Deep-water tidal sedimentology

Abstract

Tides are well-documented in modern deep-water environment, especially around areas of topography on the seafloor such as ocean ridges and continental slopes. Recognition of deep-water tidal deposits in the ancient has lagged far behind, however, with very few examples in the published literature. This paper presents a review of the current state of knowledge about both modern deep-water tidal sediments and ancient deep-water tidal deposits, including new data on tidalites from the Cretaceous Wheeler Gorge channel-levee complex (California), and the Cretaceous Cajiloa submarine canyon (Mexico). In both of these settings detailed analysis of laminae thickness trends revealed cyclicities with frequencies characteristic of tidal deposits. Recognition criteria for ancient deep-water tidal deposits include statistically significant cyclicities within thin successions (tidalites are unlikely to be very thick) in combination with mud-couplets, mud-bounded ripples, ripples with reactivation surfaces, and, more rarely, bi-directional ripple sets. Typical tidalites successions include cyclically thickening and thinning laminae (5-40 cm thick), and rippled intervals (5-20 cm thick) that exhibit large energy asymmetries (mud drapes) and an overall increase then decrease in ripple size, often arranged in cycles. Although tides are common in deep-water environments, settings where deposits may be preserved are relatively rare. Such settings must not be subject to erosive turbidity currents yet require a relatively steady sediment supply and local accommodation space. Abandoned meander bends, the backsides of levees, topographic lows on the surface of submarine landslides, and abandoned plunge pools all potentially fit this category. This paper documents a tidalite succession that is preserved within a topographic low above a submarine landslide deposit.