comparing rock and fossil records in the deep sea

Comparing rock and fossil records in the deep sea

Graeme T. Lloyd, Andrew B. Smithand Jeremy R. Young

Fossil record is our only record of the diversification of life

Diversity correlates with rockrecord on land

Peters and Foote 2001 Smith and McGowan 2007

An alternative record

• Calcareous microfossils such as coccolithophores have land-based and deep sea records

• i.e., two diversity records and two rock records

• What is the relationship between these records?

• How much does the rock record influence diversity patterns?

The database• Study groups are Coccolithophores and

planktic Foraminifera• Novel compilation from North Atlantic• Compiled from 40 years ODP/DSDP

data• 64,077+ occs from 20,723+ samples• High temporal resolution (biozones)

Deep sea species richness

Deep sea genus richness

Deep sea rock record

Correlation tests

• First both time series were log-transformed• Long term test:

– Simple correlation• Short term tests:

– First differences (absolute)– Moving average differences (relative to long

term trend)• Degree (rho) and significance (p) of

correlations determined using Spearman rank

Deep sea long-term correlation

Deep sea short-term correlation I

Deep sea short-term correlation I

Deep sea short-term correlation II

Deep sea short-term correlation II

Modeling

Modeling results

Modeling results

Subsampling

Subsampling results

Conclusions

• Deep sea diversity curve largely explicable by sampling

• Apparent rise in nannofossil diversity to present strongly associated with rise in sampling

The other side of the story

• What about the land-based record for the same groups?

• Sampling strategy based on distribution charts from primary literature

• Rock record measure is number of localities

Two rock records

Two fossil records

Summary

• Both land and sea have measurable rock biases that follow different trajectories over geological time

• Will allow a clear and explicit test of how important a role these play in shaping our fossil record