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A
Brief Tectonic History of the Permian Basin
 The
tectonic history of the Permian Basin has a direct implication on
the accumulation and preservation of the vast hydrocarbon reserves
of the Guadalupian stage. The structural development of the basin
is generally be divided into three stages: the first stage encompasses
the Cambrian through Mississippian in which the region was a broad
marine basin in which vast carbonate and clastics deposited, this
is the Tobosa Basin. The second stage of tectonic evolution of
the Permian Basin was initiated by the Hercynian Orogeny in which
the North American Craton collided with the South America from Early
Pennsylvanian through Early Permian. This orogeny caused the basin
differentiation into deep basins surrounded by shallow shelves.
The third stage of the basin development was initiated when the
basin became structurally stable and vast deposits of clastics deposited
in the deep asymmetrical basins and carbonates deposited on the
shelves.
This chapter provides
a brief overview of the tectonic development of the Permian Basin
in order to gain some understanding of the primary processes that
caused the basin to differentiate and to subsequently cause reciprocal
sedimentation of clastics and carbonates.
Basin
History
The major tectonic episodes
that resulted in the sedimentary fill of the Permian basin are described
below:
Lower
Paleozoic Passive margin (late Precambrian to Mississippian, 850-310
ma.)
The lower Paleozoic passive-margin succession
is present throughout the southwestern region of the United States
and is as much as 1.5 km thick (Sarg et al., 1999). This ancestral
Permian Basin was characterized by weak crustal extension and low
rate subsidence (Horak, 1985). A broad, shallow, gently dipping
depression known as the Tobosa Basin developed (Galley, 1958).
Sedimentation consisted mainly of relatively uniform and widespread
shelf carbonates and thin basinal shales (Hills, 1984).
Precambrian
and Cambrian
 Transcontinental
arch extended across southeastern New Mexico and west Texas. The
tectonic evolution of this area caused the collapse of this arch
as a negative feature, where the early Ordovician sea transgressed,
producing a flattened coastal plain (Adams, 1965).
The tectonic evolution
of the area involved a conversion of the crest of this peninsular
ridge into the axis of a negative basin. The sagging of this arch
was caused possibly by cooling and shrinking of the underlying crust
and mantle rocks. Early subsidence of the peninsular arch proceeded
too slowly to produce a structural basin. It produce a flattened
coastal plain across which the Early Ordovician sea slowly transgressed
(Adams, 1965).
Lower
Ordovician
The northwest-ward-transgressing Early Ordovician,
Ellenburger Sea spread a wedge of sediments across the Texas-New
Mexico area. Sediments deposited in the offshore areas consist
of evenly bedded shelf carbonates resting on thin near-shore clastics.
These coarse basal clastics were derived from weathering of the
underlying basement. The carbonate shelves were wide and shallow.
Cross-shelf circulation was limited and minor amounts of evaporites
were deposited in the more restricted areas. As a result most of
the limestones were dolomitized soon after deposition. Non-dolomitized
limestones, however, are common in the offshore areas and tongues
of limestone are preserved in the shelf sections. Progressively
younger beds onlap the basement toward the northwest. As a result
the section thins from 2,000 feet at the south to zero just north
of the Delaware basin.
The axis of this Tobosa
sag coincided approximately with the axis of the pre-Ordovician
highland on which the sag was superimposed. Toward the south the
Tobosa basin opened into the deeper Marathon embayment through
which the ocean waters circulated. A lens of mid-Ordovician, Simpson
sandstone, shale, and limestone accumulated in the lower parts
of the Tobosa sag (Adams, 1965).
Middle
Ordovicia
 Crustal
warping in later stages of the Early Ordovician divided the widespread
Lower Ordovician shelf into a series of sags and arches. A mid-Ordovician
350-mile-wide sag, the Tobosa Basin developed between the Texas
arch on the east and the Diablo arch on the west (Adams, 1965).
This region was welded solidly to the southwestern portion of the
craton and sank gradually to form the shallow Tobosa basin (Hills,
1984).
By Middle Ordovician,
the shales and limestones of the Simpson Formation covered the southern
part of the present North American craton (Scotese et al., 1979).
This formation is composed mainly of sandstone, shale and limestone
and shelf limestone in the south. In many places, the total thickness
of the Middle Ordovician reaches almost 600 m, about 50% of which
is shale.
Late
Ordovician, Silurian, and Devonian
During Late Ordovician, Silurian, and Devonian,
the axial areas of the Tobosa basin generally were sites of relatively
deep water. The waters were too deep or too acidic for extensive
limestone deposition; clastic supplies weren't enough to match subsidence
rates and many areas of the basin starved. The subsidence rates
were variable, so sometimes, marginal limestone shelves forestepped
seaward and sometimes the basin expanded landward. Dolomite and
white chert occurred in the shelves, limestone and dark chert in
the deep waters and shales in the talus slopes. The black shales
deposited in these seas contain large amounts of organic material,
much of which is preserved as carbonaceous residue. In many places,
black shale deposition continued into the Early Mississippian (Hills,
1984) and (Adams, 1965).
Early
Mississippian
Slight uplifts and erosion in Late Devonian
time exposed the marginal Silurian-Devonian and Upper Ordovician
shelf deposits to truncation. The Early Mississippian transgression
deposited the Woodford shale, an important oil source for the pre-Mississippian
reservoirs (Adams, 1965).
Middle-to-Late
Mississippian
Deposits covering most of the southern Tobosa
basin consist largely of dark gray and brown clay shales. Maximum
thickness of these shales along the axis of the Tobosa sag presented
up to 7000 feet of sediments on its deepest parts. These shales
filled the starved Devonian depressions and the surrounding shelf
areas almost to wave base. Formation of a median ridge split the
Tobosa sag into the Midland and Delaware basins at the same time
the area of active basinal subsidence was extended northward into
Kansas. The name Permian basin is applied to this segmented and
greatly expanded negative area (Adams, 1965).
Collision
phase (Late Mississippian through Pennsylvanian, 310-265 Ma)
The geometry of the Permian Basin consisting
of two sags separated by a platform was established during this
phase as a result of the Hercynian collisional orogeny. The Hercynian
orogeny was initiated by the collision of North America and Gondwana
Land (South America and Africa). This collision gave rise to the
Ouachita - Marathon fold belt and deformed the ancestral Tobosa
Basin intensively deformed along high - angle basement faults and
pre-existing zones of weaknesses (Horak, 1985).
 Rapid
basin subsidence and sedimentary filling took place during this
phase. Broad carbonate shelves became established on the western,
northern, and eastern margins of the Permian Basin and Central Basin
Platform as a result of its equatorial location during this phase.
Clastics meanwhile dominated in the basins. By Late Paleozoic time
the original Tobosa Basin was divided into the northwest-aligned
foreland basins (Delaware Basin, Midland Basin) with intervening
high areas (Central Basin Platform and Diablo platforms) (Sarg et
al., 1999).
Late
Mississippian
Vertical movement along the lines of Proterozoic
weakness deepened the eastern portion of the incipient Delaware
basin and tilted it to the east. Compression from the southwest
caused the Central Basin ridge to rise along rejuvenated steeply
dipping reverse faults. Folding, which apparently involved the basement,
began to deform both the basin and the Central Basin uplift, and
split the Tobosa Basin into Delaware Basin on the west and the Midland
basin to the east (Hills, 1984).
Early
Pennsylvanian
At this time the basin underwent rapid subsidence
resulting in extensive deep areas. The central and south areas were
sediment starved, and were later buried under shallow platform carbonates.
The Delaware basin during underwent a rapid subsidence which produced
extensive bottom areas too deep for limestone deposition. Clastic
supplies within much of the Permian basin were limited. Some of
the eroded limestone was dissolved during transit or soon after
deposition in the deep, cold basin waters. Clastic deposition
occurred on the north and northwest margins, the central and southern
parts of the basin were mainly areas of starved shale deposition
as a result of deepening (Adams, 1965).
Middle
and Late Pennsylvanian
Tectonic activity increased throughout the
region, including the Marathon fold belt. Broad carbonate shelves
grew along the basin margin. The trapping behind the carbonate banks
of clastic material derived from the northeast highlands resulted
in the starving of the basins. Compaction of the basinal sediments
and development of unventilated bottoms in the deep Delaware basin
preserved the remains of organisms that flourished in the shallow
photic zone and on shelf margins (Hills, 1984).
Permian
Basin phase (265-230 Ma.)
 Rapid
variable sedimentary filling of the basin with fluvial-deltaic siliciclastic
sediments and the development of extensive reef fringed carbonate/evaporite
platforms and shelves proceeded until only the Delaware Basin remained
as a small depocenter. This synorogenic succession contains three
angular unconformities that bracket multiple collisional pulses
and is capped by the regionally extensive middle Wolfcampian angular
unconformity. The first two upper Paleozoic supersequences (lower
Absaroka I supersequence set) are bounded by these unconformities
(Sarg et al., 1999). A final evaporitic stage filled the remnant
basin and covered the surrounding shelves (Horak, 1985).
Early
Permian (Wolfcampian)
 Characterized
by rapid basin subsidence which permitted huge accumulation (over
8,000 feet) of turbidites that produced enormous compressional
stresses in the underlying crustal rocks. The median fault-block
range between the Delaware and Midland basins was squeezed upward
several thousand additional feet. The stable Diablo arch on the
west was raised to mountainous heights. This combination of rapid
basin subsidence and rapid rising on its margins provided the accommodation
space and clastic sources. Along the eastern, western, and southwestern
margins sediments include thick beds of chert, limestone, and arkosic
boulder beds with sandstone shale, and detrital limestone. Most
of these clastics were probably distributed by turbidity flows sweeping
down the steep flanks and spreading across the deep bottoms. Most
of the clastics came from rising mountains on the northwest, west,
and southwest (Adams, 1965).
A shallow carbonate shelf
and margin developed around the edges of both the Delaware and Midland
basins (northern, northwestern, and northeastern). Shelf-edge
reefs grew along the seaward edges of these shallow shelves during
stages of still-stand or slow subsidence.
As clastic supply decreased
in the late Wolfcampian, the limestones were replaced by carbonate
beds totaling several thousand feet in thickness.
Middle-Permian
(Leonardian)
The rate of subsidence of Delaware and Midland
basins decreased substantially, and a reduced sediment supply was
reduced as a result of the leveling of the mountains on the west and
northwest. Basinal deposits consist largely of dark limestone, shale,
and fine-grained sandstone. The slowly rising median ridge on the
east was completely capped by bedded shelf limestones. The name
Central Basin Platform (CBP) generally is applied to this intra-basin
limestone bank.
This ramp-type shelf
was already developing a series of barriers along its seaward edge,
thus becoming a more distinct rimmed margin. Carbonate shelves
continued to develop and basinal circulation was severely constricted.
Circulation through channels in the carbonate shelf and through
the Hovey channel and Val Verde basin to the south kept the surface
seawater aerated and organically productive. Limestone shelves
bordered by reefs spread across the Star Mountain arch toward the
south and the Diablo arch toward the west. The broad shelves west,
north, and east of the Delaware basin were sites of widespread restricted
lagoons in which evaporites were deposited.
In the late Leonardian,
clastic supplies reaching the basin increased because of renewed
uplifts on the northwest and subsidence in the Delaware basin. The
coarseness of these sandstones was greater than earlier in the
epoch (Adams, 1965).
Late
Permian (Guadalupian)
Basinal subsidence slowed down during the Guadalupian.
From the late Wolfcampian through Guadalupian (Late Permian), the
Midland and Delaware basins were principally sites of siliciclastic
accumulation, whereas the platforms and shelves were sites of carbonate
deposition.
During the middle Guadalupian, the Eastern shelf, Midland basin,
and Central Basin platform ceased to be areas of carbonate accumulation
and instead became sites of cyclic deposition of sandstone, anhydrite,
and halite (Ward et al., 1986). Guadalupian rocks around the margins
of the Delaware basin consist of reef-bordered limestone shelves.
Deposits within the deep central basin are largely terrestrial
clastics rolled or blown across the lagoons. They flowed through
surge channels in the reefs to form steep alluvial cones on the
subaqueous talus slopes below the reef rim (Adams, 1965).
Upgrowth of the limestone shelves was checked on reaching sea-level.
The reefs and shelf edges were exposed to wave action. This wave
erosion produced large amounts of talus. As a result the reefs forestepped
rapidly beyond the earlier basin margins. Most of the shelf and
reef carbonates were partly or completely dolomitized by saturated
brines seeping from the evaporite lagoons. The forestepping of
the marginal reefs eventually closed the narrow strait between the
Star Mountain arch and the Marathon Mountains (southwest). With
the blocking of this strait the Delaware basin was converted from
a Mediterranean-type gulf to a deep evaporite lagoon with great
evaporite deposits in the Ochoan (Adams, 1965).
Toward the end of the epoch, flourishing carbonate reefs and banks
on the basin margin greatly reduced the rate of sedimentation in
the central area and further restricted circulation. Thus, the scanty
sediments that did accumulate were high in preserved organic content
(Hills, 1984).
By the close of Guadalupian sedimentation, the underlying Leonardian
sedimentary rocks were buried several thousand feet deeper under
the Guadalupian overburden.
Late Permian
(Ochoan)
The Permian basin was tectonically stable which
provided stability for sediments compaction. About mid-Ochoan time,
a new epoch of sagging occurred, practically coextensive with the
ancient Tobosa basin. The Ochoan lagoon expanded eastward and northward,
and 1,500 feet of evaporites precipitated over the northern and eastern
margins of the Delaware basin. A marine incursion late in the Ochoan
spread the Rustler Formation over the western part of the Permian
basin; it is largely dolomite and limestone within the limits of the
Delaware basin, but grades outward to evaporites. Then a shroud of
fine red clastics terminated the Permian deposition in the Delaware
basin area (Adams, 1965).
At the margins of the basin, the Guadalupian series is composed
of reef bordered limestone shelves, which protected many evaporite
lagoons. In the central parts of the basin, the sediments were mainly
sandstones and siltstones.
 The
continuing restriction of the seas resulted in deposition of the
Castile evaporite in The Delaware basin, which was filled with a
nearly impermeable sedimentary blanket 600 m thick (Hills, 1984).
Dolomitization developed, due to the circulation of saturated brines
from the evaporite lagoons. The closing of the strait at the south
converted the entire Delaware Basin to an evaporite lagoon.
The post Permian sediments are terrestrial clastics, deposited
during the Triassic subsidence, along with lower Cretaceous sandstones
and limestones and upper Cretaceous shale and flagstone.
Post-Permian
The post-Permian history of the Delaware basin area records the
development of an Upper Triassic sag superimposed on the upper Ochoan
basin deposits. This depression was filled with about 1,000 feet
of terrestrial clastics. The Lower Cretaceous Comanchean sea spread
a thin layer of sandstone and limestone completely across the basin.
Some Upper Cretaceous shale and flagstone also are preserved in
early salt-solution troughs along the southern margin of the basin.
Evidences of extensive additional post-Permian to recent salt solution
are found in many other areas. Basinal Guadalupian and Leonardian
rocks cap the Delaware Mountains at the western edge of the basin.
These mountains, uplifted by Tertiary and Quaternary faulting, form
the Cordilleran front and relate this basin to the Rocky Mountain
province. The uplifting was accompanied by minor intrusions, lava
flows, and considerable faulting (Adams, 1965).
Stable Platform
phase (Mesozoic, 230-80 Ma.)
Mobility rates were low and no significant
structures formed within the basin (Horak, 1985).
Laramide
deformation (Late Cretaceous through Early Eocene, 80-50 Ma.)
The western side of the Permian Basin was
elevated up to 4000 ft. The basin was permanently raised above
sea level during this time (Horak, 1985).
Volcanic
phase (Early Eocene through Middle Oligocene, 50-30 Ma.)
Weak extension and crustal thinning followed
the Laramide orogeny, which resulted in widespread volcanic activity
and increased regional heat flow in the southwestern Permian Basin
(Horak, 1985).
Basin and
Range tectonism (recent, 24-0 Ma.)
Rifting, crustal thinning, and high heat
flow characterized the region from the western Delaware Basin across
the southwestern U.S. to California.
 Since
the Permian, the western margin of the Delaware basin uplifted about
9,000 ft, half of this uplift occurred during the Neogene (24 Ma)
and the other half occurred during the Laramide orogeny (Horak,
1985). The figure above illustrates subsidence curves from different
areas of Permian Basin and highlights the major tectonic phases
and periods of most active basin development.
 Please
also refer to table to the left and
for more details on the general stratigraphy of the basin.
Paleogeographic
Maps
Paleogeographic Maps Illustrating Major Tectonic
Episodes that lead to the development of the Permian Basin. Maps
are obtained from Northern Arizona University and were created by
(Blakey, 2001):
- Tectonics,
Sedimentation, Paleogeography of North Atlantic Region:
The top map shows the continental plates and intervening oceans,
tectonic elements, and sedimentary facies; the second map shows
hypothetical paleogeography based on the tectonic/sedimentary
map.
- First
Order Global Tectonic: Features including oceans, continents,
plate boundaries, subduction zones, mid-ocean ridges, and mountain
belts are shown on each map.
Passive
Margin Phase (maps: 450 Ma)
 In
the latest Precambrian and early Paleozoic, the super continent Rodinia,
centered about the south pole, broke apart as blocks drifted northward.
 Most
notable of these blocks were the large continents North America
[Laurentia], Baltica, and Siberia. Numerous plates and continental
blocks approach North America from the south and east. The Taconic
arc has just collided forming the Taconic orogeny.
Collision
Phase (maps: 300 Ma)
 Laurasia
and Siberia collide to form Laurasia; meanwhile Gondwana collides
from the south.
 The
resulting Appalachian, Ouachita, Marathon, Ural, Variscan, and Hercynian
orogenies formed some of the largest mountains of all time. The
Ancestral Rockies formed in west central N. A.
Permian basin
Phase (maps: 270 Ma)
 During
the latest Paleozoic into the early Mesozoic, Pangaea lay extant,
across the equator. The super continent Pangaea dominates the Permian
Earth.
 A
new arc approaches western N. A. A new spreading center forms as
Cimmeria rifts from Gondwana and marks the opening of the Tethyan
Ocean.
Stable
platform Phase (maps: 200 Ma)
 The
great super continent begins to fracture and the central Atlantic
and Gulf of Mexico are born.
 A
great arc is built on western N. A. and the Nevadan orogeny begins.
Cimmeria begins its collision with Laurasia to form the Cimmerian
orogeny.
Laramide
Phase (maps: 60 Ma)
 As
plate positions continue to adjust to the opening of the Atlantic,
The Rocky Mountains grow and the Alps and Pyrenees are formed.
 The
modern patterns of Planet Earth begin to appear.
Basin
and Range Phase (maps: 20 Ma)
 Southwestern
North America intercepts the East Pacific Rise and a great extensional
event, the Basin and Range orogeny begins.
 Orogeny
continues in the Mediterranean region and India nears its junction
with southern Asia & .
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