THE EMPTINESS OF THE STRATIGRAPHIC RECORD: A PRELIMINARY EVALUATION OF MISSING TIME IN THE MESAVERDE GROUP, BOOK CLIFFS, UTAH, U.S.A.

摘要

Observations of modern sedimentation rates in nonmarine and shallow-marine clastic environments indicate that deposits formed in comparable settings in the ancient record could accumulate in a fraction of the time that would appear to be available according to conventional chronostratigraphic dating methods. Typically as little as 10 of elapsed time is represented by sediment, the remainder by breaks in sedimentation, many of which are inconspicuous. An examination of the chronostratigraphy and sedimentary history of the Mesaverde Group of the Book Cliffs, Utah, U.S.A., confirms this pattern. Shoreface, deltaic, and nonmarine successions are considered to be particularly fragmentary. Ravinement surfaces may each account for up to 10~5 years of missing time. In the sedimentary record of shallow-marine and nonmarine deposits stratigraphic continuity is not to be expected, and calculation of time-related issues, such as mass-balance transport rates and the trajectories of shoreline transgression and regression, must take this into account.