Coarse-grained sediment delivery and distribution in the Holocene Santa Monica Basin, California: Implications for evaluating source-to-sink flux at millennial time scales

Abstract

Utilizing accumulations of coarse-grained terrigenous sediment from deep-marine basins to evaluate the relative contributions of and history of controls on sediment fl ux through a source-to-sink system has been diffi cult as a result of limited knowledge of event timing. In this study, six new radiocarbon ( 14 C) dates are integrated with fi ve previously published dates that have been recalibrated from a 12.5-m-thick turbidite section from Ocean Drilling Program (ODP) Site 1015 in Santa Monica Basin, offshore California. This borehole is tied to highresolution seismic-refl ection profi les that cover an 1100 km 2 area of the middle and lower Hueneme submarine fan and most of the basin plain. The resulting stratigraphic framework provides the highest tem poral resolution for a thick-bedded Holocene turbidite succession to date, permitting an evaluation of source-to-sink controls at millennial (1000 yr) scales.The depositional history from 7 ka to present indicates that the recurrence interval for large turbidity-current events is relatively constant (300-360 yr), but the volume of sediment deposited on the fan and in the basin plain has increased by a factor of 2 over this period. Moreover, the amount of sand per event on the basin plain during the same interval has increased by a factor of 7. Maps of sediment distribution derived from correlation of seismic-refl ection profi les indicate that this trend cannot be attributed exclusively to autogenic processes (e.g., progradation of depocenters). The observed variability in sediment accumulation rates is thus largely controlled by allogenic factors, including: (1) increased discharge of Santa Clara River as a result of increased magnitude and frequency of El Niño-Southern Oscillation (ENSO) events from ca. 2 ka to present, (2) an apparent change in routing of coarse-grained sediment within the staging area at ca. 3 ka (i.e., from direct river input to indirect, littoral cell input into Hueneme submarine canyon), and (3) decreasing rates of sea-level rise (i.e., rate of rise slowed considerably by ca. 3 ka). The Holocene history of the Santa Clara River-Santa Monica Basin source-to-sink system demonstrates the ways in which varying sediment fl ux and changes in dispersal pathways affect the basinal stratigraphic record.

Estimation of the paleoflux of terrestrial-derived solids across ancient basin margins using the stratigraphic record

“…Sedimentation rates vary spatially within a basin due to depositional settings, basin geometry, shear-stress distributions, and loss of sediment fl ux due to deposition elsewhere in the basin (Sadler, 1981;Métivier, 2002;McCave and Swift, 1976;Pirmez et al, 1998). Linear rates from cores, measured sections, or well data may be unrepresentative of the complexity of sediment distribution patterns (Molnar, 2004), though Romans et al (2009) have shown a linear relationship between deposit thickness and deposit volumes in a simple basin-fl oor fan environment in the Santa Monica Basin. The linkage of thickness and volume works in this case because the available terrestrial-derived sediment is entirely deposited within the basin-fl oor fan (i.e., q s goes to zero at the distal end of the system, and characteristic thinning rates, governed by transport processes, lead to the observed relationship).…”

“…Sediment is primarily transported across the shelf-margin topset in two ways: (1) via shallow-marine processes driven by wind, waves, tides, storms, and currents (Kuehl et al, 1986(Kuehl et al, , 1989Niedoroda et al, 1995;Pirmez et al, 1998;Paola, 2000;Imran and Syvitski, 2000), or (2) by deltaic shoreline progradation across the topset to the shelf edge (Burgess and Hovius, 1998;Porębski and Steel, 2003). Sedimentation on modern continental margins is especially concentrated near the shoreline (Swift and Thorne, 1991), with only minor fractions of the total sediment budget contributing to the growth of the margin beyond the shelf edge, except in cases where the shelf is narrow enough to allow interaction of the shelf edge with shelfal transport mechanisms (e.g., Walsh and Nittrouer, 2003;Boyd et al, 2008;Romans et al, 2009). This pattern of sediment fl ux does not match observations of large-scale and long-term growth of continental margins in the rock record, which require large volumes of sediment delivery to the slope to drive margin progradation.…”

Highstand vs. lowstand turbidite system growth in the Makran active margin: Imprints of high-frequency external controls on sediment delivery mechanisms to deep water systems

“…Typically, small to mid-size turbidite systems associated with narrow shelves can be strongly influenced by local hydro-climatic parameters (such as hyperpycnal flows, interceptions by canyons of active longshore drift, or a combination of them). This lead to active turbidite system activity during highstands conditions, well illustrated in the California borderland fans (Piper et al, 1999;Covault et al, 2007;Romans et al, 2009) or the Var turbidite system (Mulder et al, 1998). Minor but effective highstand turbidite activity is also observed in large, mud-rich turbidite systems where canyons deeply incise the shelf and are still located close to the river mouth (i.e.…”

Evolution of deep-water stratigraphic architecture, Magallanes Basin, Chile

“…Long-term (>10 6 yr) and large-scale (>10 5 km 3 ) basin-fill patterns are commonly evaluated with extensive field mapping or subsurface datasets that combine regional stratigraphy from seismic-reflection data and lithologic and age information from boreholes (e.g., Williams et al, 1998;Galloway et al, 2000;Hadler-Jacobsen et al, 2005;Martinsen et al, 2005;Gardner et al, 2008). The terminal segment of basin-margin sedimentary systems are commonly represented by deep-water turbidites and, as such, preserve relatively complete records of sedimentation, with evidence for variability of external controls in source areas or other segments of the dispersal system (e.g., Normark and Piper, 1991;Einsele et al, 1996;Mutti et al, 2003;Allen, 2008;Covault et al, 2007;Romans et al, 2009a). Documentation of extensive deep-water outcrop belts over the past decade has led to improved understanding of turbidite system architectures and their evolution through time (Gardner et al, 2003(Gardner et al, , 2008Mutti et al, 2003;Hodgson et al, 2006;Pickering and Bayliss, 2009;Flint et al, 2011;Khan and Arnott, 2011;Kane and Hodgson, 2011;Pyles et al, 2011;Tinterri and Muzzi-Magalhaes, 2011).…”