Jurassic Period


Jurassic Period

The Jurassic period is normally divided into three main divisions, or epochs: Early, Middle, and Late; more informally, the period is labeled with lower case letters, or the early, middle, and late Jurassic. In addition, scientists often use the terms Lower, Middle, and Upper to describe the divisions of the Jurassic.

Each of these main epochs is further broken up into subdivisions. To make things more confusing, the smaller ages often have different names (and often dates), depending on whether you are using European, North American, or Australian and New Zealand nomenclature. Presented here is a general list of North American Jurassic period divisions. These dates are not absolute, and may vary slightly from source to source.

Epoch Age (approximate)
Millions of Years Ago
Early Navajo 195–178
  Kayenta 202–195
Middle Twin Creek 170–163
  Gypsum Springs 178–170
Late Morrison 156–141
  Sundance 163–156


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