Calpionellid biostratigraphy across the Ju ras sic/Cre ta ceous bound ary in San José de Iturbide, Nuevo León, north east ern Mex ico
Rafael LÓPEZ-MARTÍNEZ1, *, Ricardo BARRAGÁN1 and Daniela REHÁKOVÁ2
1 Universidad Nacional Autónoma de México, Instituto de Geología, Ciudad Universitaria, Delegación Coyoacán, C.P.
04510, México D.F., Mex ico
2 Comenius Uni ver sity, Fac ulty of Nat u ral Sci ences, De part ment of Ge ol ogy and Pa le on tol ogy, Mlynská dol ina G, 842 15 Bratislava, Slo vak Re pub lic
López-Martínez, R., Barragán, R., Reháková, D., 2015. Calpionellid biostratigraphy across the Ju ras sic/Cre ta ceous bound - ary in San José de Iturbide, Nuevo León, north east ern Mex ico. Geo log i cal Quar terly, 59 (3): 581–592, doi: 10.7306/gq.1244 De tailed bed-by-bed sam pling on an out crop of the La Casita and Taraises for ma tions in north east ern Mex ico (San José de Iturbide, Nuevo León State) al lows the de lim i ta tion of the Ju ras sic/Cre ta ceous bound ary. The Late Tithonian was de ter - mined by the pres ence of the Crassicollaria Zone (Colomi Subzone). Un der ly ing subzones (Remanei and Brevis) were not iden ti fied due to the scar city and poor pres er va tion of calpionellids. The Ju ras sic/Cre ta ceous bound ary was de fined by the acme of the small and spher i cal form of the spe cies Calpionella alpina Lorenz in sam ple IT-120. The Berriasian was di vided into two zones and five subzones: the Calpionella Zone (Alpina, Ferasini and Elliptica subzones) and the Calpionellopsis Zone (Sim plex and Oblonga subzones). The fa cies stud ied in di cate that de po si tion dur ing the Tithonian oc curred in a toe of slope en vi ron ment with oc ca sional deep shelf in cur sions. Near the Ju ras sic/Cre ta ceous bound ary, a sea level drop is re - corded and the fa cies in di cate a slope en vi ron ment with the oc cur rence of a brec cia level. A gen eral deep en ing of the en vi - ron ments re corded within the frame of the Elliptica Subzone where the de pos its pass into basinal fa cies.
Key words: Calpionellids, Ju ras sic/Cre ta ceous bound ary, Mex ico, biostratigraphy.
INTRODUCTION
The Ju ras sic/Cre ta ceous bound ary in north ern Mex ico has been dis cussed by sev eral au thors (López-Oliva, 1991; Adatte et al., 1994, 1996a; Eguiluz et al., 2012). None the less, the use of calpionellids for its de ter mi na tion is still un der dis cus sion due to the pres er va tion and abun dance of these microfossils, mainly in Tithonian de pos its. At this point, some au thors claim the low util ity of calpionellids for the de ter mi na tion of this bound - ary in Mex ico (Adatte et al., 1994, 1996a) be cause the Crassi - col aria Zone and the base of the Calpionella Zone (Alpina Subzone) can not be de ter mined with cer tainty.
In the pres ent work a de tail sam pling was car ried out in or - der to in crease the pre ci sion of calpionellid biostratigraphy to - wards the de lim i ta tion of the Ju ras sic/Cre ta ceous bound ary in a sec tion in the state of Nuevo León in north ern Mexico.
PREVIOUS MICROPALAEONTOLOGICAL STUDIES
Some micropalaeontological stud ies re gard ing the Up per Ju ras sic and Lower Cre ta ceous have been car ried out in Mex - ico, start ing with the clas si cal works of Bonet (1956) and Trejo (1975, 1980), who es tab lished the first de scrip tions and biostra - tigraphic dis tri bu tions of calpionellids and other incertae sedis from oil cores and sur face sec tions.
Cantú-Chapa (1967, 1982, 1989, 1992, 1999) stud ied some sec tions and es tab lished the Ju ras sic/Cre ta ceous boun d ary, based on ammonites and geo phys ics data. Calpio nellids were not taken into ac count, and this au thor claims that they are not of biostratigraphical im por tance in Mex ico. Due to the high ende - mism of the re ported ammonites, cor re la tions with the whole Tethys are dif fi cult. Lugo (1975) re ported that chitinoi dellids form the Up per Ju ras sic in oil cores and dem on strated the in flu ence of Med i ter ra nean Tethys in Mex ico dur ing this in ter val.
Other au thors (Adatte et al., 1993, 1994, 1996a, b; Stinnes - beck et al., 1993) de fined the Ju ras sic/Cre ta ceous bound ary by means of calpionellids and ammonites, and con firmed that calpionellid biozones used in East ern Tethys can be used with some mi nor vari a tions in Mex ico. The prob lem is con cen trated around the Crassicollaria Zone due to the scar city of spec i mens in this zone, in duced by palaeogeographic and tec tonic con di - tions dur ing Tithonian times in Mex ico. The other prob lem is re - lated with the sep a ra tion of the Elliptica Subzone, also due to the scar city of spec i mens.
* Corresponding author, e-mail: ralopezm@geologia.unam.mx Received: September 19, 2014; accepted: April 23, 2015; first published online: July 30, 2015
In con trast, Pessagno et al. (2009) ar gued for the diachro - nous ap pear ance of calpionellids be tween Eu rope and North Amer ica and, in con se quence, the im pos si bil ity to use them for the de lim i ta tion of the Ju ras sic/Cre ta ceous bound ary.
Eguiluz et al. (2012) con firmed a sea level change as so ci - ated with the Ju ras sic/Cre ta ceous bound ary re corded in the Huizachal sec tion, in con cor dance with a global sea level fall.
López-Martínez et al. (2013) found no sig nif i cant dif fer ences be tween the calpionellid biozones of Eu rope and Mex ico.
While di verse opin ions are pub lished, the prob lem of the Ju - ras sic/Cre ta ceous bound ary in Mex ico re mains con tro ver sial.
LOCATION AND GEOLOGICAL SETTING
The sec tion stud ied is lo cated at 24°43’33.68" N and 99°53’46.31" W, near the town of San José de Iturbide in Nuevo León State, north ern Mex ico (Fig. 1), and is part of the Si erra Madre Ori en tal fold-thrust belt. The sed i men tary cover of the area stud ied is mainly com posed of Ju ras sic and Cre ta ceous rocks. The pres ent study fo cuses on the Up per Ju ras sic and Lower Cre ta ceous rocks, es pe cially on those of the con tact be - tween the La Casita and Taraises for ma tions.
582 Rafael López-Martínez, Ricardo Barragán and Daniela Reháková
Fig. 1. Lo ca tion of the sec tion stud ied on a sim pli fied geo log i cal map
The sec tion stud ied is com posed of sed i men tary rocks of the up per part of the La Casita For ma tion and the lower part of the Taraises For ma tion (Fig. 2).
The La Casita For ma tion was first de scribed by Imlay (1936), and com prises a large va ri ety of rocks, such as poly - mictic con glom er ates, sand stones, cal car e ous sand stones, shales and lime stones. Fos sils are abun dant, rep re sented by pre vail ing ammonites, bel em nites, pelecypods, gas tro pods, wood frag ments, and oth ers. Microfossils are rep re sented by radio lar ians and some calpionellids. Due to its im por tance as a source rock, many works about its palaeontological com po si - tion, re gional dis tri bu tion, and stra tig ra phy can be found in the lit er a ture (Kellum, 1932; Imlay, 1936, 1937, 1938, 1953; Heim, 1940; Humphrey, 1949; Pantoja-Alor, 1962; Pérez - Rul, 1967;
Aran da-García et al., 1987; Contreras- Montero et al., 1988;
Cantú -Chapa, 1999; Olmstead, 1999; Pessagno and Mar tin, 2003). The thick nesses of the unit in out crops are vari able, with an av er age thick ness of 400 m. How ever, in subsurface, a thick ness of 1300 m was re ported by the Mex i can Pe tro leum Com pany PEMEX (1988). In the sec tion stud ied, a se quence of the La Casita For ma tion spans ap prox i ma tely 75 m in thick - ness.
Lo cally, this unit is com posed of an al ter na tion of thin, well-strat i fied shale-lime stone suc ces sions (Fig. 3A). Lev els with abun dant el lip soi dal cal car e ous con cre tions (Fig. 3B), con - tain ing well-pre served ammonites in side are fre quent (Fig. 3C).
These con cre tion lev els de crease in abun dance up wards in the sec tion. Bioturbation (Fig. 3D) and ox i da tion (Fig. 3E) are re - lated with con cre tions and are fre quent too. In the in ter val stud - ied, ammonites and other macrofossils are very scarce and badly pre served, which pre vents a real cor re la tion be tween this use ful in dex fos sil group and calpionellids. The La Casita For - ma tion grad u ally passes to a more cal car e ous fa cies, cor re s - pond ing to the Taraises For ma tion.
The Taraises For ma tion was orig i nally de scribed by Imlay (1936), who di vided the unit into two main mem bers. The lower mem ber was de scribed as a grey lime stone, re sis tant to ero -
sion; whereas the up per mem ber was iden ti fied as a fossilife - rous and clayey lime stone.
Lo cally, this unit is rep re sented by thick well-strat i fied grey lime stone (Fig. 3F). Ammonites and other macrofossils are very scarce.
MATERIAL AND METHODS
Care ful bed-by-bed samplings, in clud ing thin shale in ter ca - la tions, were car ried out. A to tal of 150 sam ples were used for thin-sec tion prep a ra tions. Microfacies and cal car e ous micro - fossils were ob served un der an Olym pus BX 60 petrographic mi cro scope.
Calpionellid biozonation was built tak ing into con sid er ation pre vi ous stud ies (Fig. 4), and adapted to the ver ti cal suc ces sion of in dex forms in the sec tion stud ied. The microfacies anal y sis of thin sec tions was basedon the stan dard meth od ol ogy out - lined by Flügel (2004).
Rock sam ples and thin sec tions are stored in the col lec tions of the Instituto de Geología, Universidad Nacional Autónoma de México (UNAM).
RESULTS
The suc ces sion of calpionellids in the sam ples stud ied yielded three stan dard zones and six subzones as fol lows:
LATE TITHONIAN CRASSICOLARIA ZONE, COLOMI SUBZONE (SAMPLES IT-100–119)
The Crassicolaria Zone is char ac ter ized by abun dant radiolaria and scarce calpionellids. The calpionellidas sociation com prises the spe cies Crassicollaria intermedia Durand-Delga (Fig. 5A), Crassicollaria parvula Remane (Fig. 5B–D), Crassi - collaria colomi Doben (Fig. 5E), Crassicollaria brevis Remane (Fig. 5F), Tintinnopsella remanei Borza (Fig. 5G), Calpionella grandalpina Nagy (Fig. 5H), Calpionella alpina Lorenz (Fig. 5I), and Tintinnopsella carpathica (Murgeanu and Filipescu). Cal - car e ous dinoflagellate cysts are scarce, be ing rep re sented by Cadosina semiradiata semiradiata (Wan ner) (Fig. 5J). The un - usual ver ti cal dis tri bu tion of the spe cies Crassicollaria inter - media Durand-Delga and Tintinnopsella remanei (Borza) – spe - cies which never ap pear so high in the strati graphic se quence – is as sumed to be a re sult of re work ing even when the spec i - mens do not ex hibit the phys i cal taphonomic fea tures of this pro cess. This as sump tion can be jus ti fied due to the vig or ous hy dro dy namic con di tions sug gested by microfacies anal y sis.
The microfacies of the Colomi Subzone can be di vided into three types:
Microfacies A: radiolarian wackestone-packstone (Fig. 6A, B), pri mar ily com posed of radiolaria and less abun dant calpionellids, sponge spicules, and cal car e ous dinocysts. The ma trix is dark with abun dant silt and or ganic mat ter. Ev i dence of resedimentation is com mon. This fa cies is sim i lar to the Stan - dard Microfacies SMF 3 and could have been de pos ited in a near toe of slope. Sed i ments were de pos ited in a dysoxic en vi - ron ment with a large amount of or ganic mat ter in put, per haps at trib ut able to upwelling cur rents that con trib uted to the nu tri ent sup ply in di cated by the abun dant radiolaria.
Microfacies B: com posed of wackestone-packstone of fil a - ments, sponge spicules, echinoderms, and poorly-de ter mined or ganic frag ments (Fig. 6C) dis play ing hor i zon tal lam i na tion.
Fig. 2. Stra tig ra phy of the area stud ied
Grey area in di cates the in ter val stud ied at the Iturbide sec tion
Stan dard microfacies SMF 1, char ac ter is tic of a deep shelf en - vi ron ment, was rec og nized. The re cord of this microfacies rep - re sents a short-term deep en ing.
Microfacies C: char ac ter ized by a microbrecciated fab ric (Fig. 6D) with an gu lar to rounded clasts that con tain some radio lar ians in side. Con tacts be tween clasts dis play dis so lu tion seams im preg nated by Fe-min er als. The microbreccia ho ri zons sit u ated close to the Ju ras sic/Cre ta ceous bound ary were pre vi - ously doc u mented by dif fer ent au thors (Olóriz et al., 1995;
Grabowski et al., 2010; Michalík and Reháková, 2011; Rehá - ková et al., 2011; Eguiluz et al., 2012). This microfacies is sim i - lar to SMF 4 and is re lated to a slope en vi ron ment.
EARLY BERRIASIAN, CALPIONELLA ZONE, ALPINA SUBZONE (SAMPLES IT-120–123)
The Early Berriasian Calpionella Zone rep re sents a change in both microfossils and fa cies com po si tion. This change oc - curs from sam ple IT-119 to IT-120 (Fig. 7A, B), where the radiolarian as so ci a tion is re placed by a near-monospecific as - so ci a tion of Calpionella alpina Lorenz with small and spher i cal forms of their loricas. This shift on the fa cies marks the be gin - ning of the Alpina Subzone within the Calpionella Zone. The on - set of the Alpina Subzone was con sid ered and dis cussed by the
Berriasian Work ing Group of the In ter na tional Com mis sion on Stra tig ra phy as one of the po ten tial events use ful to lo cate the J/K bound ary (Wimble don et al., 2011, 2013).
The calpionellid as so ci a tion is com posed of the spe cies Calpionella alpina Lorenz (Fig. 7C, D), Tintinnopsella carpa - thica (Murgeanu and Filipescu) (Fig. 7E) and Lorenziella sp.
(Fig. 7F).
Radiolarian packstone abruptly changes to calpionellid- radio larian wackestone to packstone. The ma trix is more cal - car e ous and the silt prac ti cally dis ap pears. The pres er va tion of the calpionellid loricas in creases up wards within the zone. Two main microfacies were de ter mined in this interval.
Microfacies D: calpionella-radiolarian wackestone (Fig.
7B). This microfacies is char ac ter ized by an in crease of calpio - nellids com pared with microfacies A of the pre vi ous subzone. It is sim i lar to SMF 3, where sed i ments are as sumed to have been de pos ited in the toe of a slope, as well as in deeper basinal en vi ron ments. The pre vi ous as ser tion is sup ported by the in flux of shal low wa ter de rived clasts and the pres ence of clay and land-de rived ma te rial in microfacies D. None the less, this fa cies set tled in a deeper en vi ron ment com pared to micro - facies A.
Microfacies E: slightly bioturbated calpionellid-spicule wackestone- packstone (Fig. 7G). This fa cies dis plays sim i lar
584 Rafael López-Martínez, Ricardo Barragán and Daniela Reháková
Fig. 3. Some lithological as pects of the La Casita and Taraises for ma tions as ob served in out crop
A – in ter ca la tion of thin lam i nated shale-lime stone in La Casita For ma tion; B – el lip soi dal cal car e ous con cre tions of the La Casita For ma tion;
C – some well-pre served ammonites in side the con cre tions of the La Casita For ma tion; D – ichnofossils pre served in the up per part of the La Casita For ma tion; E – ox i da tion of some bioturbation struc tures in the La Casita For ma tion; F – gen eral as pect of fa cies of the Taraises For - ma tion in the Iturbide sec tion; gen er ally rocks be long ing to this for ma tion dis play nu mer ous frac tures and cal cite veins dis play ing a sec ond - ary brecciated tex ture
fea tures to those pre vi ously de scribed, but fre quent bioturba - tion and heterolithic tex tures make it dis tinct. Sed i ments were de pos ited in the toe of a slope as for microfacies D.
CALPIONELLA ZONE, FERASINI SUBZONE (SAMPLES IT-124–127)
The base of this subzone is char ac ter ized by the First Oc - cur rence (FO) of the ge nus Remaniella with its spe cies Remaniella ferasini Catalano (Fig. 7H). Remaniella ferasini Catalano is scarce at the base of the subzone and be comes more abun dant up wards.
Microfacies D1: calpionellid-radiolarian wackestone with abun dant or ganic mat ter and py rite. Some calpionellid loricas and radiolarian tests are pyritized (Fig. 7J–L). Lo cally, phospha - tized bone frag ments were also iden ti fied (Fig. 7I). This micro - facies is a vari a tion of microfacies D, but re flects more anoxic con di tions.
CALPIONELLA ZONE, ELLIPTICA SUBZONE (SAMPLES IT-128A–132)
The on set of the subzone is de fined on the base of the FO of the spe cies Calpionella elliptica Cadish (Fig. 7N). The calpio - nellid as so ci a tion is com posed of the spe cies Calpionella alpina
Lorenz, Calpionella elliptica Cadish, Remaniella ferasini Cata - lano, and Tintinnopsella carpathica (Murgeanu and Filipescu).
The microfacies of this subzone is sim i lar to those pre vi - ously de scribed, but some as pects al low its sep a ra tion.
Microfacies F: calpionella-globochaetae wackestone with few ostracods (Fig. 8A) and ammonite aptychi (Fig. 8B). Rep re - sen ta tives of the foraminifera ge nus Lenticulina sp. and some gas tro pods are com mon (Fig. 8C). Resedimentation is less fre - quent than in pre vi ous microfacies, but is still pres ent and can be seen in geopetal struc tures in ostracods (Fig. 8A black ar - rows). This microfacies is sim i lar to SMF 3-calp (sensu Flügel, 2004) and cor re sponds to sed i ments de pos ited in a basinal en - vi ron ment.
LATE BERRIASIAN, CALPIONELLOPSIS ZONE, SIMPLEX SUBZONE (SAMPLES IT-133–136)
The Calpionellopsis Zone is de fined at the base by the FO of the ge nus Calpionellopsis and can be di vided into two main subzones, Sim plex and Oblonga, in ref er ence to the FO of the two spe cies of the ge nus, Calpionellopsis sim plex (Colom) and Calpionellopsis oblonga (Cadish), re spec tively.
The Sim plex Subzone is char ac ter ized by a calpionellid wackestone with small por tions of ostracods, foraminifera, bi - valves, cri noid frag ments, and loricas of calpionellids, from Fig. 4. Se lected calpionellid biozonations con sid ered for cor re la tion pur poses in clud ing
the biozonation con structed in this study for the Iturbide sec tion
which stand out those of Calpionellopsis sim plex (Colom) (Fig.
8D). The calpionellid as so ci a tion com prises the spe cies Calpio - nellopsis sim plex (Colom), Calpionella alpina Lorenz, Calpio - nella elliptica Cadish, Remaniella ferasini Catalano and Tintinno psella carpathica (Murgeanu and Filipescu).
CALPIONELLOPSIS ZONE, OBLONGA SUBZONE (SAMPLES IT-137–145)
The base of the Oblonga Subzone is de fined by the FO of Calpionellopsis oblonga (Cadish) (Fig. 8E).
The max i mum abun dance of calpionellids in the Iturbide sec tion is re corded within this subzone. The as sem blage is rep -
re sented by the spe cies Tintinnopsella longa (Colom) (Fig. 8F), Tintinnopsella carpathica (Murgeanu and Filipescu), Rema - niella colomi Pop (Fig. 8G), Remaniella filipescui Pop (Fig. 8H), Remaniella duranddelgai Pop (Fig. 8I), and Tintinnopsella sub - acuta (Colom) (Fig. 8J).
Among calpionellid loricas, many of them have sud denly thin ner and dam aged walls, and dis play de formed and “ab er - rant” forms (Fig. 8K, L). The same ob ser va tions were doc u - mented by Borza (un pub lished data) and Reháková (2000). On the ba sis of ob ser va tions made in sev eral sec tions, Reháková (2000) stated that events of “ab er rant” loricas were co in ci dent with the calpionellid cri sis. The first one re corded at the J/K bound ary (crassicollarian dec i ma tion), and the sec ond one at
586 Rafael López-Martínez, Ricardo Barragán and Daniela Reháková
Fig. 5. Micropalaeontological con tent of the Crassicollaria Zone A – Crassicollaria intermedia (Durand-Delga) (sam ple IT-114b); B–D – Crassicollaria parvula Remane (sam ple IT-104a); E – Crassicollaria colomi Doben (sam ple IT-103b); F – Crassicollaria brevis Remane (sam - ple IT-119); G – Tintinnopsella remanei Borza (sam ple IT-103b); H – Calpionella grandalpina Nagy (sam ple IT-104); I – Calpionella alpina Lorenz (sam ple IT-119); J – Cadosina semiradiata semiradiata (Wan ner) (sam ple IT-104a)
the end of Calpionellopsis Zone (di ver si fied calpionellid as so ci - a tions de creased in di ver sity and abun dance, later lead ing to calpionellid ex tinc tion).
The sed i ments of this subzone are sim i lar to the pre vi ously de scribed microfacies F, and they are as sumed to be de pos ited in a sim i lar en vi ron ment.
DISCUSSION
The ver ti cal dis tri bu tion of calpionellids in the Iturbide sec - tion is slightly dif fer ent from those de scribed else where for the rest of the Tethys (Figs. 4 and 9).
In the Late Tithonian up per most part of the La Casita For - ma tion, only the Colomi Subzone of the stan dard Crassicollaria Zone was de ter mined. The pre dom i nance of radio lar ians in the un der ly ing fa cies pre vented the rec og ni tion of older crasicolla - rian subzones. None the less, the calpionellid as so ci a tion of the Colomi Subzone con tains older forms such as Tintinnopsella remanei Borza and Crassicollaria intermedia (Durand-Delga), in dex mark ers of the Taxon Range Remanei and Intermedia subzones.
At the end of the Colomi Subzone, beds of brec cias ap pear sud denly. Marks of ero sion, ac com pa nied by siliciclastic in put and/or brec cia ac cu mu la tions, have been iden ti fied from co eval Late Tithonian in ter vals in many other Tethyan sec tions (Rehá - ková, 2000; Grabowski et al., 2010; Michalík and Reháková,
2011; Wimble don et al., 2013). Reháková (2000) de scribed huge, sev eral metres thick brec cia bod ies vis i ble across the West Carpathians area as ev i dence of the Zliechov Event (Reháková, 1998), which was in flu enced by a third-or der sea level fall, and which is co in ci dent with the “Purbeckian re gres - sion”. Sim i lar brec cias ac cu mu lated dur ing a co eval sea level fall were re ported from the Huizachal sec tion in north east ern Mex ico by Eguiluz et al. (2012).
The Ju ras sic/Cre ta ceous bound ary in the Iturbide sec tion was de ter mined at the base of the on set of the Alpina Subzone of the stan dard Calpionella Zone (the bloom or acme of spher i - cal forms of the spe cies Calpionella alpina Lorenz), and was lo - cally placed in sam ple IT-120 in the up per part of the La Casita For ma tion (Fig. 9). This bound ary marks a change in the depositional con di tions. Calpionellids be come abun dant and re - place the radiolarian-rich fa cies, in di cat ing slightly deeper and more sta ble con di tions. This tran si tion was grad ual, and fa cies be gan to change from the toe of the slope into the deeper parts of the ba sin. Per haps the palaeobathymetric con di tions did not change dra mat i cally, but the re cords of the de pos its are clearly dif fer ent. This phe nom e non could be ex plained by an en vi ron - men tal change, per haps in duced by the ac cel er a tion of sub si - dence, how ever, ad di tional stud ies are nec es sary.
Bat ten (1984), based on palynological re cords, and af ter - wards Adatte et al. (1996a), on the ba sis of changes in clay min - er als and sta ble iso topes, pro posed a palaeoclimate change close to the Ju ras sic/Cre ta ceous bound ary. Ac cord ing to these au thors, the palaeoclimate changed from a warm hu mid Ju ras - Fig. 6. Typ i cal microfacies of the Colomi Subzone
A, B – microfacies A, radiolarian wackestone-packstone; C – microfacies B, fil a ments, spicules and poorly de ter mined or ganic frag ments with fine hor i zon tal lam i na tion; D – microfacies C, microbreciated lime stone
588 Rafael López-Martínez, Ricardo Barragán and Daniela Reháková
Fig. 7. Fa cies and calpionellids of the Ju ras sic/Cre ta ceous bound ary and the Berriasian part of the sec tion A – radiolarian wackestone to packstone with rare calpionellids (sam ple IT-119 which rep re sents the lat est Tithonian fa cies); B – Calpionella microfacies (wackestone to packstone with acme of Calpionella alpina Lorenz) (sam ple IT-120; Early Berriasian); C, D – Calpionella alpina Lorenz (sam ple IT-121); E – Tintinnopsella carpathica (Murgeanu and Filipescu) (sam ple IT-125); F – Lorenziella sp. (sam ple IT-127); G – microfacies E, slightly bioturbated calpionellid-radiolarian wackestone (sam ple IT-122); H – Remaniella ferasini Catalano (sam ple IT-125); I – phosphatized bone frag ment in calpionellid wackestone (sam ple IT-127); J, K – Tintinnopsella carpathica (Murgeanu and Filipescu) (sam ple IT-127, pyritized calpionellids); L – Tintinnopsella longa (Colom) (sam ple IT-129, pyritized or biomineralised loricas); M – el lip soi dal form of Calpionella alpina Lorenz (sam ple IT-129); N – Calpionella elliptica Cadish (sam ple IT-130)
Fig. 8. Fa cies and calpionellids of the Berriasian part of the sec tion
A, B, C – microfacies F: Calpionella-globochaete wackestone with rare ostracods, gas tro pods, Lenticulina sp. and aptychus; black ar rows show geopetal struc tures, ev i dence that they are not in their orig i nal po si tion; D – Calpionellopsis sim plex (Colom) (sam ple IT-135); E – Calpionellopsis oblonga (Cadish) (sam ple IT-140); F – Tintinnopsella longa (Colom) (sam ple IT-141); G – Remaniella colomi Pop (sam ple IT-142); H – Remaniella filipescui Pop (sam ple IT-142); I – Remaniella duranddelgai Pop (sam ple IT-142); J – Tintinnopsella subacuta (Colom) (sam ple IT-143); K, L – ab er rant (thin-walled) and de formed calpionellid loricas in up per part of the Oblonga Subzone (sam ple IT-143)
590 Rafael López-Martínez, Ricardo Barragán and Daniela Reháková
Fig. 9. Lithological log with calpionellid oc cur rences and pro posed calpionellid biostratigraphy in the Iturbide sec tion
sic to a more con trasted (warm to dry) cli mate in the Cre ta - ceous. This palaeoclimate change and the in stal la tion of a clear open ma rine con nec tion be tween the Gulf of Mex ico and the Tethys (sensu Adatte et al., 1996a) is also vis i ble in the sec tion stud ied herein (fa cies changes re corded be tween sam ples IT-119 and IT-120) just at the Ju ras sic/Cre ta ceous bound ary.
Up wards in the sec tion, calpionellids in crease in abun dance and their di ver si fi ca tion al lows the rec og ni tion of all suc ces sive calpionellid subzones. The Ferasini and the Elliptica subzones of the stan dard Calpionella Zone were eas ily de ter mined by the FO´s of their zonal mark ers: Remaniella ferasini Catalano and Calpionella elliptica Cadish, re spec tively. A short-term sea level change is re corded within the Elliptica Subzone (calpionellid di - ver si fi ca tion) and can be cor re lated with LBZ-1, 1.5 from Haq et al. (1988), and is also in agree ment with the re sults of Adatte et al. (1996a) and Reháková (1998). Af ter wards, un til the end of the sec tion, the palaeobathymetry stayed with out dis tinc tive changes.
The Iturbide sec tion can be cor re lated with the Apulco sec - tion (López-Martínez et al., 2013). In both sec tions Crassi - collaria Zone is rep re sented only by the Colomi Subzone. The Ju ras sic/Cre ta ceous bound ary in both sec tions oc curs in the tran si tion of two co eval geo log i cal for ma tions; La Casita- Taraises in north ern Mex ico, and Pimienta-Tamaulipas in cen - tral Mex ico. The only dif fer ence be tween both sec tions is the ap pear ance of the Sim plex Subzone in the Iturbide sec tion while it was not pos si ble to de fine in the Apulco sec tion pos si bly due to resedimentation pro cesses.
Calpionellid biozones can be cor re lated in north ern and cen tral Mex ico with out sig nif i cant dif fer ences and with Eu ro - pean biozonations. This ob ser va tion is coun ter to the con clu - sions of the pre vi ous work of Pessagno et al. (2009). We have no ev i dence from the sec tions stud ied that show a diachronous ap pear ance of calpionellids be tween the Med i ter ra nean Tethys and Mex ico (at least in the sec tions stud ied). It is worth not ing a dif fer ence in the def i ni tion of diachronism be tween for ma tions and the Ju ras sic/Cre ta ceous bound ary. In Mex ico, due to ac - tive tec ton ics, geo log i cal for ma tions are mainly diachronous, even be tween nearby ar eas. This, though, does not prove diachroneity in the ap pear ance of calpionellids or of the Ju ras - sic/Cre ta ceous bound ary, which is a time plane and so can not be diachronous. On the other hand, the pres ence of one or an - other for ma tion in this in ter val only re flects the sed i men tary con di tions that can change from one ba sin to an other at dif fer - ent times. The main prob lem about the use of calpionellids for
biostratigraphical pur poses in Mex ico are fo cused on the de ter - mi na tion of two main spe cies: Calpionella alpina Lorenz and Calpionella elliptica Cadish. The de ter mi na tion of Calpionella alpina is very easy, but the cor rect dif fer en ti a tion be tween el lip - ti cal forms of Calpionella alpina and real Calpionella elliptica is dif fi cult in some in ter vals due to the sim i lar ity of both forms (see Fig. 7M, N).
CONCLUSIONS
The ver ti cal dis tri bu tion of calpionellids in the Iturbide sec - tion is slightly dif fer ent from those de scribed else where for the rest of the Tethyan re gion. The sec tion was di vided on the ba sis of calpionellid bioevents into three ma jor biozones and their cor - re spond ing subzones. The calpionellid re cord spans from the Crassicollaria Zone (Colomi Subzone) at the top of the La Casita For ma tion to the Calpionellopsis Zone (Oblonga Sub - zone) at the end of the strati graphic sec tion within the Taraises For ma tion. Microfacies of the Crassicollaria Zone rich in si li - ceous microplankton (radio lar ians), and spicules were re placed by cal car e ous oozes in which nannofossils and calpionellids dom i nated in the Oblonga Subzone.
The Ju ras sic/Cre ta ceous bound ary was de ter mined by the acme of Calpionella alpina Lorenz, and was placed near the tran si tional con tact be tween the La Casita and Taraises for ma - tions. A sea level fall, as so ci ated with the de po si tion of brec cias in the up per part of the Crassicolaria Zone, marks a ho ri zon that can be cor re lated with co eval sec tions of the east ern Tethys and with the Huizachal sec tion of north east ern Mex ico. This sea level fall fits within the global eustatic curve. A sea level rise was in ter preted within the Elliptica Subzone and re mains through out the rest of the sec tion.
Fu ture works will clar ify some as pects, such as the diachro - neity in the tran si tion be tween the La Casita and Taraises for - ma tions.
Ac knowl edge ments. This study was sup ported by grants PAPIIT IN109912, DGAPA, UNAM, and CONACyT-SEP 177510, and also by pro jects of the Slo vak Grant Agency:
VEGA 2/0068/11 and VEGA 2/0042/12. The au thors ex press their grat i tude to D. Ivanova and H. Sallouhi, whose com ments on the first draft of this manu script served to en hance the qual ity of the work.
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592 Rafael López-Martínez, Ricardo Barragán and Daniela Reháková
