Journal article
Using in situ geochemistry to investigate the depth habitat of Ammonites
Abstracts with programs - Geological Society of America, Vol.49(6)
Geological Society of America, 2017 annual meeting & exposition (2017)
2017
Abstract
Ammonites are the most iconic of extinct mollusks. Their wide spatial distribution and biostratigraphic utility make them ideally suited to investigate past climate. To date, stable isotope analyses of ammonites have focused on adult shells that can be sampled by bulk methods and have suggested adults had a nektobenthic mode of life. Eggs and hatchlings are thought to occupy a shallower position in the water column. Stratigraphic occurrence and analogy to modern cephalopods supports this hypothesis, but stable isotope analysis has not previously been applied to this question, primarily because the volume of material necessary for conventional techniques precludes sampling the diminutive embryonic shell ( approximately 700 mu m diameter). Here we test for the depth that ammonite eggs and hatchlings inhabited by using secondary ion mass spectrometry (SIMS) for in situ sampling of the shell wall compared to environmental context. Materials from the Maastrichtian Fox Hills and Owl Creek Formations of North America were sampled. Samples were assessed for diagenesis using backscattered electron and cathodoluminescence imaging. Original nacreous aragonite microstructure is visible. Electron backscatter diffraction confirmed aragonite mineralogy. Fossils from the Fox Hills Formation were from a single concretion. Samples from the Owl Creek Formation spanned several meters of section. Published bulk measurements from the location show no stratigraphic trend in delta (super 18) O, but approximately 1 ppm range. Surface and bottom water conditions inferred from delta (super 18) O analysis of coocurring organisms. Hatchling ammonite delta (super 18) O is variable within and between individuals at both sites. Shell wall precipitated before hatching in the Fox Hills Hoploscaphites suggest a benthic development ( approximately -2 ppm change at hatching) and carbon isotope data suggest influence of terrestrial runoff or the egg yolk carbon source at hatching ( approximately -5 ppm change at hatching). These pre- to post-hatching differences suggest the relationship between egg size and development depth among modern coleoids may not apply to ammonites. Owl Creek material shows no change in delta (super 18) O between varix and post-hatching shell wall, but a wide range of delta (super 18) O especially in later whorls (2 ppm in whorls 4 or more). Our data demonstrate the utility of in situ geochemical methods to better understand life history of mollusks.
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Details
- Title
- Using in situ geochemistry to investigate the depth habitat of Ammonites
- Creators
- Benjamin J. Linzmeier - Northwestern UniversityNeil H. LandmanJocelyn A. SessaShanan E. PetersIan J. OrlandKouki KitajimaReinhard KozdonJohn W. ValleyAnonymous
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.49(6)
- Conference
- Geological Society of America, 2017 annual meeting & exposition (2017)
- Publisher
- Geological Society of America (GSA)
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Biodiversity, Earth, and Environmental Science (BEES)
- Identifiers
- 991021013171604721