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siliceous shells of diatoms also survive acid wetland burial
whereas carbonate shells of snails or shellfish survive
better in neutral qbase conditions. Most Quaternary
organisms survive as original organic material
subfossils
,
since relatively little time for replacement or total
decomposition has occurred.
These examples illustrate the archaeological term
preservation context
of fossils early in environmental
reconstruction - the particular conditions determining
what survives of organisms and assemblages.
Figure 23.3
expands on the range of organisms, materials and
preservation contexts with some archaeological examples.
Bias inherent in any fossil evidence is compounded by
estimates that only approximately 10 per cent of global
species are likely to enter the fossil record, endoskeletal
organisms are rarely found as fossils and - since terrestrial
environments experience denudation - most will be
marine, shallow-water species. Some important excep-
tions include Mesozoic dinosaurs and Late Cenozoic
hominids
and
hominins
(pre- and early humans) preserved
in arid environments).
Volcanic
Glass
Obsidian
Unburnt Sediment
Burnt Flint and Stone
Slag
Pottery, Baked Earth
Precipitated Calcite
Shells
Tooth Enamel
Bone, Antler, Ivory, Teeth
Wood, Plant, Seeds, etc.
Dating methods applicable to
given artifact types
the dating method of choice.
Source: Rapp and Hill (1998)
assessed using radar, acoustic and seismic reflectance
techniques allowing us to 'see through' glacier ice to
bedrock (thereby measuring ice thickness), weathering
crusts to intact rock, and water to underlying lake- or
sea-bed landforms. Area mapping locates individual
landforms within their wider spatial context and is
particularly useful in reconstructing relict fluvial, glacial
and permafrost landsystems (see
Chapters 14,
15).
Reconstruction of relict geomorphic environments
extends by inference beyond general palaeo-climate to the
modelling of related water or ice balances, thermal
regimes, etc. Modelling of the Late Pleistocene British ice
sheet in
Figure 15.12
from geomorphic evidence extends
to ice dynamics and hence climatic conditions 'required'
to deliver it. No one was there to record the event and there
is room for error interpreting a wide range of other proxy
and analogue data used, but the reconstructed model
(one of several) illustrates their potential.
Altitudinal data, marking vertical distance above a
datum
or reference altitude such as sea level, are essential
for 3-D reconstructions of former sea and lake levels,
snowlines (glacier mass balance
equilibrium lines
), upper
limits of glaciation (
trimlines
) and river terraces. Other
proxy data are required for the reconstruction of causative
processes and events, especially in the Quaternary context
when eustatic sea level has fluctuated regularly by ±
150 m but where differentiation between isostatic,
eustatic, glacio-eustatic and glacio-tectonic mechanisms
Sedimentological and stratigraphic approaches to
environmental reconstruction emphasize the character,
preservation and sequence of buried materials. Yet as they
formed most were expressions of surface geomorphic
processes - certainly in terrestrial and shallow marine
environments and, arguably, even on the submarine
continental slope (see
Plate 12.9
).
Just as stratigraphy
records
palaeo-geomorphic
environments, so individual
landforms and their landsystem position today represent
either contemporary processes or
relicts
(rather than
'fossils') of recent Quaternary, predominantly cold-
climate processes in temperate and high latitudes. The
mean latitude of the northern hemisphere sub-arctic
boundary lies today at 69
during the
last glacial maximum 18 a ago, effectively squeezing
temperate, subtropical and tropical zones towards the
equator. As these zones recovered their former latitudes
during the Holocene, climate and geomorphic changes
centred mostly around increased desiccation - expanding
older deserts, creating new ones and evaporating conti-
nental interior lake systems.
Landforms and constituent materials provide diag-
nostic value, linked to modern analogues in active
geomorphic environments. They are mapped with
detailed accuracy and large-scale cover from airborne and
satellite remote sensing. Their subsurface character is
but extended to 45
