What makes seep carbonates ignore self-sealing and grow vertically: the role of burrowing decapod crustaceans

Abstract. The mechanisms that govern the vertical growth of seep carbonates were deciphered by studying sedimentary architecture a 15 m thick, 8 wide column limestone encased in deep-water marl middle Callovian interval Terres Noires Formation SE France Basin. body, also called “pseudobioherm”, records intense bioturbation, with predominant traces Thalassinoides/Spongeliomorpha suite, excavated decapod crustaceans. Bioturbation was organized four tiers. uppermost tier, tier 1, corresponds to shallow homogenization rather soft sediment. Tier 2 pervasive burrows dominated large Thalassinoides later passively filled pellets. Both homogenized micrite and burrow-filling pellets are depleted 13C range from ?5 ‰ ?10 ‰. 3 is characterized small have walls locally bored Trypanites; latter represent 4. diagenetic cements filling tier-3 arranged two phases. first cement generation constitutes continuous rim coats burrow wall has consistent ?13C values approximately ?8 ?12 ‰, indicative bicarbonate originating anaerobic oxidation methane. In contrast, second saddle dolomite precipitated at temperatures >80 ?C, time when pseudobioherm deeply buried. fact tubes remained open until deep burial means fluid communication possible over whole extent up seafloor during its active development. Therefore, fostered this network, providing high density localized conduits through zone carbonate precipitation, particular across sulfate–methane transition zone. Burrows prevented self-sealing blocking upward methane migration laterally deflecting flow. One key aspect geometric complexity numerous subhorizontal segments could trap sediment shed above and, hence, prevent their passive fill.