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Turonian boundary chronostratigraphy
Cretaceous Research (1997) 18, 331 – 353
Fossil occurrences in the Upper Cenomanian – Lower Turonian at Ganuza, northern Spain: an approach to Cenomanian / Turonian boundary chronostratigraphy1 Marcos A. Lamolda, *Amalia Gorostidi, †Ricard Martı´nez, †Gregori Lo´ pez and ‡Danuta Peryt * Facultad de Ciencias-UPV , Campus de Lejona , 48940 Lejona , Spain † Dept. de Geologia , Fac. de Ciencias , Univ. Autonoma , Campus de Bellaterra , 08193 Bellaterra , Spain ‡ Institute of Palaeobiology , Polish Academy of Sciences , Al. Zwirki i Wigury 93 , 02-089 Warsaw , Poland Revised manuscript accepted 22 January 1997
An Upper Cenomanian to Lower Turonian section has been sampled in the vicinity of Ganuza, northern Spain. Ammonoids, inoceramids and microfossils including foraminifera and calcareous nannofossils have been studied. We recognize three planktonic foraminiferal biozones: the Rotalipora cushmani , Whiteinella archaeocretacea and Helvetoglobotruncana helvetica Zones. We also characterize the Eiffellithus turriseiffelii and Quadrum gartneri Zones, based on nannofossil biostratigraphy. Macrofaunal occurrences are scarce but allow us to characterize the Metoicoceras geslinianum and Mammites nodosoides Zones, and two inoceramid assemblages. In the Rotalipora cushmani Zone the following sequence of biohorizons is recorded from bottom to top: (a) last occurrence (LO) of Corollithion kennedyi ; (b) LO of Rotalipora greenhornensis ; (c) LO of Axopodorhabdus albianus ; (d) first occurrence (FO) of Euomphaloceras septemseriatum , (e) LO of Lithraphidites acutus ; (f) LO of Rotalipora cushmani. In the Whiteinella archaeocretacea Zone the sequence of events is as follows: (g) FO of Calycoceras naviculare ; (h) LO of Microstaurus chiastius ; (i) FO of Quadrum intermedium ; (j) FO of Helvetoglobotruncana praehelvetica ; (k) FOs of Kamerunoceras sp. and Mytiloides submytiloides ; (l) FO of Mytiloides kossmati kossmati ; (m) FO of Kamerunoceras calvertense ; (n) FO of Quadrum gartneri ; (o) FO of Mammites nodosoides ; (p) FO of Mytiloides mytiloides . The top of this zone is marked by the FO of Helvetoglobotruncana helvetica. A possible Cenomanian-Turonian (C / T) boundary can be drawn between FOs of Kamerunoceras sp. and Mytiloides submytiloides and the FO of Mytiloides kossmati kossmati . Successive FOs of H. praehelvetica and Q. gartneri are also good proxies for the C / T boundary. ÷ 1997 Academic Press Limited KEY WORDS: Cenomanian / Turonian boundary; chronostratigraphy; planktonic foraminifera; nannofossils; inoceramids; ammonoids; northern Spain.
1. Introduction The stratigraphic succession at Ganuza, northern Spain, is a composite section of an expanded Cenomanian – Turonian (C / T) transition where the Whiteinella archaeocretacea Zone is about 45 – 50 m thick. It is located to the west of Estella, in the eastern Bascocantabrian Region (Figure 1). There is no evidence of stratigraphic gaps in the section which consists of an alternation of marl, marly limestone and limestone, with marl becoming more common towards the top, and some silty beds occurring towards the base. The sediments were deposited in a middle-outer shelf environment, according to the ostracod and foraminifera assemblages recovered (Colin et al ., 1982; Lamolda & Peryt, 1995). The macrofauna, microfauna and calcareous nannofossil biostratigraphy allows us to 1
Contribution to IGCP Project 362: Tethyan and Boreal Cretaceous.
0195 – 6671 / 97 / 030331 1 23 $25.00 / 0 / cr970061
÷ 1997 Academic Press Limited
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Figure 1. Location of the Ganuza section in northern Spain.
recognize several key events (according to Birkelund et al ., 1984) relating to C / T boundary definition. A summary of the stratigraphy and regional geology is given in Lamolda (1982). Macrofaunal assemblages were described by Wiedmann (1980) and Lamolda et al . (1989) from part of the Ganuza sections. Additional data on inoceramids and ammonoids were provided by Lo´ pez (1990) and Santamarı´a (1991) respectively. Lamolda & Peryt (1995) described the detailed biostratigraphy of the Upper Cenomanian of the section, and noted that bottom water conditions at the time of deposition of the uppermost part of Rotalipora cushmani Zone were dysaerobic. This correlates with the worldwide Cenomanian / Turonian Boundary Event (CTBE), which is also defined by nannofossil events in the section studied (Lamolda & Gorostidi, 1996). In a similar section at Menoyo, 70 km west of Ganuza, both nannofossil assemblages and a d 13C excursion have been discussed (Paul et al ., 1994). The Menoyo section provides a continuous sequence through the C / T transition in outer shelf and upper bathyal facies—limestone and marl alternations, but it is very poor in macrofauna. Lamolda (1978) noted occurrences of Inoceramus gr. labiatus and Mammites sp. Recently, we have found inoceramid specimens belonging to Mytiloides wiedmanni . All of the macrofauna is of Early Turonian age, being recorded between the first occurrences (FOs) of Quadrum gartneri and Helvetoglobotruncana helvetica . The Ganuza section represents deposition on a subsiding platform, when more than 2000 m of sediments accumulated during the Cenomanian and Turonian (Lamolda, 1982). Last occurrences (LOs) of the planktonic foraminifera
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Rotalipora greenhornensis and R. cushmani and the FO of the nannofossil species Q. gartneri are events recognized worldwide and are commonly used for correlation. Comparison of bed thicknesses between these events in the Ganuza section with coeval sections elsewhere which are considered to be the most expanded and complete record of the C / T boundary, has revealed that the Ganuza succession is about five times thicker than that at Pueblo, Colorado (USA), seven times that at Dover, southeast England (Lamolda & Peryt, 1995), and twice that at Eastbourne, southern England (Lamolda et al ., 1996). Therefore, the Upper Cenomanian and lowermost Turonian succession at Ganuza is particularly complete. In addition, its rich macro- and microfossil record makes this section especially suitable for characterizing the C / T boundary. 2. Material and methods The section at Ganuza is exposed on both sides of the road, 200 – 300 m south of Ganuza village. It is a composite section (Figure 2) whose lower and upper parts could have some levels in common; they are separated by a small fault. The succession comprises about 15 cycles of limestone and marl alternations. This cyclicity is also found in sections at Menoyo (Paul et al ., 1994) and Dover (Lamolda et al ., 1994). The lower part of the section studied, G (Figure 2), consists of two marly / silty and two calcareous sequences. At the bottom there is a 16.5-m-thick sequence of siltstone and marl with interbeded limestone as thin layers and lenticular bodies. The sequence is overlain by a 6.1-m-thick calcareous series composed mainly of limestones and nodular limestones interbedded with thin marlstones and siltstones. Higher up the section there is a 3.1-m-thick series of marly siltstone with irregular and scarce limestone interbeds. The top 4.3 m of the section comprises limestone and marlstone alternations. GS is a similar section about 100 m to the south of G. Both sections are on the east side of the road. The two uppermost G units are partly present in the base of the lower part of the GZ succession (Figure 2), although an accurate correlation between G and GZ has not been possible. The G sequence was dated as middle-late Late Cenomanian by means of macrofauna and foraminifera (Wiedmann, 1980). Lamolda et al . (1989, fig. 2) defined ‘A’ and lower ‘B’ units in the sequence, which were dated as Late Cenomanian by means of planktonic foraminifera. The GZ succession consists of 40 m of 10 or 11 cycles of marl and limestone alternations. The GZ part was dated by Wiedmann (1980) as Early Turonian on the basis of planktonic foraminifera. Neither he nor Lamolda et al . (1989) found macrofauna in GZ, but in the upper part, we have found foraminiferal assemblages characteristic of the Whiteinella archaeocretacea Zone of probable Early Turonian age according to its correlation with other neighbouring sections. The first macrofaunal data from the upper part of GZ sequence were reported by Lo´ pez (1990) and Santamarı´a (1991). Forty-three samples from a 70-m-thick sequence of the Ganuza section (the G and GZ parts), were studied for foraminifera. Four to five hundred specimens from the .100 m m size fraction were picked and for each sample all species were identified. Forty-four samples in the GS and GZ parts were studied for nannofossils using a light microscope at a magnification of 31000 and quantitative procedures described by Lamolda et al . (1994). Counting of 500 nannoliths per sample gives a 99% ( p , 0.01) confidence level of not overlooking
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Figure 2. Composite section at Ganuza to show lithology, location of micropalaeontological samples, and macrofaunal occurrences.
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any taxon present at 1% or more of the total population (Denisson & Hay, 1967). The macrofaunal assemblages were checked bed by bed throughout the section. Although generally sparsely distributed, some beds contain many fossils, such as sample GZ 4, which records an inoceramid event, and G 22, GZ 5 and GZ 6, which yield numerous ammonoids. 3. Nannofossil biostratigraphy The abundance of nannoliths in the samples studied proved to be low, with only 1 nannolith per field of view (Nan. / FOV) or less. Their preservation is also poor. 54 species have been identified. The number of taxa per sample is between 15 and 30. The assemblages are dominated by six taxa: Eiffellithus turriseiffelii , Eprolithus floralis , Prediscosphaera spp., Retecapsa spp., Rhagodiscus achlyostaurion and Watznaueria barnesae (Figure 3). Each of these comprises more than 5% of the assemblages. W. barnesae comprises 40 – 50%. In the uppermost Cenomanian several major assemblage changes are recognised. These include LOs of, from the base of the section upwards (Figures 3, 4), Corollithion kennedyi (sample GS 12; 13.2 m), Axopodorhabdus albianus (GS 16; 15.7 m), Lithraphidites acutus (GS 18; 18.6 m) and Microstaurus chiastius (GZ 73; 6.3 m 5 approximately 13.4 m above GS 18). First occurrences of biostratigraphically important taxa include Quadrum intermedium (GZ a; 7.3 m), Eprolithus octopetalus and Nannoconus multicadus (GZ 58; 14.6 m), and Q. gartneri (GZ 1; 16.5 m). Rhagodiscus asper occurs throughout the section and overlaps the range of Q. gartneri , Eprolithus octopetalus and E. eptapetalus (Gorostidi, 1993, pp. 174, 175). Nannofossils are less common in the lower part, with a minimum at the level of the Rotalipora cushmani extinction, about 3 m above the LO of Lithraphidites acutus (Figure 4). The assemblages recovered are similar to those reported from Menoyo (Gorostidi & Lamolda, 1991; Paul et al ., 1994), southeast England (Crux, 1982; Jarvis et al ., 1988; Lamolda et al ., 1994), and various localities in Northern Europe and North America (Bralower, 1988). At Ganuza ‘blooms’ of Eprolithus floralis occur above the FO of Q. gartneri , comprising up to 32% of the total assemblage, which is even greater than has been found in the Dover (10%) and Menoyo (18%) sections. We found Crux’s (1982) biozonation, established in southeast England, to be appropriate for our assemblages (Lamolda & Gorostidi, 1996). Two biozones are partly distinguished, the Eiffellithus turriseiffelii and Quadrum gartneri Zones. The former is characterized by the association of Eiffellithus turriseiffelii , Eprolithus floralis , Glaukolithus compactus , Prediscosphaera avitus , P. cretacea , Retecapsa spp., Rhagodiscus achlyostaurion , Tranolithus phacelosus , Watznaueria barnesae , W. biporta and Zeugrhabdotus embergeri . LOs of Corollithion kennedyi , Axopodorhabdus albianus , Lithraphidites acutus and Microstaurus chiastius indicate that the Upper Cenomanian sequence is complete and their order of disappearance is similar to those in other sections (Figures 3, 4) (Lamolda & Gorostidi, 1996). This sequence of bioevents is important for the biostratigraphical characterization of the uppermost Cenomanian and the C / T boundary. Furthermore, FOs of Quadrum intermedium (GZ a; 7.3 m) (Paul et al ., 1994), and Nannoconus multicadus (GZ 58; 14.6 m) (Deres & Ache´ rite´ guy, 1980; Zeighampour, 1981; Crux, 1982), enhance correlation and completeness of this C / T transition. In contrast the LO of Allemanites striatus , Rhagodiscus
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Figure 3. Range chart for calcareous nannofossils from the Ganuza section. Abundance: C 5 1 – 10 Nan. / FOV; R 5 1 Nan. / 1 – 10 FOV. Preservation: F 5 fair; P 5 poor.
achlyostaurion , R. angustus , and R. asper cited by Crux (1982) in the English Upper Cenomanian, are recorded from Lower Turonian or younger deposits in northern Spain (Gorostidi, 1993). The lower boundary of the Quadrum gartneri Zone is defined by the first occurrence of the nominate taxon (sample GZ 1; 16.5 m), which overlies the FO of Eprolithus octopetalus (GZ 58; 14.6 m), a good indicator of the C / T boundary
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Figure 4. Ranges of planktonic foraminifera, ammonoids and inoceramids, and nannofossil event locations.
(Varol, 1992). Its lower part is characterized by the taxa E. turriseiffelii , E. floralis , G. compactus , Nannoconus spp., P. cretacea , Retecapsa spp., R. achlyostaurion , T. phacelosus , W. barnesae , W. biporta and Z. embergeri. The main differences from the Eiffellithus turriseiffelii Zone assemblages are higher proportions of P. cretacea
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and Nannoconus spp., especially the latter, which is rare in the Upper Cenomanian and increases up to 3 – 9% of the total in Turonian assemblages, even higher than at Menoyo (3%; Gorostidi, 1993, p. 232). Also, E. floralis is present in higher proportions in this Turonian material, usually more than 10% (between 50 and 160 specimens counted per sample studied), whereas in the Upper Cenomanian it is less than this (between 1 and 50 specimens per sample studied). In contrast, P. avitus decreases in abundance from 5% to less than 1%. The LO of R. asper has been cited as an important indicator of the C / T boundary (Crux, 1982; Jarvis et al ., 1988; Lamolda et al ., 1994), but at Ganuza this species occurs throughout the section, and at Menoyo its LO is in Lower Turonian deposits (Paul et al ., 1994). The data from northern Spain agree better with the probable events of Bralower (1988) and with results from Kalaat Senan in Tunisia (Gartner in Robaszynski et al ., 1990). The LO of R. asper is probably diachronous depending on paleolatitude. It can no longer be regarded as biostratigraphically useful, but may have biogeographical and palaeoecological significance (Lamolda & Gorostidi, 1996). 4. Foraminifera The diversity of planktonic foraminifera is low to moderate. Abundances are highly variable throughout the Ganuza section. In the Upper Cenomanian (samples G 33 to GZ 54) their contribution to the total foraminiferal assemblage varies from 12 – 80%; in the lowermost Turonian these values are very high and almost stable at 72 – 88%. The Late Cenomanian changes in planktonic / benthonic (P / B) ratio probably reflect sea-level fluctuations and indicate an inner to outer shelf environment; the high P / B ratio in the upper part of the section suggests a rise in sea level during the latest Cenomanian and earliest Turonian to outer shelf depths. In terms of palaeoecology the composition of the planktonic foraminiferal fauna from the Ganuza section shows that the sampled interval can be divided into three parts: (1) A lower part from 4.2 – 25.8 m (samples G 33 to G 11; Figure 2) characterized by mixed, diverse assemblages, with a high proportion of keeled forms, such as the genera Rotalipora and Praeglobotruncana , and in the top part of this interval, Dicarinella . (2) A relatively short interval approximately 11.6 m thick (samples G 11 to GZ 56) characterized by a temporary, almost complete, disappearance of keeled forms from the assemblages. Dicarinella spp. are very rare scarce. They may be found with rare specimens of Praeglobotruncana spp. Low diversity planktonic foraminiferal assemblages are dominated by non-keeled, globular forms—mainly hedbergellids. This interval corresponds to the benthic faunules III and IV of Lamolda & Peryt (1995) which are characteristic of low-oxygen bottom waters. (3) An upper part approximately 27.5 m thick (samples GZ 56 to GZ 8) in which planktonic foraminifera diversify again and become very abundant; both keeled and non-keeled forms occur. Within keeled morphogroups Dicarinella spp. dominate. The change in morphotypic composition of planktonic foraminiferal fauna, e.g., the extinction of species of Rotalipora and almost complete disappearance from assemblages of Dicarinella spp., probably reflect changes in palaeoceanographic conditions related to the CTBE.
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The following planktonic foraminiferal events were identified in stratigraphic order from bottom upwards: LO of Rotalipora greenhornensis , sample G 26 (13.6 m); FO of Dicarinella spp., sample G 19 (19.4 m); LO of Rotalipora cushmani , sample G 14 (22.2 m); FO of Helvetoglobotruncana praehelvetica , sample GZ 53 (9.4 m 5 13.3 m above G 14); FO of Helvetoglobotruncana helvetica , sample GZ 8 (38.8 m). The studied interval comprises the uppermost part of the Rotalipora cushmani Zone, which is characterized by occurrences of different species of Dicarinella , mainly Dicarinella algeriana (Figure 7s, t) and D. imbricata (Figure 7q, r), but also D. elata (Figure 7i, j), D. hagni (Figure 7l – n), D. oraviensis (Figure 6q, r), Globigerinelloides bentonensis (Figure 5q, r), Guembelitria cenomana (Figure 5t), Hedbergella delrioensis (Figure 7k), H. planispira (Figures 5g, h; 7o), H. simplex (Figure 5a, b), Heterohelix moremani (Figure 5p), Praeglobotruncana aumalensis (Figure 6d, h), P. delrioensis (Figure 7c, d), P. gibba (Figure 6k, l, o, p), P. stephani (Figure 6s, t), Rotalipora greenhornensis (Figure 6a, c), and common taxa such as Rotalipora cushmani (Figure 6e, g), Whiteinella aprica (Figure 5i, j), W. archaeocretacea (Figure 5o), W. baltica (Figure 5k, l), W. brittonensis (Figure 5c, d, m, n), and W. paradubia (Figure 5e, f), mainly in the upper part of the Rotalipora cushmani Zone. The Whiteinella archaeocretacea Zone is dominated by the hedbergellids Hedbergella spp. and Whiteinella spp., and a few Praeglobotruncana spp. Rare Dicarinella spp. are also found in the lower and middle parts (uppermost Cenomanian) of this zone. Main differences from the underlying zone are occurrences of Helvetoglobotruncana praehelvetica (Trujillo) (Figure 6m, n) in most samples from the GZ sequence (Figures 2, 4), and no occurrences of rotaliporids, the LO of which marks the top of the Rotalipora cushmani Zone. The FO of the species Helvetoglobotruncana helvetica (Figures 6i, j; 7a, b), lies in sample GZ 8, at the top of the section studied. Therefore, the Whiteinella archaeocretacea Zone has a complete biostratigraphic record.
5. Inoceramids Inoceramid faunas are not abundant in the C / T transition at Ganuza. No characteristic Cenomanian inoceramid assemblages have been found. There are five levels in the Turonian with a record of inoceramids, and a lowermost level with Mytiloides submytiloides (Figure 8b) and Mytiloides sp. (sample GZ 56; 11.6 m), of doubtful age but very close to the C / T boundary. It is possible to characterize two assemblages, the lower of which is a typical earliest Turonian inoceramid association.
5.1. Mytiloides submytiloides Assemblage This is the oldest inoceramid assemblage recognized at Ganuza. It is defined by the first occurrence of the genus Mytiloides , and in particular of specimens of M. submytiloides and Mytiloides sp. (sample GZ 56), and M. kossmati kossmati (GZ 57, 1 m above GZ 56; Figures 4; 8c). These species are associated with M. wiedmanni (Figure 8d) and M. cf. kossmati kossmati 8.4 m higher up the section (sample GZ 4; Figure 4), which records an inoceramid event.
Figure 5. a, b, Hedbergella simplex , G 26; c, d, Whiteinella brittonensis , G 26; e, f, W. paradubia , G 31; g, h, H. planispira (Tappan), G 31; i, j, W. aprica , GZ 8; k, l, W. baltica , GZ 8; m, n, W . brittonensis , G 31; o, W. archaeocretacea , G 26; p, Heterohelix moremani , GZ 53; q, r, Globigerinelloides bentonensis , G 23; s, H. sp., GZ 60; t, Guembelitria cenomana , G 23. Scale bar 5 100m m.
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5.2. Mytiloides kossmati ganuzaensis Assemblage The M. k. ganuzaensis Assemblage is defined by the FO of this subspecies. Unfortunately, it has not been found in the section studied, but it is frequent in nearby sections (Lo´ pez, 1994; Martı´nez et al ., 1996). By contrast, M . mytiloides (Figure 8a), which is also characteristic of this assemblage, is present (samples GZ 6 and GZ 6a, about 12 m above GZ 4; Figure 4). Therefore, the M. k. ganuzaensis Assemblage is probably indicated in the section studied, despite the absence of the nominate taxon. The uppermost inoceramid level with M. hercynicus (Figure 8e) and M . cf. transiens (sample GZ 8, Figure 4) occurs about 7 m above the latter. 6. Ammonoids Ammonites are rare in the section; only a few beds have yielded relatively rich assemblages (Figures 2, 4). It is difficult to distinguish a biozonation. Nevertheless, our data are of significance in the context of determining the C / T boundary. Typical Upper Cenomanian species are recorded between samples G 22 and G 12. The oldest species identified is Euomphaloceras septemseriatum (Figure 9b) from sample G 22 (17.3 m) associated to Calycoceras sp. and Forbeciceras sp. In sample G 12, 7.5 m above sample G 22, we found Protacanthoceras sp. and Thomelites sp. aff. hancocki (Figure 9a). A specimen of Calycoceras naviculare , not recorded in situ , was found about 10 m above the occurrence of E. septemseriatum . This cosmopolitan species is typical of the Metoicoceras geslinianum Zone in Europe, North Africa, Angola, Madagascar, Middle East, South India, Japan and the USA. A specimen of Kamerunoceras sp. was identified in sample GZ 56, and another specimen of Kamerunoceras calvertense (Figure 9c) in level GZ 57 / 58, 5 m and 2.5 m respectively below the FO of Q. gartneri (sample GZ 1), an index for the C / T boundary according to the proposals of Birkelund et al . (1984). A specimen of Spathites (Jeanrogericeras ) sp. was found in level GZ 59 (1 m below the FO of Q. gartneri ). All ammonites identified above the FO of Q. gartneri are clearly Turonian in age. In sample GZ 3, 2.5 m above the FO of Q. gartneri , we found specimens of Mammites nodosoides (Figure 9d) and Spathites (Jeanrogericeras ) obliquus . One metre above this sample Watinoceras sp. is recorded (GZ 4), and 1 m higher, there is a level with Kamerunoceras puebloense , Fagesia cf. pachydiscoides , F . aff. rudra and Thomasites gr. gongilensis -koulavicus . A rich ammonite assemblage 11 m above (samples GZ 6 and GZ 6a) was found to comprise Scaphites ? sp., Mammites ? sp., Pachydesmoceras linderi , F . cf. pachydiscoides , K. puebloense , Lecointriceras fleuriasianum (Figure 9f) and Fagesia sp. F. pachydiscoides and Choffaticeras pavillieri (Figure 9 e) are recorded 1.8 m above this assemblage. At a higher level still, 5 m above (GZ 8, at the top of the section studied), F . aff. rudra and C. pavillieri have been found. 7. Discussion Occurrences of relevant biostratigraphical indicators for the C / T transition in the Ganuza section are summarized in Figure 10. LOs of the foraminifers R. greenhornensis and R. cushmani , and the nannofossil A. albianus have been
Figure 6. a – c, Rotalipora greenhornensis , G 26; d, h, Praeglobotruncana aumalensis , G 31; e – g, R. cushmani , G 26; i, j, Helvetoglobotruncana helvetica , GZ 8; k, l, P. gibba Klaus, G 31; m, n, H. praehelvetica , GZ 8; o, p, P. gibba , GZ 8; q, r, Dicarinella oraviensis , GZ 8; s, t, P. stephani , GZ 8. Scale bar 5 100m m.
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calibrated with d 13C curves from the literature and unpublished data from the Ganuza G section (C. R. C. Paul, pers. comm.). The FOs of the nannofossil Q. gartneri have also been calibrated with d 13C data provide by Paul et al . (1994; following observations by Gale et al ., 1993). Lithostratigraphical correlation between Anglo-Paris Basin localities have been used, especially within the Plenus Marls.
7.1. Planktonic foraminifera and nannofossils Planktonic foraminifera and nannofossil occurrences characterize the C / T transition and its completeness (Lamolda et al ., 1994). Graphic correlation between Menoyo and Dover (Shakespeare Cliff) revealed the completeness and similar pattern of deposition in these localities (Paul et al ., 1994). This can be extended to the Ganuza section studied because of its similarity with Menoyo (Lamolda & Peryt, 1995; Lamolda & Gorostidi, 1996). Two of our bioevents, LOs of R. cushmani and A. albianus , were used by Gale et al . (1993) to compare bioevents and d 13C for Eastbourne and Pueblo, showing their usefulness on both sides of the Atlantic Ocean. Nevertheless, LOs of both R. greenhornensis and R. cushmani at Pueblo are younger than elsewhere (Figure 10). This rotaliporid persistence continues with the record of endemic Anaticinella in the Western Interior Basin (USA) during Late Cenomanian. This region was a refuge for rotaliporids, which had disappeared by this time elsewhere. Successive LOs of L. acutus , R. cushmani and M. chiastius , and FOs of Q. intermedium , H. praehelvetica and Q. gartneri , characterize sediments from Upper Cenomanian (Metoicoceras geslinianum Zone) to lowermost Turonian (Watinoceras devonense Zone) All occurred during the d 13C excursion of the C / T transition. Unfortunately, these bioevents have not been well documented in the proposed C / T boundary stratotype at the Rock Canyon Anticline section, Pueblo (Bengtson, 1996) which, by contrast, favours macrofaunal events. 7.2. Inoceramids The first occurrence of the genus Mytiloides is useful for recognizing the C / T boundary (Seibert, 1979; Tro¨ ger, 1981; Birkelund et al ., 1984). On a broad scale, the basal Turonian of North America and Europe is characterized by occurrences of M. submytiloides . Tro¨ ger (1989) cited his Zone 8 (Lower Turonian) as the stratigraphical range of this species. This species has also been found in southeast France (Jolet et al ., 1995) associated with M. kossmati ganuzaensis , which is a Lower Turonian species. Nevertheless, some authors, such as Harries et al . (1996), have considered that M. submytiloides may occur in uppermost Cenomanian rocks. M. wiedmanni is found in the GZ section at Ganuza just above the FO of M. nodosoides (Figures 4, 10). In addition, we have recently also found some specimens of M. wiedmanni in Lower Turonian rocks of the Menoyo section. This species in the lowermost Turonian of Saumurois, western France was referred to as Inoceramus hercynicus by Sornay (1982). Moreover, it has been identified in Cassis, southeast France (Lo´ pez, in prep.) associated with M. submytiloides , and in the lowermost Turonian of the Bohemian Basin (S. Cech, pers. comm., 1995). M. wiedmanni is a widespread species and also occurs at Pueblo (Bengtson, 1996), associated with M. hattini and very close to the LO of Neocardioceras judii and the FO of Kamerunoceras sp.—less than 1 m below Bed
Figure 7. a, b, Helvetoglobotruncana helvetica , GZ 8; c, d, Praeglobotruncana delrioensis , GZ a; e, f, P. sp., G 31; g, h, P. sp., GZ a; i, j, Dicarinella elata , GZ 57a; k, Hedbergella delrioensis , GZ 7; l, p, D. hagni , G 26; m, n, D. hagni , GZ 59; o, H. planispira , G 23; q, r, D. imbricata , GZ 7b; s, t, D. algeriana , GZ 8. Scale bar 5 100m m.
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Figure 8. a, Mytiloides mytiloides , right valve of the specimen PalUAB no. 38222; b, M. submytiloides , left valve of the specimen PalUAB no. 38711; c, M. kossmati kossmati , right valve of the specimen PalUAB no. 38847; d, M. wiedmanni , left valve of the specimen PalUAB no. 38764; e, M. hercynicus , left valve of the specimen PalUAB no. 38490. Scale bar 5 1 cm.
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86 of the proposed C / T boundary stratotype. Therefore, its range is from uppermost Cenomanian to Lower Turonian (Figure 10). The species M. k. kossmati had been found in the Ganuza section studied (GZ 57 and GZ 4; Figure 4) and in a neighbouring section ( 5 Inoceramus (Mytiloides ) goppelnensis goppelnensis ; Lamolda et al ., 1989, text-fig. 2). It is present in Lower Turonian deposits at Bastide de Virac, Gard, southeast France (Lo´ pez, in prep.), and at Cassis (Jolet et al ., 1995). Tro¨ ger (1989) gave its stratigraphical range in western Europe as lower Middle Turonian. This wider range is in agreement with data reported by Lo´ pez (1992) and Walaszczyk (1992), and correlates with middle and upper parts of the Watinoceras coloradoense Zone. Therefore, sample GZ 57 should be of earliest Turonian age, and we can conclude that M. submytiloides and M. wiedmanni associated with M. k. kossmati in sample GZ 4, just above M. nodosoides , represents a Lower Turonian assemblage. But the presence of only a few specimens of M. submytiloides in sample GZ 56 (1 m below GZ 57) does not allow us to distinguish between uppermost Cenomanian or lowermost Turonian in this bed.
7.3. Ammonites Euomphaloceras septemseriatum and Calycoceras naviculare are largely known as cosmopolitan species, characteristic of the Upper Cenomanian Metoicoceras geslinianum Zone elsewhere (Wright & Kennedy, 1990, p. 294 and Kennedy & Juignet, 1981, p. 38, respectively). The ammonite fauna from samples G 22 to G 12 should belong to this Upper Cenomanian ammonite zone. The exact location of the C / T boundary cannot be identified by ammonites at Ganuza, but we recognize its approximate position to be very close to the FO of Kamerunoceras —a specimen of Kamerunoceras sp. was recorded from sample GZ 56—and level GZ 57 / 58, where Kamerunoceras calvertense occurs 2.5 m above. Kamerunoceras is a typical Turonian taxon, although there are occurrences in uppermost Cenomanian deposits, e. g., in bed 84 of the Bridge Creek Limestone Member of the Pueblo section, just 1 m below the FO of Watinoceras devonense (Kennedy & Cobban, 1991). Moreover, Kamerunoceras appears to have been derived from typical Upper Cenomanian E. septemseriatum (Wright & Kennedy, 1981, p. 56), which is recorded from both the Pueblo and Ganuza sections below the first occurrence of Kamerunoceras . The species K. calvertense , associated with Pseudaspidoceras flexuosum in a condensed bed, is known only in west Texas, USA and northern Chihuahua, Mexico (Kennedy et al ., 1987). These authors noted its primitive characteristics, which are close to Upper Cenomanian Acanthoceratinae. Successive upwards occurrences of Kamerunoceras sp. and M. submytiloides (GZ 56), M. k. kossmati (GZ 57) and K. calvertense (GZ 57 / 58; Figures 4, 10) are similar to those in the Pueblo sequence, where Kamerunoceras sp. is associated with N. judii , and abundant Mytiloides (M. hattini ; Elder, 1991; M . wiedmanni , Bengtson, 1996), all below the FO of W. devonense , which is overlain by a P.
Figure 9. a, Thomelites sp. aff. hancocki , lateral view of the specimen PalUAB no. 47894, G 12; b, Euomphaloceras septemseriatum , ventral view of the specimen PalUAB no. 12419, G 22; c, Kamerunoceras calvertense , ventral view of the specimen PalUAB no. 12415, GZ 57-58; d, Mammites nodosoides , lateral view of the specimen PalUAB no. 47860, GZ 3; e, Choffaticeras pavillieri , lateral view of the specimen PalUAB no. 12122, GZ 6 top; f, Lecointriceras fleuriasianum , lateral view of the specimen PalUAB no. 12116, GZ 6b. Scale bar 5 1 cm.
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Figure 10. Relative position of key bioevents associated with the C / T boundary according to several authors. Vertical scale arbitrary (Ganuza, this paper; Shakespeare Cliff after Lamolda et al ., 1994; Dover after Jarvis et al ., 1988; Pueblo after Kennedy & Cobban, 1991 and Bengtson, 1996; Texas after Kennedy et al ., 1987; B 5 Boulonnais after Robaszynski et al ., 1980).
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flexuosum assemblage, the latter recording the species K. calvertense in West Texas (see above). Furthermore, in the Ganuza section (Figures 4, 10) Q. gartneri and M. nodosoides occur above K. calvertense . Hence, the GZ 57 / 58 level with K. calvertense should be lowermost Turonian, and GZ 56, 2.5 m lower with Kamerunoceras sp. and M. submytiloides , should be uppermost Cenomanian; this is consistent with the FO of M . k . kossmati between both levels (see 7.2 above). Lower Turonian sediments can be identified by species such as M. nodosoides and S . ( J .) obliquus . The latter species cannot be used for worldwide correlation as it is endemic to the Bascocantabrian Region. It has been found in localities at Arenillas and Soncillo, Burgos (Karrenberg, 1935, p. 136), Puentedey, Burgos (Santamarı´a, 1995, p. 47) as well as in the Ganuza section, but M. nodosoides is characteristic of its nominate zone, from late Early Turonian (Chancellor et al ., 1994). Therefore, we have an interval in the lowermost Turonian with very few ammonites, which is similar to Kalaat Senan, Tunisia (Robaszynski et al ., 1990), central Tunisia (Chancellor et al., 1994) and Touraine, France (Hancock et al ., 1993). K. puebloense and C. pavillieri occur in the Pueblo section below the FO of M. nodosoides (Figure 10), and C. pavillieri is recorded from the Thomasites rollandi Zone in central Tunisia (Chancellor et al ., 1994), which is also below the FO of M. nodosoides . The Turonian species Lecointriceras fleuriasianum has been reported from several localities in Lower Turonian beds (Lamolda et al ., 1989). We have not, therefore, recognized a definitive Middle Turonian ammonoid assemblage.
8. Conclusions The Cenomanian / Turonian boundary in the Ganuza section should lie within the 1-m-thick interval between samples GZ 56 and GZ 57. A good proxy for this boundary is the FOs of both Mytiloides kossmati kossmati and Kamerunoceras spp. Successive LOs of Lithraphites acutus , Rotalipora cushmani and Microstaurus chiastius , and FOs of Quadrum intermedium , Helvetoglobotruncana praehelvetica and Quadrum gartneri characterize the completeness of C / T transitions and may be a good proxy for the C / T boundary. The FO of H. praehelvetica in levels coeval with Kamerunoceras sp. and Mytiloides submytiloides , and below FO of M. k. kossmati, is a good index for characterizing the C / T boundary. Although earlier records of Q. gartneri might have been overlooked, its FO is recorded below Mamnites nodosoides but above Mytiloides submytiloides , H . praehelvetica , M. kossmati kossmati and Kamerunoceras calvertense . It is, therefore, a good proxy for the C / T boundary.
Acknowledgements We are indebted to David Batten, Chris Paul and an anonymous referee for their critical remarks, which have improved this manuscript. The financial support for this project to D. Peryt was provided by a research grant of the Programa de Perfeccionamiento y Movilidad del Personal Investigador / 1994 of the Basque Government. The SEM photographs of the foraminifera were taken in the Institute of Palaeobiology, Polish Academy of Sciences, Warsaw. This is a contribution to the DGICYT project nos. PS90-91 and PB95-0505-C02, MEC.
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Appendix The fossils used in this study have been deposited in the collections of M.A. Lamolda (microfossils) and the Departament de Geologia, Universita`t Autonoma de Barcelona (macrofauna). List of species mentioned in text with authors and dates Nannofossils Allemanites striatus (Stradner), 1963 (Arkhangelskiella ) Axopodorhabdus albianus (Black), 1967 (Podorhabdus ) Braadurosphaera regularis Black, 1973 Broinsonia enormis (Shumenko), 1968 (Arkhangelskiella ) B. signata (Noe¨l), 1969 (Aspidolithus ) Corollithion kennedyi Crux, 1981 C. signum Stradner, 1963 Cretarhabdus conicus Bramlette & Martini, 1964 Cribrosphaerella ehrenbergii (Arkhangelsky), 1912 (Cribrosphaera ) Discorhabdus ignotus (Gorka), 1957 (Tremalithus ) Eiffellithus turriseiffelii (Deflandre), 1954 (Zygolithus) Eprolithus eptapetalus Varol, 1992 E. floralis (Stradner), 1962 (Lithastrinus ) E. octopetalus Varol, 1992 Gartnerago obliquum (Stradner), 1963 (Arkhangelskiella ) Glaukolithus compactus (Bukry), 1969 (Zygodiscus ) Haqius circumradiatus (Stover), 1966 (Coccolites ) Helicolithus traveculatus (Gorka), 1957 (Discolithus ) Lithraphidites acutus Verbeek & Manivit, 1977 L. carniolensis Deflandre, 1963 Loxolithus armilla (Black), 1959 (Cyclolithus) Mannivitella pemmatoidea (Deflandre), 1965 (Cricolithus ) Microrhabdulus belgicus Hay & Towe, 1963 M. decoratus Deflandre, 1959 Microstaurus chiastius (Worsley), 1971 (Helenea ) Nannoconus elongatus Bro¨ nnimann, 1955 N. multicadus Deflandre & Deflandre-Rigaud, 1959 N. truitti truitti Bro¨ nnimann, 1955 Prediscosphaera avitus (Black), 1973 (Deflandrius ) P. cretacea (Arkhangelsky), 1912 (Coccolithophora ) P. ponticula Bukry, 1969 P. spinosa (Bramlette & Martini), 1964 (Deflandrius ) Quadrum gartneri Prins & Perch-Nielsen, 1977 Q. intermedium Varol, 1992 Raghodiscus achlyostaurion (Hill), 1976 (Parhabdolithus ) R. angustus (Stradner), 1963 (Parhabdolithus ) R. asper (Stradner), 1963 (Discolithus ) Rotelapillus laffittei (Noe¨l), 1957 (Stephanolithion ) Stoverius achylosus (Stover), 1966 (Chiphragmalithus ) Tranolithus exiguus Stover, 1966 T. gabalus Stover, 1966 T. minimus (Bukry), 1969 (Zygodiscus) T. phacelosus Stover, 1966 Watznaueria barnesae (Black), 1969 (Tremalithus ) W. biporta Bukry, 1969 W. ovata Bukry, 1969 Zeugrhabdotus acanthus Reinhardt, 1965 Z. elegans (Gartner), 1968 (Zygodiscus ) Z. embergeri (Noe¨l), 1958 (Discolithus ) Foraminifera Dicarinella algeriana (Caron), 1966 (Praeglobotruncana ) D. elata Lamolda, 1977
Fossils in the Upper Cenomanian – Lower Turonian
D. hagni (Scheibnerova), 1962 (Praeglobotruncana ) D. imbricata (Mornod), 1949 (Globotruncana ) D. oraviensis (Scheibnerova), 1960 (Praeglobotruncana ) Globigerinelloides bentonensis (Morrow), 1934 (Anomalina ) Guembelitria cenomana Keller, 1935 Hedbergella delrioensis (Carsey), 1926 (Globigerina ) H. planispira (Tappan), 1940 (Globigerina ) H. simplex (Morrow), 1934 (Hastigerinella ) Helvetoglobotruncana helvetica (Bolli), 1945 (Globotruncana ) H. praehelvetica (Trujillo), 1960 (Rugoglobigerina ) Heterohelix moremani (Cushman), 1938 (Guembelina ) Praeglobotruncana aumalensis (Sigal), 1952 (Globigerina ) P. delrioensis (Plummer), 1931 (Globorotalia ) P. gibba Klaus, 1960 P. stephani (Gandolfi), 1942 (Globotruncana ) Rotalipora cushmani (Morrow), 1934 (Globorotalia ) R. greenhornensis (Morrow), 1934 (Globorotalia ) Whiteinella aprica (Loeblich & Tappan), 1961 (Ticinella ) W. archaeocretacea Pessagno, 1967 W. baltica Douglas & Rankin, 1969 W. brittonensis (Loeblich & Tappan), 1961 (Hedbergella ) W. paradubia (Sigal), 1952 (Globigerina ) Inoceramids Inoceramus gr. labiatus (Schlotheim), 1813 (Ostracites ) Mytiloides hattini Elder, 1991 M. hercynicus (Petrascheck), 1903 (Inoceramus ) M. kossmati ganuzaensis Lo´ pez, 1992 M. kossmati kossmati (Heinz), 1933 (Striatoceramus ) M. mytiloides (Mantell), 1822 (Inoceramus ) M. submytiloides (Seitz), 1934 (Inoceramus ) M . cf. transiens (Seitz), 1934 (Inoceramus ) M. wiedmanni Lo´ pez, 1992 Ammonites Calycoceras naviculare (Mantell), 1822 (Ammonites ) Choffaticeras pavillieri (Pervinquie`re), 1907 (Pseudotissotia ) Euomphaloceras septemseriatum (Cragin), 1893 (Scaphites ) Fagesia pachydiscoides Spath, 1925 F . aff. rudra (Stoliczka), 1865 (Ammonites ) Kamerunoceras calvertense (Powell), 1963 (Acanthoceras ) K. puebloense (Cobban & Scott), 1972 (Kanabiceras ) Lecointriceras fleuriasianum (D’Orbigny), 1841 (Ammonites ) Mammites nodosoides (Schlu¨ ter), 1871 (Ammonites ) Neocardioceras judii (Barrois & Guerne), 1878 (Ammonites ) Pachydesmoceras linderi (Grossouvre), 1894 (Pachydiscus ) Pseudaspidoceras flexuosum Powell, 1963 Spathithes (Jeanrogericeras ) obliquus (Karrenberg), 1935 (Mammites ) Thomelites sp. aff. T. hancocki Juignet & Kennedy, 1976 Watinoceras devonense Wright & Kennedy, 1981
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Fossil occurrences in the Upper Cenomanian – Lower Turonian at Ganuza, northern Spain: an approach to Cenomanian / Turonian boundary chronostratigraphy1 Marcos A. Lamolda, *Amalia Gorostidi, †Ricard Martı´nez, †Gregori Lo´ pez and ‡Danuta Peryt * Facultad de Ciencias-UPV , Campus de Lejona , 48940 Lejona , Spain † Dept. de Geologia , Fac. de Ciencias , Univ. Autonoma , Campus de Bellaterra , 08193 Bellaterra , Spain ‡ Institute of Palaeobiology , Polish Academy of Sciences , Al. Zwirki i Wigury 93 , 02-089 Warsaw , Poland Revised manuscript accepted 22 January 1997
An Upper Cenomanian to Lower Turonian section has been sampled in the vicinity of Ganuza, northern Spain. Ammonoids, inoceramids and microfossils including foraminifera and calcareous nannofossils have been studied. We recognize three planktonic foraminiferal biozones: the Rotalipora cushmani , Whiteinella archaeocretacea and Helvetoglobotruncana helvetica Zones. We also characterize the Eiffellithus turriseiffelii and Quadrum gartneri Zones, based on nannofossil biostratigraphy. Macrofaunal occurrences are scarce but allow us to characterize the Metoicoceras geslinianum and Mammites nodosoides Zones, and two inoceramid assemblages. In the Rotalipora cushmani Zone the following sequence of biohorizons is recorded from bottom to top: (a) last occurrence (LO) of Corollithion kennedyi ; (b) LO of Rotalipora greenhornensis ; (c) LO of Axopodorhabdus albianus ; (d) first occurrence (FO) of Euomphaloceras septemseriatum , (e) LO of Lithraphidites acutus ; (f) LO of Rotalipora cushmani. In the Whiteinella archaeocretacea Zone the sequence of events is as follows: (g) FO of Calycoceras naviculare ; (h) LO of Microstaurus chiastius ; (i) FO of Quadrum intermedium ; (j) FO of Helvetoglobotruncana praehelvetica ; (k) FOs of Kamerunoceras sp. and Mytiloides submytiloides ; (l) FO of Mytiloides kossmati kossmati ; (m) FO of Kamerunoceras calvertense ; (n) FO of Quadrum gartneri ; (o) FO of Mammites nodosoides ; (p) FO of Mytiloides mytiloides . The top of this zone is marked by the FO of Helvetoglobotruncana helvetica. A possible Cenomanian-Turonian (C / T) boundary can be drawn between FOs of Kamerunoceras sp. and Mytiloides submytiloides and the FO of Mytiloides kossmati kossmati . Successive FOs of H. praehelvetica and Q. gartneri are also good proxies for the C / T boundary. ÷ 1997 Academic Press Limited KEY WORDS: Cenomanian / Turonian boundary; chronostratigraphy; planktonic foraminifera; nannofossils; inoceramids; ammonoids; northern Spain.
1. Introduction The stratigraphic succession at Ganuza, northern Spain, is a composite section of an expanded Cenomanian – Turonian (C / T) transition where the Whiteinella archaeocretacea Zone is about 45 – 50 m thick. It is located to the west of Estella, in the eastern Bascocantabrian Region (Figure 1). There is no evidence of stratigraphic gaps in the section which consists of an alternation of marl, marly limestone and limestone, with marl becoming more common towards the top, and some silty beds occurring towards the base. The sediments were deposited in a middle-outer shelf environment, according to the ostracod and foraminifera assemblages recovered (Colin et al ., 1982; Lamolda & Peryt, 1995). The macrofauna, microfauna and calcareous nannofossil biostratigraphy allows us to 1
Contribution to IGCP Project 362: Tethyan and Boreal Cretaceous.
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Figure 1. Location of the Ganuza section in northern Spain.
recognize several key events (according to Birkelund et al ., 1984) relating to C / T boundary definition. A summary of the stratigraphy and regional geology is given in Lamolda (1982). Macrofaunal assemblages were described by Wiedmann (1980) and Lamolda et al . (1989) from part of the Ganuza sections. Additional data on inoceramids and ammonoids were provided by Lo´ pez (1990) and Santamarı´a (1991) respectively. Lamolda & Peryt (1995) described the detailed biostratigraphy of the Upper Cenomanian of the section, and noted that bottom water conditions at the time of deposition of the uppermost part of Rotalipora cushmani Zone were dysaerobic. This correlates with the worldwide Cenomanian / Turonian Boundary Event (CTBE), which is also defined by nannofossil events in the section studied (Lamolda & Gorostidi, 1996). In a similar section at Menoyo, 70 km west of Ganuza, both nannofossil assemblages and a d 13C excursion have been discussed (Paul et al ., 1994). The Menoyo section provides a continuous sequence through the C / T transition in outer shelf and upper bathyal facies—limestone and marl alternations, but it is very poor in macrofauna. Lamolda (1978) noted occurrences of Inoceramus gr. labiatus and Mammites sp. Recently, we have found inoceramid specimens belonging to Mytiloides wiedmanni . All of the macrofauna is of Early Turonian age, being recorded between the first occurrences (FOs) of Quadrum gartneri and Helvetoglobotruncana helvetica . The Ganuza section represents deposition on a subsiding platform, when more than 2000 m of sediments accumulated during the Cenomanian and Turonian (Lamolda, 1982). Last occurrences (LOs) of the planktonic foraminifera
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Rotalipora greenhornensis and R. cushmani and the FO of the nannofossil species Q. gartneri are events recognized worldwide and are commonly used for correlation. Comparison of bed thicknesses between these events in the Ganuza section with coeval sections elsewhere which are considered to be the most expanded and complete record of the C / T boundary, has revealed that the Ganuza succession is about five times thicker than that at Pueblo, Colorado (USA), seven times that at Dover, southeast England (Lamolda & Peryt, 1995), and twice that at Eastbourne, southern England (Lamolda et al ., 1996). Therefore, the Upper Cenomanian and lowermost Turonian succession at Ganuza is particularly complete. In addition, its rich macro- and microfossil record makes this section especially suitable for characterizing the C / T boundary. 2. Material and methods The section at Ganuza is exposed on both sides of the road, 200 – 300 m south of Ganuza village. It is a composite section (Figure 2) whose lower and upper parts could have some levels in common; they are separated by a small fault. The succession comprises about 15 cycles of limestone and marl alternations. This cyclicity is also found in sections at Menoyo (Paul et al ., 1994) and Dover (Lamolda et al ., 1994). The lower part of the section studied, G (Figure 2), consists of two marly / silty and two calcareous sequences. At the bottom there is a 16.5-m-thick sequence of siltstone and marl with interbeded limestone as thin layers and lenticular bodies. The sequence is overlain by a 6.1-m-thick calcareous series composed mainly of limestones and nodular limestones interbedded with thin marlstones and siltstones. Higher up the section there is a 3.1-m-thick series of marly siltstone with irregular and scarce limestone interbeds. The top 4.3 m of the section comprises limestone and marlstone alternations. GS is a similar section about 100 m to the south of G. Both sections are on the east side of the road. The two uppermost G units are partly present in the base of the lower part of the GZ succession (Figure 2), although an accurate correlation between G and GZ has not been possible. The G sequence was dated as middle-late Late Cenomanian by means of macrofauna and foraminifera (Wiedmann, 1980). Lamolda et al . (1989, fig. 2) defined ‘A’ and lower ‘B’ units in the sequence, which were dated as Late Cenomanian by means of planktonic foraminifera. The GZ succession consists of 40 m of 10 or 11 cycles of marl and limestone alternations. The GZ part was dated by Wiedmann (1980) as Early Turonian on the basis of planktonic foraminifera. Neither he nor Lamolda et al . (1989) found macrofauna in GZ, but in the upper part, we have found foraminiferal assemblages characteristic of the Whiteinella archaeocretacea Zone of probable Early Turonian age according to its correlation with other neighbouring sections. The first macrofaunal data from the upper part of GZ sequence were reported by Lo´ pez (1990) and Santamarı´a (1991). Forty-three samples from a 70-m-thick sequence of the Ganuza section (the G and GZ parts), were studied for foraminifera. Four to five hundred specimens from the .100 m m size fraction were picked and for each sample all species were identified. Forty-four samples in the GS and GZ parts were studied for nannofossils using a light microscope at a magnification of 31000 and quantitative procedures described by Lamolda et al . (1994). Counting of 500 nannoliths per sample gives a 99% ( p , 0.01) confidence level of not overlooking
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Figure 2. Composite section at Ganuza to show lithology, location of micropalaeontological samples, and macrofaunal occurrences.
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any taxon present at 1% or more of the total population (Denisson & Hay, 1967). The macrofaunal assemblages were checked bed by bed throughout the section. Although generally sparsely distributed, some beds contain many fossils, such as sample GZ 4, which records an inoceramid event, and G 22, GZ 5 and GZ 6, which yield numerous ammonoids. 3. Nannofossil biostratigraphy The abundance of nannoliths in the samples studied proved to be low, with only 1 nannolith per field of view (Nan. / FOV) or less. Their preservation is also poor. 54 species have been identified. The number of taxa per sample is between 15 and 30. The assemblages are dominated by six taxa: Eiffellithus turriseiffelii , Eprolithus floralis , Prediscosphaera spp., Retecapsa spp., Rhagodiscus achlyostaurion and Watznaueria barnesae (Figure 3). Each of these comprises more than 5% of the assemblages. W. barnesae comprises 40 – 50%. In the uppermost Cenomanian several major assemblage changes are recognised. These include LOs of, from the base of the section upwards (Figures 3, 4), Corollithion kennedyi (sample GS 12; 13.2 m), Axopodorhabdus albianus (GS 16; 15.7 m), Lithraphidites acutus (GS 18; 18.6 m) and Microstaurus chiastius (GZ 73; 6.3 m 5 approximately 13.4 m above GS 18). First occurrences of biostratigraphically important taxa include Quadrum intermedium (GZ a; 7.3 m), Eprolithus octopetalus and Nannoconus multicadus (GZ 58; 14.6 m), and Q. gartneri (GZ 1; 16.5 m). Rhagodiscus asper occurs throughout the section and overlaps the range of Q. gartneri , Eprolithus octopetalus and E. eptapetalus (Gorostidi, 1993, pp. 174, 175). Nannofossils are less common in the lower part, with a minimum at the level of the Rotalipora cushmani extinction, about 3 m above the LO of Lithraphidites acutus (Figure 4). The assemblages recovered are similar to those reported from Menoyo (Gorostidi & Lamolda, 1991; Paul et al ., 1994), southeast England (Crux, 1982; Jarvis et al ., 1988; Lamolda et al ., 1994), and various localities in Northern Europe and North America (Bralower, 1988). At Ganuza ‘blooms’ of Eprolithus floralis occur above the FO of Q. gartneri , comprising up to 32% of the total assemblage, which is even greater than has been found in the Dover (10%) and Menoyo (18%) sections. We found Crux’s (1982) biozonation, established in southeast England, to be appropriate for our assemblages (Lamolda & Gorostidi, 1996). Two biozones are partly distinguished, the Eiffellithus turriseiffelii and Quadrum gartneri Zones. The former is characterized by the association of Eiffellithus turriseiffelii , Eprolithus floralis , Glaukolithus compactus , Prediscosphaera avitus , P. cretacea , Retecapsa spp., Rhagodiscus achlyostaurion , Tranolithus phacelosus , Watznaueria barnesae , W. biporta and Zeugrhabdotus embergeri . LOs of Corollithion kennedyi , Axopodorhabdus albianus , Lithraphidites acutus and Microstaurus chiastius indicate that the Upper Cenomanian sequence is complete and their order of disappearance is similar to those in other sections (Figures 3, 4) (Lamolda & Gorostidi, 1996). This sequence of bioevents is important for the biostratigraphical characterization of the uppermost Cenomanian and the C / T boundary. Furthermore, FOs of Quadrum intermedium (GZ a; 7.3 m) (Paul et al ., 1994), and Nannoconus multicadus (GZ 58; 14.6 m) (Deres & Ache´ rite´ guy, 1980; Zeighampour, 1981; Crux, 1982), enhance correlation and completeness of this C / T transition. In contrast the LO of Allemanites striatus , Rhagodiscus
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Figure 3. Range chart for calcareous nannofossils from the Ganuza section. Abundance: C 5 1 – 10 Nan. / FOV; R 5 1 Nan. / 1 – 10 FOV. Preservation: F 5 fair; P 5 poor.
achlyostaurion , R. angustus , and R. asper cited by Crux (1982) in the English Upper Cenomanian, are recorded from Lower Turonian or younger deposits in northern Spain (Gorostidi, 1993). The lower boundary of the Quadrum gartneri Zone is defined by the first occurrence of the nominate taxon (sample GZ 1; 16.5 m), which overlies the FO of Eprolithus octopetalus (GZ 58; 14.6 m), a good indicator of the C / T boundary
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Figure 4. Ranges of planktonic foraminifera, ammonoids and inoceramids, and nannofossil event locations.
(Varol, 1992). Its lower part is characterized by the taxa E. turriseiffelii , E. floralis , G. compactus , Nannoconus spp., P. cretacea , Retecapsa spp., R. achlyostaurion , T. phacelosus , W. barnesae , W. biporta and Z. embergeri. The main differences from the Eiffellithus turriseiffelii Zone assemblages are higher proportions of P. cretacea
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and Nannoconus spp., especially the latter, which is rare in the Upper Cenomanian and increases up to 3 – 9% of the total in Turonian assemblages, even higher than at Menoyo (3%; Gorostidi, 1993, p. 232). Also, E. floralis is present in higher proportions in this Turonian material, usually more than 10% (between 50 and 160 specimens counted per sample studied), whereas in the Upper Cenomanian it is less than this (between 1 and 50 specimens per sample studied). In contrast, P. avitus decreases in abundance from 5% to less than 1%. The LO of R. asper has been cited as an important indicator of the C / T boundary (Crux, 1982; Jarvis et al ., 1988; Lamolda et al ., 1994), but at Ganuza this species occurs throughout the section, and at Menoyo its LO is in Lower Turonian deposits (Paul et al ., 1994). The data from northern Spain agree better with the probable events of Bralower (1988) and with results from Kalaat Senan in Tunisia (Gartner in Robaszynski et al ., 1990). The LO of R. asper is probably diachronous depending on paleolatitude. It can no longer be regarded as biostratigraphically useful, but may have biogeographical and palaeoecological significance (Lamolda & Gorostidi, 1996). 4. Foraminifera The diversity of planktonic foraminifera is low to moderate. Abundances are highly variable throughout the Ganuza section. In the Upper Cenomanian (samples G 33 to GZ 54) their contribution to the total foraminiferal assemblage varies from 12 – 80%; in the lowermost Turonian these values are very high and almost stable at 72 – 88%. The Late Cenomanian changes in planktonic / benthonic (P / B) ratio probably reflect sea-level fluctuations and indicate an inner to outer shelf environment; the high P / B ratio in the upper part of the section suggests a rise in sea level during the latest Cenomanian and earliest Turonian to outer shelf depths. In terms of palaeoecology the composition of the planktonic foraminiferal fauna from the Ganuza section shows that the sampled interval can be divided into three parts: (1) A lower part from 4.2 – 25.8 m (samples G 33 to G 11; Figure 2) characterized by mixed, diverse assemblages, with a high proportion of keeled forms, such as the genera Rotalipora and Praeglobotruncana , and in the top part of this interval, Dicarinella . (2) A relatively short interval approximately 11.6 m thick (samples G 11 to GZ 56) characterized by a temporary, almost complete, disappearance of keeled forms from the assemblages. Dicarinella spp. are very rare scarce. They may be found with rare specimens of Praeglobotruncana spp. Low diversity planktonic foraminiferal assemblages are dominated by non-keeled, globular forms—mainly hedbergellids. This interval corresponds to the benthic faunules III and IV of Lamolda & Peryt (1995) which are characteristic of low-oxygen bottom waters. (3) An upper part approximately 27.5 m thick (samples GZ 56 to GZ 8) in which planktonic foraminifera diversify again and become very abundant; both keeled and non-keeled forms occur. Within keeled morphogroups Dicarinella spp. dominate. The change in morphotypic composition of planktonic foraminiferal fauna, e.g., the extinction of species of Rotalipora and almost complete disappearance from assemblages of Dicarinella spp., probably reflect changes in palaeoceanographic conditions related to the CTBE.
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The following planktonic foraminiferal events were identified in stratigraphic order from bottom upwards: LO of Rotalipora greenhornensis , sample G 26 (13.6 m); FO of Dicarinella spp., sample G 19 (19.4 m); LO of Rotalipora cushmani , sample G 14 (22.2 m); FO of Helvetoglobotruncana praehelvetica , sample GZ 53 (9.4 m 5 13.3 m above G 14); FO of Helvetoglobotruncana helvetica , sample GZ 8 (38.8 m). The studied interval comprises the uppermost part of the Rotalipora cushmani Zone, which is characterized by occurrences of different species of Dicarinella , mainly Dicarinella algeriana (Figure 7s, t) and D. imbricata (Figure 7q, r), but also D. elata (Figure 7i, j), D. hagni (Figure 7l – n), D. oraviensis (Figure 6q, r), Globigerinelloides bentonensis (Figure 5q, r), Guembelitria cenomana (Figure 5t), Hedbergella delrioensis (Figure 7k), H. planispira (Figures 5g, h; 7o), H. simplex (Figure 5a, b), Heterohelix moremani (Figure 5p), Praeglobotruncana aumalensis (Figure 6d, h), P. delrioensis (Figure 7c, d), P. gibba (Figure 6k, l, o, p), P. stephani (Figure 6s, t), Rotalipora greenhornensis (Figure 6a, c), and common taxa such as Rotalipora cushmani (Figure 6e, g), Whiteinella aprica (Figure 5i, j), W. archaeocretacea (Figure 5o), W. baltica (Figure 5k, l), W. brittonensis (Figure 5c, d, m, n), and W. paradubia (Figure 5e, f), mainly in the upper part of the Rotalipora cushmani Zone. The Whiteinella archaeocretacea Zone is dominated by the hedbergellids Hedbergella spp. and Whiteinella spp., and a few Praeglobotruncana spp. Rare Dicarinella spp. are also found in the lower and middle parts (uppermost Cenomanian) of this zone. Main differences from the underlying zone are occurrences of Helvetoglobotruncana praehelvetica (Trujillo) (Figure 6m, n) in most samples from the GZ sequence (Figures 2, 4), and no occurrences of rotaliporids, the LO of which marks the top of the Rotalipora cushmani Zone. The FO of the species Helvetoglobotruncana helvetica (Figures 6i, j; 7a, b), lies in sample GZ 8, at the top of the section studied. Therefore, the Whiteinella archaeocretacea Zone has a complete biostratigraphic record.
5. Inoceramids Inoceramid faunas are not abundant in the C / T transition at Ganuza. No characteristic Cenomanian inoceramid assemblages have been found. There are five levels in the Turonian with a record of inoceramids, and a lowermost level with Mytiloides submytiloides (Figure 8b) and Mytiloides sp. (sample GZ 56; 11.6 m), of doubtful age but very close to the C / T boundary. It is possible to characterize two assemblages, the lower of which is a typical earliest Turonian inoceramid association.
5.1. Mytiloides submytiloides Assemblage This is the oldest inoceramid assemblage recognized at Ganuza. It is defined by the first occurrence of the genus Mytiloides , and in particular of specimens of M. submytiloides and Mytiloides sp. (sample GZ 56), and M. kossmati kossmati (GZ 57, 1 m above GZ 56; Figures 4; 8c). These species are associated with M. wiedmanni (Figure 8d) and M. cf. kossmati kossmati 8.4 m higher up the section (sample GZ 4; Figure 4), which records an inoceramid event.
Figure 5. a, b, Hedbergella simplex , G 26; c, d, Whiteinella brittonensis , G 26; e, f, W. paradubia , G 31; g, h, H. planispira (Tappan), G 31; i, j, W. aprica , GZ 8; k, l, W. baltica , GZ 8; m, n, W . brittonensis , G 31; o, W. archaeocretacea , G 26; p, Heterohelix moremani , GZ 53; q, r, Globigerinelloides bentonensis , G 23; s, H. sp., GZ 60; t, Guembelitria cenomana , G 23. Scale bar 5 100m m.
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5.2. Mytiloides kossmati ganuzaensis Assemblage The M. k. ganuzaensis Assemblage is defined by the FO of this subspecies. Unfortunately, it has not been found in the section studied, but it is frequent in nearby sections (Lo´ pez, 1994; Martı´nez et al ., 1996). By contrast, M . mytiloides (Figure 8a), which is also characteristic of this assemblage, is present (samples GZ 6 and GZ 6a, about 12 m above GZ 4; Figure 4). Therefore, the M. k. ganuzaensis Assemblage is probably indicated in the section studied, despite the absence of the nominate taxon. The uppermost inoceramid level with M. hercynicus (Figure 8e) and M . cf. transiens (sample GZ 8, Figure 4) occurs about 7 m above the latter. 6. Ammonoids Ammonites are rare in the section; only a few beds have yielded relatively rich assemblages (Figures 2, 4). It is difficult to distinguish a biozonation. Nevertheless, our data are of significance in the context of determining the C / T boundary. Typical Upper Cenomanian species are recorded between samples G 22 and G 12. The oldest species identified is Euomphaloceras septemseriatum (Figure 9b) from sample G 22 (17.3 m) associated to Calycoceras sp. and Forbeciceras sp. In sample G 12, 7.5 m above sample G 22, we found Protacanthoceras sp. and Thomelites sp. aff. hancocki (Figure 9a). A specimen of Calycoceras naviculare , not recorded in situ , was found about 10 m above the occurrence of E. septemseriatum . This cosmopolitan species is typical of the Metoicoceras geslinianum Zone in Europe, North Africa, Angola, Madagascar, Middle East, South India, Japan and the USA. A specimen of Kamerunoceras sp. was identified in sample GZ 56, and another specimen of Kamerunoceras calvertense (Figure 9c) in level GZ 57 / 58, 5 m and 2.5 m respectively below the FO of Q. gartneri (sample GZ 1), an index for the C / T boundary according to the proposals of Birkelund et al . (1984). A specimen of Spathites (Jeanrogericeras ) sp. was found in level GZ 59 (1 m below the FO of Q. gartneri ). All ammonites identified above the FO of Q. gartneri are clearly Turonian in age. In sample GZ 3, 2.5 m above the FO of Q. gartneri , we found specimens of Mammites nodosoides (Figure 9d) and Spathites (Jeanrogericeras ) obliquus . One metre above this sample Watinoceras sp. is recorded (GZ 4), and 1 m higher, there is a level with Kamerunoceras puebloense , Fagesia cf. pachydiscoides , F . aff. rudra and Thomasites gr. gongilensis -koulavicus . A rich ammonite assemblage 11 m above (samples GZ 6 and GZ 6a) was found to comprise Scaphites ? sp., Mammites ? sp., Pachydesmoceras linderi , F . cf. pachydiscoides , K. puebloense , Lecointriceras fleuriasianum (Figure 9f) and Fagesia sp. F. pachydiscoides and Choffaticeras pavillieri (Figure 9 e) are recorded 1.8 m above this assemblage. At a higher level still, 5 m above (GZ 8, at the top of the section studied), F . aff. rudra and C. pavillieri have been found. 7. Discussion Occurrences of relevant biostratigraphical indicators for the C / T transition in the Ganuza section are summarized in Figure 10. LOs of the foraminifers R. greenhornensis and R. cushmani , and the nannofossil A. albianus have been
Figure 6. a – c, Rotalipora greenhornensis , G 26; d, h, Praeglobotruncana aumalensis , G 31; e – g, R. cushmani , G 26; i, j, Helvetoglobotruncana helvetica , GZ 8; k, l, P. gibba Klaus, G 31; m, n, H. praehelvetica , GZ 8; o, p, P. gibba , GZ 8; q, r, Dicarinella oraviensis , GZ 8; s, t, P. stephani , GZ 8. Scale bar 5 100m m.
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calibrated with d 13C curves from the literature and unpublished data from the Ganuza G section (C. R. C. Paul, pers. comm.). The FOs of the nannofossil Q. gartneri have also been calibrated with d 13C data provide by Paul et al . (1994; following observations by Gale et al ., 1993). Lithostratigraphical correlation between Anglo-Paris Basin localities have been used, especially within the Plenus Marls.
7.1. Planktonic foraminifera and nannofossils Planktonic foraminifera and nannofossil occurrences characterize the C / T transition and its completeness (Lamolda et al ., 1994). Graphic correlation between Menoyo and Dover (Shakespeare Cliff) revealed the completeness and similar pattern of deposition in these localities (Paul et al ., 1994). This can be extended to the Ganuza section studied because of its similarity with Menoyo (Lamolda & Peryt, 1995; Lamolda & Gorostidi, 1996). Two of our bioevents, LOs of R. cushmani and A. albianus , were used by Gale et al . (1993) to compare bioevents and d 13C for Eastbourne and Pueblo, showing their usefulness on both sides of the Atlantic Ocean. Nevertheless, LOs of both R. greenhornensis and R. cushmani at Pueblo are younger than elsewhere (Figure 10). This rotaliporid persistence continues with the record of endemic Anaticinella in the Western Interior Basin (USA) during Late Cenomanian. This region was a refuge for rotaliporids, which had disappeared by this time elsewhere. Successive LOs of L. acutus , R. cushmani and M. chiastius , and FOs of Q. intermedium , H. praehelvetica and Q. gartneri , characterize sediments from Upper Cenomanian (Metoicoceras geslinianum Zone) to lowermost Turonian (Watinoceras devonense Zone) All occurred during the d 13C excursion of the C / T transition. Unfortunately, these bioevents have not been well documented in the proposed C / T boundary stratotype at the Rock Canyon Anticline section, Pueblo (Bengtson, 1996) which, by contrast, favours macrofaunal events. 7.2. Inoceramids The first occurrence of the genus Mytiloides is useful for recognizing the C / T boundary (Seibert, 1979; Tro¨ ger, 1981; Birkelund et al ., 1984). On a broad scale, the basal Turonian of North America and Europe is characterized by occurrences of M. submytiloides . Tro¨ ger (1989) cited his Zone 8 (Lower Turonian) as the stratigraphical range of this species. This species has also been found in southeast France (Jolet et al ., 1995) associated with M. kossmati ganuzaensis , which is a Lower Turonian species. Nevertheless, some authors, such as Harries et al . (1996), have considered that M. submytiloides may occur in uppermost Cenomanian rocks. M. wiedmanni is found in the GZ section at Ganuza just above the FO of M. nodosoides (Figures 4, 10). In addition, we have recently also found some specimens of M. wiedmanni in Lower Turonian rocks of the Menoyo section. This species in the lowermost Turonian of Saumurois, western France was referred to as Inoceramus hercynicus by Sornay (1982). Moreover, it has been identified in Cassis, southeast France (Lo´ pez, in prep.) associated with M. submytiloides , and in the lowermost Turonian of the Bohemian Basin (S. Cech, pers. comm., 1995). M. wiedmanni is a widespread species and also occurs at Pueblo (Bengtson, 1996), associated with M. hattini and very close to the LO of Neocardioceras judii and the FO of Kamerunoceras sp.—less than 1 m below Bed
Figure 7. a, b, Helvetoglobotruncana helvetica , GZ 8; c, d, Praeglobotruncana delrioensis , GZ a; e, f, P. sp., G 31; g, h, P. sp., GZ a; i, j, Dicarinella elata , GZ 57a; k, Hedbergella delrioensis , GZ 7; l, p, D. hagni , G 26; m, n, D. hagni , GZ 59; o, H. planispira , G 23; q, r, D. imbricata , GZ 7b; s, t, D. algeriana , GZ 8. Scale bar 5 100m m.
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Figure 8. a, Mytiloides mytiloides , right valve of the specimen PalUAB no. 38222; b, M. submytiloides , left valve of the specimen PalUAB no. 38711; c, M. kossmati kossmati , right valve of the specimen PalUAB no. 38847; d, M. wiedmanni , left valve of the specimen PalUAB no. 38764; e, M. hercynicus , left valve of the specimen PalUAB no. 38490. Scale bar 5 1 cm.
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86 of the proposed C / T boundary stratotype. Therefore, its range is from uppermost Cenomanian to Lower Turonian (Figure 10). The species M. k. kossmati had been found in the Ganuza section studied (GZ 57 and GZ 4; Figure 4) and in a neighbouring section ( 5 Inoceramus (Mytiloides ) goppelnensis goppelnensis ; Lamolda et al ., 1989, text-fig. 2). It is present in Lower Turonian deposits at Bastide de Virac, Gard, southeast France (Lo´ pez, in prep.), and at Cassis (Jolet et al ., 1995). Tro¨ ger (1989) gave its stratigraphical range in western Europe as lower Middle Turonian. This wider range is in agreement with data reported by Lo´ pez (1992) and Walaszczyk (1992), and correlates with middle and upper parts of the Watinoceras coloradoense Zone. Therefore, sample GZ 57 should be of earliest Turonian age, and we can conclude that M. submytiloides and M. wiedmanni associated with M. k. kossmati in sample GZ 4, just above M. nodosoides , represents a Lower Turonian assemblage. But the presence of only a few specimens of M. submytiloides in sample GZ 56 (1 m below GZ 57) does not allow us to distinguish between uppermost Cenomanian or lowermost Turonian in this bed.
7.3. Ammonites Euomphaloceras septemseriatum and Calycoceras naviculare are largely known as cosmopolitan species, characteristic of the Upper Cenomanian Metoicoceras geslinianum Zone elsewhere (Wright & Kennedy, 1990, p. 294 and Kennedy & Juignet, 1981, p. 38, respectively). The ammonite fauna from samples G 22 to G 12 should belong to this Upper Cenomanian ammonite zone. The exact location of the C / T boundary cannot be identified by ammonites at Ganuza, but we recognize its approximate position to be very close to the FO of Kamerunoceras —a specimen of Kamerunoceras sp. was recorded from sample GZ 56—and level GZ 57 / 58, where Kamerunoceras calvertense occurs 2.5 m above. Kamerunoceras is a typical Turonian taxon, although there are occurrences in uppermost Cenomanian deposits, e. g., in bed 84 of the Bridge Creek Limestone Member of the Pueblo section, just 1 m below the FO of Watinoceras devonense (Kennedy & Cobban, 1991). Moreover, Kamerunoceras appears to have been derived from typical Upper Cenomanian E. septemseriatum (Wright & Kennedy, 1981, p. 56), which is recorded from both the Pueblo and Ganuza sections below the first occurrence of Kamerunoceras . The species K. calvertense , associated with Pseudaspidoceras flexuosum in a condensed bed, is known only in west Texas, USA and northern Chihuahua, Mexico (Kennedy et al ., 1987). These authors noted its primitive characteristics, which are close to Upper Cenomanian Acanthoceratinae. Successive upwards occurrences of Kamerunoceras sp. and M. submytiloides (GZ 56), M. k. kossmati (GZ 57) and K. calvertense (GZ 57 / 58; Figures 4, 10) are similar to those in the Pueblo sequence, where Kamerunoceras sp. is associated with N. judii , and abundant Mytiloides (M. hattini ; Elder, 1991; M . wiedmanni , Bengtson, 1996), all below the FO of W. devonense , which is overlain by a P.
Figure 9. a, Thomelites sp. aff. hancocki , lateral view of the specimen PalUAB no. 47894, G 12; b, Euomphaloceras septemseriatum , ventral view of the specimen PalUAB no. 12419, G 22; c, Kamerunoceras calvertense , ventral view of the specimen PalUAB no. 12415, GZ 57-58; d, Mammites nodosoides , lateral view of the specimen PalUAB no. 47860, GZ 3; e, Choffaticeras pavillieri , lateral view of the specimen PalUAB no. 12122, GZ 6 top; f, Lecointriceras fleuriasianum , lateral view of the specimen PalUAB no. 12116, GZ 6b. Scale bar 5 1 cm.
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Figure 10. Relative position of key bioevents associated with the C / T boundary according to several authors. Vertical scale arbitrary (Ganuza, this paper; Shakespeare Cliff after Lamolda et al ., 1994; Dover after Jarvis et al ., 1988; Pueblo after Kennedy & Cobban, 1991 and Bengtson, 1996; Texas after Kennedy et al ., 1987; B 5 Boulonnais after Robaszynski et al ., 1980).
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flexuosum assemblage, the latter recording the species K. calvertense in West Texas (see above). Furthermore, in the Ganuza section (Figures 4, 10) Q. gartneri and M. nodosoides occur above K. calvertense . Hence, the GZ 57 / 58 level with K. calvertense should be lowermost Turonian, and GZ 56, 2.5 m lower with Kamerunoceras sp. and M. submytiloides , should be uppermost Cenomanian; this is consistent with the FO of M . k . kossmati between both levels (see 7.2 above). Lower Turonian sediments can be identified by species such as M. nodosoides and S . ( J .) obliquus . The latter species cannot be used for worldwide correlation as it is endemic to the Bascocantabrian Region. It has been found in localities at Arenillas and Soncillo, Burgos (Karrenberg, 1935, p. 136), Puentedey, Burgos (Santamarı´a, 1995, p. 47) as well as in the Ganuza section, but M. nodosoides is characteristic of its nominate zone, from late Early Turonian (Chancellor et al ., 1994). Therefore, we have an interval in the lowermost Turonian with very few ammonites, which is similar to Kalaat Senan, Tunisia (Robaszynski et al ., 1990), central Tunisia (Chancellor et al., 1994) and Touraine, France (Hancock et al ., 1993). K. puebloense and C. pavillieri occur in the Pueblo section below the FO of M. nodosoides (Figure 10), and C. pavillieri is recorded from the Thomasites rollandi Zone in central Tunisia (Chancellor et al ., 1994), which is also below the FO of M. nodosoides . The Turonian species Lecointriceras fleuriasianum has been reported from several localities in Lower Turonian beds (Lamolda et al ., 1989). We have not, therefore, recognized a definitive Middle Turonian ammonoid assemblage.
8. Conclusions The Cenomanian / Turonian boundary in the Ganuza section should lie within the 1-m-thick interval between samples GZ 56 and GZ 57. A good proxy for this boundary is the FOs of both Mytiloides kossmati kossmati and Kamerunoceras spp. Successive LOs of Lithraphites acutus , Rotalipora cushmani and Microstaurus chiastius , and FOs of Quadrum intermedium , Helvetoglobotruncana praehelvetica and Quadrum gartneri characterize the completeness of C / T transitions and may be a good proxy for the C / T boundary. The FO of H. praehelvetica in levels coeval with Kamerunoceras sp. and Mytiloides submytiloides , and below FO of M. k. kossmati, is a good index for characterizing the C / T boundary. Although earlier records of Q. gartneri might have been overlooked, its FO is recorded below Mamnites nodosoides but above Mytiloides submytiloides , H . praehelvetica , M. kossmati kossmati and Kamerunoceras calvertense . It is, therefore, a good proxy for the C / T boundary.
Acknowledgements We are indebted to David Batten, Chris Paul and an anonymous referee for their critical remarks, which have improved this manuscript. The financial support for this project to D. Peryt was provided by a research grant of the Programa de Perfeccionamiento y Movilidad del Personal Investigador / 1994 of the Basque Government. The SEM photographs of the foraminifera were taken in the Institute of Palaeobiology, Polish Academy of Sciences, Warsaw. This is a contribution to the DGICYT project nos. PS90-91 and PB95-0505-C02, MEC.
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Appendix The fossils used in this study have been deposited in the collections of M.A. Lamolda (microfossils) and the Departament de Geologia, Universita`t Autonoma de Barcelona (macrofauna). List of species mentioned in text with authors and dates Nannofossils Allemanites striatus (Stradner), 1963 (Arkhangelskiella ) Axopodorhabdus albianus (Black), 1967 (Podorhabdus ) Braadurosphaera regularis Black, 1973 Broinsonia enormis (Shumenko), 1968 (Arkhangelskiella ) B. signata (Noe¨l), 1969 (Aspidolithus ) Corollithion kennedyi Crux, 1981 C. signum Stradner, 1963 Cretarhabdus conicus Bramlette & Martini, 1964 Cribrosphaerella ehrenbergii (Arkhangelsky), 1912 (Cribrosphaera ) Discorhabdus ignotus (Gorka), 1957 (Tremalithus ) Eiffellithus turriseiffelii (Deflandre), 1954 (Zygolithus) Eprolithus eptapetalus Varol, 1992 E. floralis (Stradner), 1962 (Lithastrinus ) E. octopetalus Varol, 1992 Gartnerago obliquum (Stradner), 1963 (Arkhangelskiella ) Glaukolithus compactus (Bukry), 1969 (Zygodiscus ) Haqius circumradiatus (Stover), 1966 (Coccolites ) Helicolithus traveculatus (Gorka), 1957 (Discolithus ) Lithraphidites acutus Verbeek & Manivit, 1977 L. carniolensis Deflandre, 1963 Loxolithus armilla (Black), 1959 (Cyclolithus) Mannivitella pemmatoidea (Deflandre), 1965 (Cricolithus ) Microrhabdulus belgicus Hay & Towe, 1963 M. decoratus Deflandre, 1959 Microstaurus chiastius (Worsley), 1971 (Helenea ) Nannoconus elongatus Bro¨ nnimann, 1955 N. multicadus Deflandre & Deflandre-Rigaud, 1959 N. truitti truitti Bro¨ nnimann, 1955 Prediscosphaera avitus (Black), 1973 (Deflandrius ) P. cretacea (Arkhangelsky), 1912 (Coccolithophora ) P. ponticula Bukry, 1969 P. spinosa (Bramlette & Martini), 1964 (Deflandrius ) Quadrum gartneri Prins & Perch-Nielsen, 1977 Q. intermedium Varol, 1992 Raghodiscus achlyostaurion (Hill), 1976 (Parhabdolithus ) R. angustus (Stradner), 1963 (Parhabdolithus ) R. asper (Stradner), 1963 (Discolithus ) Rotelapillus laffittei (Noe¨l), 1957 (Stephanolithion ) Stoverius achylosus (Stover), 1966 (Chiphragmalithus ) Tranolithus exiguus Stover, 1966 T. gabalus Stover, 1966 T. minimus (Bukry), 1969 (Zygodiscus) T. phacelosus Stover, 1966 Watznaueria barnesae (Black), 1969 (Tremalithus ) W. biporta Bukry, 1969 W. ovata Bukry, 1969 Zeugrhabdotus acanthus Reinhardt, 1965 Z. elegans (Gartner), 1968 (Zygodiscus ) Z. embergeri (Noe¨l), 1958 (Discolithus ) Foraminifera Dicarinella algeriana (Caron), 1966 (Praeglobotruncana ) D. elata Lamolda, 1977
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D. hagni (Scheibnerova), 1962 (Praeglobotruncana ) D. imbricata (Mornod), 1949 (Globotruncana ) D. oraviensis (Scheibnerova), 1960 (Praeglobotruncana ) Globigerinelloides bentonensis (Morrow), 1934 (Anomalina ) Guembelitria cenomana Keller, 1935 Hedbergella delrioensis (Carsey), 1926 (Globigerina ) H. planispira (Tappan), 1940 (Globigerina ) H. simplex (Morrow), 1934 (Hastigerinella ) Helvetoglobotruncana helvetica (Bolli), 1945 (Globotruncana ) H. praehelvetica (Trujillo), 1960 (Rugoglobigerina ) Heterohelix moremani (Cushman), 1938 (Guembelina ) Praeglobotruncana aumalensis (Sigal), 1952 (Globigerina ) P. delrioensis (Plummer), 1931 (Globorotalia ) P. gibba Klaus, 1960 P. stephani (Gandolfi), 1942 (Globotruncana ) Rotalipora cushmani (Morrow), 1934 (Globorotalia ) R. greenhornensis (Morrow), 1934 (Globorotalia ) Whiteinella aprica (Loeblich & Tappan), 1961 (Ticinella ) W. archaeocretacea Pessagno, 1967 W. baltica Douglas & Rankin, 1969 W. brittonensis (Loeblich & Tappan), 1961 (Hedbergella ) W. paradubia (Sigal), 1952 (Globigerina ) Inoceramids Inoceramus gr. labiatus (Schlotheim), 1813 (Ostracites ) Mytiloides hattini Elder, 1991 M. hercynicus (Petrascheck), 1903 (Inoceramus ) M. kossmati ganuzaensis Lo´ pez, 1992 M. kossmati kossmati (Heinz), 1933 (Striatoceramus ) M. mytiloides (Mantell), 1822 (Inoceramus ) M. submytiloides (Seitz), 1934 (Inoceramus ) M . cf. transiens (Seitz), 1934 (Inoceramus ) M. wiedmanni Lo´ pez, 1992 Ammonites Calycoceras naviculare (Mantell), 1822 (Ammonites ) Choffaticeras pavillieri (Pervinquie`re), 1907 (Pseudotissotia ) Euomphaloceras septemseriatum (Cragin), 1893 (Scaphites ) Fagesia pachydiscoides Spath, 1925 F . aff. rudra (Stoliczka), 1865 (Ammonites ) Kamerunoceras calvertense (Powell), 1963 (Acanthoceras ) K. puebloense (Cobban & Scott), 1972 (Kanabiceras ) Lecointriceras fleuriasianum (D’Orbigny), 1841 (Ammonites ) Mammites nodosoides (Schlu¨ ter), 1871 (Ammonites ) Neocardioceras judii (Barrois & Guerne), 1878 (Ammonites ) Pachydesmoceras linderi (Grossouvre), 1894 (Pachydiscus ) Pseudaspidoceras flexuosum Powell, 1963 Spathithes (Jeanrogericeras ) obliquus (Karrenberg), 1935 (Mammites ) Thomelites sp. aff. T. hancocki Juignet & Kennedy, 1976 Watinoceras devonense Wright & Kennedy, 1981
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