Janice M. Christ1, William G. Dickson2, and James W.Granath3
Search and Discovery Article #10044 (2003)
*Adapted from “extended abstract” for presentation at the AAPG Annual Meeting, Houston, Texas, March 10-13, 2002.
1J-SEA Geoscience, The Woodlands, Texas ([email protected])
2Dickson International Geosciences, Houston, Texas ([email protected])
3Granath & Associates, Houston, Texas ([email protected])
The Pearl River Mouth Basin (PRB), offshore China, is reexamined in light of:
- advances in understanding deepwater depositional systems;
- better data analysis and display tools and techniques;
- recent experience in South Atlantic margin basins and offshore Borneo illustrating correlations between potential field data and controls on sediment distribution systems.
The Pearl River Mouth Basin (PRB) is a passive margin rift system composed of three subbasins (Figure 1). The southernmost of these, the Zhu II subbasin, is significantly extended in a new interpretation that integrates potential fields data with geological literature in a GIS-based visual database. The PRB formed over Mesozoic continental crust and inherited the pre-existing tectonic zones of weakness of that crust (Pigott and Ru, 1994). Paleogene extension that formed the depocenters of the PRB occurred mainly from Late Eocene to Late Oligocene and included a component of dextral shear (Edwards, 1992). The shear may originate from reactivation of NW-SE-trending strike slip faults (Xia and Zhou, 1993). These basement trends are well suited to imaging with potential fields data. The strike-slip faults appear to control some edges of subbasins and uplifts, including the Shenhu Uplift boundary with the Zhu II Depression. The shear trend also seems to influence the paleo-Pearl River drainage.
The initiation of seafloor spreading is marked by the 30 Ma “breakup” or T7 unconformity, a key boundary separating the more isolated depocenters containing lacustrine source-prone rift fill from the succeeding and widespread paleo-Pearl River deltaics (Chen et al., 1994). The deltaic reservoirs in the Zhu I and Zhu III subbasins have been the target of most PRB exploration. Few wells have tested the edge of the Zhu II subbasin, where a lack of reservoir quality sands has been perceived (Letsch et al., 1994). Recent advances in understanding deepwater depositional systems (i.e., Posamentier, 2000; Dickson and Macurda, 2001) predict turbidite reservoirs well outboard of the deltaic environments explored to date.
Recent work on a non-exclusive study of the South Atlantic by one of the authors (Dickson) introduced the possibility of defining controls on sediment distribution systems from regional gravity data. Examples from both Brazilian and West African basins suggested the relationship was not restricted to a single basin.
Offshore northwest Borneo, the authors identified feature patterns on gravity attribute images that correlate with interpreted channel/canyon systems (CCS). These CCS debouch into the known Tertiary Lingan Fan (Mohamad and Lobao, 1997) and additional speculative fans (Figures 2 and 3); their sources coincide with the locations of slump-scars and back-cutting shelf edges. Similar distinct CCS patterns appear to correlate to the Tertiary Pearl River fan system, initiating at the delta front (Chen et al., 1994), extending across the slope and terminating at the southern basin extension, raising the expectation for turbidite reservoirs.
This study significantly extends the Zhu II subbasin beyond the Neogene thick (Hirayama, 1991). A restricted Paleogene-aged basin is inferred, with favorable implications for source-rock deposition and with thinner total section, avoiding the overmaturity of the Baiyun depocenter. Interpretation is of a channel/canyon system that provides the clastic conduits for bringing sands into the far basin (Figure 4) to form turbidite reservoirs. Despite water depths from 1000 to 2500 m, this area seems ripe for more detailed evaluation.
Chen, J., S. Xu, S., and J. Sang, 1994, The depositional characteristics and oil potential of paleo Pearl River delta systems in the Pearl River Mouth basin, South China Sea: Tectonophysics, v. 235, p. 1-11.
Dickson, W. G., and D. B. Macurda Jr, 2001, Recognition and Analysis of a Major Tributary of the Recent Congo Fan: Some Gully! Abstract in Geological Society of London Symposium on Deepwater Depositional Systems, London, Mar, 2001.
Edwards, P.B., 1992, Structural Evolution of the Western Pearl River Mouth Basin, in J.S. Watkins, Z. Feng, and K.J. McMillen, eds., Geology and Geophysics of Continental Margins: AAPG Memoir 53, p. 43-52.
Hirayama, J., ed, 1991, Total Sedimentary Isopach Maps Offshore East Asia: CCOP Technical Bulletin 23, 116 p.
Letsch, D.K., J.W. Norris, and M.W. Heyman, 1994, Critical Factors for Exploration Success in the Pearl River Mouth Basin, in, G. Greene, H. Lian, and T.V. Tri, eds., International Symposium/Workshop on Geology, Exploration and Development Potential of Energy and Mineral Resources of Vietnam and Adjoining Regions, Program and Abstracts of Papers, Hanoi, May 30-June 2, 1994, unpublished talk (errors in abstract noted by speaker): Circum-Pacific Council/Geological Survey of Vietnam/Petrovietnam, p. 81-82.
Mohamad, M., and J.J. Lobao, 1997, The Lingan Fan: Late Miocene/Early Pliocene Turbidite Fan Complex, North-West Sabah, in, J.V.C. Howes, and R.A. Noble,eds., Proceedings of an International Conference on the Petroleum Systems of SE Asia and Australasia, Jakarta, Indonesia, May 21-23, 1997: Indonesia Petroleum Association, p.787-798.
Moldovanyi, E.P., F.M. Wall, and Zhang Jun Yan, 1995, Regional exposure events and platform evolution of Zhujiang Formation carbonates, Pearl River Mouth Basin: Evidence from primary and diagenetic seismic facies: AAPG Memoir 63, p. 125-140.
Pigott, J.D., and K. Ru, 1994, Basin superposition on the northern margin of the South China Sea: Tectonophysics, v. 235, p. 27-50.
Posamentier, H.W., and Putri Sari Wisman, 2000, Deep Water Depositional Systems -Ultra-Deep Makassar Strait, Indonesia in Deep-Water Reservoirs Of The World, 20th Annual Bob F. Perkins Research Conference, GCSSEPM, Houston.
Xia, K.Y., and D. Zhou, 1993, The geophysical characteristics and evolution of northern and southern margins of the South China Sea, in, G.H. Teh, ed, Proceedings Symposium on Tectonic Framework and Energy Resources of the Western Margin of the Pacific Basin, CPC-GSM, 29 Nov-2 Dec 1992, Kuala Lumpur, Malaysia: Bulletin of the Geological Society of Malaysia, v. 33, p. 223-240.