Evidence for early Late Miocene climate change
PROTEA 5:1984 PRINCIPAL ROCK GROUPINGS Ultrornofic hauls 17146 kg), rocks from 25E to 47Cf -50 44.2% Southwest Indian Ridge
I BosIfjc rocks
Ids
44.7%
40 30
30
20
Gobbroic rocks 8.7%
10 0
20 Erratics Mn+ . 10 2.2% Hydrothermal 0.2% 0
Lplif ted blocks along Fracture zones ndge-transform intersections
Figure 2. Four tagged dredge hauls on good weather for sorting and sawing.
Melville's fantail, awaiting
Rift volley" walls
Figure 3. Proportions of principal rock types as percentage of total sample weight dredged. Within columns are the contributions from fracture zones, spreading centers ("rift valley" walls) and uplifted blocks along ridge-transform intersections. ("kg" denotes "kilogram:' "Mn" denotes "manganese:')
References Driscoll, M.L., R.L. Fisher, and B. Parsons. In press. A comparison of Seasat altimetry and surface-ship bathymetry over the southwest Indian Ridge. Geophysical Journal of the Royal Astronomical Society.
Fisher, R.L., and J.G. Sciater. 1983. Tectonic evolution of the southwest Indian Ocean since the Mid-Cretaceous: Plate motions and stability of the pole of Antarctica/Africa for at least 80 million years. Geophysical Journal of the Royal Astronomical Society, 73, 553 - 576.
Evidence for early Late Miocene climate change
Piston cores and
Core
S. HAMBOS
Department of Geology Rutgers University Newark, New Jersey 07102
L.H. BURCKLE
We studied diatoms in sediments from five late middle to early Late Miocene sites from the southern oceans (table). Magnetostratigraphic control in one piston core (101277-25) combined with the application of foraminiferal datum levels in Deep Sea Drilling Project (DSDP) sites 278 and 512 indicate that the majority of our sites cover the interval from magnetic chrons 9 to 11 (approximately 8.5 to 10.4 million years ago). Additional paleoenvironmental control is provided by an oxygen isotope record on DSDP site 278 (Margolis, Kroopnick, and Showers 1982). 96
sites used in this study
Depth Latitude Longitude (in centimeters)
E345a 57023'S 159060'E 3,795 I0127725b 68037'S 10058'E 2,015 DSDP 278 56033'S 160004'E 3,675 DSDP 512 49052'S 40051'W 1,846 DSDP 513A 47035'S 2438'W 4,373 a "E" denotes 'Etanin." b
Lamont-Doherty Geological Observatory Palisades, New York 10964
DSDP
10" denotes "Islas Orcadas."
Our data show considerable fluctuation in abundance of individual diatoms through this time interval. In DSDP site 278 these abundance changes coincide with changes in the oxygen isotope ratio and are likely tied to water mass shifts. However, we hesitate to relate these fluctuations to north-south movements of the Polar Front since, in the present-day southern ocean and in surface sediments, diatoms also show striking changes across the subantarctic front (Burckle, Jacobs, and McLaughlin in press). In any event, during the interval of time studied, we see one northward expansion and one southward contraction of polar waters. This expansion is seen as a marked increase in abundance of Denticulopsis dimorpha accompanied by a decrease in abundance of D. praedimorpha. This response is most strikin ANTARCTIC JOURN
in the more southerly cores studied by us but is also observed in those sites taken north of the present-day Polar Front. In DSDP site 278 the increase in D. dimorpha is also marked by an oxygen enrichment. Using the magnetostratigraphy in core 101277-25 as our control, our best estimate of the age of this cooling is about 8.6 to 8.8 million years ago. A change in composition of diatom floras in the equatorial Pacific is recorded at about the same time (Burckle 1983). This latter change appears to reflect an intensification of the equatorial current system. We have evidence for a subsequent contraction of polar waters in DSDP site 278. Although we lack adequate time control on this event, our best estimate is that it occurred in the early part of magnetic chron 9 about 8.2 to 8.3 million years ago. A reduction in intensity of equatorial Pacific circulation also occurs at about this time (Burckle unpublished data). This research was supported by National Science Foundation grant OCE 76-82046 to Lloyd Burckle. We thank Dennis Cassidy
1985 REVIEW
of the Antarctic Research Facility, Florida State University and the Deep Sea Drilling Project for providing us with core materials.
References Burckle, L.H. 1983. Early late Miocene paleoclimatic event: Evidence from the Southern Ocean and the eastern equatorial Pacific. (Abstract.) Geological Society of America Annual Meeting, 15, 536. Burckle, L.H., S.S. Jacobs, and R.B. McLaughlin. In press. Late spring diatom distribution between New Zealand and the Ross Sea: Correlation with hydrography and bottom sediments. Micropaleontology. Margolis, S.V., P.M. Kroopnick, and N.J. Showers. 1982. Paleoceanography: The history of the oceans changing environment. In W. C. Ernst, and J . C. Mann (Eds.), The environment of the deep sea. New York: Prentice-Hall.
97
I BosIfjc rocks
Ids
44.7%
40 30
30
20
Gobbroic rocks 8.7%
10 0
20 Erratics Mn+ . 10 2.2% Hydrothermal 0.2% 0
Lplif ted blocks along Fracture zones ndge-transform intersections
Figure 2. Four tagged dredge hauls on good weather for sorting and sawing.
Melville's fantail, awaiting
Rift volley" walls
Figure 3. Proportions of principal rock types as percentage of total sample weight dredged. Within columns are the contributions from fracture zones, spreading centers ("rift valley" walls) and uplifted blocks along ridge-transform intersections. ("kg" denotes "kilogram:' "Mn" denotes "manganese:')
References Driscoll, M.L., R.L. Fisher, and B. Parsons. In press. A comparison of Seasat altimetry and surface-ship bathymetry over the southwest Indian Ridge. Geophysical Journal of the Royal Astronomical Society.
Fisher, R.L., and J.G. Sciater. 1983. Tectonic evolution of the southwest Indian Ocean since the Mid-Cretaceous: Plate motions and stability of the pole of Antarctica/Africa for at least 80 million years. Geophysical Journal of the Royal Astronomical Society, 73, 553 - 576.
Evidence for early Late Miocene climate change
Piston cores and
Core
S. HAMBOS
Department of Geology Rutgers University Newark, New Jersey 07102
L.H. BURCKLE
We studied diatoms in sediments from five late middle to early Late Miocene sites from the southern oceans (table). Magnetostratigraphic control in one piston core (101277-25) combined with the application of foraminiferal datum levels in Deep Sea Drilling Project (DSDP) sites 278 and 512 indicate that the majority of our sites cover the interval from magnetic chrons 9 to 11 (approximately 8.5 to 10.4 million years ago). Additional paleoenvironmental control is provided by an oxygen isotope record on DSDP site 278 (Margolis, Kroopnick, and Showers 1982). 96
sites used in this study
Depth Latitude Longitude (in centimeters)
E345a 57023'S 159060'E 3,795 I0127725b 68037'S 10058'E 2,015 DSDP 278 56033'S 160004'E 3,675 DSDP 512 49052'S 40051'W 1,846 DSDP 513A 47035'S 2438'W 4,373 a "E" denotes 'Etanin." b
Lamont-Doherty Geological Observatory Palisades, New York 10964
DSDP
10" denotes "Islas Orcadas."
Our data show considerable fluctuation in abundance of individual diatoms through this time interval. In DSDP site 278 these abundance changes coincide with changes in the oxygen isotope ratio and are likely tied to water mass shifts. However, we hesitate to relate these fluctuations to north-south movements of the Polar Front since, in the present-day southern ocean and in surface sediments, diatoms also show striking changes across the subantarctic front (Burckle, Jacobs, and McLaughlin in press). In any event, during the interval of time studied, we see one northward expansion and one southward contraction of polar waters. This expansion is seen as a marked increase in abundance of Denticulopsis dimorpha accompanied by a decrease in abundance of D. praedimorpha. This response is most strikin ANTARCTIC JOURN
in the more southerly cores studied by us but is also observed in those sites taken north of the present-day Polar Front. In DSDP site 278 the increase in D. dimorpha is also marked by an oxygen enrichment. Using the magnetostratigraphy in core 101277-25 as our control, our best estimate of the age of this cooling is about 8.6 to 8.8 million years ago. A change in composition of diatom floras in the equatorial Pacific is recorded at about the same time (Burckle 1983). This latter change appears to reflect an intensification of the equatorial current system. We have evidence for a subsequent contraction of polar waters in DSDP site 278. Although we lack adequate time control on this event, our best estimate is that it occurred in the early part of magnetic chron 9 about 8.2 to 8.3 million years ago. A reduction in intensity of equatorial Pacific circulation also occurs at about this time (Burckle unpublished data). This research was supported by National Science Foundation grant OCE 76-82046 to Lloyd Burckle. We thank Dennis Cassidy
1985 REVIEW
of the Antarctic Research Facility, Florida State University and the Deep Sea Drilling Project for providing us with core materials.
References Burckle, L.H. 1983. Early late Miocene paleoclimatic event: Evidence from the Southern Ocean and the eastern equatorial Pacific. (Abstract.) Geological Society of America Annual Meeting, 15, 536. Burckle, L.H., S.S. Jacobs, and R.B. McLaughlin. In press. Late spring diatom distribution between New Zealand and the Ross Sea: Correlation with hydrography and bottom sediments. Micropaleontology. Margolis, S.V., P.M. Kroopnick, and N.J. Showers. 1982. Paleoceanography: The history of the oceans changing environment. In W. C. Ernst, and J . C. Mann (Eds.), The environment of the deep sea. New York: Prentice-Hall.
97
