The facts of life:
The process of "reading the sedimentary record" to reconstruct Earth history is:
- anything but straightforward,
- requires the application of many different approaches, each with their own filters and biases
- never yields a completely unambiguous result.
Cretaceous stream deposits near Drumheller, AB - Not a layer cake.
- Limited in lateral extent.
- Variably preserved
- Exposed in only certain places.
- (the biggie) incorporate unconformities - intervals of non-deposition or erosion of unknown duration.
No single section records continuous sediment accumulation. We reconstruct geological history only through correlating strata widely separated in space and time. This must be approached through multiple lines of evidence, because no one type of evidence is without its biases. Possibilities include:
- Lithostratigraphy: matching of sedimentary properties of rock units.
- Sequence stratigraphy: matching of widespread unconformities.
- Chronostratigraphy: matching of rocks of similar numerical ages.
- Biostratigraphy: matching of rocks with similar index fossils.
- Chemostratigraphy: matching of rocks with similar isotopic ratios or trace element concentrations representing similar global environment.
- Magnetostratigraphy: matching of rocks with matching patterns of geomagnetic reversals.
- Seismic stratigraphy: matching of rocks by tracing their seismic reflections through the subsurface.