28
Such sediment accumulations are known from the Barents
shelf (Vorren et al. 1989) and the Neogene in the Gulf of
Alaska (several kilometers; Powell and Molnia 1989).
Deep-sea drilling in the Norwegian-Greenland Sea, e.g. at
550 to 1270 m water depth on the Yerrnak Plateau to the
northeast of Svalbard, has revealed Plio-Pleistocene silty
c1ays and muds of 200 m to more than 500 m in thickness
which contain abundant dropstones (Thiede et al. 1995).
Part of these glacially influenced sediments accumulated at
rates in excess of 100 mlMa, are overconsolidated (due to
ice load?), and show evidence of calcium carbonate dissolution as a result ofincreased CO 2 in bottom water.
Icebergs originating from dirty glaciers frequently
carry their debris load over long distances. They are
2.1.3 Summary (Glacial Deposits)
- Glacial and proglacial sediments are extremely
variable both in texture and composition, because they are usually derived from both extrabasinal and intra-basinal sources and deposited
in greatly differing subenvironments.
- Although glacial and proglacial sediments cover
wide areas on the present-day land surface, in
particular in the northern hemisphere, it is only a
part of them (predominantly glaciolacustrine and
glaciomarine sediments) which have a good
chance of being preserved in the geological record.
Chapter 2 Continental Sediments
the source of widely distributed dropstones in oceanic hemipelagic and pelagic sediments far away
from glaciated regions. Apart from these distinctive
features, glacial and interglacial deep-sea sediments
commonly vary in their contents of biogenic carbonate and opaline silica.
In the North Atlantic, for example, glacial periods are characterized by carbonate dissolution and relatively high productivity of biogenic opal, whereas interglacial sediments
tend to be richer in biogenic carbonate (coccoliths, planktic
and benthic foraminifera). These differences mainly result
from changes in the oceanic current systems (Henrich and
Baumann 1995; df. Sect. 5.6).
- Distinctive features of these deposits are
drops tones and sometimes specific deformation
structures, but they often also alternate with
glacier-generated diamicts (tills or tillites),
glaciofluvial and non-glacial sediments. Marine
muds may contain morgenstern-like glendonites.
- Flow tills (or tillites) are sometimes confused
with mud flows and debris flows of non-glacial
origin. The true nature of these deposits can
usually be found by studying the under- and
overlying strata.
Such sediment accumulations are known from the Barents
shelf (Vorren et al. 1989) and the Neogene in the Gulf of
Alaska (several kilometers; Powell and Molnia 1989).
Deep-sea drilling in the Norwegian-Greenland Sea, e.g. at
550 to 1270 m water depth on the Yerrnak Plateau to the
northeast of Svalbard, has revealed Plio-Pleistocene silty
c1ays and muds of 200 m to more than 500 m in thickness
which contain abundant dropstones (Thiede et al. 1995).
Part of these glacially influenced sediments accumulated at
rates in excess of 100 mlMa, are overconsolidated (due to
ice load?), and show evidence of calcium carbonate dissolution as a result ofincreased CO 2 in bottom water.
Icebergs originating from dirty glaciers frequently
carry their debris load over long distances. They are
2.1.3 Summary (Glacial Deposits)
- Glacial and proglacial sediments are extremely
variable both in texture and composition, because they are usually derived from both extrabasinal and intra-basinal sources and deposited
in greatly differing subenvironments.
- Although glacial and proglacial sediments cover
wide areas on the present-day land surface, in
particular in the northern hemisphere, it is only a
part of them (predominantly glaciolacustrine and
glaciomarine sediments) which have a good
chance of being preserved in the geological record.
Chapter 2 Continental Sediments
the source of widely distributed dropstones in oceanic hemipelagic and pelagic sediments far away
from glaciated regions. Apart from these distinctive
features, glacial and interglacial deep-sea sediments
commonly vary in their contents of biogenic carbonate and opaline silica.
In the North Atlantic, for example, glacial periods are characterized by carbonate dissolution and relatively high productivity of biogenic opal, whereas interglacial sediments
tend to be richer in biogenic carbonate (coccoliths, planktic
and benthic foraminifera). These differences mainly result
from changes in the oceanic current systems (Henrich and
Baumann 1995; df. Sect. 5.6).
- Distinctive features of these deposits are
drops tones and sometimes specific deformation
structures, but they often also alternate with
glacier-generated diamicts (tills or tillites),
glaciofluvial and non-glacial sediments. Marine
muds may contain morgenstern-like glendonites.
- Flow tills (or tillites) are sometimes confused
with mud flows and debris flows of non-glacial
origin. The true nature of these deposits can
usually be found by studying the under- and
overlying strata.