The Ordovician fossil record contains a diversity of marine
invertebrates, including graptolites, trilobites, brachiopods, and
conodonts (early vertebrates). A typical marine community consisted of
these animals, plus red and green algae, early fish, cephalopods,
corals, crinoids, and gastropods. A drop in sea level may have
contributed to the mass extinctions that characterized the end of the
Ordovician, in which perhaps 60% of all marine invertebrate genera went
extinct.
During the Ordovician Period in New Jersey, shallow seas gave way to deeper oceanic conditions. The shallow water limestone's and their reef-building organisms were replaced by dark colored shale's and mud stones and organisms typical of a deep-water environment. This change between environments is evident in the Valley and Ridge Province of northwestern New Jersey.
During the Ordovician Period in New Jersey, shallow seas gave way to deeper oceanic conditions. The shallow water limestone's and their reef-building organisms were replaced by dark colored shale's and mud stones and organisms typical of a deep-water environment. This change between environments is evident in the Valley and Ridge Province of northwestern New Jersey.
 | North American Paleogeography: During the Ordovician, Laurentia was located near the equator while it rotated about 45° counter-clockwise, closer to its present orientation. A shallow sea covered most of the continent, depositing limestone's, shale's, and sandstones. However, by the Middle Ordovician, its southern margin (now the East Coast) was uplifted due to a collision with an island arc. Glaciation at the end of the Ordovician resulted in a drop in sea level, so some rocks deposited earlier were exposed and eroded. |
| Geologic Maps and descriptions Courtesy of The Paleontology Portal |