Mesozoic paleoenvironment of the rifted margin off NW Australia (ODP legs 122/123)

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doi: 10.1029/GM070p0157
Author(s): von Rad, Ulrich; Exon, Neville F.; Boyd, Ron; Haq, Bilal U.
Author Affiliation(s): Primary:
Bundesanstalt für Geowissenschaffen und Rohstoffe, Hanover, Federal Republic of Germany
Other:
University of Michigan, United States
University of Wales College of Cardiff, United Kingdom
Bundesanstalt für Geowissenschaften und Rohstoffe, Federal Republic of Germany
Lamont-Doherty Geological Observatory of Columbia University, United States
Bureau of Mineral Resources, Geology and Geophysics, Australia
Dalhousie University, Canada
National Science Foundation, United States
Volume Title: Synthesis of results from scientific drilling in the Indian Ocean
Volume Author(s): Duncan, Robert A., editor; Rea, David K.; Kidd, Robert B.; von Rad, Ulrich; Weissel, Jeffrey K.
Source: Synthesis of results from scientific drilling in the Indian Ocean, edited by Robert A. Duncan, David K. Rea, Robert B. Kidd, Ulrich von Rad and Jeffrey K. Weissel. Geophysical Monograph, Vol.70, p.157-184. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0065-8448. ISBN: 978-1-118-66803-0 CODEN: GPMGAD
Note: In English with English summary. 73 refs.; illus., incl. sects., strat. cols., sketch maps
Summary: During early Mesozoic time Northwest Australia was a passive margin of eastern Gondwana facing the southern Tethys Sea. ODP Legs 122 and 123 drilled a complete transect of eight boreholes across the old, sediment-starved passive margin of the Exmouth Plateau down to the nearby abyssal plains: (1) the Wombat Plateau (Sites 759-761, 764)-Argo Abyssal Plain transect (Site 765) and (2) the central Exmouth Plateau (Sites 762, 763)-Gascoyne Abyssal Plain (Site 766) transect. Upper Triassic (Carnian-Rhaetian) fluviodeltaic to carbonate platform deposits of the Wombat Plateau document the synrift phase. The Rhaetian carbonate platform of lagoonal and reefal facies is characterized by sequence boundaries (211 and 215 Ma) and correlates with coeval facies changes in the western Tethys (Alps). During earliest Jurassic times, Wombat Plateau underwent platform drowning and early-rift volcanism, followed by a major blockfaulting episode (Callovian/Oxfordian). This resulted in uplift, rift flank tilting, subaerial erosion of the horst, and the formation of a "post-rift unconformity". A precursor of the Indian Ocean formed at the Argo Abyssal Plain after the Callovian/Oxfordian breakup of eastern Gondwana. At Wombat Plateau, this was followed by rapid subsidence and a Berriasian transgression with nearshore to hemipelagic "juvenile-ocean" sediments, characterized by a condensed section of terrigenous littoral sands and belemnite-rich sandy muds. Calcisphere-nannofossil chalks with a low-diversity opportunistic flora indicate a stressful environment. Bentonites suggest early post-breakup volcanism. The Albian/Cenomanian represents a gradual transition from hemipelagic ("juvenile ocean") to pelagic ("mature ocean") conditions. Purely pelagic conditions started after the Cenomanian/Turonian anoxic boundary event and led to declining subsidence and sedimentation rates. On the central Exmouth Plateau, "failed" breakup during late Jurassic times was followed by major uplift of the southern hinterland. This uplift was associated with renewed rifting attempts south of the Exmouth Plateau and resulted in erosion and northward progradation of a major Berriasian shelf-margin clastic wedge (Barrow Group). This late synrift sequence is overlain by a condensed Valanginian section, followed by late Valanginian/early Hauterivian final breakup between Australia and Greater India and an early Aptian transgressive "juvenile ocean" section. The Mesozoic depositional sequences are strongly affected by multistage rift tectonics, climatic changes due to plate motions, cyclic deltaic sediment input, and global sea level fluctuations. Eustasy played a significant role in generating the observed depositional sequences, especially in the Rhaetian of the Wombat Plateau and the Early Cretaceous of the central Exmouth Plateau.
Year of Publication: 1992
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Argo abyssal plain; Exmouth Plateau; Gondwana; Hemipelagic environment; Indian Ocean; Leg 122; Leg 123; Marine environment; Mesozoic; Ocean Drilling Program; Paleoenvironment; Pelagic environment; Plate tectonics; Rifting; Sea-level changes; Subsidence; Tethys; Transgression; Uplifts; Wombat Plateau
Coordinates: S203512 S163357 E1153337 E1121231
S195557 S155831 E1173430 E1102714
Record ID: 2007093160
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute.