Arabian Orbital Stratigraphy: Periodic Second-Order Sequence Boundaries?

Abstract

ABSTRACTA simplified model of orbital-forcing suggests that the Phanerozoic Eon may be represented by 38 periodic second-order depositional sequences (DS2) each lasting about 14.58 million years (my). The DS2s are separated by second-order sequence boundaries (SB2, maximum regression surface) that should be manifested as regional stratigraphic discontinuities (unconformity, disconformity, time hiatus). To test this simple model, the Arabian succession was reviewed to identify candidate regional stratigraphic discontinuities that might be periodic at 14.58 my. Of the 38 predicted SB2s, 34 regional stratigraphic discontinuities were identified within the uncertainty of biostratigraphic-radiometric age dating, or by stratigraphic position. One SB2 could not be positioned in the succession because of ambiguous biostratigraphic dating. One was predicted within a long-lasting hiatus, and another two were predicted within an undifferentiated formation. The four unidentified SB2s reflect on the limitations of the data sample, rather than on the viability of the model.Because the stratigraphic discontinuities represent age spans with bounding ages that are at best believed to have accuracies of about ± 3.0 my, the model-data correlation was considered inconclusive. The resulting analysis, however, demonstrates that the ages in million years before present (Ma) of interpreted Arabian (and possibly global) sequence stratigraphic surfaces and depositional sequences, as estimated by biostratigraphic-radiometric dating techniques, are highly inaccurate (± 5–10 my). This conclusion suggests that presently used chronostratigraphic correlations across the Arabian Platform should be treated with great caution. The correlation of model SB2s to regional stratigraphic discontinuities, affords an alternative time scale that may eventually assist in the calibration of the biostratigraphic-radiometric time scale. An orbital-forcing time scale has a decided advantage in that it comes with precise third- and fourth-order stratigraphic predictions imbedded as sea-level fluctuations. The next level of testing is whether these orbital-forcing predictions hold up to precise correlation to stratigraphy.