried
circumantarctic cold water into the middle latitudes.
Late Aptian/early Albian time is characterized by mixing of
Tethyan and southern faunal elements and a significant gradient in
Albian surface-water temperatures over 10° latitude along the
Australian margin, as indicated by planktonic foraminifers. Both
phenomena may be indicative of convergence of temperate and
antarctic waters near the Australian margin. High fertility
conditions, reflected by radiolarian cherts, are suggestive of coastal
upwelling during that time.
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Behl, R.J. & Smith, B.M. 1992. Silicification of deepsea
sediments and the oxygen isotope composition of
diagenetic siliceous rocks from the western Pacific, Pigafetta
and east Mariana Basin, Leg 129. In: Proceedings of the
Ocean Drilling Program, Scientific Results. (Larsen, R.L.,
Lancelot, Y. et al., Eds.), vol. 129. College Station, TX
(Ocean Drilling Program), pp. 81-117.
Ocean Drilling Program Leg 129 recovered chert, porcellanite,
and radiolarite from Middle Jurassic to lower Miocene strata from
the western Pacific that formed by different processes and within
distinct host rock. These cherts and porcellanite formed by (l)
replacement of chalk or limestone, (2) silicification and in-situ silica
phase-transformation of bedded clay-bearing biosiliceous deposits,
(3) high-temperature silicification adjacent to volcanic flows or sills,
and (4) silica phase-transformation of mixed biosiliceousvolcaniclastic
sediments.
Petrologic and O-isotopic studies highlight the key importance
of permeability and time in controlling the formation of dense cherts
and porcellanites. The formation of dense, vitreous cherts
apparently requires the local addition and concentration of silica.
The influence of permeability is shown by two examples, in which: (1)
fragments of originally identical radiolarite that were differentially
isolated from pore-water circulation by cement-filled fractures were
silicified to different degrees, and (2) by the development of
secondary porosity during the opal-CT to quartz inversion within
conditions of negligible permeability. The importance of time is
shown by the presence of quartz chert below, but not above, a
Paleogene hiatus at Site 802, indicating that between 30 and 52
m.y. was required for the formation of quartz chert within
calcareous-siliceous sediments.
The oxygen-isotopic composition for all Leg 129 carbonateand
Fe/Mn-oxide-free whole-rock samples of chert and porcellanite
range widely from ∂1 8 O = 27.8 ‰ to 39.8 ‰ vs. V-SMOW. Opal-CT
samples are consistently richer in 18 O (34.1 ‰ to 39.3 ‰ ) than
quartz subsamples (27.8 ‰ to 35.7 ‰ ). Using the O-isotopic
fractionation expression for quartz-water of Knauth and Epstein
(1976) and assuming ∂ 18 Opore water =-1.0 ‰, model temperatures
of formation are 7°-26°C for carbonate-replacement quartz .cherts,
22°-25°C for bedded quartz cherts, and 32°-34°C for thermal quartz
cherts. Large variations in O-isotopic composition exist at the same
burial depth between co-existing silica phases in the same sample
and within the same phase in adjacent lithologies. For example.
quartz has a wide range of isotopic compositions within a single
breccia sample: ∂ 18 O = 33.4 ‰ and 28.0 ‰ for early and late
stages of fracture-filling cementation, and 31.6 ‰ and 30.2 ‰ for
microcrystalline quartz precipitation within enclosed chert and
radiolarite fragments. Similarly, opal-CT d101 spacing varies across
lithologic or diagenetic boundaries within single samples.
Co-occurring opal-CT and chalcedonie quartz in shallowly buried
chert and porcellanite from Sites 800 and 801 have an 8.7 ‰
difference in ∂ 18 O, suggesting that pore waters in the Pigafetta
Basin underwent a Tertiary shift to strongly l8 O-depleted values due
to alteration of underlying Aptian to Albian-Cenomanian
volcaniclastic deposits after opal-CT precipitation, but prior to
precipitation of microfossil-filling chalcedony.
Bernstein, R.E., Byrne, R., Betzer, P.R. &
Greco, A.M. 1992. Morphologies and transformations of
celestite in seawater: the role of acantharians in strontium and
barium geochemistry. In: The Robert M. Garrels Memorial
Issue. (Helgeson, H.C., Eds.), vol. 56/8. Geochimica et
cosmochimica Acta, pp. 3273-3279.
Free-drifting sediment traps deployed at 400, 1500, and 3200
m were used to collect particles near the USJGOFS Time-Series
Station (31°49.5'N and 64°08.2'W) in the Atlantic Ocean.
Acantharian specimens isolated from our samples were abundant at
the 400-m depth horizon and were rare to non-existent in our 1500m
traps. No specimens were detected in the 3200-m traps. This
trend parallels those noted for the Pacific and has been linked to the
oceans' Sr/CI profiles. Our collections revealed the presence of
myriad, heretofore undocumented, minute SrSO4 particles. These
particles are most likely related to the acantharian reproductive
cycle. The extreme abundance of acantharians and acantharianderived
particles may have implications beyond the oceans' Sr
budgets. Barium/strontium molar ratios in acantharian-derived
celestite on the order of 3 X 10 -3 indicate that acantharians may
play an important role in oceanic Ba cycling.
Blome, C.D. 1992. Radiolarians from Leg 122, Exmouth
and Wombat Plateaus, Indian Ocean. In: Proceedings of the
Ocean Drilling Program, Scientific Results. (Von Rad, U.,
Haq, B.U. et al., Eds.), vol. 122. College Station, TX (Ocean
Drilling Program), pp. 633-652.