[The Journal of Geology, 2010, volume 118, p. 247–259] ! 2010 by The University of Chicago.
All rights reserved. 0022-1376/2010/11803-0002$15.00. DOI: 10.1086/651539
247
Rapid Climatic Signal Propagation from Source to Sink in a
Southern California Sediment-Routing System
Jacob A. Covault, Brian W. Romans, Andrea Fildani,
Mary McGann,1 and Stephan A. Graham2
Chevron Energy Technology Company, Clastic Stratigraphy R & D, San Ramon, California 94583, U.S.A.
(e-mail: jcovault@chevron.com)
A B S T RACT
Terrestrial source areas are linked to deep-sea basins by sediment-routing systems, which only recently have been
studied with a holistic approach focused on terrestrial and submarine components and their interactions. Here we
compare an extensive piston-core and radiocarbon-age data set from offshore southern California to contemporaneous
Holocene climate proxies in order to test the hypothesis that climatic signals are rapidly propagated from source to
sink in a spatially restricted sediment-routing system that includes the Santa Ana River drainage basin and the
Newport deep-sea depositional system. Sediment cores demonstrate that variability in rates of Holocene deep-sea
turbidite deposition is related to complex ocean-atmosphere interactions, including enhanced magnitude and fre-
quency of the North American monsoon and El Nin˜o–Southern Oscillation cycles, which increased precipitation and
fluvial discharge in southern California. This relationship is evident because, unlike many sediment-routing systems,
the Newport submarine canyon-and-channel systemwas consistently linked to the SantaAnaRiver,whichmaintained
sediment delivery even during Holocene marine transgression and highstand. Results of this study demonstrate the
efficiency of sediment transport and delivery through a spatially restricted, consistently linked routing system and
the potential utility of deep-sea turbidite depositional trends as paleoclimate proxies in such settings.
Introduction
Submarine fans comprise sediment–gravity flow
deposits at the terminus of sediment-routing sys-
tems in the deep sea, and as such, they generally
represent the final resting places of terrigenous sed-
iment (Menard 1955; Normark 1970; Allen 1997,
2008a). Therefore, deep-sea deposits often contain
relatively complete records of sediment flux from
land to sea (Einsele et al. 1996; Romans et al. 2009).
However, sediment can be sequestered en route to
a deep-sea basin in accommodation along the rout-
ing system (e.g., rivers, flood plains, estuaries, sub-
siding deltas), thereby potentially introducing sig-
nificant lag time between onshore forcings and
offshore deposition (Milliman and Syvitski 1992;
Allen 2007, 2008a). This is common in extensive
sediment-routing systems that drain large propor-
Manuscript received September 1, 2009; accepted January 25,
2010.
1 U.S. Geological Survey, Coastal andMarine Geology Team,
Menlo Park, California 94025, U.S.A.
2 Department of Geological and Environmental Sciences,
Stanford University, Stanford, California 94305, U.S.A.
tions of continents, in which the lag time might
exceed millions of years (Milliman and Syvitski
1992; Me´tivier and Gaudemer 1999; Castelltort and
Van Den Dreissche 2003). As a result, climatic sig-
nals recorded in terrestrial-derived proxies (e.g., tree
rings, pollen; Stokstad 2001) might not be faithfully
reflected by contemporaneous deep-sea fan depo-
sition.
Here we compare an extensive piston-core and
radiocarbon-age data set from the latest Pleisto-
cene-to-Holocene Newport deep-sea depositional
system offshore southern California to contempo-
raneous high-resolution paleoclimate data. Unlike
many deep-sea systems, particularly those of pas-
sive continental margins with extensive sediment-
routing systems and broad shelves (Posamentier et
al. 1991), the smaller Newport canyon-and-channel
system actively delivered sediment to the fan dur-
ing the Holocene marine transgression and high-
stand (cf. Piper and Normark 2001; Covault et al.
2007; Normark et al. 2009; Romans et al. 2009).
Therefore, the spatially restricted southern Cali-

248 J . A . C O VA U LT E T A L .
fornia sediment-routing system of this study, in-
cluding the offshore Newport deep-sea depositional
system and the onshore Santa Ana River drainage
basin, is an ideal natural laboratory in which to
assess the efficiency of climatic signal propagation
and to demonstrate the utility of deep-sea fan de-
posits as a paleoclimate proxy resource (cf. Figuei-
redo et al. 2009). This study represents an early step
toward the development of more holistic models of
sedimentary systems, including terrestrial and sub-
marine components and their interactions, and it
highlights the need for additional, highly tempo-
rally resolved studies of large and small sediment-
routing systems.
Southern California Sediment-Routing System
and Holocene Climate
The southern California sediment-routing system
of this study includes the onshore Santa Ana River
watershed, which drains steep, tectonically active
terrain of the Peninsular Ranges and the San Ga-
briel and San Bernardino mountains of the Trans-
verse Ranges and the Newport deep-sea deposi-
tional system of the California borderland
(Normark et al. 2009; fig. 1). The California bor-
derland is the tectonically active region offshore
southern California characterized by a relatively
narrow shelf and complex basin-and-ridge bathym-
etry (Shepard and Emery 1941; Ryan et al. 2009).
The Newport deep-sea system includes a tributary
network of canyons and channels that coalesce at
∼600 m below present sea level (m bpsl) in the Gulf
of Santa Catalina, which is a basin of the inner (i.e.,
landward) segment of the borderland (Normark et
al. 2009; fig. 1). The Newport channel exhibits a
serpentine morphology around prominent knolls,
and it spills into a seaward basin at ∼800 m bpsl
(fig. 1). Normark et al. (2009) indicated that the
Newport canyon-and-channel system is longer
(∼130 km) than other systems on the seafloor of the
borderland. Today, a single canyon head of the
Newport tributary network is connected to the
Santa Ana River mouth (Warrick and Milliman
2003; Normark et al. 2009; fig. 1). Normark et al.
(2009) interpreted that this single canyon received
sediment from fluvial effluents and mass-wasting
processes in the canyon and steep outer shelf during
the Holocene marine transgression and highstand
based on lack of hemipelagic sediment draping the
canyon floor and U.S. Geological Survey piston
cores containing recently deposited turbidites (Nor-
mark et al. 2009). The contribution and timing of
fluvial effluents relative to mass-wasting processes
in the canyon and steep outer shelf to the initiation
of sediment gravity flows in the Newport system
are unknown. However, it is likely that a variety
of sediment-gravity-flow initiation mechanisms—
from earthquakes associated with the tectonically
active borderland setting to hyperpycnal sediment-
laden fluvial effluents and deltaic sediment buildup
and failure—contributed to the excavation of New-
port Canyon (cf. Normark et al. 2009; Piper and
Normark 2009; Romans et al. 2009).
The sediment flux from the Santa Ana River is
among the largest fluxes reported for semiarid
southern California rivers measured during the
twentieth century, during which time its discharge
achieved hyperpycnal concentrations of suspended
sediment during El Nin˜o–Southern Oscillation
(ENSO)-induced flood events (Warrick and Milli-
man 2003). The steep terrain of the Santa Ana River
drainage basin predominantly includes relatively
resistant Jurassic and Cretaceous plutonic rocks of
the Peninsular Ranges and the relatively uncon-
solidated Tertiary and Quaternary sediment and
sedimentary rocks of the Transverse Ranges (Inman
and Jenkins 1999). The Newport Canyon head also
receives a relatively small proportion of sediment
from longshore currents of the San Pedro littoral
cell (Masters 2006; Normark et al. 2009; fig. 1).
Southern California climate has been directly
monitored since the nineteenth century, a time pe-
riod too brief to provide an understanding of cli-
matic variability and forcing mechanisms overmil-
lennial durations. Proxy measurements from lake
sediment are commonly employed in order to re-
construct climate of the more distant past, such as
the Holocene epoch (Stokstad 2001). However, lo-
cal lake conditions can limit the applicability of
such proxy records across a broad geographic area
(Verschuren 2003). Climate proxies, includingmag-
netic susceptibility, HCl-extractable Al, total in-
organic P, total organic matter, and CaCO3 per-
centage, from drill cores in Lake Elsinore of the
relatively small San Jacinto River drainage basin
(!1,240 km2; fig. 1) provide the first complete Ho-
locene record of terrestrial climate in southern Cal-
ifornia (Kirby et al. 2007; fig. 2). Figure 2 shows
plots of these climate proxy measurements, which
Kirby et al. (2007) interpreted to represent onshore
southern California variability in precipitation and
sediment flux since 9.5 ka (see also Kirby et al.
2004). These, and other, proxy measurements were
rigorously quantified in order to make qualitative,
relative estimates of paleoclimate (Kirby et al.
2007). Therefore, precise numbers of climatic var-
iability, such as precipitation or fluvial discharge,
are not available. There is a plethora of information
available for twentieth-century precipitation and