Observations from Multibeam Bathymetry and Backscatter Data, Interplay Between Active Deformation and Active Depositional Systems

Philip A. Teas¹, Daniel L. Orange¹, Peter Baillie², John Decker¹, and Widjanarko^3
1Black Gold Energy, Jakarta, Indonesia
²TGS-Nopec, West Perth, Australia
³MIGAS, Jakarta, Indonesia

Introduction

Eastern Indonesia is an extremely active tectonic region resulting in active mountain building and basin subsidence promoting vigorous depositional systems juxtaposed with actively deforming structural domains. East Indonesia is located on the eastern, leading edge of the Sunda micro-plate where it interacts with the Indo-Australia and Pacific plates in a complex distributed triple junction. The region is dominated by convergent tectonics and transform margins between shifting fragments of each of the plates. A recent marine hydrographic survey has provided a remarkable new data set imaging the interplay of structure and deposition in middle to ultra-deep water settings. With such outstanding imagery of both depositional and structural systems, we are afforded exceptional opportunities to observe the control of the structural systems on depositional patterns in situations that range from structure activity exceeding depositional activity, to the opposite where sedimentation outpaces deformation.

Convergent Systems

We will review two convergent settings, one along the leading edge of the sunda micro-plate, in the Makassar Strait, and one along the northern margin of the Indo-Australia plate where it is interacting with the Pacific. In the Makassar Strait we observe a fold and thrust belt crossed by an incising meandering canyon system. The canyon itself has several hundreds of meters of relief with internal terraces. Through the rear of the underlying fold belt there is no obvious impact of deformation on the depositional system except in one place where thin skinned deformation switched to thick skin where the canyon narrows and a marked nick point is developing. In the area of most recent deformation however, the newly developing folds cause the diversion of a branch of the depositional system into the syncline behind the fold perpendicular to the main depositional pattern.

Along the northern margin of the Indo-Australia plate a previously unknown active fold belt is crossed by several depositional systems. A variety of behaviors is apparent along the length of the fold belt. Where sediment input is low we see channels diverted and re-routed around uplifting anticlines. The general pattern is of fill and spill with channels incised at the spill point. There are also indications of drainage capture and one location where we see a mini-basin tilted by active structural growth. Moving along the fold belt we find an area of rapid sedimentation burying the fold belt. This behavior ranges from complete burial along the major axis of sedimentation to areas where deformation and sedimentation are more balanced away from the axis. Features along the margin include faulting of the depositional apron and uplift and abandonment of channel systems. Additionally there is an instance where a structure uplifted and diverted the main depositional axis.

Transform Systems

The Makassar Strait is also crossed by the Palu-Koro strikeslip fault system marking the transform margin between the Sunda micro-plate and northeast Sulawesi. The incised canyon system presented previously continues across a deep water basin and intersects transpressional ridges associated with the Paul-Koro fault system. Here the system again incises through the transpressional ridges, filling minibasins between subsequent ridges. The depositional system continues along a continuous slope crossing the active fault features and out of the region of detailed bathymetry to depths in excess of 3500m.

Again near the leading edge of the Indo-Australia plate converging with the Pacific we find a basin deformed by the major strike-slip fault system of the Terera-Aiduna. The remarkable depositional features observed in this area are a series of canyon segments displaced by a largely trans-tensional fault system. An extremely steep gradient exists here and the canyon system has had to continuously re-organize itself as the active faulting readjusts base-levels. Canyon forms vary from highly sinuous to straight scalloped edged forms with several instances of migrating nick-points.

Discussion

We will present various examples of the interplay of structure and sedimentation and discuss the implications for sediment dispersal and preservation of sediment systems in the subsurface.

AAPG Search and Discovery Article #90079©2008 AAPG Hedberg Conference, Ushuaia-Patagonia, Argentina