Allochthonous prodeltaic sediment facies in the Lower Cretaceous at the Tantallon M-41 well: Implications for the deep-water Scotian Basin

Lower Cretaceous shelf-margin deltas in the Scotian Basin prograded across a deep outer-shelf platform and may have supplied sand to the deep-water Scotian margin. Conventional core from the Tantallon M-41 well was used to evaluate sediment facies and evidence for the transfer of deltaic sand to deep water. Two cores with shallow-water lithofacies show sediment deformation structures, resulting from surficial debris flow and deeper seated landsliding of deltaic sediment, interpreted by a comparison with modern sea-floor piston cores. Both mass-movement types produced a basal strongly foliated mudstone. Such allochthonous blocks create potential pitfalls in interpretation of paleowater depth from sedimentary structures in conventional core and microfossils in ditch cuttings. Autochthonous sediment on the deep outer-shelf platform is a distinctive red-brown mudstone with rare turbidite sandstone beds. The deepest core consists of thin-bedded sandstone turbidites showing Bouma Tb-c-d intervals and fading ripples characteristic of overbank settings, deposited on a high adjacent to 50-150-m (160-500-ft) -deep channels. These sandstones provide direct evidence that sand was transferred through channels into deep water in the Early Cretaceous. Sandy turbidity currents were sourced both by prodeltaic failure and transformation and by hyperpycnal flow from the mountainous rivers that supplied sediment to the Scotian Basin.