Sedimentological characterization of the Permo-Triassic boundary in high paleolatitude, coastal plain successions of eastern Australia: no immediate change in depositional conditions
Abstract
Upper Permian to Lower Triassic coastal plain successions of the Sydney, Gunnedah, and Bowen Basins in eastern Australia have been investigated in outcrop and continuous drillcores. The purpose of the investigation is to provide an assessment of paleoenvironmental change at high southern paleolatitudes in a continental margin context for the Late Permian, across the end-Permian Extinction (EPE) event, and into the Early Triassic. These basins were affected by explosive volcanic eruptions during the Late Permian and to a much lesser extent, during the Early Triassic, allowing high-resolution age determination on the numerous tuff horizons. Age data indicate that the EPE and Permo-Triassic boundary occur above the uppermost coal, either within an immediately overlying mudrock succession or, within a succeeding channel sandstone body. Late Permian depositional environments were initially shallow marine and deltaic, but coastal plain fluvial environments with extensive coal-forming mires became progressively established during the early Late Permian, reflected in numerous preserved coal seams. The fluvial style of coastal plain channel deposits varies geographically. But apart from the loss of peat-forming mires, no significant change in environment (grain-size, architecture, or sediment dispersal direction) was noted across the EPE (pinpointed by turnover of the paleoflora). There is no evidence for immediate aridification across the boundary despite a loss of coal from successions. Rather, the EPE marks the base of a long-term, progressive trend towards better-drained alluvial conditions into the Early Triassic. Indeed, the EPE itself is closely followed by a flooding event in basinal depocenters. The character of the surface separating coal-bearing pre-EPE from coal-barren post-EPE strata varies across the basins. In basin-central locations, the contact varies from disconformable, where a fluvial channel body has cut down to the level of the top coal, to conformable where the top coal is overlain by mudrocks and interbedded sandstone-siltstone facies. In basin-marginal locations, however, the contact is a pronounced erosional unconformity with coarse-grained alluvial facies overlying older Permian rocks. There is no evidence that the contact is everywhere a disconformity or unconformity.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP21C1621F
- Keywords:
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- 1616 Climate variability;
- GLOBAL CHANGE;
- 1622 Earth system modeling;
- GLOBAL CHANGE;
- 1626 Global climate models;
- GLOBAL CHANGE;
- 4934 Insolation forcing;
- PALEOCEANOGRAPHY