Changes in Stratigraphic 

Nomenclature in the 

Cretaceous System 

East-Central Puerto Rico

By REGINALD P. BRIGGS

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1274-0

Prepared in cooperation with the 

Commonwealth of Puerto Rico 

Economic Development Administration, 

Industrial Research Department

v UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKLE, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 25 cents (paper cover)
CONTENTS

Page

Abstract _____ - 01

Introduction __ - 1

Terminology ___ _ _ - 2

The Lower Cretaceous Torrecilla Breccia ___ 7

Formation D, formation K, and pre-Robles rocks _ 7

Type section and reference sections _ _ 9

Distribution, thickness, and depositional environment _ 10

Aguas Buenas Limestone Member __________ 11

Barros Tuff Member ___________________ - 12

Contact relations of the Torrecilla Breccia ______ _ 13

Age and regional relations ____________ 14

The Lower Cretaceous Barrancas Limestone Member of the Magueyes Formation, Rio Orocovis Group ____________ __ 15 

Age ___________________________________- 17 

Regional relations and assignment of the Barrancas Limestone Member to the Magueyes Formation _________ 17 

The Rio Bauta, Botijas Limestone, and Reves Members of the Upper Cretaceous Pozas Formation ___________________ 19 

Rio Bauta Member __________________________. 21 

Correlation of the Rio Bauta Member with strata to the north 22 

Botijas Limestone Member _____________________ 23 

Reves Member _____________________________ 24 

Age of and correlations within the Pozas Formation _____ 24 

The Toyosa Member of the Upper Cretaceous Maravillas Formation 26 

Toyosa Member ____________________________. 27

Summary _________________________________ 28 

References cited ______________________________ 29

ILLUSTRATIONS

 Page

* FIGURE 1. Index map of report area, showing type localities ______ 0 3 

, 2. Generalized geologic map of report area ____________ 4

3. Chart showing volcaniclastic rock classification used in this 

jt report ________________________________ 5

4. Schematic diagram showing correlation of Torrecilla Brec- 

"-* cia and its members with previous informal stratigraphic units ___________________________ 7

5. Schematic diagram showing changes in nomenclature pertaining to the Magueyes and Pozas Formations ______ ,16 

^ 6. Cross sections showing facies changes in the Pozas For4 mation _______________________________ 20 

7. Schematic diagram showing regional variations in the

Maravillas Formation _______________________ 26

j III

CONTRIBUTIONS TO STRATIGRAPHY

CHANGES IN STRATIGRAPHIC NOMENCLATURE IN THE 

CRETACEOUS SYSTEM, EAST-CENTRAL PUERTO RICO

By REGINALD P. BRIGGS

ABSTRACT

The system of informal stratigraphic nomenclature used previously for 

part of the Cretaceous section in east-central Puerto Rico is replaced by a 

formal nomenclature based on increased data gained from continued geologic 

mapping. Only the lower part of the Lower Cretaceous Series is not treated.

The resulting changes in stratigraphic nomenclature are the following:

1. The Lower Cretaceous Torrecilla Breccia is formally established, replacing 

the informal formation D, formation K, and pre-Robles rocks in the 

Cayey, Comerio, and Barranquitas quadrangles, respectively. The Aguas 

Buenas Limestone Member is assigned to the base, and the Barros Tuff 

Member to the top, of the Torrecilla Breccia.

2. The Lower Cretaceous Barrancas Limestone Member of the Lower and 

Upper Cretaceous Magueyes Formation, Rio Orocovis Group, is established as the formal name of the limestone unit of formation L in the 

Barranquitas quadrangle. Strata previously included in formation L 

and the Cariblanco Formation in the northern Barranquitas quadrangle 

are reassigned, chiefly to formations of the Rio Orocovis Group; however, formation L strata underlying the Barrancas Limestone probably 

are stratigraphically equivalent to the Torrecilla Breccia.

3. The Rio Bauta Member is established and assigned to the base of the 

Upper Cretaceous Pozas Formation; and the Botijas Limestone and 

Reves Members, previously included within the Coamo Formation, are 

reassigned to the Pozas.

4. The Toyosa Member is established and assigned to the top of the Upper 

Cretaceous Maravillas Formation.

INTRODUCTION

Detailed geologic mapping of Puerto Rico by the U.S. Geological 

Survey in cooperation with the Puerto Rico Economic Development 

Administration began in 1955 and continues at the time of this 

writing. Early efforts in this program were largely in east-central 

Puerto Rico, where the Cretaceous volcanic stratigraphy is 

extremely complex.

Early in the mapping program, it became clear that it would 

be difficult or impossible to solve many stratigraphic problems

01
0 2 CONTRIBUTIONS TO STRATIGRAPHY

within the limits of individual mapping units, 7^-minute quadrangles. Informal stratigraphic nomenclature was therefore used 

where appreciable doubt existed as to identity, extent, or correlation of units and where it could be reasonably assumed that this 

doubt might be dispelled by later mapping in adjacent areas. In 

addition, formal stratigraphic names were applied in some areas 

where such use has since been found erroneous.

In this report, formal nomenclature is introduced where now 

considered feasible; some previous miscorrelations are corrected; 

and new correlations are made where necessary to clarify the 

stratigraphic relations of newly introduced or redescribed units. 

The report falls into four discrete parts, introducing or redefining 

the following: (1) The Lower Cretaceous Torrecilla Breccia and 

its Aguas Buenas Limestone and Barros Tuff Members, (2) the 

Lower Cretaceous Barrancas Limestone Member of the Lower 

and Upper Cretaceous Magueyes Formation, Rio Orocovis Group, 

(3) the Rio Bauta, Botijas, and Reves Members of the Upper 

Cretaceous Pozas Formation, and (4) the Toyosa Member of the 

Upper Cretaceous Maravillas Formation (fig. 1). No discussion of 

the overall Cretaceous stratigraphy of east-central Puerto Rico is 

attempted; only the previously mentioned units, all of which are 

stratigraphically above the informal formations A, B, C, and J 

(fig. 2), are dealt with here.

Some early correlations already have been changed (Glover and 

Mattson, 1967; Glover; 1967, 1969), and other modifications of 

stratigraphic nomenclature have been made (Nelson, 1966; Briggs, 

1967). Faunal lists are not included; these either have been presented elsewhere (for example, Berryhill and others, 1960; Douglass, 1961; Kauffman, 1964; Glover, 1969) or will be included in 

future reports.

Reference to publications on the following quadrangles will aid 

the reader in understanding the discussion: Barranquitas (Briggs 

and Gelabert, 1962), Cayey (Berryhill and Glover, 1960), Ciales 

(Berryhill, 1965), Coamo (Glover, 1961), Comerio (Pease and 

Briggs, 1960), Corozal (Nelson, 1966, 1967), and Florida (Nelson 

and Monroe, 1966). In addition, the hydrogeologic map of Puerto 

Rico (Briggs and Akers, 1965) provides a general view of the 

region.

TERMINOLOGY

Terminology of volcanic rocks is various and inconsistent 

(Fisher, 1966), and no single proposed system of terminology 

seems to cover satisfactorily all varieties of volcanic rock. The 

volcaniclastic rock classification used in this report is shown in
J

10 

I

FIGURE 1. Orocovis, Barranquitas, and Comerio quadrangles and adjac

showing type localities (X) for the following units: T, Torrecilla Brecc

TB, Barros Tuff Members of Torrecilla Breccia; MB, Barrancas Limest

PR, Rio Bauta Member of Pozas Formation; MT, Toyosa Member of M
04 CONTRIBUTIONS TO STRATIGRAPHY

66°30'

EXPLANATION 

SOUTH NORTH

Pozas Formation

Robles Formation 

and equivalent units

Rio Orocovis Group 

undivided, including 

Manicaboa Formation at top

PARTIAL UNCONFORMITY

Torrecilla Breccia

DISCONFORMITY

Formations A, B, C, and J

Contact

Fault

FIGURE 2. Generalized geologic map of report area.
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 05

Grain 

diameter 

(mm)

256-

1 9fl

64-

16- 

8- 

4- 

2

1 ~

1/2

1/4

1/8-

1/32 

1/64 

1/128 

Epiclastic 

rocks, except 

where 

modified

Cobble Bulder

V

& 

.a

&

Conglomerate 

or 

breccia

Granule sand

Very 

coarse

Coarse

Medium

Fine

Very 

fine

Sandstone

Siltstone

Mud stone

Pyroclastic 

rocks ash, 

lapilli, bombs, 

and blocks, 

subsequently 

compacted 

or cemented

£m O 

O

<u 

il

to 

1

XI

3=

1-

Lapilli 

tuff 

or 

very coarse 

tuff

V 

tfl

ro

3

0>

iZ

3=

Hyaloclastic 

rocksfragmented 

submarine 

lava, subsequently 

compacted 

or cemented

Lava andbreccia 

(aquagene) tuff-breccia

Aquagene tuff

Hyaloclastic breccia

or 

hyaloclastite

FIGURE 3. Volcaniclastic rock classification used in this 

report. Chiefly modified from Fisher (1960,1961), Rittman 

(1962), and Carlisle (1963).
O6

figure 3. This classification is just broad enough in scope to cover 

the needs of this report; no attempt is made to classify all volcaniclastic rocks.

Most rocks in the units under discussion were deposited in a 

marine environment. Exceptions are chiefly in the Pozas Formation, where some rocks are known to have been, and others may 

have been, deposited subaerially.

Tuff and tuff-breccia may have remained at their initial site of 

deposition, having been deposited directly from a fall through air 

or water, or may have flowed appreciable distances downslope 

following the initial deposition. The character of layering suggests 

that postdepositional flowage usually occurred. These rocks include 

some ignimbrites.

Lava or lava flow as used here consist of rocks recrystallized 

from an extruded molten mass. Lava breccia consists of blocks of 

lava in a matrix of similar material. Lava and lava breccia are 

found in both marine and subaerial sequences. Pillow lavas can be 

considered special lava breccias or hyaloclastic breccias.

Well-known terms, such as andesite and crystal-lithic tuff, are 

not defined here. However, clarifications of two adjectives applied 

to common rock terms in the following pages are necessary:

Volcanic a general adjective describing rocks believed to be 

composed chiefly of fragments of volcanic origin, no matter 

what the specific means of fragmentation and no matter 

whether in primary or reworked deposits; especially useful 

where uncertainty is high, as in areas of tropical weathering. Examples: both lava breccia and tuff-breccia are volcanic breccias; both tuffaceous sandstone and sandstone 

reworked from a volcanic provenance may be termed volcanic sandstones.

Tuffaceous an adjective describing fragmental rocks chiefly 

composed of primary volcanic ejecta; modifies common rock 

terms for moderately well sorted to well-sorted, well-stratified water-laid deposits.

Layering thicknesses, in centimeters, are classified as suggested 

by Ingram (1954):

> 100 ________________ Very thick. 

30 to 100 ________________ Thick. 

10 to 30 ________________ Medium. 

3 to 10 ________________ Thin. 

1 to 3 ________________ Very, thin. 

; 0.3 to i __________..__ Thickly laminated. 

<0.3 _______________ Thinly laminated.
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 07

Briggs and 

Gelabert pease and

(1962)- Briggs (1960) 

Barranquitas Comerio

quadrangle quadrangle

Pre-Robles

rocks

^>>^_

Concealed/'/>-

/.by'///V 

faulting '//s

o

1

6'

$0, 

a.

S

Formation

K

Aguas

Buenas

Limestone

Member^-^^

^-^\

This reportBerryhill Orocovis, Barand Glover ranquitas, 

(1960)-Cayey Comerio, and 

quadrangle Cayey quadrangles

Formation 

D

Aguas 

Buenas 

Limestone 

Member,^-''

Barros 

Tuff 

Member

^

Torrecilla 

Breccia

Aguas 

Busnas 

Limestone

FIGURE 4. Correlation of Torrecilla Breccia and its members with previous 

informal stratigraphic units.

THE LOWER CRETACEOUS TORRECILLA BRECCIA

Rocks of Early Cretaceous age previously referred to as formation D in the Cayey quadrangle (Berryhill and Glover, 1960), as 

formation K in the Comerio quadrangle (Pease and Briggs, 1960), 

and as pre-Robles rocks in the Barranquitas quadrangle (Briggs 

and Gelabert, 1962) are here named the Torrecilla Breccia for the 

double-peaked mountain, La Torrecilla, about 3 kilometers westnorthwest of the town of Barranquitas in east-central Puerto Rico 

(figs. 1,4).

The Aguas Buenas Limestone Member in the base of the Torrecilla Breccia was first described by Semmes (1919, p. 64-65). 

This limestone unit was correlated with basal strata of the 

Fajardo Formation by Berryhill and others (1960, p. 143) and was 

included in the basal parts of formation D (Berryhill and Glover, 

1960) and formation K (Pease and Briggs, 1960). It is here formally reassigned.

The Barros Tuff Member, described below, is at the top of the 

Torrecilla Breccia in its western outcrop area.

FORMATION D, FORMATION K, AND PRE-ROBLES ROCKS

In the Cayey quadrangle, Berryhill and Glover (1960) described 

formation D as consisting of the fossiliferous Aguas Buenas 

Limestone Member, sporadically exposed at the base, and the 

overlying interlayered volcanic breccia, andesite lava flows, and 

tuffaceous sandstone. The breccia and sandstone are calcareous, 

and rocks of the unit as a whole commonly have a dusky-red cast.1 

The maximum thickness of formation D was given as about 200 m,

1 Colors are in agreement with the "Rock-Color Chart" of the National Research Council 

(Gocldard, 1948).
0 8 CONTRIBUTIONS TO STRATIGRAPHY

and the formation pinches out between the overlying Robles Formation and formation C about 5 km southwest of the town of 

Cayey (figs. 1, 2). No type locality was designated for formation 

D, but a section was described by Berryhill and Glover (1960).

Formation D of the Cayey quadrangle is contiguous with formation K of the Comerio quadrangle (Pease and Briggs, 1960). 

Formation K chiefly consists of crudely stratified coarsely clastic 

rocks ranging from volcanic breccia to coarse tuff. The Aguas 

Buenas Limestone Member crops out sporadically at the base of 

formation K, and discontinuous lenses of fossiliferous limestone 

and limestone-breccia about 10 meters thick are found in other 

parts of the section. Well-stratified units of calcareous thin-bedded 

tuffaceous sandstone and siltstone as much as 50 m thick occur 

intermittently throughout formation K; lava flows are present, 

most commonly in the upper few hundred meters where locally 

they predominate. Rocks in the upper part commonly have a 

dusky-red cast, similar to those in formation D. The maximum 

thickness of formation K of the Comerio quadrangle is 2,050 m, 

considerably thicker than formation D of the Cayey quadrangle. 

Although no type section was designated in the Comerio quadrangle, Pease and Briggs (1960) gave brief descriptions of several 

localities in which rocks typical of formation K are well exposed. 

In the northernmost part of the quadrangle, north of the Quebrada 

Vicente fault, rocks that were included in formation K by Pease 

and Briggs (1960) now are included within the Rio Orocovis 

Group (Nelson, 1966).

In the eastern part of the Barranquitas quadrangle (fig. 1), the 

pre-Robles rocks of Briggs and Gelabert (1962) are contiguous 

with the upper part of formation K. Lava and lava breccia are the 

most common rock types in the pre-Robles rocks, but very thick 

bedded tuff-breccia and volcanic conglomerate also are common, 

and thin- to thick-bedded units of tuff and tuffaceous sandstone 

and siltstone are present locally. A total of at least 1,200 m and 

perhaps as much as 1,800 m of pre-Robles rocks is exposed in the 

Barranquitas quadrangle, but the full thickness is not known 

because the bottom of the section is faulted out. However, it now 

seems reasonable to assume that all pre-Robles strata in the Barranquitas quadrangle are stratigraphically equivalent to rocks 

included in formation K in the Comerio quadrangle. The Aguas 

Buenas Limestone Member is not present in the Barranquitas 

quadrangle, and the exposed pre-Robles section is at least 200 m 

and perhaps 800 m thinner than formation K.
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 9

Recent geologic mapping by the writer of this paper in the 

Orocovis quadrangle (fig. 1) has shown that an appreciable section 

of pre-Robles rocks also is present in this area. Detailed measurement of the thickness is precluded by structural complications, 

but it is probably at least 1,000 m thick, and no base is present. 

Very thick bedded coarse tuff-breccia is the most common lithologic 

type, but finer breccia and very thick bedded to thick-bedded coarse 

tuff also are found. Units that contain lava grading upward to 

lava breccia, tuff-breccia, and aquagene tuff are present near the 

top of the section, between 1 and 2 km south of the town of 

Orocovis. Thin-bedded tuffaceous sandstone and siltstone are 

uncommon in the pre-Robles rocks of the Orocovis quadrangle as 

compared with areas to the east. The Barros Tuff Member, 

described below, occurs at the top of the pre-Robles rocks in all 

but the easternmost Orocovis quadrangle exposures.

TYPE SECTION AND REFERENCE SECTIONS

The type section of the Torrecilla Breccia is here designated as 

the series of exposures of very thick bedded and thick-bedded 

tuff-breccia, lava breccia, and related rocks in the Barranquitas 

quadrangle along Highway 156 between 40,180 m N., 160,950 

m E. and 41,140 m N., 160,990 m E. (Puerto Rico rectangular 

coordinate system), about 2.1 km west of the western peak of 

La Torrecilla; also included in the type section are the nearby 

exposures in the Rio Botijas, about 100 m east of and parallel to 

this segment of Highway 156.

Other sections in which the Torrecilla Breccia is well exposed 

in the Barranquitas quadrangle are on Highway 770 along the 

western and northwestern flanks of La Torrecilla (largely tuffbreccia and tuff) and along the course of the Rio Usabon from the 

base of the Robles Formation, 3 km airline east-southeast of the 

town of Barranquitas, eastward to the confluence of the Rio 

Usabon and Rio de la Plata (largely lava breccia and lava). In 

addition, tuff-breccia, lava breccia, and volcanic conglomerate of 

the upper part of the Torrecilla Breccia crop out magnificently 

in the vertical walls of the Canon de San Cristobal, about 3 km 

southeast of Barranquitas, but here the exposures are rather 

inaccessible.

In the Comerio quadrangle, tuff-breccia, lava breccia, lava, and 

tuff of the upper part of the Torrecilla Breccia are well exposed 

along Highway 775 from 1 km south of the town of Comerio 

southward about 3.9 km airline to the saddle at the head of 

Quebrada Pina, about 0.6 km west of Cerro Viento Caliente; along
0 10 CONTRIBUTIONS TO STRATIGRAPHY

Highway 173 from the saddle at the head of Quebrada Galindo, v 

0.7 km north of Cerro Plana, to a point 0.6 km northeast of the 

meander core at Proyecto La Plata; and along Highway 14 from 

the vicinity of Cayey west-northwestward about 5 km airline to 

the point where the highway exposures pass into the overlying 

Robles Formation.

Tuff - breccia, lava breccia, and tuff of the lower Torrecilla 

Breccia are best exposed on Highway 782 from the point where 

the highway crosses Quebrada Ceiba, about 4.0 km airline north 

of the town of Cidra (fig. 1), to the outcrop of the Aguas Buenas 

Limestone Member, 2.2 km airline north-northwest of Cidra.

Fresh rock in these sections commonly is dark gray, greenish 

gray, and bluish black, but dark-reddish tints are characteristic 

of strata in parts of the upper Torrecilla Breccia.

DISTRIBUTION, THICKNESS, AND DEPOSITIONAL ENVIRONMENT

The Torrecilla Breccia crops out widely in east-central Puerto 

Rico (fig. 2). It is composed chiefly of very thick bedded fragmental volcanic rocks. Tuff-breccia and lava breccia predominate, *" 

but coarse tuff is common; andesite lava is common in the upper 

part of the formation and is present locally in other parts of the 

formation. Limestone lenses and units of thin-bedded tuffaceous 

sandstone and siltstone are relatively minor but widespread components, especially in the eastern outcrop areas. Exclusive of _, 

lavas and lava breccias, most rocks are slightly to moderately 

calcareous. ^

The Aguas Buenas Limestone Member occurs sporadically in 

the base of the formation, and the Barros Tuff Member is present 

in the top in western outcrop areas. The thickest known section of 

the Torrecilla Breccia is 2,050 m in the Comerio quadrangle. In 

the western area of outcrop, a thickness of only about 1,000 m is 

estimated, but the base of the formation is not exposed; the 

Torrecilla may be appreciably thicker here. The Torrecilla thins 

to zero toward the southeast (fig. 2).

The bulk of the Torrecilla Breccia was laid down in a marine 

environment, as indicated by the presence of calcareous units containing marine fossils, well-stratified units, and crude pillowing 

in some lavas. However, the uppermost Torrecilla Breccia in 

eastern outcrops may well have been deposited in a largely subaerial environment, as is suggested by the reddish cast of the rocks 

and an absence of evidence for marine deposition at most places 

where this reddish cast is found.
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 11

AGUAS BUENAS LIMESTONE MEMBER

The Aguas Buenas Limestone Member is here assigned to the 

base of the Torrecilla Breccia. Although the "Aguas Buenas limestone" has been in the geological literature since first described 

by Semmes in 1919, no formal descriptions of type locality or type 

section have been made. In order to make use of this generally 

accepted stratigraphic name, the Aguas Buenas Limestone Member 

is here redefined.

The Aguas Buenas Limestone Member is named for the town 

of Aguas Buenas, eastern Puerto Rico (fig. 1). The type area is 

a zone of well-developed karst topography in Barrio Sumidero in 

the Caguas quadrangle about 3 km due south of Aguas Buenas. 

Although the Caguas quadrangle has not been mapped in detail, 

correlation of the limestone occurrence in Barrio Sumidero with 

the limestone that trends northeast from the town of Cidra in the 

Comerio quadrangle is considered definite (Semmes, 1919; Pease 

and Briggs, 1960). The type locality is here designated as the 

quarry (41,430 m N., 183,640 m E.) on the northwest side of 

Quebrada La Zapera, 4.1 km north-northeast of Cidra, in the 

Comerio quadrangle (fig. 1). Here, about 30 m of dark-gray thickbedded to very thick bedded finely crystalline limestone which bears 

an extensive rudist and gastropod fauna is exposed. At the type 

locality the top of the member is faulted out, but nearby it is overlain by thin-bedded tuffaceous sandstone and siltstone that grade 

upward into coarser, very thick bedded and thick-bedded volcanic 

strata of the Torrecilla Breccia; the base of the member is poorly 

exposed, but apparently it rests on hydrothermally altered volcanic 

rock. Locally the Aguas Buenas Limestone Member contains intercalations of thin- and medium-bedded calcareous volcanic sandstone and siltstone, but in most outcrops it is virtually pure crystalline limestone.

Along strike northeast of Cidra (figs. 1, 2), the Aguas Buenas 

Limestone Member rests for the most part on intrusive rocks or 

altered strata. The member locally exhibits evidence of alteration 

in its lower part; apparently, in this area the Aguas Buenas Limestone Member and other rocks at the base of the Torrecilla Breccia 

were virtually impervious to magma and hydrothermal solutions, 

and only the underlying rocks were extensively affected (Pease 

and Briggs, 1960). Elsewhere, the Aguas Buenas Limestone Member rests disconformably on strata assigned to formations A and 

C in the Cayey quadrangle (Berryhill and Glover, 1960) and 

formation J in the Comerio quadrangle (Pease and Briggs, 1960).
0 12 CONTRIBUTIONS TO STRATIGRAPHY

The thickness of the Aguas Buenas Member generally ranges 

from 0 to 60 m; it is a lenticular reef limestone, which is present 

along only about three-fourths of the exposed base of the Torrecilla Breccia (Berryhill and Glover, 1960; Pease and Briggs, 1960).

Fossils collected from the Aguas Buenas Limestone Member 

indicate an Early Cretaceous age, probably Albian (Douglass, 

1961; N. F. Sohl, oral and written commun., 1956-1967).

BARROS TUFF MEMBER

The Barros Tuff Member of the Torrecilla Breccia is here named 

for Barrio Barros, just northwest of the town of Orocovis in the 

Orocovis quadrangle (fig. 1). The type section is along an eroded 

foot trail that descends a ridge about 1 km northwest of the town, 

between 44,280 m N., 156,120 m E. and 44,380 m N., 155,850 m E. 

Here, the base and most of the member are exposed; the top is 

concealed. The coarse tuff that is the predominant component of 

this unit is moderately to deeply weathered in most outcrops, 

generally ranging from yellowish and grayish brown to reddish 

brown. In the type section the member consists of moderately 

weathered thick-bedded and very thick bedded coarse crystallithic tuff that locally grades into coarser tuff and fine breccia 

interlayered with units of thin-bedded tuffaceous sandstone and 

siltstone 1 to 2 m thick.

Crystal components are chiefly euhedral and fragmental pyroxene and feldspar, and lithic components are chiefly andesite 

lava. Locally, coherent blocks of tuffaceous sandstone and siltstone 

as much as 1 m across are found within the coarse tuff. Attitudes 

of thin-bedded strata in the type section are not consistent. Excellent outcrops on Highway 143, southwest of Barranquitas, show 

that similarly inconsistent attitudes in strata of the overlying 

Robles Formation are due to intraformational folds and slumps. 

Although proof of similar relations in the Barros Tuff Member 

is difficult owing to lack of exposures, the inconsistent attitudes 

and the blocks in the coarse tuff do suggest penecontemporaneous, 

probably marine, sliding or flowing. The inconsistent attitudes also 

made accurate measurement of thickness impossible, but a thickness of 80 to 100 m is estimated in the type section.

The thin-bedded tuffaceous sandstone and siltstone interbeds 

in the Barros Tuff Member are identical with beds in the overlying 

Robles Formation (Pease and Briggs, 1960), indicating that the 

upper contact is gradational. The basal contact appears conformable in the type section and elsewhere.
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 13

^ The character of the coarse tuff in the Barros Tuff Member 

differs somewhat from place to place. In some outcrops feldspar 

predominates over pyroxene, and the rock is more resistant to 

weathering than in the type locality, locally forming boulders; 

in others, the Barros can be classified as a crystal-vitric tuff 

composed chiefly of pyroxene and feldspar crystals and indeter-

^ minate aphanitic material interpreted as devitrified volcanic glass. 

In the latter outcrops, the Barros Tuff Member approaches olive 

gray and bears a strong resemblance to the Cotorra Tuff, a hyaloclastite or aquagene tuff that crops out in the Upper Cretaceous 

section of the same general area (Briggs, 1967). In many places, 

particularly in the southern part of the outcrop area, the thinbedded units or blocks that are in the type section are uncommon 

or absent. In the southern part of the outcrop area, the Barros 

Tuff Member may be seen grading downward into coarsely fragmental rocks typical of the Torrecilla Breccia.

( The member crops out only in the Orocovis quadrangle. It per-

, haps ranges from 0 to 120 m in thickness.

No fossils were recovered from the Barros Tuff Member, but the 

relations described below demonstrate that most likely it is Early 

Cretaceous (Albian) in age.

CONTACT RELATIONS OF THE TORRECILLA BRECCIA

Although there are no striking unconformities at the base of 

I the Torrecilla Breccia, it is plain that the contact is not grada- 

_^ tional. The Torrecilla apparently overlaps formation A and formation C in the Cayey quadrangle (Berryhill and Glover, 1960) 

! and formation J in the Comedo quadrangle (Pease and Briggs, 

1960). In the Comerio quadrangle, local angular unconformities 

were observed. In addition, the presence of the Aguas Buenas 

4 Limestone Member in the base of the Torrecilla suggests at least 

^ an hiatus in volcanism. The ages of formations A, C, and J are not 

known; they are broadly similar in character to the Torrecilla

 < Breccia, however, so there is no reason to believe there was a great

j lapse of geologic time between their deposition and the deposition

of the Torrecilla. The Torrecilla Breccia, then, rests uncon-

* formably on rocks that may not be appreciably older than the 

. r. Torrecilla.

West of Barranquitas (fig. 1), the Torrecilla Breccia and the

J Barros Tuff Member grade upward into the Robles Formation.

^ East of Barranquitas, however, the contact appears to be disconformable. On the north side of the Rio Usabon in the eastern

-v part of the Barranquitas quadrangle, the Robles Formation is

* considerably thinner than it is in adjacent areas (Briggs and

329-575 O - 69 - 2
0 14 CONTRIBUTIONS TO STRATIGRAPHY

Gelabert, 1962). This thinning may be ascribed partly to inter- < 

fingering of the upper Robles with volcanic rocks, chiefly lava, 

referred to formation L by Briggs and Gelabert (1962), but here 

reassigned to the Rio Orocovis Group. However, in this vicinity 

much of the Torrecilla Breccia has a reddish hue, and there is 

volcanic conglomerate at the top. These relations suggest that the 

Robles may have been deposited first around, then over, a hill in y 

an eroded Torrecilla terrane.

The reddish colors and absence of evidence of marine deposition 

of the upper Torrecilla over much of the eastern outcrop area 

suggest that subaerial accumulation of upper Torrecilla rocks may 

have been widespread. Moreover, the reeflike Rio Mat6n Limestone Member (Berryhill and Glover, 1960) is present in the base w 

of the Robles Formation only east of Barranquitas, suggesting 

shallow seas and perhaps a reef fringing a volcanic landmass. 

In addition, about 2 km south-southeast of Barranquitas a lens of 

jasperoid at the Robles-Torrecilla contact perhaps represents an 

ancient soil accumulation. Thus, the upper contact of the Torrecilla Breccia is conformable on the west and largely disconformable 

on the east. This suggests that the Torrecilla Breccia may be 

thicker in the west where no base is exposed than it is in the east.

AGE AND REGIONAL RELATIONS

The age of the Torrecilla Breccia is Early Cretaceous, probably 

entirely Albian; the Aguas Buenas Limestone Member in the base \ 

probably is Albian, and the overlying Robles Formation is now 

known to range from Early Cretaceous, Albian, to Late Cretaceous, 

Santonian, in age (Briggs, 1967). The previous assignment of ; 

rocks now labeled Torrecilla Breccia to the Upper Cretaceous 

System (Berryhill and others, 1960; Pease and Briggs, 1960; 

Briggs and Gelabert, 1962) was incorrect (fig. 4). V

The sparsely detailed geologic mapping and widespread intrusive 

activity and related metamorphism in areas east of the Comerio 

quadrangle make detailed correlations eastward difficult. In the ^ 

Juncos quadrangle (Broedel, 1961), immediately east of the v 

Caguas quadrangle (fig. 1), a mineralized marble unit that strikes 

east to southeast and dips steeply northward crops out within a 

metamorphosed terrane. Structural and spatial relations suggest wthat this unit is an extension of the Aguas Buenas Limestone 

Member. If this is true, the metamorphosed very thick bedded 

volcanic rocks that crop out for a few kilometers northward from ' 

the marble to the line of an extensive fault zone are laterally 

equivalent to the Torrecilla Breccia.
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 15

Strata exposed in northeastern Puerto Rico, north of this fault 

zone, include the Fajardo Formation, stated by Berryhill, Briggs, 

and Glover (1960) to be stratigraphically equivalent to the rocks 

herein named the Torrecilla Breccia. A general correlation of the 

Torrecilla Breccia with the lower part of the Fajardo Formation 

doubtless is valid, because both the Torrecilla and the lower 

Fajardo now are considered Early Cretaceous, probably Albian, 

in age. The upper Fajardo Formation, however, probably is 

equivalent to the lower Robles Formation. Although the report of 

Berryhill, Briggs, and Glover (1960) may be interpreted as 

including the Aguas Buenas Limestone Member in the base of 

the Fajardo Formation, such an assignment is rejected here. The 

Fajardo Formation crops out only in northeastern Puerto Rico, 

whereas the Aguas Buenas Limestone Member crops out only in 

east-central Puerto Rico; nowhere are they in contact.

In the western part of the Orocovis quadrangle, the Torrecilla 

Breccia and its Barros Tuff Member are concealed by younger 

strata. The overlying Robles Formation and equivalent strata, 

however, are more or less continuously exposed westward to the 

vicinity of the Utuado batholith in the Jayuya quadrangle (Mattson, 1968). Here again the base of the Robles Formation is exposed, resting on several hundred meters of moderately to highly 

metamorphosed tuff similar in many respects to the Barros Tuff 

Member. Mattson (1967) has named this occurrence the Jayuya 

Tuff. A general stratigraphic equivalence of the Jayuya Tuff and 

the Torrecilla Breccia appears fairly certain, although the lack 

of outcrop continuity in this complex area and the complete lack 

of fossil evidence preclude usage of one stratigraphic name 

throughout.

THE LOWER CRETACEOUS BARRANCAS LIMESTONE MEMBER 

OF THE MAGUEYES FORMATION, RIO OROCOVIS GROUP

The Barrancas Limestone Member of the Magueyes Formation 

is here named for Barrio Barrancas, Municipio of Barranquitas, 

Puerto Rico, where the unit is well exposed in quarries (fig. 1). 

On the geologic map of the Barranquitas quadrangle (Briggs and 

Gelabert, 1962), this unit is described as the limestone unit of 

formation L (fig. 5). The type locality is a quarry centering at 

44,170 m N., 164,110 m E., where almost 60 m of very thick bedded 

and thick-bedded medium-dark-gray to grayish-black highly fossilferous finely crystalline limestone crops out. Several meters of 

fossiliferous mudstone occur near the base. Doubtless this mudstone was very calcareous when fresh, but the outcrop has been
016 CONTRIBUTIONS TO STRATIGRAPHY

Briggs and Gelabert

(1962)-northern 

Barranquitas quadrangle

This reportnorthern 

Barranquitas 

quadrangle

Botijas Limestone 

Member

Cariblanco 

Formation?

Lava

Tuffaceous

sandstone

and siltstone

unit

Limestone 

unit

Lava

//Concealed 

///laulting y

'Concealed by// 

' /faulting vV/

Lava (possibly

tongue of 

Perchas Formation)

Barrancas 

Limestone 

Member

Torrecilla Breccia?

'/Concealed by 

'///, faulting;//

FIGURE 5. Changes in nomenclature pertaining to the Magueyes 

and Pozas Formations.

leached. Fossils in the member are chiefly rudists and gastropods,

indicating that the rocks are organic-reef or near-reef deposits.

The upper contact of the Barrancas Member is not well exposed

at the type locality, but elsewhere it is seen to be gradational over
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 17

' about 1 m into rocks labeled on the geologic map of the Barranquitas quadrangle as the tuffaceous sandstone and siltstone unit 

of formation L (Briggs and Gelabert, 1962). Nowhere is the lower 

contact of the Barrancas Limestone Member well exposed. In most 

outcrops the Barrancas dips into the lower part of the face of an 

escarpment and away from a large fault zone that contains 

strata which form a topographic lowland; talus or colluvium from 

the Barrancas and overlying rocks commonly conceal the base of 

the Barrancas. Available outcrops indicate, however, that the 

Barrancas Limestone Member rests with structural conformity 

on volcanic rocks, chiefly lavas, that were assigned to formation 

L by Briggs and Gelabert (1962).

The Barrancas Limestone Member is exposed nearly continuously for 2.2 km west and 0.9 km east of the type locality. Farther 

west it occurs sporadically at the same horizon for about 2.0 km 

and then is faulted out; to the east it also crops out sporadically at 

the same horizon for an airline distance of about 4 km through a 

o complexly faulted terrane. The thickest section in outcrop outside 

the type area is in the valley of the Rio Hondo, the easternmost 

occurrence of the member. Nowhere does the Barrancas Limestone 

Member greatly exceed 60 m in thickness.

A limestone occurrence south of the Rio Hondo that was in- 

'N eluded in the limestone unit of formation L by Briggs and Gelabert 

i (1962) here is excluded from the Barrancas Limestone Member

for reasons given later in this paper.

A

AGE

; The fauna of the Barrancas Limestone Member indicates that 

the unit is Early Cretaceous, Albian, in age (N. F. Sohl, written 

commun., 1963). Moreover, there is a strong resemblance between 

the fauna of the Barrancas Member and the fauna in the Rio 

Maton Limestone Member (Berryhill and Glover, 1960) at the 

base of the Robles Formation (Pease and Briggs, 1960) in the 

vicinity of Comerio (fig. 1), about 8 km east of the type area of 

the Barrancas Member. The Rio Maton Limestone Member, formerly considered to be of Early and Late Cretaceous age, is now 

recognized as Early Cretaceous, Albian, in age (N. F. Sohl, oral 

commun., 1967).

REGIONAL RELATIONS AND ASSIGNMENT OF THE BARRANCAS LIMESTONE 

MEMBER TO THE MAGUEYES FORMATION

At the time the geology of the Comerio and Barranquitas quadrangles was mapped (1955-58), little was known of the geology 

of areas to the north and west. To produce a geologic map that
0 18 CONTRIBUTIONS TO STRATIGRAPHY

was both consistent with the known geology and internally consistent, Pease and Briggs (1960) introduced the informal formation L in the Comerio quadrangle, and in the Barranquitas quadrangle Briggs and Gelabert (1962) carried formation L westward. 

They also tentatively correlated tuffaceous sandstone, tuff-breccia, 

and volcanic conglomerate along the northern border of the Barranquitas quadrangle with the Cariblanco Formation that is well ^ 

exposed at the south edge of the quadrangle and in the Coamo 

quadrangle (Glover, 1961) to the south (figs. 1, 2).

Later work by Berryhill (1965) in the Ciales quadrangle to the 

northwest and by Nelson (1966, 1967) in the Corozal quadrangle 

(fig. 1) to the north has shown that modification of this early 

stratigraphy is necessary.

The Rio Orocovis Formation was defined by Berryhill (1965, p. 

19-45) in the Ciales quadrangle. As originally described, the formation included the Magueyes, Perchas, and Avispa Members and 

an interfingering basalt tuff member. Nelson (1966, p. 6-11) 

raised the Rio Orocovis to group rank (fig. 5) and the members < 

to formations. He named the basalt tuff unit the Los Negros 

Formation. The Rio Orocovis Group is believed to be stratigraphically equivalent to the Robles Formation of Early to Late Cretaceous (Albian to Santonian) age (Briggs, 1967), chiefly on the 

basis of lithologic comparison.

Strata along the north edge of the Barranquitas quadrangle 

that tentatively were correlated with the Cariblanco Formation 

are now clearly part of the Magueyes Formation (Nelson, 1966, *~ 

p. 8-9). Moreover, intercalations of basalt lava are common within the tuffaceous sandstone and siltstone of the Magueyes Formation in the Corozal quadrangle (Nelson, 1967); thus, the thick ba- ^ 

salt lava unit below the supposed Cariblanco Formation and above y 

the tuffaceous sandstone and siltstone unit of formation L on the 

Barranquitas geologic map (Briggs and Gelabert, 1962) is here 

included in the Rio Orocovis Group (fig. 5). It is either part of the } 

Magueyes Formation or possibly a tongue of the Perchas Formation. The tuffaceous sandstone and siltstone unit of formation L, 

below this lava tongue, falls logically within the Magueyes Formation and rests on the Barrancas Limestone Member. The Barrancas Limestone Member here is assigned to the Magueyes Formation and is tentatively identified as the basal unit of the )» 

formation. If this assignment is correct, the base of the Magueyes 

is exposed only in the Barranquitas quadrangle (fig. 5); if the 

Barrancas Member is not considered the base, no exposures of the y 

base of the Magueyes Formation are known.
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 19

Strata beneath the Barrancas Limestone Member also were assigned to formation L by Briggs and Gelabert (1962). Tentatively, 

these rocks now are considered correlative with the upper part of 

the Torrecilla Breccia (fig. 5).

Other rocks formerly included in formation L also are reassigned, and formation L is abandoned. Basalt lava and related 

rocks north of the Quebrada Vicente fault in the northeastern 

part of the Barranquitas quadrangle and northwestern part of 

the Comerio quadrangle are part of the Perchas Formation; the 

correlation of similar rocks south of the Quebrada Vicente fault 

and north of a west-northwest-trending fault through the northeastern Barranquitas quadrangle (Briggs and Gelabert, 1962) is 

less certain, but the rocks are certainly of the Rio Orocovis Group 

and probably of the Perchas Formation. Former formation 

L strata south of the Damian Arriba-Quebrada Vicente fault continuum now are included in the Rio Orocovis Group, probably in 

the Perchas Formation and perhaps equivalent in the upper part 

to the Avispa Formation (fig. 2).

The limestone lens south of the Rio Hondo that was formerly 

assigned to the "limestone unit of Formation L" (Briggs and 

Gelabert, 1962) is excluded from the Barrancas Limestone Member for several reasons. The Barrancas Limestone Member of the 

Magueyes Formation here is correlated with the Rio Maton Limestone Member at the base of the Robles Formation. The limestone 

lens south of the Rio Hondo therefore no longer can be correlated 

with the Barrancas Member, for it overlies a part of the Robles 

as well as strata now considered a part of the Rio Orocovis Group. 

The original correlation was made by lithologic comparison; no 

fossil evidence is available on the age of this limestone lens.

THE RIO BAUTA, BOTIJAS LIMESTONE, AND REVES MEMBERS 

OF THE UPPER CRETACEOUS POZAS FORMATION

The Pozas Formation first was described by Berryhill (1965, 

p. 49-61), in the Ciales quadrangle (fig. 1). There and in the 

Florida quadrangle (Nelson and Monroe, 1966) to the west, the 

Pozas consists of more than 2,000 m of tuff, volcanic breccia, 

conglomerate, lava, limestone, and related rocks, resting on the 

volcaniclastic Manicaboa Formation (figs. 2, 6). Faulting obscures 

the upper contact.

The Minguillo Lava Member, which is 300 m thick, is the basal 

unit of the Pozas in northern exposures in the Ciales and Florida 

quadrangles. It is overlain by the Blacho Tuff Member, a unit 

about 500 m thick that contains resistant ash-flow lenses. In
020 CONTRIBUTIONS TO STRATIGRAPHY

g

S BUCho 

E Tuff 

° Member j

» RibBauta - 

° Member

Rib Orocovis

Group undivided

Fault, contact

^15^£~3%?fi$ * "^iL~~ -:- :-'

*; rxij^

Concealed " » , £ ?

 X V X*X

Flor He Alba 

Limestone

> Lentil

Blacho Tuff 

} Member 

' Miniuillo

Lava Member

Manicaboa For

Rib Orocovis G

undivided

B A'

i

f or de Alba

Limestone 

Lentil <

Blacho Tuft

Member {

Minguillo Lava 

Member

Minicaboa 

Formation '

3 Orocovis Group

undivided

Fault contact

|

§

1

1

mation

oup

^?

<kv ^

Av

v^

"*

^)

^

"~^tl.

' ' 

^x

0°

0

c/*

"*' «»

, '0 10 20

Fault contact

_-|^^tcr*^^?pi;

A'llO-* " '' ^

*;'.'. ','; ^Eroded Fault contact

', . , ^.i >-/./-'.'%'-.

* ^ * ^L&??f_ J

Concealed r - - '--^

* - y.'-r J v - Co

" Y ^* ' ' ^"*"

»*y/y

ncealed

> Botijas 

Limestone

Member

IB H J

!H*n7'1

30 KILOMETERS

o

j

g

s METERS

- JOOO

- 2500

- 2000 

- 1500

- 1000

- 500

L 0

EXPLANATION

Limestone 

Tuff

Calcareous volcanic 

landstone and siltstone

Conglomerate

Lava,tuff,and

FIGURE 6. Facies changes in the Pozas Formation. Map shows approximate

location of sections.

outcrops in the southern parts of these quadrangles, the Minguillo 

Member is absent and the Blacho Tuff Member is at the base of 

the Pozas (fig. 6, section A-A").

The bulk of the Pozas overlying the Blacho Member is referred 

to informally by Berryhill as the upper breccia member. The top 

of this member is not exposed. Within the upper breccia member, 

about 600 m above the top of the Blacho Member, is the Flor de 

Alba Limestone Lentil (Nelson and Monroe, 1966, p. C10-C12), 

a lenticular limestone reef that is locally more than 200 m thick 

(fig. 6, section B-B') . Other thinner and less extensive limestone 

lenses also are found within the upper breccia member.

Strata now assigned to the Pozas Formation in the Ciales quadrangle formerly were assigned to the Coamo Formation of 

southern Puerto Rico (Berryhill, 1961; 1965, p. 49). Similar rocks 

exposed in' a narrow graben in the northwestern part of the Barranquitas quadrangle (Briggs and Gelabert, 1962) were also 

assigned to the Coamo. Recent geologic mapping by the writer 

of this paper in the intervening Orocovis quadrangle has demonV 

i 
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 21

strated that the Pozas of the Ciales quadrangle is continuous with 

the so-called Coamo of the Barranquitas quadrangle. The strata 

in the northwestern Barranquitas quadrangle formerly assigned 

to the Coamo Formation therefore are reassigned to the Pozas 

Formation (figs. 2, 5).

RIO BAUTA MEMBER

Calcareous mudstone, siltstone, and sandstone, conglomerate, 

and limestone that crop out in a narrow discontinuous westtrending band from the north-central to northwestern section of 

the Orocovis quadrangle are here named the Rio Bauta Member 

of the Pozas Formation for exposures in the valley of the Rio 

Bauta, a tributary of the Rio Grande de Manati (fig. 1). The type 

section is along an unpaved road that runs west-northwest downhill into the Rio Matrullas drainage from the saddle that forms 

the lowest point on the divide between the Rio Matrullas and 

the drainage basin of the Rio Bauta. The base of this section is at 

45,420 m N., 147,460 m E. and the top is at 45,200 m N., 147,970 

m E. The member also is well exposed along Highway 157 between 

45,050 m N., 148,660 m E. and 44,870 m N., 149,540 m E., and 

limestone lenses within the member crop out on Highway 157 in 

the vicinities of 44,820 m N., 150,730 m E. and 45,170 m N., 

152,850 m E.

The outcrop of the Rio Bauta Member is restricted to a structurally complex zone on the north side of the Damian Arriba fault 

(Berryhill, 1965; Nelson and Monroe, 1966). There it forms the 

base of the Pozas Formation and is overlain by the Blacho Tuff 

Member (fig. 6, section A-A"). The Rio Bauta Member rests with 

sharp unconformity on volcanic rocks, largely lava, of the Rio 

Orocovis Group. Elsewhere, the Rio Orocovis has been extensively 

subdivided (Berryhill, 1965; Nelson, 1967). In the type area of 

the Rio Bauta Member, however, almost all rock types characteristic of the Rio Orocovis Group are exposed within an extensively 

faulted and rather small and isolated area; thus, no reliable correlation with subordinate units within the Rio Orocovis is possible, 

and that group has not been subdivided here.

The contact of the Rio Bauta Member with the overlying Blacho 

Tuff Member is gradational. In the upper few meters of the Rio 

Bauta Member, medium to thick beds of noncalcareous dull-
0 22 CONTRIBUTIONS TO STRATIGRAPHY

grayish-red to dusky-red-purple mudstone and tuff characteristic 

of the Blacho Member are interlayered with calcareous beds more 

typical of the Rio Bauta Member. The contact is drawn at the top 

of the highest calcareous bed.

The Rio Bauta Member is about 100 m thick. In the type section, the base is composed of about 10 m of grayish- to dusky-red 

conglomerate, in which clasts of basalt and andesite lava typical 

of the Rio Orocovis Group are as much as 40 cm long. Most clasts 

are subround, but a few are segments of polygonal columns of 

andesite lava. The matrix of the conglomerate is clayey volcanic 

sandstone. This basal part of the Rio Bauta Member is well 

exposed only in the type section.

The bulk of the member is composed of .dark-gray, bluish-gray, 

and grayish-brown thin- and medium-bedded calcareous volcanic 

sandstone, siltstone, and mudstone; locally it contains an abundant 

gastropod fauna in addition to other fossils. East of the type 

section, discontinuous dark-gray limestone lenses are found; in 

the easternmost outcrops, one faulted lens of limestone may be 

more than 10 m thick.

The Rio Bauta Member is included in the Pozas Formation 

because of its gradational relationship with the overlying Blacho 

Tuff Member and because calcareous units, for example the Flor 

de Alba Limestone Lentil, are a characteristic of the Pozas despite 

its predominantly noncalcareous nature.

CORRELATION OF THE RIO BAUTA MEMBER WITH STRATA TO THE NORTH

In the type area of the Rio Bauta Member, the basal Pozas dips 

northward beneath younger strata on the south flank of a minor 

syncline. About 4 km north, in the Ciales quadrangle, the north 

flank of the syncline again exposes the base of the Pozas Formation (fig. 2), but there Berryhill (1965) placed the base of the 

Pozas Formation at the bottom of the Blacho Tuff Member. The 

Rio Bauta Member was not mapped, and the Pozas is shown resting on the Manicaboa Formation, which is more than 2,000 m 

thick and rests in turn on the Rio Orocovis Group (fig. 6). 

According to Berryhill (1965, p. 46, 49), the Pozas-Manicaboa 

contact is conformable except in the vicinity of Capilla del Carmen 

in the Ciales quadrangle, where he reported an angular discordance. Artificial exposures made since Berryhill mapped the area 

indicate that the apparent discordance there resulted from relatively minor, previously undiscovered faulting; the Pozas-Manicaboa contact is conformable throughout.
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 23

Berryhill concluded that the upper Manicaboa was deposited in 

shallow water, whereas the lower Manicaboa was laid down in 

deeper seas. He further noted that pebbles, cobbles, and waterworn boulders were widespread in the upper Manicaboa (Berryhill, 1965, p. 48). The uppermost strata in the Manicaboa in the 

vicinity of Capilla del Carmen are calcareous sandstone and siltstone similar to the predominant rock types in the Rio Bauta 

Member, but no conglomerate was seen in the upper 300 m of the 

Manicaboa Formation in this area.

The Rio Bauta Member of the Pozas Formation plainly is 

equivalent stratigraphically to a presently unknown part of the 

upper Manicaboa Formation, though no fossils have been recovered from the upper Manicaboa. Both units are overlain conformably by the Blacho Tuff Member of the Pozas Formation 

(except toward the north where the Minguillo Lava Member of 

the Pozas intervenes), and the Rio Bauta Member and the uppermost Manicaboa Formation are similar lithologically.

On the other hand, the Rio Bauta Member cannot be correlated 

with the entire Manicaboa Formation, for coarse tuff and volcanic 

breccia are among the principal constituents of the Manicaboa 

(Berryhill, 1965, p. 46), and these rock types are not present in 

the Rio Bauta Member. Moreover, rocks similar to those in the 

lower Manicaboa occur within the Rio Orocovis Group (Berryhill, 

1965, p. 45; Nelson, 1966, p. C8-C9); the lower Manicaboa intertongues with strata of the Rio Orocovis Group (Berryhill, 1965, 

p. 46), whereas the Rio Bauta Member rests on eroded Rio Orocovis strata.

It seems that either the unconformity at the base of the Rio 

Bauta Member has no counterpart in the Manicaboa Formation 

only 4 km to the north, or an equivalent unconformity is present 

in the middle or upper Manicaboa section but has been overlooked 

in the generally sparse and discontinuous exposures of the area 

(fig. 6, section A-A").

BOTIJAS LIMESTONE MEMBER

The Botijas Limestone Member of the Coamo Formation was 

first described by Briggs and Gelabert (1962) in the Barranquitas 

quadrangle. As stated above, the assignment of strata in the 

northwestern Barranquitas quadrangle, including the Botijas 

Limestone Member, to the Coamo Formation has since been found 

erroneous; the Botijas Member is here reassigned to the Pozas 

Formation (fig. 5). Otherwise the description remains unchanged.
0 24 CONTRIBUTIONS TO STRATIGRAPHY

REVES MEMBER

This unit was first described by Briggs and Gelabert (1962) 

as the La Reves Member of the Coamo Formation; a printing 

error caused it to appear on the explanation of the geologic map 

as the El Reves Member. For simplicity the name of this member 

is here shortened to the Reves Member, and the unit is reassigned 

to the Pozas Formation (fig. 5), for reasons stated above. The 

description is otherwise unchanged.

AGE OF AND CORRELATIONS WITHIN THE POZAS FORMATION

The age of the Pozas Formation was defined broadly in the 

Ciales and Florida quadrangle reports. Chief evidence was from 

the Flor de Alba Limestone Lentil, which was cited as Late Cretaceous, Campanian and (or) Maestrichtian, in age (Nelson and 

Monroe, 1966, p. C12). In other studies of collections from the 

Flor de Alba Limestone Lentil, this age range has been determined 

to be late Campanian to early Maestrichtian (N. F. Sohl, written 

commun., 1965).

Extensive fossil collections have been made from the Rio Bauta 

Member by Sohl. On the basis of preliminary studies, he has 

concluded that collections from the Rio Bauta Member are Late 

Cretaceous, late Santonian through Campanian, in age. Further 

work suggests an assignment of early Campanian or perhaps 

latest Santonian age (N. F. Sohl, written commun., 1965).

The Botijas Limestone Member was assigned provisionally to 

the Upper Cretaceous Series, the Maestrichtian Stage, by Sohl 

(Briggs and Gelabert, 1962). More recent studies confirm this 

assignment (N. F. Sohl, written commun., 1965). The Reves 

Member of the Pozas Formation also is Late Cretaceous, Maestrichtian, in age (Briggs and Gelabert, 1962).

No other units within the Pozas Formation have yielded diagnostic fossil collections.

In summary, ages of fossil-bearing units in the Pozas Formation 

are as follows (from oldest to youngest) : (1) Rio Bauta Member, 

late Santonian to late Campanian, probably early Campanian, 

possibly latest Santonian, (2) Flor de Alba Limestone Lentil, 

late Campanian to early Maestrichtian, (3) Botijas Limestone 

Member, Maestrichtian, and (4) Reves Member, Maestrichtian. 

Therefore, the Pozas Formation is Late Cretaceous in age, ranging 

from late Santonian to Maestrichtian, more likely early Campanian 

to Maestrichtian.

The Rio Bauta Member, 100 m thick, is the oldest unit in the 

Pozas Formation. It is correlated with the upper part of the 

Manicaboa Formation, and the Minguillo Lava and Blacho Tuff
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 25

Members in the Ciales quadrangle both rest on the Manicaboa 

Formation (Berryhill, 1965). The Minguillo Lava Member, 0 to 

300 m thick, is overlain by the Blacho Tuff Member, which is 

500 m thick in the type area. Berryhill does not state whether the 

Blacho Member is thicker or thinner where it rests on the Minguillo Member than it is to the south where it rests directly on 

the Manicaboa Formation, but a cross section seems to indicate 

a rather constant thickness for the Blacho Member in the Ciales 

quadrangle (Berryhill, 1965, pi. 3, section A-A). However, recent 

work by the writer of this paper indicates that the Blacho Tuff 

Member is at least 700 m thick in the vicinity of the boundary 

between the Orocovis and Ciales quadrangles. An interpretation 

of the relations between these three members of the Pozas Formation and the Manicaboa Formation is shown in figure 6.

The Flor de Alba Limestone Lentil, 0 to 200 m thick, occurs 

within the upper breccia member of the Pozas in the Florida and 

Ciales quadrangles, about 600 m above the Blacho Tuff Member 

and about 800 m below the uppermost exposed Pozas strata 

(Nelson and Monroe, 1966).

The Botijas Limestone Member and the overlying Reves Member 

both occur in the upper part of the Pozas Formation. They crop 

out only in the Orocovis and Barranquitas quadrangles, where 

they generally range from 100 to 350 m in aggregate thickness. 

Faulting has made it impossible to measure the full stratigraphic 

interval between the Blacho Tuff Member and the Botijas Member, 

but at least 450 m of upper Pozas is exposed beneath the Botijas 

Member. About 500 m of Pozas is exposed above the Reves Member, but, as is the case in the Florida quadrangle to the west, 

the top of the Pozas is cut out by faulting (Briggs and Gelabert, 

1962).

In the Florida, Ciales, and northwestern Orocovis quadrangles, 

nearly continuous exposures show that the Pozas Formation is 

2,000 m or more thick and that the top of the formation is missing. 

About 1,200 m of this section (the Flor de Alba Lentil and subjacent rocks) is known to be older than the Botijas and Reves 

Members and superjacent rocks of the Pozas to the east, which 

may total more than 850 m in thickness.

Thus, if none of the Pozas strata exposed above the Flor de 

Alba Lentil in the Florida quadrangle are as young as the Botijas 

Limestone Member, the total thickness of the exposed Pozas strata 

is about 2,850 m. However, such a straight summation of thicknesses may be misleading owing to the well-known lenticularity 

of volcanic strata. An interpretation of relations in the upper 

Pozas is included in figure 6 (section B-B').
026 CONTRIBUTIONS TO STRATIGRAPHY

THE TOYOSA MEMBER OF THE UPPER CRETACEOUS 

MARAVILLAS FORMATION

The Maravillas Formation was described by Mattson (1967, 

p. 16-18) in the Jayuya quadrangle as a moderately thick unit of 

feldspar-hornblende crystal tuff and thin-bedded calcareous tuffaceous sandstone that locally contains lenses of limestone.

In the Coamo quadrangle, Glover (1961) described a homogeneous unit of similar crystal tuff at the base of the Coamo 

Formation which he named the San Diego Lapilli Tuff Member. 

Overlying the San Diego Member, or separated from it by a few 

meters of tuffaceous sandstone, is the Santa Ana Limestone Member, a lenticular unit of gray finely crystalline limestone. Below 

the San Diego Lapilli Tuff Member is a discontinuous limestone 

unit, named the Sabana Hoyos Limestone Member of the Cariblanco Formation (Glover, 1961).

Recent mapping by the writer of this paper in the Orocovis 

quadrangle, between the Jayuya and Coamo quadrangles, has 

demonstrated that the San Diego Lapilli Tuff Member (now called 

San Diego Member, Glover, 1969) is traceable into and forms the 

bulk of the Maravillas Formation (fig. 7). Moreover, the Sabana 

Hoyos Member also has been traced across the Orocovis quadrangle into the Maravillas Formation, and strata considered by 

the writer to be generally equivalent to the Santa Ana Member 

are similarly traceable. Glover (1969) has accepted this correlation, has redefined the Coamo Formation to include only rocks 

overlying the Santa Ana Limestone Member, and has restricted 

the Cariblanco Formation to rocks beneath the Sabana Hoyos 

Limestone Member. In the Coamo area the Maravillas Formation, 

including the Sabana Hoyos, San Diego, and Santa Ana Members, 

now is recognized between the Cariblanco and Coamo Formations 

(fig. 2).

WNW

Mattson (1967)-

Jayuya quadrangle

(present usage)

This reportOrocovis quadrangle

(present usage)

ESE

Glover (1969)-

Coamo quadrangle

(present usage)

FIGURE 7. Regional variations in the Maravillas Formation.
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 27

The Santa Ana Limestone Member as defined by Glover (1961) 

is composed chiefly of crystalline limestone; in the Coamo area the 

relatively minor occurrences of calcareous tuffaceous sandstone 

that are found beneath the Santa Ana Member or in positions 

stratigraphically equivalent to this member were not included in 

the Santa Ana Member by Glover (fig. 7). In the Orocovis quadrangle, however, the proportions of rock types in this stratigraphic 

interval are different; calcareous tuffaceous sandstone and tuffaceous calcarenite are found to form sections as much as 350 m 

thick, and the limestone lenses that typify the Santa Ana Limestone 

Member are absent in much of the area and are only a rather 

small part of the overall calcareous section where they do occur. 

The restrictive description of the Santa Ana Limestone Member 

does not allow extension of this stratigraphic name to the Orocovis 

quadrangle occurrences. Instead, a new name, the Toyosa Member, 

is here applied to these beds (fig. 7).

TOYOSA MEMBER

The Toyosa Member of the Maravillas Formation is here named 

for Montes la Toyosa, a hill slightly less than 700 m in elevation 

in the south-central part of the Orocovis quadrangle, centering 

about 6.8 km east-northeast of the town of Villalba (fig. 1). The 

Toyosa Member is exposed intermittently over the top and south 

flank of Montes la Toyosa and in the Rio Toa Vaca along the 

southeastern and southern sides of the hill; however, the most 

accessible continuous exposures of the Toyosa Member are about 

2.8 km west of Montes la Toyosa, along Highway 111 from about 

34,460 m N., 149,370 m E. eastward to the junction of Highways 

111 and 553, then southward along Highway 553 to 33,820 m N., 

150,000 m E. This series of exposures is designated the type 

section.

In the type section, sharply defined thin to medium beds of 

calcareous tuffaceous sandstone and siltstone composed largely 

of feldspar grains in the lower part grade upward into medium 

and thick beds of similarly composed calcareous tuffaceous sandstone that have graded bedding and both sharp and gradational 

bedding contacts. Locally, fine calcareous breccia that contains 

fragments composed of finer tuff is interleaved with the sandstone. 

Some beds in the lower and middle parts of the section are more 

calcareous than others; these might well be described as tuffaceous 

calcarenite and, rarely, calcilutite. Where fresh, the rocks are 

medium gray to dark bluish gray, but strata in the upper part 

of the type section have been leached of most calcite, and beds 

commonly are grayish and yellowish brown.
0 28 CONTRIBUTIONS TO STRATIGRAPHY

Similar rocks form major parts of the Toyosa Member elsewhere; variants are the thin- to medium-bedded calcarenite that 

forms a slabby cover over part of the south slope of Montes la 

Toyosa and thick and very thick lenses of medium-gray, rather 

pure, finely crystalline limestone, such as that forming the walls 

of the Rio Toa Vaca water gap southwest of Montes la Toyosa. ,

In the type section, the Toyosa Member of the Maravillas Formation is overlain conformably but rather sharply by commonly 

dark-red and dusky-red-purple very thick and thick volcanic 

strata of the Coamo Formation. The lower contact of the Toyosa 

Member is not well exposed in the type section. Although the 

underlying San Diego Member most commonly is noncalcareous, v 

its upper part locally contains calcareous beds; the water-laid, but 

chiefly unreworked, crystal tuff of the San Diego Member appears 

to grade into the probably somewhat reworked tuffaceous sandstone of the Toyosa Member. In mapping, the contact commonly 

was drawn at the top of the highest bed that bears conspicuous 

quantities of the hornblende crystals which are characteristic of y 

the San Diego Member.

Fragments in the Toyosa Member commonly are so fine that 

recognizable fossils have been recovered from only a few localities. 

In the type section, however, fossils indicate that the Toyosa 

Member is Late Cretaceous in age, probably Campanian and 

possibly ranging into the Maestrichtian (N. F. Sohl, written v 

commun., 1965; Kauffman, 1964).

The lithologic changes, from strata typical of the Santa Ana 

Limestone Member in the Coamo area west-northwest to the 

Toyosa Member in the Orocovis quadrangle and the undivided 

Maravillas Formation in the Jayuya quadrangle (Mattson, 1968), A 

are gradational, and placing the site of these changes is an arbi- > 

trary matter. The Toyosa Member of the Maravillas Formation 

therefore has been mapped only in the Orocovis quadrangle, where 

it is well exposed and well defined (fig. 7). In the Coamo area this ) 

part of the section has a different character, and in the Jayuya 

quadrangle limited exposures precluded mapping the Toyosa 

Member separately from the bulk of the Maravillas Formation.

Strata assigned to the Toyosa Member generally range from 

40 to 350 m in thickness, and the thickest section is south of 

Montes la Toyosa. In the vicinity of the type section the Toyosa 

Member generally ranges from 80 to 150 m in thickness.

SUMMARY

Present changes in the stratigraphic nomenclature of east-central Puerto Rico may be summarized as follows:
STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 29

1. The Lower Cretaceous Torrecilla Breccia is formally established, replacing the informally described formation D, 

fomation K, and pre-Robles rocks in the Cayey, Comerio, 

and Barranquitas quadrangles, respectively. The Torrecilla 

Breccia is carried west into the Orocovis quadrangle and 

correlated with the Jayuya Tuff in the Jayuya quadrangle. 

The Aguas Buenas Limestone Member is redescribed and 

assigned to the base of the Torrecilla Breccia, and the 

Barros Tuff Member is described as occurring locally within 

the top of the Torrecilla Breccia (fig. 4).

2. The Lower Cretaceous Barrancas Limestone Member of the 

Magueyes Formation, Rio Orocovis Group, is described; thus 

a formal name is given to the "limestone unit" of formation 

L in the Barranquitas quadrangle. Strata formerly included 

in formation L and the Cariblanco Formation in the northern 

Barranquitas quadrangle are reassigned, chiefly to formations of the Rio Orocovis Group; however, formation L strata 

underlying the Barrancas Limestone Member probably are 

stratigraphically equivalent to the Torrecilla Breccia (fig. 5).

3. The Rio Bauta Member is described as the oldest unit of the 

Upper Cretaceous Pozas Formation. The Botijas Limestone 

Member and Reves Member, previously included within the 

Coamo Formation, are reassigned to the Pozas Formation 

(fig. 5).

4. The Toyosa Member is described as the topmost unit of the 

Upper Cretaceous Maravillas Formation (fig. 7) in the 

Orocovis quadrangle.

With these changes, the Upper Cretaceous strata of east-central 

Puerto Rico are wholly contained in a series of consistent formal 

sequences, facilitating future discussion. The Lower Cretaceous 

stratigraphic nomenclature is still incomplete because the rocks 

stratigraphically beneath the Torrecilla Breccia are not now sufficiently well known to permit more than tentative classification.

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0 30 CONTRIBUTIONS TO STRATIGRAPHY

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STRATIGRAPHIC NOMENCLATURE, PUERTO RICO 0 31

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U. S. GOVERNMENT PRINTING OFFICE : 1969 O - 329-S75