Shallow and marginal marine Triassic trace fossils and ichnofabric from northwest Australia (ocean drilling program leg 122)

Conference · Tue May 01 04:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6713454

Droser, M L ^[1]; O'Connell, S ^[2]

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1. Univ. of California, Riverside (USA)
2. Wesleyan Univ., Middletown, CT (USA)

The ichnofabric index method of ranking amount of bioturbation was used for the first time in conjunction with discrete trace fossils to examine shallow-water marine cores. Previous ichnological studies on cores have focused primarily on outer shelf and deep-sea discrete trace fossils. Upper Triassic cores examined in this study were recovered off northwest Australia during ODP Leg 122. These sediments were deposited in a shallow-water and continental shelf setting, which included swamp and prodelta environments. The most common lithology is siltstone with interbedded mudstone and sandstone. Sediments deposited in a swamp setting have rootlets and coal beds with an ichnological record consisting primarily of mottled bedding rather than discrete trace fossils. Ichnofabric indices 1 through 5 were recorded. Marginal marine/lagoonal facies have a low trace fossil diversity with common Chondrites, Planolites, and Teichichnus. Recorded ichnofabric indices include 1, 2, and 3. Laminated mudstones and siltstones (ii1) are most common. Fully marine open shelf strata are thoroughly bioturbated (ii5 and ii6) with Thalassinoides, Zoophycos, Teichichnus, and Planolites. Wackestone and packstone occur in discrete uppermost Triassic intervals and have ii1 through ii6 represented. In part due to the drilling process, sandstones and reefal limestones were poorly recovered and ichnofabric is not well preserved. Physical sedimentary structures and lateral facies relationships can be difficult to discern in core. In shallow marine deposits, the distribution of ichnofabric indices and discrete trace fossils within these strata provide an additional important data base to evaluate depositional environments.

• OSTI ID: 6713454
• Report Number(s): CONF-900605--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 74:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AUSTRALASIA
AUSTRALIA
COAL DEPOSITS
COAL SEAMS
DEPOSITION
FOSSILS
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGY
MESOZOIC ERA
MINERAL RESOURCES
PALEONTOLOGY
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SHALES
STRATIGRAPHY
TRIASSIC PERIOD