--> ABSTRACT: Application of a New Process-Based Classification Scheme to Modern Mixed-Process Systems: A Case Study of the Mitchell River Delta, Queensland, Australia, by Nanson, Rachel A.; Ainsworth, Bruce ; Vakarelov, Boyan; Price, David M.; #90142 (2012)

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Application of a New Process-Based Classification Scheme to Modern Mixed-Process Systems: A Case Study of the Mitchell River Delta, Queensland, Australia

Nanson, Rachel A.*1; Ainsworth, Bruce 1; Vakarelov, Boyan 1; Price, David M.2
(1) Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia.
(2) School of Earth & Environmental Sciences, University of Wollongong, Wollongong, NSW, Australia.

Work on modern coastal systems suggests that many present-day shorelines are complex and are comprised of discrete arrangements of depositional elements. The complexity described in both modern and ancient coastal depositional systems has recently been encompassed by a new process-based classification scheme (Ainsworth et al., 2011). Given that even subtle changes in local accommodation (A) and sediment flux (S), and wave (w), tide (t) and fluvial (f) processes, can result in fundamental changes in depositional style and resultant element suites, the architecture of modern mixed process systems provides an opportunity to examine the response of systems to changes in such drivers.

The Mitchell River delta, Queensland, Australia is one such morphologically complex system that has formed in an embayed, low accommodation coastal setting, similar to the North American Cretaceous Western Interior Seaway. The surface morphology of the delta illustrates considerable temporal and spatial variation in distribution of depositional elements and thus provided an ideal opportunity to examine controls on process changes within mixed influence systems.

The distribution and extent of w, t and f derived depositional elements were used to construct the evolution of the delta since the system commenced progradation approximately 6 ka BP. The classification of the overall delta system is tide dominated, fluvial influenced, wave affected (Tfw); However, such a generalisation masks considerable variation in process dominance through 3 geometrically discrete pulses of delta progradation. The system has evolved from a symmetrical wave dominated, fluvially influenced, tide affected (Wft) system in the early Holocene, to a rapidly prograding asymmetrical tide dominated, fluvially influenced, wave affected (Tfw) system in the mid-Holocene to a stalled asymmetrical Twf system at the modern shoreline.

We use Holocene climate reconstructions and inferred changes in local A and S to account for distinct pulses of delta progradation and for changes in process dominance and element architecture within each such pulse.

Ainsworth, R.B., Vakarelov, B.V., and Nanson, R.A. 2011. Dynamic Spatial and Temporal Prediction of Changes in Depositional Processes on Clastic Shorelines: Toward Improved Subsurface Uncertainty Reduction and Management. American Association of Petroleum Geologists Bulletin, v. 95, p. 267-297.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California