Late Cretaceous and Cenozoic paleoceanography from north-east Atlantic ferromanganese crust microstratigraphy

Pierre Josso,Jeremy Rushton,Paul Lusty,Adam Matthews,Simon Chenery,David Holwell,Simon J Kemp,Bramley Murton

doi:10.1016/j.margeo.2020.106122

Pierre Josso, Jeremy Rushton + Show 6 more

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https://doi.org/10.1016/j.margeo.2020.106122

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Abstract

Oceanic hydrogenetic ferromanganese (Fe-Mn) crusts precipitate directly from ambient seawater over millions of years. Their very slow growth rates and physio-chemical properties mean that they adsorb numerous elements from seawater. As such, they provide condensed records of seawater evolution through time that can be used for paleoceanographic reconstruction. Here, we present the results of a high-resolution, stratigraphic, textural and geochemical investigation of a core sample, obtained from a Fe-Mn crust pavement, located on the summit of Tropic Seamount in the tropical north-east Atlantic Ocean. A number of observations and interpretations are proposed, within the context of a well-constrained age model, spanning the last 75 ± 2 Myr. This core has textural stratigraphic coherence with Pacific Fe-Mn crusts formed since the Late Cretaceous, highlighting that global oceanic and climatic phenomena exert first-order controls on Fe-Mn crust development. All major hiatuses observed in the Fe-Mn crusts are contemporaneous with erosion events occurring throughout the Atlantic Ocean. High-resolution geochemical data indicate that there is variability in the composition of Fe-Mn crusts at the cm to μm scale. The dominant factors controlling this include major oceanographic events, mineral textures and micro-topography.

Highlights

Deep-sea hydrogenetic ferromanganese crusts, hereafter termed FeMn crusts, most commonly form on sediment-free topographic highs such as ridges, plateaus and seamounts, at water depths of 400–7000 meters below sea level (Hein et al, 2013; Lusty et al, 2018)
Given that vernadite peak at 1.42 Å is absent and that the peaks in the region 2.39–2.45 Å can be attributed to goethite and corundum, we interpret the Mn oxide phase as being dominantly amorphous following the recommendation of International Centre for Diffraction Data (ICDD)
Fe-Mn crusts from Tropic Seamount have a complex history of deposition since the Late Cretaceous, with abundant erosion contacts, overprint by phosphatisation and textural variations that resulted in significant geochemical variations

Summary

Introduction

Deep-sea hydrogenetic ferromanganese crusts, hereafter termed FeMn crusts, most commonly form on sediment-free topographic highs such as ridges, plateaus and seamounts, at water depths of 400–7000 meters below sea level (mbsl) (Hein et al, 2013; Lusty et al, 2018) These deposits form through the accumulation of Fe and Mn oxide colloids precipitating from ambient seawater. Fe-Mn crusts are of particular scientific interest because of the physio-chemical properties of the Fe and Mn oxyhydroxides and their extremely slow accumulation rates, which results in efficient and continuous enrichment in many dissolved metals from seawater (Hein et al, 2000; Koschinsky and Hein, 2003). Recently has the widespread occurrence of Fe-Mn crusts throughout the Atlantic, Indian and Arctic oceans become clear (Baturin and Dubinchuck, 2011; Muiños et al, 2013; Hein et al, 2017; Marino et al, 2017)

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