Boggs S. Principles of Sedimentology and Stratigraphy
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16.4 Kinds of Sedimenta Basins
557
Basins in Divergent Settings
Divergent tectonic settings are regions of Earth where tectonic plates are separat
ing. These regions are characterized by extensional (stretching) features. Examples
of extension include seafloor spreading along mid-ocean ridges and the stretching
and downfaulting of continental crust to form grabens. Basins form in divergent
settings owing to crustal thinning as well as to sedimentary and volcanic loading
and crustal densification (Fig. 16.2).
The early stages of rifting are characterized by breaking of the crust and
down dropping of blocks to form fault grabens called terrestrial rift valle
y
s. Rifts
(Fig. 16.3A) are narrow, fault-bounded valleys that range in size from grabens a
few kilometers wide to gigantic rifts such as the East African Rift System, which is
nearly 3000 km long and 300 km wide. Rifts result from a thermal event of some
kind that causes extension or spreading within continental crust. The East African
Rift System (Fig. 16. 4A) is an example of a young rift zone. Different stages in the
development of the rift are illustrated in Figure 16.4B. The East African Rift is
filled mainly with volcanic rocks; however, a great variety of sedimentary envi
ronments can exist within rifts, ranging from nonmarine (fluvial, lacustrine,
desert) to marginal marine (delta, estuarine, tidal flat) and marine (shelf, subma
rine fan). Thus, the deposits of rift basins can include conglomerates, sandstones,
shales, turbidites, coals, evaporites, and carbonates. Many ancient rift systems are
known from Asia, Europe, Africa, Arabia, Australia, North America, and South
America (e.g., Sengor, 1995; Leeder, 1995; Ravs and Steel, 1998). They occur
many tectonic settings (Sengor, 1995) but are particularly common in divergent
settings.
As opening of an ocean proceeds, continued extension within continental
crust leads to additional thinning of the crust and eventually rupturing, allowg
basaltic magma to rise into the axis of the rift and begin the process of forming
10° Addis
Ab�
a
E
thiopia me
(
I
�
_ \ L. Tu rkana Quaternar
y
.Mobutu
Caldera Volcano
L.
E
dward
Ken
y
�
Dome
o
o
i
l o-·
o
o
• Nairobi
.
) }
L
�
Kivu
L.Victoria 1
l.J ro..�
�
��
Salaam
100
•
/
L. Malawi
�
B
Figure 16.4
Map (A) showing the surface
configuration of the East
African Rift Zone and cross
sections (B) illustrating
stages in evolution of the rift
from late Miocene through
the Quaternary. The rift is
floored by volcanic rocks
and volcaniclastic detritus.
[From Einsele, G., 1992,
Sedimentary basins, Fig.
12.4, p. 434. Reprinted by
permission of Springer-Ver
lag, Berlin.]
558
Chapter 16 1 Basin Anahsis, Tectonics, and Sedlm�nlation
AFRJCA
Figu 16.5
V
1
e\•1 or the Red Sea,
l
ying between northeJstem .frica and Sauo1 Arbia, from Apollo 17
illfCtfL NASA phvtograph, download�d from the Internet 6/26/04
nev O�JnlC Cm�t. H1.S, krrestrial rift Valleys gr.�dua!Jy (' VOIVe intn protO·Ocean
jc rift oughs. rruto-oceanic rift are omed ( t least Ln part) b�· ucean ic crust and
ked by �i oung rifled continent�! mq;tns. Tite Red Se [Fig. 1o.3) is the t
modrn nlog of a proto-oceanic rift. Tbe l� . Sea, whJ, li beeen northeast
ern AfnL and Saudi Arabia, is 21)00 km long, is more lh 200 km wide in plac,
and has 0 x1l zone about 50 km v,·ide with some axial deFp" that extend �o
more th.n 3 km.
The axial region i oored by
y
oun
b
m._y.) ocw1ic cru,t in lhf� LJUthern
third of the Red a. The shelv� of the se,, ar underlain by stretched continental
ernst in cenLTal reas but by an abrupt ocet-conti.nental crust tTonsitic)n in the
orth ( L�e�h�t� J 999, p. 511 ). 1 o th� ��xLth, the Red Se inter�ts the slow-spreildig
CL1lf ot Adt>n dft. The extension that formed the R
e
d
started in middle Ter
tiary. Early sedimenl,1tion that accompcd rifting was c1ractedzed b\- de1p
munt of ma rginal alluvial fans and ian del t.ls, ns weH as near�hore sedimentatinn
rn both ilrckh1stic nd CMbouk environnlcnts. During rv1 wcce lime, significilnl
�hickncss � of \'apnrites were dep('l ited as rc.�11Jl of periodic io!a!ion of the
trough. Conditions rt•tued to norml li.niLie� f'l iOCl'ne tl�. Bolone S
rncntdiJnn was pa . lr!y chardctt•riLcd by dcpusltinn of fam-pp( ld �cal
�ttou�) ooz.
Basins in Intraplate Settin
Onu t oe b.u has opene,J fully dung d Wilson cycle,
e
dim
nl
.
.ry bins
mov e �·rH in a ariety o( Hlngs along the �ngin and wHhin bo�h ontinental
16.4 Kinds of Sedimenta Basins
559
and oceanic plates. Continental margins formed during opening of an ocean are
called passive margins (lacking significant seismic activity). Continental crust is
commonly thinned on passive margins and a zone of transitional crust is present
between fully continental crust and fully oceanic crust (Fig. 16.3B). Thus, sedi-
ments may be deposited settings floored by wholly continental crust, transi-
tional crust, or wholly oceanic crust.
Intraplate Basins Formed on Continental - Transitional Crust
Continental platforms are stable cratons covered by thin, laterally extensive sedi
mentary strata. Basins developed on these stable platforms are referred to as cra
tonic basins. They are commonly bowl shaped (ovate), and they are generally
filled with Paleozoic and Mesozoic sediments that formed under shallow-water
conditions. Sediments can include shallow marine sandstones, limestones, and
shales, as well as deltaic and uvial sediments. The sediments commonly thicken
toward the basin centers where they may attain thicknesses of 1000 m or more.
The North American craton is an example of a major continental platform marked
by numerous cratonic basins (Fig. 16.6). These basins filled with sediment ranging
in age from Paleozoic to Mesozoic (Sloss, 1982).
Several different kinds of basins may form in cratonic settings. Intracratonic
basins (Fig. 16.3C) are broad basins floored by fossil rifts in axial zones. They are
relatively large, commonly ovate downwarps at occur within continental interi
ors away from plate margins. Subsidence in inacratonic basins may be due largely
to mantle-lithosphere thickening and sedimentary or volcanic loading (Fig. 16.2),
however, several other causes have also been proposed, such as crustal thinning
(e.g., Klein, 1995). e presence of fossil rifts beneath intracratonic basins, such as
the Michigan Basin, suggests some crustal thinning and possibly crustal densifica
tion. Some intercraton basins are filled with marine siliciclastic, carbonate, or
evaporite sediment deposited from epicontinental seas; others contain nonmarine
sediments. Ancient North American intracratonic basins include the Hudson Bay
Basin (Canada), Michigan Basin, Illinois Basin, and Williston Basin (Fig. 16.6,
16.7). Ancient inacratonic basins on other continents include the Amadeus Basin
of Australia; the Parana Basin in southe Brazil, Paraguay, northeast Argentina,
and Uruguay; the Paris Basin in France; and the Carpentaria Basin in Australia
�
\
\
Figure 16.6
Late Mississippian-Early juras
sic cratonic basins on the
North American (mainly USA)
craton. The Michigan, Illinois,
and Williston Basins are in
tractatonic basins. [After
Sloss, 1982, The Midconti
nent provinces: United States,
in Palmer, A. R. (ed.), Perspec
tives in regional geological
synthesis: D-NAG Special
Publ. 1, Geological Society of
America, Fig. 3, p. 36. Repro
duced by permission.]
560
Chapter 16 I Basin Analysis, Te ctonics, and Sedimentation
Fire 16.7
w
WILLISTON BASIN
SEALELr,
IK"l
: HUDSON
BAY
Nesn
!ne
-T
� CRYSTALLINE
PRECAlBR1AN
E
1
2km
Schematic cross section of four in
tracratonic basins in North America.
The locations of the cross sections are
shown in the inset map. The terms
Zuni, Absaroka, Kaskaskia, Tippecanoe,
and Sauk refer to depositional se
quences identified on the craton (Sloss,
1982). [From Leighton and Kolata,
1990, Selected interior cratonic basins
and their place in the scheme of global
tectonics, in Leighton, M. W., et al.
(eds.), Interior cratonic basins: MPG
Memoir 51, Fig 35.9, p. 743. Repro
duced by permission.]
WILLISTON
-�---w
�ICHIGANr/
1 1200 km 1 BLLINOIS
(Klein, 1995; Leighton et al., 1990). The Chad Basin in Africa is an example of a
modern intracratonic basin.
Not all basins that form on cratons are intracratonic basins, as defined in
Table 16.2. Some of the North American basins shown in Figure 16.6, for example,
formed by mechanisms other than rifting. The Paradox basin formed by strike-slip
(compressional) processes. Several other basins (e.g., Oquirrh, Denver, Appalachi
an) are foreland basins, whose origins are related to collisional (compressional)
events (G. D. Klein, personal communication, 2004). The Anadarko Basin may be
an aulacogen. [These various kinds of basins are discussed subsequently.]
Continental rises and teaces are features characterized by enormous wedges
of sediment botmded on the seaward side by the gently sloping continental slope
and rise. A structural discontinuity is psent beneath e terrace-rise system be
tween normal continental crust and modified or transional crust (Fig. 16.3B). These
rises and terraces are the consequence of continental rifting within passive margins
initiated along divergent plate boundaries (Bond, Kominz, and Sheridan, 1995).
Sediments accumulate in several parts of e terrace-rise system-shelf, slope, and
contental rise at the foot of the slope. Sediments deposited in this setting can in
dude shallow neritic sands, muds, carbonates, and evaporites on the shelf;
hemipelagic muds on the slope; and turbidites on continental rises. Thick prisms of
sediment may accumulate owing to long-continued subsidence, which may. be
caused by deep crustal metamorphism (causg increase in density of lower crustal
rocks), crustal stretching and thinning, and sediment loading.
16.4 Kinds of Sedimenta Basins
561
Sedimentation on continental terraces and rises occurs after continental rift
ing is completed and a new basin has begun to form by seafloor spreading (Bond,
Kominz, and Sheridan, 1995). The basin is locked into a relatively stable interplate
position at the edge of the rifted continent. Good examples of such basins are the
basins located o the eastern United States and the southeastern Canada coast
(Blake Plateau Basin, Carolina Trough, Baltimore Canyon Trough, Georges Bank
Basin, Nova Scotian Basin; Figure 16.8) which were created in late Triassic to early
Jurassic time by rifting accompanying the breakup of Pangaea (Manspeizer, 1988).
Some of these basins were isolated from the sea and accumulated thick deposits of
arkosic
clastic sediments and lacustrine deposits, intercalated with basic volcanic
rocks. Others, with some connections to the sea, accumulated deposits ranging
from evaporites to deltaic sediments, turbidites, and black shales. Figure 16.9
shows some of the sediments in the Baltimore Canyon Trough. Other examples of
terrace-slope basins include the Campos Basin, Brazil; the northwest shelf of Aus
tralia; and the sedimentary basins of Gabon on the west coast of Africa (Edwards
and Santogrossi, 1990). Some terrace-slope basins are prolific producers of petrole
um and natural gas.
Newfoundland
Ridge Z.
George's Bank Basin
Depth to pre-Jurassic
basement i
n k
i
lometers
(contour
i
nterval = 2 km)
�
oo
�
-
2000-m isobath
_
.v
Continental margin fault
6
km
Figure 16.8
Sedimentary basins on the passive continen
t
al margin of eastern North America. F.Z.
fracture zone. [After Sheridan, R. E., 1974,
Atlantic continental margin of North Ameri
ca, in Burk, C. A., and C. L. Drake (eds.),
The geology of continental margins, Fig.
12, p. 403. Reprinted by permission of
Springer-Verlag, New York.]
562
Chapter 16 I Basin Analysis, Te ctonics, and Sedimentation
ALB. APT.
UNCON
JURASSIC
EARLY CRETACEOUS
GROWTH
SHELF EDGE
FAULTS
0
�������
0
0
0
LOWER CRETACEOUS
VOLCANIC INTRUSION
100
50
Figure 16.9
MTLE
200
KILOMETERS
100
MILES
20
w
40
0
�
z
�
0
�
80
w
a
100
300
150
200
Interpretative stratigraphic section across the Atlantic continental margin of North Ameri
ca in the vicinity of Baltimore Canyon Trough_ Based on geophysical data and drill-hole in
formation_ [After Grow, ). A., 1981, Structure of the Atlantic margin of the United States,
in Geology of passive continental margins: Am. Assoc. Petroleum Geologists Ed_ Course
Note Ser. No. 19, Fig. 13, p. 3-20. Reprinted by permission of MPG, Tulsa, Okla.]
Intraplate Basins Floored by Oceanic Crust
These oceanic basins (e.g., Fig. 16.30) occur in various parts of the deep ocean
floor. They are created by rifting and subsidence accompanying opening of an
ocean owing to continental rifting. Oceanic basins may include ocean-floor sag
basins as well as fault-bounded basins associated with ridge systems. Sedimen
that accumulate in these basins are mainly pelagic clays, biogenic oozes, and tur
bidites. Sediments deposited in oceanic basins adjacent to active margins may
eventually be subducted into a tnch and consumed during an episode of ocean
closing. Alteatively, they may be offscraped in trenches during subduction to
become part of a subduction (accretionary) complex (Fig. 16.3E). e Pacific
Ocean is a modern example of a major active ocean basin. The Gulf of Mexico is a
modem example of a dormant ocean basin, which is floored by oceanic crust that
is neither spreading nor subducting.
Bas
i
ns
i
n Convergent Sett
i
ngs
Subduction-Related Basins
Subduction-related settings (Fig. 16.3E) are features of seismically active continen
tal margins, such as the modern Pacic Ocean margin. These settings are charac
terized by a deep-sea trench, an active ·volcanic arc, and an arc-trench gap
separating the two. The most important depositional sites in subduction-related
settings are deep-sea trenches, fore-arc basins that lie within e arc-trench gap
16.4 Kinds of Sedimenta Basins
563
��
I
H = v
0
[
I I I I I
10 20 30 40 50
Scale in km
--··J�
.
� Volcantc
E Chain
E
roded �, 1
P
luton
Arc
Magmatism
(Fig. 16.10), and back-arc, or marginal, basins that lie behind the volcanic arc in
some arc-trench systems (Underwood and Moore, 1995; Dickinson, 1995; Marsaglia,
1995). Subduction-related settings may occur also along a contental-margin arc
(not shown in Fig. 16.3) rather than an oceanic arc. In these continental-marg set
tings, so-called retro-arc basins (intermontane basins within an arc orogen) may
lie on continental crust behind fold-thrust belts (e.g., Jordan, 1995). Sediments de
posited in subduction-related basins are mainly siliciclastic deposits derived
largely from volcanic sources in the volcanic arc. These deposits include sands and
muds deposited on the shelf and muds and turbidites deposited in deeper water
in slope, basin, and trench settings. Sediments in the trench may include terrige··
nous deposits transported by turbidity currents from land, together with sedi
ments scraped from a subducting oceanic plate, which together form an
accretionary complex (Fig. 16.3E; Fig. 16.10). The most characteristic kind of rock
in an accretionary wedge is melange, a chaotically mixed assemblage of rock con
sisting of brecciated blocks in a highly sheared matrix.
Examples of modern trench and fore-arc sedimentation sites include the
Sondra, Japan (Fig. 16.), Aleutian, Middle America, and Peru-Chili arc-trench
systems (Leggett, 1982; Dickinson, 1995; Underwood and Moore, 1995). Examples
of ancient fore-arc basins include the Great Va lley fore-arc basin, California; Ore
gon Coast Range; Tamworth Trough, Australia; Midland Valley, Great Britain; and
Coastal Range, Taiwan (Dickinson, 1995; Ingersoll, 1982). The Japan Sea is a good
mode example of a back-arc basin (Fig. 16.11); the Late Jurassic-Early Creta
ceous basin formed behind the Andean arc in southernmost Chile is a well-stud
ied example of an ancient back-arc basin (Marsaglia, 1995). The Taranaka Basin,
New Zealand, and the Magdalena Basin, Columbia, both petroleum producers,
are additional examples of active-margin basins (Biddle, 1991). For further insight
into subduction-related settings, see Busby and Ingersoll (1995).
Figure 16.11
Om
2000
4000
__ ,.·�
-
6000
_
__
8000
Schematic representation of an active continental margin (Japan), showing both the fore
arc and back-arc characteristics of the margin. [From Boggs, S., Jr., 1984, Quaternary sedi
mentation in the japan arc-trench system: Geol. Soc. America Bull., v. 95, Fig. 2, p. 670.]
Figure 16.10
Schematic representation
of basin structure in the
trench and fore-arc zone of
a subduction setting. [After
Dickinson, R., 1995,
Forearc basins, in Busby, C.,
and R. V. Ingersoll (eds.),
Tectonics of sedimentary
basins: Blackwell Science,
Cambridge, Mass., Fig. 6.1,
p. 221 .]
564
Chapter 16 I Basin Analysis, Te ctonics, and Sedimentation
Figure 16.12
Basins in Collision-Related Settings
Collision-related basins are formed as a result of closing of an ocean basin and
consequent collision between continents or active arc systems, or both. Figure 16.3F
illustrates some of the basins that may be generated as a result of plate collision.
For example, collision can generate compressional forces, resulting in develop
ment of fold-thrust belts and associated peripheral foreland basins along the col
lision suture belt where rifted continental margins have been pulled into
subduction zones. Figure 16.12 illustrates the ndamental elements of a foreland
basin system. Foreland basins may be isolated from the ocean and receive only
nonmarine gravels, sands, and muds, or they may have an oceanic connection and
contain carbonates, evaporites, and/ or turbidites. Examples of foreland basins in
clude those of western Taiwan, the Alpennines, and eastern Pyrenees; the Magal
lanes Basin at the southern tip of South America; basins of the northwestern
Himalayas; and various basins in the Appalachians, Rocky Mountains, and west
ern Canada (Allen and Homewood, 1986; Macqueen and Leckie, 1992; Dombek
and Ross, 1995).
Because of the irregular shapes of continents and island arcs, and the fact that
landmasses tend to approach each other obliquely during collision, portions of
old ocean basin may remain unclosed after collision occurs. These surviving em
bayments are called remnant basins. Mode remnant basins include the Mediter
ranean Sea, Gulf of Oman, and northeast South China Sea. The Marathon Basin,
Texas, provides an example of Pennsylvanian-age sedimentation in an ancient rem
nant basin adjacent to a fore-arc basin (Fig. 16.13). Structural weaknesses devel
oped in this region in the late Precambrian/ early Cambrian and were reactivated
in the late Paleozoic as reverse faults in response to compressional stresses (Wuell
ner, Lehtonen, and James, 1986). An early phase of sedimentation filled part of the
fore-arc basin with volcaniclastic detritus. Subsequently, sediments of the Te snus
Formation accumulated in the fore-arc and remnant basin. Later deposition of the
Dimple Limestone and Haymond Formation (not shown in Fig. 16.13) generated a
total of more than 3400 m of Pennsylvanian sediment in the basin. Sediments in
clude sandstones, shales, and limestones deposited in environments ranging from
shelf/platform to submarine fan (turbidite) settings. Other ancient examples of
remnant basins include the southern Uplands of Scotland (Silurian-Devonian);
Nevadan orogenic belt, Califoia Uurassic); weste Iran (Cretaceous-Paleogene);
Schematic illustration of the fundamental elements of
an orogen-foreland-basin system: a compressional
orogen and thrust belt and the foreland basin in
which erosion, sediment transportation, and deposi
tion take place. The basin may be filled to different
degrees along the strike zone depending upon the
relative rates of mass flux into the orogen, denudation
and sedimentation by surface processes, isostatic
compensation, and eustatic changes in sea level.
[After johnson, D. D., and C. Beaumont, 1995, Pre
liminary results from a planform kinematic model of
orogen evolution, surface processes and the develop
ment of clastic foreland basin stratigraphy, in
Dorobek, S.
L
., and G. M. Ross (eds.), Stratigraphic
evolution of foreland basins: SEPM Spec. Publ. 52,
Fig. 1, p. 4. Reproduced by permission.]
16.4 Kinds of Sedimenta Basins
565
N
Rapid sub�idence
of basin
Forearc basin
trap for early
volcanic detritus
� Predominant sediment influx
Position of early
arc-current position
of exhumed plutons
and metamorphic
terrane
Position of
volcanic arc
Dissected foreland facies
Shelfbreak
Early
volcanic
Met. +Piut.
detritus
Intra-arc
sediment
trap
Tobosa Basin
tinental crust
-Zone of crustal attenuation-
Figure 16.1 3
Cross-sectional diagram showing the remnant basin and associated basins that existed in
the Marathon Basin, Texas, during deposition of Carboniferous sedimentary rocks. [From
Wuellner, E. E., L. R. Lehtonen, and C. james, 1986, Sedimentary tectonic development
of the Marathon and Va l Verde basins, West Texas, U.S.A.: A Permo-Carboniferous migrat
ing foredeep, in Allen, P. A., and P. Homewood (eds.), Foreland basins: lnternat. Assoc.
Sedimentologists Spec. Pub. 8, Fig. 5, p. 354. Reproduced by permission of Blackwell Sci
entific Publications, Oxford.]
and the northeast Caribbean (Tertiary). These basins, and other examples, are dis
cussed by Ingersoll, Graham, and Dickinson (1995).
Basins in Strike-Slip/ansform-Fault-Related Settings
Strike-slip-related basins occur along ocean spreading ridges, along the transform
boundaries between some major crustal plates, on continental margins, and with
in continents on continental crust. Movement along strike-slip faults can produce
a variety of pull-apart basins, only one kind of which is illustrated in Figure 16.3G.
Faults that define strike-slip basins may be either "transform faults" that define
plate boundaries and penetrate the crust or "transcurrent faults," which are re
stricted to intraplate settings and penetrate only the upper crust (Sylvester, 1988).
Most basins formed by strike-slip faulting are small, a few tens of kilometers
across, although some may be as wide as 50 km (Nilsen and Sylvester, 1995). They
may show evidence of significant local syndepositional relief, such as the presence
of fault-flank conglomerate wedges. Because strike-slip basins occur in a variety
of settings, they may be filled with either marine or nonmarine sediments, de
pending upon the setting. Sediments in many of these basins tend to be quite
thick, because of high sedimentation rates that result from rapid stripping of ad
jacent elevated highlands, and may be marked by numerous localized facies
changes.
As shown in Table 16.2, basins in transform settings are referred to as
transtensional, transpressional, or transrotational depending upon whether the
basins formed by extension, compression, or rotation of crustal blocks along a
strike-slip fault system. The Ridge Basin, California (Fig. 16.14), is a good example
of an ancient transpressional basin. Strike-slip movement on the San Gabriel fault
in Pliocene/Miocene time created a lake basin about 15 km by 40 km in which up
s
566
Chapter 16/ Basin Analysis, Tectonics, and Sedimentation
West
Fault scarp
East
A Ope
n
lake basin
West
Fault scarp
E
ast
Figure 16.14
Paleoenvironmental reconstruction of the
Pliocene/Miocene Ridge Basin, California,
during (A) the open, deep-water lacustrine
and/or marine phase and (B) the closed,
shallow-water lacustrine phase. [After Link,
M. H., and R. H. Osborne, 1978, Lacustrine
facies in the Pliocene Ridge Basin Group,
Ridge Basin, California, in Matter, A., and
M. E. Tu cker (eds.), Modern and ancient
lake sediments: Blackwell Scientific Publica
tions, Oxford, Fig. 14, p. 185, and Fig. 15,
p. 186, reproduced by permission.]
km
breccias
Stromatolites
B Closed lake basi
n
to 9000 m of sediment eventually accumulated (Link and Osboe, 1978). Initiay,
the lake basin was open (Fig. 16.14A), allowg deltaic sediments and turbidites to
form. As a result of subsequent strike-slip displacement on the fault, exteal
drainage was blocked to the south and the lake basin became a closed system.
During the closed phase, alluvial fan, uvial, deltaic, and barrier-bar sediments
accumulated along the margins of the lake, and siliciclastic mud, zeolite mud,
dolomite, and stromatolites formed the cenal part of the basin (Fig. 16.14B).
For additional examples of strike-slip basins, see Nilsen and Sylvester, 1995.
Basins in Hybrid Seings
Aulacogens are special kinds of rifts situated at high angles to continental mar
gins, which are commonly presumed to be rifts at failed but were reactivated
during convergent tectonics (Fig. 16.3H). Other suggested origins for alaucogens in
clude doming and rifting, sike-slip-related extension, and continental rotaon
(Sengor, 1995). The long, narrow troughs that make up the arms of aulacogens ex
tend into continental cratons at a high angle from fold belts. Deposition of thick se
quences of sedent can take place in these arms during long periods of me. These
deposits may include nonmarine (e.g., alluvial-fan) sediments, marine shelf de
posits, and deeper water facies such as turbidites. Examples of aulacogens include