Geology Reference
In-Depth Information
1 4
Deep-Water Tidal Sedimentology
Mason Dykstra
Abstract
Tides are well-documented in modern deep-water environment, especially around
areas of topography on the seafl oor 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 sedi-
ments 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 charac-
teristic of tidal deposits.
Recognition criteria for ancient deep-water tidal deposits include statistically
signifi cant cyclicities within thin successions (tidalites are unlikely to be very
thick) in combination with mud-couplets, mud-bounded ripples, ripples with reac-
tivation surfaces, and, more rarely, bi-directional ripple sets. Typical tidalites suc-
cessions 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 accom-
modation space. Abandoned meander bends, the backsides of levees, topographic
lows on the surface of submarine landslides, and abandoned plunge pools all
potentially fi t this category. This paper documents a tidalite succession that is
preserved within a topographic low above a submarine landslide deposit.
14.1
Introduction
The infl uence of tides in deep-water settings was fi rst
documented in the 1950s and 1960s when researchers
noticed that the measured periods of some internal
