Potential role of event-driven sediment transport on sediment accumulation in the Cariaco Basin, Venezuela

Marine Geology xxx (2012) xxx–xxx

MARGO-04738; No of Pages 6

Contents lists available at SciVerse ScienceDirect

Marine Geology

j ourna l homepage: www.e lsev ie r .com/ locate /margeo

Letter

Potential role of event-driven sediment transport on sediment accumulation in theCariaco Basin, Venezuela

Laura Lorenzoni a,⁎, Claudia R. Benitez-Nelson b,c, Robert C. Thunell b,c, David Hollander a, Ramón Varela d,Yrene Astor d, Franck A. Audemard e, Frank E. Muller-Karger a

a College of Marine Science, University of South Florida, St. Petersburg, FL 33701, United Statesb Department of Earth & Ocean Sciences, University of South Carolina, Columbia, SC 29208, United Statesc Marine Science Program, University of South Carolina, Columbia, SC 29208, United Statesd Estación de Investigaciones Marinas de Margarita (EDIMAR), Fundación La Salle de Ciencias Naturales (FLASA), Isla de Margarita, Venezuelae Venezuelan Foundation for Seismological Research (FUNVISIS), Apartado Postal 76880, Caracas 1070-A, Venezuela

⁎ Corresponding author at: University of South Florida7th Ave. S. St. Petersburg, FL 33701, United States. Tel.: +553 1103.

E-mail address: [email protected] (L. Lorenzoni

0025-3227/$ – see front matter © 2012 Elsevier B.V. Alldoi:10.1016/j.margeo.2011.12.009

Please cite this article as: Lorenzoni, L., et asin, Venezuela, Mar. Geol. (2012), doi:10.10

a b s t r a c t

Article history:Received 8 June 2011Received in revised form 23 December 2011Accepted 27 December 2011Available online xxxx

Communicated by: J.T. Wells

Keywords:episodic eventsediment transportsediment density flowCariaco Basincontinental organic carbonManzanares Submarine Canyon

A sediment density flow was observed in the eastern Cariaco Basin during September 2008. Evidencesuggests that this flow was likely triggered by a magnitude 5.2 earthquake that occurred on August 11,2008, with an epicenter located at 10.51°N, 64.17°W (off the city of Cumaná, Venezuela). Elevated suspendedsediments near the bottomwere observed at the mouth of the Manzanares Canyon (>90 g m−2, over a depthof 165 m) and decreased to ~11 g m−2 (over a depth of 40 m) 42 km away from the canyon's mouth at theCARIACO Ocean Time-Series site. The sediment flux associated with this single event was ~10% of the totalannual sediment flux that typically reaches the Cariaco Basin deep seafloor. Carbon to nitrogen ratios and iso-tope composition confirm that most of the organic matter transferred by the sediment flow was of continen-tal origin (C/N ratios of ~17.67, δ13C of −27.04‰, and δ15N of 6.83‰). Our observations contribute to thegrowing body of evidence that suggests that submarine canyons are rapid, efficient sediment conduits of par-ticles from shallow to deep waters, and that they should be included in efforts to constrain estimates ofsediment and terrestrially derived carbon transport from the continental shelves to the deep ocean.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

Small mountainous rivers (SMRs), defined as those rivers thathave headwaters at an elevation of more than 1000 m (Millimanand Syvitski, 1992), play a key role in the transport of terrestrially-derived sediment and organic carbon (OC) to the coastal ocean(Milliman and Syvitski, 1992; Syvitski and Milliman, 2007). Yet theultimate fate of this OC remains controversial, despite its role in oxy-gen accumulation and as a potential sink for atmospheric CO2 overgeologic time (Burdige, 2007). For example, several studies suggestthat much of the river-transported terrestrial OC that is depositedon the continental margin is efficiently remineralized due to a combi-nation of remobilization and oxidation (e.g. Burdige, 2005; Aller andBlair, 2006). In contrast, in regions dominated by high erosion, highsedimentation and/or limited sediment oxidation, such as the BengalFan, continentally derived OC appears to be stored much more effec-tively (Milliman and Syvitski, 1992; Masiello, 2007; Hilton et al.,2008).

, College of Marine Science, 1401 727 553 1186; fax: +1 727

).

rights reserved.

l., Potential role of event-driv16/j.margeo.2011.12.009

Smaller rivers also are more likely to experience episodic eventssuch as floods, where the sediment and OC discharged to the sea withina narrow timeframe is considerable (Mulder and Syvitski, 1995;Warrick and Milliman, 2003; Milliman et al., 2007; Alin et al., 2008).The magnitude of this sediment discharge, as well as OC delivery andburial efficiency, is not well constrained due to both insufficient moni-toring and the highly episodic nature of discharge events (e.g.Milliman, 1995; Warrick and Milliman, 2003; Hicks et al., 2004; Alinet al., 2008; Goldsmith et al., 2008; Hilton et al., 2008). This lack ofknowledge is further exacerbated by the fact thatmany SMRs dischargeonto narrow, activemargins and/or directly intomarine canyons, whichhelp transport the sediment directly offshore (Paull et al., 2003; Puig etal., 2003; Palanques et al., 2008;Xu et al., 2010). Along seismically activemargins, earthquakes can cause slope failure and turbidity currents,particularly in areas of unstable sediment accumulation such as alluvialdeposits (Dadson et al., 2004; Syvitski andMilliman, 2007; Goldsmith etal., 2008), greatly increasing the supply of sediments to the ocean(Dadson et al., 2003; Eberhart-Phillips et al., 2003; Fine et al., 2005;Shirai et al., 2010).

Here we present observations of a turbidity flow in the ManzanaresCanyon (Venezuela) during 2008. We explore the nature and implica-tions of this event in terms of source material and mass transport tothe interior of the basin, and its potential impact on the interpretation

en sediment transport on sediment accumulation in the Cariaco Ba-

2 L. Lorenzoni et al. / Marine Geology xxx (2012) xxx–xxx

of paleoclimate records from the eastern Cariaco Basin, a tectonicallyactive area where terrigenous sediment delivery is dominated by SMRs.

2. Regional setting

Northeastern Venezuela is the most seismically active region ofthe country (Audemard, 2007). The Cariaco Basin, located betweenCabo Codera and the Araya Peninsula (Fig. 1; Schubert, 1982) likelyowes its origins to tectonic activity. The Cariaco Basin contains twosub-basins, each approximately 1400 m deep and divided by a saddleof about 900 m. The basin is separated from the open Caribbean Seaby two shallower sills (b145 m). West of the city of Cumaná lies theManzanares Submarine Canyon, which connects the Gulf of Cariacoto the eastern Cariaco Basin.

Morelock et al. (1972) estimated that the Manzanares Canyonformed during the Pleistocene and linked its origin to the El PilarFault. The El Pilar fault system is a right-lateral strike–slip fault locatedin the northeast region of Venezuela that extends ~350 km in an ap-proximately E–W direction, roughly parallel to the coast (Audemard,2007).More recent seismic surveys suggest that the canyon is not locat-ed on the active trace of the El Pilar fault (FUNVISIS, 1994). Rather,the canyon seems to have been carved by downslope sediment flows,with sediment failure in the head and walls linked to earthquakeshocks (González et al., 2004; Audemard, 2006; 2007).

The Manzanares Canyon head opens at a depth of 50 m, about 2 to3 km off the mouth of the Manzanares River, slightly to the west ofthe city of Cumaná. The Manzanares River is a SMR that drains theSerranía del Interior formation, part of the Cordillera de la Costa, com-posed of Mesozoic metamorphic and igneous rocks. Nearshore cur-rents transport river sediments to the west of the river mouth, andmost of this material is trapped by the Manzanares Canyon (Mora etal., 1968). The predominant sediments in the upper canyon are silt,clay, and coarse sand of continental origin (Morelock et al., 1972;

Fig. 1. Bathymetric map of the study area. The Manzanares Canyon, Manzanares River, the G11, 2008, earthquake. Triangles show the CARIACO Ocean Time-Series site (Station 1) and

Please cite this article as: Lorenzoni, L., et al., Potential role of event-drivsin, Venezuela, Mar. Geol. (2012), doi:10.1016/j.margeo.2011.12.009

Morelock, 1982). While most of the sediment found in the canyoncomes from the Manzanares River, the Gulf of Cariaco (Fig. 1)also contributes sediment (Mora et al., 1968; Caraballo, 1982). Thesesediments are derived from the Cautaro and the Cariaco Rivers, aswell as from several smaller seasonal rivers (arroyos) (Gade, 1961;Caraballo, 1982; Audemard et al., 2007).

The Cariaco Basin is influenced regularly by shifts in position of theIntertropical Convergence Zone (ITCZ). During the first fewmonths ofthe boreal year the basin experiences the dry season, characterized bystrong Trade Winds and little to no precipitation. Starting in May, theposition of the ITCZ migrates northward and precipitation increasesin northern Venezuela. River runoff peaks between August andSeptember (Márquez et al., 2002; Peterson and Haug, 2006). Regret-tably, none of the rivers that drain into the Cariaco Basin are currentlygaged; hence precipitation records have been used as a proxy of flu-vial discharge (Lorenzoni et al., 2009). For the Manzanares River,the precipitation measured at the city of Cumaná reflects the magni-tude of river discharge (Márquez et al., 2002), with discharge ratesusually lagging the peak in precipitation by one month (e.g., precipi-tation at Cumaná peaks during August, while river discharge peaksduring September).

3. Materials and methods

Hydrographic and light beam attenuation data were collected atthe CARIACO Ocean Time-Series site in the eastern Cariaco Basin(10°30′ N; 64°43′ W; water depth of 1400m) and at the mouth of theManzanares Canyon (10°30′ N; 64°22′ W; water depth of 1000 m,Fig. 1) between September 1–5, 2008, roughly three weeks after a mag-nitude (M) 5.2 earthquake occurred near Cumaná, Venezuela (10.51°N,64.17°W) on August 11, 2008. The mouth of the Manzanares Canyon islocated ~42 km east of the CARIACO Ocean Time-Series site. The beamattenuation coefficient of light at a wavelength of 660 nm (cp(660),

ulf of Cariaco, and the city of Cumaná are shown. Star shows the epicenter of the Augustcanyon mouth (Station 2) locations.

en sediment transport on sediment accumulation in the Cariaco Ba-

3L. Lorenzoni et al. / Marine Geology xxx (2012) xxx–xxx

m−1) was measured using a Wet Labs C-Star transmissometer with25 cm pathlength attached to a Seabird SBE25 CTD. The transmissome-ter provides a measure of water turbidity due to particles since attenua-tion by dissolved materials is negligible at 600 nm (Boss et al., 2001;Behrenfeld and Boss, 2003). The ensemble was mounted on a rosetteequipped with twelve 8 L Niskin bottles. Suspended particulate mat-ter (SPM) samples were collected within a layer of suspended sedi-ments detected using the transmissometer at the canyon mouth, at870 m depth. Water was drained into acid-cleaned containers(5 gal) and filtered through pre-combusted (450 °C for 5 h), pre-weighed GF/F filters, using an in-line polycarbonate filter holderand a submersible pump. Approximately 15 L of water were filteredthrough three to four different filters. Water was gently stirred dur-ing filtration to avoid flocculation and accumulation of suspendedmatter on the bottom of the container. Filters were refrigerated at4 °C until further analysis (~2 weeks).

In the laboratory, the filters were vacuum-rinsed with Milli-Qwater to remove salts, and dried for 8 h at 60 °C before re-weighing.SPM (g m−3) was calculated as the difference between the initialand final weight divided by total volume filtered (between 3 and6 L per filter). Filters were then acid washed under vacuum with a1 M solution of H3PO4 to remove any carbonate that might havebeen present. Particulate organic carbon (POC), particulate nitrogen(PN), and stable isotopic composition (δ13C, δ15N), were measuredsimultaneously using a Fison NA 1500 Elemental Analyzer at theUniversity of South Florida (USF) using previously established meth-odology (Werne and Hollander, 2004; Thunell et al., 2007).

4. Results

Highest beam attenuation (cp=~0.15 m−1) was observed at theManzanares Canyon (hereafter referred to as the canyon mouth) be-tween 850 and 870 m depth, within a suspended sediment layer thatspanned from the seafloor at 1000 m to ~815 m depth (Fig. 2). Out-side this turbid layer, cp was almost an order of magnitude lower(~0.025 m−1), comparable to values measured repeatedly in thebasin as part of the CARIACO Ocean Time-Series program (http://www.imars.marine.usf.edu/CAR/). At the CARIACO Ocean Time-Seriessite (hereafter referred to as the CARIACO site), we observed a layer ofhigh beam attenuation between 1215 and 1255 m, which is ~150 mabove the seafloor (Fig. 2). The cp peak in this layer was 0.078 m−1,about half of the peak value measured in the sediment layerwithin the canyon mouth. This value is almost three times higher

Fig. 2. Transmissometer profiles collected at the CARIACO Ocean Time-Series site (seg-mented line) and at the canyon mouth (black line) during September 2008. Thick grayline indicates 2-year average (2006–2008) of beam attenuation data at the CARIACOTime-Series site; gray shadow indicates standard deviation.

Please cite this article as: Lorenzoni, L., et al., Potential role of event-drivsin, Venezuela, Mar. Geol. (2012), doi:10.1016/j.margeo.2011.12.009

than the cp normally observed at similar depths in the Cariaco Basin(0.025±0.007 m−1).

Other features of the beam attenuation profile at the CARIACO sta-tion (Fig. 2) reflect the microbial community located at the oxic–an-oxic interface (peak at 200–320 m; Thunell et al., 1999; Taylor et al.,2001) and intermediate nepheloid layers (INL's) (between 120 and170 m); the latter have been observed previously and determinedto be of continental origin (Lorenzoni et al., 2009). Closer to the sur-face, high variability in particle concentrations was likely due tochanges in phytoplankton concentrations and assemblage (cp wasproportional to chlorophyll fluorescence, data not shown). AveragePOC and PN concentrations within the suspended sediment layer atthe canyon mouth were 0.128±0.01 g C m−3 (n=3) and 0.008±0.002 g N m−3 (n=3), respectively. C/N ratios in the sediment plumeat the canyon mouth averaged 16.4±2.2 (Table 1). The δ13C withinthe sediment layer averaged−27.04‰, whereas the δ15N was ~6.83‰.

A strong correlation between SPM and beam attenuation data wasobserved using the data collected during September 2008 (R2=0.82,N=16; αb0.01). This relationship was subsequently used to deter-mine SPM integrated over the depth of the observed suspended sed-iment layers at both the canyon mouth and the CARIACO site. Depth-integrated SPM at the canyon mouth (over 165 m) was ~90 g m−2,while at the CARIACO site it was ~11 g m−2 (over 40 m). Unfortunately,the suspended sediment layer was below the deepest sediment trap(1200 m) maintained at the CARIACO Ocean Time-Series site (Thunellet al., 2007). Thus, no additional particulate matter from this eventwas captured by the sediment trap located at ~1200 m.

5. Discussion

There are no significant currents in the deep portions of the Car-iaco Basin that resuspend sediments (Alvera-Azcárate et al., 2009).Monthly transmissometer profiles collected as part of the CARIACOtime series indicate that normally there are no nepheloid layers im-mediately above the sea-floor (http://www.imars.marine.usf.edu/CAR/). As a result, the water below 400 m is typically very clear andhomogenous (Virmani and Weisberg, 2009). Therefore, we suggestthat the suspended sediment layers observed during September2008 at the CARIACO site and at the mouth of theManzanares Subma-rine Canyon (Fig. 1) were the result of an event-driven sediment den-sity flow. This is the second time since the beginning of the CARIACOOcean Time-Series Program in November 1995 that turbidity layershave been observed near the bottom of the basin. In July 1997, a400 m thick turbidity layer located immediately above the bottomat the CARIACO site, was observed after a M6.8 earthquake strucknortheastern Venezuela on July 09, 1997 (Thunell et al., 1999;Audemard, 2006). High suspended particle loads of more than1.0 mg L−1 persisted at the bottom of the CARIACO site for morethan four months.

Submarine canyons are widely recognized as important conduits forthe transport of terrestrially-derived material from continental shelves

Table 1Geochemical variables measured in the canyon mouth turbidity plume (870 m).Average values±standard deviations of variables collected at the CARIACO OceanTime-Series site at 1310 m between 1996 and 2007 are also shown. SPM data for theCARIACO Time-Series site was estimated using the cp relationship described in the text.

CARIACO Time-Series site Manzanares Canyon turbidity plume

SPM (g m−3) 0.10±0.05 (N=25) 1.00±0.13 (N=3)POC (g C m−3) 0.05±0.01 (N=113) 0.128±0.01 (N=3)PN (g N m−3) 0.007±0.02 (N=113) 0.008±0.002 (N=3)C/N 8.46±4.61 (N=113) 16.4±2.2 (N=3)δ13C (o/oo) −20.7a −27.04±1.45 (N=3)δ15N (o/oo) 3.50b 6.83±0.31 (N=3)

a From Woodworth et al. (2004).b From Thunell et al. (2004).

en sediment transport on sediment accumulation in the Cariaco Ba-

4 L. Lorenzoni et al. / Marine Geology xxx (2012) xxx–xxx

to the deep ocean. (Mullenbach and Nittrouer, 2000; Johnson et al.,2001; Paull et al., 2003; Liu and Lin, 2004; Xu et al., 2010). Eventsthat enhance continentally-derived organicmatter and sediment trans-port, such as storms (Dadson et al., 2003; Palanques et al., 2008), denseshelfwater cascading (Canals et al., 2006), or turbidityflows to the deepocean are critical, since the organic matter injected into the deep sea isnot remineralized but buried. Thus, this organic material ceases to bepart of the present day global carbon cycle.

Within submarine canyons, turbidity flows can be gravity-driven,resulting from energetic events such as earthquakes (Hilton et al.,2008), or flow-driven, induced by storms and floods, among othermechanisms (Canals et al., 2006; Palanques et al., 2008). The lattermechanism is particularly important if the river mouth is locatednear the canyon head, as the river plume can be advected directlyinto the canyon in the form of a hyperpycnal plume (Mulder andSyvitski, 1995; Johnson et al., 2001; Liu et al., 2008). Hyperpycnalflows, negatively buoyant subsurface freshwater plumes, containhigh suspended sediment loads (usually in the order of tens ofgrams per L) that can be deposited inside the canyon and later remo-bilized (e.g., Kineke et al., 2000; Mullenbach and Nittrouer, 2000) orcan be funneled directly to the canyon mouth, if the density differ-ence and velocity are sufficient (e.g., Johnson et al., 2001; Paull etal., 2003). Hyperpycnal flows have never been directly observed inthe Cariaco Basin, largely because these events are generally short-lived and there is a lack of monitoring along the small rivers that sur-round the basin. Nonetheless, it is likely that such hyperpycnal flowshave occurred, linked to anomalous precipitation events that have in-duced massive river flooding, such as in November–December, 1999.In this case, the mixture of “Nortes” (Lyon, 2003) and La Niña condi-tions in the Equatorial Pacific facilitated the setting for sustained, tor-rential rains along Cordillera de la Costa. In the Cariaco Basin, atthe location of the CARIACO site, the delivery of sinking terrigenousflux increased six-fold during the 1999 flood, from an average of10.45 g m−2 month−1 (measured in the 225 m depth sediment trap)to 69.34 g m−2 month−1 (http://www.imars.marine.usf.edu/CAR/).During November–December 2010, a similar event was observed,where precipitation along the Venezuelan coast increased threefold.Unfortunately, there is no corresponding measure of beam attenuationor sediment trap fluxes for that period.

In order to determine whether the sediment plume observed inSeptember 2008 was caused by a hyperpycnal flow induced by anom-alously large river discharge, the precipitation record measured atCumaná for the month of August for the period 1967–1992 and1998–2010 was analyzed (all available data, NCDC, 2011; MINAMB,2011). The average August precipitation for this period was 88±60 mm. During August 2008 precipitation recorded at Cumanáwas 147 mm (NCDC), within the standard deviation of the precipita-tion record. In September 2008 there was no visible evidence of ahyperpycnal layer near the mouth of the Manzanares River, which isnot surprising, considering that hyperpycnal flows tend to be short-lived events (Milliman and Kao, 2005).

An alternative explanation for the observed suspended sedimentevent is that it was seismically triggered, either by the M5.2 earth-quake that took place on August 11, 2008, at 10° 30.60′ N and 64°10.20′ W (FUNVISIS, 2008) and/or by the aftershock of M3.0 thatoccurred in roughly the same location half an hour later. It is possiblethat post-seismic erosion rates near the Gulf of Cariaco and Cumanáincreased after the earthquake, due to seismically-induced landslides,but it is unlikely that this material contributed to the sediment plumeobserved near the canyon mouth. Sediment that is seismically weak-ened is generally flushed to the rivers and ultimately to the ocean bystorm runoff (Dadson et al., 2003, 2004), but as mentioned earlier,precipitation in Cumaná during the month of August was within his-torical values.

During July 1997, the turbidity flow was observed by Thunell et al.(1999) one week after the M6.8 earthquake. Data from the day before

Please cite this article as: Lorenzoni, L., et al., Potential role of event-drivsin, Venezuela, Mar. Geol. (2012), doi:10.1016/j.margeo.2011.12.009

the earthquake (July 8th) showed no sediment near the sea-floor ofthe Cariaco Basin. This suggests that sediment remobilization oc-curred shortly after the earthquake. Whether part of the sedimentin the turbidity flow observed in 1997 originated from co-seismiclandslides is not known, but if this was the case, it is likely that itwas mobilized by hyperpycnal plumes. Average precipitation for theentire month of July was 121 mm, above the historical (1967–1992;1998–2010) average of 64±45. During the July 16 sampling at theCARIACO site there was no indication of a hyperpycnal layer. The sus-pended sediment layer near the sea-floor was still visible in Novem-ber 1997 (http://www.imars.marine.usf.edu/CAR/). Similar to 1997,the suspended sediment layer after the 2008 earthquake persistedthrough December 2008.

SPM concentrations estimated near the bottom at the canyonmouth (1.0 g m−3, Table 1) were similar to SPM measurements ob-served in the high turbidity layer after the 1997 earthquake at theCARIACO site (Thunell et al.; 1999). Unfortunately, for September2008, we only have the observations at the canyon mouth and atthe CARIACO site. We used these observations along with the beamattenuation data to calculate the amount of sediment within the tur-bid layer. At the canyon mouth, ~ 90 g m−2 was estimated to be with-in the sediment plume, while at the CARIACO site this decreased to~11 g m−2. This latter estimate represents ~10% of the total averageannual vertical sinking flux measured at 1200 m at CARIACO. Sinceour observations were made several weeks after the earthquake,these earthquake-related suspended sediment concentrations shouldbe regarded as minimum estimates.

It is difficult to calculate the total amount of sediment deliveredto the deep Cariaco Basin by the August 2008 earthquake. Sedimenta-tion rates in the eastern Cariaco Basin, estimated using sediment traps(Thunell et al., 2000), are on the order of 180,000 t of sediment peryear. Thunell et al. (1999) found that approximately 145,000 t ofsediment were transported into the basin after the large (M6.8) earth-quake of July 9, 1997; this is 80% of the typical annual vertical sinkingflux measured at 1200 m. However, they assumed sediment loads tobe relatively low and uniformly distributed below the 1100 m isobath.Our 2008 observations showed significantly higher sediment concen-trations near the canyon mouth. If we assume that the 1997 event hada similar spatial distribution as that of 2008, then the amount of mate-rial delivered during the 1997 event may have been twice as largeas that estimated previously.

Average POC concentrations within the suspended sediment layerat the canyonmouth were almost three times higher than the average(1996–2007) monthly suspended POC concentrations measured at1310 m at the CARIACO site. Moreover, the POC measured at the can-yon mouth was about 10% of the SPM within the turbidity plume, anorder of magnitude higher that the POC estimated to be transportedby regional rivers to the ocean (Ludwig et al., 1996). PN concentra-tions within this sediment layer were similar to average PN valuestypically measured prior to the turbidity event. Therefore, the C/N ra-tios in the sediment plume at the canyon mouth were 16.4±2.2, orabout twice the average C/N value for sinking particles at 1200 m atthe CARIACO site. This is significantly higher than the predicted Red-field C/N ratio for marine organic matter (around 6–7, Hedges et al.,2002), which suggests this material was of continental origin.

The carbon and nitrogen isotopic composition of material withinthe suspended sediment layer at the canyon mouth is also indicativethat the POC transported into the deep basin was primarily landderived. The δ15N at the canyon (average of ~6.83‰) was higher thanthat normally seen at similar depths at the CARIACO station (~3.50‰;Thunell et al., 2004). A similar increase in δ15N, from an average of3.50‰ to ~5.70‰, in the deepest CARIACO sediment trap (1210 m)was also observed by Thunell et al. (2004) after the strong 1997 earth-quake. The δ13C (average of −27.04‰) was depleted relative to valuesobserved normally at the CARIACO site (−20.7‰; Woodworth et al.,2004), with the latter being typical of marine organic carbon. Recent

en sediment transport on sediment accumulation in the Cariaco Ba-

5L. Lorenzoni et al. / Marine Geology xxx (2012) xxx–xxx

studies by Hilton et al. (2010, 2011) suggest that a significant portion ofterrestrial POC transported to the ocean by SMRs is fossil POC from ex-posed bedrock, and that this fraction has a δ13C range that overlaps thatof modern POC. Hilton et al. (2011) further hypothesized that the higherosion rates of coastal mountain ranges result in efficient transport ofthis fossil OC into marine sediments withminimal oxidation. The directfunneling of continental POC by submarine canyons can further en-hance this transport. Though the carbon content of the Serranía del In-terior is relatively high (1–6%; Alberdi and LaFargue, 1993; Tocco et al.,1994), there is no data available on the isotopic composition of this geo-logic formation or the relative fraction of modern versus fossil OC con-tained in the sediment flow. Thus Hilton's hypotheses cannot beconfirmed or ruled out in this region.

There is significant evidence of earthquake-induced turbidityflows over geologic time in the Cariaco Basin. Sediment cores andseismic surveys of the canyon in the 1960s indicated that turbiditycurrent deposition and slumping are common features (Morales andOttmann, 1961; Morelock et al., 1972) as further documented byThunell et al. (1999). Large turbidites, as well as microturbidites,have further been identified in the sediment record in the CariacoBasin. Turbidites have previously been attributed to seismic activity,with the largest turbidites corresponding to earthquakes in 1900and 1929 (Hughen et al., 1996). Since turbidite deposition in theCariaco Basin does not seem to erode the underlying sediment, theycould serve as paleoseismic records for the region (Thunell et al.,1999; Carrillo et al., 2008; Goldfinger, 2011).

Over 60 seismic events of M4–M5 have been recorded in north-eastern Venezuela since 1996 in the area of Cumaná and the CariacoBasin. Such events may provide the necessary weakening of substratematerial and the trigger for the rapid mobilization of continentally-derived materials temporarily deposited at the head of the Manza-nares Canyon. Thus, the Manzanares Canyon is likely to be an impor-tant source of sediments to the eastern Cariaco Basin and has thepotential of funneling large quantities of terrestrially-derived organicmatter down-canyon and effectively sequestering carbon on millen-nial time scales.

6. Conclusions

Event-driven downslope mobilization of sediment is an importantmeans of continental OC sequestration and burial. A sediment densityflow was observed within the Cariaco Basin during September 2008,the possible result of an earthquake that struck near the city ofCumaná, Venezuela, on August 11th, 2008. This single event trans-ported an estimated 10% of the average annual sediment flux to theseafloor of the Cariaco Basin. Furthermore, the OC within the sedi-ment plume appeared to be predominantly continentally-derived,reinforcing the hypothesis that turbidity flow events are significantsources of terrestrial carbon and sediment to the deep ocean.

The Manzanares River mouth is located at the head of the canyon,and likely supplies most of the fine grained sediments and fresh car-bon that accumulate in the upper part of the canyon. This suggeststhat the canyon is an active depositional center, and its proximity tothe Manzanares River and Cariaco Basin is critical for sediment supplyoffshore.

The continental material estimated to have been delivered to thedeep Cariaco Basin as a result of the sediment density flow is basedonly upon twomeasurements obtained almost a month after the seis-mic event. If we use these observations and assume a linear decreasein concentration and sediment plume thickness, and integrate theSPM over the entire area of the eastern sub-basin below 1000 m (ap-proximately 1200 km2), we can loosely estimate that ~50,000 t ofsediment and ~6600 t of POC delivered to the deep portion of thebasin is a result of the sediment density flow. This would representapproximately a third of the average vertical sinking flux of sedimentand POC that normally reaches the Cariaco Basin seafloor annually, all

Please cite this article as: Lorenzoni, L., et al., Potential role of event-drivsin, Venezuela, Mar. Geol. (2012), doi:10.1016/j.margeo.2011.12.009

delivered during a single event. However, it is very difficult to accu-rately assess the amount of sediment and carbon that reached thedeep basin based solely on these observations. In order to correctlyassess the transport of continentally derived material through theManzanares Canyon, a more permanent observing system with si-multaneous points of observation is required. This would enable epi-sodic events to be captured when they occur and the ability toaccurately measure the magnitude of material delivered to the deepbasin.

Though there are other means of shelf to canyon sediment trans-port, earthquake-induced turbidites are uniquely preserved in thesediment record of the basin. Their study may provide insight intoearthquake recurrence rates in Cariaco Basin, and help advance ourunderstanding of carbon sequestration dynamics near margins thatare affected by such episodic events. These observations emphasizethe importance of submarine canyons as sediment conduits in ourefforts to constrain off-shelf sediment and carbon.

Acknowledgments

The authors wish to acknowledge Jack Morelock for providingvaluable information and publications on the area of interest, aswell as Christian Beck for his interpretation of seismic reflection pro-files of the canyon. We also thank the crew of the R/V Hermano Ginésand the CARIACO team for their help in the FOSA1 cruise. We thankEthan Goddard and the USF Paleolab for the analytical assistance pro-vided, and Gino Gonzalez at the Center for Ocean Technology for hishelp with the sediment calculations. We are extremely grateful toJohn Milliman, Steven Goldsmith and an anonymous reviewer forproviding critical and insightful comments and corrections to thismanuscript. Funding for this work was provided through NSF Chem-ical Oceanography grants OCE-0326268, OCE-0326313 and OCE-0963028. This is the Institute of Marine Remote Sensing (IMaRS) con-tribution # 143.

References

Alin, S. R., Aalto, R., Goñi, M. A., Richey, J. E. and Dietrich, W. E., 2008. Biogeochemicalcharacterization of carbon sources in the Strickland and Fly rivers, Papua NewGuinea, Journal of Geophysical Research, 113, F01S05, doi:10.1029/2006JF000625

Alberdi, M., LaFargue, E., 1993. Vertical variations of organic matter content in GuayutaGroup (upper Cretaceous), Interior Mountain Belt, Eastern Venezuela. OrganicGeochemistry 20 (4), 425–436.

Aller, R.C., Blair, N.E., 2006. Carbon remineralization in the Amazon–Guianas tropicalmobile mudbelt: a sedimentary incinerator. Continental Shelf Research 26(17–18), 2241–2259.

Alvera-Azcárate, A., Barth, A., Weisberg, R., 2009. A nested model of the Cariaco Basin(Venezuela): description of the basin's interior hydrography and interactions withthe open ocean. Ocean Dynamics 59, 97–120. doi:10.1007/s10236-008-0169-y.

Audemard, F.A., 2006. Surface rupture of the Cariaco July 09, 1997 Earthquake on the ElPilar fault, northeastern Venezuela. Tectonophysics 424, 19–39.

Audemard, F.A., 2007. Revised seismic history of El Pilar Fault, Northeastern Venezuela,after the Cariaco 1997 Earthquake and from recent preliminary paleoseismic re-sults. Journal of Seismology 11, 311–326.

Audemard, F. A., Beck, C., Moernaut, J., De Ricker, K., De Datist, M., Sanchez, J., González,M., Sanchez, C., Versteeg, W., Malave, G., Schmitz, M., Van Welden, A., Carrillo, E.,Lemus, A., 2007. La depresión submarina de Guaracayal. Estado Sucre, Venezuela:una barrera para la propagación de la ruptura cosísmica a lo largo de la Falla deEl Pilar. Interciencia 32 (11), 735–741.

Behrenfeld, M.J., Boss, E., 2003. The beam attenuation to chlorophyll ratio: an opticalindex of phytoplankton physiology in the surface ocean? Deep Sea Research I 50,1537–1549. doi:10.1016/j.dsr.2003.09.002.

Boss, E., Twardowski, M.S., Herring, S., 2001. Shape of the particulate beam attenuationspectrum and its inversion to obtain the shape of the particulate size distribution.Applied Optics 40, 4885–4893.

Burdige, D.J., 2005. Burial of terrestrial organic matter in marine sediments: a re-assessment. Global Biogeochemical Cycles, 19, GB4011, doi:10.1029/2004GB002368.

Burdige, D.J., 2007. The preservation of organic matter in marine sediments: controls,mechanisms and an imbalance in sediment organic carbon budgets? ChemicalReviews 107, 467–485.

Canals, M., Puig, P., de Madron, X.D., Heussner, S., Palanques, A., Fabres, J., 2006. Flushingsubmarine canyons. Nature 444. doi:10.1038/nature05271.

Caraballo, L.F., 1982. El Golfo de Cariaco, Parte I: Morfologia y batimetria sumbarina;estructuras y tectonismo reciente. Boletín del Instituto Oceanográfico de la Univer-disad de Oriente 21 (1–2), 13–35.

en sediment transport on sediment accumulation in the Cariaco Ba-

6 L. Lorenzoni et al. / Marine Geology xxx (2012) xxx–xxx

Carrillo, E., Beck, C., Audemard, F.A., Moreno, E., Ollarves, R., 2008. Disentangling LateQuaternary climatic and seismo-tectonic controls on Lake Mucubají sedimentation(Mérida Andes, Venezuela). Palaeogeography, Palaeoclimatology, Palaeoecology259, 284–300.

Dadson, S. J., Hovius, N., Chen, H., Dade, W. B., Lin, J.-C., Hsu, M.-L., Lin, C.-W., Horng, M.-J.,Chen, T.-C., Milliman, J., Stark, C. P., 2004. Earthquake-triggered increase in sedimentdelivery from an active mountain belt. Geology 32 (8), 733–736; DOI: 10.1130/G20639.1

Dadson, S.J., Hovius, N., Chen, H., Dade, W.B., Hsieh, M.-L., Willett, S.D., Hu, J.C., Horng,M.-J., Chen, T.-C., Stark, C.P., Lague1, D., Lin, J.-C., 2003. Links between erosion, run-off variability and seismicity in the Taiwan orogen. Nature 426, 648–651.

Eberhart-Phillips, D., Haeussler, P.J., Freymueller, J.T., Frankel, A.D., Rubin, C.M., Craw,P., Ratchkovski, N.A., Anderson, G., Carver, G.A., Crone, A.J., Dawson, T.E., Fletcher,H., Hansen, R., Harp, E.L., Harris, R.A., Hill, D.P., Hreinsdóttir, S., Jibson, R.W.,Jones, L.M., Kayen, R., Keefer, D.K., Larsen, C.F., Moran, S.C., Personius, S.F., Plafker,G., Sherrod, B., Sieh, K., Sitar, N., Wallace, W.K., 2003. The 2002 Denali Fault Earth-quake, Alaska: a large magnitude, slip-partitioned event. Science 300 (5622),1113–1118.

Fine, I.V., Rabinovich, A.B., Bornhold, B.D., Thomson, R.E., Kulikov, E.A., 2005. TheGrand Banks landslide-generated tsunami of November 18, 1929: preliminaryanalysis and numerical modeling. Marine Geology 215 (1–2), 45–57.doi:10.1016/j.margeo.2004.11.007.

FUNVISIS, 1994 Estudio Neotectónico y de Geología de Fallas Activas de la RegiónNororiental de Venezuela. 3 Vols. Proyecto Intevep 92–175. Informe de FUNVISISpara Intevep S.A.

FUNVISIS, 2008. http://www.funvisis.org.ve/.Gade, H.G., 1961. Informe sobre las condiciones hidrograficas en el Golfo de Cariaco,

para el periodo que empieza en mayo y termina en noviembre de 1960. Boletíndel Instituto Oceanográfico de la Univerdisad de Oriente 1 (1), 21–33.

Goldfinger, C., 2011. Submarine paleoseismology based on turbidite records. AnnualReviews of Marine Science 3, 35–66.

Goldsmith, S., Carey, A., Berry Lyons, W., Kao, S-J, Lee, T.-Y. and Chen, J. 2008. Extremestorm events, landscape denudation, and carbon sequestration: Typhoon Mindulle,Choshui River, Taiwan. Geology, 36 (6): 483–486; doi: 10.1130/G24624A

González, J., Schmitz, M., Audemard, F.A., Contreras, R., Mocquet, A., Delgado, J., DeSantis, F., 2004. Site effects of the 1997 Cariaco, Venezuela Earthquake. EngineeringGeology 72 (1–2), 143–177.

Hedges, J.I., Baldock, J.A., Gelinas, Y., Lee, C., Peterson, M.L., Wakeham, S.G., 2002. Thebiochemical and elemental compositions of marine plankton: a NMR perspective.Marine Chemistry 78, 47–63.

Hicks, D.M., Gomez, B., Trustrum, N.A., 2004. Event suspended sediment characteristicsand the generation of hyperpycnal plumes at river mouths: East Coast continentalmargin. North Island, New Zealand, Journal of Geology 112, 471–485.

Hilton, R., Galy, A., Hovius, N., Chen, M.-C., Horng, M.-J., Chen, H., 2008. Tropical-cyclone-driven erosion of the terrestrial biosphere from mountains. Nature Geoscience 1,759–762. doi:10.1038/ngeo333.

Hilton, R.G., Galy, A., Hovius, N., Horng, M.-J., Chen, H., 2010. The isotopic compositionof particulate organic carbon in mountain rivers of Taiwan. Geochimica et Cosmo-chimica Acta 74, 3164–3181.

Hilton, R.G., Galy, A., Hovius, N., Horng, M.-J., Chen, H., 2011. Efficient transport of fossilorganic carbon to the ocean by steep mountain rivers: an orogenic carbon seques-tration mechanism. Geology 39 (1), 71–74. doi:10.1130/G31352.1.

Hughen, K. A., Overpeck, J. T., Peterson, L. C., Anderson R. F., 1996. The nature of varvedsedimentation in the Cariaco Basin, Venezuela, and its paleoclimatic significance.In: Palaeoclimatology and palaeoceanography from Laminated Sediments. A. E. S.(ed.). Geological Society Special Publication No. 116. pp. 171–183.

Johnson, K.S., Paull, C.K., Barry, J.P., Chavez, F.P., 2001. A decadal record of underflowsfrom a coastal river into the deep sea. Geology 29 (11), 1019–1022.

Kineke, G.C., Woolfe, K.J., Kuehl, S.A., Milliman, J.D., Dellapenna, T.M., Purdon, R.G.,2000. Sediment export from the Sepik River, Papua New Guinea: Evidence for adivergent sediment plume. Cont. Shelf Res. 20, 2239–2266.

Liu, J.T., Lin, H.-L., 2004. Sediment dynamics in a submarine canyon: a case of river–seainteraction. Marine Geology 207, 55–81. doi:10.1016/j.margeo.2004.03.015.

Liu, J.P., Liu, C.S., Xu, K.H., Milliman, J.D., Chiu, J.K., Kao, J.K., Lin, S.W., 2008. Flux and fateof small mountainous rivers derived sediments into the Taiwan Strait. MarineGeology 256, 65–76. doi:10.1016/j.margeo.2008.09.007.

Lorenzoni, L., Thunell, R.C., Benitez-Nelson, C., Hollander, D., Martinez, N., Tappa, E., Varela,R., Astor, Y., Muller-Karger, F.E., 2009. The importance of subsurface nepheloid layersin transport and delivery of sediments to the Eastern Cariaco Basin, Venezuela. Deep-Sea Research I 56, 2249–2262.

Ludwig, W., Probst, J.-L., Kempe, S., 1996. Predicting the oceanic input of organic carbonby continental erosion. Global Biogeochemical Cycles 10, 23–41.

Lyon, B., 2003. Enhanced seasonal rainfall in Northern Venezuela and the extremeevents of December 1999. Journal of Climate 16, 2302–2306.

Márquez, A. Senior, W. Martínez, G. and Castañeda, J. 2002. Enviromental conditions ofthe waters of the Manzanares River, Cumaná-Sucre, Venezuela. Boletin InstitutoOceaografico de Venezuela. Universidad de Oriente. 41 (1 and 2): 15–24.

Masiello, C., 2007. Quick burial at sea. Nature 450, 360–361.Milliman, J. D., 1995. Sediment discharge to the ocean from small mountainous rivers:

the New Guinea example. Geo_Marine Letters 15, 127–133.

Please cite this article as: Lorenzoni, L., et al., Potential role of event-drivsin, Venezuela, Mar. Geol. (2012), doi:10.1016/j.margeo.2011.12.009

Milliman, J.D., Kao, S.J., 2005. Hyperpycnal discharge of fluvial sediment to the ocean:impact of Super-Typhoon Herb (1996) on Taiwanese Rivers. Journal of Geology113, 503–516.

Milliman, J.D., Lin, S., Kao, S.J., Liu, J.P., Liu, C.S., Chiu, J.K., Lin, Y.C., 2007. Short-termchanges in seafloor character due to flood-derived hyperpycnal discharge:Typhoon Mindulle, Taiwan, July 2004. Geology 35, 779–782.

Milliman, J.D., Syvitski, J.P.M., 1992. Geomorphic/tectonic control of sediment dischargeto the ocean: the importance of small mountainous rivers. Journal of Geology 100,525–544.

MINAMB, 2011. http://www.minamb.gob.ve/.Mora, C., Lopez, M., Okuda, T., 1968. Algunas observaciones hidrograficas en la costa de

Cumaná. Boletín del Instituto Oceanográfico de la Univerdisad de Oriente 6 (2),303–327.

Morales, P.R., Ottmann, F., 1961. Primer studio topográfico y geológico del Golfo de Cariaco.Boletín del Instituto Oceanográfico de la Univerdisad de Oriente 1 (1), 5–20.

Morelock, J., 1982. Marine geology of the Gulf of Cariaco. Acta Científica Venezolana 33,226–234.

Morelock, J., Maloney, N.J., Bryant, W.R., 1972. Manzanares submarine canyon. ActaCientífica Venezolana 23, 143–147.

Mulder, T., Syvitski, J.P.M., 1995. Turbidity currents generated at river mouths duringexceptional discharges to the world oceans. Journal of Geology 103, 285–299.

Mullenbach, B.L., Nittrouer, C.A., 2000. Rapid deposition of fluvial sediment in the EelCanyon, northern California. Continental Shelf Research 20, 2191–2212.

NCDC, 2011. http://www7.ncdc.noaa.gov/IPS/mcdw/mcdw.html.Palanques, A., Guillén, J., Puig, P., Durrieu de Madron, X., 2008. Storm-driven shelf-

to-canyon suspended sediment transport at the south-western end of the Gulfof Lions. Continental Shelf Research 28, 1947–1956.

Paull, C.K., Ussler, W., Greene, H.G., Keaten, R., Mitts, P., Barry, J., 2003. Caught in theact: the 20 December 2001 gravity flow event in Monterey Canyon. Geo-MarineLetters 22, 227–232.

Peterson, L.C., Haug, G.H., 2006. Variability in the mean latitude of the Atlantic Intertrop-ical Convergence Zone as recorded by riverine input of sediments to the CariacoBasin (Venezuela). Palaeogeography Palaeoclimatology Palaeoecology 234 (1),97–113.

Puig, P., Ogston, A.S., Mullenbach, B.L., Nittrouer, C.A., Sternberg, R.W., 2003. Shelf-to-canyon sediment-transport processes on the Eel continental margin (northernCalifornia). Marine Geology 193 (1–2), 129–149.

Schubert, C., 1982. Origin of Cariaco Basin, southern Caribbean Sea. Marine Geology 47,345–360.

Shirai, M., Omura, A., Wakabayashi, T., Uchida, J., Ogami, T., 2010. Depositional age andtriggering event of turbidites in the western Kumano Trough, central Japan duringthe last ca. 100 years. Marine Geology 271, 225–235.

Syvitski, J.P.M., Milliman, J.D., 2007. Geology, geography, and humans battle for domi-nance over the delivery of fluvial sediment to the coastal ocean: Journal of Geology115, 1–19. doi: 10.1086/509246.

Taylor, G.T., Scranton, M.I., Iabichella, M., Ho, T.-Y., Thunell, R.C., Varela, R., Muller-Karger,F.E., 2001. Chemoautotrophy in the redox transition zone of the Cariaco Basin: a sig-nificant source of mid-water organic carbon production. Limnology and Oceanogra-phy 46 (1), 148–163.

Tocco, R., Alberdi, M., Ruggiero, A., Jordan, N., 1994. Organic geochemistry of the CarapitaFormation and terrestrial crude oils in the Maturin Subbasin, Eastern VenezuelanBasin. Organic Geochemistry 21 (10/11), 1107–1111.

Thunell, R. C., Sigman, D. M., Muller-Karger, F., Astor, Y., Varela, R., 2004. Nitrogen iso-tope dynamics of the Cariaco Basin, Venezuela. Global Biogeochemical Cycles, 18,GB3001, doi:10.1029/2003GB002185.

Thunell, R., Tappa, E., Varela, R., Llano, M., Astor, Y., Muller-Karger, F., Bohrer, R., 1999.Increased marine sediment suspension and fluxes following an earthquake. Nature398, 233–236.

Thunell, R., Benitez-Nelson, C., Varela, R., Astor Y., Müller-Karger, F., 2007. Particulate or-ganic carbon fluxes along upwelling-dominated continental margins: rates andmechanisms. Global Biogeochemical Cycles 21, GB1022, doi:10.1029/2006GB002793.

Thunell, R., Varela, R., Llano, M., Collister, J., Muller-Karger, F., Bohrer, R., 2000. Organiccarbon flux in an anoxic water column: sediment trap results from the CariacoBasin. Limnology and Oceanography 45, 300–308.

Virmani, J., Weisberg, R., 2009. Fish affects on ocean current observations in the CariacoBasin. Journal of Geophysical Research 114, C03028. doi:10.1029/2008JC004889.

Warrick, J.A., Milliman, J.D., 2003. Hyperpycnal sediment discharge from semi-aridSouthern California rivers: implications for coastal sediment budgets. Geology 31,781–784.

Werne, J.P., Hollander, D.J., 2004. Balancing supply and demand: controls on carbonisotope fractionation in the Cariaco Basin (Venezuela) Younger Dryas to Present.Marine Chemistry 92 (1–4), 275–293.

Woodworth, M., Goñi, M., Tappa, E., Tedesco, K., Thunell, R., Astor, Y., Varela, R., Díaz,J.R., Muller-Karger, F., 2004. Oceanographic controls on the carbon isotopic com-position of sinking particles from the Cariaco Basin. Deep-Sea Research I 51,1955–1974.

Xu, J.P., Swarzenski, P.W., Noble,M., Li, A.-C., 2010. Event-driven sediment flux inHuenemeand Mugu submarine canyons, southern California. Marine Geology 269, 74–88.doi:10.1016/j.margeo.2009.12.007.

en sediment transport on sediment accumulation in the Cariaco Ba-