2 Continental Sediments
2.1 Glacial Deposits
of Lowlands, Lakes, and in the Sea
2.1.1 Continental Glacial Deposits
Introduction
Continental Ice Sheet Deposits
Glaciofluvial Sediments
Proglacial Lacustrine Deposits
2.1.2 Glaciomarine Sediments
2.1.3 Summary (Glacial Deposits)
2.1.1 Continental Glacial Deposits
Introduetion
Glaciers produce and effect numerous types of both
continental and marine sediments. From present-day
glaciated and periglacial regions we know a great
variety of features characteristic of glacial environments, ineluding many minor structures and patterns
which can be observed at or near the land surface.
Therefore it is barely possible to summarize all these
phenomena in a few simple facies models.
However, if we focus only on glacial sediments of
a high geologie al preservation potential, we can neglect glacial landforms and sediments in highly elevated mountain ranges or periglacial phenomena
such as patterned ground, gelifluction, and other
gravity mass movements on subaerial slopes. Then
the remaining environments to be considered are glaciated and proglacial lowlands, lakes, and the sea.
The following simplified facies models present some
information only on those glacial sedimentary facies
which have a relatively good chance of being preserved over long geological time.
In order to understand the sedimentary processes of these
selected environments, a general knowledge of glacial phenomena is, of course, necessary. Useful references are, for
example: Molnia (1983), Grobe (1987), Eyles (1984);
Eyles and Miall (1984), Edwards (1986), Brodzikowski
and van Loon (1991), Eyles and Eyles (1992), Eyles
(1993), Hambrey (1994), Ehlers (1996).
Continental lee Sheet Deposits
A continental ice sheet, advancing over areas of low
relief, carries debris from its usually more elevated
source area and takes up further material at its base.
If the glacier base is cold and frozen to the ground,
more basal debris is generally taken up than by "temperate" glaciers, which have a wet base sliding relatively easily over the substrate.
The debris left behind after the ice melts (Fig. 2.la
and b) is usually poorly sorted and unstratified and, if
its origin is uncertain, described as diamiet (when
unlithified also as diarnicton or mixtum). Such sediments typically contain boulders and large elasts
floating in a finer grained matrix of silt and sand.
Clays derived from weathered soils are absent (due
to the cold elirnate) or play only a rninor role. If the
debris clearly originates from glacial action, the
terms till (for unlithified material) and tillite (for
lithified material) are common; recently the term
orthotill (in contrast to paratill which has undergone
mass mcvement or is sedimented through a colurnn
of water) was recommended (e.g., Shaw 1985). Debris accumulated at the base of glaciers is termed
basal till or lodgement till, because some of the material is trapped by obstaeles in the substrate. "Coldbased" glaciers can cause deformation of the underlying bedrock (glaciotectonic structures) and rip up
large slabs or plates from the substrate by shearing.
One can also observe thrust faults and small-scale
folds within the lodgement till. Nearly horizontal or
low-angle shear zones within the till cause some
crude stratification and imbrication of coarser components. At wet-based ice margins, these phenomena
are even better developed. The partieles of the relatively thin basal debris layer often undergo intense
abrasion (ice-faceted elasts) their long axes tending
to become aligned parallel to the direction of ice
flow. Continued lodgement of elasts on top of the
substrate rnay lead to the formation of lenticular beds
of coarse grained diarniet.
Melting of glacier ice both at its surface and/or its
base leads to the release and accumulation of debris
in the form of melt-out till (Fig. 2.1 a and b). This
process I.lsually occurs where the entire ice sheet, or
at least its basal part, is stagnant. Hence melt-out till,
if not overridden by a later ice advance, is not internally deformed. Its elasts mayaiso be striated, but for
2.1 Glacial Deposits
of Lowlands, Lakes, and in the Sea
2.1.1 Continental Glacial Deposits
Introduction
Continental Ice Sheet Deposits
Glaciofluvial Sediments
Proglacial Lacustrine Deposits
2.1.2 Glaciomarine Sediments
2.1.3 Summary (Glacial Deposits)
2.1.1 Continental Glacial Deposits
Introduetion
Glaciers produce and effect numerous types of both
continental and marine sediments. From present-day
glaciated and periglacial regions we know a great
variety of features characteristic of glacial environments, ineluding many minor structures and patterns
which can be observed at or near the land surface.
Therefore it is barely possible to summarize all these
phenomena in a few simple facies models.
However, if we focus only on glacial sediments of
a high geologie al preservation potential, we can neglect glacial landforms and sediments in highly elevated mountain ranges or periglacial phenomena
such as patterned ground, gelifluction, and other
gravity mass movements on subaerial slopes. Then
the remaining environments to be considered are glaciated and proglacial lowlands, lakes, and the sea.
The following simplified facies models present some
information only on those glacial sedimentary facies
which have a relatively good chance of being preserved over long geological time.
In order to understand the sedimentary processes of these
selected environments, a general knowledge of glacial phenomena is, of course, necessary. Useful references are, for
example: Molnia (1983), Grobe (1987), Eyles (1984);
Eyles and Miall (1984), Edwards (1986), Brodzikowski
and van Loon (1991), Eyles and Eyles (1992), Eyles
(1993), Hambrey (1994), Ehlers (1996).
Continental lee Sheet Deposits
A continental ice sheet, advancing over areas of low
relief, carries debris from its usually more elevated
source area and takes up further material at its base.
If the glacier base is cold and frozen to the ground,
more basal debris is generally taken up than by "temperate" glaciers, which have a wet base sliding relatively easily over the substrate.
The debris left behind after the ice melts (Fig. 2.la
and b) is usually poorly sorted and unstratified and, if
its origin is uncertain, described as diamiet (when
unlithified also as diarnicton or mixtum). Such sediments typically contain boulders and large elasts
floating in a finer grained matrix of silt and sand.
Clays derived from weathered soils are absent (due
to the cold elirnate) or play only a rninor role. If the
debris clearly originates from glacial action, the
terms till (for unlithified material) and tillite (for
lithified material) are common; recently the term
orthotill (in contrast to paratill which has undergone
mass mcvement or is sedimented through a colurnn
of water) was recommended (e.g., Shaw 1985). Debris accumulated at the base of glaciers is termed
basal till or lodgement till, because some of the material is trapped by obstaeles in the substrate. "Coldbased" glaciers can cause deformation of the underlying bedrock (glaciotectonic structures) and rip up
large slabs or plates from the substrate by shearing.
One can also observe thrust faults and small-scale
folds within the lodgement till. Nearly horizontal or
low-angle shear zones within the till cause some
crude stratification and imbrication of coarser components. At wet-based ice margins, these phenomena
are even better developed. The partieles of the relatively thin basal debris layer often undergo intense
abrasion (ice-faceted elasts) their long axes tending
to become aligned parallel to the direction of ice
flow. Continued lodgement of elasts on top of the
substrate rnay lead to the formation of lenticular beds
of coarse grained diarniet.
Melting of glacier ice both at its surface and/or its
base leads to the release and accumulation of debris
in the form of melt-out till (Fig. 2.1 a and b). This
process I.lsually occurs where the entire ice sheet, or
at least its basal part, is stagnant. Hence melt-out till,
if not overridden by a later ice advance, is not internally deformed. Its elasts mayaiso be striated, but for