Abstract

Apatite fission track analyses of Permian to Pliocene rocks from the Rawarra-1X and Sebyar-1X wells, located along the Sebyar anticline, have constrained the regional tectonic and thermal history of the Bintuni Basin. The fission track analyses indicate that rocks sampled have recently reached their maximum paleotemperatures, probably in response to burial by Late Miocene to Recent sedimentary rocks. This is indicated by analyses of samples presently at temperatures greater than ~110°C which still contain apatite grains with ages greater than or equal to the stratigraphic age. The analyses also suggest that: (1) the rocks have not yet equilibrated to their present-day temperatures; (2) Permian rocks probably did not reach temperatures greater than ~60°C prior to uplift and erosion responsible for a regional Permo-Triassic unconformity; (3) the present-day geothermal gradients in the wells are equal to or slightly less than the maximum recorded gradients; and (4) within the limits of the data, it is conceivable that the wells experienced between 300–800 m of uplift and erosion during the middle Miocene.

Interpretation of these results suggest at least two episodes of uplift and erosion within the Birds Head region. The first episode occurred in the Early Miocene and is indicated by the occurrence of grains of Early Miocene age in the Pliocene section. The second episode at ~5 Ma resulted in uplift and erosion within the source terrains for the Bintuni Basin and was responsible for the deposition of a thick section of early Pliocene sediments into the basin.