Strontium-derived global eustasy applied to the Scotian Atlantic margin

Abstract

The published eustatic sea level curves of the seventies and eighties have caused a scientific breakthrough and emergence of sequence-stratigraphy as hydrocarbon exploration tool. However much debate has taken place on the validity of the curves as reconstructing a global average eustatic sea level is hampered by a non-agreement of sampled sites due to differing local tectonics, deposition and long wavelength dynamic topography as a result of mantle convection. In particular, the overall amplitude of global Phanerozoic long-term sea-level is poorly constrained and has been estimated to vary between ∼400m above sea level to ∼50 m below sea level. However, there is little consensus on the range of sea-level changes, though most believe that the sea-level position during most of the Phanerozoic was within ±100 meters of the present-day level. In order to overcome the limitations of curves based on local observations, we propose an alternative method to estimate global sea-level change. We utilise the well-sampled Phanerozoic strontium record, which at first order represent the trade-off between inputs from continental weathering and mantle input by volcanism. By compensating for weathering, the corrected strontium record reflects mantle inputs and is corroborated by subduction and crustal spreading models for the Mesozoic & Cenozoic. By estimating the past oceanic plate age distribution, we obtain average base of ocean floor and coastal onlap curves. When compared with other sea-level curves, we observe large similarities in the Cretaceous and Cenozoic in amplitude and trends. Main differences occur in the rate of Jurassic sea-level rise and late Permian sea-level fall. We verify our sea-level curve with the stratigraphy of the Nova Scotian passive margin and conclude the new sea-level curve agrees well with the geological record at 100 and 10 Myr timescales. In addition we compare our curve with inundation curve from a recent global compilation of gross depositional environments. We propose that the here obtained Phanerozoic sea-level curve is used as base line for second and third order sea-level curves and for sequence-stratigraphic studies at basin scale.

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015