@article{207,
  author = {Enriqueta Barrera and Gerta Keller},
  title = {Stable isotope evidence for gradual environmental changes and species survivorship across the Cretaceous/Tertiary Boundary},
  abstract = {<p>High-resolution δ13C and δ18O records have been generated from analyses of the planktonic foraminiferal species\&nbsp;<em>Heterohelix globulosa</em>\&nbsp;and the benthonic foraminiferal taxon\&nbsp;<em>Lenticulina</em>\&nbsp;spp from 3 m of a cored section spanning the Cretaceous/Tertiary (K/T) boundary at Brazos River, Texas. These are the first stable isotope records across the K/T boundary based on monospecific and monogeneric foraminiferal samples. They show a gradual decrease in δ13C values of about 2.5 permil beginning at the K/T boundary, as defined by the first appearance of Tertiary planktonic foraminifera, and continuing 17{\textendash}20 cm above the boundary, approximately 40,000 years later. Gradual\&nbsp;13C depletion contrasts with the sudden δ13C drop at the K/T boundary observed in many deep-sea sections. The surface-to-bottom δ13C gradient decreased to less than zero approximately 25,000{\textendash}30,000 years after the K/T boundary and remained negative for at least the next 140,000 years. Concomitant with change in δ13C values is a gradual decrease of about 2.5 permil in δ18C values which has not been observed at other localities. This\&nbsp;18O depletion suggests changes in temperature and/or salinity in the earliest Paleocene Gulf of Mexico. No extinction of foraminiferal species is associated with the K/T boundary or the onset of\&nbsp;18O and\&nbsp;13C depletions. Instead, two phases of Cretaceous species extinctions occur. One extinction phase is below the K/T boundary and below the tsunami bed of Bourgeois et al. [1988] and may be linked to sea level regression and environmental perturbations. The second extinction phase coincides with the minimum in δ13C and δ18O values in the Early Danian (Zone P0/Pla) and appears directly related to environmental changes reflected in the isotopic record.\&nbsp;<em>H. globulosa</em>, which is commonly present in Maastrichtian and Danian sediments, exhibits significantly lower\&nbsp;18O/16O and\&nbsp;13C/12C ratios in Tertiary sediments relative to specimens from Maastrichtian sediments, demonstrating the survival of this important Cretaceous taxon after the K/T boundary event.\&nbsp; <a href="https://geoweb.princeton.edu/research/keller/pubs/Barrera_et_al-1990-Paleoceanography.pdf" target="_blank">PDF</a></p>
},
  year = {1990},
  journal = {Paleoceanography},
  volume = {5},
  pages = {867{\textendash}890},
  month = {12/1990},
  url = {https://doi.org/10.1029/pa005i006p00867},
  doi = {10.1029/pa005i006p00867},
  language = {eng},
}