DESCRIPTION OF NORTHERN MAP UNITS
ARTIFICIAL FLL IHOLOCENE-Sana. IMseaoa. and voianc roci
~uanmooxea Mo all i.i swnm anm pu aodBahudSanjuan Shown
on m ameu near Sn juan
UULAUM IHOLOCENE)
a | Sano. cam. grawu an cabbie aeppmed a muam wiays
an Uundimmnutd MA lu unmta depn u
LAoDSULDE DEPOSITS IHOLOCENEl--nu o al. clauou cday.
S ann hnansa subnn*l
,- l BEACH DEPOSIS IHOLOCENE-Sada cnposed al nonded gm of
quUm. voianc m an am shell. Inciaudpes U bd c ama anda
cosuml-Misap depais. and longaunms send dlune of buch sand
S SWAMP DEPOSITS (HOLOCENEI-SanudyaMb uds day ma. Some
am- un*omamo by put
EOLIANITE IPLRESTOCENE--FInabr o ansodmd. hig i cambeaad
noamoeous on uamnodn company d of Ihn s coma giam ai slte
a gnment and quam. Some of di depoam aw penly submeged
On SLICA SAND DEPOSITS IPLISTOCENEI-Veay pun h tm wy fIn
-- uaMn sand dand orn che mae mny M aicl dapos by leahig
aMn n wmt ng mby ad. The dwicur sepassa a a m mu m l in
-- naunug gua
at TERRACE DEPOSITS (PLERSTOCENE-Cy. and, mad g d drpose
---- depomd on fomer food phear nom Ihmnudes sam aml-lCan
agepous
or UNDFERENTATm O SURFICIAL DEPOSIS (QUATERNARY AND
--- TERTIAR I-C,. sany clay. and and dpomu shoux n an
d44la goK1,1 c me as blnMs dnaeaPos. nma-uecea depao. and
an ner raleneo Quaunairy depoa
SCAMUY FORMATION IMIOCEPE--Qlk and lneaon camonly
som wnwls ano aind lmarugpnora lun cakl andae ue Quna a
oi doloaiCs n uppet pan lena i way pale ameang mandhm ulenana


SAYMAMO LIMESTONE IMIOCENEI-Whue m way pai oangs. localy
ps.-ylksw and grah-pikL vew pule ln~bureus maneu. nmams
mto du.-t dded genanly indurad by econday caenMaon ta a
Itoy caasia am d kdm onema. Uppae pad of unM i natla-
em are i she unand a wmy pale orange bnmgh-ylacN chluk Imisted.
ded wdh Mar lypical Mndud hInmnn CaMomI dolma u a ny
a tec r nwm mae
I AGUADA UMESTONE IMIOCENE-Thick layes o way pv arag to
ps bud alam asn lmug uib chat and unds y mMonM.
Comonacrly a-beddad and ainked a top Ioma pwe aO-
manly lm endumad Ian upper pas
T CAO FORMATION MIOaCEN AND OUCOCEME-Typrsal beds o
awse daoy. hy o i eao adn mad, IAy -v paw ona a "pa.-
yelmatwcau and muaodu-agu-pIa lacaky sund. See al ag

MldSnds Sand M I-Angulr o subangu lan Io coase quas sand
In a nmnalmrasous sily dla mnacx n Vega Ah canem undm nd
grl t gade u-wasd o klusirouis and
( TF Quebade Agnns Umaiaun Mesmbeib-Very lyh~I cwmlla desm.
uwy palo mang pIalgah-aangtne hnon am localy common
saUsagd gm oi qual umad ud abundaM hos i mnold
STcl Alaimo SueSnd M Lean-Suimwnded d as~banga, cssue I a dded pb.
blylne aocaa sand canislng quuaguame and vokcautack debdu
I. Ro Ind LianeMan Meaber-Campac bin cthlky. inapiunsl Imn-
mans. mealy pl-yeIloMrho ange. weakly bedded to nIa. and
lacaky lg11h1 ghl-anac
| T an|sMubo LiMamm Mnmb--Fm.- to andlunm-gamd cadlamnme.
cainmanWly nciumeed Imo a haud. demunsmM san. AN bua. unu b
table edWha caue caaueun compaosd lasvgy of madumnt coarse
gen bea a acobmnanly naakeud by dick bad of l*g on, shath
T 1 GuOaiw MMumba-Foausndrm calcarou clay and nionw coanm-
i n lomaim send and pa"l


( 1 MCARABOWS SAND IMOCENE AND OUGOCENE-Caawhsrac-a
E- J to elaah-bown highly carouedded ea*n o moware carut'-
mad. In Muwy of Baymiaon. un comas s grayuanr asmo t.sdo
casobedded ione asediaim send caanag mtes as kalaouos san.
nmlsans und way pae om u a g0 aita m any Oaw u
uaan on a unees Of grad
L J LARKS LUMESTONE OUGOCENEl-H&ld saket,u anu woy pupsK
ajilnmau esMe i bed 10-30 ana com ii ac nea:
whne a wy pal oanMe In wsm pa ui a ouiao area. u ng mnu
S lens o d md nd alcamu dc M cmamm uemn pMt unma cnr.e

T SAN SEBASTFIA FORMATION(OlUGOC8EW-I-dliblcn and sr
emely o cdasms dlay

m-ndyaibonueseoudclay. aclwlycaninag peablss nacicactbl aoo.
w vomcae uck laly maumm ba tos ueou eanny kmamoor

I TK UNDIFFERENTIATED LOWER TERTIARY AND CRETACEOL
---- FOPRMATIONS-Lima. draccae omnaaiau an aimonr. -
bubncas bw gnnodsam. and quma aomu


Table 1 Description of Formations and Formation Members of
Northern Puerto Rico.








was deposited in clear water. This is evident by the

abundance of reef-forming organisms such as corals and algae

making it a reef limestone. The most prominent feature of

the limestone is the escarpment.

The Cibao Formation is a heterogeneous and leticular

formation. It is composed of intergradational and

interlensing beds of calcareous clay, sandy clay, sand,

gravel and limestone. This variation in material reflects

varying amounts of sediment was carried into the Atlantic

ocean. The Cibao Formation is Oligocene-Miocene in age.

The variation in composition reflects different or diverse

conditions of sedimentation for the various members of the

formation. The formation is composed of the Guajataca

member, Almirante Sur Lentil, Quebrada Arenas Limestone

member and Miranda Sand member.

The Aguada Limestone rests conformably on the Cibao

Formation, sometimes it is difficult to distinguish between

the two formations. The major difference is that the Cibao

is porcelaneous to very finely crystalline and the Aguada

Limestone is a calcarenite and less fossiliferous. This

limestone is almost a pure limestone containing many chalky

beds. It also contains scattered grains of quartz. The age

of the Aguada Limestone is dated as lower Miocene based on

the presence of foraminifera belonging to this epoch. The

deposition of the Aguada occurred as part of a slowly

subsiding shelf. The most prominent physiographc expression

is the very closely spaced sinkholes throughout the area.




3 C/









The Aymamon Limestone rests sharply, but conformably,

on the Aguada Limestone and is a very pale orange to white,

fine, crystalline limestone. The age of the Aymamon is

classified as Early Miocene. The presence of corals, a type

of foraminifera and the fact that it is a very pure

limestone suggests that it was deposited on a relatively

flat reef in shallow water. Characteristic of the limestone

is the landforms known as mogotes or pepino hills. These

are steep-sided, conical hills that are apparently residual

hills that were left after intense weathering of the

limestone. Other prominent features are the stair-step or

hillside features and shallow dolines (depressions).

The Camuy Formation rests sharply and disconformably on

the Aymamon Limestone. It is predominantly calcareous with

appreciable quantities of quartz sand. The lower portion is

so ferrogenous that it weathers to pink or red chalk and

limestone. The study of planktonic foraminiferas suggest

the Camuy Formation was deposited in Late Miocene and early

Pliocene. The environment of deposition occurs on the

island shelf. The physiographic expression of the formation

are the low, gently sloping ridges that roughly parallel the

strike direction of the formation.


III. HYDROLOGIC SETTING

Recent studies (Torres et al. 1984) using the data

collected from wells drilled all over the karst terrain of

the north coast produce a good hydrogeologic framework for




q.65








this area (Table 2, Fig. 1.B).

There are two major aquifer systems (Fig. 3) in the

north coast; a shallow water-table formed by the Aymamon and

Aguada limestone and a deeper antesian system formed by the

Montebello limestone member of the Cibao formation (Torres

et al. 1984). The shallow water-table or alluvial aquifer

consists of medium to fine grained sand and gravel with the

thickness of the aquifer ranging from 0 to 300 feet. The

lower part consists of the Aymamon and Aguada limestone

underlying the alluvium.
The second aquifer system or the artesian system is

composed of predominantly carbonate rocks and clastics. The

potentiometric surface of this aquifer is higher than the

water table of the alluvial aquifer. The system is divided

into three components; the Montebello Artesian aquifer which

is the most productive aquifer of the north coast, the Lares

limestone which has a large recharge zone with almost entire

contact zone lying between the karst terrain and volcanic

sedimentary terrain. The third division is the San

Sebastian formation that is considered the bottom of the

fresh water flow and also the bottom of the karst sequence
of the north coast.

Water resources are also obtained from several rivers

that cross the karst terrain and supply water for the north

and central part of the island. There are nine important

river basins of them four have dams for domestic,

agricultural, and industrial water supplies which are




L^66