Eustatic sea-level controls on the flushing of a shelf-incising submarine canyon

Abstract

Turbidity currents are the principal processes responsible for carving submarine canyons and maintaining them over geological time scales. The turbidity currents that maintain or "flush" submarine canyons are some of the most voluminous sediment transport events on Earth. Long-term controls on the frequency and triggers of canyon-flushing events are poorly understood in most canyon systems due to a paucity of long sedimentary records. Here, we analyzed a 160-m-long Ocean Drilling Program (ODP) core to determine the recurrence intervals of canyonflushing events in the Nazaré Canyon over the last 1.8 m.y. We then investigated the role of global eustatic sea level in controlling the frequency and magnitude of these canyonflushing events. Canyon-flushing turbidity currents that reach the Iberian Abyssal Plain had an average recurrence interval of 2770 yr over the last 1.8 m.y. Previous research has documented no effect of global eustatic sea level on the recurrence rate of canyon flushing. However, we find that sharp changes in global eustatic sea level during the mid-Pleistocene transition (1.2-0.9 Ma) were associated with more frequent canyon-flushing events. The change into high-amplitude, long-periodicity sea-level variability during the mid-Pleistocene transition may have remobilized large volumes of shelf sediment via subaerial weathering, and temporarily increased the frequency and magnitude of canyon-flushing turbidity currents. Turbidite recurrence intervals in the Iberian Abyssal Plain have a lognormal distribution, which is fundamentally different from the exponential distribution of recurrence intervals observed in other basin turbidite records. The lognormal distribution of turbidite recurrence intervals seen in the Iberian Abyssal Plain is demonstrated to result from the variable runout distance of turbidity currents, such that distal records are less complete, with possible influence from diverse sources or triggering mechanisms. The changing form of turbidite recurrence intervals at different locations down the depositional system is important because it ultimately determines the probability of turbidity current-related geohazards.

Volume and recurrence of submarine‐fan‐building turbidity currents

“…However, many of these flows, while very frequent, dissipate prior to reaching the submarine fan (Paull et al, 2005;Talling et al, 2015) and thus must have relatively small event volumes (v e < 10 5 m 3 ). Further evidence of frequent and small-volume flows not reaching submarine fans comes from the Iberian abyssal plain (not discussed here, see Allin et al, 2017) and the Hueneme submarine fan. Romans et al (2009) suggest that frequent, thin-bedded turbidites with short recurrence intervals (Table 2) recovered in cores from the proximal Hueneme canyon by Gorsline (1996) are not represented in the Hueneme submarine fan deposits, indicating that these frequent, small magnitude flows dissipated prior to reaching the fan.…”

“…However, many of these flows, while very frequent, dissipate prior to reaching the submarine fan (Paull et al., ; Talling et al., ) and thus must have relatively small event volumes ( v e < 10 5 m 3 ). Further evidence of frequent and small‐volume flows not reaching submarine fans comes from the Iberian abyssal plain (not discussed here, see Allin et al., ) and the Hueneme submarine fan. Romans et al.…”

“…Thus, fans are constructed by flows large enough to bypass and sculpt canyons, but small enough to die out before reaching the abyssal plain. It is important to note that event volume and recurrence are not single values, but rather distributions, and it is likely that these distributions are truncated as flows move from canyon to basin plain (Allin et al., ). As more data are collected and analysed, event volume and recurrence will become better understood and better able to provide sediment flux estimates and assessments of submarine geohazards.…”

“…It is important to note that v e is an average event volume, and does not take into account the distribution of flow volumes shown in natural systems (Allin et al, 2017;Clare et al, 2014;Cooper et al, 2013;Talling et al, 2007) and the spatial distribution of beds on a submarine fan (Deptuck et al, 2008;Jobe et al, 2017b). However, not enough detail about these distributions are available to model them properly.…”

“…Event recurrence is better constrained, with Quaternary core-based studies providing recurrence interval data from multiple basins (Clare et al, 2014;Clare et al, 2016;Paull et al, 2014). Studies have also focused on the distribution of event recurrence and how allogenic forcing and position along the sediment-routing system can affect the recurrence distribution (Allin et al, 2017;Allin et al, 2016;Clare et al, 2015).…”