Abstract

The New Guinea Limestone Group is a thick, predominantly carbonate, section covering the Bomberai Peninsula area of Irian Jaya. The general depositional history of this group is indicated from studies of the stratigraphic section encountered in three wells recently drilled in this area.

The Besiri River well, located in the southern Bomberai region, penetrated the Tertiary section and bottomed in Upper Cretaceous marine sediments. Petrographic and paleontologic studies indicate that the Mesozoic section is unconformably overlain by a thick Paleocene carbonate and shale interval which was deposited in middle to outerneritic shelf conditions. The Paleocene section is unconformably overlain by a thick neritic carbonate deposit of Eocene age. Unconformably upon this Eocene section is a thin Oligocene sandstone and shale interval. This Oligocene interval is the Sirga Formation which was deposited in a middle to outer-neritic environment. Lying conformably over this clastic interval is a thick Upper Oligocene to Middle Miocene shallow-water carbonate section. This section appears to be reefal in the lower part and a back-reef deposit in the upper portion, suggesting regression or a basinward prograding reefal environment. This carbonate section is unconformably overlain by the Upper Miocene to Pliocene Buru Formation which consists of claystone deposited in a bathyal environment.

The Jamusura well, also located in South Bomberai, penetrated approximately 1000 feet of Middle Miocene New Guinea Limestone. This carbonate section consists of back-reef and outer-shelf deposits which are unconformably overlain by the Upper Miocene to Pliocene Buru section.

The Aroba well, located in the Northern Bomberai area, also tested the Upper New Guinea Limestone, penetrating approximately 250 feet of the Middle Miocene carbonate section. This carbonate interval is an open-shelf, near-reef deposit and is overlain by a regressive Upper Miocene to Pleistocene claystone section.

Well data and limited outcrop information indicate the following depositional history for the New Guinea Limestone Group in the Bomberai Peninsula area:

Paleocene

In the southern Bomberai area, middle to outer-neritic open-shelf clastic and carbonate deposition took place over an unconformable Mesozoic surface.

Eocene

Inner to middle-neritic carbonate deposition occurred. Tectonism is suggested by an Upper Eocene unconformity.

Oligocene

A transgressive clastic section was deposited, overlain by a shallow-water carbonate interval.

Early-Middle Miocene

Extensive carbonate deposition occurred with depositional environments ranging from fore-reef to reef and back-reef. Regression or regional uplift produced a Middle Miocene unconformity.

Late Miocene-Pleistocene

Carbonate deposition ended with an influx of clastic sediment. Depositional environments ranged from paralic and continental in the north to bathyal in the southern Bomberai area.