2.1 Glacial Deposits
The regular bedding of these types of lake bottom sediments may be disturbed by different processes: mass flows,
load casting (represented, for example, by small-scale balland-pillow structures), and even by burrowing organisms
(bioturbation). Overriding ice can promote compaction of
the clayey bottomsets and deform some of the lake deposits.
2.1.2 Glaciomarine Sediments
Glaciomarine sediments or sedimentary sequences
contain facies types which indicate the direct influence of glaciers. However, this clear relationship
cannot be described by a simple facies model. The
net growth of ice on the continents and the advance
of ice toward the sea during a cold period is accompanied by sea level fall and vice versa. Furthermore,
loading of the crust by thick continental ice sheets
causes isostatic subsidence and, after melting of the
ice, uplift. However, both sea level fluctuation and
isostatic adjustment of the crust do not act synchronously, the latter lagging behind the sea level
changes.
If, for example, in a nonglaciated area the global sea level
has reached its eustatic minimum level, a glaciated shelf
sea may still subside due to the isostatic effect of the iceload and therefore experience a transgressive sea. When the
global eustatic sea level has again reached its maximum,
the coastline of a formerly glaciated area may still continue
to rise, causing a regression of the sea.
In short, glaciomarine sedimentary sequences are
strongly and complexly affected by migrating co astlines over long distances. Simultaneously, the continental and lacustrine glacial associations can mi grate
back and forth a shallow sea and alternate with
glaciomarine and normal marine facies types. During
low sea level stands, the glaciers can advance over
the emerging bottom of a shelf sea and deposit a tilloutwash-periglacial-lacustrine facies association on
top ofmarine beds (Fig. 2.6a). The subsequent transgressing sea, in conjunction with a warmer climate,
will in general cause a drastic retreat of the ice margin, drown the tills and their associated continental
and lacustrine sediments, and enable the deposition
of subaqueous glaciomarine sediments.
As long as the sea is in contact with the ice margin, subglacial meltwaters can deposit submarine icecontact fans (Fig. 2.3a and 2.5a) and release their
suspended loads as plumes into the sea. Floating ice
can drop its solid material over large areas. Its fine
and coarse grained rain of particles forms massive or
stratified diamicts (Fig. 2.5b, c, and d), which locally
may be affected by bottom currents, reworked by
storm waves, or redeposited as grain flows, mud
flows and, in deeper water, as turbidity currents (Fig.
2.5e, f, and g). This facies association is highly variable, depending on the load of the ice, the configura25
tion and hydraulic regime of the marginal sea, and
many other factors. The most distinctive features of
glaciomarine sediments are dropstones in stratified
muds which also contain marine fossils and frequently display bioturbation.
During the last decade, repeated layers of icerafted detritus (IRD) of the late Quatemary, so-called
Heinrich Layers present in the North Atlantic between 40 and 50° latitude, have been intensely studied (Heinrich 1988; Bond and Lotti 1995; and many
others). These layers are characterized by a relatively
rapid sedimentation rate and may cover a layer rich
in organic carbon. The Heinrich Layers contain a
high proportion of detrital carbonate, are rich in cold
water mikro-organisms but poor in planktonic
foraminifera. These widespread beds are explained
by increased calfing of icebergs and meltwater influx
during periods of deglaciation which may have occurred at time intervals of some thousand years only.
In some modern and ancient glaciomarine environments, a
special carbonate mineral, i.e., calcium carbonate
hexahydrate (ikaite) or pseudomorphs after ikaite were
found, which are referred to as glendonites (Suess et al.
1982; Shearman and Smith 1985; Kemper 1987; Eyles et
al. 1998). This mineral occurs in morgenstern-like or
stellate aggregates, several centimeters in size, and indicates sub-zero temperature conditions in the sediments at
or somewhat below the sea floor. These minerals form from
interstitial solutions of sediments rich in organic matter.
During periods in which no ice reaches the coast of
the sea, outwash streams of nearby glaciers deposit
their bed load as proglacial fans and deltas along the
coast. Their suspended load can be distributed over
large areas of the sea, especially if flocculation of
c1ay particles and their settling as aggregates is dclayed. This is generally caused by mixing of
inflowing fresh water with sea water. In this case,
however, the marine sediments carry no direct evidence of glacial influence.
Thus, repeated advance and retreat of the ice
sheets across shelf seas can in principle lead to a cyc1ic sequence of altemating (continental) glacial,
glaciomarine and normal marine sediments (Fig.
2.6b-d). Due to glacial erosion and marine current
activity, however, the sedimentary record of these
processes on the shelf is often incomplete.
In regions of very cold climate and huge ice accumulation (as today in the Antarctic), large areas of
the sea can be covered with comparatively "clean"
thick shelf ice. Since most of the debris in these
floating ice sheets is located near their base and
dropped below the ice due to subglacial ablation, the
ice margins and floating icebergs are poor in debris
and therefore leave behind relatively little evidence
of ice action. Neogene and Quaternary proglacial
marine sediments in this environment are often rich
in diatoms, bioturbated, and contain few dropstones.
The regular bedding of these types of lake bottom sediments may be disturbed by different processes: mass flows,
load casting (represented, for example, by small-scale balland-pillow structures), and even by burrowing organisms
(bioturbation). Overriding ice can promote compaction of
the clayey bottomsets and deform some of the lake deposits.
2.1.2 Glaciomarine Sediments
Glaciomarine sediments or sedimentary sequences
contain facies types which indicate the direct influence of glaciers. However, this clear relationship
cannot be described by a simple facies model. The
net growth of ice on the continents and the advance
of ice toward the sea during a cold period is accompanied by sea level fall and vice versa. Furthermore,
loading of the crust by thick continental ice sheets
causes isostatic subsidence and, after melting of the
ice, uplift. However, both sea level fluctuation and
isostatic adjustment of the crust do not act synchronously, the latter lagging behind the sea level
changes.
If, for example, in a nonglaciated area the global sea level
has reached its eustatic minimum level, a glaciated shelf
sea may still subside due to the isostatic effect of the iceload and therefore experience a transgressive sea. When the
global eustatic sea level has again reached its maximum,
the coastline of a formerly glaciated area may still continue
to rise, causing a regression of the sea.
In short, glaciomarine sedimentary sequences are
strongly and complexly affected by migrating co astlines over long distances. Simultaneously, the continental and lacustrine glacial associations can mi grate
back and forth a shallow sea and alternate with
glaciomarine and normal marine facies types. During
low sea level stands, the glaciers can advance over
the emerging bottom of a shelf sea and deposit a tilloutwash-periglacial-lacustrine facies association on
top ofmarine beds (Fig. 2.6a). The subsequent transgressing sea, in conjunction with a warmer climate,
will in general cause a drastic retreat of the ice margin, drown the tills and their associated continental
and lacustrine sediments, and enable the deposition
of subaqueous glaciomarine sediments.
As long as the sea is in contact with the ice margin, subglacial meltwaters can deposit submarine icecontact fans (Fig. 2.3a and 2.5a) and release their
suspended loads as plumes into the sea. Floating ice
can drop its solid material over large areas. Its fine
and coarse grained rain of particles forms massive or
stratified diamicts (Fig. 2.5b, c, and d), which locally
may be affected by bottom currents, reworked by
storm waves, or redeposited as grain flows, mud
flows and, in deeper water, as turbidity currents (Fig.
2.5e, f, and g). This facies association is highly variable, depending on the load of the ice, the configura25
tion and hydraulic regime of the marginal sea, and
many other factors. The most distinctive features of
glaciomarine sediments are dropstones in stratified
muds which also contain marine fossils and frequently display bioturbation.
During the last decade, repeated layers of icerafted detritus (IRD) of the late Quatemary, so-called
Heinrich Layers present in the North Atlantic between 40 and 50° latitude, have been intensely studied (Heinrich 1988; Bond and Lotti 1995; and many
others). These layers are characterized by a relatively
rapid sedimentation rate and may cover a layer rich
in organic carbon. The Heinrich Layers contain a
high proportion of detrital carbonate, are rich in cold
water mikro-organisms but poor in planktonic
foraminifera. These widespread beds are explained
by increased calfing of icebergs and meltwater influx
during periods of deglaciation which may have occurred at time intervals of some thousand years only.
In some modern and ancient glaciomarine environments, a
special carbonate mineral, i.e., calcium carbonate
hexahydrate (ikaite) or pseudomorphs after ikaite were
found, which are referred to as glendonites (Suess et al.
1982; Shearman and Smith 1985; Kemper 1987; Eyles et
al. 1998). This mineral occurs in morgenstern-like or
stellate aggregates, several centimeters in size, and indicates sub-zero temperature conditions in the sediments at
or somewhat below the sea floor. These minerals form from
interstitial solutions of sediments rich in organic matter.
During periods in which no ice reaches the coast of
the sea, outwash streams of nearby glaciers deposit
their bed load as proglacial fans and deltas along the
coast. Their suspended load can be distributed over
large areas of the sea, especially if flocculation of
c1ay particles and their settling as aggregates is dclayed. This is generally caused by mixing of
inflowing fresh water with sea water. In this case,
however, the marine sediments carry no direct evidence of glacial influence.
Thus, repeated advance and retreat of the ice
sheets across shelf seas can in principle lead to a cyc1ic sequence of altemating (continental) glacial,
glaciomarine and normal marine sediments (Fig.
2.6b-d). Due to glacial erosion and marine current
activity, however, the sedimentary record of these
processes on the shelf is often incomplete.
In regions of very cold climate and huge ice accumulation (as today in the Antarctic), large areas of
the sea can be covered with comparatively "clean"
thick shelf ice. Since most of the debris in these
floating ice sheets is located near their base and
dropped below the ice due to subglacial ablation, the
ice margins and floating icebergs are poor in debris
and therefore leave behind relatively little evidence
of ice action. Neogene and Quaternary proglacial
marine sediments in this environment are often rich
in diatoms, bioturbated, and contain few dropstones.