Submarine Groundwater Discharge as a Catalyst for Eodiagenetic Carbonate Cements Within Marine Sedimentary Basins

Submarine groundwater discharge (SGD) is the input of freshwater into ocean water and sediments, especially in estuaries, from continental aquifers. Such meteoric water influx can occur at depths up to 3000 m. The mixing of calcium-rich meteoric water with saline marine water in the presence of organic matter can produce early calcite cement in pores. Pervasive to stratabound carbonate cementation in shallow to offshore marine sandstones has been assumed to result from long-term slow diffusion or advective processes. However, results from the sedimentologic and geochemical studies of Cretaceous calcitic concretion-bearing layers in sandstones in a marine coastal setting indicate otherwise. Permineralization of delicate fungi, liverworts, mosses, and macrophytic plant material as well as associated textures and isotopic signatures of carbonate cement within stratabound concretions in the Longarm Formation on Vancouver Island, Canada, indicate high flux flow of calcium-rich meteoric waters during very early diagenesis (eogenesis) to synsedimentary freshwater diagenesis. We propose that calcite cementation from meteoric waters along horizons in estuarine to fully marine sediments can occur through SGD directly via terrestrial aquifer flow through carbonates. Because SGD can be introduced into marine sediments along shallow coastlines as well as at great depths, this groundwater input may be an important geochemical process in the diagenesis of coastal marine sediments, and is key to fossil preservation, including permineralization of land plants along ancient coastlines and possibly the formation of Carboniferous coal balls.