Journal article
Stable isotope investigation of early ontogeny in Upper Cretaceous Owl Creek Formation ammonites
Abstracts with programs - Geological Society of America, Vol.48(7)
Geological Society of America, 2016 annual meeting & exposition (2016)
2016
Abstract
The strong contrast between egg size and hatchling ecology of ammonoids and nautiloids is thought to explain why ammonoids were more vulnerable to extinction and more prone to diversification than nautiloids throughout the fossil record. Nautiloids had large slowly developing eggs (20-30 mm) and nektobenthic juveniles and ammonoids had small eggs (0.7 mm) and potentially planktonic juveniles. Stable isotope analysis of delta (super 18) O (CaCO (sub 3) ) from early shell wall has the potential to elucidate living depth from early ontogeny that morphology and stratigraphic occurrence cannot. Conventional mechanical separation for stable isotope analysis cannot readily isolate very small domains such as the embryonic shell wall ( approximately 10 mu m). Secondary ion mass spectrometry (SIMS) overcomes the limitations of mechanical separation, because a focused Cesium ion beam performs in situ sampling of the delta (super 18) O of small domains (10 mu m) with high precision (+ or -0.3 ppm 2SD). To observe the isotope pattern from early ontogeny, we sampled two ammonites from the late Maastrichtian Owl Creek Formation in northern Mississippi. This formation was chosen because of exquisite preservation, faunal diversity that includes foraminifera and bivalves, and a preexisting dataset of bulk stable isotope analyses. Scanning electron microscopy shows the two ammonites sampled by SIMS preserve prismatic and nacreous microstructure with little diagenetic alteration. The two Discoscaphites iris that have been analyzed show no trend in delta (super 18) O values through the first several whorls of growth (n=14, 1.0 ppm 2SD and n=5, 1.4 ppm 2SD). This suggests that these individuals may have hatched and lived in the same water mass for these early few months of life. Additional sampling from other individuals and later whorls may reveal, via delta (super 18) O, habitat change through ontogeny. Analysis of foraminifera will allow for intermethod comparison with published datasets from this location.
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Details
- Title
- Stable isotope investigation of early ontogeny in Upper Cretaceous Owl Creek Formation ammonites
- Creators
- Benjamin J. Linzmeier - University of Wisconsin–MadisonJocelyn A. SessaI. J. OrlandNeil H. LandmanShanan E. PetersJohn W. ValleyAnonymous
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.48(7)
- Conference
- Geological Society of America, 2016 annual meeting & exposition (2016)
- Publisher
- Geological Society of America (GSA)
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Biodiversity, Earth, and Environmental Science (BEES)
- Identifiers
- 991021013188504721