1:45 PM - 2:00 PM
[BGM02-01] Characteristics of microdolomite associated with gas hydrate
Dolomite is commonly recognized in ancient carbonate rocks, most of which are thought to have been formed by diagenetic metasomatism of CaCO3 minerals. The process of dolomite formation caused by microbial metabolisms such as sulfate reduction has also been proposed by studies in Lagoa Vermelha, Brazil, which also involves the metasomatism of CaCO3 minerals. In recent years, microdolomite with a diameter of about 30–150 µm has been discovered in the gas hydrate of the Joetsu Basin. It is thought to be a primary dolomite crystallized around extracellular polymeric substances (EPS) secreted by microorganisms that metabolize oils. Therefore, this study aimed to further clarify the characteristics of this microdolomite and elucidate the detailed formation process.
First, microdolomite separated from gas hydrate was embedded in resin to prepare thin sections. From the observation of thin sections, two major types of microdolomite were recognized: type A, which has polygonal outline with a small black part in the center, and type B, which has relatively smooth spherical outline with concentric layers inside. Thin foil sections were prepared by focused ion beam (FIB) apparatus from thin sections containing two microdolomite types, and observed using a scanning transmission X-ray microscopy (STXM) and a transmission electron microscopy (TEM). In type A, spirally wound filament structures with a width of about 100 nm were recognized on the inner wall of the central black part, and amorphous calcium carbonate (ACC) was distributed around them, which was further surrounded by single crystal of dolomite. On the other hand, type B mainly consisted of rhombic dolomite crystals of less than about 2 µm, which constructed a repetition of scattered and dense layers. In this presentation, we will also discuss the origins of these two types. The Joetsu Basin samples used in this investigation were collected by Meiji University’s Gas Hydrate Research Laboratory under the commission of AIST from 2013-2015 as part of the methane hydrate research project funded by METI (Ministry of Economy, Trade and Industry), Japan.
First, microdolomite separated from gas hydrate was embedded in resin to prepare thin sections. From the observation of thin sections, two major types of microdolomite were recognized: type A, which has polygonal outline with a small black part in the center, and type B, which has relatively smooth spherical outline with concentric layers inside. Thin foil sections were prepared by focused ion beam (FIB) apparatus from thin sections containing two microdolomite types, and observed using a scanning transmission X-ray microscopy (STXM) and a transmission electron microscopy (TEM). In type A, spirally wound filament structures with a width of about 100 nm were recognized on the inner wall of the central black part, and amorphous calcium carbonate (ACC) was distributed around them, which was further surrounded by single crystal of dolomite. On the other hand, type B mainly consisted of rhombic dolomite crystals of less than about 2 µm, which constructed a repetition of scattered and dense layers. In this presentation, we will also discuss the origins of these two types. The Joetsu Basin samples used in this investigation were collected by Meiji University’s Gas Hydrate Research Laboratory under the commission of AIST from 2013-2015 as part of the methane hydrate research project funded by METI (Ministry of Economy, Trade and Industry), Japan.