[Experimental study of the red-bed pigment with diffuse reflectance spectroscopy]

Area of Science:

• Geology
• Mineralogy
• Sedimentology

Context:

• Continental red-beds are geological formations characterized by their distinctive red color.
• The origin of this red pigment has been debated, with a focus on the role of iron oxides.
• Previous research suggested a diagenetic origin for the red pigment, linked to high temperatures.

Purpose:

• To investigate the hypothesis that the red pigment in continental red-beds forms through a diagenetic process involving heat.
• To experimentally determine the temperature and conditions under which iron hydrates dehydrate to form hematite, the primary red pigment.

Summary:

• Black ooze from the Pearl River Delta was heated to simulate diagenetic conditions.
• Diffuse Reflectance Spectroscopy (DRS) and red-value calculations were used to analyze pigment formation.
• Experimental results confirmed that heating goethite (an iron hydrate) at approximately 150°C leads to the formation of hematite, increasing the red color.

Impact:

• Provides strong experimental evidence supporting the thermal origin of continental red-beds.
• Clarifies the diagenetic processes responsible for red pigment formation in sedimentary rocks.
• Contributes to understanding the geochemistry and mineralogy of terrestrial sedimentary environments.