Abstract: Modern Delta Progradation Rates: Implications for Relative Sea-Level Control on Timing of Turbidite Deposition with Examples from the Jurassic of the Neuquen Basin, Argentina.
BURGESS, PETE, STEVE FLINT, Stratigraphy Group, University of Liverpool; NIELS HOVIUS, Penn State Geoscience.
Estimated times required for 25 modern river systems to form
shelf-edge deltas range from 8.5 Kyrs to 116.5 Kyrs, being
dependent on magnitude
of fluvial sediment supply, delta width,
shelf volume and shelf transport rates. These values indicate that
formation of shelf-edge deltas and consequent sediment bypass into
deep-marine systems may well be significant during third-order
highstands of relative sea-level, dependent to a large extent on
magnitude
of sediment supply to the shelf. Since sediment supply is
controlled largely by climate, source area tectonics and bedrock
lithology, these factors must be as significant to timing of
turbidite deposition as relative sea-level history. Variables such
as rates of shelf transport will influence delta progradation time
while details of shelf physiography may decrease the time during a
highstand before shelf bypass occurs. Based on proportions of sand
in modern river loads, highstand shelf bypass could lead to
significant deep-marine sand deposition. Consequently
interpretation of ancient sand-rich deep-marine strata as limited
to times of lowstand is not always appropriate. Consideration of
more palaeogeographic and palaeoclimatic data is required to
determine the likelihood of highstand shelf bypass. Examples are
given from Lower and Middle Jurassic turbidite strata of the
Neuquen Basin, Argentina. Classically these strata are interpreted
as relative sea-level lowstand deposits, but considering Jurassic
palaeogeography and likely sediment budgets based on climatic and
drainage basin data, many turbidite strata could equally be
interpreted as trangsressive and/or highstand deposits.
AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah