oa Organic Matter and Sulfur Diagenesis in the Hot Sediments of Guaymas Basin (Mexico)

The organic matter and sulfur content of the basinal sediments of Guaymas Basin (Mexico) was analyzed by Rock-Eval 7S®, in order to study the kinetics and efficiency of organic matter sulfurization in this hot setting. The two selected IODP Sites, U1545 and U1546, show a similar sedimentary accumulation, but a thick magmatic intrusion at 350 m below the sea floor is present at site U1546. The organic matter content shows comparable evolution at both sites. Organic matter sulfurization occurs rapidly in the upper sediments and reaches a maximum close to the sulfate-methane transition zone, in sediments dated between 40 kyr (U1545) to 80 kyr (U1546). Sufurization decreases below ans is nearly absent at the bottom of the studied intervals (500 m below sea floor, ∼400 kyr). Long term sulfurization of the organic matter is not observed, either because the sulfurized molecules can be substrates for specific methanogens, or because the hot geothermal gradient leads to the rapid breaking of the weak sulfur bonds.