Miocene

The Miocene epoch is a period of time that extends from about 23 to 5.3 million years before the present. As with other older geologic periods, the rock beds that define the start and end are well identified, but the exact dates of the start and end of the period are uncertain. The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words meion (less) and ceno (new) and means "less recent" because it has 18% (less than the Pliocene) of modern sea invertebrates. The Miocene follows the Oligocene Epoch and is followed by the Pliocene Epoch. The Miocene is the first epoch of the Neogene period.

The Miocene boundaries are not set at an easily identified worldwide event but rather at regional boundaries between the warmer Oligocene and the cooler Pliocene.

Miocene Subdivisions

The Miocene faunal stages from youngest to oldest are:

Messinian	(7.246 – 5.332 mya)
Tortonian	(11.608 – 7.246 mya)
Serravallian	(13.65 – 11.608 mya)
Langhian	(15.97 – 13.65 mya)
Burdigalian	(20.43 – 15.97 mya)
Aquitanian	(23.03 – 20.43 mya)

The subdivisions within the Miocene are defined by the relative abundance of different species of calcareous nanofossils (calcite platelets shed by brown single-celled algae) and foraminifera (single-celled protists with diagnostic shells).

Miocene Climate

Climates remained moderately warm although the slow global cooling that eventually led to the Pleistocene glaciations continued.

Although a long-term cooling trend was well underway, there is evidence for a warm period during the Miocene when the global climate rivalled that of the Oligocene. The Miocene warming began 21 million years ago and continued until 14 million years ago, when global temperatures took a sharp drop. By 8 million years ago, temperatures dropped sharply once again, and the Antarctic ice sheet was already approaching its present-day size and thickness. Greenland may have begun to have large glaciers as early as 7 to 8 million years ago, although the climate for the most part remained warm enough to support forests there well into the Pliocene.

Miocene Paleogeography

Continents continued to drift toward their present positions. Of the modern geologic features, only the land bridge between South America and North America was absent.

Mountain building took place in Western North America and Europe. Both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines. Well studied continental exposures occur in the American Great Plains and in Argentina.

Miocene Flora

Grasslands underwent a major expansion as forests fell victim to a generally cooler and drier climate overall. Grasses also diversified greatly into a number of species and also caused a major increase in the biodiversity of large herbivores, including ruminants (of which modern cattle and deer belong to).

Miocene Fauna

Both marine and continental fauna were fairly modern. Only in isolated South America and Australia did widely divergent fauna exist.

Mammals

Recognizable wolves, raccoons, horses, beaver, deer, camels, whales, etc. existed in the Miocene.

Birds

Recognizable crows, ducks, auks, and owls appear in the Miocene.

Miocene Oceans

The oceans continue cooling, and brown algae plants, called kelp, proliferate, supporting new species of sea life, including otters, fish and various invertebrates.

References

Ogg, Jim; June, 2004, Overview of Global Boundary Stratotype Sections and Points (GSSP's) http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.

External links