Biology Reference
In-Depth Information
Figure 3.7 Magnetic polarities for the interval between about 51 and 68 Ma, with plankton
(fl oating) foraminifera and calcareous nanoplankton (microscopic) zones. Black indicates nor-
mal (i.e., present) polarity, and white indicates reversed polarity. From Berggren and others
1995, which also includes diagrams from other intervals (reproduced in Graham 1999, 171,
218, 224, 243, and 244). Used with permission from the Society for Sedimentary Geology
(SEPM), Tulsa, OK.
other geologic and biologic information they contain, are laid down in lay-
ers from oldest at the bottom to younger toward the top. They remain so
unless disturbed by tectonic or orogenic forces, and these disturbances usu-
ally leave compelling evidence in the form of faulting or reversed sequences
compared to those elsewhere. Although intuitively obvious from the pres-
ent perspective, the superposition of strata was not as clear in the eigh-
Search WWH ::




Custom Search