ABSTRACT: Late Cretaceous evolution of the Bird's Head, Irian Jaya: a failed rift?

Charlton, Tim R. , Consultant, Guildford, Surrey, United Kingdom

The Late Cretaceous Jass Megasequence in the Bird's Head comprises a lithologically mixed bathyal succession with local volcanic interbeds, showing considerable variation in stratigraphic thickness over relatively short distances. The sequence is developed above the regionally important Intra-Cretaceous Unconformity, which probably marks submergence following an interval of uplift and subaerial erosion in the mid Cretaceous. This submergence is presumed to be tectonically driven as it occurred during a period of globally falling sea levels. Regional dating of the oldest sediments above the unconformity indicates sequential onlap onto a structural high centred near to the Kalitami-1 well in the central Bintuni Basin.

It is suggested that during the Late Cretaceous the Bird's Head was the site of N-S intracontinental extension, probably related to the separation of a continental margin terrane from north of eastern Irian Jaya/Papua New Guinea. Extension commenced in about the Turonian, and continued until the Maastrichtian, at which time the continental margin terrane finally separated from Greater Australia. By the end of the Cretaceous the central and southern Bird's Head formed a subsiding block-faulted terrane, with a locally emergent structural high to the north (the Kemum block). Subsequently during Oligocene initiation of regional arc-continent collision, the extended terrane was inverted, producing the structural ridges upon which the hydrocarbon-bearing Kais reefs nucleated in the Miocene, and additionally forming deeper structural targets in the Mesozoic section.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia