Resolving Milankovitchian controversies: The Triassic Latemar Limestone and the Eocene Green River Formation
Abstract
Although orbital forcing is commonly proposed as the driverof ancient sedimentary rhythms, the lack of adequate independenttime control (radio isotopic data) to calibrate these cycleshas stood as a major challenge to evaluation of the hypothesis.Here I apply a new statistical approach to evaluate cyclicityin two historically important rhythmic units for which orbitalforcing has been proposed: the Triassic Latemar Limestone (Dolomites,Italy) and the Eocene Green River Formation (Wyoming, USA).A major advance of the new method is its explicit evaluationof the null hypothesis of no orbital signal. The null hypothesiscan be rejected with a high degree of confidence in the LatemarLimestone (probability <0.30%) and Green River Formation(probability <0.07%). The analyses also resolve controversiesabout the specific orbital calibrations at each site. Both dataseries reveal the expected precession, obliquity, and eccentricityorbital components, and yield astrochronologies that are consistentwith proposed radio isotopic based time scales.
- Publication:
-
Geology
- Pub Date:
- April 2008
- DOI:
- 10.1130/G24423A.1
- Bibcode:
- 2008Geo....36..319M