Stratigraphy Diagnostic

Quiz 04-Dec-09

1) The Prinicple of superposition of rocks was first enunciated by whom?

a) William Smithb) Adam Sedgwickc) James Huttond) Isaac Newton

2) Where on the globe do you find thousands of feet of rock exposed in natural stratigraphic section?

a) Grand Canyon, USAb) Niagara Goorge, USAc) Appalachian Mountains, USAd) Scottish Highlands

3) What are the chronostratigraphic units?

a) units defined by fossil contentb) units of time distinguished by rock recordc) rocks formed during a defined interval of

timed) units distinguished by unconformities

4) Which of the following is a chronostratigraphic unit?

a) Zoneb) Groupc) Periodd) System

5) What is the geochronological equivalent of ‘Series’?

a) Ageb) Erac) Periodd) Epoch

6) What is the primary or basic formal lithostratigraphic unit known as?

a) Groupb) Formationc) Supergroupd) Member

7) What is a bed characteristic or distinct enough for it to serve as a stratigraphic reference called?

a) key bedb) marker bedc) type bedd) zone bed

8) A body of rock that wedges into another body of a different lithology is named what?

a) lentilb) fingerc) beduled) tongue

9) Body of strata including the overlapping of the range zones of two specified taxa is what kind of biostratigraphic unit?

a) Concurrent-range Zoneb) Taxon-range Zonec) Lineage Zoned) Abundance Zone

10) What is a stratotype?

a) locality exposing fossil horizonb) horizon containing a specific taxonc) type section of a stratigraphic unitd) a lithostratigraphic unit

11) A body of strata that cannot be designated a formal stratigraphic unit is known as?

a) lithozoneb) lithoidc) lithotoped) lithosphere

12) What is the term used for a repeated set of deposits laid down by a cyclic or rhythmic sedimentation?

a) cyclolithb) cyclothemc) cyclosedimentd) cyclostrome

13) The Archaean-Proterozoic boundary occurs at how many million years?

a) 2650b) 2500c) 2200d) 2000

14) The base of the Phanerozoic is currently dated at how many million years?

a) 470b) 500c) 545d) 590

15) Which is the present stratigraphic status of Eocene?

a) Systemb) Seriesc) Staged) Substage

18) The lower part of the Carboniferous in America is named Mississippian. What is the name given to the upper part?

a) Washingtonianb) Pennsylvanianc) Nebraskiand) Alabamanian

16) The term ‘Recent’ refers to which stratigraphic unit?

a) Plioceneb) Miocenec) Pleistocened) Holocene

17) Lateral or vertical changes in the lithology of a formation is referred to as a change in what?

a) faciesb) lithodemc) lithotoped) lithotype

18-20) Branches of Stratigraphy

The Grand Canyon is a steep-sided gorge carved by the Colorado River in the United States in the state of Arizona. It is largely contained within the Grand Canyon National Park, one of the first national parks in the United States. President Theodore Roosevelt was a major proponent of preservation of the Grand Canyon area, and visited it on numerous occasions to hunt and enjoy the scenery.

The Grand Canyon is 277 miles (446 km) long, ranges in width from 4 to 18 miles (6.4 to 29 km) and attains a depth of over a mile (1.83 km) (6000 feet). Nearly two billion years of the Earth's geological history have been exposed as the Colorado River and its tributaries cut their channels through layer after layer of rock while the Colorado Plateau was uplifted]. While the specific geologic processes and timing that formed the Grand Canyon are the subject of debate by geologists, recent evidence suggests the Colorado River established its course through the canyon at least 17 million years ago.

Geology of the Grand Canyon area

The geology of the Grand Canyon area exposes one of the most complete and studied sequences of rock on the planet. The nearly 40 major sedimentary rock layers exposed in the Grand Canyon and in the Grand Canyon National Park area range in age from about 200 million to nearly 2 billion years old. Most were deposited in warm, shallow seas and near ancient, long-gone sea shores in western North America. Both marine and terrestrial sediments are represented, including fossilized sand dunes from an extinct desert. At least 14 major gaps in the geologic record are also found in the area.

Uplift of the region started about 75 million years ago in the Laramide orogeny ; a mountain-building event that is largely responsible for creating the Rocky Mountains to the east. In total the Colorado Plateau was uplifted an estimated 2 miles (3.2 km). The adjacent Basin and Range province to the west started to form about 18 million years ago as the result of crustal stretching. A drainage system that flowed through what is today the eastern Grand Canyon emptied into the now lower Basin and Range province. Opening of the Gulf of California around 6 million years ago enabled a large river to cut its way northeast from the gulf. The new river captured the older drainage to form the ancestral Colorado River, which in turn started to form the Grand Canyon.

Wetter climates brought upon by ice ages starting 2 million years ago greatly increased excavation of the Grand Canyon, which was nearly as deep as it is now by 1.2 million years ago. Volcanic activity deposited lava over the area 1.8 million to 500,000 years ago. At least 13 lava dams blocked the Colorado River, forming lakes that were up to 2,000 feet (610 m) deep. The end of the ice age and subsequent Human activity has greatly reduced the ability of the Colorado River to excavate the canyon. Dams in particular have upset patterns of sediment transport and deposition. Controlled floods from Glen Canyon Dam upstream have been conducted to see if they have a restorative effect. Earthquakes and mass wasting erosive events still affect the region.

Introduction to STRATIGRAPHY

Stratigraphy is the systematic organization and classification of rock layers (strata) based on their properties.

Many different observed properties for rocks may be employed for stratigraphy, including lithology, fossils, magnetic polarity, chemical composition, and others. Rocks also may be classified according to interpretation of age and origin (genesis). In general, units classified on the basis of one property do not coincide with units determined from other properties

Three main categories of stratigraphy are commonly used by geologists (Hedberg 1976).

1)Lithostratigraphy -- organization of rock strata into units based on their lithologic character.

2)Biostratigraphy -- organization of rock strata into units based on their fossil content.

3)Chronostratigraphy -- organization of rock strata into units based on their age relationships.

LithostratigraphyThe organization of rock strata into units based

on lithology is the foundation of stratigraphy on a local and regional basis. A lithostratigraphic unit should display a substantial degree of overall lithologic homogeneity ... as defined by observable physical features (Hedberg 1976, p. 31)

Formal lithostratigraphic units are arranged in a hierarchy as follows.

Group -- two or more formations. Formation -- primary unit of lithostratigraphy. Member -- named lithologic entity within

formation. Bed -- named distinctive layer in a

member or formation.

The formation is the basic unit for lithostragraphy in all situations. No standard values exist for thickness or lateral extent of formations. The definition of a formation derives from practical application in a given geologic setting. In eastern Kansas, for example, upper Paleozoic formations are typically a few meters to 10s of meters in thickness. In contrast, some Mesozoic formations in western Kansas are 100s to 1000s of meters thick. The lithologic character of a formation is distinguished by two principal aspects.

The lithologic character of a formation is distinguished by two principal aspects.

Composition -- This may refer to either mineralogy or chemical composition (or both).

Texture -- This refers to the size, shape, and arrangement of constituent particles that make up the rock body. It includes such aspects as sorting, porosity, permeability, fabric, and other aspects of texture.

Some rock names are based on composition only--limestone, some depend only on texture--sandstone, and others are based on both composition and texture--chalk, granite, andesite, basalt, etc. Fossils may be part of lithology, in as much as they impart certain composition physical properties of a rock body, such as density, magnetic susceptibility, seismic response, hydrologic character, and many other aspects.

Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. Usually the aim is correlation, demonstrating that a particular horizon in one geological section represents the same period of time as another horizon at some other section. The fossils are useful because sediments of the same age can look completely different because of local variations in the sedimentary environment.

For example, one section might have been made up of clays and marls while another has more chalky limestones, but if the fossil species recorded are similar, the two sediments are likely to have been laid down at the same time.

Ammonites, graptolites and trilobites are index fossils that are widely used in biostratigraphy. Microfossils such as acritarch, chitinozoans, conodonts, dinoflagellate cysts, pollen, spores and foraminiferans are also frequently used.

Different fossils work well for sediments of different ages; trilobites, for example, are particularly useful for sediments of Cambrian age.

Fossils as a basis for stratigraphic subdivision:Concept of stageA stage is a major subdivision of strata, each

systematically following the other each bearing a unique assemblage of fossils. Therefore, stages can be defined as a group of strata containing the same major fossil assemblages. French palaeontologist Alcide d'Orbigny is credited for the invention of this concept. He named stages after geographic localities with particularly good sections of rock strata that bear the characteristic fossils on which the stages are based.

Concept of zoneIn 1856 German palaeontologist Albert Oppel

introduced the concept of zone (also known as biozones or Oppel zone). A zone includes strata characterised by the overlapping range of fossils. They represent the time between the appearance of species chosen at the base of the zone and the appearance of other species chosen at the base of the next succeeding zone. Oppel's zones are named after a particular distinctive fossil species, called an index fossil. Index fossils are one of the species from the assemblage of species that characterise the zone.

The zone is the fundamental biostratigraphic unit. Its thickness range from a few to hundreds of metres, and its extant range from local to worldwide.

Biostratigraphic units are divided into six principal kinds of biozones: Taxon range biozone represent the known stratigraphic and geographic

range of occurrence of a single taxon. Concurrent range biozone include the concurrent, coincident, or

overlapping part of the range of two specified taxa. Interval biozone include the stata between two specific biostratigraphic

surfaces. It can be based on lowest or highest occurrences. Lineage biozone are strata containing species representing a specific

segment of an evolutionary lineage. Assemblage biozones are strata that contain a unique association of three

or more taxa. Abundance biozone are strata in which the abundance of a particular

taxon or group of taxa is significantly greater than in the adjacent part of the section.

Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time.

The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of the Earth.

The standard stratigraphic nomenclature is a chronostratigraphic system based on palaeontological intervals of time defined by recognised fossil assemblages (biostratigraphy). The aim of chronostratigraphy is to give a meaningful age date to these fossil assemblage intervals and interfaces.

UnitsChronostratigraphic units, with examples:eonothem - Phanerozoicerathem - Paleozoicsystem - Ordovicianseries - Upper Ordovicianstage - Ashgill

The following stratigraphic terms are adapted from Hedberg (1976).

Statum -- A layer or bed--generally a tabular body--of rock characterized by certain distinctive characters, properties or attributes that separate it from adjacent layers.

Horizon -- An interface--boundary--that marks a particular position within a sequence. The terms level, datum, marker, marker-bed, and key-bed may be used in a similar sense.

Stratotype -- A designated section or sequence of strata at a specific site that serves as the definition for a named stratigraphic unit or boundary.

Correlation -- The demonstration of correspondence in character and in stratigraphic position of rock units from different locations.

Facies -- A body of rock with distinctive aspect, nature, or character. Similarity of certain properities or attributes throughout the rock body, such as lithofacies, biofacies,