Gas origin linked to paleo BSR

Iván De La Cruz Vargas-Cordero,Joaquim P Bento,Michela Giustiniani,Umberta Tinivella,Nathan Bangs,Eduardo Contreras-Reyes,Lucia Villar-Muñoz

doi:10.1038/s41598-021-03371-z

Abstract

The Central-South Chile margin is an excellent site to address the changes in the gas hydrate system since the last deglaciation associated with tectonic uplift and great earthquakes. However, the dynamic of the gas hydrate/free gas system along south central Chile is currently not well understood. From geophysical data and modeling analyses, we evaluate gas hydrate/free gas concentrations along a seismic line, derive geothermal gradients, and model past positions of the Bottom Simulating Reflector (BSR; until 13,000 years BP). The results reveal high hydrate/free gas concentrations and local geothermal gradient anomalies related to fluid migration through faults linked to seafloor mud volcanoes. The BSR-derived geothermal gradient, the base of free gas layers, BSR distribution and models of the paleo-BSR form a basis to evaluate the origin of the gas. If paleo-BSR coincides with the base of the free gas, the gas presence can be related to the gas hydrate dissociation due to climate change and geological evolution. Only if the base of free gas reflector is deeper than the paleo-BSR, a deeper gas supply can be invoked.

Highlights

The Central-South Chile margin is an excellent site to address the changes in the gas hydrate system since the last deglaciation associated with tectonic uplift and great earthquakes
Some of the free gas (FG) can be related to the Gas hydrate (GH) dissociation at the Bottom Simulating Reflector (BSR) following a change in pressure and temperature (PT) conditions at the BSR, while the rest may accumulate from migration from shallow biogenic, or deeper thermogenic sources
FG can be produced from hydrates or formed into hydrates following PT changes associated with fluid overpressure, which are common to subduction zone s ettings[17] and are evident from seafloor mud volcanoes

Summary

Introduction

Continuous reflections (i.e. seafloor, BSR and BGR; Fig. 2) were selected to build a velocity model. The selected seismic section, MGL1701-30, was inverted considering 4 main reflectors: seafloor, horizon below it, BSR and BGR.

Results

Conclusion