Many
deep-sea fan and sheet systems include deposits of rheologically complex
sediment gravity currents (“hybrid flows”) with suggestions of turbulent,
transitional and laminar flow character, most commonly interpreted to represent
deposition in more distal regions. In this paper, Patacci et al. describe a succession deposited as strata that onlap
a confining slope. The sedimentology and geometry of these strata illustrate that
hybrid flow-associated deposits can occur in proximal settings, and on scales
of just 100s of meters, given a confining topography (e.g., onlap) that
transforms the flows. This flow hybridization mechanism provides an alternative
explanation for the occurrence of clay-rich facies development at the foot of
flow-confining seafloor slopes, and may be important for predicting trends in
reservoir quality in subsurface analogs.
Although incised valleys at
or near the highstand shoreline are common on many Holocene (and ancient)
continental margins, their dynamics remain poorly understood. To explore these
systems, Mattheus and Rodriguez use
geophysical and lithologic data and geomorphic analyses to examine the
morphology and facies architecture of coastal prism and tributary incised
valleys on the Holocene lower coastal plain of North Carolina. The results
reveal trends in Holocene coastal evolution in response to sea-level rise and
sedimentation, including the observation that incised-valley width is
proportional to drainage-basin area. They suggest that distinguishing between
valley morphologies in the coastal plain provides insight into the distribution
of sandy lithosomes, important for mapping groundwater and hydrocarbon reservoirs.
Bedforms occur in many
depositional systems, and can be influenced by unidirectional, oscillatory, or
combined flows. In this paper, Perillo et al. collected experimental
data under a wide range of unidirectional, oscillatory and combined flows to
address range of unexplored flow conditions (strong unidirectional flows and
intermediate oscillation periods) where the bedform geometry, and hence consequent
sedimentary structures, have not been explored. Under these flow conditions,
ten distinctive bedform states are identified, and the planform and
cross-sectional geometry are described. This new nomenclature unifies past
research on bedforms in both unidirectional and oscillatory flows, and thus
presents a new synopsis of bedforms developed under such flows. This new data
and analysis allows proposition of a new unified phase diagram for combined
flows.
