Analog Morphocorrelation: New Technique with Implications for High-Resolution Absolute Age Dating
Anthony J. Arnold, William C. Parker, William A. Berggren
The conventional approach to increased biostratigraphic resolution involves identifying additional datum planes defined by discrete events. Multivariate techniques used to refine a conventional taxonomic zonal scheme offer no improvement in precision; however, since the characters on which the zonal boundaries are based often show continuous stratigraphic variation, they offer an opportunity for continuous stratigraphic correlation based on the stage of evolution.
Morphometric analysis was conducted on two lineages: (1) the Globorotalia cibaoensis-G. crassaformis lineage, using a reference section from the early Pliocene of the Rio Grande rise, spanning approximately 2.6 m.y.; and (2) the G. conoidea-G. inflata lineage, using a reference section from the late Miocene to the Holocene from the southwest Pacific, spanning approximately 8 m.y. Stepwise multiple regression of morphologic variates generated an equation with an age-prediction precision (95% confidence) of ±122 k.y. in the G. crassaformis lineage and ±463 k.y. in the G. conoidea lineage (accuracy depends on calibration of absolute dates in the reference section and our knowledge of sedimentation rates over the measured interval).
Using single-equation analog morphocorrelation, any sample overlapped by the reference lineage can be correlated, which reduce the need for repeated sampling in a search for discrete events. We demonstrate that analysis of continuous morphologic variation can increase stratigraphic precision with a few carefully chosen variables, and that analog morphocorrelation can yield absolute dates, rather than relative dates with quantified error. Any disadvantages inherent in analog morphocorrelation are also found in conventional biostratigraphic techniques, but are usually unquantified and unrecognized.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.