uppertriassiccalcareous nannofossilbiostragraphy, exmouth ... ·...
TRANSCRIPT
Dissolu'on Experiment
Conclusions
Calcareous Nannofossils
Upper Triassic Calcareous Nannofossil Biostra'graphy, Exmouth Plateau, Western Australia
Bryan Hermosillo, Dr. David K Watkins, Bobbi Brace, M.S. Department of Earth & Atmospheric Sciences, University of Nebraska–Lincoln
Purpose
Stra'graphic Column
Subduction of oceanic crust has destroyed a large portion of accessible Late Triassic (200-228 Mya) sea floor sediments. This study analyzes rare Late Triassic sediment samples to better understand the earliest known nannofossil assemblages.
Biostra'graphy
Bown, 1998
http://www.msrc.sunysb.edu/octet/biological_pump.html
• Biostratigraphy − Fossil assemblage is dominated by the presence of E.
zlambachensis and P. triassica. − Average length of E. zlambachensis increases up the
drilling section. − Average diameter of P. triassica decreases up the
drilling section.
• Dissolution Experiment − The addition of hydrochloric acid has rounded the
edges of E. zlambachensis through dissolution. − The apparent diversity of short squat forms and
elongate forms is not the result of dissolution.
• Limitations − Dissolution differs at depth under increased
temperature and pressure than the atmospheric pressure and temperatures used in the experiment.
− Overall knowledge of Upper Triassic Nannofossil assemblages is still lacking due to the rarity of publicly available samples and well logs.
Young et al., 2003 Bown, 1998
Assigning relative ages of rocks based on fossil assemblage.
+ HCL acid Bown, 1998 Chandon-1
Rounded edges
After
Angular edges
Before