Patuxent Formation
Encyclopedia
The Patuxent Formation is a Cretaceous
geologic formation of the Atlantic coastal plain
.
and clay
. The sand often contains kaolinized
feldspar
, making it an arkose
. Clay lumps are common, and sand beds gradually transition to clay. Sandy beds may be crossbedded
, which is evidence of shallow water origin.
The Patuxent is the basal unit of the Coastal Plain sedimentary formations and unconformably
overlies the crystalline basement rocks
. This underlying unconformity is the subsurface equivalent of the Atlantic Seaboard Fall line
.
, a nodosaurid known from a single natural cast and mold of a hatchling, was found recovered from rocks belonging to the Patuxent Formation in Maryland.
Fossil stegosaur
tracks have been reported from the formation.
E. Dorf (1952) compared the flora identified in the Patuxent to that of the Wealden Flora in England studied by Albert Charles Seward
.
Pollen
spores have been identified in the formation by G. J. Brenner (1963).
in Maryland.
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
geologic formation of the Atlantic coastal plain
Atlantic Coastal Plain
The Atlantic coastal plain has both low elevation and low relief, but it is also a relatively flat landform extending from the New York Bight southward to a Georgia/Florida section of the Eastern Continental Divide, which demarcates the plain from the ACF River Basin in the Gulf Coastal Plain to...
.
Description
The Patuxent formation was first described by W. B. Clark in 1897. The formation is primarily unconsolidated sandSand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
and clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
. The sand often contains kaolinized
Kaolinite
Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O54. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra...
feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
, making it an arkose
Arkose
Arkose is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose....
. Clay lumps are common, and sand beds gradually transition to clay. Sandy beds may be crossbedded
Cross-bedding
In geology, the sedimentary structures known as cross-bedding refer to horizontal units that are internally composed of inclined layers. This is a case in geology in which the original depositional layering is tilted, and the tilting is not a result of post-depositional deformation...
, which is evidence of shallow water origin.
The Patuxent is the basal unit of the Coastal Plain sedimentary formations and unconformably
Unconformity
An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...
overlies the crystalline basement rocks
Basement (geology)
In geology, the terms basement and crystalline basement are used to define the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin...
. This underlying unconformity is the subsurface equivalent of the Atlantic Seaboard Fall line
Fall line
A fall line is a geomorphologic unconformity between an upland region of relatively hard crystalline basement rock and a coastal plain of softer sedimentary rock. A fall line is typically prominent when crossed by a river, for there will often be rapids or waterfalls...
.
Fossils
PropanoplosaurusPropanoplosaurus
Propanoplosaurus is a genus of herbivorous nodosaurid dinosaur from the Early Cretaceous Patuxent Formation of Maryland. Its type specimen is a natural cast and partial natural mold of a hatchling....
, a nodosaurid known from a single natural cast and mold of a hatchling, was found recovered from rocks belonging to the Patuxent Formation in Maryland.
Fossil stegosaur
Stegosauria
Known colloquially as stegosaurs, the Stegosauria are a group of herbivorous dinosaurs of the Jurassic and Early Cretaceous Periods, being found mostly in the Northern Hemisphere, predominantly in what is now North America and China....
tracks have been reported from the formation.
E. Dorf (1952) compared the flora identified in the Patuxent to that of the Wealden Flora in England studied by Albert Charles Seward
Albert Charles Seward
Albert Charles Seward FRS was a British botanist and geologist.-Life:His first education was at Lancaster Grammar School and then on to St. John's College at Cambridge following his parents' wish to dedicate his life to the Church...
.
Pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
spores have been identified in the formation by G. J. Brenner (1963).
Notable exposures
The type locality is the upper and lower valleys of the Little Patuxent River and Big Patuxent RiverPatuxent River
The Patuxent River is a tributary of the Chesapeake Bay in the state of Maryland. There are three main river drainages for central Maryland: the Potomac River to the west passing through Washington D.C., the Patapsco River to the northeast passing through Baltimore, and the Patuxent River between...
in Maryland.