A_C_TA_,_'_9_B_',_N_·_s_p~~~----
_________________O_C_E_A_N_O_L_O_G_IC_A__
Sedimentological and geochemical
trends resulting from
the breakup of Pangaea
Global sedimcnlol"i)'
Forrnu!ion of the oc e"n ~
L<t$;e deposil s
Evaporilc ~
Sidimentologie g1ob.1Ie
Fo rmation des océa n~
I><':pc)ts lac ul>tre~
Ëvaporile~
W . W . Hay
Joint Occanogmphü;: Insti tutio n Inc .• 2600 Virginia Ave . . N .W .. S ui te 512 Wal> hinglo n. D.C.
20037. USA .
,"d
Rosc nSlicl School of Marine and Atmos pheriç Sçie nce. 4600 Ric ke nb'lc kcr Causeway, Miam i.
Florid" 33149. US A.
ABSTRACT
The brcakup of Pa ngaea and fo rmltlÎon of the AI/a nlic and l odi,ln Oçenns a nd the marginal
seas has a n imporlant influence on the global gcoc hcmist ry of sediments. The initia l riflin.ll
phases ma y ha ve resulted in deposÎtio n of exte nsive fresh waler Jake depos its with high
organic carbon contents 50 tha! these sed iments may contain as much as 118 of the earth 's
sediment ury o rganic carbon . Flooding of the developing rifts by the sea and extens ive
de pos ition of evaporites followe d. The prese nt estimllte of a IOtal of 10.5 x 106 km J of
e vapo rite deposit s beneath the floor of the Gulf of Mexico, Atlant ic Dcen n. Red Sea a nd
Med iterranean Sea has doub led the known quan tit y of e vaporites . G rowth of extensive barrier
reds a nd associate d car bonate platforms a long the develo ping passive u a iling margins
pers isted arte r the evaporite phase in the Atla ntic and e nded during the middle C relaceous.
Sinee then . the majo r s ite of carbonate depos itio n has s hiftcd to the open seas in the form of
the contribution of calcareous plankton to pelagie sediments. These are significant geochemi,
cal rnlc tionations which ha ve affeCled the composition of the major 1>ed ime ntar y reservoirs.
Dam.ol. Actll. 198 1. Proçeed ings 26,h International Geologieal
sympos ium ,
RE SU MÉ
Par i ~.
Co ngTes~,
Geology of oceans
Jul y '·17, 1980, 135- 147.
Êvol ution géoc himiq ue el sédimenlologique rés ult ant du mo rcelleme nt de la
Pangée
Le morcellement de la I>angée e t la format ion de l'océan Atlantique , de l'océan Ind ien et des
mers marginales qui l'a suivi, Ont eu des répercussions im porta ntes ~u r la géOChimie
sédime ntaire .
Durant 1;1 phase initia le, au moment de 1,\ form a tion des fossés d 'effond re me nt , il y a eu
probablement dominance des dé pôt s lacustres à for te teneur en c,.rOOne orga nique . Le
cMbone orgllnique de ces dé pôts pourrait re présenter jusqu 'à 118" de la ma tière o rgnnique des
forma tio ns sédimentaires.
L'enva hissement par la meT de ces fossés d 'erro nd rement s'est trad uit pa r le dé veloppement
extensif des Co rmations évaporitiques. Le cubage de c es évaporites acc umulées sous le rond
du Golfe d u Mexique. de l'Atlantique, de la me r Ro uge e t de la Méd iterranée représente un
total prob.1ble de 10.5 x 1if' km ). Ceci représente le d o uble des estima tio ns connues s ur le
volume des évaporites.
Après celle phase évaporiliquc dans l' Atla ntique c l jusqu 'à la fin du C ré ta cé mo yen . le
dé velo ppement extens if des barrières réc ifales et des plates-fo rmes carbon;ltées li été
prépondérant dans le .. s illage .. de ces murges passives.
135
W. W. HAY
La zone pri vilégiée de sédimentation cltlcaire a ensuite dérivé ve rs le large , en r~ i son de la
contribution prépondérante du plancton carbonaté à la form ation des sédime nts pélailiques.
Telles sont les grande~ phases des fractionnements géochimiques qui ont affecté la
compoSition de ~ sédiments dans le~ principales zones d·accumulation.
Ocemwl. A cta. 1981. Actes 26< Congrès Internlltional de Géoloilie. colloque Géologie
P:lris. 7·17 juil. 1980. 135-147.
de~
océan~.
guished as diserete unils. Two of the seismic lines. uses
CDP line 5 southeas t o f Cape Cod ac ross the norlheaSlern
part of the Lo ng Island platform and USaSJIPOD line
acro:.:. Ihe ma rsin sout hea!>t of Cape Hatteras. represent
se<.:tions on arc hes. The other two cross sections allaly~ed,
based o n usas C DP line 2 and usas COI' Hne 6. are bot h
in the Baltimore Ca nyo n tro ugh and represenl a basin . Ali of
the cross sections eXlend to 300 km offshore in the original
îJlu~tralions except that ba~ed on usas cop line 2. which
ended at 240 km offshore, but wa:. projected to 300 km for
Oleasuremen\. The res ults are s hown in Figures 1 and 2.
Figures l A and B s how the average areally integrated
sedimenlHlion ra Ie and volume peT kilometer o C margin for
the two cross sections o n Mches: with A rep resenting
sediment on Ihe shelf and B sed iment on the slope/rise :
Figures 2A and B s how the same informatio n fo r the
average of the twO cross scelions in the Bal timore Canyon
trough. here considered a typical marginal basin. For the
snelL sedimentation increaselo from the Triassic to the
Jurassic. and decl ines markedly during the Cretaceous and
Tertiar y. For the slope/rbe , sedimentation is high in the
Jurassic, dec1i nes in the Cret,lceous and increases signifi·
canlly in the Tertiary. The ove rail and detrital sedimentation
r:ue .. fnr Ihe Triassic shelf arc nearly eQual in IIfeh and basin
provinces. However. assuming Ihal a volume of anh ydrite
equivalent to the vol ume of salt interpreled on the se ismic
sections is also present. and thal half of the an hydri te is
pre·salt Tria!>sic and half early Jurassic. the basin accumula·
tes more evaporile Ihan the arches, and the lImount of
evaporîte is approximatcly equa l to Ihe amount intcrprCled
as detri tal sedime nl. On both the s helf and the lotopeJrise.
I NTRODUCTION
The breaku p of l'angaea and the r orm~tion of the Atlantic
:.lnd Indian Ocean~ and their marginal seas ha~ h~d an
important in flueOl:e on the global seoche mis try of NaCI.
CaSO,. organic carbon. opaline silica and othe r clements
assodated with these phases. The fifts and smalt ocean
basins which formed initiolly would ha ve acted as sites of
chemical fra<.: tionation of sal ts d issolved in the world ocea n.
The development of a grea t area of passive trailing margins
which s ubside in a regular m~mner. and across which mos t
o f the continental area drains to the ocean has dominated
the globlll sedimentation system of the pliSt 200 MY. Superimposed on this grand pattern i ~ the de velopment of
calcareous plankton which now fix larse amounts of cal·
cium carbonale in Ihe ope n sea wit h the result thal carbonate oozes are deposited over much of the deep sea.
Hsü (1965) recognized the ~edimentological signifkance of
the continental breakup process. Sleep (1971) related Ihe
Ihermal history :Issocialed wilh continental splitting to
upli!!. erosion, sub!;equent subsidence and sediOlentalion.
Kinsman (1975 ) presented the oUll i ne~ uf the efrects of
rifti ns and continental breakup on sedimenta tion in lerms of
both rate of accum ulation and c hansins sediment type.
Southam and Hay (in press) have analyzed the sequence of
events in a semiquantitative manner to gain an impression of
the significance o f these processes for global geochemical
mas~ balance and cycling. This paper furlher develop~ these
concepts maki ns use of the significa nt new contributions
re sultins fro rn analysis o f Deep Sea Drilling Projec t dltta
(Jansa el (/1.. 1979; Watkins. Hoppe. 1979; T hierstein.
1979: Arthur. Natland. 1979) and from tne large body of
new dala produ<.:ed by usas and other in"estigallon~ of the
Atlantic margfn o f the US (Foiger el al.. 1979: Buffler
el (/1.. 1979: Klitgord. Behrendt. 1979: a row el al .. 1979;
Dillon el al .. 1979). These permit fu rt her development of a
semiquantit:llive model o f the sedimentological and geocheOlical effects o f the breakup of Pangaea. ln under~ tanding
the early development of a p:lssive margin , the most
important new information tO consider is that wnich has
becn learned from intensive s tud y of the we:.tern margin of
the No rth AlhlOtic.
.,,,
•
•••
.
>lU
•
ANALYS IS OF SEDIMENT ACCUMULATIO N OFF
T H E EAST COAST OF THE UN ITED STATES
..
' '
TRIASSIC
ÇA"JO ..... ' . ,
""
JUR ASS'C
A""'D"1II1l ,
CU_An
It..,
CRElACEOU5
[
~~
-._. ,
A N HyD~"I~f,
~"
-. .,,
-. ,
~
"
TEATIARY
Figure 1
Foiger et al. (1979) recently presenled their interpretation of
cross se c tio n ~ of the shelf and s lope ! ri~e off the east coa~1
of the United States oosed o n multichannel seismic lines.
Four of these were analyzed from measu rement of the cross
sectional area of sediment shown as Triassic. Juras~ic.
Cretaceous and Tertiary on the she lf and on the slope/Tise.
wit h the indicated "salt". <ln arbitrarily equi valent amounl
of anhydrite , and the carbonale bank or " ree C" distin-
Vo/umtS and a~ully int~Rrattd stdimtntati'/fI raitS for tht a, crugt
o f uses CDP tint j SQuthtaSf of Capt Cod und tht USeS lPOD
lint ucrou tht margin southttl.ft of Capt Hat/ trus. rtp,tSt"fin~
stdimtn/atÎon on archts. A is stdim ..n/ (J/I the sht/f. B if s~dim~nt of
tht sloprJrist. Numbus in CO /IIIII"S art "o/umes in km' pu km /e"gth
of margin. Arto/l)' i"ttgrated Sl:dimtlllatioli fottS af.. km' 1)" she/f
(A) Of $IQptfriI~ (8 ) pef lm /tnl1/h of mUTf/ül. Litha/agies Ufe
U"kllO"''' ucepl us noud. Allhydrite tq" ;,-ult,,t in amO/l1ll la Iht
ha/ite show" 0" the stc:/iQ" s 1.1 ;nftrrtd. but mu)· flut he prtsttU.
136
SEDtMENTOLOGtCAL EVOLUTtON AND BREAKUP OF PANGEA
-. ,,,
-"
•
"
..
E;
••
-"
-"
,,,
-. ,
_u
-"
•
...u ....
....".0
••
--101;--
u,
..........." .....
-.-.
• • •
m
;.
•
region dis tant (rom the s ite of fut ure passive: mMgi n
development.
1) Co ntinuing uplift a nd erosion with lac ustrine-flu vial
sed ime ntation in a rift graben formed abo ve sea level :
20 MY requ ired for the floor of the gra ben to subs ide to sea
level. Deliver y of sed iment to dis tant areas continues.
2) Development of a deep narrow graben wi th maximum
local relief and restric ted connec tion to the ocean : the high
margi na l walls tend to produce a local e vapomti ve ciimatic
regime . so that the sea in the grabe n is prone todevelopment
of un usually hypersaline condi tions or evaporite de pusition .
T his s tage is also estimated to last20 1\1 Y. Sepclration of the
continental fragments occ urs during the middle of this
phase .
3) Deve lopment of a narrow seaway with marginal moun-
,
t he basin a nd arches are best d ifferc ntia ted in the Ju rassic.
whe n sedimenta tion rates between them vary by factors of
1.5 to 4. Sedimentation rates for the basin and arches also
d iffer for both s helf and slope/rise du ring the C retaceous.
O n t he s helf. the bas in and arches are differentiated in the
Tert inry, but o n the slopefrÎse Tertiary sed ime ntatio n rates
are equal for the former bas in and a rches.
ta ins and hills. but more open connection wi th the wo rld
ocean . The o riginal s lope of the adjacent border lands is still
away from the young ocean whic h has a less extreme locnl
climate but is s till prone to development of dense water
masses wit h episodes of s tratification lliternating with
turnover. This s tage is nlso es timtlted to las t 20 MY.
4) A pcriod o( very rapid detrital sedimentation. which
occun after s ubsidenc e to sea level of eros ionally-thinned
contine ntal crust, ma rgi nal to the young ocean. This res ults
in for mat ion of the contine ntal s helf proper and also CltUSeS
reverSai of regio nal slope and drainage into the young ocean
bas in. The bulk of the detrÎtal sediment wedge produced by
the initial uplilt ilnd deposited a t a distance is re-eroded lmd
re-sedimented on the newly developed con tinental s helf.
slope a nd rise . T his phl'lSe Îs Îni ti.lled abo ut 30 MY af ter
separat io n, and is a lso t hought to last about 20 MY .
5) De velopment of Il mature margin with sediment suppl y
becoming Încreasingly focused by la rge ri vers at li few
points ; shelf subs idence ra te declines, a nd s helf a nd rise
sedimentation patterns become Slrongly affected by sel!
level c hanges.
SU MMA RY OF A MODEL FOR DEVE LO PMENT OF A
PASSIVE MA RG I N
As d iscussed below . parts of this sequence seem to be weil
def incd and cons trai ned, other parts will remain highl y
s pec ulative untÎl deep drilling on the margins can verify or
correct geop hys ic al Inte rpretations.
TRIASSIC
JURASSIC
CREU,CEOUS
TERTIARY
Figure 2
Vo lumes and areally inl egrmed sedime/llafiQn raIes for Ih e (It'tro~e
of usas cop Unn 1 (lIId 6 lou/litas/ 0/ Cupe Cud reprnentillK
sedimenlation ill a bll sin . Bullimon Cany/In Trough. A is sedimenl
0 11 Ihe she/I, B is sediment 01 Ihe slopt/ rise. Numlnrs III column s aft
~olum ts in km J pu km /eng/h 01 margin. Areully in/e8rO/ed
sedimentolion rutes urt km' un she/I (A) or s/opt/ riu (8) pt, km
It n,,11I of murgin. UI/IU/ogies an unkno ...n u cepll'lS nolf'd. Anllydrile ;l t quÎI'a/ent in omOl/1II W II,., h(,JjIf' siro ..." ml Ille seclio n)' i~'
illferrtd, huI ma)' nOI b r pnst"' .
The continental s plitting process normally invol ves uplirt ,
erosion, format ion of rift grabens, attenuat ion of the
conti nental c rust , implacement of uceanic crus t, separation
of t he continental fragment s by sea flour s preading. and
s ubs idence due 10 the r mlll contraction. The time cons tan ts
assocÎllted with these processes a re not known precisely :
the bcst estimate being for that associatcd with subs idence
due to cooli ng of ucennic crust and mantle. The refe rence
point for disc ussion of continental s pli tt ing is the time of
separaI ion . i.e . age of the oldest ocea nic crust, but this is
not a c ritical ti me as far as sedimenta tion processes are
concerned . Recause of the uncertaint ies in the time
constants associated wit h uplift , e ros ion, rift ing and a ttenuation , the model pres ented he re des cribes the dcvelop·
ment of li pass ive margin În a sc hema tic ma nner. recognizing an initial phase without sedimentation followed by four
early sed imen tation phases of eq uallength lmd a subseq ue nt
long period of maturity .
The sedimentological model for de vclopmellt of a passive
margin is described in te rms of the fol1owing phases, the
fint (our involving sedimentation on the future passive
ma rgin a re estimaled 10 last abou t 201\1 Y eac h :
TH E OVERALL LOSS OF S E DI MENT OFF PANGAEA
Hay el tJ/ . (in press) have discussed the s ize . s hape .
location , hypsography, nature of drainage a nd ciÎmalc of
Pa ngaea . The area of the ancient c o ntinent was probably
slightly larger t han the area of the present fragment s
becil use of attenuation and loss through s ubs idenc e of part
of the m'lrgiMI areas in the rifting proces s. Southam and
Hay (in press) h'lVe discussed the volume and mass of
sediment res iding on the major tec tonic units as s hown in
T able 1. About 213 of the sed ime nt present tadllY is of
Meso zoic or Cenozoic age as s hown in Table 2. Most of the
pos t- Paleozoic sediment was deri ved from Pa ngaea and
subsequently depos ited in the MesozoÎc·Cenozoic passive
margins and in the deep sea. The depos its offloaded o nto
oceanic c r ust are equ ivale nl to an additional layer of
sediments about 2.25 km thick spread ovcr al1 of the
continental blacks . At the present, the a verage thickness of
sed iments on the continental blocks, includinggeos ynclines
is about 4 km (sel.' Table 3). but only 2.4 km of this is
Paleozoic o r older. Th us the a mo un t of sediment whic h hns
been lost from the continent:11 blocks to the deep sea is
0) Upl ift and erosion wi th the sediments deposited in a
137
W. W. HAY
Tuhk 1
Di'ilrihllliou ull"JinwlIlS
Tectonic unît
Arca
" 10" km:
about eq ua l tO the amoun t of Paleozoic sediment Tcmaining
on the continents. :"Ind an cq ual amount of Meso7.oicCenozoic sediments resides in the continental shelves a nd
youngcr geosy nclines.
pre.felll lec/onk IInill
!JIt
Volume of
sediment
10'
"
.\Iahof
,edirnent
~rn '
" 10:' ~
"
How much o f the Mesoloic-Cenoloic sediment is recycled
Palcozoic and o lder sediment and how much has been
formed from the e rosion of igneous rocks? Holland (1978)
has estimatcd tha! about If3 of the present Im.cl of rivers
dcrives from wealherin~ of igneous rocks. Because at the
end of the Paleoloic the continental blocks had more
sediment on them. which wo uld tend to cover up igneou~
rocks, 113 can be considered a max imum value for the
proportion of MeS07.0ic-Cenozoic sediment derived from
weathering of igneo us rocks. It is likely that the true value is
much Jess. In any case. of the estimated total of
1,605 x 1011 S of Mesozoic-Cenozoic sedi me nt. at least
1.070 x l ij2' g was der ived by recycl ing older sed ime nt.
Thus more than hal! of the sed ime ntary material present on
Pa ngaea at the end of the Paleozoic has been recycled. and
about ha lf the recyded sediment has bcen lost o ff the
cont inen tal block. This re cycling rate is significantly higher
th a n th at suggesled by Garrels and Mackenzie (1971) who
assumed hall o f the total mass of sedimentary roc ks to be
600 MY o ld or you nger.
C-
l. Cr;ltun (most(y
Prccambrian·
Paleozoic)
1. Precamhnan·
P:lleoloic
üeosynd i l1<:~
%.3
19.1
'"
J·U
3~6
14.3
30.7
6.1
211
18.9
S24
11.1
28. 3
5.f,
103
18.1
3"
10.2
5'1.0
1J.7
414
37.1
1.027
41.3
31.8
6.3
"
' .3
2m
1\.1
17.5
'A
180
25 .1
lm
14.4
59.3
11 .7
m
33.6
812
12.6
6.3
1.1
19
1.7
'1
1.6
211-1.0
56.2
l·n
11.7
14<J
10.0
5OJ.9
99.9
1.115
99.9
2.4115
99.8
3. Me)ozoic·
Ceno7oic
(jeosyndÎnc~
Total
,. Passive " Iargin
Geo~yncline)
Sileive. (mos·
Mcsul<licCenozoic)
3. Passive Mar,;n
Siope and Rise
(Mc)o7oicCenozoic)
Total P-...s<iH'
Margins
6. Ac tive Mar,in
>l,
("l eM)~oic-
Cen01:oic)
1. Ocean Ba)ins
(McMlzoicCenoloie)
TOtal.
Ali Tectonic
UnÎt~
T H E SEQUENC E OF I3REAKU P OF PANGAEA
T he sequ ence of separation of continental fragments prese nted in Figure 3 l ollows th at presented and discussed in
deta i! by Barron el al. (in press). but adds the Gulf o f
Mexico with conti nental separation a t 150 million years ago,
fotlowing Burcler et al. (1980). The values indicaled on the
o rdinate are the le ngth of passive margi n resulting fro m
continental separat io n : on the lert margin is the length or
the rift prior to se parat ion. Figure 4 shows th e integrated
e ffec ls o f breakup o f Pangaea in terms of the four phases of
passive margin sedimentatio n. 3S discussed bclow .
Table "2
Vulll", ..J and mau ..s /JI s.. Jimlnt by live
A"
Volume
Hrkm1
Prccambrian·P..,leo1.0ic
Mel>OlOic-Cenoloic
TotlJl
'"
-'
....,"','"',
35A
1.60'
66.3
100.0
. .......
-
'i
""
]3.7
316
119
1.115
.
Ma))
x 1()ll ,
""
.-
lClO.O
2.48'
,•
_
.. _......... ..
0
>
rll ble 3
A,craj,'f' 11til"t..""Jse". ,·(,II/mu. and
IIU/n..,,·
01 S<'dim"'tt,,· utt {"(mli·
J!t'uw/ blod':'.1 mul il, OC/'U1t busi'!! by u)...'e
A\erab'.:
Volume
Thickness 10" km l
ri
Continent:,1
block
Tectonic Uni" 1-;1
PreçambrilJn2A km
l'alW.toÎc
316
33.7
1.6
311
28.4
4.0
093
5
••
.
Mass
10:'
~
r~
880
H.4
Cenol.O;c
TOlal
"9
30.1
bitS;n Tcctonic
'·1 Prceambda n-PaleOlOic::
0
-
M-
.-
..~
-,......... ...... ....._'' . . ,-.... -.....
"'
~'''''
..-,.-_._..........._,-
~Iesoloic·
-.
'''''
-,~
•
~
••
~
....,
-.
1.629
OC~lIn
Unil~
MbO~()ic -CCnOlOIC
TOlal
1.'
lA
0
O."
422
31.8
836
0
34.4
4n
99.9
1\.'\6
99.9
liGe tN MIllIO N'UliS
Figure 3
Ltnglh 01 rills unJ plluil·t tlturgius ftslllli"g lrom litt brt'ukup III
PuugUtll plO/ud uguinsi tlmll III Stpurmlo1l 01 the IraRments.
(LU
138
SEDIMENTOLOGICAL EVOLUTION AND BREAKUP OF PANGEA
-.
Fillure"
S}'1l1Jplic .w:hellw of rllt dt l·t/OplllI'III of r;flll alld PUSS;I'I'
1II0rS;II$ s lrQ",illg phllSU / .4. NI/mbers ;n coll/mn s rl'fl'rlO lhl'
riflJl pasûl'/' nrOf'Rili s ;mUcall'd ill Figute J. III pli/Ise 1. d;ugo·
no/Unts illdlcall' lhallh t rift dt ..t/llped in a "'onll hllnrid ZIJnI'
cOlldUôl'/' ra Iht dt ..tlopm l'm of strotified /okes. Ulld hence
liktl)' la ln s;lIb for OfRIlItlc Cllrboll. Vt rt ica/ scalt;1l /()J km af
/1'1111,11 of rift . In phost 2. Iht quadrille pal/trn ;ndk arts
dtposi/ion of tl'aporill'S , "'a~y lines indicall' ue/lfIsi/ion of
orllmr;c carboll·rielr black sh u/ts. Vert;cul ." alu art 10' km of
/l'U~tli of riflll/rd /01 k", af 11'''11111 of pauil'!' ,,1(1r~ill. bUlI/ue
cOlrtill en tal sepurariOlI ncc urs ;/1 lire m iddle nfthis fllw se.
/11 phust J. the "'u v)' Ullt putte", ilrdica/ts dtpositioll of
l>r~allic Cllf/xJn-ric h blt/e/.: ~'hl,lu. Vl'rtiClI 1 .I·call' ;$ JO' km of
ftllf,;llr of paHil'e margin .
III phast 4, Ihl' l't r/iral sc ull I.f 101 k", of IplI~tlr of pussil·t
ma'1l;II .
.
"'""IR.
-. !!
-. -.,
"'"1011 4
TRIASSIC
l'hase 0 - Vplill II nd eroslon pcior 10
Ctnlrlll rifl gra ben
d cn~l o pm e nl
of
JURASSIC
CRElACEOUS
lEFl TIARY
involved and complexilY of the rifting process will vary
f rom place to place , The North American-African rift w.. s
evidenlly il. very complex process, producing not only the
rift gril ben basins exposed at the s urface in Nor th Ame ricn
and Africa, but 'llso a number of dceply buried bas ins, ,I S
s uggestcd by van Houten (1977) a nd documented by Klitgord and Behrendt (1979), The splining of Pangaea invol ved
a conlinental Ihic kness about 2.25 km grenter and a seafloor
s preading system Jess weil organized Iha n Ihal of today. ft is
not unl ikeJy Ihal the intervals required from the processes
of uplift and rift ing 1cading to s plitting we re longer in the
early Mesozoic and have tended to become s hortcr as Ihe
continents have been Ihi nned by erosion and the global
se;I floor s preading system becomes mo re o rganized . The
time s pan represented by this phase might be up to 30 MY .
The a rea involved in uplift and eros ion was recognized by
Closs (1939) 10 he ex tensive. but most modern aulhors have
cons idered only Ihe s ile of the central part of the upJif!. The
m tio of length 10 widlh for individ ual Africa n uplifts, given
by Ilurke and Whitenmn (1973) varies from 2: 1 to 3:1, with
the s mallest , Adamewa and Ng:loundere . being 50 x 150 km
and the larges l, Jos, being 200 x 500 km . Where uplifls
ha ve coalesced , At:lkor·Ajjer (to form the Ahaggar) and
Barmenda-Cameroun Mt. , the length 10 ·widlh ratio is
increased to 4:1 and 8: 1. They suggest uplih of the basement
of about o ne km for ail of the eleven Africa n uplifts
analyzed.
Much larger areas may bc "ffecled by upli h . As Soulham
and Hay (in press) ha ve s hown . the profile of a t ypical
midocean ridge s uggesls signiricant up Jift extend ing to
800 km or more on eilher side of a rift. Viewed in Ihe
contexl of a continerltal area previously eroded to grade ,
suc h uplift has enormous sedimentological implications,
involving the e ros ion of a vas t volume of material. For
North America, the regional uplilt prior to 5eparalion from
Africa may have ex te nded west to near the site of the
present Mississippi, with slopes s imihtr 10 those presently
Il
Cloos (1939) desc ribed Ihe process of uplifl., rifting and
associ:ued volcanis m us ing the Rhine graben and Red Se;t
Gulf of Aden areas as examples. From experimenls, he
dele rmined that domal uplift was likely 10 produce three
crac ks at angles of approx imalely 60' to eac h olher.
Mc Kenzie a nd Mo rgan (l969) discussed seafloor spreading
al triple juncl ions as Ihe res ult of upwelling manlle plumes,
Burke and Whileman (1973) have discussed uplift a nd rift ing
in Africa and use the lerms rrr and RR R 10 distinguish
between rift triple junctions a nd seafloor spre;lding triple
junclions. Burke and Dewey (1973) asc ri bed de velopment
of a linear spreading center to coalescence of IWO arms of
eac h adjacent rrr rift triple junctio n. The third ann fail s to
become il spreading ccnter except in li few places wherc the
rrr triple rift junclion develops inlo li RRR sprcading ridge
triple ju nClion. The early ph'lse of uplift ma y be recognized
by initial ion of alkal ine volca nic ac tivi t y as suggested by
Lebas (1971).
Burke a nd Whiteman (1973) ha ve tabulated the statistics fo r
elcven rrr junc lions in o r atthc margin of Africa, ascribing
lengths of lime ra nging from 50 m. y. 10 30 m .y. for the
period o f aclive rihing associa ted with Ihese rfr junctions.
On the Atlantic margin of North America, the bas'lltic sills
and fJOWli associated wit h Triassic graben developmenl and
deposit ion of t he Newark Series (Sanders, 1%3 ; de Boer,
1968) were dated al 220·230 m, y. (Armstrong. Besa nçon,
1970 ) or 40-50 m .y. prior 10 continental separation. Howeve r . Ihe Newark Se ries exposed in Ihe easlern US may ha ve
been deposited in a fllikd rifl system a ntecedent 10 tha!
along which continental separation occurred . For the development of the model , Kinsman's es ti mate of 30 m.y. has
been cons idered app ropriate for the time s pan between
development of the rift and separa tion of the continental
fragments. Clearly, this is a generaliz.ation because the time
139
W. W. HAY
existing bctween Denver und St. Lo uis. The amount of
uplift of a con tinental area over an incipient spreading
center Clm be cstimaled using the values for thickness and
density of typical oceanic and continental crust sections
given by \Vorzel (1974). but with the modification Ihilt the
total conti nent is assumed 10 have an elevation of
+ 0.84 km , a sedimenl IhickneS!> of 4.0 km with an 'lVerage
density of 2.2, and an average den~ i t y for the igneous and
metamorphic crust of 2.84 down 10 - 33.0 km , Assuming
that the weighl of Ihe col umns musi balance at - 100 km,
laken to he the top of the asthenosphere, and Ihal the
difference between old seafloor (Worze]'s oçean crust
section) and a spreading ridge is Ihat the latler lacks
2.5 km
sediment and has the 10p of layer 2 raised to
because of warmer. less den~e mantle ma terial. the mantle
benealh the spreading center can be calculated to h:lve an
average dens ity of only 3.23 ralher th'ln the 3.30 assumed
benealh old ocean crust and benealh the continent. Assuming thal prior to rifting t he densilY of Ihe hOI man tle
material beneath the continent is 3.23 requires an lldditional
1.45 km of mantle beneath the continent and above
- 100 km. elevating the s urface of the continent by that
amounl. Ki nsman (1975). using slightly differe nt values for
the thickness and density of the unÎts. oblained <In uplift
value of 1.75 km . Tflking inlO llccount Ihe grea ter average
sediment t h ickne s~ on Pangaea (5.75 km) and its higher
average e!evation ( + 1.06 km) the uplift would he 1.42 km .
These values negleci erosion which would remove ma terial
from the area of uplift and deposi t it in unaffected region!>.
Isoslatic adjustment as erosion removes material oH the
uplift would am plif)' the effect , so Iha! to erode the cre~t of
the upli ft to the original grade and b.'lse level would requi re
erosion of 5.3 km of ma te ri lll (4.0 km of sedimcnl of density
2.2 and 1.3 km of igncous or melumo rphics of den sity 2.84)
from the present average continent. In the case of averaile
Pangaea. 5.5 km of the average 5.7 km sediment cover
would he eroded , leaving 0.2 km of sediment remaining on
basement lit the center of Ihe uplifl. If the uplih had Ihe
shape of the Mid-A llanlic Ridge , the 101 al volume of
sediment which could bc eroded oH each s ide would bc
2,000 km ) per kilo meter of lengl h if isoslatic ad just me nI
we re complete lInd crosion proceeded to Ihe origimll grade
and base Icvel. An estimate or halr Ihis amounl i ~ more
realistic becau~e erosion i ~ unlikely 10 have reduced the
surface to the. o riginal grade and base level before ~ubs i ·
dence set in .
The materilll e roded off the uplift would be deposited in the
dis tal part of the regional slope a nd beyond. In North
Ame rica the sediments eroded off the uplih prior to s plilling
of North America from Arrica. would have been deposited
above the sea level in the continental interior. Simultaneous
uplift in Ihe Gulf of Mexico and Arctic region~ and
mountains in the west bordering the Pacific subduction zone
would have ac ted to creale a very large interior basin.
Car bonale lInd o ther soluble rocks would bypa~~ the ba~in
which would acc umulate only the detrÎlal mate rial. The
Dockum, Chugwater. Spearf ish. and ot he r redbed s of the
Triassic or carly lura ... sic of the eastern Rocky Mounlain ~
probably represe nt the clay~ and sihs forming the distal
portion of this great sediment wedge originating a t the sile
of the future east coast. and would have overlain Permi;;n
rocks of the Great Plains and Midwesl. The maleriab
e roded off Ihe uplift would ha ve been largely the Permian
and Pennsylvanian detrital sedimenta ry rocks produced as a
resuh of the Appalachia n orogeny. The ~e sediments. proba.
bly in the orderof 3.5 x 106 km ), were recycled to the west.
bUI are 131er recycled back 10 the ellstlo be depositcd on the
de veloping slope and rise. following Garrel s and Mackenzie's (1971 ) rule that the last rocks deposited are the first 10
he eroded.
Alkaline volcanism. uplift and erosion mOlY precede continental se paration by as much a ... 50 MY. The sedimenlological model developed here assumh format ion of a grabe n by
rifling 30 MY prior to contincmal separat ion. allowing
20 MY for pre-rift doming and erosion. Be cau~e this imerval does nOI directly contribute sediment 10 the future
pa~s i ve margin il ma y appropriately be termed phll ... e O. llnd
precede ... Ihe phases of sedimentation on the future pa~si"e
margin.
During this carly period of uplifl. the third arm of each rrf
junction may become weil developcd causing thinning of the
crust by uplift and erosion . The third arm would extend
in land away f rom each obtuse angle devclopcd along the rift
trend. T he importance of Ihe Ihird arm is Ihat the thinning
permils s ubsequent development of a ma rginal basin. Further. subsidence along Ihe length of the failed third arm
tends to guide reorganization of the drainage, as evidenced
by the fll ct Ihal man y major rivers debouch in marginal
reenlrnnb. Figure j show~ postul:ued major rrr junctions
for Pangell !l nd indicales the rivers assoc iated wi th the failed
Ihird !lrms. The process of reorganiza tion of drainage afte r
uplift i ~ long :lnd complex but ul tjmalely fa vors capture of
olher strellms by those occupying the s ites of failed Ihird
arms.
Fi.llure .'1
Map of Pa"lIuea. showi,,/( mujtJr rifls and i"dica/inll n'I'er$ "'hicl,
he an/Jciuud "'111, triple jIUlClio1l$ KOL _ Kil /plia .
LEN ~ l~elta. OB -" Ob. SUS - SruC/"ehellla. SA V .,. SC/I·OIU1alt.
ma)'
M IS ~ M issifsippr. RIO ", Ria GrandI'. AM "" Amil:()/!. NIC _
NiKer. SF - Selll r-'ClltcÎl(·/J. CON - Congo. PAR _ p(If(mil. 01< ,.
Orange. ZAM _ Zambesi. KRI
Kri$luta. MUR - Mllrru}'.
Phase 1 _ T he ele"alcd rift valley gra ben : S('dÎmenla tÎo n in
Swam ps, fresh waler Ill kes , und sl reams
When rifting first occurs the graben is a shallow feature on
the regional uplif!. The regional uplift is likely to be the
highest area in the vicinity. and as s uc h will act 10 modiry
the local climate to serve as a \fap for rain. By analogy with
the East African Rift systems. it can bc expeCled that
paludal. lacustrine. and fluvial environmenb will dominale
in the rift. wilh margina! alluvial fans developed alo ng the
graben willls. The ~ource area for detrital sediment s is
res lriclcd to the immedialely adjacent parts of the uplift.
140
SEDIMENTOLOGICAL EVOLUTION AND BAEAKUP OF PANGEA
For Ihe model. initial ion of sed imenlal ion in Ihe rifl is
cons idered 10 s tart 30 MY before separation, and this fre s h
waler phase Is expeeted to last aboui 20 MY . At 10 MY
bdore separation the floor of the rift graben reaches sea
level a nd subsequentl y the rift can be fill ed with marine
water o r form dessicated basins below sea le vel , such aS the
Dend Sea graben a nd Afar at the present time.
The narrow growing ri!! i5 prone to great irregularity in
developmenl wil h lo ngitudinal bas ins and :lfches res ulting
from dilation and compression due to minor changes in the
strike of the walls as the central block subsides. [n the
easlern United States it is evident that the rift did not
de velop as a s ingle lo ngitudinal feature, but as a series of
quasi-p<lrallel troughs, each no more than se veral hundred
km in length (van HomM. 1977 : Klitgord , Behrendt. 1979).
The trend of the rifts follo ws pre-exisling s truc tures, and
sugges ts reac tivation of zones of weakness in the c rust.
The volume of sediment whic h accumulaled in the de veloping rift was . by comparison . a s mall fract ion of that eroded
oH the uplift . Based o n a nalogy with the Dcad Sea Rift.
Southam and Hay (in press) citcd 40 km as the average
width and 5 km as the a ve rage depth of sediment fill before
floor of the graben reac hes sea level a nd marine invas io n
can t'lke place. Hence. the sediment volume is 200 km ) per
km of length o f Ihe ri fl. Subsequent lo ngitudimll spliuing of
the graben liS conti nental separatio n takes place wo uld le,lve
each passi ve margin with 100 km J of phas e 1 rift sediment
per kilo meter of length. This estimate agrees weil wÎlh the
pre-salt Triassic detrital sediment volume of 106 km ) per km
lenglh of rirt obtained by meas uring both the salt and the
sediment below the sal t o n the cross sections of Folger el al.
( 1979), and assuming an amoun t of anhydrite equivalent to
halr of t he !kilt to be included in the sediment below .
However , the c ross sectio ns of Folger et (II . terminate ,II the
~ hore Hne , so that the estimates of volume based on them do
not include the onshore Triass ic grabens with expos ures of
the Newark Series. In Figures 6-7 the oc Triassic " detritusof
the cross sections of Polger et al. has been s hown as
r-
...
•
F
.,
l
_n
-
••
1
•••
.,,,
c.....
TII/Assle
Figure 6
JURA SSIC
•
cIIETAeEous
f [ lIf lAlI Y
Volumts (Uld (Ireull)' i" Ullruud sedimf!llllIIiOl! rat es lor the uvaase
01 USGS CDP fin e j southeasi vI Cape Cod and flle US GS IPCD
line acrou Ihe margin sauthea st 01 Cape Halleral, representins
sedimentation on tht archu in u,ms vl lhe phasu 01 passi,'e margin
del'elopment pn senud /n fh e u xl. A. il sedim ent vn Ihe shell. H is
sediment 01 the slopti rise. Numbers il t co/umnl are "olumtS in km
'
pa km leng/II 01 morgill. Areoll)' ill/ egraleu sedilllenwtiml rait! are
km' on shtll (A ) ur slupti rise (8 ) pt r km lenglh olll//lfgin.
14'
deposited duri ng phase 1. in thi s cas e between 210 and
190 MY ago. which is younger tha n the 220-230 MY da tes
on the bas altie s ill s and flows of the Newark Series obtained
by Arms trong and Besancon (1970) . but corres ponds with
their dates for the dikes and may be mo re approp riate fo r
the age of grabens buried beneat h younger s helf sediments.
So utham and Hay (in press) ha ve sugges ted that the
eleva ted rift grabens may be ah important s ink for o rga nic
ca r bon. Degens f't al. ·s (1971 : 1973) and Degens a nd
S toffers ' (1976) accounts of Lakes Tanganyika. Malawi and
Ki vu in the East Afriean Rift Sys tem demons trate that t hese
tropical lakes a re stratified , with Il weil developed thermocline separating oxygenaled surface waters from anoxie
bottom waters. Bo ttom sediments of these lakes mlly have
very high contents of orgllOic ca rbon , up to 10 % in the
sediments of Lake Tanganyika . Sout ham llOd ' Ha y assumed
an average carbon content of 5 % in aIl rift sediments
formed o ver the past 180 m.y. to estimate a total of up to
7.36 )( lO!O grams of organie carbon in rift sediments. Using
a new estimate b:.lsed on the additional rifts included in
Figure 3, but count ing only those rifts whic h developed in
humid zones . assuilling an (j verage organic car bon content
of S % a nd assuming a n a verage of 20 % lacus trine s edi·
ments in the graben fill , the estimale of the lotal of organic
carbon is reduced to 2.18 )( 10211 g of organic carbon . This
still IImo unts 10 a tcn-fold ellrichment over the average in
sediments .
ln cons truc ting Figure 4 the a ttribution of the s ite of
fo rmation of a rift to a humid or arid e nvironment was based
on its paleolatitude on the paleogeographie maps of BlUrOn
et al. (in press). The rift is assumed to have been humid a nd
to have had lakes if it developcd outside the bands 12-30" N
and S. The lakes are assumed 10 ha ve been thermally
s tra tified and to ha ve accumulated sediments ric h in organie
carbon unless the rift de veloped after the late Eocene a nd
occ upied a latitude higher tha n 30' . The o ill y Mesozoic: rift
whic h de veloped excJusively in the ass umed Mid band is
thm between No rt h America a nd Alric!! : a part of t he rift
belween South America a nd Arrica also de veloped in the
lI rid band . Lake de velopment wi thin the arid band cannot be
excluded if parts of the ri ft also extended into more humid
regions and could se rve as sources for rivers, 5uc h Ils the
Jordan, flowing liiong the length of the rift. Definition of the
bands between 12·30" N and S as a rid zo nes relies on the
assumption that the Hadley cells governing atmos pheric
circ ulation were in the same pos ition in the Mesozoic as
suggested by the almospheric models studicd by Ba rron
(1980) and the paleocJimate-paleolatitude analyses of Habic hi (1979), and that the y did nOt occup y differen t la titudes in
the Mesozoic liS s uggested by Fra kes (1979). If large
conti nental arcas affec t climatic zonation li S suggested by
Robinson (1973) a nd as used by Ziegler el al. (1979) and
Hambac h et al. (1980) in their Paleozoic rcconstruc tio ns,
then Ihe arid zones wo uld extend obliquely across the
co nti nent, s tartins at higher latitudes on the eas t and
expanding in widt h to reach lower latitudes to the we st.
Appli cat ion of this paleogeographie paleoclimatie modellO
the Pangea of 180 m.y. ago produced the interes ti ng result
that the North American-Afriean rift would have de velo ped
in a humid region (see Hay et al .. in press, Figure 5). This is
in agreement with Ihe presence of extens ive Illcus trine
depos its in the older beds of the Newark Series. A nlll ys i ~ of
the paleoposit ion of rifts with Robinson cl imatic belts would
be an interes ting e xercÎse and mighl sugges t modification of
Figure 5. It would aise be useful to seek additional evide nee
10 detetmi ne whether cJimalie boundaries c nn be signific:mtly deflected by large 11I nd areas.
w. W.
HAY
-n
r-
•
-•
- ""
-"
- ""
-
'lH
,.~
,
..
,
ua
1
.,.,
,
,,,
•
-"
-.-.
-.
Fil:ure 7
Volumes and areull)' iII/eRra/id stdi m(!II/a/;oll rtl/rI lor ",e
IH·erage ul
CDP /i"u 2 (111(1 6 l'ou/hcaSf 01 Cl.lp e Cod
usas
-"
-,.
-n
•
TAIASSIC
-"
-" ~
-,
JUAASSIC
:~
CRETACEOUS
reprt.un/i" g ~edmen/(I/;ulI in a bositr. Ba//imon Cun)'oll
Truugh ill lerms uf Ihe phases UII}(J.~sil·t margill del·t/opme,"
prese/lud i/l /he lUI . A is sediment un Ihe she/f. B il $tdimenl
of IIrt slopel rile. Nllmberl in rol",rl/lS are ,·o/umes in km' 011
slre/f (A ) or slopel riu ( H) pa km /etrgtll of margin.
TEATIARY
separat ion is an a ppropriate estimllle for Ihe length of this
phase. Il takes place white the thinning of continental cruSI
by faulling is most ac ti ve.
Whether the evaporative tendency of the ba sin will result in
act ual deposition of evaporites depcnds on the nature of the
connectio ns with the o pen ocean. If the se are through
lateral offseb in the developing margin. it is likely that
rei>lricted drculation will re~uJt and evaporite basins mny
form . If the <:on nect ion is open. as in the cas e of the Gulf of
Californ ia. the narrow sea may act a~ a site of forma tion of
wa rm ~ a1ine waler masses and these may lead 10 enhanced
turnover , both downwelling and upwelling in the narrow
sea . Spreading rate and widening of the !x...in probably
inc rease after sepa ration.
The volume of sed iment which nccumulate~ during thi ~
phase is highly v~.ria ble depending to a large extenl on the
degree of restriction of basi ns wilhin the rift. In Fi gure~ 7·9
o nly the S:il! shown on the cross ~ec tion s of FOlger and an
equivalclII amount of anhydrite s ubtracted equally from the
preceeding and s uccecding sediments is shown as the
deposit of phase 2. An amounl of a nh ydrite equivalent to
the amount of salt s hown on Ihe c ross sections b used for
Jack of a more accurate es timale of the rela ti ve proportions
of halite and anhydrite in the ~e a ncient e vaporite depo~its.
Ja nsa et (1/. (1980) have shown Ihat off eastern Canada. the
evaporites are almost exdusively hal ite. and have suggcsted
Iha t a nh ydrite was depo~iled in basins o riginalJ y more
proximal 10 the Tethys and presently on the ea ) tern side of
the Atlantic. If the ~alt orr the eas tern US is an exten~ion of
that off eastern Canada. nOllnhydrite may he present. If the
Phase 2 - The narrOW sea belwfen high walls : hypersallnity
Itnd c\'aporiles
During this ph<l~e the Boor of the rift graben has sunk below
sen le\'el while the uplift has attained ilS maximum eleva·
tion. The relid is al a maximum both because the gre a le ~ t
ele vation of Ihe basement is re:lched during this phase ;lnd
because cros ion mu)t attack older roc~s which had been
more deeply buried ;lnd had become mo re lithjfied. The
walls of the ~raben may be expccted tO average between
two and three kilomcters elevalion abave sea level. and the
widlh of the graben may increase to 100·200 km . The local
climate of the graben is likely 10 be arid e ve n if it is located
in a relati vely humid region . The marginal mountaim
formed by Ihe uplirt barde ring the graben wHll s extract
mois Iure (rom the :l it of Ihe pre v<lilinlol winds. which mU~ 1
rise over thcm a nd cool in order tO pas~. As the dry a ir fl ows
down inlo the graben it is adiabatically heated and de velops
a high evaporutive capacity. During thi!; ph:ls e. the regional
drain:li!e ;lway from the graben becomes !:leSt developed .
The length of this phase can he eSlimated from the extent of
salt deposits known on Atlantic margim . Salt depos ition can
take place befOTe the appeamnce of oceanie c rus t. 50 Ihat
no salt occurs on oceanic <:ru~1. or may take place berore
and aher separation . so Ihal salt overlies both continental
and o<:eanic c rust as indicatcd by s tudies of the Angola and
Brazil bas ins (Ca nde . Rabinowitz . 1978) and of the North
Ameriean margin (Folger el al .• 1979). lt is e videnlthal the
lime of separation i~ in the middle of this ph a~e . A total of
20 MY s p:lIIning 10 MYon either s ide of the time of
142
SEDIMENTOLOGICAL EVOLUTION AND BREAKUP OF PANGEA
ev.lporiteS off t he eastern US belong to a diffe rent depositional episode , materials ot he r than hal ite muy he expected .
The halite off the eastern US is poslulated on the bas is of
d iupiric s tructures seen in seismic sections. Anhydrite i~ not
as readily recognized on seismic sectio ns as is sail . and
ca nnot usually be d istingui shed fro rn carbo nates. T he average volume of salt (halitc) is 64 km l per ki lometer of length
of the ma rgin. but it may he assumed t hat only hulf of the
origi na l width remains with Nort h Amc rica and that an
e qu ivalent amount exists off North Africa as s uggested by
the d iscussion of Manspei zer el al. (1978). In t he case of t he
cross sections off Nort h Ame rica. the s'llt is d istributed
over 11 width of 60-100 km 50 that thc average thic k ness is
between 0.6 a nd 1.0 km . Dia pir fo rmation is thought to
require il mi nimum thickness of salt of about 1 km.
If evaporite deposition takes place d uring phase 2. s ignifica nt extraction of CaSO, and NaCI f rom the ocean may
occur. Estimates of t he a mount of salt re moved lI nd
dcposited in the North America·Africa narrow sea are abo ut
1.5 x Hl'" kml , t h,!! in t he Gulf of Mexico abou t
2.1 x 10 6 km l and in the South Atla nlic about 2 x 106 km ).
As noted by Southam a nd Hay (in press). these eJO:tfllctions
are sufficient to have had a significant effecl on oceanic
sa linity. and may have resulted in a red uctio n of the salinity
by 20 % duri ng the early and middle C retaceous. If equal
amo unts of CaSO, were removed , precipital ing out as
gyps um to be lalêr Iransformed by d iage netic me tamorphism Înlo a nhydr ite . t he io nic balance would have changed
d uring the Cretaceous. However. composition wo uld have
remuined wit hin the limits determincd by Ho l1and (1974) a nd
would no t have allowed dc position of unus ual evaporite
mine rais.
Evaporite deposition incl uding 1 km or more of halite d uring
th is phase may s tro ngly affec t the later develop ment of the
margi n. If subsequent sediment loading prod uces diapirisrn.
the margin may he one in whic h continuous defor matio n
lakes place. with the rutc of defo rmation varying wÎl h the
ra te of subseq uent sed imen tation, as in the cllse of the
no rthern margÎn of the Gulf of Mexico.
If the rift is open 10 the oce a n, evaporite formation may be
eJO:cl uded , but high o rganic produc ti vity mUy res ull from
rapid cycling of nutrients in the unstuble wa ter masses. T he
modern Gul f of Cal ifornia has high prod uc tivity and an
associa ted acc umulation of d iuto maceous sed ime nts. Rates
of sedimentation of 250 tp 500 m m.y. have been reporled
for the d iatomaceous sed ime nts of the Gya ymas slope by
C urra y el (II. (1979) and Lewis el al. (1979). Even if the
ave rage content of dia tom remains only l f3 of t he sed iment.
dintom f rustu les ;Ire sedimenting at rates of 80-160 m / M Y.
avcmging 130 m/MY . Appl ied over the 20 MY length of
phase 2 this wo uld a mo unt to H thickness of 1.6 to 3.2 km.
averaging 2,6 km of d imom frus tules. or forrlling a vol ume
of 260 k m l per kilometcr of le ngth alo ng the 100 km wid th of
the phase 2 half grabe n attached to each continentlll margin.
This is a vol ume grel,ter t han thal of the salt whic h
acc uffiu ];, led in b."lsins off the US East coast. Il is unli kely
that the high produc ti vi ty of Ihe Pleistoce ne-Ia te Pliocene in
the Gulf of California woald persist thro ug hout the e ntire
span of phl,se 2. The d ia to maceous sedime ntation in t he
Gulf of California a lso coincides wit h the developmenl of an
oxygen minimum zo ne. so tha l the sedi me nt s are enric hed in
o rganic c;lrbon.
The fixation of SiO, by d ialOms as amo rp ho us s ilicli in Ihe
Gulf of Califo rnia h a ge ochemically significant sink fo r
silica o n the global scale (Culvert. 19(6). T he ra tes of
sedimentatio n o f diato m fru stules reporled by C urray el al.
(1979) and Lewis el (lI. (1979) are about an o rder of
magnitude grellter t ha n Ihe rates of depos ition of diatomllceous ooze a round t hc Antarctic. which range up to
22 m/M Y but average abo ut 7.4 m/MY.
T he significa nce of removal of organie carbon in the Gulf of
California cannot be es timated until the detailed resulls of
DSD P Legs 64 and 65 ha ve published . However, organic
carbon values are unusuaJJy hig h in t he diatomaceo us
deposits acc umulating with in the oxygen minimum zone so
that th is is probllbly a n important s ile of acc umulat io n of
organics.
T he fa te of d ifferenl narrow se as during Ihis phase is
indicated in Figure 4. E vaporite depos ition is indicated only
along passive ma rgin segments for which undoub ted evide nce from d rill ing or seismics exislS. Because seismic
Inte rpretation of an area as underlain by sal t orten rel ies on
the prese nce of diapirs . regions wit h th in salt or wi t h only
a nh yd rite depos its would not be recognized .
ln the Cape Basin of the Sout h Atla ntic . this phase res ulted
in de position of ., black s hales" (Supko. Perch-Nielsen.
1977), as a res ult of e pisodic salinity stra tificat ion and
development of anoxie bottom wa te rs (Nmland. 1978;
Arthur. Natland. 1979).
T he situatio n in the Gulf of California. wilh deposition of
diatomllceous deposits. may be un ique. Diatoms are
unknown prior to Ihe Campa nian. so that slrictly analogous
deposits could only be eJO:pecled in the narrow oceans
associated with t he brellkup of the Lord Howe Rise.
Campbell Plateau. Aus tral ia and An tarc tica. t he separation
of t he Seychelles from India. and in the Red Sen-Gulf of
Aden. High produclivit y of other o rganisms may have
introduced o rga nie carbon into t he bo!tom sed iments in
areas occupying the proper paleolatit ude. Only the IndiaSeychelles se paration appears 10 have laken place in a
latit ude s im ilar to that of the modern Gulf of Cal iforni'l.
Phase 3 _
The narrow ocean
Dur ing th is phase the ocean widens from 200 to 600 km or
more ••md the ma rginal moun tai ns lInd hill s subside to sell
level. Local cl imatic cond itions become less severe. but still
dis tinguish Ihe na rrow ocean from the world ocean. T he
te ndency toward hype rsali ne conditions decreases but t he
narrow ocean wit h developing ma rginal shallow wa ter
embaymenls may se r ve as fi source of Wllrm salt y bottom
water. Major s treams and rive rs arc s till deflected and flo w
away fro m Ihe ocean in this phase. but the source areas for
sed ime nt begin to expa nd as the marginal uplift su bs ides.
Th is phase occ urs d uri ng the Înterval from 10 to 30 MY
af tc r se paration. At 30 MY afte r separation. heat loss
beneath the origina l upli ft has procecdcd uni il the forme r
upl ift rcac hes sea level ( Kinsman. 1975). During this phase.
the density of t he manlle beneath the continentlll margi n
increases from 3.25 10 J_2K duc 10 the Ihcrmlll contTlI(;tion.
During this phase. Ihe diffe rential re lief in the s prelld ing
ocean floor due to fracture zones related to marginal offsets
is im portant in d ividi ng the Ililrrow ocean into li series of
basi ns. Alt ho ugh the s urface watc r connections may be weil
established. deep wa te r connec tion s are not, and de nse
wate r introduced into o ne basin may not be able to s pread
into Ihe adjacent depressio ns. The impor tance of t hese s ills
between basins will decrease as the ocean becomes wider
a nd fur ther su bsidence occurs.
143
W. W. HAY
The volume of sediment whic h acc umulates during this
phase is a malter o f specul&tion . The area draining to the
narrow ocean will increase gradually, hence the source area
for detrital sediments will increase. but there is presently no
way 10 eSlim'lte how muc h sediment will be deli ve red 10 the
basin. I n applyi ng the modello the eas t CO<tSI of the United
S tates (Fig . 6·7). it has been a rbitrarily assu med that the
Grea t wedge of sediments s hown as Jurassic on the cross
sec tio ns i ~ middle and late J urassic. a nd that only the salt i:.
early Jurassic. A volume of Jurassic sediment equal to half
the vol ume of :.alt was considered to be anhydrite and
unrecognized on the seismic sectio ns. and deducted from
the total o f Jurassic sediment and placed in phase 2. Il hll:'
then been .u bitrarily assumed that o ne fourth of the
remaining Jura:.sic sediment belongs to phase 3. The truc
a mo unt could easily be half o r do uble that arbiuarily
c hosen. but this will not alter the geneml pattern o f the
sedimentatio n mode!.
Phase 3 sediments a re ass umed 10 be largely terrigenous
delri tus and reeC o r bank carbonates. Ouring this phase.
shal10w marginal seas may become sources of downwelling
plumes of warm s all y bollom wate r (WS BW) which C'1n fill
individ ual basins in the young nllrrQW ocea n. As Bras:. el al.
(in press) have dbcussed . WS Il W promotes a no xie condi·
tions in the bollom waters both by ha ving low initial oxygen
content and by producing s tratification. Episooic anoxie
conditions seem to have occ urred in Ihe Angola/Brazit basin
of the Sout h Atlantic duri ng the interval AptianCenomanian ( Perc h-N ielsen et al .• 1977 ; Bolli el al .. 1978).
The anoxie events are recognized by the presence of o rganic
carbon-rich black s hale layers in otherwise normal sedi·
ments.
Their paleolatitude d uring Ihis phase s ugges ts Ihat the Norlh
AtJanlic a nd Gulf of Mexico would also he <lppropriate
regions where analogous deposition of organic carbon could
be expected, but drilling halO no t yel penetraled into
sediments which would correspond to this phase.
This large volume of sediment must be mos t!y detri tal
malerial. If it is deri ved c hiefly from the sediments eroded
off the uplift 50 MY earlier it can be expected to he mos tly
the sands and coarse :.ilts which accumulated on the rlanks
of the uplift . The younger part of the sequence would be Ihe
finer grained deposits recycled f rom more dis tant regions.
The very high sedimentalion ra tes would promOle preservalio n of o rganic carbon. and nn overall org:mic carbon
content significantly higher tha n thal of the ave rage sed iment ca n be expec ted .
The USGS c ros!> sections off the US east COOlst show a large
carbonllle bank o r reef complex Olt the Jurassic-Cretaceous
s helf ma rgin. Ap parently. as in the case of Ihe Permia n
basin of west Texas. Ihe carbonate edge to Ihe margin is not
a barrier to the seaward transpo rt of det ri tus. because large
vol umes of sediment ar!>o accumula ted on the slope/rise.
DifferentiaI sed imenta tion between basins and a n.: hes is
pro nounced both o n the s helf a nd o n the slope/rise.
Paleolatitudinal position determine:. whe ther o r not a ma rgÎnal carbonate bank i:. likely to de velo p during this phase.
The Apulia-AnaloliaiNo rth Africa. AtlanticlNorth Africa,
Gulf
of
Mexico,
South
America/ Arrica.
and
India/Seychelles/Madagasca r margins are mos t likely tO
ha ve car bona te ba nk complexes assocÎa ted with mass ive
detrilal sedimenta tion during this phase of de velopment.
Phase 5 _
Maturily
The mature passive margin borders an ocean wide eno ugh to
dominale Ihe climate of the marginalla ndmass. The coaSlal
plain. s helf . and s lope/rise become slltbilized a nd sedimentation depends les:. on the declining ra te of thermal s ubsidence. and inc reasingly nn ~ea level c hange~ flntl ~ediment
s upply. The rate at whic h detritus is deli ve red from the
continental interior a nd the ra te al which biogenie carbonule
a nd opal a re secreted by otganis ms is also a func tion of
climale and sea level changes ( Hay. Southam. 1977).
This phase begins as the uplihed margin :.ubsides tO ... ea
level. aboui 30 MY after separation of the continental
fragments. The USGS cross sec t i on~ ~ uggest Ihat fi flood of
sediment followed depo~ition of the sal t. but s ubs idence of
the s helf 10 sea level so that drainage could reverse and
ri vers could del iver their load.!> Î!> a prerequis ite . The
du ration of Ihis phase is indeterminate. but the 20 MY
assumed i!> a reasonabJe eslimate .
T he margin reaches maturity abo ut 50 m .y. after continental
sepantlion and continues in this phas e untit ultimlllely
reorga niz'llio n of sea fl oor spreading lransform s the pa ssive
margin into a n acti ve margin .
ln the matu re phase , differenttl'ltio n of the passive margi n
shel ves iOlo deuilUs and car bonate do mina ted a reas become ~ !>ignifican1. The detrital shelves depend on river mouths
which aet tl~ concentratcd point sources for sediment
s uppl Y ; the carbonate s heJ ves draw o n Ihe ocellnic carbo·
oate !> uppl y a vailable thro ugho ut t heir lengl h and Ihus have
a diffuse s upply.
The ~o uree area for t he sediments of the mature margin
expands to include most of Ihe area of the conti nen t . bUI
depositio n of detrital sediment becomes mo re and more
concenlrated a t the moulhs of a few ri ve r~ whic h ha ve
captured portions of neighboring drainage basin!> and focus
the sediment s uppl y. Wa ve a nd current activity on the shelf
are unable to distribute large point source :.ediment inputs
so Iha t the s helf becomes oversupplied near the large river
mout hs and a delta prograding onto the slope/rise at rate:. up
to 5 kmlmy may result . The unders upplied areas of the s hel !
may experience s ignificant landward relreat o f the shelf
brea k.
The vol ume of sediments accum ulati ng duri ng this pha!>e i:.
very large ; "bout 40 'le. of the entire sediment wedge o n the
o uter shelf and 30 % of the sedimenl of the s lope and rise
belong to this phase .
Coarse grained detri tal sediments a re mast likely 10 remain
o n the shelf. Entrilinmenl in the s hore zo ne cau~e s
longs ho re drift of qua rt z sand la form a narrow band of
beach. b,irrier bar a nd isla nd deposils. Finer particulatcs a re
Phase 4 -
Firsl flooding of the shclf-re"ersa l of dntinugt'
When Ihe m'lfgin of the oceotn ~ubsi d es helow :.ea le .. eJ. it
becomes a s ite o f sedimenl accu mula tion. The regio nal
s lope reverses and drainage begins to reorganize and 10
relUrn the V1Is t volumes of sedimenl which hl1d been
depos ited on the dis tal reac hes of the uplift a nd beyond.
lnitially . drainage is Ihro ug h man y riveTS and S lream ~
reac hing the coas t : integration in to large drainage bas ins
feeding throuMh a s ingle river does not de velop until later
d uring the mature phase. The sed iment source area suddenly enlarges to become an order of mag nitude or more
larger than that s upplying the phase 3 narrow ocea n.
144
SEDIMENTOLOGICAL EVOLUTION AND BREAKUP OF PANGEA
The volume of ~iment which can aecumulate on the "l'leif
decreases with time. so that more and more ma terial
bypasses the s helf and is deposited o n the slope/rise. During
the mature phase. se" level c ha nges provide the major
conlrol over whether deposition is on the s helf or on the
slopelrise.
The basement of the continental margin subsides following
an exponcntial decay c urve as described by Sleep (1971).
Rona (1974). Parsons and Sclater (1977). and McKenzie
(1978). Most of the s ubsidence has 31ready occurred before
the passive ma rgin reaches matu rit y. but thermal subsidence iS' still s important as a fac tor affecting sedimentllt ion
unlil abou t 200 MY afler separation.
de:po:lLte:d furthe:r offs ho re: or a re: bypassed to the s lope/rise.
The overaU dfect is a tendency 10 segregate s ilica (quartz)
from the aluminos ilicates (clays) with the eHect that the
de trital rcgime form s two reser voirs wil h differing compositions_ porosities. pcrmiabili ties and porc watcr characleris-
tks.
•
ln tropical and subtropical regions the supp ly of sediment 10
Ihe shelC is chieny carbonate. fixed by benthic organisms.
Because the s upply is the Open ocean reser voir of dissolved
carbonate and o nl y secondarily depends on river input . Ihe
shelf break in the tropics-subtropics builds up close 10 sea
level during trltnsgressions. The carbonate shelf edge ca n
prograde only s lowly because large scale carbonate production by benlhic organisms is restricted to shallow water.
Conversely . as long as the shelf edge is carbonate and in a
warm cl imtlte it is unlikely ta recede land ward because of
the large oceanic s upply available througllOut its length.
A PRIM ARY OVERRID ING I NFLU ENCE. THE C RETACEOUS TRANSGRESSION
Sedimentation on the slopeJrise tends to be much more
homogenous. The soning of delritus which Decurs on the
shelf due 10 wa ve a nd current actiOn does no t take place 50
effec ti velyon t he slope and rise where the major modes of
sediment transport are by slumping a nd turbidit y flow s.
Superim posed o n the gcneral paltern of passive ma rgin
de velopment res ulting from the breakup of Pangaea is a
secondary effect. the rise in sea level to a maximum in the
mid-Cretaceous. caused by the fo rma tion of new spreading
centers and you ng oceans. The rise in sea level to abo ut
300 m above Ihat of today modified the de velopment of
passive margins. and was partic ularly important in Ihe
de velopmenl of those margins which reached phases 4 and 5
during the middle and late C retaceous. The high sea level
tended to restric t supply and to spread shelf sedimentation
over much larger inland seas. and as a resul t, reduced the
sediment deposited on the s hc:lves a nd slope/rise s ystem. As
sea level fell during the Ce nozoic. many of the Cretaceous
deposits were re-eroded and have served as a source or
material fo r Cenozoic sedimentation on the shclf. s lope and
rise. and in the deep sea.
The break in s lope at the edge of the shelf. which by
dcfinilion sepa ra tes the s helf from the slopcJrise. c .. n
migrale s ignificant distances seaward o r landward during
maturily ; the vc rtical stratigraphie section at .. ny given
point may incl ude depos its representing ve ry different
sedimentation regimes. Mos t commonl y the s helf break
recedes. sc that upper s lope sediments ca n be expected 10
be underlain by sheU sediments. Only where detrilal sediment supply l'las been very large . as in the Gulf coast of
Texas and Louis iana. the s helf is underlain by slope: and rise
sediments.
Ma rginal bas ins with ve r y thick sedime nts may or may nO I
be directly re!;l1ed to the modern she lf , slope and rise. The
erosion of the continental ma rgin whic h takes place during
phases 0-2 cannat thin the continental block tO the eXlent
Ihat more than about 2,5 km of sediment can accum ulate on
the shelf. Muc h thickcr accumulations can Decur in the
narrow strip of the continental mtlrgins whic h is tectonically
tltlenuated by lystric fauhing a nd plastic flow as separalion
t3kes place (Boit. 1979). As Le Pichon and S ibuet (in press)
have noted , the oceanic c rust may not appea r until the
continental crus t l'las been thinned 50 tha t ilS elevation
approximales that of the mid-ocean ridge . ie. is abou t
2.5 km below sea level. Tectonically allenu<tted contine ntal
c rust can accomodale a sediment thic kne u of abo ut
11 .3 km of sed imenl if the sep<tralion occurred about
150 million years aga and if Ihe top of the sed iment is a l
present day sea level. Sediment loaded onlo Deeanic crust
may be able to accumulate to tI depth of about 11.8 km
under thc same conditions. The differences in thickness of
sediment which can accumulate are d ue ta the assumption
that the ocea nic c rus t formed without a ve neer of attenuated
continental crust is s lighlly less dense than that formed
beneath a veneer of continental crust and hence will
undergo slightly more comp"c tion a nd contraction with
time .
Differentiation of basi ns and arc hes on the shelf will
become less pronounced with lime as the Ihermal subsidence s lows and olher processes. suc h a s changes of sea
level and sediment s upply, become dominant in controlling
the scd imenllllion patterns. On Ihe s lope/ rise. the differentialio n of b.1sins a nd arc hes ceases about 100 MY alte r
conti nental separation becfluse the differenlial subsidence
bccomes insignificant.
A SECONDARY OVE RRIDI NG INFLUENCE. THE
RI SE OF CA LCAREOUS PLANKTON
AI prese nt , most of the ocean floor is covered by carbona te
oozes made of the tcsts (shells) and skcletal elements
produced by plankto nic foraminife ra and coccolithophores.
The coccolithophores are calcareous a lgae a nd had their
origin during the late Triassic or earliest lurassic. The
planktonic foraminifcra are protozoans and l'lad {heir origin
in the Jurassic. Nei the r of these groups produced widespread deep sea cozes bcfore the middlc C retaceous. but
they have dominated thc pelagie sedimentation system sincc
that time . Soulham and Hay (in press) proposed that the
salinilY of the world ocean may ha ve been significanlly
reduced by extraction of salt d uring the early breakup of
Pangae .. , and il may be Ihat the c hanging nature of ocelln
water provided condit iOns necessar y for the flouri shing of
calcareous plankton.
Southam and Hay (1917) have s uggested Ihat prior to the
mid-Cretuce o us. CuCO) was ollly a minor component of
deep sca dcposits. and was largely restricted ta deposition
on the s helves and in epicontinental seas. During the late
Cretaceous. with the high stand of sea level. the coccolithplank tonic foraminiferal oozes were deposited widel y on
Ihe shelves and epeiric seas as weil as in the deep sea. Wilh
the: lowering of sca level during the Cenozoic. the cldcllreous oozes have come to be deposited almost exclusively
in the deep sca. O n the continental/slope rise:. the CDecoliths
and tests of pla nkto nic fomminifera a re mixed with tc rrigenous dcttitus to form hemi-pelagic sediments.
"5
W.W. HAY
SUW,-IARY
the most important process, dominating sedimentation patterns.
The breakup of Pangaea hall an important influence on th e
glub;:tl geochemi~lry of sed iment ... A ~im ple model tracing
the development of passh'e margins assumes uplift and
erosion, dcposÎtion in fresh water lakes in the ini t ial rift
basins, potentinl for sal t extraction as th e r ift graben
rcache s 5ea level. and e p isodic d eve!oprnent of stag nant
condition~ in the naTrow ocean a ft er separa tion of the
continental fragment. For about 80 million years Mter
continen t;t l separation. processes o n the passive m;trgin are
dominaled by the eHecls o f the rmal subsiden ce H~ the
co ntinental bloc k ~ move apar!. AS the margins o f the
na rrow ocean s ubside 10 sen level. sediment originally
e roded orr the uplift can bc returned to Ihe developing
con tinental m:lrg;n.
Superimposed on the~ generallrends are the effect .. of the
Cretaceou$ transgression which is an indi rect effect o f the
breakup of Pansaea, and the rbe of oceanic cak:treou~
planklon which may bc rel a ted indirectly 10 the breakup of
Pangaea as salt extracl i on~ of the Gul f of l\lexico. Nor lh
Atlantic and Sout h Atlan ti c altered th e sali ni ty and composition of ocean water.
Acknowl ed gemt nls
The author is indebted 10 E ric J. l1arron. John K . Southam,
J ames L. Sloan Il . and Chris tophe r G. A. H arrison for
va lu nb le discu ssio ns. The work was supporled by gmnt
OC E-78-26679 from the Oceanogrn ph y Section of the National Science Founda tio n .
As the m<lrgÎn bccomes m o re mature. sea level c hanges a nd
o rgan ization o f d m inage of the adjacent con ti nent become
REFE RENCES
CIllHrl S. E., 1')66. Accumullltion of di;nomaceous sillca in Ihe
sediment~ of the Gulf of California, Ceul. Sm:. Am. Bull .. 77,
569-596.
Cll ndl! S. C . • R.blllO,,·jll P. 1). , t9711. Mesozoie seafloor spreadinJl
bonJeril\ll conjugale continen tal margins of Angola and 8 razil. /978
Ol/short Tlchnu/u/o' Can/trtner. Hm,sIOII. Tua)" 1869- 1876.
Clom H .. 1939. Hebung·Spallung·Vulk.. nismus. Gtol. RI(I,dsch ..
JO , 405-527.
Curra)' J . R., Moore D. (; ., Agua)'o E.. Aubr)' M ...•.. f.ln~elt (;. ,
"' ornar' D. J ., Cleskes J. , Guerreru J . C., Kaslner M ., Ktlt s K ., Lyle
M . • ~hlUbli Y., Moli na-C ruz A .. Nlemlt z J .. Ruedll J . • Saunders
A. 1)., S<:hrllder n .• Simoneil K . R . T .. t979. Les M sl!eks l'videne..
on development of basins. GtQ/imu. 2", 7. lK-20.
Arm~ trOI1 I1 R. A.. Besw.l1cun J ., 1910. A Triassi<; lime scale
dîlemmll: K -Ar dating of Uppe r Triassic mafie ign«lus rocks.
eaSlern USA and Canada, and PO~I ·Triassie plutons. We ~tern
Idaho. USA. EcioRtlt Gtol. IItl,'.• 63. 15·28.
Arthur M . A.. N. Ua rld J . H .. 1979. Cllrhonaeeous sediments in tne
North and South Atlantic. Tne role of salinity in stable ~t rat ification
of Early Cretaeeous ba!>ins. ediled by M. Talwani. W. Hay and
W. B. F. Ryan in: Dcep Drilling Re ~ult. in the Atlantic Ocelln :
continental m.. rgins and paleoenvironment. Alli. Geuplzys. Ullion,
M lmr ice l' ..'iIl8 Su" J, 1-57.
Dambach R. K. , SCOIe.>e C. R. , ZleJller A. /II .. 1980. Before Pan·
gae .. : the gcographies of the Paleoloic Wo rld. Am. Sei .. 68. 26-38.
Barron E, J " 1980. l'aleogeogr'dphy anu climate. 180 million years
to the present. l'h . D. Diutr/alion. Vn;'" Miami. 280 p.
Barron E . J .. lI arrison C, G. A.. SI(»In J . L. Il , Ua}' W. W.. in
press. Paleol;eography, 180 million yean ago to lhe prc-.ent.
l'dugue Geol. Hely" 74. 1.
8011111. /II ., Rya n W. R. F.• McKniltht R. K ., Kaga mi H., Meill uen
M. , Sil.'S5H W. G" NlIl1and J. H. , 1.0llgorlll J. "' " l'rolooedm. F..
,,'o rt'!iman J . 0 " lIoltman W. E " 1978. Illi/ill i Repons ol/lrt Dup
Sta Dn'!/illg Pmjtrl. "01. 40, Wa~hington . US GOY. Prin!. Off..
25 ~ 1079p
BotIl\1. 11 . l' .. 1979. Subsidence meehanisms at passive continenml
mOlrginS. in : Geological and .Ileophysical investi.llations of continental margins. ediled by J. S" W:ltkins . L. Montadert and P. W.
Diekerson. Am. Assoc. Pt/ru/. Ctol. Mem .. 29. 8-9.
Bnlss G., nay W., Holser W .. Pelerson W .. Sallvnan E .. Siulln J. ,
SoulhaUl J ., in pre~~ . (ke(jn eirculatitm. plall' lef/unks. tl/ld
dimlllt. Nalional research Councit. Report o n Pre- P lci~toccnc
climaTe.
Buffler H. T .• Wlltkins J . S .. DIllon W. P .. 1979. Geology of the
off~hOTe southeas t Geor;i!! Embaymen\, US Atlantic con tinen tal
margin. ba~ed on mul tichannel sebmic Teflection profile). in:
Geolo@'icOlI and g«lphysical in~'eMigat ion~ of conlÎnenlal maTgin!.
ediled by J. S. W"tkins. L. l\.Iontadert und P. W. Dickerson. tlm .
Assoc. Pelrul. Geol. , l>1e/ll" 29, tt-2.~.
Buffler R. T .. Walkl ru; J. S .. Shwub F. J .. Wonel J. L., 1980.
StTuClUre and early geologîc history (lf the deep cen tral Gulf of
Mex ico. in : The origin ol/lre Gu/fol Mu;eo und Iht larl)' opt"ing
ul/ht Cenlral North A//lIntie oell"'. edi ted by R. H. PilJICT Jr.
Louisiana Geo!. SurI' .. 8alOn Rou.lle . 3-16.
Bur],;r K., De"'e}' f .. 1973. Plume generated triple junctions : key
indicator~ in applying plate leClonÎcs to old rock. J . Glol" 81.
406-433.
Burb K., Whltrm ll. n A. J ., t973. Uplif\, rifting and break·up uf
Arrica. in : Implieu/iuns ul ('OII/illt,lIl" drilt w /lre etmli Scil.'lIl·'l.
editcd by D. II. Tarling and S. K. Runcorn. Academk l're,s.
London. 2. 715-755.
dl! 800e r J . • 1968. Paleomilgnetic differentiation and correla tion of
Ihe Lute Tr iassic volcanic rocks rn the cenlral App:dilchian~ (wi th
special reterenee to the Connecticut Valley). Gml. Soc. Am. Bull"
7!i1. 609-626.
1H~ .." s t:. T .. Slofftn P.. 1976. $ Iratified Waler~ D~ 11 kcy tO the
pas!. NMure. 263, 12·27.
IHII<!I\!l E. T .. "un Hen.en R. P.. Won/! H. K .. 1971. Lake Tanga·
nyika : water chemiSlry . ~ediment s and geological ~truC lure .
Nmur .. ;)unJdJUlltll. 58, 129-241.
Delten.~ E. T .. ,·o n Hrrzen R. I'., WonR H. K.. (kouw r W. G ..
Jannasth Il . W ., 1973. Lake Kivu : ~truc lUre . chemistry Olnd
biology of an Easl Afriean rifl lake. Gtol. Rundsrll" 62, 245-277.
Dillon W. l' .. l'aull C. K .. Buffler R. T .. Fail J .-I'" 1979. Structure
and developmcnt of the sou theaSI Georgia Emba ymcnl and northern Blake Plateau: preliminary analysis. in : Geol"llic~,1 and
JleophysicaJ investigations of continent .. 1 margins , edited by J . S.
Watki ns. L. Mon tadeTt and P. W. l)ickerson. Am. Anor. Pt/rul.
geul. Mem .. 2!i1, 27-4 1.
Fol~r D. W ., Dillon W. P ., GrowJ. A. , Klitllord K. D" $chtee- J . S ..
1979. E'olution of the Atlanti c con tÎnenlll1 margin of the United
St.lle~. in : lkep Drilling Resulu În the Atlantic Ocean : conlÎnental
margins and p:.leoenvironment. edited by M . TOllw:rni. W. Hay and
W. B. F. Ryan. Am. Gt'upll)'J. V/lion" Maurice E ...ing Ser" 3.
87-1011.
Frakrs L., 1979. CUmultJ IIrro .. gllo .. / geologie lilllt'. EI~evier.
Amsterdam. 310 p.
Garrels R. M .. Mac:Keraie ... . T .. 1971. E"o/u/ion 0/ stdimtlltar)'
rocks. W . W. Norton. Co.. New YOI'k . 26 - 397 p.
Grow J . A., Mattlck R. E.. SeMee- J . S .• 1979. Mullichannel sej,mk
depth ~ection~ and interval \'elocit ie~ over o uter continental shelf
and upper continenlal ~lope between Cape H allen. ~ and Cape Cod.
in : Geologkal and geophysical in\'estig;llÎon~ of eontinentnl margins. edited by J. S. Watkin~. L. Montadert IInu P. W. Dickerson.
Am Assoc. Pnrol. Geol .. Mtm" 29, 65·83.
146
•
SEolMENTOLOGICAL EVOLUTION AND BAEAKUP OF PANGEA
Hablt hl J. , 1979. Pll leoclimaie. paleo magnetism, and continent al
drift . Am. Assor. ' >etrol. Owl .. S tud. Oeol .. 9, 31 p.
N.lIand J . H., 1978. Composi ti on, pro venance. and dillgenesis of
Cretaceous dastk sedimen ts driIJw on the Atlantic continental rise
o U sou thern Arrica , DS DP site 361. Implica tions for the eurly
circulation of the South Atlantic. in : Initial Rlf1QnS of thl Dttp Sta
/)Tilling Proi«t, edited by H. M . Bolli , W. B. F. Rya n tt al ..
"01. 40, Washington. US Go v. Prin t. Off.. 1025·10S0.
l'a rS005 n. , Scl"tl'r J. G .. 1917. An analy~is of the "'lIria tion of
ocean floo r bathymetry and heM flow wittl Age , J. GtOpltys. Res.,
82, 803·827.
l'frch. Nlelse n K. , Supko P. R., Neproc:hno ... \' . 1'., Zlnm.erman
H. B., McCoy F., Kumllf N.. Tblede J ., BOI\llIlI E., Fodor R.,
BotDma A., Dlnkelman M. G .. Carlson R. L., 1977. Initilll Repons
of Ihe Detp &a Drilling Proj«l. ,'01. J9, Washington, US Gov.
Print. Off .. 25 ~ llJ9 p.
Rublo!iOn P. J••, 1973. l'aleoc limatolOi:Y and co ntinental drift , in:
Implications of continental drifl 10 Ih~ eorth Jciencu. edited hy
D. H. Tarling a nd S. K. Runcorn. Lonuon, Academic Pre ~s, l ,
431 · 476.
ROI\ll P. A. , 1974. Subsidence of Atlant ic co ntinental margin s.
Tu tonophy.fics, 22, 283·299.
Sanden J . E.. 1963. Late Triassic teClonic his!ory of nort h--C:lIstern
Uni ted States. Am. J. Sei., 261 , 500-524.
Sleep N. H .. 1971 . The rmal eHects of the forma tion of Atlantic
continental margins by continental bre ll kup. Owphys. J. R. Astmn .
SO<' .. 24, 325-350.
Southarn J. R. , Hay W. W. , 1977. T ime scales and dynamic modcb
of deep sea sedimenta tion , J. G/'(Iph ys. Ru .. 82, 31125·31W2.
Southllrn J . R., Uay W. \V ., in pre n. Global sedimenlary man
balance and sea II' ... el changes. in : The Sen, "01. 7, edited by C.
Emiliani. John Wiley and Sons. New Yo rk.
Supko P. R .. Perch·Nlorlsen K .. 1917. geotral S ynthesis of Cen tral
IInd South Atlan tic Drilling Re sul!s, Leg 39, l)eep Sea Drilling
Projeet. in : In;';lll Rtports of the Deep Sta Drilling Projtct. edited
by P. R. Sup ko . K. Perch·Nielse" tt al. , m l. J9 , Washington, US
Gov. Pri nt. Off., 1099- 1132.
Thlersteln H. 11:. , 1979. PaleoceanogtAp hic imp lica tions of organic
carbon and carbona te di stribution in Meso1.oic dee p sea sediment s,
in : Deep Drilling Results in ttle Atlanlic Ocean: con tinental
margin s and paleoen ... ironmcn t. editcd by M Talwani. W. W . Hay
and W. B. F. Ryan, Alli. Gtophys. Union. MeU/riet Ewing Su.. J,
1·57.
~an Houten .' . B.. 1977. Triassic· Liassic deposits of Moroceo and
eas tern Nonh America, Am. Assoc. Pt/ml. J.' tvl. Bull .. 61 , 79-99.
Watklm J. S., Hoppe K. W., 1979. Seismic ref1eet ion reconnais·
sunee of the Atla ntic Mllr!!; n of Moroceo, in : l)cep Drilli ng Re sults
in the Atlan tic Ocenn : continental ma rijins IInd paleoen ... ironment ,
edi ted by M. Talwan i. W. W. Hay and W. B. F. Rya n. Am.
Geophys. UII;on. Mouriet Ewing Str.. J, l ·j7.
Won:el J. L. , 1974. Stand ard oceanic and continen tal structure , in :
Th~ IItology of contlntnt(ll murgins. edÎted by C. A. Burk and C. L.
Dmke. Springtr Verlag. Heidelberto. 59·66.
Zkgler A. M. , Scc:ttne C. 11. .. McKerro ..· W, S., Johnsun M . E..
BllmblK h R. K. , 1919. '>a leOl': oÎe paleogeography . Atut. Re.'. EUTII,
PI,me/ Sei .• 7, 473·302 .
Hay W. W. , Southam J. R.. 1977. Modulation of marine sedimenm·
tion by the continental sheh·es. in : The fatt of fossU fuel CO, illthl
OClaIlS. wite<! by N. R. Ande rsen and A. L. Millahoff. Plenum
Press. New York , 569·604.
Hay W. W .. Barron E. J ., Siolln J . L. Il , Soulham J . 11. .. in press.
Continental drift and ItiC global p"ttern of sedimentfltion. Oelli.
Rrmdsch .
1I00Iand H. O., 1974. Marine evapOrites and the composi tion of sell
water during the Phanero7.Oic. Studies in paleooceanography.
edited by W. W. Hay, S<>c:. Ecoll . PllltOnlOl. Mintr.. Sptc. Pub/.,
20, 187· 192.
HoUa~ Il. O., 1978. Thil chemistry of Ihr ulmusp hrn ,wd oceans.
John Wiley & Sons, New York. 24 + 3'1 p.
Hsü K. J ., 1965. Isos ta sy, crustal th inning, man tle c tlan~es, and thc
di sappearance of ancien t landmasses. Am. J. Sc:I .. 263, 97·109.
J ynsa 1•. F. , Buja" J . l'., Wllllan.s G. L .. 1980. Uppe r Triassic salt
deposit s of the weStern Norttl Atlantic. Can. J. Ellrth Sei .. 17 ,
547·559 .
Jansa L. )-' ., ElI05 P. , Tocholke B. E. , Gntdlteln F. M., Sherkl an
R. E.. 1979. Mesozoic·Cenozoic sedimen tary forma tions of the
North America n Basin : We stern North Atlan tic , in : Deep Drill ing
Results in the Atlantic Ocea n : con tinental margins alll.! paleoenvj·
ronmen!. edited by M. Talwani, W. W. Hay and W. B. F. Ry:,".
Am. Otophys. Y niun, Mau rice E",ing Str.. J , 1·57.
Klnsman O. J. J ., 1975. Rift valley basins and sedimentary history
of trailing conlinent.al margins. in : P~trollum a/Id global /telonics,
edited by A. G. Fi~cher and S. 1OOson. Princeton Univ. Press,
Princeton. N.J .. 83·126.
Klltgord K. D., Hetlrfndt J . C .. 1979. Basin structure of the US
Atlantic margin, in : Geologieal and ~eophyskal investigat ions of
continental margin s, edited by J . S. Watkin s, L. MontadeT! and
P. W. Dickerso n, Am. A ssoc. Perrol. Genl. , Mt/II .. 29, 85· 112.
Lebali M. J., 1971. "eralkaline vu lcanism. crustul
rifting. Nat. Phys. Sci .. 230, 85.
s ""ellin~
and
Le Pkllon X., Sibuel J .·C .. in press. Passive margins : a model of
formation.
l.ewlii B. T. R. , Robinson P.. 1H0000n R. N., BlloIfklnton G., Cambon
P., Day R., Ounnebler ... K., Flower M .. Gulierrt l ·El;trad a M. ,
III111ner J . G. , Kud o A. M .. Morrlso n M. A. , RanR! n c., Salisbury
M. Il ., S<: hmlncke H., Slephen R., Zolotare v 8. P., 1979. Le~ 65
drill s into young ocean crust. Oto/imtS. 24, 8, ](i.. l l1.
~hll5poelur
W., Puffer J . Il . , CousOllner H. L.. 1978. $eparll tio n of
Mo rocco and eas tern North America : a Triassic· Liassic stmtigra·
phie record , Gw l. 50<:. Am .. Bull .. 89, 901·920.
Mc K~ nde D. , 1978. Sonlt remarks on the de ... elopment of sedimentary basins. EfJrth l'tuntt. Sei. t t t/ .. ~ , 25·)2 .
McKende D. P., MorlClln W. J ., 1969. EvolUlion of triple junctio ns.
Nilturt. 224, 125· 133.
147
148