GEOL 340 Sedimentology and Stratigraphy
Lecture 29
1. Biostratigraphy
2. Graphic Correlation
1. Biostratigraphy
Biostratigraphy - characterization and correlation of
rock units based on their fossil content
organisms have gone through successive changes through geologic
time
Principle of Faunal Succession - any particular geologic time interval can be recognized and distinguished from other time periods by the fossil content - Strata Smith late 1700's
Stage - large-scale groups of strata containing the same major fossil assemblages
Zone - small-scale units defined by overlapping ranges of fossils
2. Graphic Correlation
Interval zonations alone do not yield high-precision age dating due to lateral migration of organisms within facies altering horizons of first or last appearance
Graphic Correlation
Shaw (1964) statistical treatment of first and last occurrences
plots the stratigraphic elevation of first and last occurrences
against other sections
step through example given in Figures 17.16 through 17.19
a. cross-plot all elevations of first and occurrences of fossils,
as well as "events"
events = regionally synchronous events
ash falls
changes in seawater chemistry (isotope shifts)
b. calculate and draw a best-fit regression line (position checked
with events)
c. points well off regression line indicate significant "changes"
between sections
organism migrations
changes in sedimentation rates (hiatuses)
faulting