Dynamic Stratigraphy: Controls and Products

by

Rob Gawthorpe and Catherine Hunt, University of Manchester

Most stratigraphy and/or sedimentology courses teach the main elements of stratigraphy (lithostratigraphy, chronostratigraphy and bio-stratigraphy). However, it is often difficult in lectures and practicals for students to appreciate the dynamic aspects of stratigraphy. This module is designed to address some of these difficulties by looking at the processes involved in the accumulation of strata, the rates at which these processes occur and how the processes interact. The module is intended for second-year students with a basic knowledge of classical stratigraphy, taking courses in stratigraphy, sedimentology and sedimentary basin dynamics. It can also be used to provide background material for third-year courses in seismic and sequence stratigraphy and basin evolution.

The module occupies approximately 15 Mb and is divided into seven sections which are accessed from a main menu. The first four sections introduce the basic controls that affect stratigraphy and allow users to see how the stratigraphic product is influenced by changes in the rates and magnitudes of these controlling processes. The next two sections provide an introduction to sequence stratigraphy. The final section consists of two case studies which draw on the ideas introduced in the preceding sections and allow users to test their understanding of these ideas. Users can work through the sections in any order but they should be aware that an understanding of the topics covered in early sections is assumed in later sections. The sections are accessed from this menu.

Basic Principles

Summary of the classical elements of stratigraphy (lithostratigraphy, chronostratigraphy and bio-stratigraphy). Simple examples applying these ideas.

Genetic Relationships

Walther's Law and genetically related successions. Progradation, retrogradation, aggradation; regression, transgression. Examples from different sedimentary systems (fluvio-deltaic, carbonate platform). Expression in vertical profile and cross-section.

Users can interact in a variety of ways

Hiatuses and Facies Shifts

Types of unconformity and the nature of hiatuses (erosional vs non-depositional). Stratal patterns (onlap, toplap, erosional truncation, downlap) and examples of facies shifts.

Short movies illustrate how the rates and magnitudes of processes control stratigraphy

Controls on Stratigraphy

Inter-relationships of major controls and feedbacks. Eustasy (tectonic and glacial), tectonics (variation with basin-forming processes), sediment flux. Relative sea-level and accommodation. Interactive investigation of how changes in rates and magnitudes of each main process affect stratigraphy and how their interaction controls stacking patterns and stratal geometry.

Users investigate stratal geometries and facies relationships

Sequence Stratigraphy I

Cyclicity and cycles of relative sea-level rise and fall. Stratal terminations and stacking patterns. Stratigraphic record in terms of recurring packages that have characteristic geometries. Sequences and their component parts; parasequences and marine flooding surfaces.

Sequence Stratigraphy II

Systems tracts and position within a cycle of relative sea-level change. Key stratal surfaces. Forced regressive/falling stage systems tract, lowstand systems tract, transgressive systems tract, highstand systems tract.

Users also investigate the chronostratigraphic expression of stratal terminations

Integrated Study

Two case studies: one clastic (using outcrop and borehole data from Book Cliffs, Utah, USA), the other carbonate (based on the Vercors platform, France).

This section looks in some detail at parasequences and how they form

Running the software

Navigation around the module is by means of buttons along the base of the screen. Users are encouraged to complete all the interactions on one page before proceeding to the next, but are not forced to do so. A glossary provides definitions of terminology used in the module.

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