| Summary: | Earth's climatic history during much of the cenozoic has been controlled by Milankovitch variations in the planetary orbit comprising alternate periods of expansions and contractions of large ice sheets. In this context, whereas a plethora of outcrop studies made on Plio-Pleistocene deposits have enphasized the stratigraphic response to high-frequency, orbitally-driven eustatic sea-level changes, comparatively less attention has been focused on the attempt to relate miocene eustatic sea-level changes directly to shallow-marine sequences. As a result, far less is known about these sediments that, having been deposited during a period of Southern Hemisphere-driven glacio-eustasy, should feature a very similar record in term of sedimentary cyclicity. This bias is likely to arise from the general paucity of high-quality geological records documenting the associated transgressions and regressions across the World's continental shelves as most of the continental margins remain flooded. a detailed sequence stratigraphic analysis of the shallow-marine, Miocene Angostura Formation (Ecuador) and Caleta Herradura Formation (Northern Chile) led to the indentification of an extraordinary record of cyclical high-frequency sea-level changes. these two formations comprise eight and twenty-five, meter to tens of meter-scale high-frequency sequences, respectively. the architectural style of these sequences is remarcably similar to that described for high-frequency sequences formed under severe icehouse regimes characterised by repeated glacio-eustatic oscillations in sea level, such as during the Permian, the Oligo-Miocene , or the Plio-Pleistocene. a reasonable correlation between sequences and the contemporaneous high-frequency glacio-eustatic changes leads to the conclusion that: i) glacio-eustasy regulated by astronomicalvariations might has been the principar factor controlling stratigraphic packaging; and ii) these sequences provide and excellent shallow-marine outcrop record of middle to late Miocene Antarctic glaciations.
|
|---|