KEYNOTE: EARTH-SYSTEM INTEGRATION: THE KEY ROLE PLAYED BY SEQUENCE STRATIGRAPHY

The complex interplay of first-order processes acting on the Earth's surface, including tectonism, climate change and sea-level change, leave their mark primarily in the sedimentary record. It is through methods of basin analysis that we have assembled the most complete documentation of Earth's evolving paleogeographies and of the major changes in global climate through deep geologic time.

Modern methods of sequence stratigraphy provide the most powerful practical theoretical framework for exploring basin history and unraveling earth processes. Proposed initially as a method of regional and global stratigraphic correlation for the purposes of petroleum exploration, sequence stratigraphic methodology has become the primary means of integrating a wide array of geophysical, geochemical, structural and sedimentological data. The central concept is that earth-system changes generate predictable stratigraphic responses, some synchronous and some not. Many such system changes are episodic, or cyclic, and generate cyclic stratigraphic responses, which provide the basis for the subdivision of basin fills into discrete sequences.

A critical component of sequence analysis is correlation. Traditional methods of chronostratigraphic correlation are essential for testing the synchroneity of events and processes identified at different locations. Only precisely correlated events can be used to construct regional and global models of earth-system change. For example, much geologic change reflects tectonic driving forces acting over time periods of millions of years and longer. These are modulated by shorter-term processes, including climate change driven by orbital forcing, acting over time scales of tens to hundreds of thousands of years. Substantial environmental change may occur through orbital cycles, but the time-scale of change may be below the resolving power of available chronostratigraphic data, which could introduce substantial regional and temporal errors in the construction of tectonic and climatic models.

Given these provisos, substantial advances in our understanding of earth processes have flowed from the use of sequence-stratigraphic theory, whereby sequence data have been used to test broader geological concepts. Examples will be described.