『Abstract
Quartz silt is a widespread detrital sediment with large aeolian
(loess) and alluvial silt deposits forming important components
of many contemporary landscapes. Despite research findings which
indicate that a range of opportunities exist for the comminution
of quartz into silt particles within a wide variety of geomorphic
environments (e.g. glacial grinding, fluvial comminution, aeolian
abrasion, frost weathering, salt weathering, insolation weathering
and deep weathering), the ‘glacial-aeolian’ hypothesis has traditionally
been favoured as the most likely explanation for loess formation
and loess is seen as primarily a Quaternary phenomenon. As a consequence
there has been a tendency to underestimate sediment inputs into
loess systems by geomorphological processes operating within pre-Quaternary
environments. In particular, earth scientists may have considerably
underestimated the role of weathering in global silt generation,
as there are now many references to the existence of a patchy
but widespread distribution of pre-Quaternary weathering profiles
across the glacial and periglacial landscapes of the Northern
Hemisphere (e.g. North America, British Isles, north and central
Europe), landscapes within which many of the classical loess deposits
are located. These observations suggest that weathering profiles
may have covered large tracts of the Northern Hemisphere land
surface prior to the Quaternary glaciations. This, in turn, may
have important implications for quartz silt generation as: (1)
experimental studies indicate that many weathering processes are
capable of generating significant quantities of silt-sized debris,
and (2) particle characteristics display by saprolitic material
that has developed on quartz rich crystalline source rocks often
include significant quantities of either silt-sized material,
or quartz grains that are weakened by weathering derived microfractures.
Thus, weathering profiles may represent ‘mines’ of actual and
potential quartz silt, available for release into sedimentary
systems when these profiles are subsequently reworked by geomorphological
processes such as glacial, fluvial and aeolian erosion.
Keywords: Frost weathering; Salt weathering; Granitoid weathering;
Microfracture initiation; Silt 』
1. Introduction
2. Mechanisms of silt generation
3. Weathering as a generator of silt
4. Silt in the weathering profile
5. Microfracture initiation within weathering profiles
6. Microfracture characteristics of the weathering debris
7. Implications for detrital silt deposits
8. Conclusion
Acknowledgements
References