A Ponded Basin Floor Fan Outcrop Analogue: Bunkers Sandstone, Northern Flinders Ranges, Australia

Abstract

The Donkey Bore Syncline in the Northern Flinders Ranges of South Australia contains a generally finegrained deepwater succession of Early Cambrian age (Bunkers Sandstone) that outcrops on three sides of a syncline and flanks an active salt diapir to the east (Wirrealpa Diapir). Within the succession lies a basal sand-prone interval interpreted as a basin floor fan (BFF) ponded within a mini-basin on a topographically complex slope.The BFF comprises over 30 m of section with deposits that are dominantly massive clean sandstone beds (0.1– 3 m thick) that are stacked or interbedded with siltstones and pinch out along strike.Eight stratigraphic sections and accompanying spectral gamma ray logs (using a hand held scintillometer) were measured through the BFF. Using spectral gamma ray log analysis combined with stratigraphic logs, four alternative correlation panels were constructed.Quantitative analysis of sand-prone intervals interpreted in each of the panels provided data on the vertical and horizontal connectivity within the BFF as different correlation methods were explored and the geological model improved. Quantitative analysis of vertical and horizontal connectivity values indicates a high degree of heterogeneity within the BFF, with poor–moderate vertical connectivity, with individual beds rarely correlating >500 m along strike. This heterogeneity is poorly resolved using conventional wireline log suites, but is greatly improved if spectral gamma ray logs are used (especially Thorium).The data set provides a high-resolution analogue for understanding the internal architecture of deepwater hydrocarbon reservoirs.

Cambrian stratigraphy and biostratigraphy of the Flinders Ranges and the north coast of Kangaroo Island, South Australia

“…The limestone shows considerable thickness variations with 100-500 m in many sections, up to 800 m in the Bunkers Graben (Clark, 1990) and over 2,500 m in the Nepabunna Trough (Gravestock, 1995 Nepabunna Siltstone) that intertongue with limestones of the Mernmerna Formation. Sequence C -1.3 commences with the Bunkers Sandstone, which in the Bunkers Graben comprises up to 300 m of cross bedded, quartz sandstone, but elsewhere it is mainly either quite thin or missing; however, in the Donkey Bore Syncline, to the NE, it comprises deeper water basin floor fan deposits (Reilly and Lang, 2003). The distinctive khaki Oraparinna Shale represents a transgressive unit; in the eastern Nepabunna Trough the Oraparinna Shale intertongues with fine to medium grained feldspathic sandstones of the Narina Greywacke (Gravestock, 1995).…”

New bradoriids from the lower Cambrian Mernmerna Formation, South Australia: systematics, biostratigraphy and biogeography

“…The Bunkers Sandstone is dominated by medium-grained quartz (>95%) with minor amounts of feldspar. Cross-bedding is evident in a number of horizons, but the lack of internal structures, grading and flat conformable bases led Reilly & Lang (2003) and Ceglar et al (2004) Shale, represent transgressive deposits associated with sequence package Є1.3 of Gravestock & Cowley (1995). The upper Mernmerna Formation consists of dark grey, micritic limestones interbedded with fine to medium grained quartz calcarenite beds.…”