EXAM 1. REVIEW

Stratigraphy. Define stratigraphy:

Who developed the following principles and define each (use sketches where possible):

Define these other important stratigraphic concepts:

1. conformable sequence

2. unconformable sequence

3. gradational contact

4. erosional contact

5. stratigraphic correlation

6. angular unconformity

SEDIMENTARY ENVIRONMENTS

The character of sedimentary rocks provides clues to the geologic history of a region. The character of a rock is determined by the environmental conditions under which it formed. Environmental Conditions = tectonic setting and environment of deposition (review each if required). Environmental conditions influence many aspects of sedimentary deposits such as texture and primary sedimentary structures.

Define the following related concepts:

1. Texture

2. Planar cross bedding

3. Trough cross bedding

EXAMPLES OF SEDIMENTARY ROCKS RELATED TO DEPOSITIONAL ENVIRONMENT

For each of the following describe the character of the rock and where each typically forms:

1. Graywacke

2. Arkose

3. Quartz sandstone

4. Shale

5. Carbonates

PALEOGEOGRAPHY & FACIES

Rock units. Define the following:

1. Formation

2. Member

3. Group

The major inadequacy in this approach is that no regard is made to TIME BOUNDARIES and, consequently, formations may be DIACHRONOUS. The solution is:

Time-rock units (Chronostratigraphic units): This refers to sedimentary rocks deposited during the same time period. Unlike rock units, lithology can vary greatly within time-rock units, and the upper and lower boundaries consist of time-planes. The fundamental time-rock unit is the SYSTEM, which corresponds to a PERIOD of geologic time. This approach enables PALEOGEOGRAPHIC MAPS to be constructed (i.e. maps showing the geography of a region at a given instant in the geologic past).

Facies: An important question is.."how do you interpret the environment of deposition?" Answer = the facies concept. A facies is a description of the attributes of a sedimentary rock which are specifically related to to its environment of deposition and is intended to aid in the interpretation of that environment. Good examples of environmental change are global, or EUSTATIC, sea-level changes that have resulted in inland seas, referred to as EPEIRIC SEAS, covering as much as 2/3 of the North American continent. Much of the sedimentary rock record of the Paleozoic and Mesozoic Eras were deposited during these periods of marine inundation.

Fossilization. Define the following:

1. Permineralization

2. Replacement

3. Carbonization

4. Mold

5. Cast

6.Trace Fossils

Classifying Organisms:

The modern system of classification is referred to as TAXONOMY. The smallest taxonomic unit = SPECIES - "group of organisms basically alike in their structural and functional characteristics; can interbreed and produce fertile offspring" (proves genetically related). The rest of the system is hierarchical levels of kinship (kingdom-phylum-class-order-family-genus-species). Organism usually identified by genus and species eg. Homo sapiens (Man); Canis lupus (Wolf).

THE GEOLOGIC TIME SCALE

The standard geologic time scale was not developed in an organized and systematic manner. Instead, the scale took shape over centuries as a number of geologists discovered and named the various intervals, on the basis of time-rock units identified by superposition, fossils and correlation (absolute ages from radiometric dating have only recently been added). Often the units were named after the local area or the type of rocks present.

Divisions:

Eons – Hadean, Archean, Proterozoic (Precambrian) + Phanerozoic (evident life)

Eras - Based on major changes in fossils. Paleozoic (544-245 mybp); Mesozoic (245-66 mybp); Cenozoic (66mybp-present day).

Periods: Again, based on fossil changes. Named after local features i.e.

1. Cambrian; after cambria (latin for Wales) 
2. Ordovician; after ordocvices, early celtic tribe
3. Silurian; after silures, English/Welsh tribe
4. Devonian; after Devonshire
5. Mississippian; from the Mississippi River basin
6. Pennsylvanian; rock outcrops in Pennsylvania
(last two only used in N. America, elsewhere = Carboniferous)
7. Permian; from Perm, a province of Russia
8. Triassic; rocks in Germany, 3 divisions
9. Jurassic; the Jura mountains in Switzerland
10. Cretaceous; from 'creta' for chalk
11. Tertiary; suggested by an Italian geologist
12. Quaternary; suggested by a french geologist
(Absolute ages were not available when these divisions were first made)

Based on radioactive decay i.e. the nucleus of certain elements (PARENT ELEMENT) spontaneously emit atomic particles and in so doing change to a different element (DAUGHTER ELEMENT). When dealing with a large number of atoms, studies have shown how long it will take FOR HALF OF THEM TO DECAY - this is the HALF LIFE. The ratio of PARENT ELEMENT to DAUGHTER ELEMENT thus follows a predictable pattern. Therefore, radiometric dating methods are based on finding the radioactive element in a mineral from which none of the daughter element has escaped and calculating the ratio between them to find the age of the mineral.

Orogenesis; Continental Growth by Accretion:

When continental plates converge, subduction does not occur because the continental masses are too thick and buoyant. Instead, the 2 continents become welded together along a SUTURE ZONE. The force of the collision folds up the crustal rocks and former oceanic sediments, creating metamorphic rocks and uplifted mountains. This period of mountain building is termed an OROGENY. An example is the creation of the Himalayas mountain chain about 25 million years ago, when the Indian-Australian plate collided with the Eurasian plate.

Mountain building also occurs during continental-oceanic plate collisions. The oceanic plate is subducted beneath the continental plate. All orogenies have common features:

1. compression, buckling and uplift at the edge of the continent.
2. emplacement of igneous rock masses
3. folding, faulting and metamorphism
4. Erosion of the growing mountains and deposition adjacent to the mountains
5. (in oceanic-continental collisions)scraping off, folding and uplift of sea floor rock and sediments onto the edge of the continent - resulting in:
Continental Growth By Accretion
Caused by the "plastering on" of material at the edge of a continental plate adjacent to a subduction zone. The material that accumulates in this fashion can be small continental masses MICROCONTINENTS or oceanic features such as volcanic arcs and seamounts. The Seychelles Bank in the Indian Ocean is an example of a microcontinent, which has apparently become detached from Africa. These larger masses of rock are scraped off the subducting plate and plastered onto the continent to form ALLOCHTHONOUS or EXOTIC TERRANES (meaning they had originated elsewhere). Example: Wrangellia consists of basaltic island arc volcanic rocks, deep marine shales and shallow marine limestones. This material originated in the area presently around New Guinea in Triassic time (225 million years ago) - travelling some 10 000 km to its present location.

(Multiple Choice)

1. William "strata" smith developed the principle of:
a. biological succession b. original lateral continuity
c. cross-cutting relationships d. original horizontality
e. uniformitarianism

2. Which two time periods are missing from the following sequence; Triassic, _________, Cretaceous, ________, Quaternary:
a. Silurian, Cambrian b. Devonian, Permian c. Jurassic, Tertiary d. Devonian, Ordovician e. Jurassic, Pennsylvanian

3. In which of the following are the eras ordered from oldest to yougest:
a. mesozoic, paleozoic, cenozoic b. cenozoic, mesozoic, paleozoic 
c. paleozoic, cenozoic, mesozoic d. paleozoic, mesozoic, cenozoic 
e. cenozoic, paleozoic, mesozoic

(Short Answer)

4. Define "superposition".
5. Define "angular unconformity".
6. Define "half-life".

(Longer Answer)

7. Describe the characteristics and typical origin of TWO of the following rock types: graywacke; quartz sandstone; arkose.

8. What is an orogenic belt? What are common characteristics?