Milankovitch Forcing in Equatorial, Late Triassic Pangea: (Deep River; Dan River, and Richmond Basins, Southeastern USA)

Details Milankovitch Forcing in Equatorial, Late Triassic Pangea: (Deep River; Dan River, and Richmond Basins, Southeastern USA) Milankovitch Forcing in Equatorial, Late Triassic Pangea: (Deep River; Dan River, and Richmond Basins, Southeastern USA)

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmpp42d..01o&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #PP42D-01

Physics

1620 Climate Dynamics (3309), 1739 Solar/Planetary Relationships, 1845 Limnology, 3240 Chaos, 9609 Mesozoic

Scientific paper

The Milankovitch character of lake level fluctuations in the tropics of central Pangea has been well established since the pioneering work of Van Houten in the 1960's (1) that laid the foundation for quantitative analysis of core and outcrops in the 1990's (2,3). In the region from about 3° to 10° N latitude giant rift lakes fluctuated to the classic Milankovitch frequencies of precessional forcing of ~20, 96, 128, and 404 ky, as well as the less well known 1.75 and 3.5 m.y. cycles. The latter are the Triassic values for the periods of g4-g3 of eccentricity related precessional forcing and the secular resonance, theta (2(g4- g3) - (s4-s3)), of precessional and obliquity related forcing. We attribute the forcing of lake depth largely to modulation of the strength of tropical convergence. Late Triassic rifts located from 0° to 3° N latitude show similar patterns, except with a strong tendency towards a doubling of the climatic precessional frequency and a lack of evaporites as previously reported from the Dan River basin (4,5,6). Here we report on new analyses of coal-bearing cores and drill holes from the Deep River, Dan River, and Richmond basin of older Late Triassic lacustrine strata that reinforce this pattern but show that the doubling of the precessional frequency is not ubiquitous at the equator and also show that very strong climatic transitions appear related to the 1.75 and 3.5 m.y. cycles juxtaposing coals and caliches in vertical sequence and sometimes coinciding with major faunal and floral transitions. (1) Van Houten FB. 1964. Kansas Geol. Surv. Bull. 169:497. (2) Olsen PE & Kent DV. 1996. Palaeogeo. Palaeoclim. Palaeoecol. 122:1-26. (3) Olsen PE & Kent DV. 1999. Phil. Trans. Roy. Soc. Lond. (A) 357:1761-1787. (4) Olsen PE & Kent DV.1996. Eos, Trans., AGU 77(46), Suppl.:301. (5) Olsen PE. 1997. Ann. Rev. Earth Planet. Sci. 25:337-401. (6) Olsen PE & Kent DV. 2000. in Bachmann G. and Lerche I. (eds.), Epicontinental Triassic, Vol. 3, Zent. Geol. Palaont. VIII:1475-1496.

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