1. Clay mineral assemblages in surficial continental
margin sediments west of the Antarctic Peninsula consist of smectite, chlorite,
and illite, with kaolinite occurring in trace amounts only. High smectite
concentrations typify the shelf sediments off northern Graham Land, whereas
chlorite and illite dominate in shelf deposits offshore from the southern
Antarctic Peninsula. At the continental rise a bottom current transports
smectite supplied from the northern Antarctic Peninsula to the southwest (Fig.
2. An upper Quaternary sediment sequence
from site PS1565 comprises an interglacial clay mineral assemblage with high
smectite amounts and a glacial assemblage characterized by enhanced chlorite
concentrations. During glacial periods, chlorite-enriched detritus was supplied
to the continental rise by gravitational downslope processes triggered by
the advance of grounded ice streams to the shelf break.
3. Upper Miocene to Quaternary sediments
recovered at ODP Leg 178 continental rise Sites 1095 and 1096 exhibit clay
mineral fluctuations alternating between two endmember assemblages. One assemblage
is characterized by <20% smectite and >40% chlorite. The other assemblage
has >20% smectite and <40% chlorite. The clay mineral fluctuations
are similar to those observed at site PS1565. The short-term changes in clay
mineral composition at Sites 1095 and 1096 we ascribe to repeated ice advances
and retreats across the shelf west of the Antarctic Peninsula, reflecting
glacial-interglacial cyclicity (Fig. 2). We conclude that oscillations in
Antarctic ice volume may have influenced the global climate already during
the late Miocene.
4. Only slight long-term changes are observed
in the clay mineral assemblages deposited at ODP Sites 1095 and 1096. A slight
enhancement of smectite contents between ~7.3 Ma and ~5.3 Ma at Site 1095
may be a consequence of a higher smectite supply caused by an intensification
of volcanism on the South Shetland Islands and by a strengthening of glacial
erosion in northern Graham Land in response to local uplift associated with
ridge crest?trench collision. An increase of illite at Site 1096 between
~1.5 Ma and ~0.2 Ma is probably caused by changes in the supply of glacial
debris from different source areas on the southern Antarctic Peninsula.
5. The clay mineral assemblages deposited
at Sites 1095 and 1096 point to an onset of vast glaciation in the Antarctic
Peninsula region before 9 m.y., but give no evidence for major deglaciation
events since then.
The results have been summarized in two papers:
C.-D. und Ehrmann, W. (2001): Distribution of Clay
Minerals in Drift Sediments on the Continental Rise West of the
Antarctic Peninsula, ODP Leg 178, Sites 1095 and 1096. - In: Barker,
P.F., Camerlenghi, A., Acton, G.D. & Ramsay, A.T.S. (Eds.):
Proc. ODP, Sci. Results, 178: 1-29 (PDF-Format)
Hillenbrand, C.-D. & Ehrmann, W.
(2005): Late Neogene to Quaternary environmental changes in
the Antarctic Peninsula region: Evidence from drift sediments.
- Global and Planetary Change, 45: 165-191.