Record of sea-level fall in shallow-water hemipelagic strata: Case study and numerical modelling

Abstract

Hemipelagic rhythmites of the Bohemian Cretaceous Basin and two-dimensional numerical modelling of coexisting hemipelagic and siliciclastic depositional systems reveal important details on hemipelagic sequence stratigraphy. Lowstand systems tracts of c. 400 ka sequences are marked by distinct (up to 100 ka) phase lags between maxima in bottom shear stress (omission surfaces) and maxima in siliciclastic deposition (mudstone intercalations) in the shallowest zone of this hemipelagic setting. Importantly, sediment redistribution caused by local differences in bathymetry induces up to 100 ka shifts in lithological markers, thus changing the hemipelagic expression of sea-level falls. Both results underscore the frequently neglected fact that lithological and geochemical data on siliciclastic fluxes (e.g. quartz contents, Ti/Al) provide nonlinear proxies of eustatic and relative sea-level changes. Hemipelagic records of climatic and orbital forcings can be markedly distorted in phases and magnitudes. Two-dimensional modelling can be instrumental in extracting unbiased signals. © 2010 Blackwell Publishing Ltd.