The IETM interval shows a dramatic departure from both these background trends, however.This is marked by prolonged hiatuses (0.1 and 0.6 Myr duration) in turbidity current activity in contrast to the arithmetic mean recurrence, λ, for the full records (λ=0.007 and 0.0125 Myr).
References: Ostermann, M., Sanders, D., Prager, C., Kramers, J., 2007, Aragonite and calcite cementation in 'boulder-controlled' meteoric environments on the Fern Pass rockslide (Austria): implications for radiometric age-dating of catastrophic mass movements. Prager, C., Zangerl, C., Patzelt, G., Brandner, R., 2008.
Age distribution of fossil landslides in the Tyrol (Austria) and its surrounding areas.
The study focuses on two sedimentary intervals that straddle the IETM and we discuss implications for turbidity current triggering.
We present the results of statistical analyses (regression, generalised linear model, and proportional hazards model) for extensive turbidite records from an outcrop at Zumaia in NE Spain (N=285; 54.0 to 56.5 Ma) and based on ODP site 1068 on the Iberian Margin (N=1571; 48.2 to 67.6 Ma).
In addition, in a pilot study on the carbonate-lithic rockslide of Fern Pass (Tyrol, Austria) it was demonstrated that U/Th dating of diagenetic cement formed newly within the rockslide deposit can provide a good proxy age of the mass-wasting event (Ostermann et al., 2007; Prager et al., 2009).
Proxy-dating carbonate-lithic rockslides with the U/Th method is based on Ca CO³ precipitates (cements, stalactites) formed along the underside of rockslide boulders.
Dramatic global warming appears to exert a strong control on inhibiting turbidity current activity; whereas the effects of sea level change are not shown to be statistically significant.
Rapid global warming is often implicated as a potential landslide trigger, due to dissociation of gas hydrates in response to elevated ocean temperatures.
The sedimentary sequences provide clear differentiation between hemipelagic and turbiditic mud with only negligible evidence of erosion.
We infer dates for turbidites by converting hemipelagic bed thicknesses to time using interval-averaged accumulation rates.
Because the Ca CO³ precipitates form only after mass-wasting, their U/Th age represents a minimum proxy age of the event.