Citation:

0377-8398(93)90025-S

Name: Occurrence of tethyan radiolarian species in early Cretaceous sediments of ODP Hole 123-765C in the Northeast Indian Ocean (Fig. 4)
Creator: Peter O Baumgartner
Published: 1993
License: https://creativecommons.org/licenses/by/3.0/

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Abstract:

During ODP Leg 123, abundant and well-preserved Neocomian radiolarians were recovered at Site 765 (Argo Abyssal Plain) and Site 766 (lower Exmouth Plateau). Assemblages are characterized by the numerical dominance of a small number of non-tethyan forms and by the scarcity of tethyan taxa. Remarkable contrasts exist between radiolarian assemblages extracted from claystones of Site 765 and reexamined DSDP Site 261, and faunas recovered from radiolarian sand layers, only found at Site 765. Clay faunas are unusual in their low diversity of apparently ecologically tolerant (or solution resistant?), ubiquist species, whereas sand faunas are dominated by non-tethyan taxa. Comparisons with Sites 766 and 261, as well as sedimentological observations, lead to the conclusion that this faunal contrast resulted from a difference in provenance, rather than from hydraulic sorting or selective dissolution.

The ranges of 27 tethyan taxa from Site 765 were compared to the tethyan radiolarian zonation by Jud ( 1992 ) by means of the Unitary Associations Method. This calculation allows to directly date the Site 765 assemblages and to estimate the amount of truncation of ranges for tethyan taxa. Over 70% of the already few tethyan species of Site 765, have truncated ranges during the Valanginian-Hauterivian.

Radiolarian assemblages recovered from claystones at Sites 765 and 261 in the Argo Basin apparently reflect restricted oceanic conditions during the latest Jurassic-Barremian. Neither sedimentary facies nor faunal associations bear any resemblance to what we know from typical tethyan sequences. We conclude that the Argo Basin was paleoceanographically separated from the Tethys during the Late Jurassic and part of the Early Cretaceous by its position at higher paleolatitudes and/or by enclosing land masses.

Assemblages recovered from radiolarian sand layers are dominated by non-tethyan species that are interpreted as circumantarctic. Their first appearance in the late Berriasian-early Valanginian predates the oceanization of the Indo-Australian breakup (M11, late Valanginian), but coincides with a sharp increase in margin-derived pelagic turbidites. The Indo-Australian rift zone and the adjacent margins must have been submerged deeply enough to allow an intermittent influx of circumantarctic cold water into the Argo Basin, creating increased bottom current activity. Cold-water radiolarians carried into the Argo Basin upwelled along the margin, died, and accumulated in radiolarite layers due to winnowing by bottom currents. High rates of faunal change and the sharp increase of bottom current activity are thought to be synchronous with possible pronounced late Berriasian-early Valanginian lowstands in sea level. Hypothetically, both phenomena might have been caused by a tendency to 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-Early Cretaceous sea-floor spreading.

The absence of most typical tethyan radiolarian species during the Valanginian-Hauterivian is interpreted as reflecting a time of strong influx of circumantarctic cold water following oceanization (M 11) and rapid spreading between Southeast India and West Australia.

The reappearance and gradual abundance/diversity increase of tethyan taxa, along with the still dominant circumantarctic species are thought to result from overall more equitable climatic conditions during the Barremian-early Aptian and from the establishment of an oceanic connection with the Tethys Ocean during the early Aptian.

Project(s):

Ocean Drilling Program (ODP)

Coverage:

Latitude: -15.976000 * Longitude: 117.575200

Date/Time Start: 1988-09-11T04:25:00 * Date/Time End: 1988-09-22T10:30:00

Minimum Elevation: -5728.0 m * Maximum Elevation: -5728.0 m

Event(s):

123-765C * Latitude: -15.976000 * Longitude: 117.575200 * Date/Time Start: 1988-09-11T04:25:00 * Date/Time End: 1988-09-22T10:30:00 * Elevation: -5728.0 m * Penetration: 963.9 m * Recovery: 373.35 m * Location: South Indian Ridge, South Indian Ocean * Campaign: * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 65 cores; 613.7 m cored; 0 m drilled; 60.8 % recovery

Comment:

Species abundance: X = present, - = not present

Parameter(s):

#	Name	Short Name	Principal Investigator	Method/Device	Comment
1	Sample code/label	Sample label	Baumgartner, Peter O	DSDP/ODP/IODP sample designation
2	Comment	Comment	Baumgartner, Peter O		unitary association (U.A.)
3	Comment 2 (continued)	Comm 2	Baumgartner, Peter O		observed maximal horizons
4	Parvicingula sphaerica	P. sphaerica	Baumgartner, Peter O
5	Paronella tubulata mercedes	P. tubulata mercedes	Baumgartner, Peter O		genus questionable
6	Obesacapsula verbana	O. verbana	Baumgartner, Peter O
7	Podocapsa amphitreptera	P. amphitreptera	Baumgartner, Peter O
8	Sethocapsa dorysphaeroides	S. dorysphaeroides	Baumgartner, Peter O
9	Pantanellium squinaboli cantuchapai	P. squinaboli cantuchapai	Baumgartner, Peter O
10	Pantanellium squinaboli squinaboli	P. squinaboli squinaboli	Baumgartner, Peter O
11	Acaeniotyle umbilicata	A. umbilicata	Baumgartner, Peter O
12	Obesacapsula cetia	O. cetia	Baumgartner, Peter O
13	Sethocapsa trachyostraca trachyostraca	S. trachy. trachyostraca	Baumgartner, Peter O
14	Acanthocircus trizonalis	A. trizonalis	Baumgartner, Peter O
15	Cecrops septemporatus	C. septemporatus	Baumgartner, Peter O
16	Acaeniotyle diaphorogona	A. diaphorogona	Baumgartner, Peter O		Acaeniotyle diaphorogona gr.
17	Alievium helenae	A. helenae	Baumgartner, Peter O
18	Mirifusus chenodes	M. chenodes	Baumgartner, Peter O
19	Cyclastrum infundibuliforme	C. infundibuliforme	Baumgartner, Peter O		Cyclastrum infundibuliforme gr.
20	Stichocapsa perspicua	S. perspicua	Baumgartner, Peter O		genus questionable
21	Triactoma echiodes	T. echiodes	Baumgartner, Peter O
22	Lithatractus pusillus	L. pusillus	Baumgartner, Peter O
23	Eucyrtis columbaria	E. columbaria	Baumgartner, Peter O
24	Cyclastrum pianum	C. pianum	Baumgartner, Peter O
25	Orbiculiforma tecta	O. tecta	Baumgartner, Peter O		genus questionable
26	Pseudodictyomitra lilyae	P. lilyae	Baumgartner, Peter O
27	Stephanastrum inflexum	S. inflexum	Baumgartner, Peter O
28	Spongotripus trigonus	S. trigonus	Baumgartner, Peter O		genus questionable
29	Crucella cachensis	C. cachensis	Baumgartner, Peter O
30	Foremanella diamphidia	F. diamphidia	Baumgartner, Peter O

License:

Creative Commons Attribution 3.0 Unported (CC-BY-3.0)

Size:

1290 data points

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