Fig. 2: The iron ooid organic carbon records.
From: The geologic history of marine dissolved organic carbon from iron oxides
a,b, Fe-OC loadings (wt%) (a) and δ13C values (% VPDB) (b) since the late Palaeoproterozoic, separated by mineralogy (blue represents goethite; orange represents haematite). Opaque markers and vertical black lines are 100 Ma time-binned averages and ±1σ uncertainties, whereas semi-transparent markers are individual sample results. The orange box indicates the PETM-aged Bakchar Horizon, which contains petrographic evidence for the presence of 13C-depleted CH4 during ooid precipitation (Supplementary Discussion and Supplementary Figs. 33 and 34). The fact that this formation yields lower δ13C values than those in immediately older and younger time bins indicates incorporation of CH4-derived carbon and supports the notion that Fe-OC captures in situ signals. This notion is further strengthened by the fact that goethite and haematite loadings are statistically identical in the Ordovician, in which both mineralogies overlap (Supplementary Discussion). In general, we observe lower Fe-OC loadings and δ13C values in the Proterozoic relative to the Phanerozoic.
