uppertriassiccalcareous nannofossilbiostragraphy, exmouth ... ·...

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