PLATE I: Vertical beds, Canon de la Huasteca

126 GEOLOGY OF THE CANON DE LA HUASTECA AREA IN THE SIERRA MADRE ORIENTAL, NUEVO LEON, MEXICO HAROLD E. VOKES .PROFESSOR OF' GEOLOGY TULANE UNITTERSJTY

I. ABSTRACT The observations reported in the present paper result from investigations by the stu­ dents at the Tulane University Summer Field Camp in Geology during the years 1960- 1962. The area involved is in the front range of the Sierra Madre Oriental of Mexico and includes the well-known Canon de la Hua­ steca and the valleys immediately to the south, locally known as the Valle de San Paulo and the Valle de Muralla. The area is a segment of the Los Muertos anticline whose core consists of the Upper Jurassic Zuloaga Limestone, which is much deformed and locally has been intruded by masses of gypsum. Overlying is a 1200 foot sequence of shales and siltstones that have Portlandian, Upper Jurassic fossils in the lower portion; these are here named the Figure 1. Geographic Location of the Muralla Shale. Gradationally above are al­ Huasteca Canon Area. most 1200 feet of arkosic sandstones and arkose with minor conglomerates that con­ rora Limestone, incomplete sections of which tain an Upper Jurassic fauna, and are here form the outer flanks of the Los Muertos named the San Paulo Sandstone. These two anticline. new formations are referred to the La Casita Near the western end of the Valle de Mu­ Group. ralla an isolated mass of Tertiary (? ) clay Lower Cretaceous formations represented rests upon the eroded edges of the Taraises include the Taraises Formation in which two Formation. The clays are believed to repre­ members can be recognized. The basal mem­ sent lacustrine deposition, but a wholly satis­ ber, consisting of approximately 200 feet of factory explanation of their occurrence has shale and highly fossiliferous limestone is yet to be advanced. Alluvium and colluvium, here named the Los Nogales Member. This some of it cemented with caliche, masks the member is of late Valangian and/ or early floors and lower slopes of the valleys. Hauterivian age, and rests on the San Paulo There is stratigraphic evidence of an east­ Sandstone with, apparently, a paraconform­ west trending fault along the floor of the able contact. Valle de San Paulo to the south of the pres­ The main mountain ridges bordering the ent outcrop trend of the Zuloaga Limestone; valleys are composed of the rudistid-bearing it is suggested that movement along this Cupido Limestone, 2300 feet thick, the very fault may have been a contributory factor in fossiliferous, marly La Pena Formation, 50 the gypsum intrusions into the adjacent to 100 feet thick, and the thick-bedded Au- Zuloaga Limestone.

EDITORIAL COMMITTEE FOR THIS PAPER:

RALPH W. IMLAY, United States Geological Survey, Washington, D. C. LEWIS B. KELLUM, Museum of Paleontology, University of Michigan, Ann Arbor, Michigan GROVER E. MURRAY, Louisiana State University, Baton Rouge, Louisiana

127 Vol. 1 128 Tulane Stitdies in Geology

II. INTRODUCTION tired), at that time advisor to the Rector _of "The geology and stratigr~phy of t~e the Instituto Tecnol6gico y de Estud10s mountains in northeast Mexico are still Superiores de Monterrey, sugges.ted ~hat the almost absolutely unknown; even in late geological faculty of Tul~~e_Umversity. :~n­ years the mighty ranges an~ deep canyons sider the feasibility of uulizrng the facilmes of the Sierra Madre Oriental east of Saltillo and south of Monterrey ha_ve of the Instituro as headquarters for a sum­ scarcely even been crossed by a geologist mer field camp. A short visit ro the area and much less been studied." (Bose, 1923, during the Easter period of that y~ar was p. 127) sufficient to demonstrate that the region had much ro offer geologically, and that the fa­ The fact that the above statement is al­ cilities of the Instituro would afford a super­ most as true today as when it was first made, lative base for a summer camp. The only forty years ago, is justification for the fol­ obvious drawback was the lack of topo­ lowing detailed notes on the geology ~f a graphic map coverage; but, aerial photo­ small part of this region. The observations graphs were available. It was conclud~d that here recorded result from investigations car­ the superior exposures of t.he geologic sec­ ried on by students attending the Tulane tion in this almost unstudied area offered University Summer Field Camp in Geology many projects for student thes.es and d~s­ during the years 1960-196~. In~luded . are sertations which with the available aenal details of a number of straugraphIC sections phorographs more than offset the lack ~f through the formations represented,. with topographic coverage. Subsequ~nt expert­ description of two new Upper JurassIC for­ ence in which we have combined plane­ mations and one new member of the Lower tabl~ topographic and geologic mapping, has Cretaceous Taraises Formation. demonstrated that there are some advantages The area involved in the study is a part in that experience thus gained gives the stu­ of the front range of the Sierra Madre Ori­ dent confidence in his ability tO handle any ental of Mexico, and includes the well­ mapping problem, with or without base known Canon de la Huasteca and the val­ maps. . leys immediately behind it (see fig. 1). It A "test-run" of the camp and the field lies immediately southwest of Monterrey, area was made in the summer of 1960 with Nuevo Leon, and is south and southeast of four students; in 1961 the student number the town of Santa Catarina, from which a was increased t0 seven, all of w horn were paved road may be taken to the entrance of graduate students at Tulane; and in 1962, the Huasteca. both graduate students and seniors from Tu­ Structurally the region is part of the Los lane and other schools participated in the Muertos anticline, the most northerly of the program. The following report and geologic several folds that constitute this portion of map are based in large measure upon the the Sierra. The valley of the Rio Santa work of these groups. Catarina bisects this major structure in the mapped area and the water gaps of the main III. ACKNOWLEDGMENTS channel form the Canon de la Huasteca on The writer wishes to acknowledge his the north flank of the anticline and the sincere indebtedness ro the late Commodore Canon de Morteros on the south. The core Carroll for calling our attention to the region of the anticline has been eroded to form a as a possible site for the field camp, and also moderately broad east-west valley traversed for his vigorous assistance in advancing the by intermittent streams tributary to the Santa work of the group in the Monterrey area. Catarina. The tributary valley west of the Many local geologists, who were made aware main river channel is locally known as the of our project through Commodore Car­ Valle de San Paulo and that to the east con­ roll's interest gave much helpful assistance stitutes the Valle de Muralla. These names and advice; all cannot be separately men­ are here adopted and utilized as the geo­ tioned and thanked here, but I cannot fail t0 graphic element in the names of the two new express our deep appreciation for the hospi­ formations here proposed. tality and courtesies extended to us and our The writer first became interested in the students by Mr. Walter H. Triplett, former Huasteca area early in 1960 when the late chief geologist for the Compania Mineria de Commodore Penn L. Carroll ( U.S.N., re- Penoles, S. A. No. 4 Geology of the Canon de la Huasteca Area 129

The officials at the Instituto Tecnol6gico mates of the thicknesses of some of the de­ have proved unflaggingly helpful and anxious posits and list characteristic fossils from to advance the work of the camp. All can­ certain units; but, as in the earlier paper, not be thanked individually, but special they do not apply local formational names mention must be made of Ing. Fernando to the units observed. Garcia Roel, the Rector of the Instituto and Finally, Humphrey (1949) makes pass­ companion in the field when his official ing mention of certain of the formations duties permit. To him, as well as to Ing. present in this region while he is discussing Francisco Mancillas, Dean of the Escuela the stratigraphy of the Cortinas Canyon area Verano, to Mr. Harold Wise, Assistant to and the western part of the Los Muertos the Dean, and to Colonel Carter Hilsabeck structure. (U.S.A., retired) , successor to Commodore Carroll, go our sincerest appreciation for IV. STRATIGRAPHY their efforts in behalf of the camp project. General Statement.-The geologic section Finally, the present writer must express exposed in the Los Muertos anticline within his very real indebtedness to the students the area of the present study consists pri­ whose field work is here utilized, and whose marily of sediments of upper Jurassic and project reports are freely employed; they lower Cretaceous age. Resting upon these have made the present report possible. In­ near the village of Los Nogales is a small cluded in the group of 1960 were: James A. deposit of clay of Tertiary or post-Tertiary Holliday, Anthony T. L'Orsa, Arthur D. age; elsewhere a mantle of Quaternary or Piaggio and Emily H. Vokes, all from Tu­ Recent alluvium and colluvium covers the lane University. The 1961 group included: valley floors and extends for some distance Robert F. Beyer, Jr., Victor V. Cavaroc, Jr., up the adjacent slopes. The stratigraphic William E. Daughdrill, Gerald C. Glaser, sections of the Mesozoic rocks exposed in Harold J. Morrow, John Sandy, Jr., and the two flanks of the anticline are shown jn Albert P. Selph III. 1962 participants were figure 2. The term, "Los Nogales Member Theodore T. Gittinger, Gary 0. G. Greiner, of the Taraises Formation," was proposed by and Louis A. Oswald, Jr., all from St. Mary's Piaggio in 1962 (unpublished M.S. thesis, University at San Antonio, Texas; Mr. Tulane University ). The San Paulo Sand­ Joshua H. Rosenfeld, a former graduate stu­ srone and the Muralla Shale are new forma­ dent at Louisiana State University; and Le­ tion names here first proposed. land Dennis II, a senior, and Harold J. Morrow, a graduate student from Tulane. JURASSIC SYSTEM Mr. Piaggio of the 1960 group and Mr. Sabinas Series 1 Morrow in 1962 were engaged in work on ZULOAGA STAGE field projects for their Master of Science Zuloaga Limestone theses. The term Zuloaga limestone was pro­ PREVIOUS WORK posed by Imlay (1938, p. 1675) to designate Although the Huasteca area has long been the offshore equivalent of the la Gloria known as a scenic attraction, either under formation with the type locality in the Sierra that name or as the Canon de Santa Cata­ Sombreretillo, north of Melchor Ocampo, on rina, the first significant mention of the the Coahuila-Zacatecas border. Here there geology of the region was by Bose in 1923 are about 1800 feet of gray limestone, main­ (his introduction to that paper is quoted ly thick-bedded. Most of the complete sec­ above) . Bose sketches the general strati­ tions known elsewhere appear to be thinner. graphic sequence and publishes (p. 200) The beds so named by Imlay are those that small diagrammatic cross-sections, one of had previously been referred to as the which probably would cross the area of the "N erinea limestone" or the "Gray limestone present geologic map. Bose and Cavins with Nerinean by Burckhardt (1906; 1930) (1928, p. 17-18) note the occurrence of and by Bose (1923). "sandstones and conglomerates of the Port­ 1 For a discussion of the origin and his­ landian (Jurassic) " and of limestones and tory of the "series" and "stage" names used marls of "Infracretaceous" and "Mesocre­ in this report, see Murray, 1961, pp. 287-8; taceous" age. They also give rough esti- 292; 297-301; 307-8. 130 Tztlane Studies in Geology Vol. 1

MESOZOIC DEPOSITS of the Los MuERTOS ANTICLINE

1--.::~ ~ ~ COLUMNAR SECTIONS a: ~ FORMATIONAL UNITS ~ V) V) ~ South Flank North Flank Q) ...c A UHOHA LIMESTONE 0 >- Medium - to thick - bedded, da1·k gray limestone's, c I- rudistid- bcaring; some beds with irregular nodules 0 z of black chert. Important ridge-forming formation. E 0:: 0 I- LA PENA FORMATION (_) ~=~~-- iii==ifi1== ~50'±--..:-lil 80'± Fossi I ifcrous shaly marls and Ii mes ton e ~.

(j) ~ 0 w (_) z <[ 0 CUPrno LIMESTONE w h---'--r-'--r-'--.-'-~1 ti Mainly medium- to thick-bedded and massive lime- I- _J stones, medium to dark gray in color, fossiliferous w with abundant rudistids and rare Nerinea and cora l s. (L 0 Beds with gray nodular chert in upper portion, and (_) 0 > some dolomitic strata in the middle portion of the w section. Most important ridge- forming formation ::J :::::> in this part of Mexico. ....c z (L 0 w 0 s (_) 0 _J .... ------~-...,. TAHAJSES FORMATION . ....,. "-1 · - · ~ ~member - Argillaccous liml's loncs, gray 0 F:"5,~--'oe,~"'='i~.i 0 (!) black, with a few fossiliferous beds. Weathers to z j;:;I~~i:::· ...~~-+-~'-;:;-~ ~ shaly slopes. --, . ..., ~- <{ ·-i ..; 0:: 1------:::::> Los Nogalt'S Mc'mbcr - Basal gray limestones, fos ­ 0 siliferous; overlain by shale; with a sandy, brown ­ wcathering fossiliferous limestone at top ...... :::::::::::::::::::::::::::::::·:·:·:::::::::::.:

.::::.:.::::-:t···Mt?'.i.·: LA CASITA GROUP SAN PAULO SANDSTONE (_) 1Wdif:i??·?}'"g A rkosic sandstones and arkosc, gray lo brown in (j) color, thin - to thick- bedded, fossiliferous; with :.·:::.+:.::--:::·:::-:::::::·:::::<:.: - lenticular conglomcralcs and, near lhc ba sP, g1·a y (j) ~ Covered 1 Cf) ;..;.:Y:·M·M·~: ..;y:~·~·A· shaly sandstone~. <[ <{ 0 ....~\!,1.,"'0::.7'.:;:.7'~7.: U) ~~":""~~..:..:--:--~~~~~· (L (_) ;:~~~~~B~7,:..;:.;.:-::.; 0 ...... - ' . . . ~ c -r ,.-, ...- ...... <{ ______------.--~--.- J -- ...0 _J 0 (L (j) MUHALLA SllALE Shale and si l tstonC's, light gray, tan, and buff in color; w I------basal units with richly fossiliferous concretions; 1- -_-_-_-_-....:-_-_- N Q_ 1-- -_-_-_-_-_-_-_- - fauna includes amrnonilcs and bivalves. Prcs(•nl 1-- -__:-_-_-_-_-_ -_- Q_ 1-- _-_-_-_-:_-_-_ on north flank of antic I inc onl y. Mostly cove1·c•d by r------­ valley alluvium. ~ r------­

ZULOAGA LIMESTONE Gray l imt•ston<'S, finely crystalline to cakilulilic; lwdding obscure; intruded by gypsum. Form~ low morros in c·cnl<.'r of thC' anticlin:i.I struclur e. Figure 2. Stratigraphic columns comparing the Mesozoic deposits cropping out on the north and south flanks of the Los Muertos Anticline. 132 Tulane Studies in Geology Vol. 1

\ ---:.v-l ' ~-~-- .. ·-<·, - _: __ -~~~· __ --,

Figure 3. Valle de San Paulo; view looking westward along the north side of the val­ ley from slopes immediately above east side of Rio de Santa Catarina.

caracteristica del Anticlinorio de Arteaga, ured sections, varying from 240 to 285 feet el autor considera que el yeso Minas in thickness. Two lithologic members were Viej as subyace a dicho anticlinorio y que otro·s afloramientos de esta unidad, seran recognized: a lower one that "consists of revelados con estudios posteriores mas gray conglomeratic sandstone and ranges in detallados. thickness from about 20 to 75 feet or more. "Por su posicion estratigrafica, el yeso At the top, in most sections, are a few inches Minas Viejas se considera perteneciente of friable sandstone, which contains brachi­ al Divesiano; su desarrollo ha sido con­ trolado por la proximidad relativa del opods bivalves, and belemnites. The upper mar y por las condiciones climatericas member consists principally of black shales prevalecientes durante su dep6sito." but includes some buff or gray sandy shales, short lenses of sandstone and arenaceous LA CASITA STAGE limestone, and lenticular limestone nodules. La Casita Group Some of the nodules contain well-preserved In 1936 (p. 1110) Imlay described a La mollusks." The formation was stated ( p. Casita Formation to include "the shales, 604) to be of Kimmeridgian and Port­ sandstones, and intercalated limestone beds landian age. "The basal sandstones may be lying between the La Gloria formation (be­ of Oxfordian age." low) and the Taraises formation (above)." Subsequent work has revealed much The type locality was designated as Canon lithologic variability in the sequence of de la Casita, located about 10 miles south strata that occupies the position of the La pf General Cepeda and about 30 miles Casita Formation. In 1956 Humphrey and southwest of Saltillo. The type region was Diaz, in a table giving the "Correlation of described in 1937 (pp. 601-2) with meas- the Mesozoic Strata of Northeast Mexico" No. 4 Geology of the Canon de la Huasteca Area 133

Figure 4. South flank of Los M uertos Anticline; view showing east end of Valle de San Paulo and the Valle de Muralla.

(see Humphrey, 1956, pp. 32-34) used the ness varymg from 2200 to 2400 feet and term "La Casita group" to specify the are readily divisible into two units which Jurassic strata of varying lithology that over­ were designated as "members" of the La lie the Zuloaga or La Gloria formations. Casita Formation by Humphrey ( 1949, pp. Murray ( 1961, p. 292) pointed out that 97-100) but which are here raised to the the term as thus applied was in a time-rock rank of formational units. The lower, herein sense and added "Because these strata are denominated the Muralla Shale varies in exposed and well known in northeastern thickness from 1164 to 1211 feet in sections Mexico, inasmuch as they are laterally con­ measured in the region of the present study; tinuous with strata in the coastal province it appears to be essentially correlative with of Mexico and the United States, and be­ cause they are reasonably accessible, La Ca­ the La Casita Formation of Imlay at its type sita is used herein as a provincial stage for area. The upper formation, here named the the youngest known late Jurassic in the San Paulo Sandstone, consists mainly of fine­ coastal province to include rocks which can to coarse-grained, usually arkosic sandstones, be equated in any reasonable way to typical with a number of lenticular conglomeratic La Casita and La Caja sequences." It is to horizons and occasional beds and lenses of be noted that this usage, since it includes very sandy limestones. Measured sections strata that contain fossils of Tithonian age, give thicknesses varying between 1130 and is an extension of the range of the La Casita 12 5 5 feet. A large fauna of pelecypod Mol­ Formation at its type locality. lusca is present together with a few sand­ Within the Los .Muertos anticline the de­ stone casts of ammonites. The general fauna! posits of the La Ca.sita stage have a thick- evidence seems to suggest that this unit is 134 Tulane Studies in Geology Vol. 1 probably of upper Portlandian and Tithon­ Unit Feet 5. Finely laminated siltstones ian age. and silty fissile shales, Muralla Shale gray to brownish-gray in color, weathering to buff. Definition.-The name Muralla Shale is The lower 500 feet with here applied t0 a sequence of sandy tO silty gypsum beds in veinlets, shales and thin-bedded siltstones with oc­ but with occasional beds up to one foot in thick- casional beds of highly argillaceous lime­ ness. No fossils found ____ _ 782 stone and, roward the upper part, a few fine 4. Shale and finely laminated grained sandstones that generally are cal­ silts, pinkish to buff in color, weathering light careous and more resistant to erosion than gray. Occasional gypsum the adjacent shaly strata. Zones of dark gray in bands 14 to 1h inch limestone concretions occur within the lower thick. U nfossiliferous ______52 3. Siltstones in beds up to 12 250 feet of the formation; these contain inches thick with inter­ abundant Kimmeridgian ammonites and oc­ bedded silty shale. Color casional pelecypods, including Aulacomyella light-gTay, weathering neogeae Imlay. Certain horizons within the white. Thin beds of lim­ onite interbedded from 44 silty shale sequence also have compressed to 48 feet above the base. and flattened casts of ammonites some of U nfossiliferous ______76 which appear to represent species of Ido­ 2. Shale, pink to pinkish buff in color, punky in texture, ceras. The type section is in the Valle de weathers to fine chips, Muralla, on the north flank of the Los light to medium gray in Muertos anticline approximately two and color. A bed of black colored silt 70 feet above one-quarter miles east-northeast of the school base. A few indetermi­ house at Los Nogales. An almost completely nate outlines of com­ exposed section may be seen northward from pressed ammonites ob­ served on bedding surfaces 170 the contact with the Zuloaga Limestone on 1. Shale, and thin shaly silt­ the northern side of hill 3044. stones, light gray to buff Stratigraphic and lithologic features.-The in color, weathering buff. Occasional zones of gray non-resistant nature of the sediments com­ calcareous concretions, up prising the Muralla Shale has resulted in a to one foot in diameter; general dearth of exposures. Over much of one 85 to 90 feet above the base with abundant the area studied, the formation is topo­ ammonites and occasional graphically lowest in the erosional valleys pelecypods and petrified flanking the row of Zuloaga morros in the wood. Some of the con­ central part of the Los Muertos structure, cretions in this zone when broken reveal cores, or and consequently the strata are buried under marginal zones of limoni­ a cover of valley alluvium and colluvium. tic dust. Aptychi and flat­ No outcrops of the Muralla have been found tened ammonites occur on on the south limb of the anticline and there shale bedding planes both is reason to believe that the formation may above and below the zone._ 131 be missing here due to strike faulting along 1,211 or near the anticlinal crest; this will be dis­ cussed in a later part of this report. The A section approximately seven miles to most completely exposed sections are lo­ the west of the type area was measured by cated on the north limb of the structure near W. E. Daughdrill, H. J. Morrow and John the eastern and western limits of the mapped Sandy, Jr., of the 1961 field group. This area, where the streams tributary to the Rio section, which is located roward the western Santa Catarina have not eroded their courses end of the mapped area, follows : as deeply as they have near their confluence Unit Feet with the main stream channel. l.4. Calcareous shales and shaly The section at the type locality, measured limestones, tan to gray in color, weathering to gray by Gary 0. G. Greiner and the writer in­ shale slopes. About 420 cludes the following units: feet above the base there No. 4 Geology of the Canon de la Huasteca Area 135

Unit Feet Unit Feet is a 12 ft. zone with calcite uppermost foot marked by veins 4 to 6 in. thick, sug­ abundant, rather large gestive of mineralization concretions (averaging 14 along folding glide planes. x 10 x 4 in., and flattened U nfossiliferous ______640 along the bedding plane) 13. Tan to gray silty calcareous usually containing numer- sh a 1es with occasional ous small ammonites ______132 gray fine-grained sand­ 1. Covered interval to the Zu- stones, weathering brown, loaga Limestone ______32 and more resistant to ero­ sion, forming ledges. Un- 1,202.5 fossilif erous ______103 12. Sandstone, fine-grained, The contact of the Muralla Shale with dense, calcareous, light brown m color, weathers the underlying Zuloaga Limestone has been to form a rusty brown observed only on the north side of the sec­ ledge; no fossils ______3 ond morro (elev. 2877 ft. ) west of the Rio 11. Shale, calcareous, light gray, Santa Catarina. There the basal bed of the unfossiliferous ______37 Zuloaga is overturned, dipping 83 ° S. Al­ 10. Sandstone similar to unit 12 7 9. Silty shale and siltstone, though the contact is conformable, a strati­ thin-bedded, light brown in graphic break is suggested because the basal color, with a very few, unit of the Muralla consists of a 6 inch bed thin, fine-grained sand­ of highly sandy limestone overlain by a 6 stone interbeds. Unfo.s- sil iferou s ______123 inch bed of coarse, poorly sorted grit. The 8. Sandstone, light gray, slope of the hill down to the stream channel weathering to rusty which interrupts the section, reveals 291.5 brown, fine- to very fine­ feet of strata, mainly buff to orange-buff grained with calcareous claystone and silty mudstone. Ammonites cement ------11 7. Shale, light buff to light and aptychi have been found in the clay­ gray in color, with local stones 15 and 70 feet above the base; in a beds and lenses of hard 1.5 foot, black calcareous sandstone 87 feet calcareous b 1a ck shale. Selenite veins and crystals above the base; in calcareous concretions 192 common ------14 to 198 feet above the base, and in claystones 6. Sandstone, as in unit 8 ______2.5 220 feet above the base. 5. Shale similar to unit 7 ______68 4. Sandstone, calcareous, fine- San Paulo Sandstone to very fine-grained, light brown m color, weather- Definition.-The name San Paulo Sand­ ing dark brown ______3 stone is here applied to a sequence of fine­ 3. Shale, light gray, buff to to coarse-grained calcareous sandstones and white in color, with some sandy limestones that include numerous spo­ zones and lenses of black shale; resembles a dia­ radic lenticular conglomerates. The type sec­ tomaceous shale; selenite tion is exposed in the first draw west of a abundant on bedding ridge north of the second morro west of the planes; fossils sporadically Rio Santa Catarina (see above). This ridge abundant on the bedding planes, especially in the is easily recognized by a cap of a large col­ light gray colored beds, in­ lapsed mass of Cupido Limestone that rests cluding aptychi, flattened upon the San Paulo Sandstone. The type sec­ unidentifiable ammonites tion includes 1,160 feet of beds; Humphrey and pelecypods, fish scales and occasional leaf frag- ( 1949, pp. 98-9) gives a measured section ments ------27 of his "upper member" of the La Casita 2. Calcareous shale, light gray Formation which includes 1,190 ft. of strata. to buff in color, with occa­ sional thin ( 3 to 6 in.) Stratigraphic and Lithologic features.-The fine-grained sandstone or San Paulo Sandstone is composed primarily siltstone interbeds; sele­ of marine arkosic sandstone and arkose, but nite veins common; cal­ its most characteristic feature 1s the great careous concretions, often amount of lithologic variation, both laterally with ammonites, occurring in zones toward the upper and vertically; no two sections are alike in part of the unit; the sequence, and individual units prove to be 136 Tulane Studies in Geology Vol. 1 highly lenticular, changing rapidly in thick­ Unit Feet dark gray, weathering ness, color and grain size along the strike. dark brownish gray; con­ Sandstones, so highly calcareous as almost tains abundant specimens t0 ment designation as arenaceous lime­ of Exogyra sp.; Gresslya stones are replaced by pebble conglomerates and "L1lcina" present ____ _ 8 30. Sandstone, arkosic, noncal­ within a few hundred yards along the strike. careous, medium- to fine­ Conglomerate lenses three feet thick have grained, dark yellowish an outcrop length of less than two hundred brown, we..ithering light feet and pebbles as much as two inches in yellowish brown, thin­ bedded and much frac- greatest diameter. tured with calcite veins __ _ 15 The type section, measured by the writer 29. Sandstone, fine-grained, and his wife, Emily H. Vokes, follows: well-sorted, noncalcareous, UnU Fe~ medium light gray in 40. Marl, sflty, very soft, light color, weathering rusty gray, weathers yellow _____ 2 brown, with a very hackly 39. Limestone, sandy, dark gray, fracture _ 6 weatherin~· medium gray, 28. Sandstone, arkosic, coarse­ lower half mottled brown­ grained to a grit conglo­ ish with much dissemin- merate, dark gray, weath­ ated siderite ______3 ering dark brown; fossili­ 38. Sandstone, arkosic, coarse­ ferous, fauna includes Ber­ grained, very calcareous, riasella ( ?) sp., Exogyra dark gray, weathering a cf. E. potosina Castillo & medium brownish gTay; Aguilera, and Trigonia n. one bed ______8 sp., aff. T. vyschetzkii 37. Sandstone, arkosic, medium Cragin, N erinea sp. 7 to coarse-grained, calcare­ 27. Sandstone, arkosic, fine to ous, much disseminated medium grained, light siderite (?), brownish olive gray, mostly non­ gray, weathering brown; ca1careous, but with scat­ bedding obscure; many tered ca 1 ca reo us zones small vu gs with calei te which weather in a manner and quartz crystals ______32 suggestive of concretions 36. Arkose, medium-grained, or boulders up to 6 in. in noncalcareous, pale yellow­ diameter ______16 ish brown in color, weath­ 26. Sandstone, fine- and medi­ ering a slightly lighter um-grained, medium gray, tone; thin - bedded and weathering medium light much jointed ______13 gray, in beds up to one 35. Arkose as in unit 36, but foot thick, much fractured; massive bedded and cal­ Exogyra sp., Pinna cf. P. careous, lower 2 ft. with quadrifrons Cragin --·------11 abundant pelecypods 25. Sandstone, arkosic, similar including Trigonia and to unit 27; Exogyra sp. ___ _ 17 Pholadomya (?),in matrix 24. Silty shale, dark gray to too hard to permit collect- black, weathers to pencil- ing ------15 cleavage like fragments ___ _ 10 34. Sandstone, slightly arkosic, 23. Sandstone, as in unit 29 ____ _ 1.5 noncalcareous, medium to '22. Sandstone, fine-grained, coarse-grained, with small hard, calcareous, medium disseminated siderite nod­ gray, weathering brown­ ules, light olive gray, ish gray; one massive weathering medium light bed; fossiliferous; Pleu­ gray; in one massive bed _ 10 romya ? cf. P. inconstans 33. Arkose, as in unit 35, but Castillo & Aguilera ______4 one massive bed with a few 21. Sandstone, fine- to medium­ scattered fossil fragments 16.5 grained, light to medium 32. Sandstone, very arkosic, cal­ gray, weathering gray careous, medium-grained, brown; in two hard beds, dark gTay, weathering the lower of which has brownish gray ; casts of scattered quartz grains up large pelecypods ( indeter- to 2 mm in diameter ______7.5 minate) near base ______41 20. Conglomerate, and coarse 31. Sandstone, very arkosic with gritty sandstone with scat­ abundant disseminated tered pebbles of quartzitic mica flakes, calcareous, and rhyolitic ( ?) composi- No. 4 Geology of the Canon de la Huaste'ca Area 137

Unit Feet Unit Feet tion; fossiliferous with ded with arkose, thin­ unidentifiable Pelecypoda 2 bedded, fine to very fine­ 19. Sandstone, similar to unit g rained, noncalcareous, 27, but wholly noncalcare- · medium light gray, weath- ous, massive bedded ______27 ering light olive gray ______89.5 18. Sandstone, fine- to very 7. Sandstone, very fine­ fine-grained, noncalcare­ g rained, noncalcareous, ous, shaly, medium light medium gray in color, gray, weathering light thin-bedded and strongly gray ______21 jointed, weathering to 17. Sandstone, medium- to coarse "pencil structure" coarse-grained with lenses fragments ______27 of grit conglomerate, cal­ 6. Arkose, similar to the medi­ careous, medium dark um-grained units rn 8, gray, weathering brown­ moderately thick-bedded ___ _ 51 ish gray, scattered fossil 5. Sandstone, very fine grained, fragments, E xogyra sp. __ _ 31 as in unit 7 ______32 16. Arkose, coarse-grained, vari­ 4. Sandstone, very fine grained egated dark gray and olive and silty, slightly calcare­ gray, weathers light olive ous, thin-bedded and much gray __ _ 9 fractured with calcite 15. Sandstone, arkosic, with veins __ _ _ ------128 much disseminated sid­ 3. Sil ts tone, noncalcareous, erite (?),light olive gray, medium dark gray, weath­ fine-grained below becom­ ering light yellowish gray, ing more coarse-grained, with an 18 in. bed of silty almost a fine conglomerate claystone, pale red in color, at top ______33 at the top and three 6 in. 14. Sandstone, fine-grained, non­ beds of similar composi­ calcareous, medium to tion and color interbedded dark gray, weathering between 16 and 19 ft. very dark gray ______23.5 from the top ______238.5 13. Sandstone, similar to unit 2. Sandstone, fine- to medium­ 15; Gresslyci sp. _ ___ _ 12 grained, micaceous, cal­ 12. Sandstone, arkosic, fine­ careous, hard, medium g rained, noncalcareous, gray, weathering brownish medium gray to medium gray, in two massive beds, dark gray, weathering the upper 2.5 and the medium gray _ 15 lower 4 ft. thick separated 11. Conglomerate, with quartz by 1.5 ft. of siltstone as pebbles 5 to 10 mm in in unit 3. The two resist­ diameter, medium gray, ant sandstone beds stand weathering light gray __ _ 2.5 as dike-like ridges 18 to 20 10. Sandstone, similar to unit feet high on the east wall 12, with lenses of gritty of the tributary valley conglomerate, and a con­ along which the section glomerate lense 8 inches was measured ______8 thick 25 ft. below the top 1. Arkose, medium-grained, with fractured chert peb­ micaceous, noncalcareous, bles up to 2 in. in dia- medium dark gray, weath­ meter ______85 ering olive gray, thin-bed­ 9. Sandstone, very poorly ded and becoming some­ sorted, fine- to· very what finer grained toward coarse-grained, locally the base ______16 conglomeratic, the coarse sand grains and the peb­ 1,160.5 bles rn the conglomeratic lenses of chert and quartz, Stratigraphic reiations.-The contact of noncalcareous, medium the San Paulo Sandstone with the under­ light gray, weathering dark yellowish brown; lying Muralla Shale is gradational, the line casts of Gresslya (?) 24 being drawn where the lithology changes to 26 ft. above base ______66 from predominantly silty shale to fine­ 8. Arkose, medium- to fine­ grained arkosic sandstones. In general the grained, medium dark Muralla Shale weathers to a lighter gray gray, weathering light brownish gray, moderate­ tone while the shales of the San Paulo tend ly thick-bedded; interbed- to be darker gray, often with a brownish 138 Tulane Stttdies in Geology Vol. 1

color derived from the iron content of the or dark gray, and weathered surfaces are arkose impurities. light yellowish-gray or cream. Fossils are Fossils and age.-The arkosic sandstones found throughout but are especially abun­ and conglomeratic beds of the San Paulo dant near the base .... The ammonite contain abundant, but usually poorly pre­ genus Olcostephanus ('Asteria') is repre­ served, pelecypods, including at least three sented by many species and numerous indi­ species of Trigonia) together with Gresslya) viduals." The lower member, about 245 Pleuromya) Pholadomya) Panopea) 11Thracia/' feet thick, "consists of gray limestones, and 11Lucina/' Astarte s.l., Exogyra) and Gry­ is more resistant to erosion than is the over­ phaea (?). The gastropods include N erinea) lying member. Weathered surfaces are an 11Actaeonella/) and naticoid forms; the inconspicuous medium gray. Ammonites are cephalopods, a few ammonites and rare be­ found throughout but are abundant only lemni tes. The ammonites are usually in the near the top." form of sandstone casts which preserve the In 1938 Imlay summarized the strati­ coarser details of ornamentation, but lack graphy of the Taraises Formation in the sutures. Ten feet above the base of the northern Zacatecas-southern Coahuila re­ formation in its eastern exposures near the gion, and presented a systematic description type area of the Muralla Shale, a specimen of the ammonite faunas. He concluded was collected consisting of approximately (1938, pp. 550-552) that "in the more one-half whorl, marked by a whorl section southern localities studied" the lower mem­ approximately two-thirds as wide as high, ber "contains fossils which indicate both with a rounded venter, and ornamented by Berriasian and Valanginian ages" but to the moderately strong, slightly prosoradiate ribs north "the presence of Olcostephanus in the that bifurcate approximately half way down lowest beds suggests an age not older than the side of the whorl and are directly con­ the Valanginian." The upper member was tinuous across the venter. The sum of these regarded as being of lower Hauterivian age. characteristics is suggestive of the genus Ber­ The deposits correlated with the Taraises riasella. Somewhat higher in the section a Formation in the Valle de San Paulo-Valle specimen with rather compressed planulate de Muralla area are likewise divisible into whorls marked by numerous fine prosoradi­ two members which differ, however, litho­ ate ribs adjacent to the venter and appar­ logically from the Taraises as developed in ently otherwise smooth on the sides, re­ its type area. The lower member, further­ sembles so far as can be determined from more contains, near its base, abundant repre­ its poor preservation, illustrations of species sentatives of the ammonite genera Acantho­ referred to the genus Proniceras. A large discus) Leopoldia and Distoloceras) an asso­ specimen collected within the upper 30 feet ciation which Imlay ( 1938, p. 552) believes of the section appears to represent a is indicative of a lower Hauterivian age. Kossmatia-Iike form. If these fossils be cor­ Hence it is believed that the deposits here rectly assigned they indicate that the San referred to the Taraises Formation represent Paulo Sandstone is wholly of Tithonian age. correlatives only of the upper member of the formation as present in its type locality. CRETACEOUS SYSTEM The contact of the Taraises Formation Coahuila Series with the underlying San Paulo Sandstone is DURANGO STAGE apparently conformable although marked by Taraises Formation a sharp lithologic change. However, if as The name, Taraises Formation was pro­ indicated above, the basal member of the posed by Imlay ( 1936, p. 1111) for "a Taraises is of Hauterivian age, and the San limestone formation of Valanginian age, Paulo is of Tithonian age a stratigraphic in­ which crops out in the western part of the terval equivalent to the Berriasian and Va­ Sierra de Parras." In the type region the langinian stages is apparently absent from formation ranges from 470 to 487 feet in the section, and the contact is therefore to thickness and is divisible into two members, be described as paraconformable. the upper, 225 feet thick, "consists of thin­ Los Nogales Member.-The lower mem­ bedded limestones and nodular to splintery ber of the Taraises Formation as exposed in shaly limestones. Fresh surfaces are light gray the area of the present study was named the No. 4 Geology of the Canon de la Hitasteca Area 139

Los Nogales Member by Piaggio rn 1962 Unit Feet (unpublished M.S. thesis, Tulane Univer­ careous toward top where several medium-bedded ( 6 sity) who applied the term to a "sequence to 12 inch) dark-gray, of alternating shales and limestones which silty, fossiliferous lime­ crop out in the ... eastern part of the Los stones that weather yel­ Muertos anticline. . . . This unit lies with low-brown are intercalated 22 8. Interbedded limestones and apparent conformity (actually paraconform­ shales: limestone, dark­ ably) above the calcareous sandstones of the gray to black, weathers [San Paulo Sandstone) and below the dis­ yellow-brown, medium­ tinctive limestones of the upper member of bedded (3 to 12 inches) the Taraises Formation. An excellent ex­ becoming more evenly bed­ ded and increasingly silty posure of these strata in a small arroyo on toward the top of the the north flank of the Los Muertos anticline, unit; fossiliferous, with approximately 750 yards west-southwest of terebratulid brachiopods, La Cuchilla, lS designated as the type lo­ belemnites and some pele­ cypods; alternates with cality." shale, fissile, brownish­ "The Los Nogales Member ranges m gray, weathering tan. · thickness from 130 to 135 feet on the south Limestone-shale ratio, in­ flank of the anticline, and from 185 to 198 creases upwards with shale zones approximately 10 ft. feet on the north flank. Obscure faulting in thick at bottom and 2-3 the thick mass of shale which makes up the ft. thick at top __ 38.5 middle part of the unit may be the cause of 7. Shale, dark-gray to black, the thinning on the south flank." weathering brownish-gray, calcareous, very brittle The member is divisible into three litho­ and poorly fissile; near logic units, a basal sequence of resistant, the top are several 4 to 8 ridge-forming limestones, a middle unit of inch beds of silty, dark­ soft shales that form a topographic saddle gr ay limestones that weather medium gray ______53 behind the limestone ridge, and an upper 6. Shale, brownish-gray, zone of sandy limestones, dark gray on fresh weathering yellowish­ surface, that weather a rusty brown color. brown, fissile, highly con­ The type section, as measured by P iaggio torted with distinct slaty cleavage and well-devel­ includes the following strata: oped pencil structure; at Unit Feet base a 6 inch bed of very 10. Limestone, dark gray to silty, unevenly-bedded black, weathering yellow­ dark- gray limestone that ish brown, sandy with weathers gray --·--- ______30.5 subangular to subrounded 5. Shale, light-gray, weather­ quartz grains; contains ing yellowish-white, cal­ irregular patches of bright careous, platy, marly; at orange siderite, some al­ base a 2 inch bed of light tered to limonite; fossili­ brown limonitic shale that ferous, fauna includes weathers a bright yellow­ terebratulid brachiopods, brown which has been crinoid segments, belem­ traced laterally for more nites, an olcostephanid and than one-half mile on the other ammonites, and nu­ north side of the Valle de merous smaller mollusks. San Paufo ______8 A one foot zone of green­ 4. Shale, dark-gray to black, ish-brown fissile shale weathering yellowish­ weathering yellowish­ brown, calcareous, platy, brown that contains pyri­ poorly fissile; at base a 2 tized (altered to limonite) inch bed of crystalline echinoids and olcostepha- white calcite with minute nid ammonites ______5.5 partings of non-calcareous 9. Shale, greenish-brown, black shale ______13.5 weathering pale· yellowish­ 3. Marl, chalky-white, weath­ brown, very fissile, with ering a dirty-yellow, soft small silty limestone con­ and powdery, with occa­ cretions that contain dis­ sional thin beds of black torted echinoids. Unit be­ limestone that weather comes increasingly cal- gray; fossiliferous with 140 Tulane Studies in Geology Vol. 1

U~t ~cl of limesrone is not greatly different from limonitic concretions con- that on the north flank. taining echinoids, and ech- Upper Member Taraises Formation.-The inoids and ammonites re- 1 placed by limonite --·------10 upper member of the Taraises Formation 2. Limestone, dark-gray, consists of a rather monot0nous sequence of weathering medium gray, black, fine-grained, dense limest0nes that very fine grained to sub­ weather t0 a light gray color and usually lithographic, dense, with numerous white calcite break down tO shale-like slopes. As a result veins up to one inch thick the inter-valley ridges appear to be under­ transverse to the bedding; lain by a sequence of shales, whereas the a thick (3' 10") bed at fresh exposures in the valleys reveal the base, becoming increasing­ ly thin-bedded upwards; calcareous nature of the member. Some of abundantly fossiliferous the beds yield a strong fetid odor when with many ammonites struck with a hammer; a sample of such (Acanthodiscus, Distolo- material dissolved in acid left a minor sludge ceras, Leopoldia,, Neo­ co?nites, T hurrnanniceras of carbonaceous material and minute crystals (?),etc.), belemnites, pele­ of pyrite. The whole is suggestive of depo­ cypods, occasional rhyn­ sition under euxenic conditions. Some bed­ chonellid and terebratulid ding planes, however, bear fucoidal impres­ brachiopods, crinoid seg- ments, and rare corals____ 9 sions suggestive of a bottOm fauna, and a 1. Interbedded thin- to medium­ few fossils, including ammonites and pele­ bedded 1i mes tones and cypods occur, though not uniformly dis­ marls: limestones, similar tributed throughout the section. A unit some to, unit 2, with same five feet thick, located approximately 60 feet fauna; marly interbeds, 2 to 7 inches thick. A 3 below the t0p of the formation has yielded foot limestone bed at base 8.5 numerous specimens of a gigantic species of Harpagodes (?). Hence it is evident that, 198.5 if the depositional environment was occa­ In addition t0 the lesser thickness of the sionally euxenic, such conditions did not per­ Los Nogales Member on the south flank of sist throughout the entire time interval en­ the Los Muertos anticline, measured sections compassed within the member. The Harpa­ reveal the following differences from those godes (? ) zone has been recognized in all on the north flank of the structure: ( 1 ) the sections where the interval of its occurrence basal limesrone sequence is slightly thicker, is exposed, and it constitutes a useful strati­ averaging 26 feet in thickness, and is most graphic marker in this region. notably different in the almost complete A section measured on the north flank of absence of ammonites which are so con­ the anticline by James A. Holliday follows; spicuously present on the north flank. These it was measured along a small draw immedi­ beds appear rather sparsely fossiliferous in ately above an abandoned swimming pool outcrop with a fauna that includes belem­ that is located to the east of the saddle nites, brachiopods, crinoid segments, rare formed on the shales of the Los Nogales corals and bryozoa. Thin sections, however, Member above the collapse block of Cupido reveal that some of the beds contain abun­ Limest0ne adjacent t0 the type section of dant fragments of colonial cyclost0me bryo­ the San Paulo Formation: zoans and echinoid plates and spines. ( 2) Unit Feet The middle shale segment is thinner, 76 to 9. Limestone, dark grayish 80 feet thick, but not greatly different, litho­ black, weathering medium logically from that of the north flank. ( 3) light gray, obscurely cross­ The dark gray tO black, brown weathering bedded, weathers to shaly slope; rocks yield strong arenaceous and sideritic limest0nes with fetid odor when struck____ 65 terebratulid bachiopods and other fossils, are 8. Limestone, dark grayish in general thinner-bedded and have thicker black, weathers medium shale units (up to 4 feet thick) intercalated light gray, in 1 to 2 foot between them. As a result the upper se­ beds; fossiliferous with many specimens of Harpa- quence is thicker, measuring up to 27 feet godes (?) sp. ______5 in some sections, although the tOtal amount 7. Limestone, similar to unit 9, No. 4 Geology of the Canon de la Huasteca Area 141

Unit Feet Unit Feet gray black, weathering more resistant and marked brownish gray with rough by limonitic stains ______456 sandy surface; beds 4 to 5 feet thick; some highly 692 fossiliferous beds in inter­ val 20 to 55 feet below top 33 NUEVO LEON STAGE 6. Limestone, medium-bedded to massive, with thin shaly Cupido Limestone interbeds; limestone The Cupido Limestone, named by Imlay weathers to shaly slopes __ _ 565 (193 7, p. 606) for 1,415 feet of thick-bedded 5. Shale, gray black, weather­ gray limestone exposed in the middle part ing brownish gray, cal- careous ------· ______0.5 of the Sierra de Parras, is the major ridge­ 4. Limestone, gray black, forming formation in southeastern Nuevo weathering light gray; Leon and adjacent areas of Coahuila. It contains a few pelecypods crops out as strike ridges forming the north and ammonites that have been limonitized and are and south walls of both the Valle de San poorly preserved ______1 Paulo and the Valle de Muralla. Both the 3. Shale, similar to unit 5 ______1.5 Canon de Huasteca on the north and Canon 2. Limestone, similar to unit 9, de Mortems on the south of the map area medium- to thick-bedded _ 51 1. Limestone, similar to unit 2, are cut through these strike ridges. but with much pyrite that The formation is composed of thin- to weathers to limonitic thick-bedded and massive limestones, light stains ------30 brown to light gray, dark gray and black in color, and rudistid-bearing. Stylolitic sutur­ 752 ing of the bedding planes is commonly pres­ A section measured on the south flank of ent. Humphrey ( 1949, p. 102) states that the anticline, on the west side of a large trib­ in the western part of the Sierra de Los utary canyon approximately one and three­ Muertos "the base is everywhere marked by quarters miles west of Canon de Mortems a thick-bedded unit of dolomite and dolo­ by R. F. Beyer, Jr., V. V. Cavaroc, Jr., and mitic limestones." In the area here under G. C. Glaser, well illustrates the lithologic study the basal beds are all non-dolomitic consistency of the member: limestones. There are, however, some dolo­ mitic limestones and one or two beds of Unit Feet 4. Limestone, dark gray to dolostone toward the middle part of the black, weathering light sequence. gray, dense, thick- to mas­ The contact of the Cupido Limestone with sive-bedded, emits a fetid the underlying Taraises Formation is con­ odor when struck; rock weathers along joints and formable and is here drawn where the lime­ bedding planes to develop stone becomes thick-bedded, resistant and a resistant "blocky" sur- cliff-forming. face residue ______7 4 Although the section in the Canon de la 3. Limestone, dark gTay, weath­ ers grayish-white, thick­ Huasteca is perhaps more spectacularly ex­ bedded, fossiliferous, with hibited, and is certainly better known to numerous large Harpa- geologists and visitors, that in the Canon de godes (?) sp. ______10 Mortems to the south is more completely 2. Limestone, dark gray, weathering medium gray, exposed. A section measured mainly along weathers to a shaly slope; the eastern wall of this canyon, with the rock is medium-bedded be­ basal beds bein~ measured on the western low and becomes thicker wall, follows. The measurements were made bedded toward the top ; thin shale interbeds. Some by Anthony T. l'Orsa in 1961: beds sparsely fossiliferous 152 Unit Feet 1. Limestone, light to dark 19. Talus and caliche covered ____ 6 gray, argillaceous, dense, 18. Limestone, medium to dark weathers light gray to gray, weathering medium brownish buff in color gray, thin- to. very thick­ forming fragments. simu­ bedded; upper foot thinly lating a shale ; basal beds laminated; occasional ru- of more pure limestone, distid pelecypods ______20 142 Titlane Studies in Geology Vol. 1

Unit Feet Unit Feet 17. Limestone breccia, light to colors alternating every dark gray, weathering few feet; weathers in medium dark gray; ap­ light to dark brownish pears to be intraforma­ gray bands with medium tional breccia with slabs brownish gray predomi­ up to four feet long______3 nating; a few isolated 16. Limestone, medium gray to strata are dolomitic; black, weathering medi­ thick- to very thick-bed­ um to dark gray, with a ded; sparsely fossiliferous 606 few interstratified light 8. Limestone, light brownish to gray beds; some rusty light olive gray, weather­ weathering-, nodular, gray ing light gray, fine cry­ chert; rudistid bearing; stalline; thick- to very stylolite columns up to one thick-bedded; fauna in­ foot in length ______204 cludes rudistids and large 15. Limestone, dark gray, weath­ N erinea ------68 ering medium gray, finely 7. Limestone, medium to dark crystalline crowded with gray, weathering medium monopleurid ( ?) rudistids gray, thick- to very thick­ that have been recrystal­ bedded; some beds crowd­ lized to white calcite. This ed with rudistids, others rock has been locally sparsely fossiliferous; a "quarried" for terrazzo single coral was observed 268 stone ------7 6. Covered interval, a single 14. Limestone, medium to dark limestone bed two feet gray, weathering light to thick exposed near center, medium gray, thick-bed­ medium gray, weathering ded, stylolitic; some frac­ lighter gTay, with abun- tures contain small quartz dant rudistids ______52 crystals embedded in cal­ 5. Limestone, argillaceous, cite fracture fillings and thinly laminated, medium small vugs; moderately gray, weathering medium fossiliferous with a rudi- gray to fissile-like frag­ stid fauna ______255 ments ------3 13. Limestone, medium gray to 4. Limestone, grayish black, light brownish gray, weathering dark gray, weathers medium to light thick-bedded, stylolitic ___ _ 14 brownish gray, thick- to 3. Limestone, argillaceous, with very thick-bedded, styloli­ thin uneven laminations, tic with columns up to 8 light to dark gray and in. long-; rudistids mod- brownish gray, weather­ erately abundant ______181 ing same; interbedded 12. Limestone, dolomitic, medi­ with a lesser amount of um gray, weathering me­ thick-bedded limestone, dium gray with a rough non-argillaceous, dark sugary textured surface. gray weathering medium Rock is more coarsely gray ------35 crystalline than adjacent 2. Talus covered interval ______15 limestones ______16 1. Limestone, dark gray, 11. Limestone, light to medium weathering medium gray, brownish gray with the thick-bedded, stylolitic ___ _ 26 lighter and darker layers alternating; weathering 2,380 color corresponds approxi­ mately to color of fresh surface; medium to very Comanche Series thick-bedded; lighter col­ TRINITY STAGE ored beds tend to be sub­ La Pena Formation li t:,.,ogra phic in texture, and more fossiliferous Imlay proposed the term La Pena Forma­ than the darker; fauna tion in 19 36 ( p. 1119) for the "lower and mainly rudistid but some middle portions of the mountain-forming N erinea were noted ______598.5 limestones, as exposed in the Sierra de Par­ 10. Dolostone, medium gray, ras, lying stratigraphically between the Par­ weathering brownish gray, sugary in texture ______2.5 ritas formation (below) and the Aurora 9. Limestone, light brownish limestone (above)." Two members were gray to dark gray with recognized, a lower consisting of "about No. 4 Geology of the Canon de la Huasteca Area 143

1400 feet of light- to dark-gray, thick- to Untt Feci medium-bedded limesrones, which include fossiliferous with fauna including ammonites, be­ some shaly partings," and an upper member lemnites, echinoids and ranging from S0 ro 80 feet in thickness rare pelecypods ______10 which "consists of thin-bedded limesrones 3. Shale, medium light gray, and shales." A measured section of the lower weathers light gray, very member in Canon Platanos south of Parras, marly; fauna includes echinoids, belemnites and included 2190 feet of limestones with minor occasional ammonites ______1.5 shale. 2. Limestone, medium dark In 1937 (p. 606) he proposed the name gray, weathering a gTayish Cupido Formation for "thick-, medium-, ~nd yellow-brown, very nodu­ thin-bedded limesrones above the Taraises lar and unevenly bedded with interbeds of gray formation and below La Pena formation" marly shale; highly fos­ but continued ro include a thick limestone siliferous, with abundant sequence as the basal member ~f th~ over­ ammonoids that include almost all species described lying La Pena the contact ~erng drawn by Humphrey (1949), to­ where thin-bedded and platy limestones be­ gether with nautiloids, be­ come abundant." The distinction between lemnoids, rare pelecypods, the two limestone units is not apparent in gastropods, and echinoids; the sections exposed in the Nuevo Leon fossils chara.cteristically red-colored on surface ____ 8 area, the limestones being medium- to thick­ 1. Limestone, dark gray, bedded throughout the entire sequence. T~e weathering brownish gray, writer follows Humphrey (1949, p. 103) rn thin- to medium-bedded, applying the name ~upido Li1::i~stone ro the very argillaceous, with entire sequence while recognizrng that tl:ie thin interbeds of marly gray shale; fossiliferous, upper portion probably corresponds rn fauna including Plicatula stratigraphic position to the lower. member sp., Astarte (s.l.) and · of Imlay's original La Pena Formation. The other pelecypods together latter name is thus restricted to a sequence with rare brachiopods ____ 5 of marls and shaly limesrones with one or exposed thickness ______24.5 two more resistant limesrone strata that are the stratigraphic equivalent of the upper On the north side of the anticline there member of Imlay' s La Pena. These beds, is a characteristic erosional notch on the which are abundantly fossiliferous with a east wall of the Canon de la Huasteca near rich ammonite fauna of upper Aptian age, the entrance of the canyon. Unfortunately, are much less resistant than the adjacent however, the strata here are covered with massive limestones of the Cupido and Aurora talus from the adjoining Cupido and Aurora formations and weather to a narrow strike limestones and no section can be studied. valley whose surface is strewn with t~l~s to On the west side of the canyon, immediately the point that outcrops are rare and difficult above the end of the paved road from Santa to locate. Catarina a few fossils, collected from the No section adequately exposed for meas­ saddle a~ the crest of the ridge are sufficient urement has been located in the present to establish the presence of La Pena at this mapped area, but a partial section exposing position in the structure. the lower beds of the formation is well The contact with the underlying Cupido shown adjacent to a shaft sunk by the Limestone is concordant and sharp, the Comisi6n Agua Potable de Monterrey._ The uppermost Cupido strata forming ~ distinct section penetrated in this project was slightly wall adjacent to the basal La Pena strata. in excess of 15 meters thick (oral com­ Present knowledge of the faunas of the munication) . The portion exposed includes upper part of the Cupido Limes~one is in­ the following units: sufficient to permit any conclusions as to lli~ ~cl whether the sharp lithologic change between 4. Limestone, dark gray weath­ the two formations is simply a change in ers medium gray, in beds about 1 foot thick, dense, deposition regime or is indicative of a time argillaceous; moderately lapse between them. 144 Tulane Studies in Geology Vol. 1

TRINITY ( ? ) AND FREDERICKSBURG out all the residue passed a 200-mesh screen. STAGES There was no trace of swelling, although the Aurora Limestone leached sample, after drying, disaggregated The Aurora Limestone, named by Burrows in water. ( 1910, pp. 96-97) for 600 to 1500 feet of The origin of the clay deposit is not clear­ cherry limestones in the Sierra de La Aldea ly understood. The thin, even bedding, in northeastern Chihuahua, is, like the clearly indicates subaequeous deposition, Cupido Limestone, an important mountain­ and the fineness of the material strongly forming unit. In the area of the present implies relatively quiet waters; hence a la­ study it crops out at the northern entrance custrine origin is suggested. Nevertheless, to the Canon de la Huasteca, forming the it is difficult to explain the absence of any front of the first ridge of the Sierra Madre coarser debris, especially since the deposit Oriental, and on the southern flank of the lies on the Taraises Formation at a point Los Muertos structure it occurs at the south­ less than 400 feet from high-standing, re­ ern entrance to the Canon de Morteros to sistant, cliff-forming strata of the Cupido form the north wall of the broad synclinal Limestone. Careful examination along the valley south of the Valle de San Paulo­ entire face of the quarried area has failed to Valle de Muralla area. Only the basal beds reveal even a single pebble of limestone. are exposed in both outcrop belts. Fresh sur­ Furthermore, there are no traces of organic faces of the limestone are dark gray to gray­ material, save for rootlets of plants that have ish black in color and weather a medium penetrated into the deposit from above, and gray in color. The beds are medium to very it is to be expected that a lake in this gen­ thick, or massive, and characteristically con­ eral region would contain some traces of tain brownish-weathering black chert in ir­ leaves, or wood, and especially should have regularly shaped nodules and concretions. had a molluscan fauna that would have left Stylolitic suturing of bedding surfaces is occasional shells in the bottom sediment. generally to be observed and rudistids are It has been suggested that the absence of not rare in some of the strata, though absent coarse material might be explained if we in others. assume that the adjacent Cupido cliffs were beneath the waters of the lake. This would TERTIARY (?) OR QUATERNARY SYSTEM require a water depth of 800 to 1000 feet "enigma clay" and, in the general regional topographic set­ The informal designation, "enigma clay," ting now indicated, would have resulted in has been applied in the field to a small de­ a lake many hundreds of square miles in posit located immediately southwest of the area. In the light of so large a body of water schoolhouse in the poblaci6n of Los Nogales. it is difficult to explain the absence of any The deposit consists of approximately 60 evidences of its existence other than the one feet of thin-bedded, calcareous clay in thin small clay deposit now known. beds, one to three inches thick, that are more or less alternately light grayish yellow and QUATERNARY SYSTEM orange buff in color. The deposit rests upon Alluvial Deposits a water-worn eroded surface of the upper Extensive alluvium and colluvium covers member of the Taraises Formation, with, the floors of both the Valle de San Paulo in the small area where the floor is exposed, and the Valle de Muralla, and alluvium is no trace of a basal sandy, or conglomeratic, present in both the Canon de la Huasteca layer. The Taraises has a strike of N. 65 ° and the Canon de Morteros. These materials W. and dips 85 ° to the south; the clays include, in addition to normal valley channel strike N. 40° E. with dips varying between and flood plain deposits, a veneer of caliche­ 23 ° and 31 ° S. Overlying the clays is a cemented piedmont debris covering the low­ coarse bouldery alluvium containing large er slopes of the ridges that margin the val­ blocks of the Cupido Limestone. leys. For some reason not yet understood the In the laboratory, samples of the clay caliche-cemented deposits appear to be more prove to contain twenty-five percent CaC03 extensively developed in the Valle de Mural­ ( by weight), gave a positive test with ben­ la, especially toward the western end where zidine, and after the lime had been leached they occur at elevations as much as 600 feet No. 4 Geology of the Canon de la Huasteca Area 145 above the present valley floor, reaching alti­ in the northern part of the valley, there is a tudes of almost 3, 100 feet above sea level. gradual increase in the angle until 60 degree In the Valle de San Paulo they seldom occur dips are recorded toward the western termi­ more than 200 feet above the valley floor. nus of the mapped area. Over most of the area the caliche-cemented An apparent fault near the axis of the deposit is sharply delimited from the valley anticline also complicates the interpretation alluvium, and the former is interpreted as of the Los Muertos structure in the Valle de the product of a depositional period char­ San Paulo area. This fault is nowhere visi­ acterized by a more pluvial climate than that ble, its trace apparently lying below the presently existing in the region. alluviated valley of the intermittent stream which flows along the south side of the V. STRUCTURAL FEATURES Zuloaga morros that mark the anticlinal crest. The presence of the fault is inferred The Cafion de la Huasteca area lies within primarily from the insufficient r?om be­ the broad regional structure known as the tween the outcrops of the Zuloaga Limestone Los Muertos anticline, the prominent fold and the San Paulo Sandstone on the south whose northern limb forms the front of the limb of the anticline for a thickness of Mu­ Sierra Madre Oriental in the immediate vi­ ralla Shale equivalent to that measured on cinity of Monterrey and westward into the the north flank of the structure (see Fig. 2). eastern part of the State of Coahuila. With­ Other evidence is that the few dips which in the area studied the anticline is asym­ could be obtained in the Zuloaga Limestone metrical with the strata on the north flank in the Valle de San Paulo section are all dipping 80 to 90 degrees or overturned, and steeply overturned, but the San Paulo Sand­ those on the south flank, in general, dipping stone on the south limb of the structure less steeply. There is, however, variation. in (and less than one thousand feet from the the attitude of the beds. The steepest dips Zuloaga) dips from 36 to 59 degrees to the recorded are in the general vicinity of the south. Finally, just beyond the western e~d Cafion de la Huasteca on the north flank, of the mapped area on the southern margin and of the Cafion de Morteros on the south. of a Zuloaga morro the dark gray limestone On the north flank of the structure, within is completely brecciated in~o fragme~ts the Valle de San Paulo there is a progressive "floating" in a matrix of white crystalline reduction in the dip angle westward from calcite. The limestone fragments, only a few the Huasteca, until, near the western edge of inches in greatest length, are separated by the mapped area the dips are mainly in the from one to four inches of calcite. range of 50 to 60 degrees. Outside of the It is of interest to note, in this connec­ Valle de San Paulo, on the northern side of tion that, although Bose had earlier ( 1923, the Cupido-Aurora Limestone ridge, ~here p. 129) commented that "one o~ the. most is a reversal of this situation, with the ndge­ astonishing features of the reg10n is the forming limestones becoming more and absence of faults and overthrusts," he recog­ more overturned westward from the Canon nized the probable existence of the pres~nt de la Huasteca until, as may be observed fault which he shows in a small cross-section from the Monterrey-Saltillo Highway, the (p. 200) and he states (p. 324) _: "Along dips in the upper portions of the ridsse are the middle of the valley probably lies a fault approximately 60 degrees to the south. of small importance; toward the south the On the south flank of the anticline in the Oxfordian [Zuloaga] limestone seems to Valle de San Paulo the Cupido and Taraises break off where the beds should begin to formations have dips of 84 to 85 degrees to dip toward the south." the south at stream level, but the arching of Some evidence as to the nature of the the strata into the anticlinal structure is re­ vealed in dips as low as 70 degrees o?- the fault may be gained from a study of the higher ridge elevations. Less than a mile to well developed axial-plane cleavage or fan­ the west, however, dips of 36 and 38 de­ jointing which strikes parallel to all of ~he grees are recorded in the San Paulo Sand­ observable regional structures. A compila­ stone and the Los Nogales member of the tion of the dip pattern of this cleavage was Taraises Formation. From this point west­ made by V. V. Cavaroc, Jr., of the .19~1 field ward , in contrast to the situation observed group. This revealed that the proJections of 146 Tulane Studies in Geology Vol. 1 the cleavage dips measured on the south Zuloaga Limestone in the Valle de San Paulo flank of the anticline converged at a point area, and in the Sierra del Fraile t0 the northward from the convergence point of northwest. It is here suggested that the gyp­ those measured on the north flank, and also sum intrusions in the Valle de San Paulo somewhat deeper below the surface. Mr. area may have been one result of the fault­ Cavaroc concluded ( unpublished field re­ ing in this valley, and it might even be pos­ port): "While the number of fan dips taken sible that the underthrust mass, moving into [were not sufficient to permit a positive a series of strata of gypsum and anhydrite statement], the results are consistent enough would act more or less like a plunger being to strongly indicate a major, low angle, axial forced into a cylinder of liquid, to displace thrust fault dipping about 25 ° northward." the evaporites and to force their movement, The amount of displacement would be in perhaps in part along the fault plane, and the magnitude of 800 to 1,200 feet, depend­ especially along the bedding-planes between ing upon whether or not a portion of the the massive limestone layers of the Zuloaga. Zuloaga Limestone on the south limb of the It thus may be significant that the only oc­ fold was also displaced as suggested by Bose. currences of intrusive gypsum in the region There is general agreement that the forces coincide rather precisely with the limits of which deformed the Jurassic and Cretaceous the area in which the evidence for faulting sediments into the folds now represented in noted above are to be observed. the Coahuila-Nuevo Leon portion of the The anomalous structural features are not Sierra Madre Oriental of Mexico were de­ continued laterally into the Valle de Muralla rived from the south-southwest (Bose, 1923, to the east of the valley of the Rio Santa p. 333 ; Humphrey, 1949, p. 113; 1956, p. Catarina and there is no evidence to sug­ 28; De Cserna, 1956, p. 69; etc.), and this gest the presence of a fault at the crest of is well shown in the Canon de la Huasteca the anticline in this region. Dips are rela­ area by the steepened north dips and over­ tively steep on both flanks, although some­ turning on the northern flank of the Los what more steep on the north than the south. Muertos anticline as compared with the Cross faults, or tear faults, noted by gentler dips on the southern flank. But this Humphrey ( 1949, pp. 114-5) on the north same consideration implies that the fault flank of the anticline in the region to the movement occurred as an underthrust move­ west of the present area have not been ob­ ment from the south to the north. It also served during the course of the present study. has been generally agreed that one cause of There is, on the other hand, an apparent the strong overfolding to the north is that slight southerly offset of the formations in the sediments folded were caught between the core region of the anticline on the east the forces from the south-southwest and the side of the valley of the Rio Santa Catarina margins of a now buried block of Paleozoic as compared with those on the left. Further­ and early Mesozoic sediments and associated more the fact that the caliche-cemented al­ igneous rocks that was positive in late Juras­ luvial deposits occur at much higher slope sic time (and was the source of the elastics elevations in the Valle de Muralla than they represented in the Muralla Shale and, espe­ do in the Valle de San Paulo, and the much cially, in the San Paulo Sandstone) . This broader outcrop width of the Zuloaga Lime­ block represents the "Ancient Continent" of stone belt in the Valle de Muralla, all tend Bose (1923) and Burckhardt 0930-31) and to suggest the presence of a small cross fault the Coahuila and Tamaulipas peninsulas of near the present course of the Rio Santa Kellum, Imlay and Kane ( 1936) , Imlay Catarina, and also to indicate that the east ( 1943) and of subsequent authors. side was uplifted with respect to the west. It is somewhat difficult for the present On the other hand, the fault either did not writer to visualize underthrusting in the affect the Canon de Mortems on the south­ present region which should be situated ern flank, or else the movement was strictly rather near the margins of the hypothecated parallel with the direction of dip, for one positive block, unless some special condi­ can easily observe the continuation of the tions occurred. These may be found in the individual strata directly opposite each other presence of the gypsum in the region, as evi­ in the canyon walls. The rather sinuous denced by the intruded gypsum noted in the course of the Canon de la Huasteca makes No. 4 Geology of the Canon de la Huasteca Area 147 it a bit more difficult to check the individual VI. LITERATURE CITED beds on the opposite walls, but they appear BosE, EMIL, 1923, Vestiges of an ancient to be continuous across the structure, and continent in northeast Mexico: Amer. Jour. Sci., (5), 6 (whole no. 206), pp. 127- there is no striking difference in dip on the 136, 196-214, 310-337, 4 text figs. two sides as was reported by Humphrey BOSE, EMIL and 0. A. CAVINS, 1928, The from the area near Las Cortinas canyon Cretaceous and Tertiary of southern (1949, p. 115). Texas and northern Mexico: Univ. Texas Bull., 2748, pp. 7-142. Collapse structures.-Incidental mention BURCKHARDT, CARLOS, 1906, La faune Juras­ has been made of a ridge north of the sec­ sique de Mazapil, avec un appendice sur ond Zuloaga morro west of the Rio Santa les fossil es du Cretacique inferieur : Inst. Geol. Mexico, Bol. 23, 219, pp. 43 pls. Catarina that is capped by a large collapse BURCKHARDT, CARLOS, 1930-31, Etude syn­ mass of Cupido Limestone resting on the thetique sur le mesozoi:que mexicain: Soc. upturned edges of the San Paulo Sandstone. Paleont. Suisse, Mem., 49, pp. 1-122; so, This limestone mass cannot be interpreted pp. 123-280. as an example of rock fall or talus because, BURROWS, R. H., 1910, Geology of northern Mexico: Soc. Geol., Mexico, Bol., 7, pp. 85- although now somewhat broken up by 103, map. undercutting resulting from the weathering DE CSERNA, ZOLTAN, 1956, Tect6nica de la of the softer San Paulo strata around the Sierra Madre Oriental de Mexico, entre Torreon y Monterrey: XX Congreso Geo- margins of the mass, the material obviously 16gico Internacional, Excursion C-5, 87 reached its present position without notable pp., Frontispiece, 7 pls., 1 table, 9 text disruption. The mass is here interpreted as figs. representing a form of "slip-sheet," defined DIAZ-GONZALES, TEODORO E., 1956, Generali­ dades sobre la geol6gia del norte de by Harrison and Falcon, ( 1934; 1936) as Mexico: XX Congreso Geol6gico Interna­ "a slab of rock which has become detached cional, Excursion A-13, pp. 9-14. from its original place on a dip-slope and HARRISON, J. v., and N. L. FALCON, 1934, has slipped down, remaining more or less Collapse Structures: Geol. Mag., 71, pp. intact" ( 1936, p. 92). In the present in­ 529-539, 6 figs. HARRISON, J. v., and N. L. FALCON, 1936, stance, however, the slab has slipped down Gravity Collapse Structures and Moun­ on the inner side of the fold, rather than tain Ranges as exemplified in South­ down a dip-slope, apparently because the western Iran: Quart. J our. Geol. Soc., London, 92, pp. 91-100, 4 text figs. differential erosion of the softer Taraises HUMPHREY, WILLIAM E., 1949, Geology of sediments and the highly resistant Cupido the Sierra. de Los Muertos Area, Mexico limestones left an almost vertical block of (with descriptions of Aptian Cephalopods the latter without adequate buttressing. It from the La Pena Formation) : Geol. Soc. Amer., Bull., 60, pp. 89-176, 18 pls., seems that the block must have been weak­ 2 text figs. ened below, either by erosion or because of HUMPHREY, WILLIAM E., 1954, Stratigraphy excessive joint or fracturing at the base, and of Cortinas Canyon section, Sierra de Los thus have slid as a unit, rather than have Muertos, Coahuila, Mexico: South Texas Geol. Soc., Guidebook, 21st Field Trip, toppled over from above, since the latter p. 18, Correlation Table. assuredly would have resulted in the free HUMPHREY, WILLIAM E., 1956, Tectonic fall of a major portion of the mass, disrupt­ framework of northeast Mexico: Gulf ing it to form rock-fall debris. Coast Assoc. Geol. Socs., Trans., 6, pp. 25-30. There is a second, well-exposed, and ap­ HUMPHREY, WILLIAM E., and TEODORO E. parently more recently formed example of a DIAZ-GONZALES, 1956, Correlation of the collapse structure exhibited on the north wall Mesozoic Strata of Northeastern Mexico: Gulf Coast Assoc. Geol. Socs., Trans., 6, of the synclinal canyon immediately to the pp. 32-34. south of the mapped area. It is located four IMLAY, RALPH w., 1936, Evolution of the to five miles east of the southern terminus Coahuila Peninsula, Mexico: Part IV. of the Cafion de Morteros. Determination Geology of the western part of the Sierra de Parras: Geol. Soc. Amer., Bull., 47, pp. as to whether it represents a "flap" or a 1091-1152, 10 pls., 3 figs. "slip-sheet" must await careful examination IMLAY, RALPH w., 1937, Geology of the of the strata involved. middle part of the Sierra de Parras, 148 Tulane Stztdies in Geology Vol. 1

Coahuila, Mexico: GeoL Soc. Amer., Bull., Atlantic and Gulf Coastal Province of 48, pp. 587-630, 14 pls., 4 figs. North America: New York, Harper and IMLAY, RALPH w., 1938, Studies of the Brothers, xvii + 692 pp., 573 ill., and end Mexican geosyncline: Geol. Soc. Amer., papers. Bull., 49, pp. 1651-1694, 7 pls., 6 figs. PIAGGIO, ARTHUR D., 1962, The Los Nogales IMLAY, RALPH W., 1943, Evidence for Up­ Member of the Taraises Formation, near per Jurassic landmass in eastern Mexico: Monterrey, Nuevo Leon, Mexico: unpub­ Amer. Assoc. Petrol. Geol., Bull., 27, pp. lished Master of Science thesis, Tulane 524-529, 1 fig. University, vi + 82 pp., 11 plates, 4 text KELLUM, LEWIS B., RALPH w. IMLAY and w. figs. and table. G. KANE, 1936, Evolution of the Coahuila WALL, JAMES R., GROVER E . MURRAY and Peninsula, Mexico: Part I, Relation of TEODORO DIAZ-G., 1961, Geologic occur­ structure, stratigraphy, and igneous ac­ rence of intrusive gypsum and its effect tivity to an early continental margin: on structural forms in Coahuila marginal Geol. Soc. Amer., Bull., 47, pp. 969-1008, folded province of northeastern Mexico: 3 pls., 3 figs. Amer. Assoc. Petrol. Geol., Bull., 45, pp. MURRAY, GROVER E., 1961, Geology of the 1504-1522, 14 figs.