Late Precambrian paradoxical glaciation and obliquity of the Earth - a discussion of dynamical constraints

G.E, Williams' observations on Late Precambrian glaciogenic sequences pose some major challenges to the understanding of the dynamical evolution of th e Earth's orbit and spin that have not yet been adequately addressed. In th is paper, we investigate whether dissipative core-mantle coupling is an eff ective mechanism for reducing the obliquity by such a large amount as sugge sted by Williams [G.E. Williams, Earth Sci, Rev. 112 (1993) 1-45], and we e xamine the relationship between the obliquity and spin rate in the presence of such coupling. We show that this mechanism not only cannot explain the rapid and substantial decrease in obliquity, but also that such a decrease is in contradiction with existing paleorotation evidence for the same perio d, thus confirming the previous findings of Ni ron de Surgy and Laskar [O. Neron de Surgy, J. Laskar, Astron. Astrophys. 318 (1997) 975-989]. (C) 1999 Elsevier Science B.V. All rights reserved.