Lukasik, Jeff¹, Noel P. James² 
(1) Petro-Canada Oil and Gas, Calgary, AB 
(2) Queen's University, Kingston, ON

ABSTRACT: Effect of Climate Change on Miocene Temperate-Water Carbonate Sequence Development, Murray Basin, South Australia

The style of stratigraphic packaging in Lower to Middle Miocene temperate-water, epeiric ramp carbonate sequences varies in response to changes in glacioeustatic amplitude and regional to global climate. Environmental conditions evolved from an early Miocene cool, moist climate regime that supplied abundant nutrients to the temperate sea into middle Miocene warm-temperate waters with reduced levels of trophic resources associated with increasingly arid climate. Strata spanning this interval form three distinct, 2.75 to 1.25 Ma sequences. Each sequence comprises a transgressive (TST) and regressive (RST) interval separated by a transition zone of variable thickness and character representing maximum rate of sea-level fall. Transgressive, open marine strata evolved from infaunal- to epifaunal-dominant facies from the early to middle Miocene. Regressive strata comprise heterozoan, nearshore clay to seagrass facies in all sequences. The transition zone varies from an amalgamated grainstone bed to a 5 m thick gradational intercalation of beds generated in response to the ability of the evolving carbonate factory to track changes governed by falling sea level (with implications for the application of sequence stratigraphic concepts). Accordingly, levels of stratigraphic completeness dramatically increased in the Middle Miocene sequence where climate-induced elevated rates of sediment production and accumulation enabled the carbonate factory to “keep up” with falling sea level. The paradox of having a more complete sequence generated in an evolving ice-house world highlights that even slight changes in the carbonate factory related to climate had a profound affect on the completeness and style of stratigraphic sequences within this temperate-water system.

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