Boletín de la Sociedad Geológica Mexicana ISSN: 1405-3322 [email protected] Sociedad Geológica Mexicana, A.C. México

Esquivel-Macías, Carlos; León-Olvera, Rita Gabriela; Flores-Castro, Kinardo Paleoenvironment and biostratigraphy of the Upper Sinemurian (Lower Jurassic) of the Huayacocotla Formation in East-Central Mexico Boletín de la Sociedad Geológica Mexicana, vol. 69, núm. 3, 2017, pp. 739-770 Sociedad Geológica Mexicana, A.C. Distrito Federal, México

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How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative P. 739‒770 VOL. 69NO. 3 BOL. SOC.GEOL.MEX.2017 researcher.Independent Rita GabrielaLeón-Olvera UAEH Pachuca, Hidalgo. C.P. 42184. AcadémicodeCienciaslaTierra, Cuerpo Kinardo Flores-Castro [email protected] Carlos Esquivel-Macías Carlos Jurassic) oftheHuayacocotlaFormationinEast-CentralMexico Paleoenvironment and biostratigraphy of the Upper Sinemurian (Lower Manuscript August accepted: 16,2017 Corrected manuscript received: June 20,2017 Manuscript received: December2,2016 Esquivel-Macías , Rita Gabriela cotla, Mexico, Biostratigraphy. Keywords: Jurassic, Sinemurian, Huayaco Congress. Jurassic the 10thInternational in the context of Early Jurassic marine paleobasins, the knowledge of as wellabout asto encourage academic discussions tribute to this subject,andmaybe other related topics, encourage interested researchers inthisfield to con Jurassic This written field tripguidewastolead and reported was from rian deposits at least one outcrop. Obtusum rian homotaxial events. inthe Lower Therea gap is Early Sinemu tentatively explained to be the result of biozonation were noticed, and these anomalies are some local divergences with respect to the standard Densinodulum Sinemurian diverse chronozones, especially the Huayacocotla Fm. spannedseveral Late tion of newstudiesrevealedErben. These that the deposi zonationstratigraphic proposed byBurckhardt and analyses developed in the 2000’s, accurate the bio biostratigraphical Mexico. modern The of Gulf the expansion of simultaneously with the process of sedimentation, generated this sequence siliciclastic, Mexico opening. paleobasin with highrate The of of the Gulf stagesof phase and thefirst collision sition reveals tectonic features related to the Pangea compo igneous intermediate tions. Itsprotolith of arcback paleobasin, withsuboxic toeuxiniccondi Huayacocotla in asemi-restricted Fm. wasdeposited several formations. Today, it is well known that the including several facies rather than a complex unit of quence, but canbe better regarded unit, asasingle that the Huayacocotla Fm.isnotacondensedse logic andgeochemical techniques. They concluded structural aspects, taphonomic, petro incorporating paleoenvironmental, paleoecological, geologic, and paleontological, this time including a wide range of studies resumedthe 2000’s in by Mexican researchers, interest in thisunitfaded a longtime ago. However, were notcommercially productive. Consequently, the (1948), whomeventually concluded that theserocks and European geologist during the twentieth century Sinemurian), studiedbyfirst was several American LowerThe JurassicHuayacocotla (Upper Fm. ABSTRACT León-Olvera fua,bttepeec fLower Sinemu faunas, but the presence of , and Raricostatum Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín , Kinardo subzones. Nevertheless, Oxynotum Flores-Castro ------, ellas decayó. Durante la primera década de los 2000’s mercialmente productivas. Enconsecuencia el interés en (1948), queconcluyeron queestas rocas no eran co gos norteamericanos y europeos durante elsiglo veinte (Sinemuriano Superior) estudiada fue por varios geólo La Formación Huayacocotla del Jurásico Inferior RESUMEN Huayacocotla, México, Bioestratigrafía. Palabras clave: Jurásico, Sinemuriano, JurásicoCongreso Internacional. paleocuenca marina como del mundo, en elmarco del X conocimientos a otras secciones jurásicas, tanto de esta ampliar estos y colaboración que permitan información campo a investigadores interesados el intercambioen de de comoapoyo para conducir en unrecorrido formula ción durante la zona Obtusum.La presente guíase Inferior, de la fosiliza conunamarcada interrupción homotaxiales relacionados al Sinemuriano como eventos bargo, numerosas anomalías faunísticas se explican de Sinemuriano Superior centradas alrededor de las Zonas durante las cronozonasesta secuencia se desarrolló del Erben alprincipio del siglo veinte.que Esto evidenció generales por Burckhardt y fica indicadatérminos en estas localidades, que afinan la zonación bioestratigrá también se elaboraron trabajos sobre en bioestratigrafía sión que originó al Golfo deMéxico. Desdeel2000 siliciclástica, simultáneamentecon elproceso de expan ca conalta tasa de sedimentación, generó esta secuencia fases de la apertura del Golfo deMéxico. La paleocuen la faseen decolisión de laPangealas yenprimeras delata rasgos tectónicos involucrados ígnea intermedia nes subóxicas aeuxínicas;cuyo protolito de composición cuenca intrarco semirestringida, con fondos de condicio se sabe que la Fm. Huayacocotla representa una paleo y que resultaron ser facies de una sola Formación. Ahora principio que en parecía dividida varias en formaciones (sensu nocondensada), de unasecuencia desarrollada encontrar que setrata mica y petrología, lo cual permitió y técnicas de tafonomía,incorporando geoquí conceptos de investigadores mexicanos,y paleoambiental a cargo se retoma suestudio ahorael aspecto en paleontológico Oxynotum , Densinodulum /2017 y Raricostatum ; sinem 739 ------

Paleoenvironment and Biostratigraphy of Huayacocotla Formation ABSTRACT Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION 740 740 1.1 HUAYACOCOTLA FORMATION 1. Introduction 19) Zongozotla. 9) Temascalapa; 10) Ten-Río/Las Juntas;11)PeñaBlanca; 12)Honey;13)Potrero;14) Chipotla;15)Tv4;16)Ten1; 17)Ten3;18)7; Figure 1 province. Here, the most influential villages are villages influential most the Here, province. Madre Sierra Oriental The sector of ernmost Otomí-TepehuaThe range is located at thesouth Fromthere, theroad toSanBartolo Tutotepec be Alejo, there is aroad leading to Tenango de Doria. after Tulancingo.Alejo is a few kilometers At San Pachuca—Tulancingo toSan turn segment. The dalgo, andthenbyFederal Highway130 inthe Highway 85from Mexico Cityto Pachuca, Hi Pahuatlán. place can be reached This by Federal Tenango deDoria,SanBartolo Tutotepec, and / Outcrops localization: 1) La Fiesta; 2) Bopo 1; 3) Bopo 2; 4) Bopo Centro; 5) Bopo 3; 6) Bopo 4; 7) Bopo 5; 8) Temapá; 8) 5; Bopo 7) 4; Bopo 6) 3; Bopo 5) Centro; Bopo 4) 2; Bopo 3) 1; Bopo 2) Fiesta; La 1) localization: Outcrops Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - /2017 Schmidt-Effing (1984) defined four units around four defined (1984) Schmidt-Effing and and Schlatter (1980) Schmidt-Effing Later, ing 400–500minhisVinasco river type locality. averagand described deposits thick siliciclastic more than 100taxa, including 52newspecies, tent detailed was byErben (1956),who recorded thology, withsilt-sandy variants. faunal con The the region. Likewise, they described the main li based onthe ammonite stratigraphyrassic of Imlay by proposed first Formation, Huayacocotla The tion inthearea (Figure 1). Burckhardt (1930) was the first to apply a biozona and Lenk (1889-1899) and later by Böse (1898). gins.been rangestudied in1889by has This Felix et al. (1948), was referred to the Early Ju - - - - - scribed more ammonite species from the Tenan 2008), andMeister Meister (2000), Blau biostra important researchtigraphic outbycarried was Blau and century, twenty-first the In sandstonesinthickbeds.along withfine-grained shale, lightly slaty andorthogonally fractured, of la Formation sequence mentioning an alternating the Huayacocot complemented the description of On the other hand, Dueñas-García Puebla State. Hidalgo State andnorthof Veracruz State,north of lyingtothe northeast of ded sandy limestone. They are outcropped in the rine sandstone, siltstone, and shale with interbed ma area sequenceof described(Erben,1956)as the Jurassic. HuayacocotlaThe Formation rocks connection throughduring the Mexican territory proto-Atlantic–Pacific marine the discussed they genusand two newammonitespecies, bywhich go formations. Blau Juntas,ing Despí,Las Temascalapa, andTenan the considered Huayacocotla Formation as agroup, contain They lithofacies. different four Tenango deDoria,represented bythe town of al. Arenas-Islas dos-León (2007),Hernández-Velázquez (2007), (2005, 2007),Gayosso-Morales (2007),Grana Esquivel-Macías (2003), Esquivel-Macías with began studies paleoenvironmental first The basin related totheWestern Paleotethys. explained that in a paleo this unit was deposited the Mesozoic faunas, Westermann(1996, 2000b) of domains and kingdoms of classification the on Mexico. eastern However,Early Jurassicof based the mentioned scarcely but region, circum-pacific about the Jurassiccompiled information inthe literature.example An Westermann is (2004) who advanced thanwhatrevealed is in international more is formation this a result,As theknowledge of ological unitsproposed by Schmidt-Effing (1980). the four lith unit bysingle itsorigin, regardless of the Huayacocotla2006), suggested Fm. to be a research (Angeles-Cruz, 2006; Flores-Castro go de Doria area. In addition, the geochemistry (2014).Inthese papers, the sedimentary only et al. (2009), and Esquivel-Macías et al. et al. et al. (2001)describedanew (2002,2005), who de (2000,2001,2003, et al. (1992) et al. et al. Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín et ------, 1.2. LITHOSTRATIGRAPHYREGIONAL AND GEOLOGY cal studies (Aberhan, 1994; AberhanandMuster, last issue,On this there are other paleontologi and Ochoa-Camarillo Cantú-Chapa (1971, 1998), Silva-Pineda (1978), include: Díaz-Lozano leontological papers (1916), 1997b), and Arellano-Gil da-Gaxiola (1980), Suter (1980), Mendoza-Rosales Schmidt-Effing (1978), Basañez-Loyola (1965), Aguayo-Camargo (1977),Pedrazzini and been conducted byErben (1956), Carrillo-Bravo these rockshave Mexico. geological studies of The Lower Jurassicrocksum isthe relativein scarcity of One reason to study the Huayacocotla anticlinori and bioticcomponentsare considered. Mesozoic sequence is possibly covered elsewhere. the Huizachal Formation (Triassic),although this Cahuasas Formation (Middle Jurassic)and overlies 1979), the Huayacocotla Formation underlies the the standard locality (López-Ramos, description of served in SGM1:50000(2004). According to the this region, andtheir geologic contacts canbeob to the Earlyrassic Cenozoic are outcropping in Formationsfrom the interval between EarlyJu clude layers withfossil plants. continental origin, which terrigenous in beds of of marine Sinemurian and Schmidt-Effing (1984), Schlatter and (1980) Schmidt-Effing by scriptions thick. It is also consistent with the de limeters mil bothlithologies are inthe order of layersof with thislithology,thickness although sediment Imlay dy-siltstone. withthe description byagrees This fine-sandstone/san of alternation an of consists mostoutcrops inthe study area of lithology The associated fossils Mexico andits of the Gulf related to the origin of adjacent Middle Jurassic sequences presence of ( the Liassic the proto-Atlantic. importance of The through such connections between the Pacific and several taxa thepassageof pertinent evidence of 1997; Aberhan,1998;Damborenea, 2000) with sensu BloosandPage, 2002)unitsalsoinvolve the et al. et al. (98:svrltosn eeso (1948): several of thousand meters (1993), Ochoa-Camarillo (1997a, et al. et al. (1997b). (1998), while the pa et al. /2017 (1992), Rue 741 741 ------

Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION 742 742 1.3.1. SEQUENCE STRATIGRAPHY 1.3. PALEOENVIRONMENT ANDBASIN EVOLUTION (1975). Figure 2 sas andTepexic (Figure 2and3). lowed by the Middle Jurassic Cahua formations: At the type locality, the Huayacocotla Fm. isfol ersn ag ato the Jurassicand mark a represent alarge part of These formations. regional Jurassic different by cles, unlikethe Huayacocotla Fm., are represented tigraphy, but apparently cy the main sedimentary sequences stra of There are no studies in terms / Regionalgeology 1:50000.Modified (SGM, 2004),onthebasisoflithological principlesofPettijohn from F14-D73 Chart Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - - /2017 that the Huayacocotla Fm. represents the initial inthe area, perhaps highlighting ent formations differ the through documented are phases These theCentralAtlantic. subsequent expansion of (Cantú-Chapa, 1998; Sedlock Mexico of the Gulf ally through the opening of eventu and paleo-Pacific, the to communicated basin anepicontinental opening of sive stages of during the Permian,gaea throughpassing progres thePan an obliteratedby basin of the integration increments, depth starting with general trend of et al. , 1993) and the - - - - principles of Pettijohn (1975). principles ofPettijohn Figure 3 Lithologiccolumn. (UPP.Upper; FM. Formation). Modified(SGM, 2004),onthebasisof from thelithological F14-D73 Chart Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín /2017 743 743

Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION 744 744 tion towards the west. This basin was filled by filled argillaceous sediments containingabundant was sedi basin This west. the towards tion ronment, associatedin subduc basin with adeep (and basins western Tethys and Pacific the between 2000) borenea, hypothesis,paleocorridor (Hispanic communication andfaunal exchange processof rsin ad ersin o ifrn odr of orders different of regressions and gressions fore, the Huayacocotla Fm. canindicate trans lower discordance withcoastal sequences. There andinthe formations discordance basin withdeep upper the in observed is it Also, filling. sediment tions generated by anerosive, eustatic, and rapid aregressive context undercondi a part was of basin. It is well known that the Huayacocotla Fm. in a back-arcnatural unit deposited sedimentary HuayacocotlaThe asa consistent Fm. appears continentalorigin. of red sandstones Huizachal Fm.,whichof consists detailed chronostratigraphy isnotknown inthe Triassicbeds, but its the presence of dication of the reviewed Mesozoic sequence, there is anin of cycles.sedimentary Onthe other hand, at the base second-order relationshipbetween these sets of also presentis inthearea, which would meana Fm. Taraises/Sanctuario the of Neocomian The thethird order.last relationship would beof havenot This do field verification. contacts ferred gian), orthePimienta(Portlandian).Fm. in These (OxfordianFm. age), the Tamán(Kimmerid Fm. manyUpper Jurassic units, such asthe Santiago ally complexallows and discordant contactswith structur is region the on, then verification. From ported and even mappedroughly, withoutdetailed Middle Jurassic) are not clear, although widely re contacts withthe TepexicTheir Fm.(Callovian, tacts that are also due to structural deformations. quence, thenunderlies the Bathonian inother con with the Bajocian Formation inathird-order se Thus, the Huayacocotla Fm. contacts structurally proper arc. the trans-arc basinandtherefore the velopment of the subduction plane would have triggered the de that would prove its expansion towards the west; mentary-exhalative minerals(from blacksmokers) / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín vice versa ) ina back-arc envi sensu Dam ------/2017 1.3.2. FACIES hc rdcdple fsea level changes along which produced pulses of tive tectonic continental separation environment, time, consideringthat it was a very ac just a brief time.during the deposition units represent These ic sealevels both seemstable ( ous, andthusthe predominant relative and eustat tracts the are parasequences andsystems notobvi Within sequencesthat are(as this), notcondensed thePangea collision. of Mexico asthe edge of the tectonic integration of Tuzancoa Fm.,which represents an ancient phase Guacamaya/ the of flysch the with contact in bly situated chronostratigraphically belowand possi also compatibleis with the underlying Triassicsets, magnitude, trend. underagenerally deepening It ftheHuayacocotlasequence. Fm. With respect of onomy demonstrate that Temascalapa is a facies is relevant This since bothgeochemistry andtax lower slopesequence. facies, which to a rhythmical obviouslyconform mid-distal upper fauna as the neritic sandstones of from mid-distal environments containthe same hemi-pelagic sediments withneritic sandstones of cies (Figure 4a)the cyclic accumulation uniform an example,As inthe turbiditic Temascalapa fa recognition asaFormation. its (Angeles-Cruz, 2006) allowsthe assertion of cies withgeochemical and fauna content criteria fa of unification However, the lithofacies. other ammonitesthaninthe thesametaxa of fossilsof sandstonesandshales, withfewer of alternation turbiditic features,has evident froma rhythmic slate-shaleous lithofacies. Temascalapa The unit ly. They alsorecognized Las Juntas for itsfossilifer slate-shales and siltstones respective composed of are Despí and Tenango differences; lithological Despí. Theydescribed the clearly recognizable Juntas,Las units: Temascalapa, Tenango, and four defined (1984) Schmidt-Effing and Schlatter dicated by Esquivel-Macías intense siliciclastic sedimentation rate, already in resents a fewhundred thousand years under an such that a basin suggests it rep stability of The years that theJurassic lasted. the millionsof et al. sensu (2005). Coe et al. , 2003) ------Figure 4 best representatives of such lithology; d) Black siltstone (red ofrepresentatives arrows) suchlithology;d) Blacksiltstone best fromTenandoPiedras facies Negras at outcrop. the one of is It outcrop. Temapá at faciesDespí c) River; Camarones siltstoneat black slaty seen as can be It facies. JunasLas b) village; n etmtro sediment represents approxi one centimeter of sedi structures,mentary from a weak tide cycle where hummocky and flasser both by evidenced set belongs to an intra-arch basin, epicontinental tidal cycles. The ident thin layers asa product of with ev representa neriticplatform, in deposition ure 4d) ( Both the Despí (Figure 4c)andTenango facies(Fig 4b). (Figure (1984) Schmidt-Effing and Schlatter the Camarones River,named LasJuntas andis by and outcrops shales at themouthof cumulation of slower ac acocotla sequence isa consequence of the Huay years. distal facies of more The uniform representpulses imentary fewhundred thousand and itssed coast-oceangradient, of thirdterms in the area, the this faciesis to the other facies of Somedifferent detailsinthefield stopsduring thetrip.a)Temascalapafacies, ascanbeseenalong theroutetoTemascalapa sensu Schlatter and Schmidt-Effing, 1984) and Schlatter Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------1.3.3. TAPHOFACIES ANDSEDIMENTOLOGY In such conditions, the minor sedimentological and scarce nektonic benthicelements. ization of sedimentation rate, were favorable for the fossil conditions,the bottom. These coupled with ahigh water column andreduced oxygen conditions at ductivity inphysical-chemical inthe parameters to high pro sea, with normal ed epicontinental HuayacocotlaThe paleobasin was asemi-restrict evidence. taphofaciesandsedimentology with thehelpof the ly discuss paleoenvironmental basin analysis et al. sedimentation (Esquivel-Macías mately a year of variants or taphofacies characterization assess , 2005).Therefore,now itis pertinent to brief /2017 745 745 - - - - -

Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION 746 746 also usedto calculate their particular function present.and bivalves ammonoids The found were can bepartially umn deduced bythe ammonoids the water col other hand, the characteristics of regimes, anddistancefrom depth, shore. Onthe as: sedimentation rate, environmental energy, tidal such features, sedimentary specific unveil ments noids andammonites. cri the slope, concentrating the fragments of of parts upper and/or margin shelf the of edge the 1 and2;it represents gravitational landslides from Taphofacies 6 origin. different their reflecting orientation, and attrition of degrees different with remains organic trated concen to led has that influence fluvial temporal Taphofacies 3 to 5 tain theirtaxonomic identity. and crowded them even while letting them main valves with moderate drag level, which oriented and bi ammonoids phenomena withremains of Taphofacies 2 that are notincontactwitheach other. large ammonites stones orshaleswithremains of may be sandy lithology silt The neritic platform. Taphofacies 1 the following taphofacies were recognized: paleoenvironmental dynamics. On this basis, of each taphofacies isevidence by the conditionsof bioclastsgenerated of damage pattern phonomic the remains (Figure 5).Inparticular, the ta tion of trendsdepicting related to attrition and preserva for visually diagrams were represented in ternary preservation, anddissolution.Allthese attributes fragmentation,sition, orientation, deformation, shells, epibionts, disarticulation, po as: drilling of correlated them withtaphonomicattributes, such related to distance, ortopography, depth, and taphofacies associated with itsminorvariants of Esquivel-Macías the paleoenvironment. Arenas-Islas(2012) and of tain relevant for modelingthedetails information and abundance indexes. Thus, it is possible to ob ment (habitatswell spectrum),as the diversity as frequencies regarding the environal-morphology / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín : Developed in thesame lithofacies as : Implies normal sedimentation ina : Impliesnormal : Involves high-energy intermittent et al. eonzda h rdc f: Recognized as the product of (2014) allowed the definition ------/2017 1.3.4. FAUNAL ANDFLORAL COMPOSITION the tectonicregime, bothindicate reduced oxygen produced under an islandarc (back-arc basin),and igneous composition, intermediate the protolith of the outcrops. Similarly,of most in common is pH (disoxic).gen conditions disoxic The level andhigh geochemical analyses also indicate reduced oxy theelement’sconcentrations these in behaviorof paleobasin. For example, the virtually identical this designandevolution the contemporary of of events, leobasin anduniquesedimentary interms 2014), indicating a relationship between the pa Castro Flores vided by geochemical data (Angeles-Cruz, 2006; sistent withpaleoenvironmental indications pro areanalysis thetaphonomic con resultsThe of el-Macías (Damborenea, 2000). Onthe other Esquiv hand, interchange across Paleo-corridorthe Hispanic faunistic an bivalves, which of support the theory el-Macías until Esquiv other or echinoderms mollusks of However, at this study area there were no records refined andsomenewspecies were described. nas-Islas 2008; Esquivel-Macías 1984; Meister Schmidt-Effing, and Schlatter 1984; Núñez, and Contreras 1980; 1977, (Schmidt-Effing, butions recognized byErben (1956).Insubsequentcontri well(1930) as as more than100taxa that were later Burckhardt by reported and identified species the outcropsThe to be visited show the occurrence of the onedescribedinFigure 5. to propose ataphonomicallyconsistentmodel, as the outcrops, it is favorable nature and identity of the the shells.putting Bytogether the evidence of pH,which favored the dissolution of high value of ditions.also consistentwiththe anomaly is This here, the reducing environmentalconfirming con the europium’sisotopes found concentrations of to these data, there is a positive anomaly inthe andorigin. In addition their deposition common inall the outcrops,identical pattern which indicate conditions. majorandtrace elements have The an et al. et al. et al. , 2009), those determinations were , 2009),thosedeterminations (2012) reported the first Sinemuri first the reported (2012) et al. et al. (2005) reported pseudoplanktonic , 2002,2005;Blau , 2008;Esquivel-Macías et al. , 2005, 2012; Are et al. , 2003, et al. ------, edge neritic platforminhabitant; e)Theexistenceof anislands arcisproposed onthebasis of thegeochemicalanalysis;f-j) Environs developed in the watercolumn; b)Transport of theremainstowardszone of Deposit; deposit; d)Presenceof c) Figure 5 l) Schemeof thetaphofaciesto their taphonomic gradientwith respect place. the deposit attributes at assigned tothetaphofacies (Tf) interpreted with ternary taphograms; k) Terrigenous duetothe possiblepresenceofariver; deposits Taphonomic patterns. Theenvironment corresponds toadistal neritic were platform: organisms a)Theammonites whose life Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín /2017 Phylloceras asan 747 747

Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION 748 748 1.3.5. PALEOECOLOGY ANDBENTHICFAUNA nated by ammonoids, accompaniedby someclams domi largely are fauna and flora the both Thus, tifiable palynomorphs. ground,ing from spores, firm and various uniden from theserocksshow vegetable remains originat from the Temapá outcrop. remaining The biota as wellisocrinids as microgastropods (Figure 6a) zone paleoenvironment. basinwasinhabited This mid-proximal/neritic a represent outcrops rian respective taphonomic associations, most Sinemu In summary, according to their fossilsand their facies (Esquivel-Macías variantsphonomic whichcharacterize thetapho waveaddition, there action.In are alsoother ta er distances, with previousfragmentations due to representing stronger energetic events from larg were originated at the subtidal level. Also they are nied byand faunalelements crinoids when they ed, taxonomically unrecognizable, but accompa these remains canbe found much more fragment trawling levels events.ergy and intermittent Even accumulation, representing moderate en of gree dominated by the with some de same ammonoids other remains. Also, there are often associations Sometimes there are alsoabundantand clams surfaces, which as are interpreted their relative shells lie down parallel to the bedding the outcrops, complete Ortechioceratidae and of In the shaly andsandy siltstonespresent at most 2014; Arenas-Islas features (Esquivel-Macías and bivalves is obtained from their taphonomic ammonoids the for situ in dragging/depositing of On the other hand, the criterion for the recognition 1994; Landman data (Aberhan, of thiskind abundant source of molluskshellsisan of tations. morphology The whichstructures theorganic adap as interprets analysis, the morphofunctional is cal conclusions the premises that enable paleoecologi One of Jurassic, asseenbelow. paleoecological models publishedfor theLower with the agree serpulids taphonomic evidence of and scarce(Figure crinoids 6b), andtherefore, the / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín et al. et al. , 1996). , 2009). et al. et al. , 2014). , 2005,2007,2012, in situ deposits. ------/2017 from Despífacies. assemblages: a) Microgastropodfrom Despífacies; b)Crinoid Figure 6 reported that the fossilization occurred in suboxic geles-Cruz (2006) andFlores-Castro the bottom waters, An the nature of Concerning monoids andclamsinthesamples. am the abundant by as shown feeders, filter by 2006). Therefore, these waters were dominated shown (trace and major elements) (Angeles-Cruz, nutrientsductivity, according to the amount of infer that the water pro had highprimary masses Regarding conditions, the oceanographic we can sedimentation rates. anunstable nature with high siliciclastic were of as well as shallow infaunal habits. sediments The by with nektonic,benthonic-epifaunal, organisms Benthicmicrofauna arevery commonintheammonoids et al. (2008) - - - habits, found insubtidal neritic proximal hard (epibyssate bivalve with probably suspensivorous water that had high organic content), lowsandy bottoms withsuspensivorous habits in oroushabits), coastal environments andhadpassive suspensiv ated either suboxic distal environment and disoxic habits), reclinedwith suspensivorous in softsand passive microphagous habits), biofilm shallow benthic mobile with of sediments, inhabitant filtering passive Among these, there are: structure tothisfossil association. ter-feeders and predators which give the particular fil the especially value, paleoenvironmental with ammonoids andbivalves with the biodiversity of guilds (Bambach, 1983)are represented along Formation, all the “bambachian” ecological mega Considering the in the organisms Huayacocotla pyritization. anoxic facies andlow-energywith high conditions distal/deeper a involvehere slate-shales The ties. to euxinic conditions, even disoxic at some locali clam the 0.95 inducedby the particular abundance of total value was 0.87,witha dominance value of and bivalves: ammonoids the calculated species of (Figure 1) to demonstrate the diversity with25 WilsonThe used inthe Chipotla ID was outcrop outcrops are collectively considered. when LAFIESTA, TEMAPA, PEÑABLANCA themappear together tive suspensivorous).All of herbivorous) (upper infaunal ac andserpulids tionally, there are gastropods active (epifaunal Phylloceras eratids (possibly carnivorousor herbivorous) and byobjects carried organic rivers), multiple echioc floating to attached organisms (pseudoplanktonic carnivorous crinoids isocrinids neritic epifaunal), Brachyura? crustacean water),unidentified (active suspensivorousin oxygenated and slightlyunclear organic matter), of found insoftsandy bottoms with a high content bottoms), Neocrassina Gervillaria Posidonotis semiplicata sp. (active nektonic carnivore). Addi Neocrassina Weyla alata sp. sp. and Protocardia sp. (infaunal and not byssate, (naiato theshal (inhabitant of Bakevellia Nuculana (epifaunal, byssate, (epifaunal, sp. (infaunal shallow, sp. (theytoler sp. (infaunal Gervillela sp. Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------moderate drag, but they postmortem also suggest and concordant withbeddingplanes, indicating of specimens which12.7 mm, meant abioclastselection.Allthe cies. Inlayer 5 and7,the size structurearound was site representing thesandymatrix shallow in fa was moderate, sincethey lived onthe deposition ulated and their sizes sothe drag were uniform; Gervillela centimeter order withcomplete shells. Here, of a wavyments in sandy matrix, andother intervals instance, inlayer 6, there were millimetric frag its size structure (Esquivel-Macías the Huayacocotla Fm., wasanalyzed to determine outcrop, This whichconsidered is representative of Muddy Sand Community Fm. are nektonic ammonoids(McKerrow, 1978). the Huayacocotla thedominant faunain rest of bambachianguilds, althoughthe of hereterms in a faunal structure very similar to those described monite, crinoids, and pectinids, serpulids, building deroceras Silty Clay Community pared asfollows: and 66“muddy(McKerrow, sand” 1978) are com for the Jurassic communitiesclay” type 65 “silty disoxicbottoms,and euxinic theinterpretations Considering that the fauna was retained at the shallow facies. a of representatives are which of all Brachyura?, Protocardia bledownense riched with only complexat thanthose layers5 and7,which have et al. requirements, (Esquivel-Macíasinterpreted itis environmental different represent which outcrop, this the25taxa of layerAs 6contained19outof aspara-autochthonous.these are interpreted is large and very smallunselected clams appear; outcrop, this shell size theammonoid layerIn 3 of lated valves among the forty tychus givendisaggregation, absence of theconsistent 02 stepouto acommunity more , 2012)asthe product of P. rothpletzi . The same is indicated sameis . The bythe twenty articu as demersal/epibenthonic functional am functional demersal/epibenthonic as and sp., , P. rothpletzi Gleviceras Neocrassina Paltechioceras rothpletzi . On the other hand, layer 6 is en Neocrassina from Early Jurassicshows cf. had functional epibenthic hadfunctional epibenthic , shells could stillbeartic shells chofatti Weyla sp., Neocrassina sp., , Gervillela Paltechioceras /2017 et al. were complete Nuculana , 2012).For sp. valves. sp., and

sp., hard 749 749 Eo ap ------

Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION 750 750 1.4. BIOSTRATIGRAPHY1.4. ANDCHRONOSTRATIGRAPHY tonic elements explainingpara-autoch thehigh oxygenated along with many neritic platform nek from particularcomes faunalmix The the well ammonoids. versity of accumulation taphonomic a great is di product of butand serpulids, in Huayacocotla Fm., the main and nektoniccephalopods, isocrinids, pectinids, the Earlyto theLate Sinemurian (Figure 3).This HuayacocotlaThe covers Fm. an age range from tized fossils. shales, andmay containpyritized and calcopyri ence. sedimentsproduce These dark to black gray influ hydrothermal exhalative even and activity, matterganic concentration, anaerobic bacterial sulphidesderived from or high concentrations of or completely anoxic (euxinic) environments with oxygen with evenbasins lower concentrations of (Aberhan and Pálfy, 1996).There are also suboxic bivalves,and some such as is restricted to somerhynchonellid brachiopods ygen marine sediments. Thus, indisaerobic(Ox basins level, based onchemicalof andbioticconditions oxygenation their by defined are and studied ly hypoxic havebasins epicontinental been thorough According to Landman outcrop. Chipotla the of layer 6 in as sediment final the in several facies toms.explains the presence This of cumulation from to disoxic neritic platforms bot sediments thatgravitationally slip after their ac rivers, producing the accumulation of presence of environmentalsuggests that conditions require the than 482m(Westermann,deeper 1996).Allthis that an empty shell found collapsed was deposited ceras water shell collapse limit for column. The fromwith the dead nektonic shellsdeposited the curred over still living benthicassociations mixed with articulated that clams suggests the burial oc bioclasts thony; also, of the random arrangement / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín was calculated was whichto be482m, indicates circa [0.3 and 1.0 ml/l]), the benthic fauna benthic the ml/l]), 1.0 and [0.3 et al. Posidonotis (1996), the Jurassic and Phyllo Bositra ------/2017

show this pattern through show de this pattern biostratigraphical the HuayacocotlaFurthermore, Fm. the data of the“developed” sequence tradicts the qualityof zone isrevealed, that apparently a pattern con taxonomic elements from the absence of ic ranges basedonEuropean zonation, a persistent contrasting the faunallistswithchronostratigraph reported changes in thebiozones. However, by rapid than the geological ones, asindicated by the tion rate. Therefore, the faunal changes were more Craig sense of a non-condensed sequence (“developed” in the environmental stability.condition produced This ing that occurred in a framework deposition of is arelatively shortgeological interval consider ing, 1984). (Schmidt-Effing, 1980; Schlatter and Schmidt-Eff formations different were they that proposal the taphofacies withinthe same paleobasin,despite observed were as mere lithofacies and interpreted arguments that suggest thelithological variations of convergences these All profile. compositional les-Cruz 2006; Flores-Castro geochemical2009). The data (Angeles-Cruz, 2007; Granados-León, 2007;Arenas-Islas Hernández-Velázquez, 2007; Gayosso-Morales, 2008; Esquivel-Macías 1984; Meister ammonoidfaunas(Contreras andNúñez, ence of the outcrops considered by the pres in each of zones throughout the region, which are evident the rent presence of Suchwith therecurconsistent is an assessment (Figure 7). pattern” willbenamed“interrupted pattern This Sinemurian. ence to the upper and top uppermost lowing outcrops descriptionsare inobviousrefer Sinemurian taxonomic elements listed in the fol Lower presence contradictory of seemingly The ferent researchs which supportthe 17outcropsproduced bymany dif of scriptions et al. , 2007) also show a uniform protolith, 2007)alsoshow auniform et al. et al. , 2002,2005;Blau , 1993)withhighsedimenta et al. Oxynotum et al. , 2006,2008;Ange , 2005, 2012, 2014; and Obtusum et al. Raricostatum Obtusum , 2003, et al. gap. ------,

Figure 7 Biozonation ranges (Europe standard zonation). Modified fromPálfy Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín et al. (1994). /2017 751 751

Paleoenvironment and Biostratigraphy of Huayacocotla Formation INTRODUCTION Paleoenvironment and Biostratigraphy of Huayacocotla Formation FIELD STOPS 752 752 2.1.2. STOP 2LACRUZ DETENANGO 2.1.1. STOP 1CALDERA OFTULANCINGO 2.1. DAY 1 2. Fieldstops may occasionallyoccur. Also,blocking landslides the wayto these outcrops outcropsin the region.common is for quarrying these someof the local situation, since the use of localities to be visited mayThe varyaccording to pine-oak forest, tentatively mapped as the Pachu saltic spill, already very eroded and covered by ba and tuff consolidated Tertiary Upper an on curves uptheslope road proceeds withaseriesof cones that ejected red pumice (“Tezontle”). The cineritic left behind. To the East there is aset of the pleistocene alluvial debris is After Metepec, curves at sharp thehighway. duce aseriesof Tulancingo, which pro the Caldera of activity of the post-explosive (Figure 8a), the last remains of the city liesthe dacitic domes and southwest of thesematerials. Tomassive thewest extrusion of shows pulses of this quarry section of ed. The are pumicestones extract where large volumesof go, under industrial exploitation there is a quarry Federal roads. Onthe main road acrossTulancin in various sitesalong the Pachuca - Tulancingo solidated tuffs with obsidian remains, is easily seen and con daciticashes jas Range, whicha setof is structures (Figure 3). To the northwest, the Nava dera, which issurrounded by remarkable igneous Tulancingo valleylocatedis a volcanicinside cal any material considered importantfor research. scales. survey The leader the right has to request butor geological and metric notGPS technology and cameras will be possible, hammers the use of will beproperly tion purposes treated. Therefore, be collected. Sampling for academic collabora may when somematerial for purposes personal However, the surveyleader will give indications It is recommended to avoid collecting material. / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------/2017 2.1.3. STOP 3ELMIRADOR/ESTRIBO 2.1.4. STOP 4TERTIARY/JURASSIC CONTACT San Bartolo Tutotepec village and the Pantepec onymousvillage. view from The here includes the Tenango de Doria gorge lies the hom bottom of the la states (Figure 8b). To the left (northwest) of right on the border between HidalgoandPueb viewfrom Stop 3, situated There are two of angles area canbeseen. “traps” and consolidated tuffs in the “El Mirador” the vegetation. transition towards The the basaltic de Doriacanyonsbegins, withnotable changes in land summits, Tenango the descent into the deep recognized in someplaces. After the dense wood ca volcanicgroup. Poorlykaolinized be can ashes siltstones. the Jurassic has been derived from the erosion of soil sell and verytypical fabrics fertile agricultural etation have changed dramatically. Localstores and Lower Jurassic looms. climate The and veg towardsthe southwest between the basaltictraps Jurassic-Tertiaryseen. The ibo is clear contact is Mirador/Estr the from view inverse the church, original colonial layout and its eighteenth-century On the road, justafter Tenango village, withits Huayacocotla Fm.outcrops to visit. lán Valley canbeseen,whichadditional contains gorge, thedeep thePahuat ibo,”to theright of between Puebla andHidalgo states. Inthe “Estr Tulancingo activity,Caldera of the ridges forming originated type) fall” (“ash sands tuffaceous the by the village, there are eroded of the high terrains the Tertiary–Jurassic boundary. To the West, in shales. Tenangobuilt was on Jurassichills, near the Lower Jurassic andMiddle Jurassicsilty sands the Pimienta whichFm., lie on careous rocksof Jurassic hillsandthe folded Upper Jurassic cal the Tertiary volcanics with the small Lower tact of 2004). From thisangle, one can observe the con lán geologic map F14 D73(1:50000 scale) (SGM, Jurassicunits canbe seen, asshown inthe Pahuat relationshipbetween Lower, MiddleandUpper the of view magnificent a days, sunny River.On ------2.1.5. STOP 5LA FIESTA (20°20’54.3”N;98°15’05.9”W) Jurassic/Pleistocene contact. Figure 8 paleontological value, andthe outcropon ahill is outcropmaterial were despite their quarry usedas road toElDesdavícommunity. rocks The at this Tenango deDoriavillage, Hidalgo,the access on LA FIESTA outcropis located 3.5 kmfrom the Sowerby,in aretheybut reported, also are 1816] Metophioceras Arnioceras However, horizons. licence/rothpletzi and favrei subzone (Meister subzones, and probably centered in in the gion by Erben (1956), indicate an age range with 1956). Many species, already reported in thisre per incaguasiense (Trueman and Williams, 1925), burckhardti downense (Hauer, 1856), proved by the presence of: outcrop This from the Late Sinemurian age, as trix (Arenas-Islas ma a silty in sandstones fine very of stratification 30-meter-thick sectionwithmillimetric laminated cantly altered bylogging. outcrop The presents a signifi forests semi-deciduous tropical with side Twogeologicalstructuresexhibiting thestratigraphicrelationsexpressed intheregionalcolumn: a)Daciticdomes;b) (Erben,1956), Raricostatum (Crickmay, 1929-1930),

(Erben,1956), ceratitoides (Hillebrandt, 2002), sp. (Spath, 1923) [ P. rothpletzi et al. et al. zone, Plesechioceras cihuacoatlae ( sensu , 2009)(Figure 9). , 2005, figure 3) within the within 3) figure 2005, , Hillebrandt, 1981) and aplanatum (Böse, 1898), Paltechioceras tardecrescens Ortechioceras jamesdanae Ammonites Ortechioceras pau Paltechioceras to Ortechioceras densinodulum raricostatum

coneybeary P. harble (Erben, cf. gr. gr. Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------

2.1.6. STOP 6PIEDRASNEGRAS from Huayacocotla. siltstones Figure 9 so it might correspond to the Middle Sinemurian graphically,aboveJUNTAS,is TEN-RÍO/LAS it Topographically, but not necessarilybiostrati Huayacocotla Fm., it has not produced fossils. the cial) contact with the fossiliferous siltstonesof itstransitional (fa Sinemurian inage because of outcropshaly Although this considered is tobe et al to the Hettangian and Lower Sinemurian (Meister theyconsistent since were often referred tobelong Some characteristic sedimentary structures Somecharacteristic onsandy ., 2005)(Figure 7). /2017 753 753 - -

Paleoenvironment and Biostratigraphy of Huayacocotla Formation FIELD STOPS Paleoenvironment and Biostratigraphy of Huayacocotla Formation FIELD STOPS 754 754 2.1.7. STOP 7ELBOPOOUTCROP SERIES meters before village(Figuremeters 4d). PiedrasNegras TAS. rocks These are cut by the Despí creek, a few Sinemurian (LS)outcrops atTEN-RÍO/LAS JUN rian (US) outcrops at LA FIESTA andLower (MS), located between the several Upper Sinemu This outcropThis is Late Sinemurian, belonging to (20°21’30.3”; N 98°12’42.6”W). BOPO Centro BOPO3(Figure 7). part of zone and the the top of bledownense chioceras reported fauna includes: 1-meter high. The so-Morales (2007), the outcrop is 3-meter wide and ure 1c)withthenumber 2.According toGayos Meister by identified was outcrop W). N; 98°13’15.9” BOPO 2(20°21’52.4” siltstone, approximately uniform. sandy has a 10-meter front and similar height of chronostratigraphically correct (Figure site 7).The the BOPO series, which couldalsobe the rest of current lowercompared position to topographic the BOPO series, given its the outcrops of rest of the bly top of referred tobelong totheLate Sinemurian, possi taxodontid clams.such Basedon evidence, itwas the old collection (Meister 1984). Thereonly is nally called TEN 2 (Schlatter and Schmidt-Effing, exhausted1 is a seemingly outcrop. It was origi W). N;98°13’15.9” BOPO 1(20°21’43.3” with theTV/s-seriesoutcrops. (1984), Schimdt-Effing and Schlatter and (1980), The route to the Bopo is shown by Schmidt-Effing Bopo 3and4are regarded as the most interesting. are several outcrops nearby which canbe visited; tate to the access fossilmaterial, although there an intenseerosionprocess which doesnotfacili Huayacocotlasection isunder anticlinorium. This tectonicblockthat produced was a normal bythe Bopo outcropThe along the slope of series occurs / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín aff. favrei (Crickmay,referred 1929-1930). Itis to mexicanum Obtusum horizon, consistentwiththe upper Raricostatum Phylloceras (Erben, 1956) and . This isconsistentwiththe . This zone, et al. sp.from surviving , 2005)andpaleo raricostatum et al. (2005, fig (2005, P. hard BOPO sub Palte This This ------/2017 Sinemurian, proven by the presence of: tion as compared to the previous ones. It is Upper outcrop seemsto have resolu better stratigraphic W). N; 98°12’54.7” BOPO 3(20°21’48.2” two meters. ness of eri aplanatum the region, focusing exclusively on Sinemurian of chronostratigraphicThe interval is the uppermost collections inthe region by authors. the former cens Gleviceras dicated bythe presence of: the 2002); meanwhile, the lower part corresponds, at Meister by (called 4 T/V 7, TEN 3, TEN part with BOPOcorresponds 4 and the TEN 1, bly, the 2005 sampling was insufficient. The upper between the middle part and the new top. Possi last criterion adopted is because there are gaps tulated by Meister (2) the top part is much more extensive than pos the outcropparts in (low, middleandupper), or implies two possibilities: (1) This there are three crassicostatum donelli the aff. Gayosso-Morales (2007) reports the presence of the outcrop (Figure 11a). However,lower part of as belonging to an upper part and a interpreted bohemi subzone, focused on tends its range to the and the following taxa: subzoneto echioceras andlymense horizons, with the in the range of et al. the region byErben (1956).According toMeister danae noticeras P icaum . / burckhardti recticostatum (Hauer, 1856),which comefrom more recent mexicanum Raricostatum Raricostatum (2005), this assemblage provides for a location O oto these were previouslyreported in . Mostof (Erben, 1956) (Figure 10a), and /cf. . aff. jamesdanae sp.1913-1919), and (Buckman, subzone, from aplanatum intermedium soemani tothe , and Gleviceras horizons(Figure a thick 7).Ithas zone, withinthe zone (Meister (Figure faunaalsoex 10b). The (Dumortier, 1867), and P O aureolum . et al. Raricostatum . aff. subzones, from hardbledownense Raricostatum horizons, which have been sp.,1918), (Buckman, raricostatum (2005). Accordingly, the soemani aureolum horizons (Figure 7). A. floresi A. et al. zone, (Dumortier, 1867) P zone, / / raricostatum . crassicostatum tardecrecens which indicate (Erben,1956), hardbledownense , 2005), as in raricostatum densinodulum P raricostatum P. tardecre . aff. O. james , / This This et al. Oxy mac mex oost to / P ------, . ,

2.1.8. STOP 8TEMAPÁ(20°22’04.1”N;98°13’10.9”W) mexicanum data, based onthe presence of described underthe it issamecriteria 5, thus and T/V and 6 T/V to close quite located is outcrop W). N; 98°12’53.1” BOPO 5(20°21’25.9” tatus sp.assignable is tothe des ure 10c), BOPO 4 blockwith “b” of so-Morales, 2007)(Figure 7). Meanwhile, the part aplanatum costatum dicates a Late Sinemurian age, precisely in mexicanum jamesdanae block Bopo 4blockhas: This “a”. into two blocks duetoanechelon fault above the BOPO 4 belongstoLate Sinemurian, divided W). N; 98°13’02.1” BOPO 4(20°21’45.6” TEN 3,and7. least partially, with T/V 4, T/V 5, T/V 6, TEN 1, (Metophioceras), 10d), presence of beds areThe Late Sinemurian in age, given the pseudoplanktonic echinoderms. plates of tafofaciesbear bedstiny 1,2,and 3.The columnar of alternation an shows It 1980). Schmidt-Effing, al. wavystructures sedimentary (Esquivel-Macías the US (Arenas-Islas of siltstones sandy laminated fine very of outcrop high, withbeds tilted at about 30°. It is atypical et al. outcrop This wasdiscovered by Esquivel-Macías 2005; Gayosso-Morales, 2007)(Figure 7). aplanatum doubt, including the should be in the clive siense , 2005),corresponding( tothe Despí Fm. (Quenstaedt) (Rosenberg, indicate 1909). These the place subzone, asreported by Meister (2005). It is 30 meters wide and 26 meters wide and26meters 30 meters (2005).It is (Hillebrandt, 2002),and O zone, upper . cf. subzones (Blau horizons (Meister Angulaticeras , , , O O O. jamesdanae . aff. . . incaguasiense P pauper . aff. . sensu soemani Phylloceras Raricostatum , and mexicanum raricostatum sp., Prinz (1895), and et al. densinodulum Obtusum , , (Dumortier, 1867), et al. Partsicheras P. burckhardti Coroniceras O. pauper, , 2009) with flasser and flasser with 2009) , sp. (Figure 10e), P. hardbledownense , 2003;Meister et al. , zone without any Proclivioceras subzone, zone and the P. tardecrecens P . , rothpletzi , 2005; Gayos P. tardecrecens raricostatum

sp., aff. ? O et al. . This set in . This . cf. A. ceratitoi macdonelli Phylloceras (2005). conybeary aff. (Figure incagua , P P (Fig et al. Rari and deno This This sensu . aff. . . aff. Sul , pro Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín O et ------, . ,

98°13’40” W) 2.2.2. STOP 2TEN-RÍO/LASJUNTAS (20°21’54.09”N; W) 2.2.1. STOP 1TEMASCALAPA (20°22’06.3” N; 98°12’52.1” 2.2. DAY 2 and PEÑABLANCA,BOPO45. TEN 1, TEN 3, TEN 7, LAFIESTA, POTRERO taxonomiccommon 6 T/V 4, T/V elements with the LA FIESTA outcrop. Here, there are many sentative; therebyit correlates almostexactly with subzone, the found inthisoutcrop (Figure 7). Inthe the proper index of prove its location in subzone denotatus. However, Phylloceras the the presence of range centered in the al. Esquivel-Macías in reported 1883], Quenstedt, ciferites tom where pyrites often originate, which meansit et al. al. ered a Huayacocotla Fm. facies(Esquivel-Macías Schmidt-Effing, Currently, 1984). they consid are deformed and slaty, belong to LasJuntas look (Schlatter Fm. and which stratification, subtle with the Pantepec River begins. fossiliferous The shales Pantepec andCamaronesRiver mouths, where outcrop This isonthe pond produced by Despí, this faciesasbelongingtotheHuayacocotla Fm. about anythe leaders fossils useful indocumenting Therefore, the attendees to inform will beasked this. confirm may which fossils, find to order in atids were found here. outcrop The willbe visited recentlyonly It is that poorlypreserved echiocer posited at moderate (Angeles-Cruz, 2006). depths theHuayacocotlade Fm. just aslopefaciesof is although nowthere geochemical is evidence that it (1984) regarded it as the Temascalapa Formation, the decimeter order. Schlatter and Schmidt-Effing of sandstone siltstone/quartzitic sandy of quence At TEMASCALAPA, there isarhythmicse (2005), and , 2014) especially taphofacies 1 (Esquivel-Macías , 2005, 2014). This represents , 2005,2014).This ananoxicbot cf. sp. (Meister stenorhynchus rothpletzi O . jamesdanae Obtusum Obtusum (Lange, 1951),[ horizonreprethe most is et al. Raricostatum , 2005),which serves to zone, sinceit includes . This set a comprises . This intervalnot been has /2017 zone, despite Angulaticeras raricostatum 755 755 et et ------

Paleoenvironment and Biostratigraphy of Huayacocotla Formation FIELD STOPS Paleoenvironment and Biostratigraphy of Huayacocotla Formation FIELD STOPS 756 756 Figure 10 Bopo outcrops;d) jamesdanae / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Examples of the fauna of Huayacocotla: a) Huayacocotla: faunaof the Examplesof (Trueman and Williams, 1925) from Peña Blanca outcrop; c) c) outcrop; Blanca Peña from 1925) (TruemanWilliams, and Paltechioceras

rothpletzi (Böse, 1898)from Chipotla outcrop;e) Paltechioceras /2017 aff. mexicaum Paltechioceras (Erben, 1956) from Temapá outcrop; b) outcrop; Temapá from (Erben,1956) Phylloceras

hardbledownense sp.(Suess,1866) from La Fiestaoutcrop. (Crickmay, 1929-1930) from 1929-1930) (Crickmay, Ortechioceras

change; b)Lower Jurassic rocksin PeñaBlancaoutcrop,averyproductiveoutcropfrom theUpper Sinemurian intheTenango deDoria Figure 11 the very fine sandstone-siltstone layers.the veryfinesandstone-siltstone Potrero outcrop,/ SanBartololocality; c) Despí facies. Thisfacies showsasubtle sedimentary condensation duetoanalternation of and includingthe lower the Lower Sinemurian centered in Meister et al. (Guérin-Franiatte, 1966)were reported byMeister iceras Metophioceras molineroi Metophioceras (Sowerby, 1816), (Erben, 1956). cotla Fm. the Huayaco wereof described ascomponents and 1981), (Figure 12a), dominant presence of: Early Sinemurian age (LS), given the fauna of is the only sampledoutcropThis which hasthe theHuayacocotla Fm. is themostdistalfaciesof Someoutcropstobeseeninthe trip:a)Bopo 3upper partand alower part.Thedashed red linemarkstheinterpreted fauna (2002, 2005). The biostratigraphy (2002, 2005). The reported by sp.1923), and (Fucini, Juraphyllites nardii Arnioceras miserabile Arnioceras et al. (?) (2005)indicates anage range within Arnioceras ceratitoides Arnioceras anaberthae Calliphylloceras (Meister (Meneghini, 1853), which Arnioceras (Quenstedt, 1883-1885), Obtusum (Meister Metophioceras conybeari et al. Arnioceras sp. (Spath, 1927), sp. (Hyatt, 1867) zone (Figure 7), , 2005), (Hillebrandt, Bucklandi et al aff. ., 2002), Partsch zone oppeli Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - -

tion artifact. This outcroption artifact. This elements hascommon Sinemurian, distribu generating ageographical theLower Sinemurian extending totheUpper of phenomenon which involves taxonomic elements is calling the attention to a possible homotaxial or because this genus an accurate determination the material did not allow because the quality of level,ally correspond tothisstratigraphic either a reasonable doubt if exceed the the faunistic set does not weighttratigraphic of zone.considered that authors These the chronos yond the Upper Sinemurian till the et al. whichthe upperlimitrecognizedis byMeister tophioceras BOPO 4, as with TEMAPA, LAFIESTA, POTRERO and (2005), although , Coroniceras obtusum Plesechioceras subzone.a result, As there is , and Partschiceras Partschiceras , Phyloceras Arnioceras sp. extends be /2017 may not actu .

ceratitoides Raricostatum , 757 757 Me - - - - -

Paleoenvironment and Biostratigraphy of Huayacocotla Formation FIELD STOPS Paleoenvironment and Biostratigraphy of Huayacocotla Formation FIELD STOPS 758 758 2.3.1. STOP 1HONEY (20°15¨34.40”N;98°11¨31.19”W) 2.3. DAY 3 2.2.3. STOP 3PEÑABLANCA(20°23’54.4”N;98°14’56”W) 12b), P. rothpletzi stones, according to the presence of: belonging totheUS, withsandylaminated silt PEÑA BLANCA isa typical outcrop (Figure 11b) an invalid in the study zone. determination Thus, ( the supposedpresenceis of solvedrepositories. the authors main query The cause theycoordinates,do notspecify or maps Contreras and Núñez(1984), be observations of the Sinemurian inthisregion, based onthe of zoning There are doubts about some the formal provenance.unclear stratigraphical the lastthree taxa of Erben (1956), (Figure 7). Besides, inthe report of the same authors according to of the conclusions gion. However, themaredoubt stillin manyof abjectum Arnioceras Paltechioceras bosei per 1907; Oxynoticeras of Contreras andNúñez(1984)reported the presence 2007; Hernández-Velázquez, 2007). Meister Upper Sinemurian (Esquivel-Macías TEMAPA, which are also centered around the TEN 2,3,LAFIESTA, CHIPOTLA, and TEN1, 6, T/V 5, T/V with taxa common shows outcrop(25 m). The thickness of few meters clear,is mity withthe Despí Fm. but fora only obviouscontinuityThe andlithological unifor have beenvery narrow (Figure 7). although the vertical distribution of ure 3), withthe bythe tum arespecies focusedthe in / Aegyloticeras Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ), Aegyloticeras to Gleviceras O. pauper Paltechioceras bavaricum raricostatum densinodulum et al. , sp., ), a fact that Erben as (1956) dismissed P. mexicanum sp., , 2005, figure 2; Granados-León, 2; figure 2005, , sp. ( , and favrei aff. G. chofatti , and subzone (Meister P. rothpletzi subzones, probably dominated sensu and Phylloceras vinascoi Arnioceras Vermiceras vinascoi

Geyeria , Raricostatum licence ( O. incaguasiense

, pauper , Eparietites Oxynoticeras Arnioceras monjeslopezi Arnioceras Arnioceras s.Mn fthese sp. Manyof and / ), rothpletzi ( Geyeria serorugata Ortechioceras pau et al. Vermiceras P. tardecrescens zone, ), Pompeckj, and et al. aff. P. rothpletzi , 2005, fig in thisre horizons, (Figure , 2005; aplana Geyeria Victori have ------/2017 , , , ,

2.3.2. STOP 2POTRERO (20°16’40.9”N;98°10’21.3”W) 2.3.3. STOP 3CHIPOTLA (20°16´21.6”N;98°09´23.6”W) index species: It belongs to the Late Sinemurian age, given the sandysiltstone (Hernández-Velázquez, 2007). fine very of accumulation regular the by erated siltysandstone, gen produced decimeter strata of horizontally (Figure sedimentation 11c). The has Potrero showsa 5-meter section, whose layerslie beds (Contreras andNúñez,1984). lie in direct contact with the Upper Triassicred because the Upper Sinemurian ammonoidbeds characteristicand also ammonoids the absence of Lower Sinemuriannot settled, indicated was as by study the that,it will be accepted in the area of 2; Granados-León, 2007;Hernández-Velázquez, T/V 4, TEN 3, TEN 7 (Meister BLANCA, TEMAPA,FIESTA,LA POTRERO, thisregion arewith HONEY, common of PEÑA taxonomicalSchmidt-Effing, elements The 1980). ( Fm. Despí the with consistent is meters five licence (Meister subzone due to the narrow range of outcropprobably is focused onthe raricostatum the 12d) and zone, despite the presence of downense cording to the presence of Rocksat this outcrop have doubtless US age, ac 2005, figure 2). (see map in Blau 4 BOPO and 4, JUNTAS,T/V TEN-RÍO/LAS ESTA, CHIPOTLA, HONEY, TEN1,3, ments withTEMAPA, PEÑABLANCA,LAFI outcropThis presents taxonomiccommon ele theLate Sinemurian (Figure 7). the upper part of and the with 3), figure 2005, al., et (Meister zone tum age, the them are assigned to the Late Sinemurian All of coatlae subzones, probably raricostatum centered sub Obtusum licence hrzn.Teltooia otniyo its horizons. lithological continuity The of (Figure 12c),and , which assign a range in the Raricostatum et al. / Phylloceras rothpletzi and , 2005, figure 3), within 3), figure 2005, , P. rothpletzi Oxynotum et al. horizons,they thus belong to sp. that would be related to zone, , 2003; Meister Arnioceras , P. harbledownense zones. Thereafter, the P. rothpletzi densinodulum G. chofatti sp. (Hyatt, 1867). et al. , 2005, figure and et al. Raricostatum to P. rothpletzi favrei , (Figure P. harble P. cihua , 2002, aplana and favrei sensu ------

outcrop. outcrop; c) Figure 12 a) Plesechioceras cihuacoatlae Arnioceras sp. (Hyatt, 1867) from Las Juntas outcrop; b) outcrop; Juntas Las from 1867) (Hyatt, sp. (Erben, 1956)fromBopo3outcrop;d) Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Ortechioceras incaguasiense Gleviceras chofatti (Buckman,1913-1919)from Potrero (Hillebrandt, 2002) from La Fiesta Lafrom (Hillebrandt,2002) /2017 759 759

Paleoenvironment and Biostratigraphy of Huayacocotla Formation FIELD STOPS COMPLEMENTARY OUTCROPS (NOT Paleoenvironment and Biostratigraphy of Huayacocotla Formation VISITED) 760 760 3.2. TEN1(20°21’13.1”N;98°13’17.3”W) 3.1. T/V4(20°19’56”N;98°11’46.9”W) 3. Complementary outcrops (notvisited) confirm the existence of the “Interrupted Pat the“Interrupted of existence the confirm them knowledge.stratigraphical Atpresent, all of series completes the HuayacocotlaThis bio Fm. 2007) (Figure 7). the complete Sinemurian. Other taxa in the same occupation of zone.results a falseimage of in This (2001) considerthat itreaches till the ported from the same two zones, but Blau the Euerbenites bravoi casewith The re Vietnam. ported from the Lower Sinemurian of first was it since controversial is assignation the aff. Prinz (1895), in the Arnioceras of the presence reported (1977) Schmidt-Effing (Figure 7). pearance of (Meister from the (Meister goense zone and from theupper the other hand,thisoutcrop includescomponents the upper byMeister also (2001), in the Upper Sinemurian beds. There is Blau by 4 T/V on report the with troversy Vietnam in con for the Lower Sinemurian of tocentrites does not have any new collections. It includes described First by Schmidt-Effing (1977), this area referred toabove.tern”, / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Obtusum Bucklandi domerguessi Euerbenites corinnae (Meister sp. (Canavari, 1888), originally described aff. et al. et al raricostatum Oxynotum Obtusum et al. / Gleviceras / Denotatus ., 2005), based on the recorded., 2005),basedon ap , 2002).Italsoshowscharacteristics Semicostatum (Meister ceratitoides et al. (2005)andtherefore, itbelongsto (Tilmann, 1917) is reported (Tilmann,1917)is from Ectocentrites Oxynotum zone and zone to the , 2002) and subzone, with Semicostatum aff. zones while (Blau (Quenstedt, 1883), et al. chollai zone to the zone. However, thisage sp. maybe the same. , 2002) was found in denotatus et al. (Taylor Gleviceras aztecorum zone; Raricostatum , 2003), reported E. corinnae Bifericeras tenan subzone. On Raricostatum Raricostatum et al. Ectocentrites , 2001) zone is re is et al. et al. sensu Ec ------/2017

3.3. TEN3(20°21’24.59”N;98°13’17.39”W) 3.5. ZONGOZOTLA (19°59’50”N;97°43’56”W) 3.4. TEN7(20°21’0.5”N;98°13’19.1”W) et al. subzones includingthe “old collections”(Meister regionthis hadarange from ter and partially by Blau fauna was reported byThis Meister cens natum subzone, and (Erben, 1956) inthe noticeras range are: h ecito fBlau description of The TEN 3. POTLA, BOPO 1, 2, 3 4, CENTRO, T/V 4, and TEMAPA, LAFIESTA, PEÑABLANCA,CHI same Upper Sinemurian faunaare: POTRERO, and ter E. corinnae ter shows: (1977). It is very similarto the TEN 3outcrop and This locality was first described by Schmidt-Effing CA, BOPO1,2,3,4,andCENTRO. TRERO,FIESTA, TEMAPÁ, LA PEÑA BLAN 7). Other outcropswith the same faunasare: PO ni, 1923),and P Erben (1956), O. jamesdanae mense 2003), corinnae to the presence of: sum area an intervalThis suggests from the . cf. and zn otetpo the zone to thetopof et al. et al. et al. , 2005). P. rothpletzi (Erben, 1956), subzone thefollowingtaxa occur: rothpletzi (Blau G. aztecorum A. floresi A.

, 2002), (2002). Theyindicated that thefaunain palomense , 2002), Plesechioceras (Blau Phylloceras (Trueman and Williams, 1925), et al. , edmundi Oxinoticeras (Figure 7).Other outcropswith the (Erben, 1956), Phylloceras P. tardecrecens Gleviceras choffati Gleviceras (Erben, 1956) and Ectocentrites et al , 2001), (Meister sp. (Figure 7). sp. inthe E. bravoi Raricostatum horizon. Finally, inthe ., 2001), et al. Gleviceras sp. (Suess, 1866)(Figure sp., (2001, 2003), and Meis Euerbenites et al. , sp. (Canavari, 1888), bucklandi Raricostatum (Tilmann,1917), Partschiceras et al P sp. (Erben, 1956), Denotatus (2008) mentions a B. tenangoense . (?), G. aztecorum zone, (Pompekj, 1907), ., 2002), hardbledownense sp. (Blau to P. cihuacoatlae et al. densinodulum zone, raricostatum zone due sp. (Fuci P. tardecre (2005), O. palo (Meis (Meis Obtu et al. apla sensu Oxy E. ------, ,

4. Discussionandconclusions Also, there are many taxonomic records involving is reported to be in the Lower Sinemurian too. range whose species some find to common also is Upper Sinemurian species, but it concentration of In manyoutcrops, thereof a shared is pattern BOPO 2,3,4,5,and6(Figure 7). and BLANCA, PEÑA 6, T/V TEMAPA, with al. which involves the aureolum horizon (Meister the accurately based on the subzones ranging from however, it is possible to focusits location more from the the East-Central Mexico. complete set ranges The al. Ectocentrites and Despí Fm.,given the presence of: this outcrop with the of lithological uniformity comes necessary to seek anexplanationcomes necessary consistent were basedonlow-quality material. itbe Then, (1956), although some individual determinations that errors have been discarded ever since Erben materialThe abundantso is andconvincing or the index fossilsfrom the MS markingthe absenceof taxa from LS. InFigure 11, areal can be seen gap exclusiveJUNTAS displays TEN–RÍO/LAS and the US (BOPO 3 andTEN1), three zones of outcropsdisplay two or US faunas.couple of A et al. ( 6 T/V former 5 BOPO ZOTLA, CENTRO, HONEY, CHIPOTLA, ZONGO outcrops(BOPO 1, BOPO 2, BOPO a group of POTRERO, TEN3,and7).There is also 4, T/V 4, BOPO FIESTA,(TEMAPA, LA zone that have asegmentbelonging to the LS based onthe outcrops is pattern interrupted The Obtusum rian and practically none indicating directly the datacontradictory regarding the Lower Sinemu , 2005;Blau in time first the for reported are they (2008), raricostatum , 2002),andPEÑA BLANCA)thatyield only P. mexicanum Obtusum zone. Oxynotum

hillebrandtii zone. t h oe ato the to the lower part of et al. . While zone to the , 2008).Itcanbecorrelated are also reported by Blau Gleviceras Raricostatum aff. P . gr. sensu palomense Burckhardti aplanatum Bucklandi Meister zone; and Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín et et - - - ,

effects, like the Time Averaging effect, given the given effect, Averaging Time the like effects, situation This maynot beduetotaphonomic between“gap” the latter and the the fill to recorded is none but taxa, Sinemurian also arisesatFIESTA theLA outcrop, withLower reach upper Hettangian. However, even thissame anomaly could and confirmed, and reported outcrop, where theLower Sinemurian age was JUNTAS TEN-RÍO/LAS the with instead tent Sinemurianit consis contradictsthisandmakes presence of it to the topmost Sinemurian. Nevertheless, the eras For example, at Temapá outcrop where pattern. with theinterrupted such Lower Sinemurian faunafrom the Pacif sibility that the paleocorridor, which introduced uncertainty about this idea includes the pos The Western Pacific. Sinemurian after spreading from itsorigininthe the Huayacocotla paleobasin during the Upper (Meister by Meister Ectocentrites Sinemurian. Aspecialcontroversyemerges with realm, although it should be focused onthe Upper Pacificevents,the homotaxial relatedwith of tion range could be duetoacombina stratigraphic the outcrops. Anotherlikelyexplanationthat is the lithological continuity andtheof small thickness although it dismissed, is improbable due to the basin during the lower aroundan ecological barrier the Huayacocotla Given such patterns, the possible presence of unlikely. its possible this looks local origin(highendemism), atids have a wider range than reported. But given ternative is that outcrops, except the to explain the entire Sinemurian range in several doesnotallow to anyassume ogy condensation zones, horizonsand ages. Nevertheless, the lithol zones, sub condensationThe impliesachange of (Arenas-Islas, 2012;Esquivel-Macías workalready out in the same outcropscarried appears, there are certain speciesthat assign et al. , which wasreported from Vietnam et al. Coroniceras , 2005). This suggests thatsuggests itentered , 2005).This P. rothpletzi (2002) and later at Zongozotla Obtusum ( Metophioceras Obtusum andother ortechiocer zone. the al Then, zone cannot be Raricostatum /2017 fthe Lower ) of et al. , 2014). Phylloc zone. 761 761 ------

COMPLEMENTARY OUTCROPS (NOT VISITED) / Paleoenvironment and Biostratigraphy of Huayacocotla Formation DISCUSSION AND CONCLUSIONS Paleoenvironment and Biostratigraphy of Huayacocotla Formation DISCUSSION AND CONCLUSIONS 762 762 4.1. INTERNATIONAL CORRELATION evidences for couldbe that interval.pattern This zone, because no other outcrop showsindex-fossil without leaving any record inthe lower until the Upper Sinemurianfauna should persist LAS JUNTAS outcropfauna. Also, hadthis the have been since intermittent, only the TEN-RÍO/ ic realm ( England. these faunas to of least Mexicothe corridor was isolation, orthat ageographic at of somekind of the fauna after the break sal center for some of Mexicoa disper acted as either that thispart of within the same range.gland might suggest This Mexico, but these include more time than in En Paltechioceras Oxynoticeras Upper Sinemurian taxa in England– thesetaxafrom East-CentralMexico. center of originanddispersion the region of es are part of cations andthus, it could be argued that both plac clear to denote the Lower Sinemurian inbothlo in East-Central Mexico. Otherwise, is the pattern Erben (1956), for the Upper Sinemurian, but not as anisolated homotaxial event, also mentioned by paper, therea mentionof is iceras zones and horizons, supported by Obtusum (Bloos and Page,England 2002), the and YorkshireStarting with Dorset in the coast of it istoday. closer to the Huayacocotla Formation then, than tectonic status, thisregion haveshould been much theLower Jurassic.Considering the Jurassic ing of Europe Northwestern the standard supports zon not letevident zonation change. continuityrepresented andsmallthickness here do seems unlikelytoo because the same lithological the Hettangian-Lower Sinemurian. However, this Sinemurian anditslower part with corresponds 1 becausesurelycentered itis the Upper alsoon Finally,outcrops most are comparable toTEN explained consideringendemism. / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín , Metophioceras zones are present, with homonymoussub sensu , cicd ihtoeo East-Central –coincide withthoseof Gleviceras Westermann 2000a, 2000b), may , and , Eoderoceras Vermiceras Microderoceras , Arnioceras . In the same . In Echioceras Bucklandi Angulaticeras , probably Obtusum , Coron , and and ------/2017 ,

or expanded. being clearwhatin they sense would have moved gested that both localities were connected, without deroceras al. zone from at Herfor–Diebrock Germany (Blau correlationThe is clear with the entire tophioceras subzone, basedonthe presence of veryaccurate with the ico. Thus, insouthwest the correlation England is ed, which is not represented in East-Central Mex Angulaticeras the rather questionable presence of Britain, the extreme ranges and For this part of in East-Central in Mexico, maybe duetothesame MS, as in Europe,as occurring refers to a lack of lowerThe and Mexico, by assuggested the Portuguese fauna. the ra-Tethys, inthe case that existed abarrier during have happened simultaneously inEurope, viapa invoked.is would involve This Mexico andmay a homotaxial phenomenon the Lower Jurassic if the fauna of of dispersal could be a source of Arnioceras guessi paleo-Pacific the Realm. The of representative is Vietnam corridor. uation would beacasetotally opposed toafaunal Bucklandi betweenan ecologic barrier) the top veals that a sedimentation isalsopossible gap (as Europe.re This South America,andtherest of complete Sinemurian range at NorthAmerica, part at that locality, andcontrastsitwiththe separates it clearly from the Sinemurian upper the endemism of 2010; Comas-Rengifo P. tardecrecens of finding the on based Mexico, tral Cen are represented, resembling the outcrops of Moel, boththe In Portugal, considering the section at San Pedro 00 ae ntepeec f, 2000)basedonthe presence of Obtusum , alsodescribed in Mexico, and , Gleviceras zones inEast-Central Mexico. Such asit (Meister and Obtusum suggest that suggest zone Europe between Northwestern and Bucklandi Coroniceras oxynotum and Gleviceras Obtusum zone with et al. zonepresent is with Paltechioceras Bucklandi et al. . and Obtusum , 2002).Therefore, this zone at San Pedro Moel sp. (Dommergues , 2013).But the high Arnioceras semicostatum Arnioceras raricostatum zone and zone wasinclud . It could be sug Vermiceras Echioceras Vermiceras Arnioceras Obtusum Raricostatum P. rothpletzi subzones E. domer conybeari , et al. , and and and Me Eo et ------, , ,

Pliensbachian). Figure 13 fauna from Mexico arrived when with the barrier ofam monoids were unless the so-called LS dispersed, groups how these to know difficult is It corridor. a multiple should be of paleocorridor Hispanic the the Sinemurian. Thus, perhaps the idea of with Europe, which alsoshowsthe full range of with Mexico, dispersion andalso disruptions of fewer had Pacific the of region this least at that Aberhan, 1994,1998).With all this, it seems was clear (Damborenea and Manceñido, 1979; Europethe Hettangian since to thePliensbachian fauna, thecommunicationtoward anddispersion bivalve Pacific to regard with America, South In cause, which prevented toMexico. thedispersion International stratigraphic correlation compared with the stratigraphic rangeFm. (H.Hettangian;correlation compared International ofHuayacocotla PLIENS. withthestratigraphic stratigraphic Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - eras sized. Queen Charlotte Islands also yielded MS isolationthe Huayacocotla in empha is Fm. atemporary areistics represented, so the idea of (Pálfy In Canada, at Queen Charlotte Islands, B.C. Damborenea, 1987,2000;Aberhan,1993). (Damborenea and Manceñido, 1979,1988,2005; rocksin thisarea without the fossilsin the region Mexico andwould explain the many siliciclastic the MS inEast-Central isolationa temporary of Bucklandi zone and during a prior LS communication in the tered in the during the MS interruption en fauna its US, and the Pacific brokeduring the and et al. and Juraphyllites , 1994),all the Sinemurian character Semicostatum . InQueen Charlotte Islands, zones. Allthispointsto /2017 Obtusum Arnioc 763 763 - - - -

Paleoenvironment and Biostratigraphy of Huayacocotla Formation DISCUSSION AND CONCLUSIONS DISCUSSION AND CONCLUSIONS / Paleoenvironment and Biostratigraphy of Huayacocotla Formation ACKNOWLEDGEMENTS / REFERENCES 764 764 7. References 5. Acknowledgements zonation for NorthAmericabasedonthe Queen is noMS. AlthoughPálfy evident (Pálfy while, inlocalities in Yukon the LS presence is Metophioceras Gleviceras the correlation of Aberhan, M.,1998,EarlyJurassic Bivalvia Aberhan, M.,1994,EarlyJurassic Bivalvia Aberhan, M., 1993, Benthic macroinvertebrate thecurrent paper. is themotive of on Jurassic tional Congress whichSystem, 2018” the“10 liant rolethe in organization of Huayacocotla Formation, and indeed for her bril aFieldguideto BSGMandtheoriginal idea of of for the invitation toparticipate the current in issue script. We speciallythankAnaBertha Villaseñor manu forpatient his with the several versionsof Francisco Vega BSGM, Vera, associated editor of thetext. Weimproveriously thank thequalityof servations andcareful advice allowed us to noto three anonymousreviewers whose detailed ob structivetext. on comments Wethe alsothank from La Plata, Argentina for valuable and con We acknowledge gratefully Susana Damborenea Europe. complete Sinemurian interval, as in presence of Charlotte fauna (Figure 13),theyalso report the / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Isofilibranchia: Beringeria: Zürich, WesternCanada. Part I. Subclasses of Beringeria: Switzerland 13,108p. Isofilibranchia: Palaeotaxodonta, and Pteriomorphia Chile Part Northern I. Subclasses of Geológica deChile, 20(2),105–136. Chile (26-29° S):Revista northern of basin theEarlyJurassic back-arc segments of in associations on a carbonate-clastic ramp withUS is clear, while s.ats h rsneo LS. Mean sp. attest the presence of et al. P. harbledownense , 1999),but apparently there et al. (1994) proposed a Arnioceras , Echioceras th Interna sp. and and ------/2017 Aguayo-Camargo, J.E., 1977,Sedimentación Palfy,Aberhan, M., J.,low 1996,A oxygen tolerant Aberhan, M.,Muster, H.,1997,Palaeobiology Arenas-Islas, D.,Tafonómico 2012, Análisis Arellano-Gil, J., Vachard, S.D., Yussim,D., Angeles-Cruz, C., Flores-Castro, K.,Esquivel- Angeles-Cruz, C., 2006,Geoquímicadelas de Hidalgo y San Luis: Revista del Instituto estados afloramientos, en (JurásicoSuperior) Diagénesis delaFormacióny “Chipoco” 993–1006. Earth Sciences, 33, Canadian Journal of the Canadian cordillera: the lower Jurassicof east pacific flat clam ( Western Canada: Paleontology, 40,799–815. Zürich, Early Jurassic Bakevellid Bivalves fromof Beringeria: Switzerland, 21,57–150. Isofilibranchia: Palaeotaxodonta, and Pteriomorphia superior (Jurásico Inferior), en la Formación de rocas siliciclásticas del sinemuriano Ciencias Geológicas, 15(1),9–13. Hidalgo, México:Revista Mexicana de al Inferior Jurásico Inferior enPemuxco, Estadode y Pérmico del estructurales paleogeográficos estratigráficos, Aspectos de Dios-González, A.,1998, Flores p. Cruz-Ortiz, L. (eds.), ACTAS 164 INAGEQ, J.S.,Armstrong-Altrin, Flores-Castro, K., Nacional de Geoquímica, 1-6 Oct., 2007, utilizando biomarcadores, (México): Implicaciones paleoambientales (Jurásico Inferior), estados de Hidalgo y Puebla de la Formaciónsiliciclásticas Huayacocotla de Carotenoides aromáticos enrocas Torres-Valencia, J.M.,2007, Presencia Macías, J.S., C.,Armstrong-Altrim, Estado deHidalgo, Tesis profesional, 155p. Hidalgo, México, Universidad Autónoma del Hidalgo): Implicaciones paleoambientales: (Tenango de Doria-San Bartolo Tutotepec, fosilíferas Madre de la Sierra Oriental rocas sedimentarias jurásicas en localidades Mexicano delPetróleo, 9(2),11–37. Posidontis in XVII Congreso XVIICongreso

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