Integrated study of the sedimentology, stratigraphy, and geochemistry of the mudstones of the Chuar Group reveals many important details of the break-up of Rodinia, the rise of early macroscopic eukaryotes, and conditions leading up to the first Neoproterozoic Snowball Earth episodes.

Mudstones of the Kwagunt Formation (~500 m thick), Chuar Group, accumulated in an intracratonic, marine rift basin on the western edge of Laurentia. They display a wide range of sedimentary and geochemical characteristics that suggest that organic carbon burial in Kwagunt Formation was mediated by benthic microbial mats. Pseudo-cross laminated structures, carbonaceous lenses, crinkly, silty, anastomosing and discontinuous laminations occur in deeper-water intervals, and fenestral laminations, roll-up features and pustular surfaces, indicative of mat desiccation, are more common in shallower regions. The occurrence of even-over-odd preferences in n-alkane distributions and possible monomethyl-alkane series support the interpretation of theses sedimentary structures as benthic microbial mats with associated sulfide-oxidizing bacteria and accord with previous observations of quaternary-branched-diethylalkanes and monomethyl-alkane series by other researchers.

Detailed mudstone stratigraphy displays two modes in the relation between total organic carbon (TOC) and silt content. The bulk of the stratigraphic section (~425 m) is TOC-poor (0-5 %TOC) and displays a positive relation between silt content and TOC. Two TOC-rich (> 5 %TOC) intervals within the Walcott Member, the uppermost member of the Kwagunt formation, demonstrate an inverse relation where silt content is to proportional to 1/%TOC. These two trends are attributed to variations in basin evolution, sediment distribution and dilution, along with increased primary production and more reducing conditions that enhance carbon burial. Greater %TOC associated with increased silt delivery may be the result of increased riverine nutrient delivery or chemocline rise during wetter conditions. The two TOC-rich intervals within the Walcott Member are likely a result of basin deepening and expansion that traps silt nearshore which fosters the deposition TOC-rich black shales ( >5% TOC) by limiting siliclastic dilution.