STRATIGRAPHIC CORRELATION OF APTIAN TRANSGRESSIVE SEQUENCES IN NORTHEAST MEXICO

Ricardo Barragan, Depat1ment of Geology, Florida International Univcrsit' , University Park Campus, Miami, Fl. 33199, USA. e-mail: rbarraOUt:Yiu.eclu

Introduction Barremian-Aptian marine sequences of cmbonate platform deposits ::tre well e:-.:posed in northeastern Mexico where they have been tl1e focus o( extensive stratigraphic investigations since the early part of this century (Bose, 1923: Burckhardt, 1930: Imlay 1936, 1937). The sequences in that 11rea of Mexico show facies thm have been described as the Cupido Formation (Imlay. 1937: Humphrey. 1949), the La Pe11a Fom1ation (Imlay, 1936; Humphrey. 19.:)9). and the UJ\\'Cr Tamaulipas Formation (Imlay, I 937). The Cupido f<tcies represents deposits on a distinct shallow platfom1 thnt c:-.:isted from Barremian to Lower Aptian and extended fro m the following states, starting in western Nuevo Leon to Coahuilil. Dumngo and Chihuahua to the northwest, the deep-water facies lateral cquiv<llcm to the southeast is represented by the Lower Tamaulipas Fonmllion (Smith. 198 1: Fig. h1). Biocalciruditc with rudists 11nd biocalcarenite wi th ooli tes and rich benthonic fomminifeml assemblages typical of the sh<Jllo\\'-m<Jrine platfoml environment were abruptly tcm1inated at the end of lower Aptian \l'ith the sudden increase in terrigenous components characteristic of the marls and shaly limestones with ammoni tes and planktonic foraminifcm of the La Pcfia Fom1ation. Facies of the La Pef\a Formation accumulated throughout the Aptian and are interpreted to represent a transcominental transgression that took place in a SE to NW direction. In genemL the typical paleogeographic reconstruction of the middle to upper Aptian in northeastern !vfe:-:ico is defined by four facies belt s: (J) an itmer clastic narro\\' zone in the northwcstem areas, (2) a ccntwl zone chamcrerizcd by shallow-water carbonales deposits concspo11ding to the remains of the Cupido Platfom1. (3 ) a mmginal zone with marls, shaly limestones, and deep-w~ter carbon:-1tes m1d sh;1 lcs represented by !he La Pei'ia FormMion, and(4)ane:-:ternalzoncthatconsistsof decp basinal hemipelagic limestones (Smith. 1981: Fig. lb}. The Cupido-La Penn fom1ational contact is broadly accepted as indicati\·e of the onset of the transgressive event that drowned the caJbonatc platform in northeastern Mexico throughout the Aptian. The present study discusses the prcliminmy results from detailed anal~ ses of three strat igraphic sequences that span the Barremian and Aptian in northeastern ~v1cxico. Typical Apti<ln ammonites dominate the macrofauna at all three sequences and the presence ofkc~· index taxa has a!IO\\·cd for the recognition of standard biozones for this area of Me:-:ico. and therefore for correlation or the biostrai igr::1 phic units at a regional scale. Ammonites and characteristic microfossi ls fou nd in the transition zone from the Cupido to the Ul Pe1la Fonnations further corroborate the north\\'esterly direction of the Aptian transgressive event in this area. The biochronology of the facies ch<mges cha mcteristic of the 111 o fonmtions has been defined on ammonite and planktonic foraminifera index ta:-:a used as datums. and funhcr correl8tcd 1rith the standard ammonite zonation for rhe Lower Cretaceous seties of the Medi terranean Region defined by Hocdemaeker. eta!. , 1993.

Regional Geological Settin g The three sequences studied are loc11tcd in c:-:posed limbs of open Laramide antic li nes of the structurally complex nol1hcastem Mexican folded sedimc:ntarv Cordillera. or Sierra Madre Oriental. The overall topographic fea tures of the :mticlines in the area of ll1ese sequences nre part of the mountnins consti tuted rf well e:-:posed, intensely folded and thrust Jurassic and Cretaceous rocks. typical of nonheastem Mexico. Figure 2 shows the location of the stratigmphic sections from La Boca Cam· on located southeast of the citv of Monterrey in Nuevo Leon State. Prcsa Fmncisco ZMco. located southl\;est of Torreon City in Durango State, and Tanque Nuevo located north of the Sierra de Pams in Co<~huila Stare.

264

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)lethods -:-he stratign1phic analysis in the present study focu~ccl on detailed lithological and paleontologicil l :hmacteristics, and thicknesses of individm1 l strata in the sequences in order to characterize the primary :::mtrolling parameters of the depositional system and the occurrence of the ammonites. Resulting detailed sr;atigmphic columns summarized in Figme 3 haYc been constructed from the field dilta for each sequence. ::::d empll<lsize the va riations observed. and the z.onntion is based on c:-\act position of occurrence of the ::!1lmonite taxa. The ammonite faunal data yielded taxa that allow for the recognition of the standard :-.iozoncs preYiously recognized for that area of l'v1exico (Contreras y Montero. 1977). :..~boratory analyses of rock samples include thin sections studies for microfacies characterization and ~ iostrat igrnphy of index rnicrofossiis, and clctcrrni n:n ion of total cmbon and carbonate content. Special emphas is has been given to the il mmonite success ions in order to establish the biostratigraphic zonation. as ·.;·ell as the assemblages correlated to lithologic chamctcrist ics which. will shed light to further understand :heir relationships to sedi mentary processes. p:tleogeography . <t nd potential efTccts of eli mil tic changes on :heir variations. Further emph<tsis has also been giYen to the ammonites and microfacies in the transition z.ones at the fom1ational contacts bet\\·cen the Cupido Fonnat ion and Lil Peiia Formation ilt Presa Francisco Zarco and Tanque Nuero sections. and the l m, er T~mauli pas formation ilnd La Pena Fonnat ion in La Boca Canyon section, to better correlate the c,·ent associated with the facies changes with the st~ndard :nnmonite biozones for the LO\\"Cr Cretaceous of the lvlcdi tcmmcan region.

Results Figure 3 snmmarizes the results of this research in \rhich the daring of the beginning of the trnnsgression !bat drowned the carbonate platform duri ng the. Aptian in northc.astem Me:-\ ico was the m<lin goal. The Jeginning of this trilnsgressive event is identified in Northeast Mexico with the beginning of the deposition of the La Pcila Fonnation on top of the Cupido Limestone and Lower Tamaulipas Fonnation, and such horizon was anchored to ammonite datums of the standard ilmmonite biozonation for the Lower Cretaceous of the Mediterranean Region. The Lm,·er Tilm:mlip[]S Formation ill the La Boca Ca nyon section is a deep­water lateml equivalent of the Cupido Limestone

265

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2. Presa Franci sco Zarco

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Figure 2. Map of Mexico displaying the location or northeast Mexico and the three stnltigmphic sequences used for this study.

Conclu sions The regional study of the Cltpido-L8 Pcfia cont:tct (LO\\'Cr Tnmnulipas-Ln Pciia a! Lil Boc<t Canyon section) is in agreement '"ith pre,·ious models that suggcs! theSE to N\V direction of the Aptian transgression that drowned the carbonate platform in not1 hcnst Mc:-; ico. The timing or the depositio n of the transgressive La Pef'ia Formation in the area or s t ud~· is b:tscd on the appcamnce of typical Aptian ammonites in the sequences. lndex species of the genera Ot~fi·enoyia. RhyTtdohnplites. J3urckhl1rdtites. Colombic:eras. Cheloniccras, Parahoplites. and Pseudohaplocera.1 haw: been recognized in the sequences and were used as index ta:-;a to define the biozoniltion cstnblished for n0!1 hcastcrn Mexico. The biochronologic rcli<1bility cf this Mexican zonation is based on correlat ion '' ith the sl<lnd:Hd <tmmonitc zonation for the Lower Cretaceous of the Meditermncan Region \\hich is accepted as the most precise and most detailed biochronology. Thus, in the SE of the studied :trca (L<l Boca C:myon section), the beginning of the ·deposi tion of the La Pcfia Fo rmation concspo ncls to :1 !O\\Cl' AptHtn age and can be concliiicd with the Deshavesites deshayesi Zone of the aforementioned btostrnt igraphic ;.omtion for the Tethyan real m. Fur1her to the west (Prcsa Francisco Zarco section). the La Pcila stance! its deposition during the lower Aptinn ns well, but the first recognized ammonite <tssemblagc in this l ocalit~ is better correlated wi th the Dufi·ennyia

266

furcata Zone. The Cupido-La Pci1a contact becomes progrcssi\'cly younger to\Yards the NNW, whereb~· this event takes place in the upper Aptian \Yithin the span of time of the Acrmlhohopli!es no/ani Zone.

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Figure 3. Correlation chart shm1 ing the time at ,,·hich the depOsit io n of the La Pci1a Fonn<~tion st<Jr!ed. The stratigraphic columns not at SC<llc. The biochronolog;· for NE !Vlc:-.:ico was adapted from Contreras Montero. 1977 for this swdv.

References Bose, E.. 1923. Algwms fmums crct:\cic1s de Zac<ltccas. Durango ;. Guerrero. Bolctfn del lnstituto de Geologia de Mc.\ico. n. 42, 219 p .. I 9 l:'uns

Burckhardt. C. 1930. Etude sYnthctiC]UC sur lc M cso/.oique l\1c:-.:icain. Soc. Pal. Snis .. Mem 49-50. 2XOp.

Contrews. M. B .. 1977. Biocstmtigr:1 ria de l:1s Formaciones Tarn iscs y Ln Pc ri<J (Crct:.\cico Inferior), de La Goleta. Coahuila y Mini lias. Nuevo Leon. Re,· ista del IMP. ' !X. n. 1. p. X- 17.

Hoedemaeker. P. J; Company. M: Aguinc-Urrcl<l. M. B.; Awam. E.: Bogdanm;l. T. N.: Bujtor. L .. Bulat. L.; Cccca, F.: Delanoy. G.: Ett;Khlini. 1\.L 'vkmmi. L.: 0\Ycn. H. G.: Rmvson, P. F.; Sandov<JL 1.; Taver:L J. M.: Thieulo). J. P.: To,·bina. S Z: and Vasicek. Z .. J 993. Ammonite Zonation for the Lower Cretaceous of the .l\1cditcrrnne<m Region: Bilsis for the Stratigmphic Co!Tclations within IGCP­Project 262. Revista Espmiola de Palcontologia. R (l ). p. 117-120.

Humphrey. W. E. 1949. Geology of the Sierra de Los Mucrtos arcil. Me.\ico (\\'ith descriptions of Apti<Jn Cephalopods from the L1 Penn Form;llion) Gcologic81 Society of America Bulletin. Y. 60, p. 8')-176.

Imlay. R. W .. I ')36. Evolution of the Coahuila Peninsul:i. Mc.\ico: Part fV. Geology of the \'.·estcm part cf the Sierra de Parras. Geological Society of Amcnc1 Bulletin. \·. 4 7. p. 1 091-l 152.

Imlay. R. W .. 1937. Geology· of the middle pan or the Sicrm de Pamts. Coahuila. Mexico. Geological Society of America Bulletin. Y. -18. p. 5R7-610.

Smith. C. I.. 1981. Review of the geologic seiling. stratigraph~. and facies distribution of the Lower Cretaceous in northern Mexico. in Smith. C l. (cd. ). Lower Cretaceous stratigraphy and slrnctnrc, northern Mexico. West Texas Gcol Soc. Pub 81-7.:l. p. 1-27.

267