Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Different Styles of Fluvial Termination Deposits Around a Large Playa
(1) Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia.
Sediment deposits at the fluvial-playa interface are the subaerial equivalent of deltas. Fan-shaped deposits called Terminal Splay Complexes (TSCs) have been described from Lake Eyre, central Australia; used as analogues for hydrocarbon reservoirs around the world. However, key questions important for application of these analogues have not previously been addressed: How likely is it that a river will build a terminal deposit? What are the different deposit geometries? What controls their distribution, occurrence and form? How typical are the studied examples? To answer these questions, we analysed 234 river mouths around Lake Eyre, combining satellite image, map and field data. Lake Eyre covers 9600 km2 and is the depocentre of a large continental interior basin with monsoon-influenced semi-arid to hyperarid climates. River catchments range from 361000 to <100 km2. Styles of fluvial termination are: 1) Constructive-on playa; 2) Constructive-in embayment/estuary; 3) Constructive-on playa with filled embayment/estuary upstream; 4) Non-constructive; 5) Undefined (poor image quality). Type 1 deposits were subdivided into: widths >300m, of which all have been counted; and widths <300m, some of which will be below image resolution. We present the relative proportions of different styles of fluvial termination, including length/width dimensions of deposits and river channels, deposit areas, and the distribution of different styles. Key findings include: 70% of rivers construct a sediment deposit at their mouth, of which 51% construct directly on the playa. Distribution of river mouth terminations per km shoreline varies greatly, and is probably a function of catchment area and land-surface composition. Most Type 2 and 3 deposits occur in one area, which we relate to surface geology and wet-phase shoreline processes. The total area of fluvial termination deposits is 397 km2, 98.6% of which is Type 1. Type 1 deposits can be described as: Confined (Type 1a) which have well-developed channels proximally and amalgamated splay lobes distally; and Unconfined (Type 1b) which do not contain channels. Type 1a/1b morphology is not related to deposit size or river catchment area, and may be related to sediment load, shoreline morphology and lake bathymetry. Assuming that Lake Eyre is a suitable modern analogue, the studied Lake Eyre TSCs are a good analogue for fluvial termination deposits. However, Type 1 deposit type may have a substantial impact on reservoir quality.