Stable isotopic and stratigraphic proxy records of local, regional, and global climate.

Abstract

Utilization of stable isotopic compositions from various lacustrine deposits allows for development of a more complete understanding of mechanisms by which continental climates change. Study of the Miocene Camp Davis limestone has illustrated that paleoelevation can play a significant role in determining both the isotopic composition of meteoric precipitation as well as the nature of regional climate in which precipitation occurs. Evaluation of the isotopic composition of Holocene marl lake sediment from Michigan and Indiana has required reevaluation of mechanisms conventually ascribed to $\delta\sp{18}$O-$\delta\sp{13}$C covariance in lake sediment. Lithological, mineralogical, and isotopic data from the lower Cretaceous Peterson Limestone indicate that climatically controlled cyclic transitions from carbonate-rich to terrigenous-rich intervals occurred within individual limestone beds as well as at the formational scale. Statistical and modeling studies of marine platform carbonate deposits have allowed for an evaluation of their utility as recorders of climatically controlled global sealevel change. Systematic appraisal of forward model response of cycle stacking pattern to changing input parameters (sealevel, sedimentation, subsidence rate) demonstrates that interpretation of hierarchical structure based on an assumed one-to-one correspondence between forcing function frequencies and cycle thicknesses may be incorrect. Statistical considerations indicate that many cyclic carbonate sequences are indistinguishable from random thickness associations, and relatively few exhibit trends commensurate with long-term change in the rate of creation of accommodation space. Similarly, thickness distributions of carbonate cycles are incompatible with commonly invoked models of periodic deposition, and likely record stochastic processes of sediment accumulation. In light of these results it is clear that most, if not all, marine platform carbonate cycles formed in a random manner independent of any periodic extrabasinal process or mechanism.