A stratigraphic analysis of Paleogene deposition in northwest Europe and the role of graphic correlation in sequence stratigraphy
Neal, John Edward
Vail, Peter R.
Doctor of Philosophy thesis
A sequence stratigraphic analysis of Paleogene deposits, using subsurface data (well logs, seismic data, and biostratigraphy) from the Central North Sea and published outcrop information from northwest Europe, has documented a framework of 30 "third order" depositional sequences nested within 5 "second order" major regression/transgression cycles. The order of a cycle is based on observations concerning its constituents and its impact on the depositional systems of the basin, not strictly on its duration. Integration of composite standard biostratigraphy with sequence stratigraphy builds a consistent chronostratigraphic depositional framework. The framework is based on the identification of hiatal intervals in wells, boreholes, and outcrop using graphic correlation. Hiatal interval is a generic term that differs from condensed section. Discontinuous sedimentation is assumed of across some units traditionally called "condensed sections". This assumption is based on evidence from regional correlation of graphic correlation terraces. An ideal relationship of graphic correlation terraces within a sequence stratigraphic model is presented, providing the theoretical basis for regional correlations. Weaknesses in graphic correlation (underuse and static application) are countered with strengths in sequence stratigraphy (widespread use and dynamic application). Conversely, weaknesses in sequence stratigraphy (documentation and consistency) are the strengths of graphic correlation. This study emphasizes the interdependence of the two methodologies. A depositional model is also proposed as a variant of the classic Vail model. This model considers the effect of depositional profile and sediment supply in the preservation and distribution of systems tracts. Recent revisions in Central North Sea lithostratigraphy and sequence stratigraphy provide an opportunity for comparison between different methods and data resolutions. The stratigraphic framework built from subsurface data is compared with age-equivalent deposits outcropping in Northwest Europe. This correlation reveals that sedimentation in the deep basin occurs as depositional pulses, separated by time-correlative graphic correlation terraces (hiatal intervals). Data terraces expand into thick deposits in Northwest Europe. Not all sequence boundaries are resolvable by graphic correlation, but the method brackets packages defined by seismic, log interpretation and biostratigraphy. By correlating outcrops and subsurface data, it is possible to construct a relative sea level signal for the entire basin.