Investigation of Cretaceous Molluscan Shell Material for Isotopic Integrity: Examples and Implications from the Baculites compressus/cuneatus Biozones (Campanian) of the Western Interior Seaway
Year: 2006
Type: article
Abstract: Whether a global greenhouse interval is a distinct or distant future, it is important\nto understand the dynamics of a greenhouse system. During such intervals the oceans, in\nthe absence of sizeable polar ice caps, flood the continental shelf. The stratification and\ncirculation of these epicontinental seas are open to debate, because there are no Recent\nanalogs. The carbon and oxygen stable isotope record of fossil molluscan shell from\nepicontinental seas has the potential to reveal their stratification and seasonal cycles.\nWhether a global greenhouse interval is a distinct or distant future, it is important\nto understand the dynamics of a greenhouse system. During such intervals the oceans, in\nthe absence of sizeable polar ice caps, flood the continental shelf. The stratification and\ncirculation of these epicontinental seas are open to debate, because there are no Recent\nanalogs. The carbon and oxygen stable isotope record of fossil molluscan shell from\nepicontinental seas has the potential to reveal their stratification and seasonal cycles.\nAs a study sample, mollusks from the\nBaculites compressus and Baculites\ncuneatus\nbiozones of the Western Interior Seaway of North America were collected from\nthree locations: Kremmling, Colorado; Trask Ranch, South Dakota; Game Ranch, South\nDakota. These fossils date to the Campanian (Late Cretaceous). Taxa include\nammonites, bivalves, gastropods, and nautiloids.\nThe first part of this investigation, described in Chapter 2, investigates the degree\nof alteration in these specimens. Elevated concentrations of minor elements such as\nmagnesium and strontium reveal alteration from the original aragonite and/or calcite\nskeletons. Concentrations of these elements obtained by ICP-OES analysis are compared\nwithin several suites of specimens: mode of preservation, shell testing location, shell\ncolor, cementation, appearance under light microscope, and appearance under scanning\nelectron microscope. Each of these suites tests a hypothesis about optimal shell\npreservation. Shell was found to be preserved best in shale rather than concretions,\nammonite phragmacone rather than septa, opalescent specimens rather that nonopalescent\nones, and uncemented shells rather than cemented shells, especially those with\nsecond-order versus first-order cement. Salinity and temperature values were derived for\nthe organisms in the Western Interior Seaway: while bivalves produced unusually low\ntemperatures, the others were reasonable for an inland sea.\nThe second part of this study, described in Chapter 3, examines the isotopic\nrecord within exemplary mollusk shells, taken perpendicular to growth lines. The data\nfor this investigation in sclerochronology documents the dominant isotopically enigmatic\nbottom-water habitat of the\nInoceramus, the geochemical signature of the overlying water\nmass inhabited by\nBaculites, and short-term migrations between the two water masses in\nthe nautiloid\nEutrephoceras.
Author: Ashley da Silva
Institution: University of South Florida
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Life below water
Open Access status: green
OpenAlex ID: W1574505773