USING INOCERAMID BIVALVE TAPHONOMY AS A PALEOENVIRONMENTAL INDICATOR ACROSS THE CENOMANIAN/TURONIAN HORIZION AT THE PUEBLO, COLORADO GSSP

The end of Oceanic Anoxic Event II (OAEII), 93.5 Ma, is currently correlated with multiple contemporaneous positive δ⁺¹³C_org spikes. There are many discrepancies in scientific literature interpreting these δ⁺¹³C_org spikes, however, which makes the true end of OAEII difficult to determine. Taphonomic data is widely used to interpret paleoenvironments, and such data may further characterize the environment(s) indicative of global OAEII, and serve to detect the end of this event.

The calcite portions of inoceramid bivalve shells are expected to have differential taphonomy in anoxic and oxic environments in regards to recrystallization of calcite, fragmentation, and amount partial dissolution. The characters can be described qualitatively with values of high, medium, low, none, and can be compared statistically. It is expected that biominearlized calcite in anoxic conditions has taphonomic characterisitics of low to no recrystallization and fragmentation, and high calcite remaining.

Inoceramids that spanned OAEII were collected from sediments deposited in the Cretaceous Interior Seaway at the Cenomanian/Turonian Global Boundary Stratotype and Point (GSSP) in Pueblo, Colorado. The bivalves at the GSSP exhibited independence, P(χ² > 0.2.1681) = 0.5383 (d.f. = 3), in recrystallized calcite during OAEII and after OAEII (beds 62 and 115, respectively).

Using the chi-square goodness of fit test, taphonomic signatures of bivalves in other beds could be compared to bed 62 in order to determine if environmental conditions were similar or dissimilar to OAEII. Examination of inoceramids collected from bed 72 will undergo this study. Significant similarities could characterize benthic oxygen levels at the time of deposition of bed 72. This technique, if expanded upon, may offer a better idea of when OAEII ended, or even the degree to which OAEII was expressed in the paleoenvironment that once existed at the Pueblo GSSP.