EOSC 326 Lecture Notes - Chronostratigraphy, Oceanic Crust, Sea Level Rise
DepartmentEarth and Ocean Sciences
Course CodeEOSC 326
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MODULE A: Geological Principles
1. Geological Time
a. Age of the Earth
James Ussher (1581-1665) - Archbishop of Armagh
- one of earliest and most inﬂuential ﬁgures in interpretation of geological time
- published a chronology of Earth's history using all dates mentioned in Bible to establish a timeline
-established ﬁrst day of creation was Oct 22 4004BC, which would make Earth a little over 6000 years
George Louis De Buffon (1707-1788)
-believed Earth to have been initially hot molten mass
-heated iron spheres (thought was reasonable model for structure of planet) and calculated time they
took to cool
-using this method Buffon believed Earth was 75,000 years old
-published paper in 1899 in which he estimated Earth's oceans (which he believed to be same age
as the planet) to be about 90 million years old
-calculated this by estimating how long it would take for the oceans to reach their current salinity (from
an original fresh water state) as salt is added via erosion of minerals in the rocks.
-radioactive decay in minerals is the technique which provided us with the current age of the Earth at
4.6 Billion yrs.
b. Deep Time
Deep time: concept of trying to understand the evolution of the Earth and its biological systems
2. Geological Concepts and Terminology
Mineral: a naturally occurring crystalline solid with a characteristic chemical composition, a highly
ordered atomic structure, and speciﬁc physical properties
Rock: an aggregate of minerals. Rocks fall into a basic 3-fold classiﬁcation:
A. Igneous Rocks
Igneous rocks: (derived from latin "ignis" meaning ﬁre) formed by the cooling of magma or lava.
Generally composed of interlocking crystals of varying sizes
-if magma cools within Earth's crust it is referred to as an intrusive igneous rock. As they cool slowly
they often develop large crystals
-if magma escapes via volcanic activity and forms a lava the igneous rock is called extrusive igneous
rock. These rocks cool quickly, so crystals that form are very small and often invisible to human eye
B. Metamorphic Rocks
Metamorphic rocks: form as a result of the transformation of an existing rock via heat, pressure and/or
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the action of ﬂuids.
- commonly occur deep in Earth's crust
C. Sedimentary Rocks
Sedimentary rocks: form in response to particular environmental conditions and as such, provide
clues to Earth's past including climate, ancient geography and life forms.
-form via sedimentation of materials at the Earth's surface and within water bodies, commonly in
layers called strata or sedimentary beds.
Diagensis: transformation of sediments into a sedimentary rock via a collective variety of chemical,
physical and sometimes biological processes.
D. Clastic Sedimentary Rocks
Most sedimentary rocks are produced by the erosion of pre-existing rocks producing fragments or
grains that are transported and deposited at various distances from the site of erosion --> these rocks
are called clastic sedimentary rocks
-Clastic sedimentary rocks provide a simple tool that can be used to determine the source, origin and
length of transport of a particular sediment prior to it becoming a sedimentary rock
-If a sediment is deposited close to rocks from which it originally eroded, it will have a number of
characteristics that will uniquely identify it as such:
- large number of coarse/angular grains and clasts (greater than 4mm), higher proportion of unstable
minerals and fragments of rocks, exhibit poor sorting (variation in clast/grain sizes)
-sediment with characteristics as described above is called an immature sediment
-mature sediment: undergone extensive transport, ﬁne grained, composed mostly of well-rounded
and well-sorted quartz grains
E. Calcium Carbonate
calcium carbonate: precipitated sediments by various creatures including corals and mollusks to form
thick deposits of limestone
-microplankton are also calcium carbonate producers, such as cocclithophores. During Creatceous,
warm shallow oceans covered much of Earth's continents providing perfect conditions for proliferation
of cocclithophores and ultimately the generation of vast thicknesses of ﬁne grained limestone
Evaporites: intense evaporation of water precipitate sediments in the form of salt crystals
-can form a number of ways including: inland sea or part of ocean with restricted contact to wider
ocean (occur in arid areas with limited freshwater input)
stratigraphy: study of how rock layers are arranged.
a. Principle of Superposition:
-states that in layered strata, the oldest layer will be at the bottom of the exposed strata and the
youngest at the top
b. Principle of Original Horizontality: sediments are deposited horizontally, after transformed into rock
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