Jane Cunneen¹

(1) The University of Western Australia, Nedlands, Australia

ABSTRACT: Hourglass Fault Structures in the Timor Sea, Australia

Neogene fault reactivation in the Timor Sea, Northwest Australia has produced "hourglass" fault structures, consisting of two or more opposite-dipping normal faults which intersect in the Tertiary section. Hourglass faults are classified into two broad types determined by size, intersection point, complexity and amount of fault displacement. Their distribution depends on the amount of Neogene strain and thickness of Tertiary sediments.

The first type of hourglass faults formed from a single phase of extension and occur mainly on the Sahul and Ashmore Platforms, where there is thin Tertiary cover. They converge between the Early Miocene and Early Pliocene horizons and show minor normal displacement. The second type of hourglass faults are formed by at least two stages of movement and are the result of linking faults which nucleate above Mesozoic horst structures and propagate in both directions, converging in the early Eocene horizons. They occur in areas of high strain and thick Tertiary cover, such as the Laminaria area and the Cartier Trough.

Hydrocarbon traps in the Timor Sea are often associated with Mesozoic rift structures and the exact nature of the intersection of hourglass faults is important in predicting trap breach. Detailed analysis of 3D seismic data from the Laminaria area suggests that in areas of high strain, hourglass structures become discontinous detached faults with an area of sub-seismic faulting at the crossover point

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado