Neogene and Oligocene silicoflagellate biostratigraphic ...
Neogene and Oligocene silicoflagellate biostratigraphic zonation for the southern ocean PAUL F. CIESIELSKI
Antarctic Research Facility Department of Geology Florida State University Tallahassee, Florida 32306 A detailed micropaleontological analysis of eight Eltanin piston cores, and of 11 drill cores from eight Deep Sea Drilling Project (DSDP) leg 28 sites (fig. 1), has established a silicofiagellate biostratigraphic zonation (fig. 2) of Recent to Early Oligocene southern ocean sediments. All cores on which the zonation is based are located in antarctic or subantarctic waters south of the Antarctic Convergence. The established zonation includes 15 zones and two subzones; of these, 10 zones and two subzones are described for the first time. New zones and subzones include: the Distephanus speculum Zone A, D. speculum Zone B, D. boliviensis Zone, Dictyocha aspera variety pygmaea-D. fibula variety pumila Zone, Mesocena diodon Zone, Dictyocha mutabilis Zone, N. regularis Zone, N. robusta Zone, N. biapiculata Zone, Dictyocha deflandrei Zone, D. frenguellii Subzone, and Mesocena apiculata Subzone. All zone and subzone definitions and respectitve geologic ages are given in fig. 2. Barren stratigraphic sequences occurring both above and below the Mesocena circulus Zone (fig. 2) currently prevent precise definition of its zonal boundaries between those of the Mesocena diodon Zone (above) 140 5 E
and the Dictyocha mutabilis Zone (below). For this reason, dual zonal definitions are presented for the upper and lower boundaries of the Mesocena circulus zone. Further refinement of these zonal boundaries must await recovery of continuous silicofiagellatebearing sequences between these zones. At DSDP site 274 the Distephanus boliviensis Zone lies conformably above the Dictyocha pseudo fibula Zone instead of above the Dictyocha aspera variety pygmaea-D. fibula variety pumila Zone. An apparent early Pliocene ecologic restriction of D. aspera variety pygmaea and D. fibula variety pumila north of 69°S. results in the conformable positions of the Distephanus boliviensis and Dictyocha pseudo fibula zones at this site. Studies of this and other silicofiagellate biofacies relationships are in progress (Ciesielski, in preparation) and should aid in regional applications of this zonation. Studies of seven of the paleomagnetically dated Eltanin cores relate the zonal scheme to paleomagnetic chronostratigraphy for the last 4.65 million years before present (Brunhes through lower Gilbert magnetic epochs) (Ciesielski, in preparation). Whenever possible, older silicofiagellate zones have been related to type sections by correlation to calcareous nannofossil zones (Burns, in press). Noticeable differences occurring between this zonation and other previously established silicofiagellate zonations underscore the provinciality of many antarctic silicofiagellate assemblages. Only a few cosmopolitan zones such as the early and middle Miocene Gorbisema triacantha Zone and the Naviculopis zones are recognized. For details of zonal correlations and assemblages, 1605E
0W
rEALAND
E 36 20 E
fE 4-8
1405W
E38_7-..$E 38-8 •E50-28S.'
•DSDP
269
ODSDP 274 DSDP 273a 273A
DSDP 266
Figure 1. Location map of Eltanin piston cores and Deep Sea Drilling Project drill cores utilized in construction of silicofla gel late biostratigrapliic zonation.
)SDP 271
E 13 -17 .
I.
00 E
267A267B
CA 40 5 S
September-October 1974
605S
POLE
80S
655S
271
PLEISTOCENE
Distephanus speculum Zone A
First consistent common occurrence of long-spined Distephanus speculum in the absence of Distephanus bol ioiensjs
UPPER PLIOCENE Distephanus
LOWER PLIOCENE
Not defined but the zone includes all floras above the initial consistent common occurrence of longOpined Distephanus speculum morphotypes
Zone
Dictyocha fibula var. pumila Zone
Last consistent common occurrence of Distephanus boliviensis in the presence of a Distephanus speculum group dominated by short-spined morphttypes Last consistent occurrence of lictyocha aspera oar. pygmaea and 0. fibula var. pumila First common occurrence of Eictyocha aspera oar. pygmaea and I. fibula oar. punila First common occurrence of Eictyocha pseudofibula
Iii iiviery. First consistent occurrence of Mesocena diodon/ Last consistent occurrence of Mes ocena circu lus
UPPER MIOCENE
First consistent occurrence of Mesocena circulus/ Last consistent occurrence of Dictyocha mutabilis Dictyocha mutabilis First consistent occurrence of Dictyocha nutabilis
MIDDLE MIOCENE Eistephanus longispinus Zone
Last consistent occurrence of Corbisema triacantha Corbisema triacantha Zone
Naviculopsis naoicula Zone LOWER MIOCENE
Last occurrence of Naviculopsisnavicula and N. regularis First consistent occurrence of
navicula
Naviculopsis regularis Zone Last common occurrence of Naviculopsis robusta Naviculopsis robusta Zone First common occurrence of Naoiculopsis robusta
UPPER OLIGOCENE
LOWER OLIGOCENE
Nnviculopsis biapiculata Zone
Dictyocha defi andrei Zone
Uictyocha frnuelli, Subzone Mesocena api cul ata Sub zo me
Last consistent occurrence of Elctyocha deflandrei
First common occurrence of Uictyocha frenguellii First consistent common occurrence of Oictyocha deflandrei above the last common occurrence of Dictyocha heuacantha
silicofiagellate biostratigraphy, paleoecology, and systematic paleontology, reference should be made to Ciesielski (in press). This research partially was supported by National Science Foundation grant Gv-42650.
Figure 2. Neogene and Oligocene silicofiagellate zone and subzone definitions. Diagonal lines represent barren stratigraphic sequences.
Pleurosigma in plankton from the Scotia Sea
ANDREW M. GOMBOS, JR.
References
Department of Geology Antarctic Research Facility Florida State University Tallahassee, Florida 32306
Burns, D. A. In press. Nannofossil biostratigraphy for antarctic sediments, leg 28, Deep Sea Drilling Project. In: Initial Reports of the Deep Sea Drilling Project (Hayes, D. E., et al.), 28. Washington, D.C., U.S. Government Printing Office. Ciesielski. P. F. In press. Biostratigraphy and paleoecology of Neogene and Oligocene silicoflagellates from cores recovered during antarctic leg 28, Deep Sea Drilling Project. In: Initial Reports of the Deep Sea Drilling Project (Hayes, D. E., et al.), 28. Washington, D.C., U.S. Government Printing Office. Ciesielski, P. F. In preparation. Biostratigraphy and paleoecology of Neogene and Oligocene silicoflagellates recovered from piston and drill cores off East Antarctica. Tallahassee, Sedimentology Research Laboratory, Department of Geology, Florida State University. Contribution, 41.
During the recent leg 36 of the Deep Sea Drilling Project (DSDP) I took several plankton samples from the Scotia Sea. Examination of the samples revealed representatives of the diatom genus Pleurosigma (fig.) in a living state. The samples in which Pleurosigma were observed were taken from about 15 meters below the water surface at 56°09'S. 38°11 1W. and 56°20'S. 40 0 25'W. The nearest land is South Georgia Island, more than 210 kilometers to the northeast. Pleurosigma generally is, considered to be a nearshore, benthic diatom. It has, however, been reported from deep ocean sediments by several authors. Kolbe (1954) observed it to occur throughout Swedish Deep Sea Expedition core 76, although it occurred comparatively seldom. Bukry and Foster (1973) recorded
272
ANTARCTIC JOURNAL
Antarctic Research Facility Department of Geology Florida State University Tallahassee, Florida 32306 A detailed micropaleontological analysis of eight Eltanin piston cores, and of 11 drill cores from eight Deep Sea Drilling Project (DSDP) leg 28 sites (fig. 1), has established a silicofiagellate biostratigraphic zonation (fig. 2) of Recent to Early Oligocene southern ocean sediments. All cores on which the zonation is based are located in antarctic or subantarctic waters south of the Antarctic Convergence. The established zonation includes 15 zones and two subzones; of these, 10 zones and two subzones are described for the first time. New zones and subzones include: the Distephanus speculum Zone A, D. speculum Zone B, D. boliviensis Zone, Dictyocha aspera variety pygmaea-D. fibula variety pumila Zone, Mesocena diodon Zone, Dictyocha mutabilis Zone, N. regularis Zone, N. robusta Zone, N. biapiculata Zone, Dictyocha deflandrei Zone, D. frenguellii Subzone, and Mesocena apiculata Subzone. All zone and subzone definitions and respectitve geologic ages are given in fig. 2. Barren stratigraphic sequences occurring both above and below the Mesocena circulus Zone (fig. 2) currently prevent precise definition of its zonal boundaries between those of the Mesocena diodon Zone (above) 140 5 E
and the Dictyocha mutabilis Zone (below). For this reason, dual zonal definitions are presented for the upper and lower boundaries of the Mesocena circulus zone. Further refinement of these zonal boundaries must await recovery of continuous silicofiagellatebearing sequences between these zones. At DSDP site 274 the Distephanus boliviensis Zone lies conformably above the Dictyocha pseudo fibula Zone instead of above the Dictyocha aspera variety pygmaea-D. fibula variety pumila Zone. An apparent early Pliocene ecologic restriction of D. aspera variety pygmaea and D. fibula variety pumila north of 69°S. results in the conformable positions of the Distephanus boliviensis and Dictyocha pseudo fibula zones at this site. Studies of this and other silicofiagellate biofacies relationships are in progress (Ciesielski, in preparation) and should aid in regional applications of this zonation. Studies of seven of the paleomagnetically dated Eltanin cores relate the zonal scheme to paleomagnetic chronostratigraphy for the last 4.65 million years before present (Brunhes through lower Gilbert magnetic epochs) (Ciesielski, in preparation). Whenever possible, older silicofiagellate zones have been related to type sections by correlation to calcareous nannofossil zones (Burns, in press). Noticeable differences occurring between this zonation and other previously established silicofiagellate zonations underscore the provinciality of many antarctic silicofiagellate assemblages. Only a few cosmopolitan zones such as the early and middle Miocene Gorbisema triacantha Zone and the Naviculopis zones are recognized. For details of zonal correlations and assemblages, 1605E
0W
rEALAND
E 36 20 E
fE 4-8
1405W
E38_7-..$E 38-8 •E50-28S.'
•DSDP
269
ODSDP 274 DSDP 273a 273A
DSDP 266
Figure 1. Location map of Eltanin piston cores and Deep Sea Drilling Project drill cores utilized in construction of silicofla gel late biostratigrapliic zonation.
)SDP 271
E 13 -17 .
I.
00 E
267A267B
CA 40 5 S
September-October 1974
605S
POLE
80S
655S
271
PLEISTOCENE
Distephanus speculum Zone A
First consistent common occurrence of long-spined Distephanus speculum in the absence of Distephanus bol ioiensjs
UPPER PLIOCENE Distephanus
LOWER PLIOCENE
Not defined but the zone includes all floras above the initial consistent common occurrence of longOpined Distephanus speculum morphotypes
Zone
Dictyocha fibula var. pumila Zone
Last consistent common occurrence of Distephanus boliviensis in the presence of a Distephanus speculum group dominated by short-spined morphttypes Last consistent occurrence of lictyocha aspera oar. pygmaea and 0. fibula var. pumila First common occurrence of Eictyocha aspera oar. pygmaea and I. fibula oar. punila First common occurrence of Eictyocha pseudofibula
Iii iiviery. First consistent occurrence of Mesocena diodon/ Last consistent occurrence of Mes ocena circu lus
UPPER MIOCENE
First consistent occurrence of Mesocena circulus/ Last consistent occurrence of Dictyocha mutabilis Dictyocha mutabilis First consistent occurrence of Dictyocha nutabilis
MIDDLE MIOCENE Eistephanus longispinus Zone
Last consistent occurrence of Corbisema triacantha Corbisema triacantha Zone
Naviculopsis naoicula Zone LOWER MIOCENE
Last occurrence of Naviculopsisnavicula and N. regularis First consistent occurrence of
navicula
Naviculopsis regularis Zone Last common occurrence of Naviculopsis robusta Naviculopsis robusta Zone First common occurrence of Naoiculopsis robusta
UPPER OLIGOCENE
LOWER OLIGOCENE
Nnviculopsis biapiculata Zone
Dictyocha defi andrei Zone
Uictyocha frnuelli, Subzone Mesocena api cul ata Sub zo me
Last consistent occurrence of Elctyocha deflandrei
First common occurrence of Uictyocha frenguellii First consistent common occurrence of Oictyocha deflandrei above the last common occurrence of Dictyocha heuacantha
silicofiagellate biostratigraphy, paleoecology, and systematic paleontology, reference should be made to Ciesielski (in press). This research partially was supported by National Science Foundation grant Gv-42650.
Figure 2. Neogene and Oligocene silicofiagellate zone and subzone definitions. Diagonal lines represent barren stratigraphic sequences.
Pleurosigma in plankton from the Scotia Sea
ANDREW M. GOMBOS, JR.
References
Department of Geology Antarctic Research Facility Florida State University Tallahassee, Florida 32306
Burns, D. A. In press. Nannofossil biostratigraphy for antarctic sediments, leg 28, Deep Sea Drilling Project. In: Initial Reports of the Deep Sea Drilling Project (Hayes, D. E., et al.), 28. Washington, D.C., U.S. Government Printing Office. Ciesielski. P. F. In press. Biostratigraphy and paleoecology of Neogene and Oligocene silicoflagellates from cores recovered during antarctic leg 28, Deep Sea Drilling Project. In: Initial Reports of the Deep Sea Drilling Project (Hayes, D. E., et al.), 28. Washington, D.C., U.S. Government Printing Office. Ciesielski, P. F. In preparation. Biostratigraphy and paleoecology of Neogene and Oligocene silicoflagellates recovered from piston and drill cores off East Antarctica. Tallahassee, Sedimentology Research Laboratory, Department of Geology, Florida State University. Contribution, 41.
During the recent leg 36 of the Deep Sea Drilling Project (DSDP) I took several plankton samples from the Scotia Sea. Examination of the samples revealed representatives of the diatom genus Pleurosigma (fig.) in a living state. The samples in which Pleurosigma were observed were taken from about 15 meters below the water surface at 56°09'S. 38°11 1W. and 56°20'S. 40 0 25'W. The nearest land is South Georgia Island, more than 210 kilometers to the northeast. Pleurosigma generally is, considered to be a nearshore, benthic diatom. It has, however, been reported from deep ocean sediments by several authors. Kolbe (1954) observed it to occur throughout Swedish Deep Sea Expedition core 76, although it occurred comparatively seldom. Bukry and Foster (1973) recorded
272
ANTARCTIC JOURNAL
