Molar tooth structures are poorly understood early diagenetic, microspar-filled voids in clay-
rich carbonate sediments. They are a common structure in sedimentary successions dating
from 2600–720 Ma, but do not occur in rocks older or younger, with the exception of two
isolated Ediacaran occurrences. Despite being locally volumetrically significant in carbonate
rocks of this age, their formation and disappearance in the geological record remain
enigmatic. Here we present iron isotope data, supported by carbon and oxygen isotopes …

Molar tooth structures are enigmatic carbonate structures that occur as microcrystalline
calcite ribbons and blobs within argillaceous carbonates. Field observations indicate that
they formed in the uppermost sediment column, prior to lithification of the host rock. Molar
tooth structures have been found in numerous Proterozoic basins throughout the world, and
are observed in the sedimentary record between approximately 2600-720 Ma. Despite their
widespread occurrence, both their cause of formation and disappearance from the …