Sequence stratigraphy: Fact, fantasy, or work in progress
- Geological survey of Canada, Calgary, Alberta (Canada)
Sequence stratigraphy has been hailed as a magic elixir to cure exploration problems in mature and frontier basins. Yet, like most cure-alls, analyses of modern depositional systems show that critical assumptions regarding sequence stratigraphy merit further review. An example from the modern Canterbury Plains, New Zealand, demonstrates some of the potential pit- falls of sequence stratigraphy and its application to hydrocarbon exploration. The Canterbury Plains, New Zealand, bounded by the Southern Alps and Pacific Ocean, are 60 km wide and 185 km long, and traversed by four large gravel rivers. The Canterbury basin is up to 750 m deep, filled primarily with gravel. The coastline is wave dominated and microtidal, with high rates of north-directed longshore drift. The southern coast is transgressive with 22 in wave-cut cliffs in Pleistocene gravel. Beaches are gravel and sand. Coastal erosion at approximately 1 m/yr steepens the fluvial gradient, causing the rivers to incise 1.5-4.2 mm/yr during the present highstand. River headwaters in the Southern Alps are uplifting, tectonically causing incision, which decreases seaward. Thus, fluvial incision takes place in the west due to mountain uplift and in the east due to the transgressing shoreline. A zone of null valley incision occurs 8-15 km from the coast. Existing sequence stratigraphic models suggest that downcutting should occur during falling sea level, not during transgression. The southern coastline is separated from the northern coast-line by Banks Peninsula, a resistant volcanic complex that acts as a large groyne to southerly waves. The northern coastline progrades approximately I m/yr and is largely sandy. Thus, the coastline within the same basin during the present sea level highstand is at one locale progradational and elsewhere transgressive. Gravel reaches the transgressive coast, where a steep gradient is maintained by downcutting.
- OSTI ID:
- 161846
- Journal Information:
- AAPG Bulletin, Vol. 79, Issue 11; Other Information: PBD: Nov 1995
- Country of Publication:
- United States
- Language:
- English
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