CARBON PRESERVATION IN DEEP MARINE SETTINGS: THE ROLE OF SEDIMENT TRANSPORT IN THE DEPOSITION OF ORGANIC-RICH CARBONATES IN THE EOCENE OF THE LEVANT BASIN

Proximal open ocean depositional settings receive organic carbon (OC) inputs that may be more than an order of magnitude greater than productivity-related dissolved and particulate OC produced near the ocean surface. However, transport of OC from continental and shallow marine settings to deep-sea ecosystems may be overlooked in mass-balance calculations for deep-time depositional systems.

The lower 150 m of a new land-based core in northern Israel bottoming in the Early Eocene is composed primarily organic-rich chalks interleaved with displaced neritic limestones. TOC values range between 1.5 and 14%, averaging 4.5%. Displaced limestones are composed of a variety of poorly cemented mud- and wackestones with low-diversity assemblages of larger foraminifera associated with planktonic foraminifera, suggesting deposition on the outer ramp under oligophotic conditions but below the energetic zone. Features indicating transport include soft-sediment deformation (SSD), partially lithified rip-ups, folds, small diapirs, bed-scale imbrication, brecciation and synsedimentary shear. Detachment, movement and emplacement followed initial sedimentation, in some instances repeatedly.

Principal component analysis was used for clustering elemental XRF data with TOC, petrophysical measurements, and sedimentological features. High Zn, P, S and Cr values clustered with organic-rich samples, most likely related to the affinity of micronutrients to marine OC, and to natural in-sediment sulfurization processes related to its preservation. Ca clustered broadly with organic-lean samples. Elements of terrestrial affiliation (i.e., Al, Si, Fe and K), high abundance of benthic fauna, and high magnetic susceptibility values clustered with the highest OC-rich samples, advocating a link between sedimentary transport and accumulation and/or preservation of OC. These results support the high impact of sediment transport on TOC values, by supplying OC from continental and shallow settings to the deep sea, complemented by rapid burial and preservation of ambient deep-sea OC. These processes thereby substantially enhanced the amount of carbon stored in proximal oceanic basins over geological time.