PROCEEDINGS
of the
2 nd Symposium on the
GEOLOGY of
.: , l;
the BAHAMAS
June 1984
CCFL ~ahamian Pield Station
PHTSICAL STRAT I GR APHY OF
SA ~
SALVADOR I SL AND, BAHAMAS
Robe rt Tit u s
Depa r taent o f Geology
Hartwick Colleg e
Oneonu , ~Y
13820
Ab at r act
In s evera l
e ar lie r reports (Titu6 , 1980; 1983a; 19 83b) a
general frame work ~as been worked out f o r t~e lat e Qua te rnar y
st ratigr aphy
of
San
Sal v a dor .
Two formation a have been
recogn ized;
each d is p lays a n eaergent f aeiea pattern. Re c ent
studiea have revealed aore about th e ver y lateat P le iatoee n e and
Holocene atra t igraphy of the ialand.
Sea
cl iff s , wa ve-cut notches and lak e depoaita all
indicate that t he r e waa a aea level ris e of about 2 . 5 a in the
recent
past .
Application of aiaple s tr atig r a ph ic principles
deaonat r atea th a t
these featu re a a r e yery latest Pl eistocene in
age and v ery likely they foraed during t~ e sea lev el r iae that
Car e w and Myl r oie ( 198 3) haye a r gued for .
During the late Holocene ae a le ve ls have riaen to th ei r
preaent day le vels .
Du rin g t llis transgression bea cll a cc r etion
r idges lIave formed at a number of loc at i ons on tile periphery o f
t il e island .
A g r o w1ng body of e viden c e is s u pporting tile v ie w t hat
tlle r e hav e
be e n tllre e episo d es o f se a- l ev el lIigll .tand. during
tile late Quatern a r y .
One e nd ed about 120 , 000 year, ago.
A
aecond occ urred soon th e r eafte r.
The third appear. to be the
cont r o versial lIigll atsnd at 35 , 000 yeaTS ago as advocated by ThOll
(1973) .
Introduction
,
St ratigr aphic
nearly
e ve r ywlle r e
ve rt ical
a nalysis
else.
sequences
in
t he Bshaaas i a diffe r ent fro a
Classical a t r atigrap h y focuses up on the
of sedisenta ry roc k s .
FaC ie. int e rpretations
ma,
add an importnnt 1I0ri zonta l com ponent, but ve rt teal a equ e nces
are
of
para . o unt i. po rt anee .
Salvador ,
like
aequence
of
Sediaents
trallsgressions ,
of
".
r es t of the Ba haaas , lia s been d omina t e d by a
sho r t
reg r eSSions .
pa r ioda
the
The late Quat er nary his t o r y of San
r e worked
ellaergence.
rapid
lis ve
.. ari ne
been
tran sg r essiona
deposited
during
an d
aa rine
d uri ng regreS Sions , and eeaented during
Dep oaitio n
20'
~8S
occurred
aostl y in low
ly1nl
areaa around the periphery of the island , araaa .oat essil,
affected by tranalressi on ,
Deposition
hsa
Instead,
will
c al l
ao ~e
of
Hole
Settlement
Beach
of
these
San
The
vi cinity
unifo r .
sheets
of
are
lIind
pstterns account for
l arl e dune de poa i ts of the Line
an
e%ample
o f auch a province.
in pr otected e.bay_enta consti tute a anothe r for .
Carne r
of
the
island.
La ke depoalta _ake up a
of province found wi thi n the is land' a interio r.
Sal vsdor
provinces .
thin
A lood e%a.pla of thla type occura at Sand, Hook on
ao uthea at
type
" provinces ".
provincea.
accretion
third
produced
depoaition haa be en concentrated into v hat I
s e dillentary
province.
the
not
is
made
up
of
a
seriea
of
such
Thus
sedimen t a r ,
Ove r 8 period of time they have been a cc r atin l around
the peripher, of the island and it as g c o v n in aize.
To
understsnd
the
hiatory
of the ialand , esch province
.uat
be
cecolnized , correctl, interpreted, dated and then placed
into
s
that
wo rkinl out the .tratie r aphy and hiator, of San Sa lvad o r has
logical
sequen ce
of events .
This ia one of the CeaSon"
been a d tff icul t and t ime-conaum inl ta"k.
The
purpose
stu d ies
reported
ea rlier
reports
waa
divided
Baach
viewed
aa
repreaenting
unita,
esrlier
article
is
to
update and revise
(Titus, 1980; 1983a; 19f33b).
In these
th e late Quaternary atratilraph, of San Ssl vador
between
Limea ton e
thia
of
and
tvo
majo r
the
Crahams
s tratilrsphi c un it. , the Gro tto
Hsrbour Limeatone.
Both ve re
being Pletatocene in sge , and both were interpreted a"
episode s
Pleistocene
of
lake
eme rle nce.
and
Othe r leaser atratllraphic
Holocene beach depoaita, were alao
'>0
d e.c ribe d .
Re cent
ltgh t
• ore
a nd
the re
extensive
has
ho " e ve r,
of
.hed
a gres t deal o f
Ssn Ss lvsdor snd no " the esr l i er
re vi sion .
In brief, lIo l ocene rocks ar e
on San Ssl vador than h.d been pr eviou.lr r eco gnixed,
we r e
\40,000
paper
" ork,
atrstig ra phr
need
co •• on
pa.t
The
the
On
.t ud ies
Held
ia
not
th r ee,
t .. o
episodes o f elle rg ence during t he
reara.
Thia rep or t .. ill focus on .the.e revi sions .
not
a comprehenaive o ne . bu t instaad, is mellnt to
compleme n t the earlier reporta, eapec i a llr Titu s (1983b) .
lIolocen e Str a tigraphY
Beach
years
7
sea
•
of
accre t io n
le vela h a ve been ri si ng.
t he i r
to
tillie ,
successive
ca n
accuaulate
penllanant
see n
be
Gra h alls
at
accreted
of
par ts
claa r ly
on
a nd
the island.
Theae a.dl "prov i ncea n
north
Point ,
With
becslle ce.en t ed so s. to
ae rial ph otograph s .
Barkera
BonaHah
loc. t iona on tha ialand.
va ri oua
r idges
Harbo ur,
Settlelilent,
As they app r oac hed to .. l thln
p r esen t l e vel, a ae r ie. o f bea t h accretion r idges
began
becolle
ridgea -- Ov er the paat se ve ral t ho u sand
Ther are found at
f r o.
Vi cto ria
Kill
Bar . Sandy Po in t, F r ench Bay and San dy lIook
(aee index .ap of San Sa l vador) .
The
r eais tant
Grah a lls
up o n
depoaits
enough
lI ar bo u r .
la te
to
are
produ ce
not
.. ell
cellented.
but
they
are
10" s e a cliffa. auc h as the one a t
Where expoaed the a e depOS its l ie un c onforllab ly
Pl eiato cene
d ep oa it s .
The
l o .. er bada a re generally
beach de poaits .. hich g r ade up war d s into dune depoaita.
Fr o .
the
ai r,
a c lear pa tt ern Cs n be see n.
211
A r idge and
topograpby deweloped aa tbe aueeessiwe ridges were for.ed.
inspection
higher
ean
reweala
eleution
be
tban
tbat
eaeb
ridge
fo r .ed
at aligbtly
tile prew10ua one (Fig. 1).
related to tbe rlae in aea lewel of tbe paat fe w tllousand
yeara .
~s
sea
Beeause
of
thia
lev el a
the
water
tables
roae aa well.
tile oldest . fartheat inland dune ridges are no w
Behi n d
flooded •
roae
each
ridge
province there is thu S a pond or a
• wa.p wh e r e this aub.ergence haa occu rred.
The
a1x
a
about
.ost
recently
for.ed of tile beach r1dgea riae about
abowe sea level. the .oat aneient ones are aubae rge d below
1
of
(I
pond
wat er.
Consequent ly
it wo uld appear that
depoaltion
of t b ese ridgea began wilen sea level r oae t o about 7 II
below
present
If
its
level . and 1t has continued ever since then.
aea levels continue to r1ae in tbe futur e . then the dunes will
continue
to
ace ret e setl wtlrda "hi1e the olde r dunea lI i ll continue
to be flooded by an enlarging pond .
Beach
Holocene
the
aedi.entarJ
ialand.
occur r ed .
These
Htghwtly
On
the
going on along the we atern ,lde of
eaatarn aide , howew er, different proeesaes
There, great heapa of dune mster ial lIere being forlled.
dunes
from
are f ound firat at Uni ted Est a t es etlst of the Queens
Horthea at
A
l.ake.
proeeaa
accretion waa the do.inant late
second
to
Point
dune
the eoaat eaat of Brandy Hill
npr owince"
oecura
eaat of Stor r'a
Stor r'. Lake "a a iaolated and for_ed wh en theae dunes were
depoaited.
The t hi rd dune prowince oeeura eaat of Pigeon Creek .
It accounta for the for_tltion of Pigeon Cr eek.
These
dunat
depoaita
'1'
are
hUliliocky
,,1th
no
obvio us
.-
.,;01 ...
,. •' 8
••
,.
,
':
z
g
c
1
-
213
depoaitional
the
It
1.
possible that . as in the west of
island, an accretionar, pr oceaa haa occu rred .
acc r etion
At
patterns.
ri dges . t he dune elayatlons are higher near the ocean.
United
pond"
Like the beach
Estates there a re pond" lying be hin d the dunes.
are
Th eae
reminiscent of t h e ponds whi ch formed behind the beach
"ccretion ridges aa aea levall r ose .
froa
The
Late
Holocane dune depolitl sre ealil, diatlnguilhed
older
Late
Pleiatocene
Holocene
sands
ceaented
at
we"k
are
ses
surficial
c r us t
and
poorly
leYll
Cfu at
above
depolits
ceaented .
which occur nearby.
The
alon, the coaats.
depoe1ta
are
The
best
They a l ao hlye a very
of li,htl, ceaented saterial.
Beneath the
sea leval th e depoa ita are acarcely ceaented at
II 11.
Thalaan
the
and
Teeter (1983) have suggested that aeye ral of
bluffs whi ch occu r along thia Ho l ocene cosat lI e r e once island
which
served
as
nuclei
for the adjacent dunea to fora a r o und .
bluff
south
The
bluff
sa, or as, not have been an island, but it probabl, is
older
it
tl ... e
than
does
to
of Holida, Track Settleaent ia a good
e~aa ple.
The
su rr ounding sedtaen t ..
Unli ke adjacent d u ne deposits
have a karat cruat . a fea ture whi ch muat have taken some
hsve
forlled.
This
is the rounge"t ksrst c ru st on the
ia1and snd it is unde rl atn br entlrel, uncesented sands.
The
it
age
of the eaatern dune tracta 1a hard to prove , but
does seea reaaonable to aasuae that they a r e contsapo r a r , wi th
the acc r etion ridges of the we.t snd thus late Holocane.
Pleiatocene St r ati gr aph'
'"
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r-'J
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·••
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"~ •0,
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,~
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~2!
A
Late Pleistocene vave-cut
the
lste
Holocene
s ea
cliff on the landward side.
aout~ w estern
exalUple
well
on aerial
old
bet ween
This
is
Point
e~ s mple
occurs from
Hill
sample
C-S) .
t~ e
The r e , a
Another
Settlement and Line Hole
ve r y high, but it does show up
not
This bench li e s upon rocka
photograp~s.
with a low
to Grot t o Besch .
1983,
Victoria
is
benc~
into rocka which are probably
cut
(Care w,
cUff
beat
T~e
Sandy
cliff
years
occurs
Settlement.
of
sea
100 , 000
about
-- At several loc ations
depos i ts lie upon a wav e-c ut
corner
veIL-develop e d
benc~
w hlc~
are
about 75 , 000 years old (Carev , 1983 , ssmple C-4).
The
age relationships sre clear .
late
t he
75,000 year old rocks it is cut into .
and
Hylroie
they
Holocen e
v hic~
th e
(1983)
argue
bet ween
date
ev id ence
deposits
the
from
The bench is older than
lie upon it , and younger thsn
Carew (1983) and Car ew
that there was a sea level rise which
and
35,000
physical
40,000
ye/Hs
of
sge.
The
stratigraphy of the island is quite
consistent with their vie v s .
Lake
the
Point
t~e
of
Same
vere
seem
If
Th e base
a sea level rise of this magnitude actually
and
their shorelines would ha ve co r res ponded v ith
2.5 m contour .
ahoreline
the
to have an elevation of about 2 . 5 III.
then it can b e predicted that the lakes of San Sahador
expanded
today's
Grottoa cut at this ti me on
sea cliff at Victoria Hill Settlement appellrs to have th e
elevation .
occurred,
st
Th e Ilea level rise v hich accounted for
va v e-cut bench v as a modest one .
Sandy
a
Cockburn
2.5
To test this hypothesis , evidence of such
vss searched for v ith some success.
m
contour is tare.
'"
Exposed bedrock
Nevertheless, many boulders and
cobbles
have
number
of
been turn ed up by road building and agriculture.
locations
containing
fossils
at
th e
2.5
m
level
have
diagnnstic of shorelines .
A
yi e ld ed ro c k s
Seve ra l species of
the
gen er a
Anomalocsrdia and Cerlthidea wer e particularly COmmOn
and
useful
in re cognizing shorelines.
fossil
the
assemblages
pre d iction
level .
along
The di6tribution of these
the 2 . 5 m contour apparently beara out
that the lak e s of San Salvador did
e~pand
to that
At that time msny of the presently separated la k es merged
to f orm a single large lake, La ke Coc k burn (see Titua, 1983b).
Thalman
vicinity
a
sea
had been subme rged and conv erte d into a tidal estuary by
rise
le., el
agree
snd Teet er (1983) discovered that the Granny Lake
fully
which
they suggeated "a a Sang a llon in age .
I
that the Gr anny Lake vicinity "a s indee d an estuary ,
but I differ in regards to its sg e.
As
that
a
sge
there
Sangamonian ses level rise is universally accepted,
is a ve ry attrative one .
interp r etation
Nevertheless,
is no need for the estuary to be t hat old, and t here . ay be
SOme problems with such an age estimate.
The
adequate
the
2.5
II
sea
level
rise
postulated
above
ma kes an
explanation for all the observed Pleistoc ene fea ture s of
Grsnny
estusry
Lake
during
estuary .
Inde ed,
Sangamonian
even
if
there h ad bee n an
time, it " ould have had to have been
reflooded during the later event .
An
in
are
this
mOre
Wisconsin
extensive
article
(see
problems
sged
Wisconsin s e dimentary history Is argu ed for
with
deposits
be lo w) .
the
mig h t
If this wSS the c a se , then th ere
Sangamonian hypothesis.
well
2H
ExtenS i ve
hav e been expected to hsve
buried
fo r
all
or auch of the Granny Lak e estuary.
exaaple ,
eleyation
a
very
feature
vell-preaeryed
a tght
haye
The eatuery haa,
tidal channel.
Su ch a lov
aurvived auch a lonl ti.e without
bei n l burled , but thia doea not aeea likely.
Tile
geOlraplli c
in conaiete nt
v ith
Granny
Lake
eatuary
Pigeon
Cr eek
either
aide
dune
to
aetting of the Granny Lake eetuary .. ay be
Sanla ~onian
tile
wa /J located at the very nor tlle rnlll os t tip of
( Hina/Jn,
by
Tlla 1I0uth o f the
e stimate.
the
1980;
1983 ) .
Tha
aouth .. aa bounded on
at rata vhich no w .ake up (err Mount and the
depoaita of South Victo r ia Hill Settleaent.
lIave
been there before the e.tua r y.
theae
deposits
Dixon
Kill
Tllua
These ro cka had
Aa wi ll be arlue d later,
are ragardad aa belonging to tile poat Sa n g •• o n ian
Lill e stone
and
a r e probably about 75 , 000 yeara old .
tile Granny Lake Eatuary would lIave to be younga r than 75 , 000
yeara and not Sangamonian.
Aa
(1983)
diacuaaed
ha",e
occurred
baaed
earlie r, Care .. ( 1983 ) and Care .. and Hylroi e
propoaed
about
tllat
35 , 000
a
aea
leyel
riae
to 40,000 yeara ago .
o f a fa .. aetera
Tilts concluaton vas
on a a ta lagatte o f tllis age contai n i n g aerpulld wora tubea.
Thia
com pelling
but
scanty eVidence can no v be unified with the
concluaiona
preaented
the
bench ,
2.5
eatuary
eyent:
a
aa
lIerein.
The atalagaite, tile a ea cliff and
well aa tile Lake Cockburn and Granny Lak e
depoaita. all now appear to belong to the eaae hiatorical
the cnn tro",era ia l Late Wia cons in aea lev. 1 ria. (aee Thoa ,
1973).
In aeveral earlier
reporta
( Titu s ,
1980;
1983a;
21.
1983b),
I
argued
for
a
Late
the
Pleistocene
Tbi.
unit
g r ading
deac r i bed
~ aa
up wa rda
in t o
"Graha.s
..,
Harbour" li. estone ,
.s being coaposed o f .ubtidal deposita
dune
fa eies ,
thua
it represented.
period of eaergence ,
The
of
a
its
Gr ahaa.
se r iea
la rge
Harbour
liaeatone wa . aapped upon t he basis
of unconforai t ies as well a. b J the d ia trib ution of
obvioua
a r cua t e
duna
depo"i t s .
The un co nforaitiea
we re, b, and latge, mis i nte rp rete d .
The
depoa ita
recent
haa
gone
a
of
the
inte r p ret ation
t,p e
retognition
l ong
of
the
extenaive late Holocene
lI ay tO ll a rd " under.!ning th e o riginal
Grahaaa
Ha rb ou r li.e.tone.
The aupp osed
" e c t ton of the unit wa s the aea clif f weat o f th e CC Fl Field
Station
part
1n
Gr ahama
Harbour.
Thet a ee cliff i a n Oli kno wn to be
of the Holo cene beach a cc r e t ion r id g e sya t ema and thus thoae
depo"its
Thua ,
are 1n no wa J relat ed to the dun e ridSe ,
and
t hia
ia
further i nl a n d.
emba r aaaing. the tJPe section o f the Grehaaa
Harbour limestone does not belong to thst f o rm ation .
Des pit e
beli eve
that
old
redefined,
thia
a
probsbly
unpr ec e dented
error .
I
still
vsl i d unit c an be retrie ved fro. th e s h a mbl es of
Graha..
Harbour
r e nllaed
and ,
lia.stone,
The
unlt
needs
to
be
eapee atlly. a ne w type lo ca lity a ust be
Chos en .
The
The
ca ve
Queens
at
High waJ
locali ty .
q Ullrry
ne ll
The
expoae s
un it
Di xon
.h all
Hill
be naaed the Dixo n Hil l Lia e s t one .
and thll qua rry on th e we a t aide of th e
about I k.
to t he no r th ahall eonstitute the ty pe
ea ve e x poses ol d er dune depos i t. o f t h e unit , t h e
10u nger
beach a n d dune d epos it s.
2>,
There .ay lIell
be
an
at the baae of the quar r y (lee Saaa in Adaaa ,
~ncon f oraity
1980 ; 1983) .
The
Liaeatone
Harbo~ r
~ t th
Di%on Hill Liaeatone conaiata of the old Grahaa.
ne~
the
wi t hout
a d dition
of
the Holocen e be ach ridge depoaita and
tha
dune
deposits
immediately
west of
Storr's La k '" (. "' ''' index lIap of Ssn SlIlvlldor) ,
The
uni t
photograph
is
froa
Plantation
easily
on a aa p or ae r ial
recogni~ed
its la r g", a r cuate dune ridge depoaits .
depoaita
e%tenai~e
aost
aite
e%tend
froa
Cr ab
(Titua , 1983b).
Cay
to
the
Its aos t
Sandy Point
There the unit il a thinner a n d
ao r e diacontiuous venee r depoait than haa been earlier deacribed .
The
vicinitl
bl
D1%on
Liaeatone
is
o f t he Lin e Ho l e Settlement .
the
D1%on
Un ited
Hill
Hill
Liaeaton",
slao
in
t he
Other leaaer areas co ve r", d
a r e found in the tlpe locality o f
Estate. snd exte n d ina froa Poll, Hill Settleaent to Little
Fortune
Hill .
~icinity
of the airport at Cockburn To wn.
~
Lillaatone
gathe r ed
There
Dl %on
had
emerg"'nce ,
in
wideap r ead
but
ia
Hill
been
a aino r aeries of dune depoaita in t he
eaerle nce
i n terprete d
this
waa
The
aa
primaril,
ol d
Gr ahaaa Ha r bou r
r ep r eaenting
on
t he
a n epiaode of
ba. i a
of evidenc ",
f r o m the exposure. in Gra haas Harbour which are Holocene
Deapite
age.
thia
erro r ,
the o r iginal inte r p r etationa ca n
atill be considered valid; othar linea of evidence confira thia.
The
rocka
grading
deposits.
can
eae r gent
be
upwarda
Shallo ~
Seen
faciea
in
pattern
into
beach
conaiata of
deposits
ahallo ~
follo wed
by
aarine
dun e
aarine depOSits , overlain by beach aedtaenta ,
aeveral
of
t he
220
dolines
at
th'"
Line
Hole
in
deposits overlain by dune deposits can be Seen
Beac~
Settlement .
several
of
tile quarries along tbe Queens
Hig~way
on
t~e
east
side of tbe island.
structure
T~e
an
elllergence .
Dixon
of tile dune deposits slso aeem to indicate
Chsracteristically .
Hill Limestone
area
eac~
multiple arcuate dune r idge systema.
~as
Line
Hole
Settlement
prominent
dune
system south of Duc k Pond .
t~e
of
appro x imstely
dune
set
from
the
20
m.
for
of
example,
dune
t~is
there is a second
Its sverage elevation is
t~e
first snd thus is younger.
A third
found still furtller to wards the sho r e
deposits
the second and its elevation is still lo wer. sbout 13 m.
plsin
before
wbic~
sets
dune
sets .
saole
way.
was
of
set are
the
the
Dixon
of
The
.III
young e st dunes , s evera l
t~e
above sea lev el .
t~ese
on e
before it.
Hill Limestone
Sill U arly , tbe otbe r
~ave
provinces seem to
matcbing accreted
~ave
been forlled the
dune syste lII s were deposited on e at a tillle as
draining
On
o f dun e s acc r eted one at a time , each one at a
than
Al l
cha ra e te r is t ic
t~trd
<h'
rise only 4 to 6
elevation
" provinces "
is a
I t re ach e s e levations
Nor t h of
m.
there
In
This dune system lies shore wa rd from tbe first ; it
Tbus
sea
30
accreted a f ter
~ave
small sets
lower
to
vicinity .
ridge system. next to Littl e Lake.
sbout
must
25
blanketed by the
f rom
comillon
San Salvador .
to
all
T~is
provinces
t~e
is the most stri k ing
of
t~e
Dixon
Hill
Limestone .
The
Unconformity
The "Grshsms Hsrbour " Limestone , aa
originally
misinterpreted,
prominent
island- Wi de
wa s
viewed
unconformity.
as
Ho st
being underlain by a
ex poaures
of
this
unconformit,
Thu 8
depo s it s .
exposures
Among
hav e
turned
Otlt
a
on l y
to be at the base of th e Holocene
locationa
fe~
re~ain
~h tch
Li~estone.
of the basal unconfor mit, of the Dixon Htll
those
ia
the
can
be
s e en ove rlying ree f deposits at Crab Cay.
Anothe r
quarr, at the Sandy Point Plantatioo si t e .
~
Adams, 1980; 1983} reported an unconfo r mity
the
quarry
north
unconfor mit,
of
Dixon
Hill
Although
A}.
red solIs at
Still
another
To ~ n .
the
evidence for an
less
extensive
see~s
to be a logical expectation .
The
light
{Quar ry
~ ith
Sass
can be seen beneath the dune d e posit s along the r oad
south of the airport in Cockburn
ne~
be valid
~ay
than
it
had
previously
Grotto Beach Limeatone
on
the
nature
island-~ide
of
unconformity ia
been thought, it atlll
Re cent work has shed little
thia
unit .
It needs very little
revision.
In
Grotto
Beach
Grahams
is
late
the
original
Lim e atone
Harbour
1I0St
~as
Limestone .
likely
Holocene
d e sc r iption
aaid
to
of
the
type section, the
have been overlain by the
The material above the uncon f ormity
Late Holocene in age and corr e lated
deposits
to
the
aouth
(see
index
~ith
simllar
lIIap
of San
Salvador} .
Grotto
unconformity
r e ve a ls
an
that
on
that
unusual
Sandy
it
Limestone
Hook .
~er e
deposita
Further
atudy
reported below an
of
this
hori z on
is not an unconfor mi ty at all but instead it is
coral
horizon
unconformity .
Beach
bearing
formed
•
storm depoait.
small
bench
Resistant to erOsion ,
which
looka
like
an
Oth e r
bet .. e en
Grot t o
Rocky
Point
and
are actually exposures
Micrite
mi c r ite
most
are
so
Common
t he
.. ere
reported
Theae
at t he Di x on Hill Lim e stone .
Ba in
(1984)
h aa
argued
that
the
San Salvador, are d i agene t ic in origin .
in
the
dolines
and ca ve s of the island .
correct in regards to the shin)"
beaches
although
that
depoaita
He
certainly correct in re gards to those grey pebbles .. hich
p r obably
on
on
Limestone
Graha ms Harbour (Titus , 1983b) .
pebbles
pebbles ,
is
Beach
a
and
.. ithin
difterent
there
He 1a
j e t black pebbles found
Pl ei a t ocen e d ep oaits of the island ,
p r oces s must hav e f o r med them .
is a black micrite unit
Th e chanc e
on the island no w a pp ea ra t o
be re .. ote .
SUlll ma rI
Figure
hypothesis
history
it
pr e sen ta
2
for
8
summary
of
the
cur ren t
wor k ing
the Late Qua t er nary hiatory of San Salvad o r .
begins
at appro x im ate ly 120 , 000 yeara ago.
The
At that t i me
is li k ely that all or almost all of the isl and wa s sublllerged .
Th e
Sangamonian
end .
Soon ,
levels
" ith
" auld
Deposition ,
Later,
sa
d e posi t s
Beach
interglacisl
the
d r op
at
ona et
and
atage ,
of
ho o/ever,
t he
.. ss comi n g to an
Wiacoosin glaciat ion, aea
a long period of emergenc e would be gin .
thia t i me, began wtth Shalla .. s u btid a l deposits.
the
i sland
formed.
Lilllestone
actus 11)'
All
and
of
this
e merg ed,
these
deposits
e mergent
besch
and
th e n dun e
b e lo o g t o the Grott o
sequence makes up t he right
hand bracket of Figur e 2 .
After
perh a pa
ten
or
fifteen
thoua an d year a o f ac tua l
eeerienee
epiaode
there
.. aa
anethar
pertod of rtatng sea le"els.
This
.. aa of "e r 1 ahert duratien and it .. aa follo .. ed by anether
peried
ef
eaergenee.
folle .. ed
b1
beach
e.ergent
sequence
Onee
and
again
shal le .. ,
aubtidal
dun e
depesits
.. ere fereed.
then
falla
.. ithin
the
bracket
en
deposits
This
tha . id dle eC
Figure 2 and it aakes up the ro cks of the Dixon Htll Lieestone .
There
oC
yesrs
the
th e
felle .. ed a period eC thirty te fort1 thousand
expoaure.
karst
higher
then
Sea
festures
le"els d ropped eons id erably and eost of
ef the ialand began to fere.
(Seae areas o f
el.ystions, such aa Sand, Peint , .. ere no t aubee rged du ring
Dixon
earlie r
Hill
start
aea
and
le"el
rise
and there karat fasture get an
foraed ever lenge r perieda ef tiee . )
Moat ef
the eavea and de lines of the Island probabl, date to t hi a tisI' .
The
to
next
40 , 000
,eara
rea ched
2. 5
depeeita
of
1 0 .. -1,ing
riae
•
ago .
abeve
thla
aress
afCected
It
the
event
of
.. aa
a brief event and the riae onl1
present
1eve1a .
The enlr e xtenaiye
are t he thin lake depeaita feund in the
the
ialand ( Lake Ceekbu rn ).
Thia ses leye1
the i aland p riear il, in ear"ing the aea eliffa and
.. ave-cut
notehea
Hany
the
ef
aea level riae eeeu rred at apprexieately 30 , 000
areund
the
aouth .. estern
and .. eatern eoasta .
lsland's dolinea .. ere filled or psrtiall, filled at
thia tiee.
The
last
The
eajor
aesa
plat fore .
It
formed
this tie..
Holocene
at
s.a
le"el
dratned
drop
eoepletel,
follo ... d
im.ediatel,
off the San Sal "ador
is eoat 11kely that the ou ter ea,a of San Sa ludor
depoaita
and
The eaya are better eeeented than the late
ae
they are prebably older.
22.
The eays do
not
sboy sny evidence of tbe
sea
level
rise
probably
younge r
deposits
and
are
of
notcbes produced during tbe
35 , 000 to 40,000 years ago and tbus tbey are
tban
younger
probably
~ave -cut
early
tbis event.
Older than the late Holocene
than tbe lates t Pleiaocene units , the cays
Holocene
or
about tyenty tbousand years in
sge.
The
formation
last
of
depositional
tbe
beach
event
ac c retion
on
Ssn
Salvador
yas the
r idges (Figure 1). a process
which cootinu es today.
Acknowledgments
Kuch
of
this
College.
of
paper
I
the
.... as
recent field "ork that .... ent into tbe making
done "hile on sabbatical lesve frO R Ha r t"ick
" ould like to e9pe cia11y thank Donald Gerace and the
CCFL Bab SRian Field S tation for the generous support given to me.
22'
'->t , ,
SAN SALVADOR
I
\\
\
("...... " "
' ""'''
I
)
Quote.""ry Strotigrophy
o
/ 1-1 0...
Kolo....
at
.,"""" ...
I... 1G,ot' o
H.II U _ _
-~ U..." ...
'....
226
-
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'"