ABSTRACT: Miocene Glacioeustasy below the Resolution of Multiple, Planktic, Biostratigraphic Correlation Schemes
SNYDER, STEPHEN W., North Carolina State University, Raleigh, NC, ALBERT C. HINE, University of South Florida, St. Petersburg, FL, and SCOTT W. SNYDER and STANLEY R. RIGGS, East Carolina University, Greenville, NC
Stratigraphic analyses from a dense grid of over 20,000 km of very high-resolution seismic reflection data have delineated 18 Miocene sequences bound by physical unconformities that were traced and mapped across the continental margin of North Carolina. The unconformities are chiefly erosional and can be attributed to subaerial (fluvial channel scars) or submarine (boundary current scour) processes regulated by relative changes in sea level.
Biostratigraphic analyses of planktic microfossils (forams, nannos, rads, and diatoms) as well as paleoenvironmental interpretations of benthic foraminiferal assemblages from vibracores penetrating these sequences/unconformities were integrated and utilized to constrain the timing, duration, and amplitudes of relative sea level change. Results demonstrated the following. (1) Juxtaposition of the four different planktic microfossil biochronozones as defined by the Haq et al. (1988) scheme appears to be most consistent with the empirical microfossil data set from the North Carolina continental margin. (2) The multiple microfossil data set could not resolve the quantity of time missing across most of the unconformity surfaces. (3) The discrete Miocene sea level cycles are characterized b high-amplitudes (>60 m) and short periodicities (within the Milankovitch realm, or <500 Ka). They grossly simulate the ice growth/decay cycles of the last 700 Ka.
The high-frequency (fourth-order) glacioeustatic cycles are superimposed on a lower-frequency cyclicity that appears to have a periodicity of ~2.5 Ma. While the nondepositional (or erosional) episodes separating each lower-frequency cycle were easily identified and quantified in the biostratigraphic data set, the unconformities separating the higher-frequency cycles could not be resolved. Hence, in the biostratigraphic data set, these stratal sections appear as an interval of continuous deposition even though the seismic data have demonstrated they consist of a stack of sequences and unconformities; and the physical expression of unconformities developed during the higher frequency sea level events are sometimes more dramatic than the unconformities separating the lower-frequency cycl s.
AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)