Fig 5. ToF-SIMS ion images of a 300μm × 300μm area of the back chert facies with an organic matter layer in the center.

The pixel brightness reflects the signal intensity of (from the left): Si = [Si]⁺, representing the chert matrix; Ca = sum of [Ca]⁺, [CaO]⁺, and [CaOH]⁺, representing CaCO₃; C_org = sum of major hydrocarbon ions [C₂H₃]⁺, [C₂H₅]⁺, [C₃H]⁺, [C₃H₂]⁺, and [C₃H₃]⁺, representing organic matter. Pixel brightness in Ca and color coded overlay of Si (red) and C_org (green) is enhanced to increase image contrast.