Geoscience Reference
In-Depth Information
In the vicinity of the Colorado River,
major changes in sediment supply and
transport have been identified and, as a
result, oceanic (rather than fluvial) hydro-
dynamic forces now exert the major influ-
ence on sediment dynamics within the
estuary and delta (Carriquiry & Sánchez
1999). Rather than a predominant north
to south (fluvial to basinal) transfer of sedi-
ment, sediment is now transported from
south-east to north-west along the eastern
side of the NGC into the estuarine basin,
and then reworked southwards along the
western sides of the NGC (Case Fig. 1.1).
Despite significant reductions in fluvial
sediment input from the Colorado River,
however, average sedimentation rates in
this NGC are reported to have remained
relatively constant over the past 100 years.
This is attributed to a transition in the
source areas that supply sediment to the
Gulf (Carriquiry et al. 2001). In particular,
a high proportion of sediment is now
supplied from resuspension and reworking
of the Colorado Delta sediments and from
the shallower part of the NGC shelf. These
sediments form the Colorado River Delta
Province and dominate the central areas
of the NGC marine basin (Case Fig. 1.1).
Additional sources of sediment are derived
from the desert areas of north-west Mexico
and south-west USA. These form the Concepción River Province and feed into the basin via
the Sonoita and Concepción Rivers (Case Fig. 1.1). In addition, intense desert winds from
the Sonora Desert represent an important transport medium for aeolian sediment transport
into the Gulf. These sediments are rich in zircon and garnet, and contribute primarily to the
Transitional Sediment Province. The area therefore emphasizes the effects of anthropogenic-
ally influenced reductions in sediment supply through fluvial systems, and the consequent
'downstream' impacts on both sediment transport pathways and on the composition of the
accumulating marine sediments.
Colorado River Province
Transitional Province
Baja California Province
Concepcion Province
USA
Colorado
River
Northern Gulf
of California
Colorado River
MEXICO
Sonoita
River
Northern
Gulf
of
California
Concepcion
River
N
BAJA
CALIFORNIA
Pacific
Ocean
20 km
Prevailing sediment transport direction
Tidally-influenced sediment transport
Case Fig. 1.1
Distribution of the main sediment provinces in
the Northern Gulf of California. The main sediment transport
pathways in the vicinity of the Colorado River Delta are also
shown. (Adapted from Carriquiry & Sánchez 1999; Carriquiry
et al. 2001.)
Relevant reading
Carriquiry, J.D. & Sánchez, A. (1999) Sedimentation in the Colorado River delta and Upper Gulf of California
after nearly a century of discharge loss.
Marine Geology
158
, 125- 45.
Carriquiry, J.D., Sánchez, A. & Camacho-Ibar, V.F. (2001) Sedimentation in the northern Gulf of California
after cessation of the Colorado River discharge.
Sedimentary Geology
144
, 37- 62.
