Fault-Related Folds and Cenozoic Stratigraphy within the Aure Fold and Thrust Belt, Gulf of Papua, Papua New Guinea

Khib A. Kugler

Integration of modern reflection seismic data with new well information and field work has better defined the Cenozoic stratigraphy, fault-related folds and sequence of deformation in the outer 75 km of the Aure Fold and Thrust Belt (AFTB) in the Gulf of Papua, Papua New Guinea.

Anticlinal axes and thrust faults, strike N25°W, can be traced up to 75 km. Listric thrust faults with offsets of less than 2 km break cylindrical, crestally eroded anticlines with amplitudes as great as 3500 m. Fold wavelength is 8-12 km, however a 4-8 km wavelength is observed in the northeastern portion of the study area. Hanging wall anticlines are upright to slightly inclined in the direction of thrust displacement. Thrust fault-bound triangle zones in anticlinal cores are common. Foreland directed thrust faults dip toward the interior of the AFTB and cut up-section from sub-horizontal detachment zones in the Pliocene, Upper Miocene and the Middle Miocene to Paleocene. Seismic data provide no conclusive evidence that crystalline basement is involved in the deformation, but a least four deep-seated thrust faults penetrate into the pre-Tertiary strata and extend below the seismic record.

Across the 75 km wide mapped area, average estimated minima for shortening are 18 km (20%) for Late Miocene strata, 6 km (8%) for Early Pliocene strata, and 1.5 km (2%) for Late Pliocene to Pleistocene strata. Where mappable, earliest Tertiary strata have been shortened a minimum of 1.4 km (3%). Backthrust faults have accommodated greater than 50 percent of the shortening of Late Miocene and Early Pliocene strata.

Within the study area the first observable stage of shortening occurred by Late Miocene (~5.3-7.2 Ma) and structures propagated toward the foreland with an 8-12 km wavelength. A period of ~0.8 million years is suggested to be the time required for the mature development of a typical folded structure in this portion of the AFTB.

Deformation continues today in the youngest strata at the toe of the AFTB, and continued shortening has reactivated older structures well within the interior. This is indicated by gentle folding and minor thrust faulting of Pleistocene and younger strata in the seismic data and by strongly folded (dips up to 60°) and thrust faulted Pleistocene strata onshore.

Mud diapirism and minor downslope gravity slumping occur within Pliocene to Pleistocene strata. Minor normal faults also occur locally within these strata, but are less commonly observed within Miocene strata.

The southern limit of Paleocene to Miocene carbonate development and northern and western limits of the Miocene volcanics are defined and mapped.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995