Volume 47 Number 1

BULLETIN of the AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS

JANUARY, 1963

CRETACEOUS STRATIGRAPHY OF CENTRAL ANDES OF PERU'

JOHN J. WILSON^ Lima, Peru

ABSTRACT Cretaceous facias in Peru commonly fall into a lower, mainly clastic, group of formations and an upper group consisting of limestones, dolomites and shales. The clastic formations are largely non-marine. Over much of the country they range in age from Valanginian to Late Aptian or Albian, though in eastern Peru they extend into the Upper Cretaceous. The basal part of the limestone and shale group of formations is commonly Albian in age, though it is younger in the east. Tuffs and flows form an important part of the Cretaceous sequence of coastal Peru, but are not common elsewhere in the country. These Cretaceous units are overlain by redbed formations, some of which may be as old as the Campanian. The relationships between the redbeds and the underlying units range from conformity to slight angular unconformity. The Cretaceous formations range in thickness from about 3,000 meters on the western flank of the Andes and 2,000 m. in eastern Peru to 1,000 m. or less in the intervening region. On this basis the Andean belt is believed to have consisted of two troughs (the West Peruvian trough and East Peruvian trough of this report) separated by a relatively positive area called the Maranon geanticline. The clastic sequence in the West Peruvian trough was probably derived from the geanticline and from tectonic lands on the southwest. The elastics in the East Peruvian trough were contributed by the Brazilian shield, and probably by the geanticline. Although there were temporar3' marine advances into the troughs during the Neocomian and Aptian the main transgression did not begin until the Albian. The West Peruvian trough and the Maranon geanti- cUne were submerged by the Medial Albian, and marine conditions began to spread into the northern part of the East Peruvian trough. The latter was not completely submerged, however, until the sea reached its greatest extent during the Coniacian. Although there was Late Albian tectonism in parts of the Andean belt, widespread emergence did not begin until the Santonian or Campanian, when the West Peruvian trough was uplifted. Subsequently the whole of the belt was folded and uplifted by orogenic phases which took place possibly in the Miocene and Pliocene. The Andean belt in central Peru may be divided into structural provinces, which are from south­ west to northeast: Paleozoic massifs; gently folded and block-faulted Mesozoic sediments and volcanics; batholith; strongly folded Cretaceous formations; folded and metamorphosed Paleozoic formations overlain by gently folded Mesozoic and Cenozoic formations; and moderately folded Mesozoic and Cenozoic formations.

INTRODUCTION paid to the nature of the Upper Cretaceous car- The present study was undertaken in order to ^'O^^te rocks, and to the petrology and directional determine the age, nature, and origins of the sedimentary structures of the pre-Albian sand- Cretaceous formations of central Peru and their j- , , , , , , TT- i • I C ,. r field of Andean geology. His geological maps ot parts oi relations to formations of similar age in other the Central Andes are the only ones available, and parts of the country. Particular attention was greatly facilitated the field work for this report. The field work was made possible by the financial ,,f .. -lA tiom^i -J assistance and hospitahty of the following companies: 1 Manuscript received, August 18, 1961; revised, ^erro de Pasco Copper Corporation, Cerro de Pasco uctooer 1 , ivoz. Petroleum Corporation, Compania Peruana de Petroleo ^ Comision de la Carta Geol6gica Nacional. "El Oriente," Compania de Petroleo Ganzo Azul The writer is indebted to J. V. Harrison of Oxford Ltda., Compania de Petroleo Shell del Peru, Interna- University for first directing his interests toward the tional Petroleum Company Ltd., Latin American 1 JOH-N J. WILSO.X stones. The stratigrapliic dala were used to obtain The Coastal Region is a narrow strip of desert a clearer understanding of the tectonic framework between the Pacific Ocean and the .Andean Re­ of Peru during the Cretaceous, 'J'he stratigraphic gion. There is a narrow coastal plain in parts of data are summarized briefly in the Ajjpendix. northern and southern Peru, but in the central Brief descriptions of the measured sections may part of the region spurs extend from the .Andes be found in the Appendix. More complete de­ almost to the shoreline. Throughout the Coastal scriptions will be published in the Boletin of the Region vegetation is meager or non-existent ex­ Sociedad Geologica del Peru. cept where mountain streams provide water. The .Andean Region is a belt of highlands about PRFA'IOt:S WORK 200 km. broad. In central Peru it consists of a .Although exploitation of the mineral resources plateau with a mean elevation of about 4,000 m. of the Peruvian .Andes has been going on for some bounded both on the east and the west by high time there have been relatively few attempts at Cordilleras. Much of the Western Cordillera ex­ regional stratigraphic studies. McLaughlin (1924) ceeds 5,000 m. in elevation, and several peaks rise made an excellent summary of what was then more than 6,000 m. above sea-level. The Eastern known of the stratigraphy of the Peruvian Cen­ Cordillera is generally lower, though elevations of tral Andes, a region in which Harrison (1940, 5,000 m. are not uncommon. Whereas the plateau 1943, 1951a, 1951b, 1953, 1956a, and 1956b) has has a gently rolling topography the flanks of the since carried out an extensive program of geo­ Cordilleras are deeply dissected. Steep canyons logical mapping. Other studies include those of have been eroded to depths of more than 1,000 m. Kummel (1948) on a large area of eastern Peru; The vegetation varies from an incomplete cover of Fischer (1956) on northwestern Peru; Jenks tussocky grass at high elevations to thorn scrub (1948) on the Arequipa region; Newell (1949) on or jungle at lower altitudes. The nature of the ex­ the region about Lake Titicaca; and Benavides posures depends on the elevation. Above 4,000 m. (1956) on the Northern Andes. the Cordilleras show abundant evidence of GEOGRAPHY Pleistocene glaciation, and exposures are excel­ Peru lies astride the Andean chain between the lent. Beneath that elevation the valle\' sides have Equator and Latitude 18° South. The country is a mantle of soil and terrace material, and good conventionally divided into three natural regions sections can be obtained only along ridge tops and which are, from southwest to northeast, the low stream courses. Coastal Region, the mountainous .'Vndean Region, The Eastern Lowlands extend from the An­ and the broad river valleys of the Eastern Low­ dean foothills into the broad river valleys of the lands. Amazon basin. They are in contrast to the .An­ dean region in every way, and are characterized Mines Ltd., Mobil Oil Company del Peru, Peruvian by heavy precipitation, continuous high tempera­ Gulf Oil Company, Peruvian Oils and Minerals Ltd., Petroleo Sullana Ltda., Petrolera Peruana S.A., Rich­ tures, and abundant vegetation. The broad river mond Oil Company. valleys lie at elevations of 300 m. or less, and the Many people gave unselfishly of their time and energy to make the visits both profitable and pleasant. The watersheds do not usually rise above 1,000 m. writer wishes to acknowledge in particular the assist­ The area of central Peru considered in this ance of Victor Benavides (International Petroleum report lies between Latitudes 9°30' South and 12° Company), James Birkbeck (Latin American Mines), Andres Bravo Bresani (director de Minas), Jorge A. South, and extends from the Pacific Ocean east­ Broggi (Instituto Geol6gico), Enrique Normand (So­ ward beyond the Continental Divide. It includes ciedad Nacional de Mineria y Petroleo), and Georg Petersen (Empresa Petrolera Fiscal). those parts of the Coastal and Andean Regions of The laboratory work was carried out in the Depart­ central Peru (Fig. 1). ment of Geology, Harvard University. The report was submitted in partial fulfilment of the requirements for FIELD TECHNIQUE the degree of Ph.D. The faculty and graduate students of this department were generous in their assistance to The field work for this report was carried out in the writer throughout his stay. The writer is particu­ the summers of 1958 and 1959. Stratigraphic sec­ larly indebted to Professor Bernhard Kummel for many discussions on the problems of Andean geology and for tions were located by driving over all available helpful criticisms during the preparation of the report. roads, and by travelling with animals over the The manuscript was also read and criticized by Profes­ sor Raymond Siever and Professor Marland P. Billings. extensive areas which could not be reached by The opinions expressed are, however, those of the writer. vehicles. The locations of the sections are shown CRFTACFOUS STRATIGRAPFIV OF CENTRAL PKRU

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FIG. 1.—Geomor])hic provinces of Peru. JOHN J. WILSOX

The western flank of the geanticline is overlain by a relatively thin sequence of Mesozoic and Ceno­ zoic sedimentary formations. Although the sedi­ mentary cover has been folded and locally thrust, structures are less complicated than farther west. The region east of the Maranon geanticline is underlain by Mesozoic and Cenozoic formations. Little information has been published on the structure of this large area, though it appears to constitute a belt of moderate to gentle folding.

CRETACEOUS STRATIGRAPHY Figure 3 illustrates the area of the Peruvian Andes underlain by outcropping Mesozoic forma­ tions, the majority of which are Cretaceous. In Northern and Central Peru the Cretaceous out­ crop is divided into two major parts by a north­ SAN LOWeNtO west-southeast-trending belt of pre-Mesozoic FIG. 2.—Outcrop of Cretaceous System and location rocks (Fig. 3), the Maranon geanticline of Bena­ of sections in central Peru. vides (1956), a positive structure which strongly influenced sedimentation during the Early Cre­ in Figure 2. Each section was measured by means taceous. Benavides (1956) noted that during the of tape and Brunton. Cretaceous the geanticline was flanked on the northeast and southwest by linear areas of sub­ STRUCTURAL GEOLOGY sidence which are here called respectively the East Field work and a study of the available htera- Peruvian trough and the West Peruvian trough ture indicate that the Andean belt in central Peru (Fig. 4). can be divided into northwest-southeast-trending Kummel (1948) described the Cretaceous rocks structural provinces (Fig. 3). of the East Peruvian trough as consisting of two The most southwesterly structural province formations of continental orthoquartzites and consists of Paleozoic and Pre-Cambrian massifs protoquartzites (the Oriente and Vivian Forma­ which have been described southeast of Lima tions) separated by the marine shales and lime­ (Ruegg, 1957) and in northwestern Peru (Fischer, stones of the Chonta Formation. The formations 1956). East of these massifs, and forming the deposited in the West Peruvian Trough, however, coast of much of central Peru, Mesozoic rocks consist of graywackes, shales, and volcanics in the have been gently folded and block-faulted. Paral­ area of coastal Peru, and protoquartzites, ortho­ leling the coast, and in some places extending to quartzites, shales, and carbonates in the Andean it, is a petrologically complex batholith approxi­ Region. The formations lying on the western mately 30 km. wide. The intrusion has not pro­ flank of the geanticline are made up of a lower unit duced intense deformation and metamorphism in of orthoquartzites and protoquartzites overlain the surrounding rocks, except near the contact. by Albian to Santonian carbonate rocks. Between the batholith and the Continental Between Latitudes 7° and 11°45' South the pre- Divide is a belt of strongly folded Cretaceous Albian fades of the West Peruvian trough is quite formations unconformably overlain by Cenozoic distinct from that of the Maranon geanticline. volcanics. The Cretaceous formations have been West of a line extending from about Rio Pallanga folded into a series of thrust anticlines and syn- to Celendin the pre-Albian formations are thick clines, with overturning mainly toward the north­ and contain marine facies, whereas east of the line east. the sequence is thinner and does not contain any East of the Continental Divide in central Peru evidence of marine deposition. In central Peru the lies a belt of strongly folded, metamorphosed, and change in thickness and lithologic character is so intruded Paleozoic and Pre-Cambrian rocks which nearly coincidental with the Continental Divide Benavides (1956) named the Maranon geanticline. that for practical purposes the divide is regarded CRETACEOUS STRATIGRAPHY OF CENTRAL PERU

CENOZOIC SEDIMENTS

E3 CENOZOIC VOLCANI C S

BATHOLITHIC ROCKS

MESOZOIC ROCKS

PALEOZOIC ROCKS

FIG. 3.—Generalized geological map of Peru. JOH.N J. WILSON

Jurassic and Lower Cretaceous by Leatiza (1945, 1947). The Puente Piedra Formation has no known equivalents elsewhere in Peru except in the Huaytara area east of Pisco, where Bellido (1956) found Berriasian ammonites in a shale and sandstone sequence. The Salta del Fraile Formation, the Herradura Formation, and the Marcavilca Formation consti­ tute a predominantly clastic sequence which is more than 600 m. thick on the island of San Lorenzo (Rosenzweig, 195,3) and about 400 m. thick south of Lima (Fernandez Concha, 1958). The Salta del Fraile Formation is light brown, medium-bedded sandstone and is readily dis­ tinguished from the intercalated shales, sand­ stones, and thin limestones of the Herradura Formation. The Marcavilca Formation is thick- bedded, white or gray-colored sandstone. FIG. 4.—Cretaceous tectonic framework of Peru. Thin section study of fourteen specimens col­ lected at regular stratigraphic intervals from the as the junction between the two facies. aforementioned formations indicates a fairly con­ The Cretaceous rocks which crop out in the area tinuous change in composition from the base of of this report were deposited in the West Peruvian the Salta del Fraile Formation to the top of the trough and on the flank of the Maranon geanti­ Marcavilca Formation. The sandstones of the cline. As the outcrop area is divided geographi­ Salta del Fraile and Herradura Formations are cally into a Coastal Region and an Andean Region, subgraywackes and protoquartzites (PI. la and this division is maintained in the description of b). The average of nine estimated modal analyses the stratigraphy. of these two formations is: Quartz-|-Chert 70-75% C0AST.4L REGION Rock fragments 10% Feldspar 10% Along the coast of central Peru is a narrow strip Matrix 5-10% of Mesozoic sediments and volcanics about which little is known. Stratigraphic sections were meas­ The rock fragments are, in order of decreasing ured at Lima, Chancay, and Huarmey (sections abundance, quartzite, volcanics, and a quartz- 1-4). oligoclase type. The feldspar is predominantly plagioclase (average composition Anao), though Lima Area perthite and orthoclase are also present. The The stratigraphic nomenclature of the Lima sand-size grains are subangular to subrounded, section (section 1) officially adopted by the Insti­ the interstices between them being filled with tute Geologico del Peru (Rivera, 1951), and used silty or shaly matrix. by Rosenzweig (1953) and Fernandez Concha The five thin sections from the Marcavilca (1958) is tabulated in Figure 8. Formation are protoquartzites and orthoquartz- The Puente Piedra Formation was described by ites consisting of 90 per cent or more of quartz, Rivera (1951) as consisting of approximately with minor amounts of rock fragments, feldspar, 1,900 m. of andesites and water-laid andesitic and matrix. The grains are subrounded, and the tuffs with interbedded shales and sandstones. Six interstices are filled with a sihca cement. hundred meters above the base of the formation is Cross-bedding of festoon type is common in the a fossiliferous shale unit 15 m. thick. Rivera sandstones of the Lima area, occurring in units up (1951) considers the ammonites from this unit to to a meter thick. Ripple marks are also present. be no older than Late Tithonian and no younger Six measurements of cross-bedding indicate that than Berriasian, a conclusion which is in agree­ the sandstones were deposited by a current flow­ ment with the zonation of the Argentinian Upper ing toward the east-northeast. CRETACKOUS STRATIGRAPHY OF CF.NTRAL I'FRU

I'L. 1.—Photomicrographs of Cretaceous rocks of coastal Peru. a. Subarkose, La Herradura Formation, Lima. Ordinary light, X30. Consists of quartz (clear), feldspar (clouded), volcanic rock fragments (dark colored), and matrix. b. Subgraywacke, La Herradura Formation, Lima. Crossed nicols, X30. Quartz, quartz-oligoclase fragment, andesitic fragments (dark gray), and matrix. c. Graywacke, unnamed formation, Chancay. Ordinary light, X30. Angular fragments of quartz, feldspar, and volcanics set in abundant fine-grained matrix. d. Tuff, unnamed formation, section 4. Ordinary light, X30. Angular fragments of clear quartz and sub- angular volcanics set in matrix of small feldspar crystals and fine ash. 8 JOHN J. WILSON

The arenaceous formations of the Lima area age composition of three graywackes studied in contain a variety of plant fragments and moUusks. thin section is: The plant fragments have been considered Late Quartz 55% Jurassic by Berry (1922) and other workers, Rock fragments 15% though the ammonites were believed by Lisson Feldspar 5% Matrix 25% (1942, p.76) to indicate a Valanginian age. On the basis of the zonation of the Argentinian section by Graded bedding is found in some of the gray­ Leanza (1945, 1947) the Salta del Fraile, Herra- wacke beds. Load structures occurring between dura, and Marcavilca Formations are believed to the graywackes and shales, and contorted bedding be Valanginian. They are correlative with the within the graywackes show a general asymmetry Chimu Formation of the Andean Region, and toward the east. Two measurements made on a possibly with the Neocomian clastic formations load cast and a slump structure indicate that at elsewhere in Peru (Fig. 8). the time of deposition there was a slope toward The Pamplona Formation consists of thinly the southeast. bedded limestones and shales, and contains a One bed almost at the top of the unit contains molluscan fauna which Lisson (1942) believed ammonite molds, one of which was tentatively indicative of the Late Valanginian or the Haute- identified by the writer as Lyelliceras sp. indet. rivian. The Atocongo Formation is fine-grained, This genus is restricted to the Lower and Middle thick-bedded limestone which has not yet yielded Albian. It is common in the Middle Albian Paria- diagnostic fossils, though Rivera (1951) sug­ tambo Formation of the Central and Northern gested a Hauterivian age on the basis that it con­ Andes, with which the Chancay sequence is there­ formably overlies the Pamplona Formation. fore correlated. Faulting prohibits the measuring of complete sec­ The pyritic nature of the shales and the ap­ tions, and the thickness of the two formations can parent absence of benthonic fauna suggest deposi­ only be estimated as several hundred meters. tion in a reducing environment. The graywackes The Puente Piedra Formation is interpreted as are interpreted as turbidity-current deposits on a submarine accumulation of lavas and pyroclas- the basis of the graded bedding (Kuenen, 1951). tics on the basis of the water-laid tuffs and the The contorted bedding and the asymmetrical load presence of interbedded marine shales. The flora casts suggest a slope dipping toward the east. and fauna found in the Lower Cretaceous sand­ stones indicate deposition under alternately ter­ Huarmey Area restrial and shallow marine conditions. The terres­ Two sections were investigated near Huarmey trial sediments were possibly laid down as deltas (sections 3 and 4). Section 3 is on the western side which became temporarily submerged during of the Panamerican Highway at Km. 254, south oi minor marine advances. Precise data on the en­ the town. Section 4 is at Km. 315 north of Huar­ vironments of deposition of the Pamplona and mey, and consists of two parts lying on either side Atocongo Formations are not available, but it ap­ of the highway. pears probable that Steinmann (1929) was correct Section 3 is made up of 700 m. of thin-bedded in interpreting them as shallow marine deposits. shales and fine-grained, commonly tuffaceous, graywackes (PI. Ic). The average composition of Chancay Area the ten graywacke specimens studied in this sec­ Approximately 300 m. of interbedded gray- tion is: wackes, shales, and sills, or flows are exposed on Quartz 40% the southern flank of the promontory near the Volcanic rock fragments 20% town of Chancay (section 2). The upper 100 m. of Feldspar 15% Matrix 25% the sequence is separated from the lower part by a normal fault with which is associated a small basic Massive beds of agglomerate also occur, made up intrusion. The upper unit consists of medium- and of fragments of volcanic glass, grains of feldspar, coarse-grained graywacke in beds up to 2 m. and shaly rock fragments. The fragments of vol­ thick. Thin dark beds of pyritic shale separate canic glass are angular, and contain laths of the graywacke beds from one another. The aver­ feldspar showing parallel extinction. Weathering CRET.\CEOUS STRATIGRAPHY OF CENTRAL PERU

WESTERN FACIES SOUTHERN TTT^rrTTiEi

I. !III III! ORTHOQUARTZIT0 E S TOOUARTZITE 8 SHALE II p ROTOQUARTZITE SUBARKOSE S MESTONE PROTOQUARTZITE

FIG. 5.—Lithological relationships between fades of Goyllarisquisga Group. prevents the recognition of many of the grains of sequence is provisionally regarded as Cretaceou- feldspar in thin section studies, though oligoclase in this report. and andesine appear to be common types. The graywackes and tuffs of sections 3 and 4 are At section 4, north of Huarmey, the sequence is interpreted as deposits laid down in a region of interrupted by folding and faulting. A lower unit, active volcanicity. Large quantities of tuffaceous 690 m. thick, lies east of the road; the upper unit, material were explosively erupted, and submarine 896 m. thick, is situated west of the road. The lava flows also took place. The graded bedding stratigraphic gap between the two units is esti­ seen in the graywackes suggests that at least part mated at about 100 m. of the material was transported by turbidity cur­ Of the 21 thin sections studied from section 4, 8 rents. are graywacke, 5 are tuffs, 4 are volcanic flows or ANDEAN REGION" sills, 2 are agglomerates, and 2 are limestones. Goyllarisquisga Group The graywackes have an estimated average composition of: The pre-Albian clastic sequence east of the Quartz 20% Continental Divide in central Peru was called by Rock fragments 20% McLaughlin (1924) the Goyllarisquisga-Jatun- Feldspar 30% huasi sandstone, though Jenks (1951) changed the Matrix 30% name to the Goyllarisquisga Formation. West of The rock fragments consist of approximately the Continental Divide, and separated from the equal proportions of andesite and metaquartzite. type area by a belt of Albian and L^pper Creta­ About half of the feldspar is orthoclase, the re­ ceous carbonate rocks, is a thicker and more varied mainder being sodic plagioclase with an average sequence of largely clastic pre-Albian rocks. It is composition of Aojo. The agglomerate and tuff proposed that the term Goyllarisquisga Group be include both vitric and lithic types, and have an adopted to refer to all the Cretaceous rocks under­ average composition close to that of andesite (PI. lying the Albian limestones in the Central and Ic). Varying amounts of calcium carbonate are Northern Andes. No divisions of the group are present in the tuffs, one of which approaches a made in the eastern outcrop area. On the west, tuffaceous limestone in composition. The flows or however, the following formations are recognized sills are pyroxene andesites and basalts. The lime­ in ascending order: Oyon Formation, Chimu stones occur as thin discontinuous bands, and are Formation, Santa Formation, Carhuaz Forma­ fine-grained, non-fossiliferous, and silty. tion, and Farrat Formation (Fig. 8). The rocks of sections 3 and 4 do not contain a The Goyllarisquisga Group can be divided into great variety of sedimentary structures, though three facies, the lithologic characters and relative examples of graded bedding were seen. Slump thicknesses of which are shown diagrammatically structures also occur, though exposures were too in Figure 5. The western facies, which is a thick poor to permit an accurate determination of the sequence of sandstones, shales, and some lime­ direction of sediment transport. stones, lies west of the Continental Divide, and No fossils were found at sections 3 and 4. On extends from Canta northwestward into the the basis of an hoplitid ammonite found in the Northern Andes. The eastern facies is a sequence Huarmey area by Broggi (Lisson, 1942, p. 71) the of orthoquartzites mainly east of the Continental 10 JOHN J. WILSON

Divide, and stretches for several hundred kilo­ exhibited in the sandstones of tliis facies, and rip­ meters northwestward from Cerro de Pasco. The ple marks are also present. Slump structures were Goyllarisquisga Group southeast of Rio Pallanga found at several horizons in the subarkose unit of differs in thickness and lithologic character from section 22. both the eastern and western facies, and is here Twenty-eight measurements of slump struc­ referred to as the southern facies. The facies may tures and cross-bedding were made in the areas of extend as far south as Huancvelica, where Fernan­ sections 17-22. The seven measurements made at dez Concha (1952) reported a sequence similar to sections 20 and 21 indicate a current direction that of section 22. toward the west. The remaining measurements made at sections 17, 18, 19, and 22 indicate an SOUTHERN FACIES average current flow toward the east and north­ The Goyllarisquisga Group is represented by a east. variable thickness of sandstones and shales at The only fossils found to date in the southern sections 17-22. The group is more than 800 m. facies of the Goyllarisquisga Group are plant thick at section 22, but averages only 200 m. at fragments, collected from dark shales. Berry the other sections. (1922) found Thuites leptocladoides Berry and Field observations indicate that the southern Equisetites sp. indet. at Jatunhuasi, near section facies of the group may be divided into two units 22. These fossils are inadequate for dating the which are of more or less equal thickness at any strata within which they lie, as different workers one section. The lower unit is a sequence of pink place them in the Upper Jurassic or Lower Cre­ or purple sandstones, conglomerates, and gray taceous. The majority of workers believe that the limestone, whereas the upper unit consists of flora has Neocomian affinities. Fernandez Con­ white or yellowish weathering sandstones which cha (1952) mentioned finding corals in limestone commonly contain coaly layers. beds within the Lower Cretaceous sandstones of Thin-section studies of the lower unit show it to Huancavelica. Study of this material may facili­ be a moderately well sorted subarkose. The tate the precise dating and correlation of this average modal analysis of fourteen specimens is: facies. Quartz-l-chert >80% The anomalous sequence at section 21 poses a Feldspar < 10% problem. Whereas at sections 17-20 the Lower Rock fragments < 5% Cretaceous lies directly on the Lower Jurassic- Matrix > 5% Upper Triassic limestones, at section 21 the The feldspar is mostly plagioclase (average com­ Goyllarisquisga Group disconformably overlies a position Anso), with minor amounts of orthoclase, 300-m. sequence of conglomerates and arkoses, microcline, and perthite. The majority of rock which are in turn disconformably underlain by fragments are metaquartzite grains, though vol­ Lower Jurassic. Of what age are the sub-Goylla- canic fragments also occur. risquisga elastics, as they are called in this report? Thin-bedded limestones are found within the Are they merely a basal unit of the Goyllaris­ lower unit at sections 17, 18, and 22. The lime­ quisga Group, or are they appreciably older? stones contain shell fragments, but no identifiable The Goyllarisquisga Group is very uniform in remains were found. this region, as shown by the similarity in thick­ The upper unit of the southern facies of the ness and lithological characteristics between sec­ Goyllarisquisga Group is a sequence of ortho- tions 20 and 21. In none of the surrounding sec­ quartzites and protoquartzites. The eight thin tions, 17-20, is there evidence of considerable re­ sections of this unit which were studied gave an lief on the sub-Goyllarisquisga surface. It is there­ estimated average composition of: fore unlikely that the sub-Goyllarisquisga elastics Quartz >90% represent the infilling of a basin by a basal unit of Rock fragments < 5% the Goyllarisquisga Group. The writer believes Matrix 5% that the arkoses and conglomerates of section 21 Feldspar is present in small amounts, but is not may represent a unit appreciably older than the quantitatively important. Goyllarisquisga Group itself. This belief is sup­ Cross-bedding of the festoon type is abundantly ported by the observation that the sub-Goylla- CRETACP:0US STRATIGRAPHY OF CENTRAL PERU 11 risquisga elastics are cross-bedded from the west of the quartz grains is estimated at approximately whereas the Goyllarisquisga Group was derived 0.5 mm. In almost all places the rock has been in­ from the northeast and east. This difference in durated with a silica cement, giving a hard, dense source area indicates paleogeographic changes of quartzite (PI. 2b). some magnitude, which in turn suggests the Thin beds of carbonaceous shale and coaly passage of a not inconsiderable period of time. layers are interbedded with the sandstones, but From this above discussion it can be concluded rarely make up more than 1 or 2 per cent of this that although the sub-Goyllarisquisga elastics facies. Poorly sorted beds of gravel and con­ may be a basal unit of the Goyllarisquisga glomerate are not uncommon. Group, the evidence at present available suggests The sandstone units are cross-bedded in units that they are considerably older. As they overlie up to 2 meters thick. It is estimated that approxi­ the Lower Jurassic and underlie the Lower Creta­ mately two-thirds of the cross-bedding is of the ceous they must represent a part of the Middle or festoon type, the remainder being torrential. Upper Jurassic. Whereas the Middle Jurassic is Ripple marks are also common. The average of poorly developed in Peru, Upper Jurassic elastics thirteen measurements of directional sedimentary are relatively common. On this basis the sub- structures (sections 6, 10, 11, 15) indicates a cur­ Gojdlarisquisga elastics are provisionally regarded rent flow toward the west-southwest. This is sup­ as Upper Jurassic. ported by numerous estimates of cross-bedding We are therefore faced with the possibility that directions which were made without correcting for the Upper Triassic-Lower Jurassic limestones the dip of the beds. were at one time covered by a clastic formation Brachyphyllum pompeckji Salfeld and Oloza- which was largely eroded before the deposition of mites neumanni Zeiler were collected from shales the Lower Cretaceous Goyllarisquisga Group. at Goyllarisquisga. These plants are inadequate for This is a point which should be borne in mind by precise dating. The facies is provisionally regarded field geologists working in the Peruvian Andes, as Neocomian to Lower Albian on the basis that it where it has previously been the custom to con­ is overlain by the Middle Albian. It is therefore sider as Lower Cretaceous any elastics overlying correlative with much of the Oriente Formation in the Lower Jurassic limestones. eastern Peru (Kummel, 1948), and with the On the basis of the coal seams, the sedimentary Murco Formation of the Arequipa area (Jenks. structures in the sandstones, and the presence of 1948). limestone beds, the southern facies of the Goy­ The plant-bearing shales and coaly layers which llarisquisga Group is interpreted as a mixed deltaic are found at numerous horizons in the sequence, and shallow marine sequence. The poorly sorted coupled with the complete absence of marine in­ and immature sandstones in the lower part of the vertebrates, suggest that this facies of the Goy­ facies suggest rather rapid accumulation, whereas llarisquisga Group is of terrestrial origin. Moderate the orthoquartzites at the top of the sequence in­ or high current velocities are inferred from the dicate a considerable amount of weathering and pebble bands. The facies was probably deposited winnowing prior to deposition. in deltas or in river floodplains.

E.VSTERN FACIES WESTERN FACIES The eastern facies of the Goyllarisquisga Group The western facies of the Goyllarisquisga is a sequence of orthoquartzites with a fairly uni­ Group is considerably thicker and lithologically form thickness of 500-600 m. at sections 6, 9, 10, more varied than its eastern equivalent. The 11, 14, and 15. group is more than 1,500 m. thick at section 8, and The seventeen thin sections studied from this at Carhuaz, 100 km. northwest, the Lower Cre­ facies are orthoquartzites containing more than taceous elastics are about 2,000 m. thick (Bena- 95 per cent of subrounded and rounded quartz vides, 1956). Although the western facies of the grains. Feldspar, rock fragments, and matrix Goyllarisquisga Group contains white quartz usually constitute less than 5 per cent of the rock. sandstones of the type which characterize the Heavy minerals are rare, and consist of rounded eastern facies, it includes a much higher propor­ grains of zircon and tourmaline. The median size tion of shales and siltstones. Limestones are 12 JOHX J. WILSOX

a

PL. 2.—Photomicrographs of rocks of Goyllarisquisga Group, Chulec Formation, and Jumasha Formation. a. SubarJiOse, Goyllarisquisga Group, southern facies, section 22. Ordinary light, X30. Quartz (clear), com­ monly with overgrowths, and weathered feldspar. b. Orthoquartzite, Goyllarisquisga Group, eastern facies, section IS. Crossed nicols, XIS. Rounded grains of quartz held together by silica cement. c. Fossil fragmental limestone, Chulec Formation, section 6. Ordinary light, X30. Recrystallized fragments of shell material set in matrix of granular calcite and silt. d. Fossil fragmental dolomite, Jumasha Formation, section 15. Ordinary light, X30. Recrystallized fragments of macrofossils and foraminifera, in a matrix of medium-grained dolomite. present both in the Santa Formation and the the Lower Cretaceous Coal Measures. The type Carhuaz Formation. section is in the thrust anticline directly west of Oyon Formation.—This formational name is the town of Oyon, where the formation is repre- proposed for the unit referred to by Harrison as sented by approximately 100 m. of thinly bedded CRETACEOUS STRATIGRAPHY OF CENTRAL PERU 13

subgraywackes, shales, and lenticular coal seams. along this weak horizon is the principal type of The formation is not present outside of the Cen­ deformation. tral Andes, and is nowhere seen in its entirety Chimu Formation.—Benavides (1956) defined within the region. From north to south it is ex­ the Chimu Formation at Baiios de Chimu in the posed at sections 5, 6, 13, and 16. It does not Chicama Valley of northern Peru as 685 m. of occur east of the Continental Divide, where quartz sandstones with intercalated shales and quartz sandstones lie directly on the limestones of coal. It is disconformably underlain by the shales of the Pucara Formation. of the Tithonian Chicama Formation, and con­ Although the base of the formation is not seen, formably overlain by the limestones and shales of because of structural complexities, the upper the Santa Formation. In the Central Andes a limit is well defined by the change from the thin- 500-700-m. sequence of metaquartzites is corre­ bedded sandstones and shales of the Oyon Forma­ lated with the Chimu Formation on the basis of tion to the thick-bedded sandstones of the Chimu its similar lithologic character and stratigraphic Formation. position beneath the Santa Formation. The writer did not find any identifiable plant The Chimu Formation has a fairly constant fragments in the Oyon Formation, but Berry thickness and lithologic character over the whole (1922) reported Otozamites goepperiianus (Dun­ of its outcrop area, which extends between Lati­ keld) and WeichseUa cf. manlelli (Dunkeld) from tudes 7°30' and 11°45' South. It usually maintains the type section. Lisson (1942) considered this a thickness of between 500 and 700 m. The study flora indicative of the Neocomian, though Berry of ten thin sections shows the formation to be pre­ (1922) believed that a Jurassic age was possible. dominantly an orthoquartzite consisting of well The oldest dated horizon in the Andean Creta­ rounded quartz grains held together by a silica ceous, the Upper Valanginian Santa Formation, cement. Rock fragments are rare, and are re­ lies about 600 m. stratigraphically above the stricted to rounded particles of metaquartzite. Oyon Formation, whose age is therefore probably Feldspar is absent, and matrix nowhere makes up Early Valanginian or Berriasian. A Tithonian age more than 5 per cent of the rock. Only two or three can not, however, be completely ruled out. Al­ grains of heavy minerals are seen in any one thin though precise correlation is not yet possible, the section, the assemblage consisting of zircon, Oyon Formation is probably equivalent to the tourmaline, and titanite. From the foregoing it lower parts of both the sandstone sequence at can be seen that the formation strongly resembles Lima and the Murco Formation in the Arequipa the eastern fades of the Goyllarisquisga Group. area (Jenks, 1948). The mean grain size for the formation is esti­ The fine-grained, but rather poorly sorted mated as a medium sand though conglomeratic nature of the rocks suggests a weak current sys­ and silty bands are not unknown. Black carbona­ tem. This factor, together with the presence of ceous shales, locally associated with anthracite, coal seams, suggests that the Oyon Formation are found interbedded with the orthoquartzites. may have been deposited in a system of swamps. The sandstones of the Chimu Formation are The Oyon Formation is an important horizon medium- to thick-bedded. Cross-bedding of both in Andean tectonics. During the Andean orogeny festoon and torrential type is common. Ripple this formation acted as a plane of weakness along marks are also abundant, though slump struc­ which movements commonly occurred. Where tures were seen only in the area of section 7. present, it is associated with complex structures, a Eleven measurements of cross-bedding and slump common type being the thrusting of the Chimu structures give an average direction of sediment Formation over younger rocks, with the Oyon transport toward the southwest. Numerous Formation acting as a lubricant. East of the Con­ estimates made without allowing for the dip of tinental Divide, where the Oyon Formation is the beds confirm this direction. missing, structures are more open and thrusting is The only fossils found in the Chimu Formation less common. Although geological mapping is not are plant fragments. On the basis of the probably yet adequate to justify a final statement, it seems Late Valanginian age of the Santa Formation, the that the area underlain by the Oyon Formation Chimu Formation is placed in the Valanginian. It forms a structural unit in which decollement is therefore correlative with the sandstone forma- u JOHN J. WILSON tions of the Lima area, and possibly with the ic beds, and the absence of pelagic invertebrates Lower Cretaceous sandstones of eastern Peru suggest deposition in a near-shore environment. (Kummel, 1948). This interpretation is supported by the abundance The Chimu Formation is similar to the eastern of bioclastic material in the formation. fades of the Goyllarisqui.sga Group in lithologic Carhuaz Formation.- litna^viAcs (1956) defined character, sedimentary structures, and fossil con­ the Carhuaz Formation for 1,554 m. of sandstones tent. It is therefore believed to have been de­ and shales exposed in the Santa valley. The for­ posited in the same sedimentary environment of mation crops out extensively on the western flank deltas and floodjilains. of the Peruvian Andes, but does not extend east of Santa Formation.—The Santa Formation was the Continental Divide in central Peru. defined by Benavides (1956) for 341 m. of lime­ The lower contact of the formation is conform­ stones and shales which croj) out 6 km. northwest able at all the sections visited. Fossiliferous sand­ of Carhuaz. A similar unit occurs in the Central stones and shales at the base of the formation Andes. It is well exposed in the Chiquian area grade downward into the limestones of the Santa (section 8), where it consists of 14 m. of shales and Formation. At the type section the top unit of the thin-bedded sandstones overlain by 139 m. of formation is medium-bedded orthoquartzite and medium-bedded limestones, shales, and dolo­ protoquartzite. The writer considers this unit to mites. This unit is correlated with the Santa For­ be the lateral equivalent of a thick metaquartzite mation on the basis of lithologic similarity and unit found at this horizon in the Northern Andes, stratigraphic position. The formation is also and named the Farrat Quartzite by Stappenbeck present at sections 5, 7, 8, 12, 13, and 16. (1929). Benavides (1956) correlated the Farrat Section 8 is the only section visited in which Quartzite of the Northern .\ndes with the Central both the upper and lower contacts of the Santa Andean Goyllarisquisga Formation of Jenks Formation can be clearly observed. The lower (1951). However, the Farrat Quartzite is equiva­ contact, which is placed at the top of the medium- lent to only part of the Goyllarisquisga Formation bedded quartzites of the Chimu Formation, is of Jenks (1951), and should be named the Farrat conformable. The upper contact is placed at the Formation to avoid ambiguity. In this report the top of the limestone sequence, above which lie the medium-bedded sandstones at the top of the sandstones of the Carhuaz Formation. Carhuaz Formation of Benavides (1956) are re­ The basal unit of the Santa Formation consists garded as equivalent to the Farrat Formation, of up to 50 m. of cross-bedded sandstones and and are named accordingly. The upper contact of shales containing small plant fragments. The the Carhuaz Formation as here defined is grada- carbonates of the upper unit of the formation tional at most sections, and is drawn where medi­ commonly consist of comminuted shell debris set um-bedded sandstones begin to constitute more in a fine-grained calcium carbonate matrix. than 50 per cent of the sequence. Silicified oolitic limestones, some of which show The Carhuaz Formation is predominantly a ripple marking, are present, but do not constitute clastic sequence consisting of thin- to medium- more than 5 per cent of the formation at any one bedded sandstones, siltstones, and shales which of the sections visited. Beds of rusty weathering weather to browns, yellows, and reds. At the top dolomite up to 1 m. thick occur in some of the of the formation is a variegated siltstone unit. The sections. sandstones of the Carhuaz Formation are poorly Benavides found Valanginites hroggii (Lisson) sorted protoquartzites. Dark shales, commonly in the Santa Formation of northern Peru, and associated with coaly layers, make up from a considered it probably indicative of the Late quarter to a half of the formation, the proportion Valanginian. The formation did not yield any increasing toward the west. Thin beds of lime­ diagnostic fossils in central Peru, but is probably stone occur, and they too are most common in the the same age as in northern Peru. It is therefore west. correlative with the Pamplona Formation of the The sandstones and siltstones of the Carhuaz Lima area, and probably has equivalents in the Formation contain a variety of sedimentary Lower Cretaceous sandstone formations of other structures. Small-scale cross-bedding and current parts of the Andes. ripple marks are common. Examples of flow casts The ripple marks, sporadically distributed oolit­ are seen on the soles of some of the sandstone beds. CRKIACKOLS STRATKlRAl'in' OF CKXTRAF I'FRL' 15

Poor exposures and tlie small scale of the cross- The formation consists of medium- to coarse­ bedding prevent accurate measurements in manv grained, moderately to jjoorly sorted protocjuartz- places. The nine observations which were made ites and orthoquartzites. The average composition indicate an average current direction toward I he of the sandstones was estimated from the study of west. ten thin sections as: The dark shales of the Carhuaz Formation con­ Quartz 90% tain molds and casts of pelecypods and gastro­ Rock fragments < 5% pods. The writer has identified the gastropod as Matrix > 5% Paraglauconia cf. studeri, which also occurs in the Although sedimentary structures are not com­ type section. Cyrena hiiarazensis Fritzsche is also mon in the Farrat Formation, four observations common. of festoon-type cross-bedding were made. These No ammonites were found in the Carhuaz measurements indicate an average current direc­ Formation. The age range can, however, be ob­ tion toward the southwest. tained from the fact that the underlying Santa No fossils were found in the Farrat Formation, Formation is Late Valanginian, whereas the first but its stratigraphic position beneath the Lower diagnostic fossils above the formation are Early Albian Pariahuanca Formation suggests that it is Albian. The Carhuaz Formation is therefore Late Aptian in age. It is correlated with the upper Early Hauterivian to Aptian in age. part of the eastern facies of the Goyllarisquisga Stratigraphic relations suggest that the forma­ Group on the basis of litholog}' and stratigraphic tion is correlative with the eastern facies of the position. The formation is also correlated with the Goyllarisquisga Group. It is equivalent to part of Agua Caliente Member of eastern Peru (Kummel, the Oriente Formation of eastern Peru, where 1948), for the reason that both units are regressive Kummel (1948) found Aptian fossils in the sandstones overlying brackish-water and marine Esperanza Member. The Carhuaz Formation is beds of known Aptian age. also correlated with the Murco Formation of The Farrat Formation is interpreted as a regres­ Arequipa (Jenks, 1948) on the basis of similar sive sandstone unit deposited when deltaic or lithological characteristics and stratigraphic posi­ fluviatile conditions spread into the West Peru­ tion. The Huancane Formation of the Titicaca vian Trough at the end of the Aptian. area (Newell, 1949) is probably a partial equiva­ Pariahuanca Forma.tion.—Lying above the lent. Farrat Formation are several tens of meters of Both Paraglauconia and Cyrena are characteris­ medium-bedded limestones and calcareous sand­ tic of brackish-water deposits. As plants and coaly stones which are correlated with the Pariahuanca layers are also common it seems that the environ­ Formation of Benavides (1956). The lower part ment of deposition was a widespread system of of the formation consists of calcareous sandstones coastal swamps. The beds of oolitic limestone in­ which are distinguished from the sandstones of the dicate the sporadic development of shallow marine Farrat Formation by their calcareous content, conditions. greater tendency to be eroded, and the fact that Farrat Formation.—Although the Farrat For­ they weather yellowish brown rather than white mation of the Northern Andes is several hundred or gray. The upper limit of the formation is placed meters thick, it is represented in the Central where the medium-bedded limestones pass into Andes by only a few tens of meters of sandstones the thin-bedded marls, calcareous sandstones, which lie conformably on variegated siltstones of and limestones of the Chulec Formation. the Carhuaz Formation. At section 7, however, The Pariahuanca Formation has a maximum the formation appears to be separated from the thickness in the Central Andes of Peru at section Carhuaz Formation by an angular unconformity 16, northeast of Canta, where it is represented by of about 5°. The upper contact is drawn where the 210 m. of medium-bedded gray limestone with a quartz sandstones become brownish and cal­ few intercalations of dolomite, shale, and sand­ careous, indicating the base of the Pariahuanca stone. The formation wedges out eastward, and Formation. does not occur east of the Continental Divide. The maximum thickness of the formation in The thinning process is well displayed in the Oyon central Peru, measured at section 7, is 80 m. The area by sections 12 and 13, where the formation is average thickness for the region is about 40 m. respectively 120 m. and 54 m. thick. 16 JOHN J. WILSON

The limestones which make up the bulk of the stones of the formation may be a littoral fades on formation consist of shell material set in a matrix the basis that they are overlain by fully marine of fine-grained calcium carbonate. Some beds are limestones and underlain by the terrestrial Farrat virtual shell banks, with gastropods and Exogyra Formation. occurring in profusion. Many of the shells are Chulec Formation.—This unit was first de­ whole, though fragmental material is also com­ scribed by McLaughlin (1924) as the lower mem­ mon. Except at the base of the formation, terrig­ ber of his Machay Formation. In 1956 Benavides enous elastics do not occur in significant quanti­ raised the Chulec to the rank of formation, a ties. Oolites are not commonly found in the forma­ practice which is followed in this report. tion. The formation consists of 100-200 m. of marl, The Pariahuanca Formation is fossiliferous, limestone, and calcareous sandstone. It can be containing numerous poorly preserved specimens divided into two units, the upper being made up of of a limited number of species. The most common thin-bedded limestones and marls, and the lower fossil is a large Exogyra sp. indet. Specimens of of calcareous sandstones and marls. The ratio of Nerinea with delicately tapered spires up to IS cm. the lower unit to the upper unit decreases east­ tall are also abundant. A Natica sp. indet. is ward. common in some beds, and rudistid fragments also The Chulec Formation is underlain in the west occur. Part of the mold of a large cephalopod, by the limestones of the Pariahuanca Formation possibly Farahopliies, was found at section 8, east and in the east by the quartz sandstones of the of Chiquian. Goyllarisquisga Group. The lower contact of the Benavides reported a single ammonite, Para- Chulec Formation appears conformable, though hoplites, from the type section of the Pariahuanca gravel banks at the top of the Goyllarisquisga Formation and believed it to represent an Early Group at section 15 and the presence of coal Albian age. Fritzsche (1924) and Steinmann seams at the Chulec-Goyllarisquisga contact at (1929) considered the rudistid fauna to be Bar- section 22 may indicate disconformity. In the remian. The material collected by the writer is in­ west the base of the formation is taken as the adequate for the solution of the problem, but the horizon at which the first marls appear above the presence of the lower Middle Albian Chulec Pariahuanca Formation. In the east the base is Formation conformably above the Pariahuanca regarded as the first calcareous and fossiliferous Formation suggests an Early Albian age for the horizon above the sandstones of the Goyllaris­ latter. quisga Group. The upper limit of the formation is As the Inca Formation of the Northern Andes placed where the limestones and marls become contains Parahoplites and lies in the same strati- bituminous. graphic position as the Pariahuanca Formation In the southern part of the Central Andes a (Benavides, 1956), the two formations are be­ massive, light gray, coquinoid limestone up to 8 lieved to be time equivalents. The top beds of the m. thick forms the topmost unit of the Chulec eastern fades of the Goyllarisquisga Group are Formation, and is overlain by the dark-colored, correlated with the Pariahuanca Formation on thinly bedded shales and limestones of the Paria- the basis that they both lie conformably beneath tambo Formation. the Chulec Formation. The Aptian-Albian Eight thin sections were made to study the na­ Arcurquina Formation of the Arequipa area ture of the calcareous sandstones and the lime­ (Jenks, 1948) also contains Pariahuanca equiva­ stones. The former consist of subangular to sub- lents. In eastern Peru the oldest beds of the Huaya rounded quartz grains more or less surrounded by Member are Albian in age (Kummel, 1948), and calcareous cement. The limestones contain abun­ may be correlative with the Pariahuanca Forma­ dant shell fragments (PI. 2c), and are commonly tion. Where the basal Huaya is younger than dolomitic. Oolitic and silty limestones also occur. Albian, the Pariahuanca equivalent lies in the The faunal list for the formation is as follows.^ Agua Caliente Member. ' The significance of the symbols used in this and The fauna of the Pariahuanca Formation, succeeding faunal lists is: particularly the rudistids, implies deposition in a • Found only in the Central Andes (this report). shallow sea. The extreme rarity of pelagic in­ • • Found only in the Northern Andes (Benavides, 1956). vertebrates in the formation suggests a near- No period. Found in both the Central and Northern shore environment. The basal calcareous sand­ Andes. CRET.ACEOUS STRATIGRAPHY OF CENTRAL PERU 17

CEPHALOPODA Chonta Formation in eastern Peru (Kumniel, Protanisoceras blancheti (Pictet and Campiche)' 1948) indicates that these units are equivalent to Douvilleiceras monile (Sowerby) Parengonoceras pernodosum (Sommermeier) the Chulec Formation. The common Chulec Parengonoceras telranodosum (Lisson) echinoid, Holectypus {Coenholectypus) planatus Parengonoceras haasi Benavides' Roemer, has been reported from the Arcurquina Knemiceras raimondii Lisson Knemiceras attenuatum Hyatt Formation of .Arequipa by Newell (1949), which Knemiceras syriacum (von Buch) suggests a possible correlation between the two Knemiceras gabbi Hyatt Knemiceras iriangidare Benavides' formations. Knemiceras ovale Benavides' The lateral and vertical changes in rock type Knemiceras ziczag Breistroffer and faunal composition within the Chulec Brancoceras aegoceratoides Steinmann Lyelliceras lyelli (Leymerie) Formation indicate a marine transgression from the west, in which direction the sea deepened. The PELECYPODA lower unit is regarded as littoral or near-shore CucuUea brais Gerhardt facies, whereas the upper member indicates Ctwullea gerhardti Olsson Modiolus mutissus Olsson slightly deeper-water conditions. Neithea morrisi Pictet and Renevier Pariatamho Formation.—The Pariatambo For­ Exogyra aquila Brogniart mation was originally defined by McLaughlin Exogyra boussingauUi d'Orbigny Myopholas peruviana Olsson (1924) as the upper member of the Machay Yaadia hondaana (Lea) Formation, with a type section near Oroya. Fol­ Bucholrigonia abrupta (von Buch) Pterotrigonia tocaimaana (Lea) lowing the practice of Benavides (1956) the Cardita subparallela Gerhardt Pariatambo Formation is regarded as a separate Astarte debilidens Gerhardt formation in this report. Prolocardium elongatum Gerhardt Nucula turgida Olsson The Pariatambo Formation is found through­ Pinna sp. indet.'' out the Central Andes and much of the Northern Modiola pongena Olsson'' Pecten cf. tenouklensis Coquand'" Andes of Peru. It consists of a few tens of meters Pecten cf. sieversi Steinmann"' of thin-bedded shale, limestone, and dolomite. Both the carbonates and the shale are bituminous, GASTROPODA and dark gray or black in color. The rocks give off Turritella peruvianum Gabb'' a strong fetid odor, even after contact meta- ECHINOIDEA morphism. Enallaster peruanus Gabb The upper and lower limits of the Pariatambo Holectypus {Coenholectypus) planatus numismalis Formation are distinct throughout the Central Gabb Andes. The black or dark gray color of the forma­ Phymosoma texanum Roemer Echinobrissus subquadratus d'Orbigny tion clearly distinguishes it from the light-colored Bothriopygus compressus Gabb Chulec and Jumasha Formations. The relative abundance of the foregoing genera varies Chert nodules and veins are found throughout, within a section and from section to section, a variation but show a tendency to be most abundant at the that is related to the rock type. The lower, more clastic, fades of the formation is characterized by the following top of the formation. The chert is dark gray, and fossils in order of decreasing abundance: E. minos, N. occurs in nodular bands about 5 cm. thick. quinquecostata, H. planatus, and many bivalves. The The formation undergoes a marked facies upper, more calcareous, facies of the formation has fewer specimens of E. minos and H. planatus, but con­ change when traced from west to east. West of the tains ammonites and gastropods in large numbers. Continental Divide the formation contains a high proportion of black, strongly bituminous, shales. Although most early workers considered the Limestone occurs most commonly as nodules and Chulec Formation Aptian in age, the presence of concretions. The beds of limestone that are such ammonites as Knemiceras and Douvilleiceras present vary in thickness and give the impression led Benavides (1956) to conclude that the forma­ that they have formed as the result of the growth tion is actually early Medial iMbian in age. The of concretions along bedding planes. East of the fauna of the Chulec Formation in the Central Continental Divide the formation appears in a Andes substantiates Benavides' conclusion. calcareous shale-dolomite-limestone facies which The presence of Knemiceras in the lower beds is only slightly bituminous. The carbonates occur of the Crisnejas Formation of the Northern Andes in regular beds rather than as concretions. Of the (Benavides, 1956) and in the lower part of the five eastern facies carbonate rocks studied in thin 18 JOHN J. \V]LS()-\

section, four are silty, granular dolomites contain­ commonly incomplete, sections occur in synclines ing shell fragments and foraminifera. The remain­ on the east and west. ing specimen is very fine-grained limestone. Both the upper and the lower boundaries of the The faunal list of the I'ariatambo Formation is formation are conformable. The lower limit is as follows. easily discerned, as the medium-bedded, light- weathering limestones of the Jumasha Formation CEPHALOPODA are in contrast to the thinly bedded, dark-colored Desmoceras latidorsatum (Michelin)" Oxytropidoceras carbonarium (Gabh) limestones and shales of the Pariatambo Forma­ Oxylropidoceras douglasi Knechtel tion. The upper limit of the formation is placed Venezoliceras venezolannm (Stieier) Venezoliceras harrisoni Benavides' where the limestone becomes interbedded with Dipoloceras sp. marls containing the Celendin fauna. Brancoceras aegoceratoides Steinmann The average thickness of the Jumasha Forma­ Lyelliceras lyelli (Leymerie) (d'Orbigny) Lyelliceras pseudolyelli (Parona and Bonarelli) tion in the Central Andes is about 400 m. though Lyelliceras ulrichi Knechtel at section 17, Morococha, and section 20, Oroya,

PELECYPODA it is less than 200 m. thick. A casual survey of the Inoceramus concentricus Parker formation in the strongly folded and faulted Inoceramus salomoni d'Orbigny region near to the Continental Divide suggests Anomia sp. indet. considerable thicknesses, but closer examination Exogyra minos Coquand'' reveals that many apparently conformable se­ Fish scales and teeth quences consist of a series of sheets thrust one The fauna of the Pariatambo Formation west above the other. of the Continental Divide consists principally of The study of thirty-five thin sections of the ammonites, many of the specimens occurring in Jumasha Formation indicates a variety of lime­ calcareous concretions. Some of the shale beds stone and dolomite types. Although there are contain numerous compressed specimens of Ino­ many intermediate rock types, three main micro- ceramus concentricus. East of the divide the ratio facies are distinguished: of pelagic to benthonic forms decreases, and Fossil fragmental limestone and dolomite Inoceramus and Exogyra minos become the most Pelletal limestone and dolomite Fine-grained limestone and dolomite abundant forms. The Pariatambo Formation of the Northern Each microfacies has a wide horizontal extent and and Central Andes, the Muerto Formation of lateral facies changes are seldom seen. Vertical northwestern Peru (Fischer, 1956), and the gradations are abrupt, however, as the micro­ Chonta Formation of eastern Peru (Kummel, facies occur in units as thin as 1 m. The micro­ 1948) contain the late Medial Albian ammonite, facies are described here in order of decreasing Oxytropidoceras carbonarium- (Gabb). The se­ importance. quence exposed at section 2 is probably an Fossil fragmental limestone and dolomite.—Most equivalent of the formation, for it contains of the Jumasha Formation consists of commi­ Lyelliceras, a genus which is common in the Pa­ nuted shell debris set in a matrix of fine- to me­ riatambo Formation. dium-grained limestone or dolomite (PL 2d). The lithologic types and faunal assemblages Although the majority of shell fragments are suggest that euxinic conditions prevailed west of unidentifiable, some beds are made up of the the divide during Pariatambo time, and that the unbroken shells of various species of Exogyra, sea shallowed eastward. Ostrea, and Actaeonella. Foraminiferal tests do Jumasha Formation.—The Jumasha Formation occur, but do not constitute more than 10 per cent was first described by McLaughlin (1924), and of any rock studied. Euhedra of authigenic consists of several hundred meters of medium- quartz are commonly present, reaching a length bedded limestones and dolomites. The formation of approximately 0.1 mm. is topographically prominent and has a character­ Pelletal limestone and dolomite.—Several rock istic light gray color which facilitates its recogni­ specimens were found to consist of small, dark, tion during reconnaissance work. The main out­ structureless pellets set in a granular matrix of crop is restricted to the mountains along the dolomite or calcite (PI. 3a). The pellets are mainly Continental Divide in central Peru, though other, spherical, though irregular shapes are also com- CRKT.VCKOUS STRATIGRAPHY OF CENTRAL PERU 19

»,V * ••• • *

'*iw*^'l' .,4-. ^ ^ _«B *^"^ • '•• .. ^

PL. 3. -Photomicrographs of rocks of Jumasha Formation and Celendin ]'"ormation. a. Pelletai dolomite, Jumasha l''ormation, section 11. Ordinary light, X30. Fine-grained, roughly sj)heri(:al pellets set in matrix of fine-grained dolomite. b. Homogenous dolomite, Jumasha Formation, section 15. Ordinary light, X270. ("onsists of very small interlocking crystals of dolomite. c. Fine-grained limestone, Jumasha Formation, section 18. Ordinary light, XIOO. Consists completely of fine-grained calcite. d. Dolomitic limestone, Celendin Formation, section 6. Ordinary light, X50. Foraminiferal tests set in matrix of dolomite and calcite. mon. The size of the pellets is variable, and though some of them can be seen to contain dolo­ within a single thin section examples may be mite rhombs. One or two thin sections consist of found ranging from less than 0.1 mm. to more pellets which grade into the matrix without hav­ than 0.5 mm. It is usually impossible to deter­ ing a distinct boundary. mine the mineralogic character of the pellets. It is possible that some of the fine-grained 20 JOHN J. WILSOX

limestones are derived from pelletal limestones intraformational conglomerate approximately 10 which have lost all trace of internal structures as cm. thick, though no other clearly defined ex­ a result of diagenesis. Some of the pelletal lime­ amples are known in the formation. stones and dolomites contain oolites, the concen­ The faunal list of the Jumasha Formation is as tric layering of which is in contrast to the struc­ follows: tureless interiors of the pellets. Rocks made up CEPHALOPODA predominantly of oolites are, however, rare in the LydUceras idrichi Knechtei' Jumasha Formation. Oxytropidoceras douglasi Knechtei' Fine-grained limestones and dolomites.—Some PELECYPODA beds of the Jumasha Formation consist of fine­ Lima sp. indet.'' grained limestone or dolomite devoid of pellets Anomia sp. indet.'' and shell material. The dolomites occur as yellow­ Area sp. indet."' ish weathering, 1 m.-thick beds which can be Exogyra ponderosa Steinmann'' followed continuously for more than 2 km. Thin GASTROPODA section studies indicate that the rock is made up Actaeonella sp. indet.'' of interlocking dolomite crystals with a mean Natica sp. indet.'' length of approximately 30 microns (PI. 3b). The ECHINOIDEA uniform texture and clear-cut upper and lower Bothriopygus compressus Gabb'' contacts suggest that dolomitization occurred penecontemporaneously rather than considerably The ammonite species indicate that the Ju­ after the time of deposition. masha Formation dates from the Late Albian. The fine-grained limestone occurs typically as As the formation is conformably overlain by approximately 1 m.-thick beds which weather to a Santonian, its age range is considered Late light gray color. Vertical gradations into bio- Albian through Coniacian. clastic and pelletal carbonates are common. The The stratigraphic position of the Jumasha rock consists of a mosaic of interlocking crystals Formation between the Pariatambo and Celendin which give it a uniform texture (PI. 3c). Formations is occupied in the Northern Andes by On the east, at sections 6, 9-11, 14, 19-20, and a thick sequence of limestones and shales which 22, the relative abundance of the various micro- Benavides (1956) divided into the Cajamarca facies is as follows: Formation, the Quillquiiian Group, and the Fossil fragmental limestone and dolomite 40% Puillcana Group. In northwestern Peru the Pelletal limestone and dolomite 20% Jumasha equivalent is the Copa Sombrero Forma­ Fine-grained limestone and dolomite 15% tion (Fischer, 1956). The Late Albian through Intermediates 25% Coniacian sequence in eastern Peru includes part Dolomites of all types constitute more than 50 of the marine shales and limestones of the Chonta per cent of the formation at these sections. On the Formation and their sandy lateral equivalents. west much or all of the formation has been re­ Although the Jumasha Formation is commonly moved by erosion at sections 5, 7, 8, 12, 13, and a bioclastic limestone, few of the fossils are whole. 16. It is difficult to determine the relative abun­ The most important genera numerically are dance of the various microfacies in these areas, Exogyra and Ostrea, which are the only fossils though the following estimate has been made: found in most sections. Benavides (1956) found Fossil fragmental limestone and dolomite 20% that in the Northern Andes the limestones and Pelletal limestone and dolomite 30% shales equivalent in age to the Jumasha Forma­ Fine-grained limestone and dolomite 25% tion contained an abundant and varied fauna. Intermediates 25% The rocks of the Jumasha Formation do not Limestone is more abundant than dolomite at indicate any reason why the population should these sections, in contrast to the situation east of have consisted of so few types. Indeed, the bio­ the Continental Divide. clastic limestones suggest that invertebrates may Sedimentary structures are uncommon in the have been abundant. Diagenetic changes may Jumasha Formation. Ripple marks are seen in have destroyed many of the fossils, and a further some outcrops, and micro-cross-bedding is found possibility is that scavengers may have broken up in some of the silty rocks. At section 18 there is an much of the shell material. This latter possibility CRETACEOUS STRATIGRAPHY OF CENTRAL PERU 21

is supported by the following facts: (a) shell mites, and calcareous shales which are referred to debris is abundant; (b) the majority of identifi­ the Celendin Formation. Between sections 17 and able fossils are thick-shclled and difficult to 18 the formation wedges out and at the latter the break; (c) the current system was apparently Jumasha Formation is overlain directly by the weak and unlikely to have been an efficient means redbeds of the Casapalca Formation. of shell destruction; (d) fossils are very abundant The principal fo.ssils of the Celendin Formation in the bituminous Pariatambo Formation, which are: was deposited in an oxygen deficient environment. CEPHALOPOD.\ As soon as the content of organic carbon de­ Barroisiceras sp.' creases the fossil content becomes limited, sug­ Tissotia hedbergi Benavides' gesting that when the bottom waters became Heterotissotia peroni Lisson' aerated scavengers became important. Buckiceras bilobatum Hyatt' Desmophyllites gaudama (Forbes)' The Jumasha Formation was deposited in a sea Texanites sp." which was shallow enough to permit the growth Tissotia steinmanni Lisson Tissotia fourneli (Bayle) of extensive banks of Exogyra and Ostrea. The Lenticeras baltai Lisson' limestone conglomerates imply that in some areas Lenticeras lissoni Knechtel' shoaling took place. There was very little trans­ PELECYPODA port of terrigenous material into the Jumasha sea, Inoceramus sp. due possibly to a combination of weak currents Lima sp. and distance from a source area. Ostrea nicaisei Coquand Celendin Formation.—The type section of this Cardium pulchrum Bruggen Pinna sp. formation is near the town of Celendin in northern Peru, where it is represented by 255 m. of richly ECHINOIDEA fossiliferous shales and limestones of Coniacian Ilemiaster fourneli Deshayes Goniopygus hemicidariformis Bruggen' and Santonian age. In the Central Andes a sim­ Goniopygus superbus Cotteau and Gauthier • ilar lithologic character is found here and there in the same stratigraphic position, directly beneath The species of Tissotia found in the Celendin the redbed formations. Although diagnostic fossils Formation in the Central Andes occur only at the are not common at this horizon in the Central top of the sequence at the type section. On this Andes there seems little doubt that the facies basis the Central Andean Celendin Formation is represents the Celendin Formation. regarded as a time equivalent only of the upper In the Central Andes the lower limit of the part of the type section, and is therefore Santon­ formation is made where the thin-bedded shales ian in age. and limestones pass conformably downward into The Celendin Formation probably is correla­ the medium- or thick-bedded limestones of the tive with the Vivian Formation of eastern Peru, Jumasha Formation. The contact between the which Kummel (1948) placed in the Senonian on Celendin Formation and the overlying redbed the basis of its stratigraphic position. formations is marked by a change in color from The fauna of the Celendin Formation indicates cream to bright red, the relationship being one of a shallow marine environment. Toward the end conformity or slight angular unconformity. of Celendin time circulation became restricted and Four thin sections indicate the presence of both evaporite beds were deposited locally. Finally limestones and dolomites in the formation. The emergence took place and redbed deposition carbonates are fine-grained or pelletal, and con­ commenced. tain varying quantities of shell material and Redbed formations.—Overlying the Cretaceous foraminiferal tests (PL 3d). marls and limestones in parts of the Peruvian Passing southward the formation appears with Central Andes are varying thicknesses of non- reduced thickness at section 9. In the area of fossiliferous redbeds with intercalated limestones section 13 it is seen as a sequence of gray calcare­ and conglomerates. The redbeds occur mainly, ous shales and limestones passing gradationally though not exclusively, east of the Continental up into the redbeds of the Pocabamba Formation. Divide. In large areas west of the divide the In the southern part of the region, section 17 has youngest Cretaceous rocks are Albian, and the 115 m. of creamy weathering limestones, dolo­ redbed formations are poorly represented. In some 22 JOHN J. WILSON

're'w than 1,000 m. Farther east they become thinner and wedge out altogether near the Paleozoic out­ HUARAS O crop. Thick redbed sequences occur in eastern Peru, thicknesses of several kilometers having 1 *^* HUANUCO been reported by Ruegg (1949). Id's — Although conglomerates of limestone and quartzite fragments are common, the redbed •-•4 formations consist mainly of bright red siltstones

\ OYONoj CERRO DE PASCO and fine sandstones. Limestone units are present o locally, occurring as white weathering lenticular masses. Volcanics are interbedded with the silt­ \ HUACHO stones of the Casapalca Formation, though they «-4 are not common in the Pocabamba Formation. As the redbed formations have not yielded 7^ QOROYA diagnostic fossils their precise age is unknown. The fact that they are locally interbedded with 1 LIMA HUANCAYO. 6^ « the Santonian indicates that they are at least • DIRECTION OF 1^ partly Cretaceous in age. Where they overlie the CURRENT OR SLOPE ^v Lower Cretaceous they may be even older than 100 KM. ^ Santonian. 1 7»'* On the basis that the redbed formations contain FIG. 6.—Current and slope directions in central limestones and locally grade down into the Peru during Early Cretaceous. Celendin Formation it is possible that they are partly of marine origin. The conglomerates of areas, e.g., on the Continental Divide east of rounded cobbles are, however, identical with the Oyon, the contact between the redbeds and the modern fluviatile deposits of the region, and sug­ Celendin Formation is gradational, with inter- gest principally continental conditions for the bedding of fossiliferous gray calcareous shales and deposition of the redbed formations. red siltstones. At the majority of sections, how­ ever, the redbed formations are separated from the Upper Cretaceous carbonates by an erosion surface. At Oroya there is an angular unconform­ ity of approximately 5°, though a disconformable relationship is more common. The top of the redbed formations is rarely seen. The overlying rocks are Lower Cenozoic volcanics which crop out close to the Continental Divide. Farther east the redbeds are commonly the youngest rocks present. McLaughlin (1924) named the redbeds of the Goyllarisquisga area the Pocabamba Formation. The thick sequences which crop out about the head of the Rimac Valley and on the east were named by him the Casapalca Formation. These formations are at least partly equivalent to one another. The redbed formations vary greatly in thick­ ness. At the Continental Divide northeast of Canta only a few meters of red conglomerate lie between the Cretaceous limestones and the Cenozoic volcanics. In synclinal basins east of the FIG. 7.—Isopach map of Lower Cretaceous divide thev reach an estimated thickness of more formations of central Peru. CRKTACEOUS STRATIGRAPHY OF CKNTRAL I'KRU 2,1

SOURCE .AREAS OF GOYLLARISQUISGA GROUP Peruvian trough (Fig, 11). The Maranon geanti­ The origin of the elastics wliich make up the cline was not inundated, and evidently stood as a Goyllarisquisga Group of the Northern and Cen­ barrier between the two troughs. If this is so, it is tral Andes has not yet been determined. Deriva­ difficult to see how sediments from the Brazilian tion of tens of thousands of cubic kilometers of shield could have reached the West Peruvian elastics is a problem in itself. The fact that ortho- trough. quartzites and protoquartzites alone amount to Although the shield can not be ruled out as a more than 3X10* cu. km. indicates that the source of the Goyllarisquisga Group, the Maraiion problem consists not only of determining the geanticline seems to be more suitably situated. origin of a large volume of elastics, but also of Very little is known of the pre-Cretaceous units of accounting for the overwhelming predominance of the geanticline. Traverses made by the writer quartzose sandstones in the group. across parts of the geanticline indicate an abun­ Studies of directional sedimentary structures dance of schists, phyllites, slates, and graywackes, (Fig. 6) indicate that during the Early Cretaceous ranging in age from pre-Cambrian to Lower central Peru had two principal current regimes. Paleozoic. A general eastward transport of sediment char­ Overlying the basement rocks are Upper Pale­ acterized coastal Peru and the area of sections 17, ozoic formations such as the Mississippian Ambo 18, 19, and 22. In the remainder of the Central Group (300 m. of subgraywacke, shale, and con­ Andes currents were directed toward the west. glomerate), the Pennsylvanian Tarma Formation The origin of the westerly derived sandstones is (250 m. of sandstone and shale with intercalated considered first. limestones), the Lower and Middle Permian Where studies of the Mesozoic of coastal Peru Copacabana Formation (200 m, of limestone and have been made, as in northwestern Peru (Fischer, shale), the Upper Permian Mitu Group (variable 1956), and south of Lima (Ruegg, 1957), the thicknesses of arkose, red shale, and andesitic Lower Cretaceous or Tithonian has been found on volcanics), and the Upper Triassic and Liassic top of folded Lower Jurassic or Triassic forma­ limestones of the Pucara Group. The dirty sand­ tions. On this basis it is believed that parts of stones of the Upper Paleozoic represent a possible coastal Peru were subjected to uplift and erosion source rock for the Goyllarisquisga Group. The during the Medial and Late Jurassic. The Lower erosion and reworking of these arkoses and sub- Cretaceous elastics of coastal Peru were derived graywackes, bringing about the elimination of the from these tectonic lands. less stable minerals, could lead to the formation of The problem of the origin of the easterly protoquartzites and orthoquartzites such as derived facies of the Goyllarisquisga Group is characterize the Goyllarisquisga Group, Indeed, more difficult, and the location and nature of the in the Pataz area of northern Peru, in the vicinity source areas remain uncertain. McLaughlin of the geanticline, the writer has seen Lower (1924) believed that the Goyllarisquisga Group Cretaceous sandstones directly overlying units of was derived from the basement rocks of what is the Mitu and Ambo Groups. now known as the Maranon geanticline. Harrison The sub-Goyllarisquisga elastics found in sec­ (1943) also assumed, on the basis of the pebble tion 21 may represent a subsidiary source rock of bands in the Lower Cretaceous, that the source the Goyllarisquisga Group, though the precise area was nearby. Benavides (1956), on the other significance of these conglomerates and arkoses hand, suggested an origin in the Brazilian shield. will not be known until more data are available Whereas the Brazilian shield did shed material concerning their extent. into the East Peruvian trough, it is unhkely that The status of the problem of the origin of the it contributed significantly to the West Peruvian Goyllarisquisga Group may be briefly summa­ trough, for the following reason. The Esperanza rized as follows. It is probable, though not certain, Member of the Oriente Formation (Kummel, that the source area of the easterly derived facies 1948) represents an Aptian marine transgression lay in the geanticline. There is no indication that from the north and west into the East Peruvian the older Paleozoic and pre-Cambrian rocks were trough. Oolitic fimestones within the Carhuaz extensively exposed there during the Early Formation indicate that at about the same time Cretaceous, but the Upper Paleozoic formations there were marine incursions into the West certainly contributed. The source of the westerly FIG. 8.—Correlation table. CRETACEOUS STRATIGRAPHY OF CENTRAL PERU 25 derived facies of the group probably lay in the Formation and a time equivalent of much of the tectonic lands which were uplifted in coastal Peru Carhuaz and Farrat Formations. by a Late Jurassic orogeny. Except in southern Peru the post-Aptian forma­ tions of the Andean Region are fossiliferous lime­ CORRELATION AND STRATIGRAPHIC stones and shales, the age ranges of which are RELATIONS OF CRETACEOUS shown in Figure 8. FORMATIONS OF PERU Figure 9 shows the inferred stratigraphic rela­ Figure 8 shows the age relationships of the tionships of the Cretaceous formations in Peru, Cretaceous formations in central Peru, and their and is based on observed field relations and the correlation with the Cretaceous formations in correlations made in Figure 8. The central parts other parts of the country. of sections AB and CDEF represent the writer's A major problem lies in the correlation of the concept of the stratigraphic relationships in those non-fossiliferous graywacke-volcanic-shale se­ areas prior to the erosion of the Cretaceous forma­ quences of the coastal Cretaceous with the tions. Although the Goyllarisquisga Group is Andean sequence of quartzose sandstones and shown extending with greatly reduced thickness carbonates. Until more paleontological data be­ across the axis of the Marafion geanticline, it is come available it is impossible to correlate the possible that the first Cretaceous sediments to be greater part of the coastal sequence with the laid down there were facies equivalents of the Andean formations. Chulec Formation. Correlation between the Lower Cretaceous sandstone-shale-limestone sequences of the An­ TECTONIC FRAMEWORK OF ANDEAN BELT dean Region constitute a further problem. From Figures 9 and 10 it is apparent that dur­ Although the Murco and Huancane Formations ing the Cretaceous the Andean belt was the site of of southern Peru, the Goyllarisquisga Group of two linear troughs separated by a relatively posi­ central and northern Peru, and the greater part of tive area. the Oriente Formation of eastern Peru are known The West Peruvian trough consists of two large to be Lower Cretaceous, precise age relationships basins separated by a minor arch situated at remain to be ascertained. The oldest diagnostic approximately Latitude 8° South. Both basins fossils found in the Cretaceous of these areas are subsided at least 3,000 m. during the Cretaceous. as follows: Late Valanginian in the western slopes During the Neocomian and Aptian the trough of the Central and Northern Andes (Benavides, was separated from the Marafion geanticline by a 1956); Medial Albian in the eastern part of the hinge-line which extended in a fairly straight line Western Cordillera in the Central and Northern from about Rio Pallanga to the neighborhood of Andes (Benavides, 1956, and this report); Aptian Celendin. The effect of the hinge-line on the facies or Albian in the Arequipa region (Jenks, 1948); and thickness of the Lower Cretaceous formations and Aptian in eastern Peru (Kummel, 1948). In in the Central Andes is apparent in Figures 9 and these circumstances correlation is attempted 10. The fact that the western facies of the Goy­ largely on the basis of lithology and stratigraphic llarisquisga Group is not found east of the Rio position with respect to dated horizons. Pallanga-Celendin line suggests that the position As explained earlier in this report there is a of the hinge remained constant during much of relatively local problem of the relationships be­ the Early Cretaceous. The post-Aptian history of tween the eastern and western facies of the Goy­ the hinge-line is uncertain. Although the Chulec llarisquisga Group. Benavides (1956) believed and Pariatambo Formations have slightly differ­ that the eastern facies was a lateral equivalent of ent facies on the flank of the geanticline and in the Farrat Formation and part of the Carhuaz the West Peruvian trough, there is no evidence of Formation, but that it lay disconformably on the marked movement along the hinge-line. The Santa and Chimu Formations. In the Central straightness and constant position of the hinge- Andes it is apparent that the Chimu Formation line suggest that it represents a series of faults in and the eastern facies of the Goyllarisquisga the basement. Group form parts of the same stratigraphic unit. Southeast of Rio Pallanga there is no clear line In this report the eastern facies of the group is of demarcation between the West Peruvian regarded as a facies equivalent of the Chimu trough and the geanticline. Extending out into FIG. 9.—Stratigraphic relations of Cretaceous formations of Peru. ('RKTACKOUS S ^RATI(;R.\PH^• OF CKXTRAL I'I:RU 27

FIG. 10.—Isopach map of Cretaceous formations of Peru. the trough from the Yauli area is a platform-like The East Peruvian trough was formed by a prolongation of the geanticline. The western limit slight basining of the margin of the Brazilian of the platform is unknown, for it is covered by shield, the maximum subsidence during the Cenozoic volcanics. Cretaceous being about 2,500 m. The work of Southeast of Yauli the relationships between Kummel (1948) suggests that the trough merged the geanticline and the trough become even more gradually eastward with the shield. There is no obscure. On the basis of the similarity between information available on the relationships be­ the Cretaceous sequences at Huancavelica (Fer­ tween the western part of the trough and the nandez Concha, 1952), in the Huancayo area Maraiion geanticline. The trough continued north­ (Miranda, 1956), and at section 22, it appears westward into eastern Ecuador, though subsid­ possible that the trough extended as far east as ence there was less than in eastern Peru (Tschopp, these areas 1953). The extension of the trough toward the 28 JOHN J. WILSON

southeast is known in a general way as far as the marine units is shown in Figure 11. Limestones Rio Pachitea (Singewald, 1928), from beyond found within the Lower Cretaceous sandstones at which there is no published information. section 22 and at Huancavelica (Fernandez Concha, 1952) may indicate that these areas were HISTORICAL GEOLOGY also submerged at this time. Marine conditions At the end of the Jurassic the Andean belt did not, however, extend to the Arequipa region began to be divided into tectonic units, the at this time. The source areas southwest of Lima positions of which are shown in Figure 3. The may have been submerged by the transgression, oldest units deposited in the West Peruvian but the fact that marine units extend only to the trough were the shales of the Tithonian Chicama Rio Pallanga-Celendin Kne suggests that the Formation (Stappenbeck, 1929) and the sand­ Maraiion geanticline remained emergent. stones which Ruegg (1957) found southeast of By the end of the Early Hauterivian the seas Lima. Both these formations are of marine origin. had begun to withdraw from the West Peruvian Fischer (1956) found the oldest Cretaceous in the trough. The disconformity between the Santa and far northwest of Peru to be Albian, indicating that Carhuaz Formations indicates minor erosion at the trough was closed in that direction. Jenks this time, though in the Central Andes sedimenta­ (1948) found Upper Jurassic units in Arequipa, tion was continuous. suggesting that the trough extended at least that From the Medial Hauterivian to the end of the far southeast. Aptian the two troughs accumulated mainly con­ There was a minor regression at the end of the tinental sandstones and shales, while the Maraiion Tithonian (Ruegg, 1957), followed by the local geanticline continued to act as a barrier between renewal of marine conditions in the Berriasian, them. The Carhuaz Formation of the West when the volcanics of the Puente Piedra Forma­ Peruvian trough was deposited in brackish-vi'ater tion were poured out in the vicinity of Lima. The swamps which were occasionally inundated by main phase of subsidence did not begin until the short-lived marine transgressions from the west. Valanginian, however, when sandstones, shales, The overlying fluviatile sands of the Farrat and coal seams began to be deposited over a great Formation indicate a regression at the end of the part of the trough. The elastics in the Lima area Aptian. were derived from tectonic lands on the south­ The East Peruvian trough had a similar history. west, and deposited under alternately marine and Fluviatile conditions gave way in the Aptian to a non-marine conditions. Non-marine conditions minor marine transgression (Kummel, 1948) prevailed throughout the eastern part of the which gave the Esperanza Member of the Oriente trough, where the sandstones and shales of the Formation. The advancing sea probably entered Oyon and Chimu Formations were deposited. the trough by a gap in the geanticline in northern The corresponding history of the East Peruvian Peru. The transgression was short-lived, however, trough has not yet been deciphered. All that can for the Paco and .Agua Caliente Members indicate be said is that the trough probably began to a return to fluviatile conditions. subside early in the Neocomian, the initial de­ While these events were progressing in the two posits being the non-marine sandstones of the troughs, sediments began to accumulate on the Cushabatay Member of the Oriente Formation flanks of the geanticline. The deltaic or fluviatile (Kummel, 1948). The Lower Cretaceous se­ orthoquartzites of the eastern fades of the quence in eastern Ecuador is thin (Tschopp, Goyllarisquisga Group were deposited as lateral 1953), which may mean that subsidence com­ equivalents of the sandstones and shales of the menced there later than in eastern Peru. The con­ Carhuaz Formation. The facies change takes tinuation of the East Peruvian trough to the place at about the Rio Pallanga-Celendin line, southeast is known only as far as the Rio Pachitea, which must have been acting as a hinge at this from beyond which there is no information time. Conditions on the eastern side of the geanti­ available. cline remain unknown. The presence of Lower In the Late Valanginian the sea transgressed Cretaceous sandstones at the Boqueron on the from the west into the West Peruvian trough and eastern flank of the geanticline (Ruegg, 1949) deposited the limestones of the Santa and Pam­ suggests a symmetrical distribution of an ortho- plona Formations. The probable extent of the quartzite-protoquartzite facies on either side of CRETACEOUS STRATIGRAPHY OF CENTRAL PERU 29

10 S-

'78* IQUlToSr-"

TS { ( f-^\ V^\5 1 1 TRUJILL^ V 1 \PUCALtPA -^ •A \\j\ AA \' 1 \ 1 -lO'S A]—rV 1 ( \ '°'^' "\-"]— 1 \ 1 ^ Py'ceRRO PE \ 1 fj-H-A PASCO C^ EARLY LIMA VTI,^ ALBIAN \v 500 KM. .75*W

GRAYWACKE, SHALE, AND VOLCANICS \i. -fl LIMESTONE AND SHALE

|:::::::: j SANDSTONE (ORTHOQUARTZITE, PROTOQUARTZITE, ETC.) MARL

LIMESTONE AND DOLOMITE |-^>-^j REDBEOS

l^l; •• :| SANDSTONE AND SHALE 1 AREAS OF EROSION

FIG. IL-Lithofacies maps of northern and central Peru, Valanginian-Early Cenomanian. 30 J(^HN J. WILSON'

TURONIAN

'75*W lOUlTOSr^ 5'sS .Pi^^B upEp5^'^«

TRUJILLO \^^ ^;;;;S^ycAUUPA •

-IO*S ^^^^:;\: itfS-

LIMA V ' SANTONIAN MAESTRICHTIAN

, SOO KM. .75'W

FIG. 12.—Lithofacies maps of northern and central Peru, Turonian-Maestrichtian, the geanticlinal axis (Fig. U). The predomi­ places within the Andean belt at the end of the nantly sandstone sequences on the eastern and Aptian. At section 7, northeast of Chiquian, the western flanks of the geanticline grade respec­ Farrat Formation lies with angular unconformity tively into the sandstones and shales of the East on the Carhuaz Formation, and in northern Peru Peruvian trough and the West Peruvian trough. Benavides (1956) found the Lower Albian Inca Minor tilting and warping occurred at scattered Formation disconformably overlying the Aptian. C'RKIACKOUS .ST'R.VriGR.APHY OF Cl-ATR.AL PERU M

In the Early Alhiau there began a marine followed disconformably by the Cotacucho Group. transgression which eventually extended marine Continental conditions prevailed in the Titicaca conditions over much of the Andean Belt. At first region from the Turonian onward, the Cotacucho the sea reached only as far east as the hinge-line Group, Vilquechico Formation, and Munani (Fig. 11), giving the carbonates of the Inca Formation l)eing non-fossiliferous continental Formation in northern Peru (Benavides, 1956), elastics. the Pariahuanca Formation in central Peru, and It is not known what conditions prevailed in the Arcurquina Formation in the Arequipa region the Arequipa region during the Late Cretaceous of southern Peru (Jenks, 1948). During the Medial as the youngest Cretaceous deposits found are .•\lbian most of northwestern Peru and the .Albian (Jenks, 1948). The marine Cenomanian of geanticlinal region became inundated (Fig. 11). the Titicaca region suggests that marine condi­ The sea reached also into parts of the East Peru­ tions also persisted in the Arequipa area at least vian trough (Ducloz and Rivera, 1956) and into until that time, and possibly until much later eastern Ecuador (Tschopp, 195,3). Continental in the Cretaceous. sandstones continued to be deposited in the During the Turonian the marine advance central and southern parts of the East Peruvian reached the Cushabatay area of the East Peruvian trough, and in the Titicaca area (Newell, 1949). trough (Fig. 12). Essential!}' continental or very- Volcanic activity began to be important in the shallow marine conditions prevailed in the Titi­ West Peruvian trough during the Albian. Gray- caca area. Marine conditions persisted over the wackes, shales, and volcanics were deposited in remainder of the Andean belt in Peru. Limestones the area of section 2, while interbedded pyro- predominated in the area of the present Cordil­ clastics and shales were also being deposited in lera, while pyroclastics and shales continued to northwestern Peru (Fischer, 1956) and western accumulate in northwestern Peru (Fischer, 1956). Ecuador (Tschopp, 1953). During the Coniacian the sea achieved its During the Late Albian parts of the Andean belt greatest extent in the East Peruvian trough, were uplifted. The Late Albian-Cenomanian reaching east of the Ucayali River into the Con- Rosa Formation of Benavides was laid down as an tamana Mountains (Kummel, 1948). As the essentially continental deposit resulting from the Central and Northern Andes received an influx of erosion of an uphfted part of the Marafion elastics at this time, depositing the marls of the geanticline. Benavides (1956) also indicated that Celendin Formation, the greatest advance of the the Jequetepeque Valley of northern coastal Peru sea in that region ma}' have been pre-Coniacian. began to receive elastics at this time. As carbon­ The Santonian was a time of emergence (Fig. ates were simultaneously being deposited on the 12). The sea withdrew from northwestern Peru east the source of the elastics may have been an (Fischer, 1956), while the continental Vivian uplifted area on the west. Formation accumulated over large areas of the The sea continued its advance during the East Peruvian trough (Kummel, 1948). The Cenomanian. In the East Peruvian trough marine increasing clastic-carbonate ratio over much of conditions spread farther south and east, in which the Andean belt suggests that the sea was with­ direction the base of the Chonta Formation drawing from that region too. becomes younger (Ducloz and Rivera, 1956). In The influx of terrigenous elastics which began the West Peruvian trough the volcanism which in the Coniacian and Santonian culminated in the began in the Albian continued, thick sequences of general replacement of carbonate deposition by shales, pyroclastics, and graywackes being de­ redbed deposition in the Campanian and Mae­ posited in northwestern Peru (Fischer, 1956). The strichtian (Fig. 12). Although the sea advanced tufifaceous shales and graywackes of sections 3 into northwestern Peru and marine-brackish-water and 4 may represent a southward extension of this sediments accumulated in eastern Peru, the Cam­ facies. A fossiliferous limestone in the Moho panian was essentially a time of emergence. The Group of the Titicaca area indicates that the sea emergence was more or less complete by the advanced into this region by the Cenomanian Maestrichtian when marine conditions continued (Newell, 1949). There was, however, withdrawal only in northwestern Peru (Fischer, 1956) and in of the sea and some erosion possibly before the northern Peru (Rivera, 1956). end of the Cenomanian, for the Moho Group is The shedding of thick, locally conglomeratic, 32 JOHN' J. WILSON

TABLE I. THICKNESSES (METERS) OF CRETACEOUS FORMATIONS IN CENTRAL ANDES OF PERU

Oyon1Chim|San|Carh|Fa• Phua Chul' Pta Juma Gel Hedbd FOHMATIONS aceous GoyllarisquisRa Gp. SECTIONS

1025+ 94+ 76 603 30 87 135+ 5 Machac 1212+ 485+ 138 25 433 131 200+ 6 La Union 768+ 53^*+ 80 117 12 25+ 7 Aquia 1129+ 50+ I'^g 796 134 100+ 8 Pomapata + 991 600 ,122 70 17^ 25 150+ 9 W. of BanoB 810+ 337+ 107 76 290 80 + 10 E. of Banos"*"

1177+ 250+ 266 44 617 500+ 11 Lauricocha 1804+ 98+ 487 146 549 36 120 118 50 200+ 12 Churin - Oyon 1296+ 400+ 121 490 i 42 3'^ 135 5^ 20 + 13 E. of Oyon 89*^+ 280+ 107 59 443 25 1000+ 14 Yanahuanca 627+ 478 149+ 15 Goyllarisquisga 2050 215+ 517 112 496 65 210 198 137 100+ 16 Cerro La Viuda 722 138 232 52 185 115 200+ 17 Morococha 655 156 241 k7 211 200+ 18 Huallacochai 733+ 217 350 86 80+ 19 Carahuacra"*" 591 167 230 59 135 200+ 20 Oroya"*" 480+ 253 227+ 21 NE. of Oroya "^ 1512 851 280 44 337 250+ 22 Jatunhuasi redbed deposits over much of the Andean belt (1958), however, after a thorough consideration during the Campanian and the Maestrichtian of the uphf t of the Andes, concluded that phases indicates the initial phase of the Andean orogeny of strong folding took place in the Eocene and (the Peruvian phase of Steinmann, 1929). The Oligocene. Following the outpouring of consider­ distribution and texture of the redbed formations able thicknesses of volcanics in various parts of suggests that this phase of uplift was centered in the Andes, the final phase of the Andean orogeny the West Peruvian trough. The erosion products (the Quichuan phase of Steinmann, 1929) prob­ of the tectonic lands were shed eastward, where ably took place in the Pliocene. continental and neritic conditions persisted. The geanticline may also have been uplifted at this APPENDIX time, though strong folding did not occur. Eastern Owing to restrictions on space the descriptions Peru continued to subside, and accumulated great of the measured sections can not be included in thicknesses of redbed elastics. this report. They will be published in the Boletin At some time in the Cenozoic a more active de la Sociedad Geologica del Peru. However, the phase of orogeny commenced (the Incaic phase of sections 1-4 in coastal Peru are given here in Steinmann, 1929). The redbeds and underlying abbreviated form, and the Andean sections 5-22 strata were folded and faulted to varying degrees are summarized in Table I. A -{- sign beside the throughout the breadth of the Andean belt in name of the section indicates that the Goyllaris­ Peru. The precise date of this phase of the orogeny quisga Group is not differentiated into formations is not known. Newell (1949) suggested a Miocene i.e., in the case of the eastern and southern facies age for this phase in the Titicaca area. Petersen of the group. CRETACEOUS STRATIGRAPHY OF CENTRAL PERU 33

The alabreviations used in the table for the cimiento Geologico de los yacimientos petroliferos del departamento de Puno: Bol. Cuerpo de Ing. de names of the formations are as follows: Chimu Minas v Petrol, del Peru, Dept. de Petr61eo, no. Formation (Chim), Santa Formation (San), 115, 100 p. Carhuaz Formation (Carh), Farrat Formation Ducloz, C, and Rivera, R., 1956, La Formacion Chonta en la Region del Rio Cahuapanas, Loreto: Bol. Soc. (Fa), Pariahuanca Formation (Phua), Chulec Geol. Peru, Tomo 30, p. 131-140. Formation (Chul), Pariatambo Formation (Pta), Fernandez Concha, J., Yates, R. G., and Kent, D. F., Jumasha Formation (Juma), Celendin Formation 1952, Geologfa del Distrito Mercurifero de Huan­ cavelica: Inst. Nacional de Investigaciones y Fomento (Cel). The redbed formations (Pocabamba For­ Mineros, bol. 5. mation and Casapalca Formation) are grouped 1958, Geologfa del Morro Solar, Lima: Bol. Soc. Geol. Peru, Tomo 33, p. 3-50. together under the abbreviation (Redbd). Fischer, A. G., 1956, DesarroUo Geologico del Noroeste All thicknesses, both in the descriptions of sec­ Peruano Durante el Mesozoico: Bol. Soc. Geol. Peru, tions 1-4 and in the Table I, are in meters. Tomo 30, p. 177-190. Harrison, J. V., 1940, Nota Preliminar Sobre la Geologfa de los Andes Centrales del Peru: Bol. Soc. Geol. Peru, Tomo 10, 52 p. SECTLOK 1, LIMA 1943, Geologfa de los .^.ndes Orientales en parte Thick. del Departamento de Junin, Peru: Bol. Soc. Geol. {Meters) Peru, Tomo 16, 97 p. Atocongo Formation 1951a, Geologfa de los .-^ndes Orientales del Limestone, gray, medium-bedded 200 Peru: Bol. Soc. Geol. Peru, Tomo 21, 97 p. Pamplona Formation 1951b, Geologfa Entre Pomacocha y Quebrada Limestone and shale, dark gray, thin- Tinaja: Bol. Soc. Geol. Peru, Tomo 23, 28 p. bedded 200 1953, Geologfa de la Zona del Camino Entre Marcavilca Formation Canta y Huayllay: Inst. Nacional de Investigaci6n y Sandstone, gray white, medium-bedded. . 298 Fomento Mineros, bol. 9, 36 p. Herradura Formation 1956a, La Geologfa de la Regi6n Casca—Junin; Sandstone and shale, gray and brown, La Geologia del Valle del Rfo Mantaro: Inst. Na­ thin-bedded 666 cional de Investigacion y Fomento Mineros, bol. 15., Salta del Fraile Formation p. 7-55. Sandstone, brown, medium-bedded 50 1956b, Geologia de la Carretera Huancayo- Puente Piedra Formation Santa Beatriz en el Peril Central: Bol. Soc. Geol. Andesitic lavas and breccias, gray-green, Peru, Tomo 28, 47 p. well bedded, with yellowish shale mem­ • Geologfa de la regi6n entre Vinchos y Churin: ber near base 1,794 (in preparation). Total Cretaceous 2,558 Iddings, Arthur, and Olsson, A. A., 1928, Geology of northwestern Peru: Am. .'^ssoc. Petroleum Geologists Bull.,v. 12,p. 1-40. SECTION 2, CHANCAY Jenks, W. F., 1948, Geology of the Arequipa quadrangle: Inst. Geol. Peru, bol. 9, 204 p. Sill, andesitic, dark gray, massive 20 1951, Triassic to Tertiary stratigraphy, Cerro de Gray^acke and shale, gray and black, with Pasco, Peru: Geol. Soc. America Bull., v. 62, p. 203- slump structures 95 219. Fault Kummel, B., 1948, Geological reconnaissance of the Sandstone, brown, with shale interbeds, and Contamana region, Peru: Geol. Soc. America Bull., sill or flow at base 170 V. 59, p. 1217-1265. Total Cretaceous 285 1950, Stratigraphic studies in northern Peru: Am. Jour. Sci., V. 248, p. 249-263. SECTION 3, KM. 254, OF PANAMEKICAN HIGHWAY Leanza, A. F., 1945, Ammonites del Jurassico Superior Feldspathic graywacke and agglomerate, in- y del Cretaceo Inferior de la Sierra Azul, en la parte terbedded with dark shale 700 meridional de la provincia de Mendoza: Anal. Mus. la Plata, N. Ser. Paleont., no. 1. SECTION 4, KM. 315 OF PAN AMERICAN HIGHWAY Lisson, C. I., and Bolt, B., 1942, Edad de los f6siles Graywacke, andesitic tuff and agglomerate, peruanos y distribucion de sus dep6sitos: Cuarta and dark shale 1,586 edici6n, Lima, 320 p. McLaughUn, D. H., 1924, Geology and physiography of the Peruvian Cordillera, Departments of Junin and Lima: Geol. Soc. America Bull., v. 35, p. 591-632. BIBLIOGRAPHY Miranda, L. A., 1956, El yacimiento mineral de Cerca- Bellido, E., 1956, Geologfa del Curso Medio del Rfo puquio (Junfn) y la Brunckita, mineral peruano: Huaytara, Huancavelica: Bol. Soc. Geol. Peru, Geol. Soc. Peru, Primer Congreso Nac., p. 243-252. Tomo 30, p. 33-47. Newell, N. D., 1949, Geology of the Lake Titicaca re­ Benavides-Caceres, V., 1956, Cretaceous System in gion, Peru and Bolivia: Geol. Soc. America Mem. 36, northern Peru: Am. Mus. Nat. Hist. Bull., v. 108, 111 p. art. 4, p. 252-494. Olsson, .4. A., 1934, Cretaceous of the Amotape region: Berry, E. W., 1922, The Mesozoic flora of Peru: Johns Am. Paleont. Bulls., v. 20, no. 69, 104 p. Hopkins Univ. Studies in Geology, no. 4, 49 p. Rivera, R., 1951, La fauna de los Estratos Puente Inga, Cabrera La Rosa, A., and Petersen, G., 1936, Recono- Lima: Bol. Soc. Geol. Peru, v. 22, 53 p. M JOHN J. WILSON

1956, Kosiles Maeslrichtianos de Pongo de 1957, Geologie zwischen Caiiete-San Juan Rentema, Amazonas: Bol. Soc. Geol. Peru, Tomo 30, 13° 60'-15° 24' Sudperu: Geol. Rundschau, Bandes Parte 1, p. 323-327. 45, Heft 3, p. 775-858. Rosenzweig, A., 1953a, Geologia de la Isla de San Singewald, J. T., Jr., 1927, Pongo de Manseriche: Geol. Lorenzo: Inst. Nacional de Investigacion y Fomento Soc. America Bull., v. 38, p. 479-492. Mineros, bol. 7, 30 p. 1928, Geology of the Pichis and Pachitea Rivers: 1953b, Reconocimiento Geologico en el Curso Geol. Soc. America Bull, v. 39, p. 447-464. Medio del Rio Huallaga: Bol. Soc. Geol. Peru, Tomo Stappenbeck, R., 1929, Geologie dos Chicamatales in 26, p. 155-189. Nordperu und seiner Anthrozitlagerstatten: Geol. u. Ruegg, W., 1947, Estratigrafia Comparada del Oriente Palaont. Abhandt., Neu ser., v. 16, no. 4, p. 305-355. Peruano: Bol. Soc. Geol. Peru, Tomo 20, p. 57-100. Steinmann, G., 1929, Geologie von Peru: Carl Winters and Fyfe, D., 1949, Algunos Aspectos sobre la Universitats-buchhandlung, Heidelberg, 488 p. f^structuracion de la Cuenca del Alto .Amazonas: Tschopp, H. J., 1953, Oil explorations in the Oriente of Bol. del Inst. Sudamericano del Petroleo, v. 3, no. 2, Ecuador: Am. Assoc. Petroleum Geologists Bull., v. p. 5-25. 37, p. 2303-2347.