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El Kef blind test IV results
mlr ELSEVIER
OGY
Marine Micropaleontology29 (1997) 65- 103
MicroNotes
El Kef blind test IV results Xabier Orue-etxebarria Paleontologia, Facultad de Ciencias, Vniversidad Del Pais Vasco, Apartado 644 Postakutxa, E-48080 Bilbao, Spain
Received 12 April 1996; accepted 12 June 1996
1. Methods Owing to the small size of some latest Cretaceous/earliest Tertiary species, two size-fractions were prepared of each sample: 40-63 km, and >63 wrn, this latter being the one to be analyzed for the blind test. A splitter was used to obtain a representative fraction of the larger size grade. From this fraction, depending on the richness of each sample, 250 to 500 specimens were separated to obtain the ratio between planktic and benthic species as well as the relative abundance for each species. A further personal step was the analysis of the whole sample to find and identify rare Maastrichtian species.
2. Results First, I present my own results with some discussion on several specific taxa, that are, in my opinion, not identified correctly by the others. Then I comment on the results of the other testers and compare them with my own.
2.1. Cretaceous samples As can be seen from the three samples from the end of the Cretaceous (Fig. lo), I found a total of 61 species of planktic foraminifera in the fraction of >63 pm, of which I identified 60 species, as compared with the 45-50 species reported by the other testers from the same samples. The difference
is because I examined the entire sample searching for the rare species. Between 73 and 80% of the total number of the specimens present in the samples correspond to different species of heterohelicids. Among these, the most abundant species is Heterohelix globulosa (Ehrenberg, 1840) whose specimens represent approximately 40% of the total. Several species are quite rare; among them are: Gublerina acuta de Klasz, 1953, Planoglobulina acervulinoides (Egger, 1899) Pseudotextularia elegans (Rzehak, 1891) Pseudotextularia inter-media de Klasz, 1953, Globotruncana dupeublei Caron et al., 1984, Globotruncana orientalis El Naggar, 1966, Globotruncanita angulata (Tilev, 1951) Globotruncanita conica (White, 1928), Rosita contusa (Cushman, 1926) Abathomphalus mayaroensis Bolli, 195 1, Heterohelix postsemicostata (Vasilenko, 1961) which is fairly common (1%) in sample 3809, and Globigerinelloides prairiehillensis Pessagno, 1967 among others. I found three or four small specimens of Abathomphalus mavaroensis in each of the samples from the Cretaceous, but only after examining the entire sample. The failure to find these rare species in a small sample (ca. 20 g) such as the one we testers analyzed, can lead to erroneous interpretations. For example, I did not find R. contusa in the last sample from the Cretaceous, but in a sample that I collected myself from 1 cm below the K/T boundary during the sampling in 1992, I did find several specimens.
0377-8398/97/$17.00 Copyright 0 1997 Elsevier Science B.V. All rights reserved. SSDI 0377-8398(96)00043-6
86
El Kef blind test/Marine
Micropaleontology
29 (1997) 65-103
El Kef blind test/Marine Micropaleontology 29 (1997) 65-103
Furthermore, two of the other testers did find R. contusa in their last Cretaceous sample. In my opinion therefore, all the species extend to the K/T boundary and there are no pre-boundary extinctions. In contrast, Canudo’s results show that 7 of 47 species disappear below the K/T boundary (Fig. 4); Olsson found only 3 of 44 species disappearing below the boundary (Fig. 6); and Masters reported that 15 of 52 species disappeared below the boundary (Fig. 5). Regarding the triseriated forms of small size, most of the specimens found in samples from the Cretaceous correspond to Guembelitria trifolia (Morozova, 1961) and not to Guembelitria cretuceu Cushman, 1933. These last two species, as well as Globotruncunellu curuvucuensis Smit, 1982, are more frequent in the fraction of ~63 pm that I have also analyzed. Moreover, in the fraction between 40 and 63 pm, I have also found Shuckoinu multispinutu (Cushman and Wickenden, 1930) and Hedbergellu hillebrundti (Orue-etxebania, 1985). The later was first described from the base of the Tertiary of the Sopelana section (Basque Country) and is therefore, one of the species surviving the massive extinction. 2.2. Tertiary samples The extinction event that occurred at the K/T boundary included more than 50% of the species existing at the end of the Maastrichtian (Fig. 10). These species disappear through zones PO and Pla. In the first two Tertiary samples, G. trifoliu is more abundant than G. cretuceu, but this ratio is reversed in sample 3802. In the three samples from the base of the Tertiary, I have found only two species characteristic of this age, one form assigned to Globoconusu conusu Khalilov, 1956 and one other included in Purvulurugoglobigerinu longiuperturu (Blow, 1979). Regarding this last species, I think that those forms identified as Globigerinu eugubinu Luterbacher and Premoli-Silva, 1964 are in most instances, both in El Kef and in any other sections, specimens of p longiuperturu because they present a distinct elongated aperture positioned on the front wall of the last formed chamber. In contrast, the original description of the holotype of G. eugubinu indicates the presence of an aperture on the umbilical position.
87
Furthermore, the holotype described by H.P. Luterbather (pers. commun.), does not have any elongated aperture. The percentage of Cretaceous species found above the boundary is variable; I found 50%, Canudo nearly 45% (Fig. 4), Olsson 34% (Fig. 6), and Masters 31% (Fig. 5). 3. Discussion Two inherent problems make it difficult to compare the results among we four testers and between our results and those of Keller and Smit. First, many of the species are quite rare and without an exhaustive search, not all analysts will find all of them. For example, I found six more species than the other testers and they reported 25 species that I did not find. The second problem is the differences in taxonomy between us. For example, I consider that the multiseriated heterohelicids that occur in El Kef, and that are usually considered as Plunoglobulinu multicumerutu (de Klasz, 1953), actually correspond to individuals off! meyerhofi Seiglie, 1960. Regarding a possible extinction below the K/T boundary, as proposed by Keller (1988b, 1989a), I found instead that all the species extend up to the boundary (Fig. 10). According to Keller (1988b), Planoglobulinu cursevae (Plummer, 193 l), Globotruncunitu stuartiformis (Dalbiez, 1955), and Rucemiguembelinu fructicosu (Egger, 1899) disappear below the boundary, but all four of us found that they occur in the sample just below the boundary. Other species such as Hedbergellu holmdelensis Olsson, 1964, Ventilubrellu eggeri Cushman, 1928 (= P: multicumerutu of other authors), and P. eleguns have been identified in the last Maastrichtian sample by at least three of us. The inherent difficulties of finding all these rare species may explain the differencies between our results and those of Keller. Keller’s hypothesis of a gradual extinction below the boundary would require that reworking explains our findings. For several reasons I believe that there are many more Cretaceous species that occur above the boundary than the few proposed by Smit (1982, 1990) and that these are survivors rather than reworked specimens. First, the walls of the Cretaceous species are almost identical to those of the Tertiary species with
88
El Kef blind test/Marine Micropaleontology 29 (1997) 65-103
which they occur. Second, if many of these species are reworked, they ought to be those with solid and thick-walled tests, rather than the thin-walled mainly heterohelicids that are found. Third, the same cooccurrence of Cretaceous and Tertiary species in the El Kef section, is found at other sections across the K/T boundary: Caravaca (Canudo et al., 1991), Brazos River (Keller, 1989a), and new sections I am studying that occur on both sides of the Pyrenees. And fourth, most of the Cretaceous specimens found above the boundary are smaller than those of the same species just below the boundary.
4. Conclusions (1) All the planktic foraminifers of the latest Cretaceous reach the K/T boundary, as proposed by Smit (1982, 1990). (2) The sudden extinction event at the end of the Cretaceous affected a little more than 50% of the planktic species according to my results. (3) Most of the more than 40% of Cretaceous species found in samples above the boundary are survivors and not reworked specimens in agreement with the interpretations of Keller (1988b).
OGY
Marine Micropaleontology29 (1997) 65- 103
MicroNotes
El Kef blind test IV results Xabier Orue-etxebarria Paleontologia, Facultad de Ciencias, Vniversidad Del Pais Vasco, Apartado 644 Postakutxa, E-48080 Bilbao, Spain
Received 12 April 1996; accepted 12 June 1996
1. Methods Owing to the small size of some latest Cretaceous/earliest Tertiary species, two size-fractions were prepared of each sample: 40-63 km, and >63 wrn, this latter being the one to be analyzed for the blind test. A splitter was used to obtain a representative fraction of the larger size grade. From this fraction, depending on the richness of each sample, 250 to 500 specimens were separated to obtain the ratio between planktic and benthic species as well as the relative abundance for each species. A further personal step was the analysis of the whole sample to find and identify rare Maastrichtian species.
2. Results First, I present my own results with some discussion on several specific taxa, that are, in my opinion, not identified correctly by the others. Then I comment on the results of the other testers and compare them with my own.
2.1. Cretaceous samples As can be seen from the three samples from the end of the Cretaceous (Fig. lo), I found a total of 61 species of planktic foraminifera in the fraction of >63 pm, of which I identified 60 species, as compared with the 45-50 species reported by the other testers from the same samples. The difference
is because I examined the entire sample searching for the rare species. Between 73 and 80% of the total number of the specimens present in the samples correspond to different species of heterohelicids. Among these, the most abundant species is Heterohelix globulosa (Ehrenberg, 1840) whose specimens represent approximately 40% of the total. Several species are quite rare; among them are: Gublerina acuta de Klasz, 1953, Planoglobulina acervulinoides (Egger, 1899) Pseudotextularia elegans (Rzehak, 1891) Pseudotextularia inter-media de Klasz, 1953, Globotruncana dupeublei Caron et al., 1984, Globotruncana orientalis El Naggar, 1966, Globotruncanita angulata (Tilev, 1951) Globotruncanita conica (White, 1928), Rosita contusa (Cushman, 1926) Abathomphalus mayaroensis Bolli, 195 1, Heterohelix postsemicostata (Vasilenko, 1961) which is fairly common (1%) in sample 3809, and Globigerinelloides prairiehillensis Pessagno, 1967 among others. I found three or four small specimens of Abathomphalus mavaroensis in each of the samples from the Cretaceous, but only after examining the entire sample. The failure to find these rare species in a small sample (ca. 20 g) such as the one we testers analyzed, can lead to erroneous interpretations. For example, I did not find R. contusa in the last sample from the Cretaceous, but in a sample that I collected myself from 1 cm below the K/T boundary during the sampling in 1992, I did find several specimens.
0377-8398/97/$17.00 Copyright 0 1997 Elsevier Science B.V. All rights reserved. SSDI 0377-8398(96)00043-6
86
El Kef blind test/Marine
Micropaleontology
29 (1997) 65-103
El Kef blind test/Marine Micropaleontology 29 (1997) 65-103
Furthermore, two of the other testers did find R. contusa in their last Cretaceous sample. In my opinion therefore, all the species extend to the K/T boundary and there are no pre-boundary extinctions. In contrast, Canudo’s results show that 7 of 47 species disappear below the K/T boundary (Fig. 4); Olsson found only 3 of 44 species disappearing below the boundary (Fig. 6); and Masters reported that 15 of 52 species disappeared below the boundary (Fig. 5). Regarding the triseriated forms of small size, most of the specimens found in samples from the Cretaceous correspond to Guembelitria trifolia (Morozova, 1961) and not to Guembelitria cretuceu Cushman, 1933. These last two species, as well as Globotruncunellu curuvucuensis Smit, 1982, are more frequent in the fraction of ~63 pm that I have also analyzed. Moreover, in the fraction between 40 and 63 pm, I have also found Shuckoinu multispinutu (Cushman and Wickenden, 1930) and Hedbergellu hillebrundti (Orue-etxebania, 1985). The later was first described from the base of the Tertiary of the Sopelana section (Basque Country) and is therefore, one of the species surviving the massive extinction. 2.2. Tertiary samples The extinction event that occurred at the K/T boundary included more than 50% of the species existing at the end of the Maastrichtian (Fig. 10). These species disappear through zones PO and Pla. In the first two Tertiary samples, G. trifoliu is more abundant than G. cretuceu, but this ratio is reversed in sample 3802. In the three samples from the base of the Tertiary, I have found only two species characteristic of this age, one form assigned to Globoconusu conusu Khalilov, 1956 and one other included in Purvulurugoglobigerinu longiuperturu (Blow, 1979). Regarding this last species, I think that those forms identified as Globigerinu eugubinu Luterbacher and Premoli-Silva, 1964 are in most instances, both in El Kef and in any other sections, specimens of p longiuperturu because they present a distinct elongated aperture positioned on the front wall of the last formed chamber. In contrast, the original description of the holotype of G. eugubinu indicates the presence of an aperture on the umbilical position.
87
Furthermore, the holotype described by H.P. Luterbather (pers. commun.), does not have any elongated aperture. The percentage of Cretaceous species found above the boundary is variable; I found 50%, Canudo nearly 45% (Fig. 4), Olsson 34% (Fig. 6), and Masters 31% (Fig. 5). 3. Discussion Two inherent problems make it difficult to compare the results among we four testers and between our results and those of Keller and Smit. First, many of the species are quite rare and without an exhaustive search, not all analysts will find all of them. For example, I found six more species than the other testers and they reported 25 species that I did not find. The second problem is the differences in taxonomy between us. For example, I consider that the multiseriated heterohelicids that occur in El Kef, and that are usually considered as Plunoglobulinu multicumerutu (de Klasz, 1953), actually correspond to individuals off! meyerhofi Seiglie, 1960. Regarding a possible extinction below the K/T boundary, as proposed by Keller (1988b, 1989a), I found instead that all the species extend up to the boundary (Fig. 10). According to Keller (1988b), Planoglobulinu cursevae (Plummer, 193 l), Globotruncunitu stuartiformis (Dalbiez, 1955), and Rucemiguembelinu fructicosu (Egger, 1899) disappear below the boundary, but all four of us found that they occur in the sample just below the boundary. Other species such as Hedbergellu holmdelensis Olsson, 1964, Ventilubrellu eggeri Cushman, 1928 (= P: multicumerutu of other authors), and P. eleguns have been identified in the last Maastrichtian sample by at least three of us. The inherent difficulties of finding all these rare species may explain the differencies between our results and those of Keller. Keller’s hypothesis of a gradual extinction below the boundary would require that reworking explains our findings. For several reasons I believe that there are many more Cretaceous species that occur above the boundary than the few proposed by Smit (1982, 1990) and that these are survivors rather than reworked specimens. First, the walls of the Cretaceous species are almost identical to those of the Tertiary species with
88
El Kef blind test/Marine Micropaleontology 29 (1997) 65-103
which they occur. Second, if many of these species are reworked, they ought to be those with solid and thick-walled tests, rather than the thin-walled mainly heterohelicids that are found. Third, the same cooccurrence of Cretaceous and Tertiary species in the El Kef section, is found at other sections across the K/T boundary: Caravaca (Canudo et al., 1991), Brazos River (Keller, 1989a), and new sections I am studying that occur on both sides of the Pyrenees. And fourth, most of the Cretaceous specimens found above the boundary are smaller than those of the same species just below the boundary.
4. Conclusions (1) All the planktic foraminifers of the latest Cretaceous reach the K/T boundary, as proposed by Smit (1982, 1990). (2) The sudden extinction event at the end of the Cretaceous affected a little more than 50% of the planktic species according to my results. (3) Most of the more than 40% of Cretaceous species found in samples above the boundary are survivors and not reworked specimens in agreement with the interpretations of Keller (1988b).