Prairie Bluff Chalk Formation
Encyclopedia
The Prairie Bluff Chalk Formation is a geological formation in North America
, within the U.S.
state of Alabama
. The chalk
was formed by marine sediments
deposited along the eastern edge of the Mississippi embayment
during the Maastrichtian stage of the Late Cretaceous
. It is a unit of the Selma Group
and marks the end of the Cretaceous in Alabama. Evidence has been found within the formation at Braggs, Moscow
, and Millers Ferry
in Alabama indicating an instantaneous to brief erosional event, most likely a tsunami, at the K–T boundary
. It is hypothesized that this event, along with faulting and liquification
of the Prairie Bluff Chalk, is related to the meteorite
impact at the Chicxulub crater
site, directly south, across the Gulf of Mexico
, from the formation.
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, within the U.S.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
state of Alabama
Alabama
Alabama is a state located in the southeastern region of the United States. It is bordered by Tennessee to the north, Georgia to the east, Florida and the Gulf of Mexico to the south, and Mississippi to the west. Alabama ranks 30th in total land area and ranks second in the size of its inland...
. The chalk
Chalk
Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....
was formed by marine sediments
Pelagic sediments
Pelagic sediment or pelagite is a fine-grained sediment that has accumulated by the settling of particles through the water column to the ocean floor beneath the open ocean far from land. These particles consist primarily of either the microscopic, calcareous or siliceous shells of phytoplankton or...
deposited along the eastern edge of the Mississippi embayment
Mississippi embayment
The Mississippi Embayment is a physiographic feature in the south-central United States, part of the Mississippi Alluvial Plain. It is essentially a northward continuation of the fluvial sediments of the Mississippi River Delta to its confluence with the Ohio River at Cairo, Illinois. The embayment...
during the Maastrichtian stage of the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
. It is a unit of the Selma Group
Selma Group
The Selma Group is a geological formation in North America, within the U.S. states of Alabama, Mississippi, and Tennessee. The strata date from the Santonian to the Maastrichtian stages of the Late Cretaceous. The group is composed of, in ascending order, the Mooreville Chalk Formation, Demopolis...
and marks the end of the Cretaceous in Alabama. Evidence has been found within the formation at Braggs, Moscow
Moscow, Alabama
Moscow is an unincorporated community in Marengo County, Alabama.-Geography:Moscow is located at and has an elevation of ....
, and Millers Ferry
Millers Ferry, Alabama
Millers Ferry is an unincorporated community in Wilcox County, Alabama, United States. The Millers Ferry Lock and Dam is located near the community on the Alabama River.-Geography:Millers Ferry is located at and its elevation is .-Tornadoes:...
in Alabama indicating an instantaneous to brief erosional event, most likely a tsunami, at the K–T boundary
K–T boundary
The K–T boundary is a geological signature, usually a thin band, dated to 65.5 ± 0.3 Ma ago. K is the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period...
. It is hypothesized that this event, along with faulting and liquification
Liquification
In physics, to liquefy means to turn something into the liquid state.-In Geology:In geology, liquefaction refers to the process by which saturated, unconsolidated sediments are transformed into a substance that acts like a liquid.Earthquakes can cause soil liquefaction where loosely packed,...
of the Prairie Bluff Chalk, is related to the meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
impact at the Chicxulub crater
Chicxulub Crater
The Chicxulub crater is an ancient impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named...
site, directly south, across the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
, from the formation.