Geoscience Reference
In-Depth Information
communities comprising their biosphere; and active
processes whereby these materials and organisms are
energized, interact and become transformed, leading to
dynamic changes of continuous and episodic (event)
nature. Processes and change leave their evidence and
environmental reconstruction seeks to interpret this
record of previous or palaeo -environments. This is a
complex procedure when we consider how much eye-
witness statements of the 'facts' of a crime or a sporting
incident can vary. Physical and perceived viewpoints
differ but witnesses also inject their own deliberate or
inadvertent bias into the significance and interpreta-
tion of events. Environmental reconstruction depends
on survival, collection and successful interpretation of
incomplete and indirect, or proxy , records of past events
and rarely with direct observation or complete records.
This changed with the advent of scientific instruments
capable of measuring environmental parameters, such as
British weather records commencing in AD 1659. It is now
greatly enhanced by comprehensive instrumental records
and environmental monitoring, remote sensing, advanced
analytical technology, data processing and analysis. Most
reconstruction, however, concerns events and environ-
ments pre-dating not only the post-medieval European
Ages of Discovery and Enlightenment, which stimulated
the emergence of modern science and instrumentation,
but also documents of recorded history. We set out, first,
the broad principles, materials and methodology of
environmental reconstruction and then explore its
operation through a number of case studies.
Environmental processes reorganize existing planetary
materials into different assemblages and locations and, in
so doing, leave their trace or signature . Living organisms
occupy these spaces, make their own mark and then
usually contribute to the assemblage as corpses and, later,
fossils after death. The most useful bundle of processes is
the erosion, transport and deposition of Earth materials
as sediments and sedimentary rocks and their exchange
processes with the atmosphere, hydrosphere and bios-
phere. Sediments include layered accumulations of snow
and ice, volcanic ash, chemical precipitates, detrital
erosion products and plant and animal remains. Sedi-
ments (and other specific, biosphere indicators) are
therefore incremental in nature with regular additions of
material, most usefully as seasonally or annually banded
layers such as lake varves and glacier ice. The principal
sediments and sedimentary environments widely used in
environmental reconstruction are identified in Chapter 12
(pp. 265-72).
Environmental reconstruction uses the principles of
sedimentology , focusing on sediments themselves, and the
Plate 23.1 The composite stratigraphy of slope deposits on
the Great Orme, Llandudno, North Wales. Basal matrix-rich
clastic colluvium passes upwards into a younger, clast-rich
debris flow capped with clay-rich subsoil, and the whole is
capped by nineteenth-century road construction waste.
Photo: Ken Addison
and even chaotic responses to climate change. Small
disturbances may suddenly accelerate beyond critical the
threshold or tipping point of environmental sensitivity,
and positive feedback may rapidly develop into wider,
chaotic disturbance of Earth systems. Environmental
reconstruction is more than a fascinating enquiry into
Earth's environmental history. It is also an important tool
aiding environmental management and forecasting. This
chapter explores how it works.
PRINCIPLES OF ENVIRONMENTAL
RECONSTRUCTION
Contemporary environments possess measurable attrib-
utes, including the character, range and spatial distribu-
tion of
component materials and individuals and
 
 
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