INTRAPLATE DEFORMATION OF LATE NEOGENE AND QUATERNARY MARINE TERRACES, CAPE LIPTRAP, SOUTHEASTERN VICTORIA, AUSTRALIA

Cape Liptrap, lying within the Late Paleozoic Lachlan Fold Belt along the SE Victorian coast, exhibits Quaternary reactivation of a favorably oriented (relative to the modern stress field) Paleozoic structure, the Waratah Fault. Radiocarbon, optically stimulated luminescence (OSL), and cosmogenic radionuclide dating of marine terraces along the cape allow for reconstruction of Quaternary movement along the Waratah Fault.

Six marine terraces are well preserved at Cape Liptrap with altitudes ranging from ~3 m to ~180 m amsl. The lowest terrace, Qt6, yielded barnacles in wave-cut notches ~3 m amsl, is dated at 5220 y BP, and reflects the local Holocene sea level highstand. Qt5 yielded 4 OSL ages from scattered locations around the cape ranging from 80 - 130 ka. It reflects the last interglacial seal level highstand (OIS 5) around 125 ka. Inner edge elevations (approximate high tide line) for Qt5 occur at distinctly different elevations along opposite sides of the Waratah Fault. Offsets of inner edges across the fault range from 1.3 - 4.0 m with uplift rates ranging from 0.01 - 0.03 mm/yr. Qt4 is one of the most extensive terraces, and yielded 2 cosmogenic radionuclide ages of 0.858 ± 0.16 Ma and 1.25 ± 0.265 Ma. Qt4 has a surface elevation of ~36 m on the up-thrown side of the Waratah Fault and an elevation of ~14 m on the down thrown side, consistent with the lower uplift rate calculated from Qt5. This suggests that deformation at Cape Liptrap has been ongoing at least since the middle Pleistocene. Qt3 (~110 m amsl), Tt2 (~140 m) and Tt1 (~180 m) are undated, but most likely correlate to sea level highstands in the Early Pleistocene, Pliocene and possibly Miocene.

The Waratah Fault, a northeast trending, high angle, reverse fault is seismically active with the largest recorded earthquake M 5.7. Sources of stress on the Australian plate in southeast Australia are probably far-field and may reflect increased coupling of the Australian and Pacific plate boundary in the late Miocene as suggested by Sandiford et al., 2004.