GEOL 440 Sedimentology and stratigraphy:
processes, environments and deposits
Lecture 2: Sedimentology – a very brief history: concepts, developments and bandwagons; The physical properties of sediments and sediment classification: weathering and sediment yield.
Sedimentology – a very brief
history: concepts, developments and
bandwagons ..a very personal
(and biased!) selection
The ‘methodology’ of Sedimentology
(Okada and Smith, 2005)
1508-09
Leonardo da Vinci (1452-1519)
1515
James Hutton (1726-1797)
Hutton proposed that geologic time had been
infinitely long……’no vestige of a beginning, no prospect of an end’…..he discovered ‘angular unconformities’ to
show this
William Smith (1769-1839)
Stratigraphy and correlation
Georges Cuvier (1769-1832)
Stratigraphy and correlation Paris Basin
Sir Charles Lyell (1797-1875)
Uniformitarianism; interpreting
change within sediments
oh…and of course Charles Darwin (1809-1882)
Harriet (1830-2006)
Henry Clifton Sorby (1826-1908)
Minerals under the microscope; cross-stratification
Johannes Walther (1860-1937)
Walther’s Law: ‘Facies adjacent to one another in a continuous
vertical sequence also accumulated adjacent to one
another laterally’
Bob Folk, U Texas
Peter Vail, Rice U
Mike Leeder, UEA
John Bridge,
Binghamton Chris Paola,
Minnesota
Weathering • physical • chemical • biological
• physical - e.g. freeze-thaw, unloading, salt crystallisation • chemical - alteration, H20 vital • biological - organic acids, soil development, microbes
The physical properties of sediments and sediment classification: weathering and sediment yield.
• Physical weathering: •Freeze-thaw •Insolation •Salt •Wetting and Drying •Stress release
Freeze-thaw
•Insolation
•Wetting and
Drying
So, mechanical weathering yields… •Smaller bits of rock •An increased surface area •More routes for fluid (water) movement
….these all thus promote chemical weathering
Also SACRED to the Memory of MR. WILLIAM JONES
for many years Master of a respectable School in this Parish
who departed this life on the 20th day of January 1836
Aged 59 Years The inflexible integrity of his
Character and the social and domestic Virtues
which adorned his private Life, will long be cherished in the
recollection (of) all those who knew him.
Gravestones
• Chemical weathering: •Solution, esp. calcite, halite etc
•Hydrolysis, silicate minerals and acids
•Oxidation and reduction, esp. Fe and Mn in minerals
•Hydration/dehydration, water added tio mineral…e.g. anhydrite-gypsum
Mineral stability – Bowens reaction series/Goldich stability series
Most stable: Most silica, most covalent bonds
Least stable: Most cations, most ionic bonds
So, chemical weathering causes… •Destruction of many minerals •An increased relative abundance of stable minerals (i.e. quartz) •Production of new Al and Fe bearing minerals •Groundwater rich in bicarbonate (HCO3
-) •Acidic waters from pyrite weathering • yields ions (Na+, K+, Mg2+, Ca2+, Si4+ to solution) •Soil production
….these all thus cause increasing sediment ‘maturity’
Controls on weathering
Main points from today: •A view of at least a few of the main developers of Sedimentology as a science •The principal types of weathering •Main controls on weathering
Think…what does the grain type in a sedimentary rock therefore tell you………
Reading: B&D, Chapter 3, p. 45-66; Boggs Chapter 1; Nichols: Chapter 6
