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’

Ralph Bagnold (1886-1990)

Bob Folk, U Texas

Peter Vail, Rice U

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 ofMR. WILLIAM JONES

for many years Master ofa respectable School in this Parish

who departed this lifeon the 20th day of January 1836

Aged 59 YearsThe inflexible integrity of his

Characterand 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