Boyd, Ron¹, Dale A. Leckie²
(1) University of Newcastle, Callaghan, Australia
(2) Nexen Inc, Calgary, AB

ABSTRACT: Comparison of the Cretaceous Paddy Estuary, Canada and the Modern Hervey Bay, Australia – Insights from Analog Modeling

Analog models of modern depositional systems continue to be an important technique for the interpretation of ancient sediments. The Cretaceous Paddy-Cadotte interval, Western Canada, a prolific gas producer, is an anomalous unit interpreted as a very large open estuary facing a wave-dominated coastline. The embayment was formed by longshore sediment transport, forming a spit over 200 km long, enclosing a water body with diluted salinity over 20,000 km2. Although evidence of sediment texture, sedimentary structures, micropaleontology, palynology and trace fossils support this interpretation, the scale and character of the Paddy system did not fit with established models of estuarine sedimentation.
The eastern Australian coast has a modern estuary with many characteristics of the Paddy system, suggesting an appropriate modern analog. Longshore transport has extended a quartzose barrier 120 km, extending Fraser Island at a divergent angle to the coastline. The resulting embayment (Hervey Bay) is over 3,600 km2 and fed by Mary River in a bay head delta, resulting in reduced salinities throughout Hervey Bay. Tidal range increases from 2 m at the open ocean to 4 m at the head of the bay. Extensive low-energy coastal deposits are developed on the landward shoreline and a complex barrier with tidal inlets, tidal deltas and a high energy shoreface is developed on the seaward side. The ability to identify a similar modern environment that can be characterized in terms of reservoir properties and three dimensional facies architecture enables a more realistic predictive model to be constructed for subsurface exploration and production.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.