Hybrid turbidite-drift channel complexes: An integrated multiscale model

A Fuhrmann,E Bonamini,E Schomacker,F.A Contreras,I.A Kane,M.A Clare,R.A Ferguson

doi:10.1130/g47179.1

Abstract

Abstract The interaction of deep-marine bottom currents with episodic, unsteady sediment gravity flows affects global sediment transport, forms climate archives, and controls the evolution of continental slopes. Despite their importance, contradictory hypotheses for reconstructing past flow regimes have arisen from a paucity of studies and the lack of direct monitoring of such hybrid systems. Here, we address this controversy by analyzing deposits, high-resolution seafloor data, and near-bed current measurements from two sites where eastward-flowing gravity flows interact(ed) with northward-flowing bottom currents. Extensive seismic and core data from offshore Tanzania reveal a 1650-m-thick asymmetric hybrid channel levee-drift system, deposited over a period of ∼20 m.y. (Upper Cretaceous to Paleocene). High-resolution modern seafloor data from offshore Mozambique reveal similar asymmetric channel geometries, which are related to northward-flowing near-bed currents with measured velocities of up to 1.4 m/s. Higher sediment accumulation occurs on the downstream flank of channel margins (with respect to bottom currents), with inhibited deposition or scouring on the upstream flank (where velocities are highest). Toes of the drift deposits, consisting of thick laminated muddy siltstone, which progressively step back into the channel axis over time, result in an interfingering relationship with the sandstone-dominated channel fill. Bottom-current flow directions contrast with those of previous models, which lacked direct current measurements or paleoflow indicators. We finally show how large-scale depositional architecture is built through the temporally variable coupling of these two globally important sediment transport processes. Our findings enable more-robust reconstructions of past oceanic circulation and diagnosis of ancient hybrid turbidite-drift systems.

Highlights

As the terminal part of sedimentary sourceto-sink systems, deep-sea deposits have been used to reconstruct past climates, sediment and carbon budgets, and the distribution of anthropogenic pollution (Sømme et al, 2009; Masson et al, 2010; Rebesco et al, 2014; Drinkorn et al, 2019; Kane and Clare, 2019)
Contradictory hypotheses for reconstructing past flow regimes have arisen from a paucity of studies and the lack of direct monitoring of such hybrid systems
While the influence of bottom currents on submarine channel architecture has been recognized, interpretation has been hampered by a lack of direct monitoring data (Shanmugam et al, 1993; Gong et al, 2018; Sansom, 2018; Fonnesu et al, 2020)

Summary

INTRODUCTION

As the terminal part of sedimentary sourceto-sink systems, deep-sea deposits have been used to reconstruct past climates, sediment and carbon budgets, and the distribution of anthropogenic pollution (Sømme et al, 2009; Masson et al, 2010; Rebesco et al, 2014; Drinkorn et al, 2019; Kane and Clare, 2019). Modern, integrated data sets, including direct measurements and monitoring of bottom currents, are of great importance in understanding the complexity of oceanographic processes (Fierens et al, 2019; Miramontes et al, 2019; Thiéblemont et al, 2019), sediment gravity flows (Clare et al, 2016; Azpiroz-Zabala et al, 2017; Symons et al, 2017), and the preservation of strata within submarine channel complexes (Gamberi et al, 2013; Vendettuoli et al, 2019). This study combines an integrated subsurface study (three-dimensional [3-D] seismic, core, and well-log data) with modern seafloor geomorphology and near-bed bottom-current measurements to develop a process-product–based sedimentological model for bottom current– influenced submarine channel complexes.

E SW Well A

A Core log of well A

CONCLUSIONS