Mixed Carbonate-Siliciclastic Systems: Implications for the Development of Deepwater Turbidites in the Nova Scotian Margin

Abstract

The progradation of major deltaic systems that are capable to reach the shelf-edge is considered a primary mechanism for the delivery of sand to the slope and basin floor region within continental margins including the offshore region of Nova Scotia. However, sediment bypass processes can dominate the outer-shelf to upper-slope transition causing poor preservation of reservoir quality sands in the upper slope. As a consequence, thick and abundant sandstone bodies can be tracked down to the shelf break but abrupt facies transitions can be frequent immediately down dip of shelf-edge deltas that act as the main delivery systems. Despite the absence of sands in the upper slope, turbidity flows can carry the bulk of the coarse fraction downdip where a thicker sand pile can be deposited once the so-called channel-to-lobe transition is reached. Predicting this lateral and vertical variability along the slope is a great challenge for explorationists; however, this configuration can be further complicated when mixed carbonate-siliciclastic systems are developed in the outer shelf. In this work, we explore the implications of two potential case scenarios: (1) One in which the carbonate factory is still dominant and the development of extensive carbonate reefs and pinnacles in the outer shelf prevents the passage of siliciclastic systems beyond the shelf-break, in this case the siliciclastic component is sequestered within the inner and outer shelf and chances for sediment bypass to deepwater are minimal and (2) the second scenario takes place when conditions that were favorable for carbonate production gradually change by the activation of major fluvial/deltaic systems. In this case, low relief, carbonate shoals tend to be ubiquitous in the outer shelf representing the last outboard remnants of the carbonate factory. Shelf-edge deltas can erode and breach these carbonate shoals establishing sedimentary pathways in the shelf-break region that can feed deep-water turbidites.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016