Abstract:
Well-preserved nannofossil and stable isotope records from the mid-Cretaceous
of ODP Leg 171B (western North Atlantic) indicate cyclical, productivity-based
variations in surface water characteristics, suggesting orbitally paced changes
in upwelling intensity and the strength of deep mixing associated with Oceanic
Anoxic Event (OAE) 1d. Paleontologic and isotopic evidence suggest that
collapse
... of upper water column stratification associated with OAE1d was
preceded by approximately 1 m.y. of progressively decreasing water column
stability and increasing surface water fertility. Thirteen species went
extinct during a short (ca. 200 k.y.) interval associated with OAE1d. Nine of
these have morphological characters suggesting adaptation to specific depths
in the photic zone. Simultaneous extinction of these depth-zoned species
suggests that stratification collapse disrupted the habitat space for these
specialized forms, resulting in extinction. A cyclostratigraphic model
provides age estimates of several important nannofossil datums including the
first appearances of Eiffellithus turriseiffelii (100.95 Ma) and Corollithion
kennedyi (99.55 Ma).
The study materials are of late Albian to early Cenomanian age. They were collected
from two Ocean Drilling Program holes on the Blake Nose in the western North Atlantic:
Hole 1052E (29 57.08 N, 76 37.6W
at 1355.0 meters below sea level) and
Hole 1050C (30 6.0 N, 76 14.1 W at 2308.0 meters below sea level).
#1 Data series "Watkins051" contains calcareous nannofossil assemblage count data
for the major taxa from 58 samples spanning an upper Albian and lower Cenomanian
composite section from Holes 1050C and 1052E. Reflectance values were measured by the
Leg 171B Shipboard Science Party. Nutrient Index values are calculated from major taxa
abundances (see original publication for details).
#2 Data series "Watkins052" contains raw calcareous nannofossil species abundance counts
for samples from Section 1052E-39-5. Species richness, Shannon diversity, Nutrient Index,
and evenness were calculated from these nannofossil counts. Column PCA1 contains
loadings for the first Principal Component of Principal Components Analysis
(as described in original publication). Reflectance values were measured by the Leg 171B
Shipboard Science Party. Carbon isotopes were determined using a Europa Geo 20-20
mass spectrometer with a CAPS preparation system. The precision of these analyses
was better than 0.10 relative to the Vienna Pee Dee Belemnite (VPDB) standard. 
