Gypsum ridges as conduits for deep methane emission in an evaporite basin– Insights into the origin of atmospheric methane on Mars

Abstract

The origin of atmospheric methane on Mars is attracting much attention because of its possible biological origin. We report the first detection of methane-dominated hydrocarbons trapped between the {010} cleavage planes of gypsum megacrysts from the evaporative Qaidam Basin, in the northern Tibetan Plateau. The gypsum makes ridges of kilometers long, tens of meters wide, and high that are deposited from deep circulated brine and later exhumed to the surface by wind erosion. The δ13C of methane (-33.3 ± 4.1 ‰), high CO2/CH4 ratio but low C1/(C2+C3) ratio indicate their thermogenic sources. These gypsum ridges are formed on intrabasin salt domes and form conduits for the volatile hydrocarbons to diffuse upward and escape into the atmosphere. We suggest the atmospheric methane on Mars is also derived from the deep basins and is emitted by the same pathway since the gypsum ridges/seams/veins in the Qaidam Basin show striking similarities to the irregular polygonal ridge networks and veins on Mars.