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Thermoluminescence (TL) age determinations of alluvial sediments in the tropics are evaluated by comparison with U/Th age determinations of pedogenic accumulations in the alluvium of the lower Gilbert River, a large fan delta in the wet-dry tropics of northern Queensland, Australia. This study extends U/Th dating by applying it not only to calcretes, but also to Fe/Mn oxyhydroxide/oxide accumulations. While a direct correlation cannot be made between U/Th dates from secondary minerals and TL dates from the host sediments, both sets of data show broad consistency. In addition to providing a minima for acceptable TL ages, U/Th dates are useful for determining the chronology of pedogenesis/diagenesis. They show that calcretes and ferricretes have formed under similar climatic conditions in the wet-dry tropics of northern Australia during the late pleistocene. Beneath about 5–12 m the Gilbert fan delta consists of an extensive sand body older than 85,000 yr and probably about 120,000 yr in age, representative of a period of major fluvial activity not repeated since this time. Above are muds and fine sandy muds that extend uninterrupted to the present surface except in the downstream fan where they are bisected by a thin unit of medium sand that TL dates at 40,000–50,000 yr B.P. A system of sandy distributary channels over the fan surface represents an early Holocene fluvial phase probably more active than at present.

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In the coastal region, the highest magnitude storms cannot always be invoked to account for large-scale, anomalous sediment features. Any coastline in the Pacific Ocean region can be affected by tsunamis, including Australia which historically lacks evidence of such events. Geologically, tsunamis along the New South Wales coast have deposited a suite of Holocene features that consist of anomalous boulder masses, either chaotically tossed onto rock platforms and backshores or jammed into crevices; highly bimodal mixtures of sand and boulders; and dump deposits consisting of well sorted coarse debris. In addition many coastal aboriginal middens were disturbed by such events. Within estuaries, tsunamis have left a record of stranded run-up ridges which have been interrupted mistakenly as cheniers. Dating of such deposits indicates that several events have affected this coastline since 3000 BP. In contrast to storm waves, tsunamis can leave a depositional imprint of their passage that is characterized by chaotic sorting and mixing of sediments either from different coastal environments or of different sediment sizes. The preservation potential of these deposits is high where sediments have been deposited above present sea-level or stranded inland.

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