Exploring a link between Atlantic coral mounds and Phanerozoic carbonate mudmounds: Insights from pore water fluorescent dissolved organic matter (FDOM), Pen Duick mounds, offshore Morocco

Abstract

This study explores a genetic link between modern Atlantic coral mounds and ancient, sponge-rich carbonate mudmounds based on Ca-carbonate authigenesis driven by induced-and-supported organomineralization (ISOM). The potential for ISOM in Atlantic coral mounds is tracked by peak patterns of fluorescent dissolved organic matter (FDOM) present in pore waters down to 3m of sediment depth (Gamma mound, Beta mound, Pen Duick escarpment, offshore Morocco).All pore waters display a biological activity (protein-like fluorescence) with two local maxima, occurring from the surface to about 1m of sediment depth and below 2m of sediment depth. Protein-like fluorescence correlates well with the fluorescence of porphyrin-like compounds. A sample of bottom water displays a blue-shifted variety of protein-like fluorescence suggesting hydrolysis and diffusion from the benthic realm into the water column. A significant accumulation of refractory FDOM does not occur in shallower than 2m of sediment depth. It is accompanied by a late stage of biodegradation of organic matter (peak Geol.-A; ex. 224±2nm; em. 385±8nm) and the occurrence of a new fluorescence peak Q that is expressed along an emission band with peak Geol.-A (peak Q; ex. 295±5nm; em. 385±1nm). With caution, peak Q represents a product of exudation from anaerobic microorganisms and/or derives from siderophore-like pigments (pyocyanine-like; from Pseudomonas species).Permineralizing fluids that are characteristic for ISOM are locally present within the shallow subsurface and reach a maximum intensity at about 1m of sediment depth. However, no ISOM-related authigenic carbonate was observed. Both the lack of organic substrates that is due to the absence of degrading connective tissues from a cryptic community and the high amount of infiltrated mud that acts as a sorbent might explain the absence of ISOM in Gamma mound sediments. Labyrinthine deposits of coral rubble or current-swept coral mounds are prone to host a sponge-rich cryptic community and therefore, in their deeper parts, should provide a variety of substrates for ISOM during suboxic cycling of natural organic matter. In such a view, the modern coral-rich mound system, which by itself appears diverse and with a variety of controlling factors, maintains an excellent potential to drive ISOM and to share a crucial process of early diagenesis with Phanerozoic sponge-rich carbonate mudmounds.