Carbon isotope stratigraphy of T orinosu‐type limestone in the western P aleo‐ P acific and its implication to paleoceanography in the L ate J urassic and earliest C retaceous

Carbon isotope stratigraphy of the L ate J urassic and earliest C retaceous was revealed from T orinosu‐type limestone, which was deposited in a shallow‐marine setting in the western P aleo‐ P acific, in J apan. Two sections were examined; the N akanosawa section of the late K immeridgian to early T ithonian age ( F ukushima P refecture, N ortheast J apan), and the F uruichi section of the late K immeridgian to early B erriasian age ( E hime P refecture, S outhwest J apan). The age‐model was established using S r isotope ratio and fossil occurrence. The limestone samples have a low M n/ S r ratio (mostly <0.5) and lack a distinct correlation between δ 13 C and δ 18 O , indicating a low degree of diagenetic alteration. Our composite δ 13 C profile from the two limestone sections shows three stratigraphic correlation points that can be correlated with the profiles of relevant ages from the A lpine T ethyan region: a large‐amplitude fluctuation (the lower upper K immeridgian, ∼152 Ma), a positive anomaly (above the K immeridgian/ T ithonian boundary, ∼150 Ma), and a negative anomaly (the upper lower T ithonian, ∼148 Ma). In addition, we found that δ 13 C values of the T orinosu‐type limestone are ∼1‰ lower than the T ethyan values in the late K immeridgian. This inter‐regional difference in δ 13 C values is likely to have resulted from a higher productivity and/or an organic burial in the T ethyan region. The difference gradually reduces and disappears in the late T ithonian, where the T ethyan and our δ 13 C records show similar stable values of 1.5–2.0‰. This isotopic homogenization is probably due to changes in the continental distribution and the global ocean circulation, which propagated the 13 C ‐depleted signature from the larger P aleo‐ P acific to the smaller T ethys O cean during this time.