Neotectonism on the eastern Australian passive margin: evidence from the Lapstone Structural Complex  

Authors / CoAuthors

McPherson, A. | Clark, D. | Macphail, M. | Cupper, M.

Abstract

Faults of the Lapstone Structural Complex (LSC) underlie 100 km, and perhaps as much as 160 km, of the eastern range front of the Blue Mountains, west of Sydney, Australia. More than a dozen major faults and monoclinal flexures have been mapped along its extent. Debate continues as to the age of formation of the ~400 m or more of relief relating to the LSC, with estimates ranging from Palaeozoic to Pliocene. The results of an investigation of Mountain Lagoon, a small basin bound on its eastern side by the Kurrajong Fault in the central part of the LSC, favour a predominantly pre-Neogene origin. Drilling on the eastern margin of the lagoon identified 15 m of fluvial, colluvial and lacustrine sediments, overlying shale bedrock. The sediments are trapped behind a sandstone barrier corresponding to the Kurrajong Fault. Dating of pollen grains preserved in sediments at the base of this sediment column suggest that the fault-angle depression began trapping sediment in the Early to Middle Miocene. Strongly heated Permo-Triassic gymnosperm pollen in the same strata provides circumstantial evidence that sediment accumulation post-dates the ca. 18.8 Ma emplacement of the nearby Green Scrub basalt. Our data indicate that only 15 m of the 130 m of throw across the Kurrajong Fault has occurred during the Neogene suggesting a predominantly erosional exhumation origin for current relief at the eastern edge of the Blue Mountains plateau. Sedimentation since the Late Pleistocene appears to have been controlled largely by climatic processes, with tectonism exerting little or no influence.

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nonGeographicDataset

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74765

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• External PublicationAbstract

( Theme )

• earthquakes

( Theme )

• geomorphology

( Theme )

• tectonic history

• AU-NSW

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

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2012-01-01T00:00:00

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Creative Commons Attribution 4.0 International Licence    

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