Paleoecology of cool-water, subtidal cycles in mid-cenozoic limestones, Eucla Platform, Southern Australia

Journal Article · Sat Oct 01 04:00:00 EDT 1994 · Palaios

DOI:https://doi.org/10.2307/3515136· OSTI ID:54486

James, N P ^[1]; Bone, Y ^[2]

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1. Queen`s Univ., Kingston, Ontario (Canada)
2. Univ. of Adelaide (Australia)

The open-shelf, subtidal, bryozoan-rich Abrakurrie Limestone beneath the Nullarbor Plain (Eucla Platform) is cyclic at the meter-scale. Best developed cycles are asymmetric and comprise three distinct parts with a capping hardground. The basal part (A) is a thin, coarse, grainstone or rudstone that is rich in robust bryosoan and epifaunal echinoid fragments and pecten bivalves, reflecting growth and accumulation in generally high energy, hard bottom environments. The middle part (B), intepreted as a low-energy, sub-swellbase accumulation, is a burrowed to planar cross-laminated fine grainstone or packstone with a low diversity, delicate-branching bryozoan assemblage and little else except scattered infaunal echinoids and pectens. The upper part (C) is a burrowed, abundantly fossilferous (bryozoan, bivalve, echinoid) rudstone or floatstone. Upward increases in the numbers and diversity of Mg-calcite and aragonitic cheilostome bryozoans (especially erect rigid, flat robust branching and nodular/arborescent types), gastropods, infaunal bivalves, and infaunal echinoids points to a high-energy environment. Sediments at the top of C are variably cemented by inclusion-rich marine cement (now calcite) that formed a hardground which was subsequently physically and biologically eroded and stained by iron oxides during a period of non-deposition. Sediments from the next overlying cycle succeed cements in uppermost intergranular pores and fill open crustacean burrows. Variably developed cyclicity is interpreted, on the basis of comparable Holocene cool-water shelf sediments, to reflect deposition in generally sub-photic environments that ranged from just below swell base (B) upwards towards the zone of wave abrasion (A and C). Hardgrounds (H) formed when the seafloor was within the zone of wave abrasion. Shallowing and deepening of these critical interfaces was controlled by fluctuating sea level and/or climatic change. 55 refs., 12 figs.

• Sponsoring Organization: USDOE
• OSTI ID: 54486
• Journal Information: Palaios, Journal Name: Palaios Journal Issue: 5 Vol. 9; ISSN PALAEM; ISSN 0883-1351
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
CENOZOIC ERA
CLIMATIC CHANGE
EARTH PLANET
PALEOCLIMATOLOGY