Download Springfield Plateau

Geology of Arkansas
Ozarks Plateau
Salem Plateau
Dolostone with interbedded shale in the Powell Formation
The Salem Plateau contains the oldest rock at the surface - Ordovician dolostones,
sandstones and limestones. This is also the lowest plateau surface with some of the highest
elevations reaching between 800 and 1400 feet above sea level.
Dolostone in the Cotter Formation at Cotter, AR
Springfield Plateau
Boone Formation forming buttresses along Bear Creek in Searcy County.
The Springfield Plateau contains mostly Mississippian age limestone and chert from the Boone
Formation at the surface. This plateau is intermediate in elevation with some of its highest elevations
reaching 1800 feet above sea level. The plateau surface consists mostly of gently rolling hills or an
undulating topography, however in some places the Boone Formation forms steep hillsides separated
by ravine-like drainages.
The Springfield Plateau (foreground) near Marshall, Arkansas.
Boston Mountains Plateau
Bloyd Formation near Phillips Ford
The Boston Mts. Plateau contains the youngest rock at the surface - Early Pennsylvanian sandstones
and shales with minor limestones. This is also the highest plateau surface with some of the highest
elevations reaching 2200-2500 feet above sea level.
"middle Bloyd sandstone" at Buzzards Roost
The geology of the Ozark Plateau Region is characterized by slightly southward-dipping
sedimentary rock deposited mostly by shallow marine seas from the Ordovician through the
Pennsylvanian Period. Caves and sinkholes are common in limestones of the Springfield
Plateau with less karst development in the dolostones in the Salem Plateau. The Boston Mt.
Plateau surface contains mostly sandstones and shales deposited by south/southwestward
flowing streams during times of low sea level.
Arkansas River Valley
The Arkansas River and surrounding low-lying land as seen from Petit Jean Mountain
The Arkansas River Valley is a low-lying region surrounding the valley of the Arkansas River and its
major tributaries. The highest point in Arkansas (Mount Magazine – 2753 ft.) is found among several
mountain ridges that rise above the lowlands in the southern portion of the river valley. The mountain
ridges are separated by broad valleys. Surface rocks in this region consist of a sequence of coal-bearing
sandstones and shales.
Sandstone and shale on Magazine Mountain
The Arkansas River Valley represents the northern extent of the Ouachita orogenic (mountain building)
system in Arkansas. Once flat-lying, these Pennsylvanian sedimentary rocks have been compressed into
well developed east-west trending open folds (anticlines and synclines) and faults, which gradually
diminish northward into the Ozark Plateau Region.
Shaded relief map of the Arkansas River Valley. Canoe and cigar-shaped structures represent anticlines and synclines.
Diagram showing structures in the river valley. Most of the higher elevations exposed
in the river valley are actually what is left of the center if the syncline. Nearly all of the
rocks from the surrounding anticlinal limbs have been eroded away.
Ouachitas
The Ouachita Mountain Region consists of a series of sharp ridges, mostly east-west
trending and often buckled and distorted, separated by narrow to broad valleys. Surface
rocks from this region are mostly shales, sandstone, novaculite, chert and minor
limestone.
Inclined bedding in the Stanley Shale in Hot Springs Arkansas
Folded strata in the Big Fork Chert near Hot Springs
Gulf Coastal Plain
The West Gulf Coastal Plain is a south sloping plain of gently rolling hills and can be divided into
two areas based on the age of the rocks. The area in orange consists of Tertiary clays, sands and
silts with lignite deposits and Quaternary gravels, sands and clays. The area in green consists of
Cretaceous sand, clay, gravel, marl, limestone, chalk and Quaternary sand and gravel.
This part of the state contains mostly early Tertiary aged rocks, mostly sands, silts and clays, deposited in streams, swamps
and shallow marine water. Lignite beds occur throughout the sequence. Quaternary alluvium and terrace deposits are present
from rivers in the area. Underneath the Tertiary deposits are the sands, gravels, limestones, chalks and marls seen in the
Cretaceous area.
The geology of the
Cretaceous area within the
West Gulf Coastal Plain is
characterized by gently
southward-dipping
sedimentary rocks
deposited mostly in shallow
marine water of the Gulf of
Mexico that once extended
into Arkansas. Alluvium
deposits from older and
present day streams are
common
The Annona Formation at Whitecliffs near Millwood Lake
Gypsum beds in the DeQueen Limestone
Tokio Gravel
Mississippi River Alluvial Plain
The Mississippi River Alluvial Plain is a relatively level plain with elevations varying between 100300 feet except for Crowley’s Ridge with some of its highest points reaching 400-560 feet. This
region contains mostly unconsolidated sediments such as sand, clay, silt, gravel and loess.
Loess canyon on Crowley’s Ridge
The geology of the Mississippi River Alluvial Plain is characterized by unconsolidated
flat-lying alluvium from present day and older streams, overlying poorly consolidated
Tertiary formations that are dipping slightly to the south.
Quaternary terrace sand and gravels on top of Crowley’s Ridge
Tertiary deposits