2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 4
Presentation Time: 2:15 PM

LATE CRETACEOUS - EARLY PALEOCENE BIVALVE STABLE ISOTOPE RECORD FROM SEYMOUR ISLAND, ANTARCTICA


DUTTON, Andrea L.1, LOHMANN, Kyger C.1 and ZINSMEISTER, William J.2, (1)Geological Sciences, Univ of Michigan, 425 E. University St, 2534 C.C.Little, Ann Arbor, MI 48109-1063, (2)Purdue Univ, 1397 Civil Engineering, West Lafayette, IN 47907-1397, adutton@umich.edu

The K/T boundary sequence on Seymour Island, Antarctica consists of a relatively thick, continuous section of mid-shelf siliciclastic sediment containing a well-preserved macrofauna.  The K/T boundary itself is characterized by a glauconite sandstone associated with a fish mortality horizon closely overlying an iridium anomaly.  Previous studies of this stratigraphic section have primarily focused on the paleontology and temporal nature of the extinction.  Here we present stable isotope (d18O, d13C) and elemental (Ca, Mg, Sr, Fe, Mn) analyses of bivalve carbonate that span this Late Cretaceous – early Paleocene interval, representing a duration of ~2.5 m.y. 

Four aragonite bivalve genera have been analyzed to produce a record of climate.  This record consists of 360 individual analyses where each specimen is represented by three analyses to provide an estimate for bulk shell composition.  Fe and Mn concentrations were measured to evaluate diagenesis and were elevated with respect to biogenic marine aragonite in only a few samples.  Cross-plots of d18O vs. Fe+Mn and d13C vs. Fe+Mn suggest that carbonate in equilibrium with diagenetic fluids has a d18O value of ~1.2‰ and ~1.0‰ for d13C. 

The Maastrichtian bivalve d18O record parallels the trend observed at southern high latitude deep sea localities (Sites 690 and 511) and has similar absolute values.  Bivalve d18O values increase until ~66.5 m.y.a. and then steadily decrease until the K/T transition.  Bivalve d13C values remain relatively invariant during the ~2 m.y. prior to the K/T boundary.  Near the boundary, there is an apparent negative d13C excursion (recorded in one shell) immediately followed by a 0.5‰ decrease in d18O, which corresponds to a warming of 2.5°C.  Both the d18O and d13C records rebound to pre-excursion values after ~200 k.y. 

Interestingly, two bivalve genera that persist across the K/T transition, Cucullaea and Lahillia, appear to be offset from each other with respect to both d13C and d18O except at one horizon near the K/T boundary where these stable isotope records converge.  This offset may be due to different seasons of shell growth where convergence of these records is the result of a collapse in seasonality.  This hypothesis will be tested using high-resolution sampling to evaluate seasonal amplitudes of d13C and d18O in these bivalves through this interval.