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PALEONTOLOGY

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BULLETINS

OF

AMERICAN PALEONTOLOGY

VOL. XXXVIII

1957-1958

Paleontological Research Institution Ithaca, New York U.S. A;

ZANTHSON SS |

S FEB 4 4959 LIBRARN

os we

CONTENTS OF VOLUME XXXVII

Bulletin No.

165.

166.

167.

168.

169.

170.

171.

174.

Notes on the Cabo Blanco Area, Venezuela ByaNosmampiss W CIS ponding 90... e-toc eco

Variation in American Oligocene Species of Lepidocyelina IBA NSIS HIG) 8S) 1 G16) Fears nine ee Re

The Ostracoda of the Yorktown Formation in the York-James Peninsula of Virginia (With notes on the collections made by Denise Mongin from the area)

ByejamesmOeMicikecaniee... a0) ee aan, re LS

Stratigraphy of the New Providence Formation (Mississippian) in Jefferson and Bullitt Counties, Kentueky, and fauna of the Coral Ridge member

By aines By COBRIG Cia. :. 2- cc .ctilioesadhikec

Springvaleia, a Late Miocene Xenophora-like Turritellid from Trinidad

BVA ba Doe WiOOURIN Oar teeny cerca sees eae

Names and Variation in Certain Larger Foram- inifera—No. 1 BYR Wee SLOLES COC oo. is scheint eeeeeise

Larger Foraminifera from Carriacou, British West Indies Esyap Wee LOLI Si @OLGt ace tees Ort A ecane ee etter

2. New Mollusks from Tropical West America

By A. Myra Keen ...... ORE Te ee EN er eS

Names of and Variation in Certain American Larger Foraminifera—No. 2 Bie WS LOLES GON Crees, nss ee: crateeetnee tenses see

The American Species of Asterophyllites, Annularia, and Spenophyllum

[BS yieh, bot Sam Un 2\| 9] 06) | ema ke Ee eee

The Geology of Carriacou Bye Penile arbi ayer. cerns. c-k-cneeenesretensees scene:

Names of and Variation in Certain American Larger Foraminifera, Particularly the Discocylinids—No. 3 YEW AS COLIS COLE). wig ae Ae ee en ents

Plates

13-16

17

18-25

32-34

50-53

26- 51

52-103

104-157

158-174

175-213

214-233

234-255

256-284

285-390

391-405

406-430 431-448

BWHEE TINS °

OF

~ AMERICAN PALEONTOLOGY

* VOU RXXVIE * | Zeus UNys PN NUMBER 165 / he ' PRIZ 1957 yp SUIBRARY Lod? 1957 bias opie

Paleontological Research Institution Ithaca, New York ULSi/A:

PALEONTOLOGICAL RESEARCH INSTITUTION

1955-56 PRESENT) Se i oe ene oa lak 3) Webs tar SoLomMon C. HOLLISTER VICE-PRESIDENT | <.s:.th Js. oc ores OY es Sa eae CO NORMAN E. WEISBORD SECRETARY-“BREASURER’ Je. ape ee) et eee) REBECCA §., HARRIS DIRECTOR’. =. .cc0No. SUR Cha a Oe hee ea res KATHERINE V, W. PALMER COBRINSEES OS Noh Ne be 0 2 eI 36 ee Ea ARMAND L. ADAMs Trustees KENNETH E. CASTER: (1954-1960) KATHERINE V. W. PALMER (Life) W. Storrs Core \(1952+58) ‘Ratpo A. Lippte (1950-56) WInIFRED GOLDRING (1955-1961) AXEL A. OLsson (Life) Repecca S. Harris (Life) NorMAN E. WEIsBorp (1951-57)

SoLoMON C, HOoLuisTER (1953-59)

BULLETINS OF AMERICAN PALEONTOLOGY and

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KATHERINE V. W. PALMER, Editor Lempi H. SINCEBAUGH, Secretary

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BULLETINS OF AMERICAN PALEONTOLOGY

Vol. 38

No. 165

NOTES ON THE GEOLOGY OF THE CABO BLANCO AREA, VENEZUELA

By Norman E. Weisbord

Research Associate in Geology The Florida State University

March 15, 1957

Paleontological Research Institution Ithaca, New York, U.S.A.

Library of Congress Catalog Card Number: GS 57-301

Printed in the United States of America

TABLE OF CONTENTS

Page

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Abisinta: fotmatiOmi.s3..cces-oscsoss eee ee 20 Occurrence \)..oc sos. hemes be reno eee 20 Description: 0:85: staeonts cinch. Wane gy tee ean ee 20 Stratigraphic relations: «......::..: 0.000 y nee 21 ABE oo cececscoissnaes pevtdeer stevia atime eae oe er 21

FREGERE adie ces cs eaicigeiee be Nes Sisega rt bees ee Oe Se re ee De SERUGHITECL eco tee a ae a ee ae, Bt eee 22 Geologic HIstOry s2..10-0/...-s0teks.. Stuaten steer eet hehe oo 24 References cited... ioc he ee 25

NOTES ON THE GEOLOGY OF THE CABO BLANCO AREA, VENEZUELA

NorRMAN E. WEISBORD

Research Associate in Geology The Florida State University

ABSTRACT

This paper describes the Tertiary and Quaternary sediments of the Cabo Blanco area and discusses briefly their structural involvement and geologic history. Two new names, Catia and Maiquetia, are proposed as members or facies differ- entiates of the Playa Grande formation, and a new formation name, the Abisinia, is proposed for Quaternary deposits immediately pre-dating the Recent ones.

INTRODUCTION

Cabo Blanco is a small, low-lying cape fronting the Caribbean Sea 15 kilometers (9 miles) northwest of Caracas, Venezuela. Just south of the cape, and extending parallel with the shore in an east-west direction, are a series of hills composed of Tertiary and Quaternary sediments to which the name Cabo Blanco was first applied by Humboldt in 1801 and which are still so designated (under the classification of group) by present-day geologists. The oldest formation of the group is not fos- siliferous but several of the younger formations are, and some of the fossils contained in one or another of the younger formations have been mentioned or described by a number of writers ever since the publication of Humboldt’s “Relation historique du voyages aux régions equinoxi- ales du Nouveau Continent” in 1814-1825. It seems, however, that the fossils from a particular locality or formation have been determined as one age by some authors and a different one by others, whereas converse- ly, an identical age has been assigned in some instances to formations oc- cupying widely different positions in the stratigraphic column. Geolo- gists in Venezuela have long been aware of these conflicting interpre- tations. As a preliminary step in resolving the problems, the Cabo Blanco area was mapped in 1947-1948 by Gabriel Dengo (1953) and then in more detail in 1954 by professors and students of the Department cf Geology and Mines, Central University of Venezuela. The results

MAR 9209 40r9

6 BULLETIN 165

of the latter work are contained in a student thesis, parts of which have been summarized in the ‘“Léxico Estratigrafico de Venezuela’’ (1956) by Prof. Royo y Gomez (Cuaternario en Venezuela, p. 199-209) and Prof. Frances de Rivero (Cabo Blanco, Grupo, p. 116-121). A geologic and topographic contour map!, scale 1:5,000, accompanies the thesis, and it is that informative map, revised to accord with this writer's ob- servations, which appears in the present paper. Since the whole of the area shown was surveyed by the writer with pace and compass only, the planimetry of the map presented is of limited accuracy even though all traverses were adjusted to certain points previously established on the thesis map.

In 1955 and 1956, the writer spent a number of weekends mapping the geology of the Cabo Blanco area, and in this paper the results of the investigation are discussed. My remarks are based on independent field work, but I have been guided by the contributions of my predecessors, especially those affiliated with the Central University of Venezuela, who are to be commended for doing a job that had to be done and in doing it well. I also wish to thank the Socony Mobil Oil Company de Vene- zuela for permission to publish this article.

GENERAL REMARKS

The area discussed in this paper lies north and west of the Mat- quetia airfield which is 19 kilometers (11.5 miles) by road from the out- skirts of Caracas. South of the airfield is the Cordillera de La Costa, or Venezuelan Coast Range, which is composed for the most part of met- amorphic rocks and attains a maximum elevation at Pico Naiguata of 2,765 meters (9,072 feet). As shown on the geologic map by Dengo (1953), the seaward flank of the metamorphics is fringed by Tertiary and Quaternary deposits, and these comprise the terrain around Cabo Blanco from which locality they extend westward toward Catia La Mar, and eastward toward Maiquetia. The maximum width of this belt is only 2.4 kilometers, but this small area cradles such a wealth of geologic phe- nomena that it may harbor the key for unraveling the late Cenozoic his- tory of northern Venezuela. For example, the attitudes of the strata and

1Mapa Geoldgico-Topografico del Area de Cabo Blanco, 1954. The authors’ names appearing on the map are: A. Alarcon, C. Alcantara, P. Gamboa Bauza, A. Menendez, J. V. Solis, and M. Tello Campodonico.

GEOLOGY CABO BLANCO, VENEZUELA: WEISBORD i

the unconformities between formations suggest several periods of move- ment and erosion since mid-Tertiary time, while the character of the sedi- ments indicates deposition in nonmarine, paralic, and marine environ- ments during the intervals of their accumulation. The ages of the forma- tions should eventually be determinable from a study of the fossils (now being undertaken by the writer), and the chronology of tectonic events should be deducible from a detailed investigation of the folds and faults. The faults noted seem to be of a normal, reverse, and strike-slip variety, and the latest of them may well have developed in Quaternary time. Finally, the slightly inclined terraces at successively lower levels document the process of marine abrasion and of differential uplift or eustatic change during Pleistocene and Recent times.

TOPOGRAPHY AND DRAINAGE

Topographically, the most dominant features of the Cabo Blanco area are the hills paralleling the coast and the terraces at Playa Grande and the Maiquetia airfield. The Maiquetia airfield, at an elevation of some 35 meters (115 feet)?, is built on a plain composed of outwash from the mountains. As pointed out by Royo y Gomez (1956, p. 200), the plain seems to have originated through aggradation of the piedmont and by scour and fill of the sea before the terraced surface attained its present elevation. A higher and somewhat older terrace is present at the village of Playa Grande. At the east end of the village, the terrace surface has an elevation of about 62 meters (203 feet), and the red, sandy and gravelly clay composing the terrace contains occasional large corals and some small gastropods which resemble those inhabiting the strand today. Thus, the Playa Grande terrace is of marine origin and was probably developed in the Pleistocene. Still older but smaller ter- races are present at levels between 80 and 110 meters (262 and 361 feet) south and east of Playa Grande, while the oldest and highest terrace may be represented by the small gravelled surface 135 meters (443 feet) above sea level on which the Cabo Blanco lighthouse is situated. The youngest marine terraces are displayed along the present seashore. The coast road here and there follows an elevated beach some 3 to 5 meters above sea level, while the lowest and most recent bench is just awash of

2All elevations mentioned are from the Mapa Geoldgico-Topografico del Area de Cabo Blanco, 1954.

8 BULLETIN 165

high tide. This bench consists of conglomerates (containing occasional Recent shells) and is being formed through the cementation of present- day beach debris.

The largest stream in the Cabo Blanco area is Quebrada Las Pailas, the headwaters of which are in the Coast Range 4.5 kilometers due south of Cabo Blanco. The quebrada is generally dry except during heavy rains. A narrow watershed separates Quebrada Las Pailas from the coast, and the highest point of this drainage divide is occupied by the Cabo Blanco lighthouse at an elevation of approximately 135 meters. The short streams flowing north to the sea, and south to Quebrada Las Pailas, have steep gradients. The channels are usually dry, but when it rains torrentially, as it does occasionally in the wet season, run-off is rapid, and a considerable amount of sand and gravel is washed down them.

STRATIGRAPHY

CABO BLANCO GROUP

Except for Recent deposits, the entire group of sediments lying north of the Coast Range metamorphics in this area has long been re- ferred to as Cabo Blanco, and this name is retained even though a mid- Tertiary to Quaternary time span is involved.

The Cabo Blanco group is made up of a heterogeneous array of strata which from bottom to top are divided into the following units:

Las Pailas formation Playa Grande formation Mare formation Abisinia formation

LAS PAILAS FORMATION TYPE LOCALITY

The Las Pailas formation outcrops on both sides of the watershed between Quebrada Las Pailas and the coast. The type section is exposed along the coastal side of the watershed and extends from the mouth of Quebrada Las Pailas westward for a distance of 2.6 kilometers. The for- mation was first described by Frances de Rivero (1956).

GEOLOGY CABO BLANCO, VENEZUELA: WEISBORD 9

DESCRIPTION

The outstanding characteristic of the Las Pailas formation is the light gray color of the coarser clastics which are present throughout the section but more abundantly so in the upper part of it.

The succession of strata within the Las Pailas formation is conform- able from bottom to top. The lower half of the formation consists of mudstones, siltstones, and fine sandstones, interbedded with occasional coarse sandstones and conglomerates. The upper half of the formation consists largely of conglomerates and coarse sandstones with occasional intervals of the same type of fine-grained sediments that make up the lower half of the formation.

At whatever position they occur, the siltstones and fine sandstones of the Las Pailas formation are soft, gray to tan in color, and generally highly micaceous. These fine sediments may occur in well-defined beds, they may be intermingled with coarser material, or they may be homo- geneous and massive. Parting planes of the siltstones are often coated with a soft, soapy textured mudstone which is also found interbedded or interlaminated with the fine sandstones. At W-9, the siltstone con- tains peatlike plant fibers, and at several localities, it contains irregular nodules, some three centimeters or so in diameter, of fine-grained, indur- ated sandstone. In some places, there are soft, gray sandstones dis- seminated with rusty brown particles.

The mudstones of the Las Pailas formation are also distributed throughout the entire Las Pailas section but are thinner and not so abundant as the siltstones. The mudstones are soft to moderately com- pact, are either dull gray or chocolate brown in color, and are often soapy textured or glazed in appearance. They usually occur interbedded or in- termingled with the siltstones or fine sandstones but are sometimes in- tercalated with coarser sediments. Near the headwaters of the two streams 900 meters and 1,300 meters southwest of the lighthouse, there are several feet of pure mudstone at the top of the Las Pailas section where they immediately and unconformably underlie the basal conglom- erates of the Playa Grande formation. Elsewhere, the mudstones often contain nests of light gray silt and sand, just as the siltstones and sand- stones contain pockets of the greasy mudstone.

The coarser clastics of the Las Pailas formation consist of granular sandstones and conglomerates. These are rather poorly cemented and

10 BULLETIN 165

are generally light gray in tone although there is a zone some 700 meters long and 20 meters wide just north of and paralleling the fault between section lines C-C’ and D-D’ where the conglomerates are brown in color. The Las Pailas conglomerates are composed of subangular to subrounded granules, pebbles, and cobbles embedded in a coarse, somewhat friable sandstone which may contain a little disseminated gypsum. The larger constituents of the conglomerates are mainly quartz, gneiss, and schist, and these were in all probability originally derived from the Coast Range whose present foothills lie a short distance south of the Maiquetia airfield. The quartz is usually milky white but some of it is smoky blue. The gneiss is light-colored and streaked with black femic min- erals, and the schists are green and black and often highly micaceous.

Although the coarse clastics of the Las Pailas formation exhibit « little lenticularity and cross-bedding, individual beds are generally evenly disposed and separated by clean-cut parting planes.

THICKNESS

Along section line C-C’, where the Las Pailas formation is exposed at the shore and extends southward to the Bruscas fault, the thickness of the Las Pailas section is 375 meters (1,230 feet). The maximum thickness of the formation is undoubtedly greater than this and depends in part on how far out to sea the south-dipping beds extend.

STRATIGRAPHIC BOUNDARIES

The base of the Las Pailas formation has not been observed, and its relationship to the rocks immediately underlying it is not known. On the other hand, uplift and erosion of the Las Pailas prior to the deposi- tion of the overlying Playa Grande formation has resulted in a marked angular unconformity between the two formations, with a difference in dip between them of as much as 40 degrees. In mapping, this uncon- formity is considered the upper boundary of the Las Pailas formation.

AGE AND CORRELATION

The Las Pailas formation is devoid of shelly organisms although it does contain a little vegetable material. The formation is probably of continental origin and may have been laid down in a fresh-water or brackish water lagoon. The conglomerates contain reworked rocks which are the same as those composing the nearby Venezuelan Coast

GEOLOGY CABO BLANCO, VENEZUELA: WEISBORD gi

Range, and it is inferred that the Las Pailas material was derived from this range, if not in the immediately preceding cycle, then from a forma- tion which itself was made up of debris from the then existing moun- tains.

The absence of determinable fossils precludes a definite age assign- ment for the Las Pailas formation. However, its position below upper Tertiary beds, and its resemblance to certain formations whose age has been bracketed elsewhere in Venezuela, suggest that this formation was laid down in mid-Tertiary time.

PLAYA GRANDE FORMATION OCCURRENCE

The Playa Grande formation was first described by Frances de Rivero (1956). It takes its name from the village of Playa Grande where part of the formation forms the slopes below the terrace on which the village is situated. From Playa Grande, the formation extends west- ward to the beach resort of Catia La Mar. East of Playa Grande, it is exposed along the upper part of the lighthouse scarp and in the low hills just north of the Maiquetia airfield.

DESCRIPTION

The Playa Grande formation consists of a variegated assemblage of rocks and starts at the base with a brown conglomerate. The type locality of this basal conglomerate is the scarp below the lighthouse where it attains its maximum thickness of about 65 feet. In the western part of the area, it occurs as a ribbon along the northern and upper flank of the coastal scarp and, near the Costa fault, it is only a foot or two in thickness. The deposit is a lenticular body lying with pronounced angular unconformity on the Las Pailas formation but in general con- formability with overlying members of the Playa Grande formation. The conglomerate is composed mainly of quartz, gneiss, and mica schist in granule to boulder dimensions. The quartz is white to yel- lowish brown, and some of the schist pebbles are flattened as they may be elsewhere throughout the Playa Grande formation. Near the head- waters of the gully 70 meters west of the lighthouse, a large block of gray, banded sandstone lies erratically within the conglomerate, and inasmuch as this sandstone, as well as some of the other fragmental

ie BULLETIN 165

material, is identical with that in the Las Pailas formation, there is little doubt that some of the constituents of the basal conglomerate have been reworked from the Las Pailas formation. The conglomerate is haphazardly sorted, poorly cemented, and nonfossiliferous. It marks the base of the Playa Grande formation, but in view of the lenticular nature of the Playa Grande deposits, it is probable that the conglomerate as such is not always present at this position.

Since there is no connecting stratigraphic sequence between the Playa Grande formation in the northern part of the Cabo Blanco area and that of the south, it may be appropriate to divide the Playa Grande formation into two members for which the names Catia and Maiquetia are proposed. The Catia member, which is much the thicker of the two, is exposed north of the Bruscas fault, whereas the Maiquetia member is exposed south of the fault and extends from the vicinity of Abisinia westward along the north edge of the Maiquetia airfield. The Maiquetia facies with its characteristic dull gray rocks has not been observed north of the Bruscas fault although south of the fault the Maiquetia member is interfingered with certain sediments that are lithologically identical with those of the Catia member. However, since the Catia beds immediately overlie the basal conglomerate of the Playa Grande for- mation, they are believed to occupy the lower part of the formation, whereas the Maiquetia beds which unconformably underlie the Mare formation are presumed to occupy the upper part of the Playa Grande formation. Nevertheless, nowhere is there a continuous section across the grain of the Playa Grande formation, and the relationship of the two members as given above is suggestive rather than definitive.

The thickest development of the Catia member is on the Litoral anticline near the village of Playa Grande and along the scarp south of the coast road leading to Catia La Mar. Here and elsewhere, the Catia member consists mainly of siltstones, sandstones, and conglomerates which are interbedded with a number of coquinas, an occasional mud- stone, and sporadic limestones. Macroscopic and microscopic fossils are generally present in greater or less abundance throughout the Catia member, and many of the rocks are calcareous.

The siltstones of the Catia member are usually massive but in places they are poorly bedded. The massive variety has a yellowish tan appear- ance, and this color is distinctive of the member particularly at Playa Grande where the formation is exposed in new road cuts. The bedded

GEOLOGY CABO BLANCO, VENEZUELA: WEISBORD 13

variety, on the other hand, is generally gray to tan in aspect. The silt- stones are soft or hard, the former often grading irregularly into hard, fine-grained sandstones which are both calcareous and gypsiferous, and produce the knobby surface so characteristic of certain beds throughout the Playa Grande formation. Another feature of the siltstone-sand- stone deposits is the occurrence, normal to the bedding, of long, roughly cylindrical sandstone bodies as much as four centimeters in diameter. The branching nature of some of these casts and the tapering conical form of others lead the writer to surmise that they are the fillings of plant stems, perhaps of mangrove.

Although many of the sandstones of the Catia member are massive, fine-to-medium-grained, and calcareous or gypsiferous or both, a few of them are hard, flaggy, and sparkling, while others are coarse-grained to conglomeratic. Fossils are rare or absent in the more siliceous sand- stones but are present in the calcareous ones.

The conglomerates of the Catia member are of two types. One is poorly consolidated but well sorted, and contains rounded cobbles and boulders of metamorphic rocks in a coarse earthy matrix. The other variety is a heterogeneous one containing large and small fragments of gneiss, schist, and quartz, and rough, irregular chunks of coarse sand- stone. These latter conglomerates are thicker and more extensive than the well-sorted variety but both of them may be overlain or underlain by siltstones, sandstones, or shell beds. The shell beds occur at various levels within the Catia member, and in places the fossils are so abundant that they form impure coquinas. Examples of these are at W-21 and W-22, and the Ostrea bed east of W-22. The Ostrea bed is about 6 feet thick and directly overlies a well-sorted boulder conglomerate. Other coquinas composed largely of the barnacle Balanus are present in the scarp east of the Costa fault where they lie a short distance above the basal conglomerate of the Playa Grande formation. However, a similar barnacle coquina is present in the Maiquetia member in the scarp southwest of W-11, and this bed could be much higher in the Playa Grande section than the foregoing.

The total thickness of the Catia member of the Playa Grande for- mation is not known. On the Litoral anticline, the thickness from the Costa fault to the contact with the Abisinia formation is 525 feet, and from the Costa fault to the west end of section line F-F’, it is 770 feet. These are believed to be minimum thicknesses.

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The Maiquetia member as defined in this paper refers to the assemblage of shales, siltstones, sandstones, and conglomerates outcrop- ping north and west of the Maiquetia airfield and lying unconformably below the Mare formation. The rocks are generally drab gray and dull tan in color, and produce a rather cheerless looking terrain. Associated with these rocks, however, are lighter colored sediments similar to those of the Catia facies.

The easternmost outcrop of the Maiquetia member is near Abisinia at W-25 where it projects through talus on the south flank of the Punta Gorda anticline and unconformably underlies boulder gravels of the Abisinia formation. From this unconformity downward, the Maiquetia member is composed of the following strata:

Feet Description

) Cobble conglomerate; matrix of coarse earthy sand.

2 Dull tan, fine-grained sandstone.

5 Lenticular pebble conglomerate with dull tan to drab gray, fine-grained sandstone.

3 Drab gray and tan, fine-grained sandstone. 1 Blue-black, gritty siltstone grading down to pebble conglom- erate.

10 Yellow-tan, fine-grained sandstone interbedded with pebble conglomerate; gray, soapy textured mudstone; tan, finely micaceous siltstone; and drab gray siltstone.

5 Talus,

At W-23 on the north flank of the Punta Gorda anticline, the Maiquetia member is unconformably overlain by three feet or so of fossiliferous Mare sandstone which in turn is capped disconformably by 15 feet of Abisinia gravels. From the unconformity at the base of the Mare wedge, the Maiquetia member consists at the top of about 20 feet of boulder to pebble conglomerates whose contained fragments are larger above than they are below. The rocks which make up this conglo- merate are mostly greenstones, gneiss, mica schist, graphite schist, and garnetiferous schist, together with a little quartz. Below this poorly sorted conglomerate is a one-foot bed of evenly sorted, flattened, and elongated cobbles resting directly on a 7-foot reef composed of Litho- thamnium which is garnished with a fair assortment of mollusks. Under

GEOLOGY CABO BLANCO, VENEZUELA: WEISBORD 15

the reef is another heterogeneous conglomerate some two feet thick down to the bottom of the outcrop at road level. The Lithothamnium reef is exposed along the south side of the coast road for a distance of 150 meters and is the largest of such reefs observed in the Cabo Blanco area. Somewhat farther west, and along the same general strike, there are other outcrops of Lithothamnium-bearing strata, and these seem to be stratigraphically close to the reef described above.

In Quebrada Mare Abajo and on the lower slopes of the hills adjoining it, the Maiquetia member is made up of soft, dull gray and dull brown clay shales interbedded with, or grading into, dull gray gypsiferous siltstones and sandstones, and interlensed with dull-toned argillaceous grits and rather loosely cemented pebble conglomerates. Near W-12, the clay shales are encrusted with a rusty yellow substance which is believed to be the mineral jarosite and, in the small tributary east of W-12, the grits contain platy selenite layers a few millimeters in thickness. The pebbles of the conglomerates consist mainly, as they do in both older and younger conglomerates of the Cabo Blanco area, of gray-black mica schist, olive-green schist, white quartz, gneiss, and other metamorphic rocks. The schist pebbles are the most abundant, and many of them are flattish, smooth, and rounded at the edges. It is estimated that the thickness of the Maiquetia member at Quebrada Mare Abajo is 100 feet. At the south, the Maiquetia member is directly over- lain, with angular unconformity, by the basal fossiliferous grits of the Mare formation. Downdip and to the north, the Maiquetia member is blanketed with Quaternary sediments beneath which there may be another 100 feet or more of Maiquetia sediments lying above the exposed 100 feet. The thickness of the Maiquetia section below the lowest exposed bed is not known.

Approximately 280 meters west of Quebrada Mare Abajo, Mat- quetia strata reappear in the bed of a small stream where they are again unconformably overlain by basal fossiliferous grits of the Mare forma- tion. Here, the average dip of the Maiquetia beds is 30 degrees north (as contrasted with four degrees north of the Mare grits), and it is estimated that the exposed Maiquetia section is about 85 feet thick. In this stream, the Maiquetia member is made up of alternating pebble conglomerates and gray to chocolate brown siltstones overlain by soft marly sands. ‘The matrix of the conglomerates is a coarse, friable sandstone in which are embedded flattened pebbles of schist, subangular

16 BULLETIN 165

to subrounded pebbles of white quartz, and minor amounts of gneiss. The siltstones are soft and drab gray to chocolate brown in color, and contain, in one place or another, thin shale partings with nests of ashy gray silty sand, and lamellae of decayed vegetable material. The silt- stones here are reminiscent of those in the upper part of the Las Pailas formation at W-9.

A partial but continuous section of the Maiquetia member is ex- posed in the stream-cut scarp 50 meters southwest of W-11. At this locality, the lower 50 feet consist of drab gray and dull brown granule, pebble, and cobble conglomerates with some dark gray clay shales and silty shales at the base. The top of this sequence is conformably over- lain by a coquina-like bed containing many barnacles, and this in turn is overlain by marly sandstones and knobby calcareous sandstones which are identical with such sandstones in the Catia member north of the Bruscas fault. Similar calcareous sandstones underlie the conglomerates and are exposed on both flanks of the Maiquetia anticline.

Maiquetia beds, some of them steep, are also exposed in Quebrada Las Pailas just west of the Maiquetia airfield. Here, there are at least two separate Lithothamnium banks interbedded with selenite-bearing gray sandstones, bleached gypsiferous clays, micaceous sandstones, peb- ble conglomerates, and massive gray mudstone containing nodules of hard white chalk.

FOSSILS

Macroscopic and microscopic fossils are present throughout the Playa Grande formation, and these indicate that the beds were laid down in shallow marine waters. One of the most interesting of the fossil occurrences is the calcareous alga Lithothamnium. ‘This occurs in both the Catia and Maiquetia facies but has been observed more fre- quently in the latter. The largest Lithothamnium reef observed is at Punta Gorda (W-23) and consists of pinkish, subovate colonies of algae averaging about four centimeters or so in diameter. On top of the reef, and associated with it, are a number of mollusks of which Oliva, Venericardia, Glycymeris, and a beautifully ornate Codakia have been identified.

Along the scarp west and east of W-15 at Playa Grande, and particularly in the gully west of W-15 is Pecten arnoldi Aguerrevere which is the largest and most robust of the bivalves collected in the

GEOLOGY CABO BLANCO, VENEZUELA: WEISBORD L7

Playa Grande formation. At W-15, the following Foraminifera have been recognized: Textularia, Liebusella, Quinqueloculina, Pyrgo, Robu- lus, Marginulina, Saracenaria, Lagena, Nonion-Nonionella, Elphidium, Buliminella, Bulimina, Virgulina, Bolivina, Uvigerina, Reusella/Tri- farina, Discorbis, Eponides, Rotalia, Siphonina, Amphistegina, Cassi- dulina, Globigerina, Orbulina, Globorotalia, Cibicides, and Planulina. With these Foraminifera occur some ostracods.

At W-21 are the mangrove (?) casts mentioned earlier, and these are immediately underlain by strata containing many specimens of Ostrea cf. haitensis Sowerby. Farther east, at W-22, and stratigraphi- cally lower than the foregoing, is another fossil bed which is filled with Ostrea cf. haitensis, Spondylus, Pecten, and Balanus, as well as an occasional thick-shelled Chama. The Ostrea bed east of W-22, whose trace is shown on the geologic map, is a near-coquina and lies about 60 feet stratigraphically lower than the W-22 bed.

Coquinas consisting principally of the barnacle Balanus are present in discontinuous reefs in the scarp east of the Costa fault. These may be as much as four feet thick and have been observed in an interval 20 to 60 feet above the basal conglomerate of the Playa Grande formation. Another Balanus bed, a foot or so thick, outcrops in the cliff 50 meters southwest of W-11 (Cross Section B-B’-B”), but its position with reference to the basal conglomerate is not known. It may be consider- ably higher stratigraphically than the ones referred to above.

At W-4 in the south bank of Quebrada Las Pailas, and at stream level, is a dark blue, slightly gritty mudstone overlain by soft, tan silt- stones which contain, among other fossils, Dosinia, V enericardia, Conus, Architectonica, and Turritella. The same species of Twrritella (often to the exclusion of all other shells) occurs in many localities around W-4, and although some of these Turritellas are from the same horizon, others of the same species are from different horizons within the Playa Grande formation of this area.

AGE

Many of the fossils in the Playa Grande formation closely resemble those of the overlying Mare formation although there are some which seem to be restricted to one or the other of these formations. A careful study will be required to establish the age of the Playa Grande formation, but the writer tentatively considers it to be Miocene-Pliocene.

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MARE FORMATION

TYPE LOCALITY

The type locality of the Mare formation is the area adjacent to Quebrada Mare Abajo where it constitutes part of the hills overlooking this small stream. From the Mare Abajo drainage system, the formation extends along the edge of the Maiquetia airfield and continues north- westward for a distance of 500 meters. Here it disappears, as it does east of Quebrada Mare Abajo, under a mantle of younger debris, although farther east small wedges of the formation are exposed south of the village of Mare Abajo and on the south flank of the Punta Gorda anticline.

The Mare formation was first described by Frances de Rivero in the “Léxico Estratigrafico de Venezuela” (1956).

DESCRIPTION

The Mare formation is a shallow-water marine deposit. It is about 40 feet thick at the type locality but attains a maximum thickness of per- haps 60 feet elsewhere. The lower 10 to 15 feet are made up of inco- herent grits and sands containing many well-preserved fossils. This lower member starts as a pebble to granule gravel or ‘‘grit’’ (with occa- sional stringers of cobbles) and grades upward to a sand of decreasing coarseness. The upper 30 feet or so of the Mare formation consist of tan, homogenous, and slightly compacted silts of a fine and even texture. These silts conformably overlie the coarser sediments at the base of the Mare formation, but the contact between them is usually rather sharp. Like the grits, the silts of the Mare formation are also highly fossili- ferous, albeit more so below than above, and, at the top of the formation, the silts may be barren of visible fossils.

STRATIGRAPHIC RELATIONS

By definition, the fossiliferous grit represents the base of the Mare formation, and this lies unconformably on one member or another of the Playa Grande formation. At the type locality, where the Mare for- mation is in contact with the Maiquetia beds, the unconformity is markedly angular. With respect to its upper boundary, the Mare forma- tion is overlain disconformably by nearly horizontal deposits of the Abisinia formation. Near the edge of the Maiquetia airfield where the

GEOLOGY CABO BLANCO, VENEZUELA: WEISBORD 19

Mare and overlying Abisinia formations are in contact, the Mare beds are also nearly flat although northward therefrom they dip locally to the north.

FOSSILS

A distinguishing feature of the Mare formation is its many well- preserved shells. One of the most striking of these is the bivalve Macrocallista maculata (Linné)