Spatial Quantification of Aggrading, Backstepping, and Drowning Patterns of a Frasnian Carbonate Platform System (Bugle Gap, Canning Basin, Western

Adams, Erwin W.¹, Claude-Alain Hasler² (1) Shell International E&P, Rijswijk, Netherlands (2) University of Geneva, Geneva, Switzerland

One of the key differentiating factors between carbonate and siliciclastic transgressive systems tracts is the ability of carbonate systems to aggrade rather than backstep. If a platform is aggrading and rates of accommodation increase and sedimentation remain constant, the relief of the platform automatically increases. As a result, syndepositional fissures develop and the margin becomes steep and erosional by successive collapses. Pinnacle reefs with aggrading and backstepping relationships are found in the Bugle Gap area, where exhumed, well-preserved outcrops allow quantitative spatial analyses of the carbonate system similar to geographic information systems (GIS) based remote-sensing studies of modern carbonate depositional systems. Using precise differential RTK GPS surveying (with an accuracy of approximately 2 cm) it was possible to quantitatively record and study the spatial organization and depositional relationships of the carbonate system. The stratigraphic boundaries and sedimentary bodies of interest were digitally mapped by physically walking with the RTK GPS unit. A digital elevation model (DEM) was constructed from datapoints that were systematically acquired across the outcrop. Combining the collected datapoints with the DEM enabled a clear understanding of the interaction between geology and outcrop topography. The digitally recorded data was assembled, visualized, and modeled creating a 3D digital outcrop model (DOM). The DOM captured the development of the pinnacle reef system and quantified the aggrading, backstepping, and drowning patterns. Forward modeling confirmed the impact of accommodation increase on the development of the Devonian pinnacle reef system of the Bugle Gap.