Questions for Olsen and Kent (1996)

1. Why can't Olsen and Kent match their record to an astronomical solution as was done for the late Neogene records of deMenocal and others?

p. 17-18: "It is not yet possible to produce an insolation time series for any portion of the Mesozoic because of inherent limitations in the precision of the celestial mechanical constants, uncertainties in the long term recession rate of the moon, and small effects of the chaotic behavior of planetary orbits."

2. Describe the hierarchy of cycles in the Newark Basin section, including the names of the cycles, their lengths and their durations.

The actual visible cycles in the lithology are the Van Houten and McLaughlin cycles. The short and long modulating cycles are systematic changes in the amplitude of the two visible cycles.

Name

Length (m)

Duration (kyr)

Van Houten cycle

4

20

short modulating cycle

18

100

McLaughlin cycle

60

412.9

long modulating cycle

260

2,000

3. Olsen and Kent do not say why Interval 1 includes the best spectra. Based on the information they do provide, why do you think this is so?

Interval I is the deepest facies and contains the greatest proportion of laminated black shales. This record is least likely to include any hiatuses (erosional events) that would have removed sediment and therefore time from the record. The resulting gaps would cause the spectral peaks to be broader in the frequency domain because of the addition of noise.

4. Why are the climatic effects of insolation changes related obliquity not observed in the Newark Basin?

The climate of the late Triassic was apparently not greatly affected by high-latitude processes. The linkages between high and low latitude climate processes were not strong at this time, which runs counter to Pedelaborde's description of the mechanics of the modern monsoon.

5. What is the crux of Olsen and Kent's argument for orbital forcing as the cause of the rhythmic bedding in the Newark Basin? That is, what feature of the rhythmicity argues that the cause is cyclic changes of orbital geometry?

The ratios of observed frequencies with respect to each other match the ratios expected via a Milankovitch forcing mechanism. It is very unlikely that this particular hierarchy of frequencies could appear by other means.