Milankovitch cyclicity and sea-level change in the Late Eocene-Early Oligocene interval: evidence for rapid and extensive Antarctic glaciation at 33.5 Ma? (abstract of paper presented at EUG XI, Strasbourg, France, 8-12 April 2001)

摘要

We have studied an expanded succession of coastal marine,estuarine and lacustrine sediments of Late Eocene-EarlyOligocene age in the Isle of Wight southern England. In thissuccession, a strong Milankovitch signal (406, 100, 40 andweaker 20Ka) is recorded from the relative abundance ofneoformed illite and illite-smectite, which formed in soilsby seasonal wetting and drying. The orbital timescale iscalibrated using magnetostratigraphic, and to a lesserextent, biostratigraphic data. Combined orbital calibrationand sequence stratigraphic analysis allows us to identify themajor control on sea-level as the 406Ka long eccentricitycycle, which caused sea-level to fluctuate by 10-15 m.These values have been determined from the amount ofincision at observed at sequence boundaries on a regionalscale. Minor sea-level changes of 1-3 m were controlled byobliquity. The position of the Early Oligocene heavy ?18Oevent can be inferred in the Isle of Wight from its magnetostratigraphicproxy (base of chron 13n). We have determinedthe sea-level fall at this level to be approximately12 m, close in magnitude to drops associated with thepreceding 3 Late Eocene 406 Ka sequences. This evidencedoes not support recent estimates of a 50-90 m sea-level fallwithin the Early Oligocene based on the calculation that asignificant part of the oxygen isotope event was caused byrapid Antarctic ice buildup. Rather, orbitally driven sealevelchanges throughout the Late Eocene-Early Oligocene,although probably glacioeustatic in origin, remained ofsimilar magnitude.