Late Eocene foraminifera from DSDP site 26713
(Brady), Globocassidulina subglobosa (Brady), and Egerella nitens (Wiesner) dominate the benthic taxa. Population analyses of 12 samples from cores 15 and 16 indicate that the majority of the foraminifera are in situ and represent biocoenoses or near biocoenoses. This is based on faunal stability, diversity, stratigraphic population trends, the minimal degree of reworking, and preservation. Relative-abundance histograms for each population (benthics and planktonics) were based on random counting of at least 300 tests, whenever possible. Five samples exhibit signs of post mortem influence. However, these modified assemblages are comparable in taxa content to the wellpreserved faunas. In summary it may be concluded that in the calcareous succession at site 265, two distinctive and probably bithermal assemblages contribute to a combined biocoenosis: a planktonic population that lived in near-surface waters at temperatures of 8° to 17°C and a contemporaneous stable, bathyal, cold-water (0° to 2°C) benthic fauna. A strongly stratified water column existed. It appears that during the early to late Miocene (approximately 10 to 7 million years ago), gradual surface-water cooling occurred because of progressive ice buildup in Antarctica; sometime between 7 and 4 million years ago, the proto-Antarctic Convergence moved northward of the site 265 area in response to cooling conditions, and site 265 moved southward in response to sea floor spreading. Intense glaciation in the early Pliocene is further substantiated by the truncation of seawarddipping sequences in the Ross Sea, probably caused by erosive action of a grounded Ross Ice Shelf and the northward movement of the siliceous ooze/glacial-marine sediment boundary offshore the Adélie and George V Coasts (Kemp et al. 1975). This sequence of events would be re-corded in a short temporal and sediment interval, probably in the early Pliocene (approximately 5 million years ago), as suggested by Hayes and others (1975).
Late Eocene foraminifera from DSDP site 26713, southeast Indian Ocean
MICHAEL J. STYZEN and PEmR-N0EL WEBB** Department of Geology Northern Illinois University DeKaib, Illinois 60115 * Mobil Exploration and Production Services Company, Dallas, Texas 75221. ** Department of Geology and Mineralogy, The Ohio State University, Columbus, Ohio 43210
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This work was supported by National Science Foundation grant DPP 79-07043. The results reported here are taken from research for the master of science degree by Nancy L. Engelhardt. Principal investigator was Peter-Noel Webb.
References Burns, D. A. 1975. Nannofossil biostratigraphy for antarctic sediments. In D. E. Hayes, L. A. Frakes, etal., Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Engelhardt, N. L. 1980. Late Miocene foraminiferal biostratigraphy and paleoecology at DSDP site 265, southeast Indian Ocean. Unpublished master's thesis, Northern Illinois University. Hayes, D. E., Frakes, L. A., Barrett, P. J . , Burns, D. A., Chen, P. H., Ford, A. B., Kaneps, A. C., Kemp, E. M., McCollum, D.. W., Piper, D. J . W., Wall, R. E., and Webb, P. N. 1975. Deep Sea Drilling Project, leg 28. In D. E. Hayes, L. A. Frakes et. al., Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Jenkins, D. G. 1971. New Zealand Cenozoic planktonic foraminifera. New Zealand Geological Survey, Paleontological Bulletin 42, 1-278. Jenkins, D. G. 1975. Cenozoic planktonic formaminiferal biostratigraphy of the southwestern Pacific and Tasman Sea (Vol. 29). Washington, D.C.: U.S. Government Printing Office. Kaneps, A. G. 1975. Cenozoic planktonic foraminifera from antarctic deep sea sediments. In D. E. Hayes, L. A. Frakes et. al., Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Kemp, E. M., Frakes, L. A., and Hayes, D. E. 1975. Paleoclimatic significance of diachronous biogenic facies. In D. E. Hayes, L. A. Frakes et. al., initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Stainforth, R. M. 1975. Cenozoic planktonic foraminiferal zonation and characteristics of index forms. In University of Kansas paleontological contributions. Lawrence: University of Kansas.
From the time of its initial opening in the latest Paleocene until deep circulation with the South Pacific was established in the early Oligocene, the southeast Indian Ocean basin contained a distinct water mass. In late Eocene the basin was a wide gulf, open to the Indian Ocean on the west but with only shallow circulation over the south Tasman Rise to the Pacific in the east (Kennett and Houtz 1974; Weissel and Hayes 1972). Several foraminiferal faunas of late Eocene age have been studied from marginal basins along the southern coast of Australia (Ludbrook and Lindsay 1969). These studies are usually from shallow fades and provide only indirect information about open ocean conditions. The foraminiferal fauna preserved in the short (0.5-meter) section of nannoforam chalk recovered from the bottom of Deep Sea Drilling Project (DsDP) hole 267B (core 10) provides a unique ANTARCTIC JOURNAL
opportunity to gage Eocene open ocean conditions between Australia and Antarctica. Hole 267B is one of three drilled at site 267 in the southeast Indian Ocean. Hole 267B was drilled at 59°15.74'S 104°29.30'E; holes 267 and 267A were drilled 2.6 kilometers to the south. Hayes and others (1975) identified three lithologic units in cores from each locality. The upper unit is a variable clay-silt-diatom sediment of mid-Miocene to Pliocene age. This unit unconformably overlies a tan-colored nanno-foram chalk. The chalk rests on oceanic basalt dated at 40.0 to 41.5 million years (late Eocene) by means of magnetic anomalies. The base of the chalk in holes 267 and 267A was assigned an earliest possible age of mid-Oligocene by biostratigraphy (Hayes et al. 1975). Hole 267B represents a successful attempt to recover sediment of late Eocene age overlying the basalt. Styzen (1980) reported large faunas of both benthic and planktonic foraminifera recovered from five evenly spaced horizons in the thin chalk section from the bottom of hole 26Th. The benthic fauna is a high-dominance/high-diversity assemblage consisting of 69 species and 36 genera. The fauna consists almost exclusively of calcareous benthics, but a few calcareous agglutinated forms are also present. The dominant taxon, Globocassidulina subglobosa (Brady), contributes over 30 percent of the fauna. Eight other prominent species each contribute over 1 percent of the fauna: Epistominella exigua (Brady) (8.9 percent), Eponides weddellensis (Earland) (7.5 percent), Eponides aff. formosulus (Todd and Low) (5.0 percent), Buliminella browni (Finlay) (3.8 percent), Eggerella nitens (Weisner) (3.6 percent), Oridorsalis aff. vanapertura (Belford) (2.6 percent), Oridorsalis tenera (Brady) (2.5 percent), and Orthomorphina antillea (Cushman) (1.3 percent). Rare (less than 1 percent) forms contribute almost 30 percent of the fauna. This type of fauna is typical of assemblages found at lower bathyal depths. The fauna is quite similar to shelf faunas of the same age (Hornibrook 1%1) but bears striking resemblance to Neogene faunas of similar bathymetry (Boltovskoy 1978; Engelhardt 1980). Only minor changes in dominance were noted through the section, indicating stable benthic conditions throughout the time of deposition. The planktonic fauna is a high-diversity/low-dominance assemblage of 19 species. This type of diversity/ dominance realtionship points to temperate surface temperatures at the time of deposition. This interpretation agrees with paleoclimate interpretations by Kemp (1978). The fauna has much in common with upper Eocene faunas of South Australia and bears similarities to faunas of similar age in New Zealand and East Africa. The planktonic fauna is correlative to the Globorotalia aculeata zone of South Australia, the Globigerina linaperta zone and Runangan stage of New Zealand, and P15 to P16 of the Blow zonation. This age is based mainly on the presence of Globorotalia aculeata (Jenkins) which, according to Ludbrook and Lindsay (1967), is restricted to the C. aculeata zone in South Australia. Other 1980 REviEw
characteristic late Eocene taxa identified include Globigerina linaperta (Finlay), Globanomalina micra (Cole), and ChUbgumbellina cubensis (Palmer). A profound change in the planktonic fauna was noted close to the contact with the underlying basalt. A less diverse and more poorly preserved fauna, with fewer similarities to the fauna as a whole, was noted at the interval closest to the basalt. A close examination of the abundance of each taxon at each sampled interval revealed trends of preservation resembling diagenetic change noted by Schlanger, Douglas, Lancelot, Moore, and Roth (1973) in nanno chalk from the North Pacific. The change in the fauna from 267B is unique, however, in that the diagenetic effect usually seen over meters or tens of meters is evident over a space of a few centimeters. This compression of diagenesis may be caused by local chemistry, compaction, or poor sampling. It is interesting to note, however, that biostratigraphic evidence indicates deposition of the chalk occurred within 2 million years of the emplacement of the basaltic basement. It is possible that heat flow or very lowgrade hydrothermal activity associated with the cooling of the basalt may be responsible for the observed fauna! change. This work is supported by National Science Foundation grant DPP 79-07043. The results reported here are based on master of science degree research by Michael J. Styzen. Peter-Noel Webb was principal investigator. References Boltovskoy, E. 1978. Late Cenozoic benthonic foraminifera of the Nineteyeast Ridge (Indian Ocean). Marine Geology, 26, 139-175. Engelhardt, N. L. 1980. Paleoecologic and biostratigraphic interpretations of late Miocene foraminifera at DSDP site 265, southeast Indian Ocean. Unpublished master's thesis, Northern Illinois University. Hayes, D. E., Frakes, L. A. et al. 1975. Site 267: Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Hornibrook, N. de B. 1961. Tertiary foraminifera from Oamaru District (N.Z.), Part 1 Systematics and Distribution. New Zealand Geological Survey, Paleontological Bulletin 32, 1, 558. Kaneps, A. G. 1975. Cenozoic planktonic foraminifera from antarctic deep sea sediments. In D. E. Hayes, L. A. Frakes et al. Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Kemp, E. M. 1978. Tertiary climatic evolution and vegetation history in the southeast Indian Ocean region. Paleogeography, Paleoclimatology, Paleoecology, 24, 169-208. Kennett, J . P., and Houtz, R. E. 1974. Initial reports of the Deep Sea Drilling Project, Vol. 29. Washington, D.C.: U.S. Government Printing Office. Ludbrook, N. H., and Lindsay, J . M. 1969. Tertiary foraminiferal zones in South Australia. In P. Bronnemann and H. H. Renz
131
(Eds.), Proceedings of the First International Conference on Plank- Styzen, M. J . 1980. Late Eocene foraminiferal systematics, biostratonic Microfossils (Vol. 2). Geneva: E. J. Brill, Leiden. tigraphy and paleoecology of DSDP hole 267B, southeast Indian Ocean. Unpublished master's thesis, Northern Illinois Schianger, S.O., Douglas, R.G., Lancelot, Y., Moore, T. C., and Roth, University. P. H. 1973. Fossil preservation and diagenesis of pelagic carbonates from the Magellan Rise, central north Pacific Ocean. In E. L. Weissel, J . K., and Hayes, D. E. 1972. Magnetic anomalies in the Winterer et al. (Eds.), Initial reports of the Deep Sea Drilling Project, southeast Indian Ocean. In Antarctic Research Series (Vol. 19). Vol. 17. Washington, D.C.: U.S. Government Printing Office. Washington, D.C.: American Geophysical Union.
Distribution of Recent deep-sea benthonic foraminifera from the southwest Indian Ocean BRUCE H. CORLISS
Woods Hole Oceanographic Institution Woods Hole, Massachusetts 02543
Deep-sea benthonic foraminifera have been studied from a suite of 58 trigger core tops in the Crozet, Madagascar, and Mascarene Basins of the southwest Indian Ocean from 9° to
45°S latitude and 45° to 80°E longitude (figure 1) to determine faunal/water-mass relationships. Principal component analysis of the faunal data reveals distinct faunal trends related to depth and bottom-water potential temperature (figure 1). Principal component 1 represents an average of all of the fauna! data. The negative values of principal component 2 reflect the importance of Epistominella umbonifera and are found generally south of 35°S latitude in the Crozet Basin and on the flanks of the Madagascar, Southwest Indian, and Southeast Indian Ridges. These values are associated with bottom-water potential temperatures ranging from — 0.1° to 1.2°C, with the high relative values ( — 0.4) found generally with potential temperatures of :5 0.8°C. Positive values of principal
40' 50' 60' 70' 80'E
Figure 1. Distribution of principal component 2 of the benthonic foraminiferal data from the southwest Indian Ocean plotted with water depth and potential temperature. The range of values is from — ito + 1; negative values of principal component 2 reflect the Importance of Epistominella umbonifsic, and positive values reflect the importance of Planuilna wu.Ilerstorfi; rare species (< 3 percent), Globocassidullna subglobosa, and Astrononion echolsL
132
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Late Eocene foraminifera from DSDP site 26713, southeast Indian Ocean
MICHAEL J. STYZEN and PEmR-N0EL WEBB** Department of Geology Northern Illinois University DeKaib, Illinois 60115 * Mobil Exploration and Production Services Company, Dallas, Texas 75221. ** Department of Geology and Mineralogy, The Ohio State University, Columbus, Ohio 43210
130
This work was supported by National Science Foundation grant DPP 79-07043. The results reported here are taken from research for the master of science degree by Nancy L. Engelhardt. Principal investigator was Peter-Noel Webb.
References Burns, D. A. 1975. Nannofossil biostratigraphy for antarctic sediments. In D. E. Hayes, L. A. Frakes, etal., Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Engelhardt, N. L. 1980. Late Miocene foraminiferal biostratigraphy and paleoecology at DSDP site 265, southeast Indian Ocean. Unpublished master's thesis, Northern Illinois University. Hayes, D. E., Frakes, L. A., Barrett, P. J . , Burns, D. A., Chen, P. H., Ford, A. B., Kaneps, A. C., Kemp, E. M., McCollum, D.. W., Piper, D. J . W., Wall, R. E., and Webb, P. N. 1975. Deep Sea Drilling Project, leg 28. In D. E. Hayes, L. A. Frakes et. al., Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Jenkins, D. G. 1971. New Zealand Cenozoic planktonic foraminifera. New Zealand Geological Survey, Paleontological Bulletin 42, 1-278. Jenkins, D. G. 1975. Cenozoic planktonic formaminiferal biostratigraphy of the southwestern Pacific and Tasman Sea (Vol. 29). Washington, D.C.: U.S. Government Printing Office. Kaneps, A. G. 1975. Cenozoic planktonic foraminifera from antarctic deep sea sediments. In D. E. Hayes, L. A. Frakes et. al., Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Kemp, E. M., Frakes, L. A., and Hayes, D. E. 1975. Paleoclimatic significance of diachronous biogenic facies. In D. E. Hayes, L. A. Frakes et. al., initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Stainforth, R. M. 1975. Cenozoic planktonic foraminiferal zonation and characteristics of index forms. In University of Kansas paleontological contributions. Lawrence: University of Kansas.
From the time of its initial opening in the latest Paleocene until deep circulation with the South Pacific was established in the early Oligocene, the southeast Indian Ocean basin contained a distinct water mass. In late Eocene the basin was a wide gulf, open to the Indian Ocean on the west but with only shallow circulation over the south Tasman Rise to the Pacific in the east (Kennett and Houtz 1974; Weissel and Hayes 1972). Several foraminiferal faunas of late Eocene age have been studied from marginal basins along the southern coast of Australia (Ludbrook and Lindsay 1969). These studies are usually from shallow fades and provide only indirect information about open ocean conditions. The foraminiferal fauna preserved in the short (0.5-meter) section of nannoforam chalk recovered from the bottom of Deep Sea Drilling Project (DsDP) hole 267B (core 10) provides a unique ANTARCTIC JOURNAL
opportunity to gage Eocene open ocean conditions between Australia and Antarctica. Hole 267B is one of three drilled at site 267 in the southeast Indian Ocean. Hole 267B was drilled at 59°15.74'S 104°29.30'E; holes 267 and 267A were drilled 2.6 kilometers to the south. Hayes and others (1975) identified three lithologic units in cores from each locality. The upper unit is a variable clay-silt-diatom sediment of mid-Miocene to Pliocene age. This unit unconformably overlies a tan-colored nanno-foram chalk. The chalk rests on oceanic basalt dated at 40.0 to 41.5 million years (late Eocene) by means of magnetic anomalies. The base of the chalk in holes 267 and 267A was assigned an earliest possible age of mid-Oligocene by biostratigraphy (Hayes et al. 1975). Hole 267B represents a successful attempt to recover sediment of late Eocene age overlying the basalt. Styzen (1980) reported large faunas of both benthic and planktonic foraminifera recovered from five evenly spaced horizons in the thin chalk section from the bottom of hole 26Th. The benthic fauna is a high-dominance/high-diversity assemblage consisting of 69 species and 36 genera. The fauna consists almost exclusively of calcareous benthics, but a few calcareous agglutinated forms are also present. The dominant taxon, Globocassidulina subglobosa (Brady), contributes over 30 percent of the fauna. Eight other prominent species each contribute over 1 percent of the fauna: Epistominella exigua (Brady) (8.9 percent), Eponides weddellensis (Earland) (7.5 percent), Eponides aff. formosulus (Todd and Low) (5.0 percent), Buliminella browni (Finlay) (3.8 percent), Eggerella nitens (Weisner) (3.6 percent), Oridorsalis aff. vanapertura (Belford) (2.6 percent), Oridorsalis tenera (Brady) (2.5 percent), and Orthomorphina antillea (Cushman) (1.3 percent). Rare (less than 1 percent) forms contribute almost 30 percent of the fauna. This type of fauna is typical of assemblages found at lower bathyal depths. The fauna is quite similar to shelf faunas of the same age (Hornibrook 1%1) but bears striking resemblance to Neogene faunas of similar bathymetry (Boltovskoy 1978; Engelhardt 1980). Only minor changes in dominance were noted through the section, indicating stable benthic conditions throughout the time of deposition. The planktonic fauna is a high-diversity/low-dominance assemblage of 19 species. This type of diversity/ dominance realtionship points to temperate surface temperatures at the time of deposition. This interpretation agrees with paleoclimate interpretations by Kemp (1978). The fauna has much in common with upper Eocene faunas of South Australia and bears similarities to faunas of similar age in New Zealand and East Africa. The planktonic fauna is correlative to the Globorotalia aculeata zone of South Australia, the Globigerina linaperta zone and Runangan stage of New Zealand, and P15 to P16 of the Blow zonation. This age is based mainly on the presence of Globorotalia aculeata (Jenkins) which, according to Ludbrook and Lindsay (1967), is restricted to the C. aculeata zone in South Australia. Other 1980 REviEw
characteristic late Eocene taxa identified include Globigerina linaperta (Finlay), Globanomalina micra (Cole), and ChUbgumbellina cubensis (Palmer). A profound change in the planktonic fauna was noted close to the contact with the underlying basalt. A less diverse and more poorly preserved fauna, with fewer similarities to the fauna as a whole, was noted at the interval closest to the basalt. A close examination of the abundance of each taxon at each sampled interval revealed trends of preservation resembling diagenetic change noted by Schlanger, Douglas, Lancelot, Moore, and Roth (1973) in nanno chalk from the North Pacific. The change in the fauna from 267B is unique, however, in that the diagenetic effect usually seen over meters or tens of meters is evident over a space of a few centimeters. This compression of diagenesis may be caused by local chemistry, compaction, or poor sampling. It is interesting to note, however, that biostratigraphic evidence indicates deposition of the chalk occurred within 2 million years of the emplacement of the basaltic basement. It is possible that heat flow or very lowgrade hydrothermal activity associated with the cooling of the basalt may be responsible for the observed fauna! change. This work is supported by National Science Foundation grant DPP 79-07043. The results reported here are based on master of science degree research by Michael J. Styzen. Peter-Noel Webb was principal investigator. References Boltovskoy, E. 1978. Late Cenozoic benthonic foraminifera of the Nineteyeast Ridge (Indian Ocean). Marine Geology, 26, 139-175. Engelhardt, N. L. 1980. Paleoecologic and biostratigraphic interpretations of late Miocene foraminifera at DSDP site 265, southeast Indian Ocean. Unpublished master's thesis, Northern Illinois University. Hayes, D. E., Frakes, L. A. et al. 1975. Site 267: Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Hornibrook, N. de B. 1961. Tertiary foraminifera from Oamaru District (N.Z.), Part 1 Systematics and Distribution. New Zealand Geological Survey, Paleontological Bulletin 32, 1, 558. Kaneps, A. G. 1975. Cenozoic planktonic foraminifera from antarctic deep sea sediments. In D. E. Hayes, L. A. Frakes et al. Initial reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Kemp, E. M. 1978. Tertiary climatic evolution and vegetation history in the southeast Indian Ocean region. Paleogeography, Paleoclimatology, Paleoecology, 24, 169-208. Kennett, J . P., and Houtz, R. E. 1974. Initial reports of the Deep Sea Drilling Project, Vol. 29. Washington, D.C.: U.S. Government Printing Office. Ludbrook, N. H., and Lindsay, J . M. 1969. Tertiary foraminiferal zones in South Australia. In P. Bronnemann and H. H. Renz
131
(Eds.), Proceedings of the First International Conference on Plank- Styzen, M. J . 1980. Late Eocene foraminiferal systematics, biostratonic Microfossils (Vol. 2). Geneva: E. J. Brill, Leiden. tigraphy and paleoecology of DSDP hole 267B, southeast Indian Ocean. Unpublished master's thesis, Northern Illinois Schianger, S.O., Douglas, R.G., Lancelot, Y., Moore, T. C., and Roth, University. P. H. 1973. Fossil preservation and diagenesis of pelagic carbonates from the Magellan Rise, central north Pacific Ocean. In E. L. Weissel, J . K., and Hayes, D. E. 1972. Magnetic anomalies in the Winterer et al. (Eds.), Initial reports of the Deep Sea Drilling Project, southeast Indian Ocean. In Antarctic Research Series (Vol. 19). Vol. 17. Washington, D.C.: U.S. Government Printing Office. Washington, D.C.: American Geophysical Union.
Distribution of Recent deep-sea benthonic foraminifera from the southwest Indian Ocean BRUCE H. CORLISS
Woods Hole Oceanographic Institution Woods Hole, Massachusetts 02543
Deep-sea benthonic foraminifera have been studied from a suite of 58 trigger core tops in the Crozet, Madagascar, and Mascarene Basins of the southwest Indian Ocean from 9° to
45°S latitude and 45° to 80°E longitude (figure 1) to determine faunal/water-mass relationships. Principal component analysis of the faunal data reveals distinct faunal trends related to depth and bottom-water potential temperature (figure 1). Principal component 1 represents an average of all of the fauna! data. The negative values of principal component 2 reflect the importance of Epistominella umbonifera and are found generally south of 35°S latitude in the Crozet Basin and on the flanks of the Madagascar, Southwest Indian, and Southeast Indian Ridges. These values are associated with bottom-water potential temperatures ranging from — 0.1° to 1.2°C, with the high relative values ( — 0.4) found generally with potential temperatures of :5 0.8°C. Positive values of principal
40' 50' 60' 70' 80'E
Figure 1. Distribution of principal component 2 of the benthonic foraminiferal data from the southwest Indian Ocean plotted with water depth and potential temperature. The range of values is from — ito + 1; negative values of principal component 2 reflect the Importance of Epistominella umbonifsic, and positive values reflect the importance of Planuilna wu.Ilerstorfi; rare species (< 3 percent), Globocassidullna subglobosa, and Astrononion echolsL
132
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