2A18 HotE Test 1

Eon

The largest division of geologic time

What are the four eons

Hadean (4.54Ga - 4Ga), Archean (4Ga - 2.5 Ga), Proterozoic (2.5Ga - 541 Ma), Phanerozoic (541Ma - present)

What is the current eon

Phanerozoic

What is the precambrian

An unofficial unit of geological time made up of the Hadean, Archean, and Proterozoic eons, where most of earth's history happened

Era

Second largest unit of geological time - 10 in total

Eras in the Phanerozoic

Paleozoic (541Ma - 252Ma) , Mesozoic (252Ma - 66Ma), Cenozoic (66Ma - present)

What is the current era

Cenozoic

Period

Third largest unit of geological time

Periods in the Paleozoic

Cambrian (oldest), Ordovican, Silurian, Devonian, Carboniferous, Permian (youngest)

Periods in the Mesozoic

Triassic (oldest), Jurassic, Cretaceous (youngest)

Periods in the Cenozoic

Paleogene (oldest), Neogene, Quaternary (youngest)

Pangea

A supercontinent containing all of Earth's land that began forming ~430Ma and broke up ~200-175 Ma (Triassic)

Ice Age

Long period of time where the Earth's surface and atmospheric temperatures are reduced to allow for the formations of ice sheets and glaciers - Made up of glacial and interglacial periods

Anthropocene

The modern geological epoch during which humans have dramatically affected the environment such that evidence can be seen in the rock record

Age of the Canyon Diablo Meteorite

4.55Ga +/- 70Ma, meaning it must be from when earth was just a solar nebula

Latent plastic value

The theory that creatures were directly created from the soil and rock

Catastrophism

The theory that major, short lived events are responsible for many of the features on earth - geological epochs ended with a sudden and violent natural catastrophe

What was the basis of catastrophism theory

They thought the world was very new (~4004 BC) meaning the various epochs had to have occurred very rapidly

Neptunism

The theory that all rocks were precipitated from the sea, with mountains forming with lowering sea levels - explained why we found fossils on top of mountains

Geological map of Great Britain, 1815

Map by William Smith detailing the stratigraphy and features of Britain's geology, deemed the "first" of its kind

Turin Papyrus Map

An ancient egyptian map (˜1150 BCE) showing the route through a section of the Wadi Hammamat

Absolute geologic age

When did an event happen or how old is a layer

Relative geologic age

The age of a layer or event relative to others - which came first?

Stratigraphy

The study of layered rocks in order to understand their composition, origin, and changes in space and time

Principles of stratigraphic dating

Principle of superposition, principle of original horizontality, principle of cross-cutting relationships, principle of inclusions, principle of faunal succession, unconformities

Principle of superposition

The oldest layer is at the bottom and the youngest at the top

Principle of original horizontality

Sediment is deposited in horizontal beds, and any tilt occurs after

Principle of cross-cutting relationships

A feature that cuts across another body of rock must be younger than the penetrated rock

Principle of inclusions

Fragments included in the host rock are older than the host rock

Principle of faunal succession

Fossil species succeed one another in a recognizable order

Unconformity

A gap in the geological record due to erosion or lack of deposition

Types of unconformities

Disconformity, Angular unconformity, Nonconformity

Disconformity

A surface of buried erosional relief between parallel sediment layers (aka layers are missing)

Angular unconformity

Titled strata are overlain by younger flat-lying strata

Nonconformity

When layered sedimentary rock overlays an erosion surface developed on metamorphic or igneous rock

Types of stratigraphic correlation

Lithostratigraphy, Biostratigraphy, Chemostratigraphy, Magnetostratigraphy

Lithostratigraphy

Matching the strata from one region to another

Biostratigraphy

Zoning of stratigraphic layers, and arrangement of those layers according to relative time of deposition using the ranges of fossils

Chemostratigraphy

Using ratios of chemical isotopes to date rocks

Magnetostratigraphy

Changes in magnetic polarity directions recorded in rocks and sediment

Formation

Distinctive rock units that can be mapped over a large area

Member

The various rock layers that make up a formation

Group

Many rock formations lumped together

James Ussher

Creationist who calculated the creation of the earth to be 4004 BC based on the bible

Abraham Werner

German geologisy who believed in Neptunism/ catastrophism

James Hutton

Recognized that the earth's surface is constantly changing, and recognized unconformities

Lord Kelvin

Calculated the age of the earth to be between 20-40 million year - he would have been right but did not account for radioactive heat release or mantel convection

Isotopic dating

Determining the age of a rock through its radioactive elements (using half life and amount of daughter isotope present)

Best isotopes for dating

those commonly found in rock-forming minerals or those with a unique daughter isotope (ex. K-40)

Best rocks to date

Igneous, then metamorphic, then sedimentary

The Big Gap

A geological unconformity that occurs between the mesozoic and the cenozoic

The great unconformity

A gap in the geological record at the end of the Proterozoic where younger sedimentary rocks lie on top of very old igneous or metamorphic rock

Plutonism

The theory that igneous rock originated from the cooling of magma deep within the earth, which was later uplifted

Uniformitarianism

A principle that geologic processes that occurred in the past can be explained by current geologic processes

Sediment

Loose solid particles formed by weathering or erosion of pre-existing rocks OR by chemical precipitation from solution

Types of particles making up sediment

Clasts eroded from pre-existing rock, skeletal debris, and crystals precipitated from solution

Lithification

The process by which sediment is turned into sedimentary rock through compaction and cementation

Compaction

Decrease in rock volume due to weight of overlying sediment

Cementation

Bind grains together with cement (i.e CO3 or SiO2)

Diagenesis

The process of turning one type of sedimentary rock into another

Formation of dolostone

Limestone is altered by the movement of Mg-rich fluid through the rock, which turns 2 CaCO3 -> CaMg(CO3)2, creating vugs in the precess due to volume decrease because Mg is smaller than Ca

Clastic sedimentary rock

Made of fragments of pre-existing rock or organic particles (bioclasts)

Clastic sedimentary rock composes ___

70% of the earth's surface but only 5% of the worlds volume, and contains most of the world's energy reserves and fossils

Wentworth scale

the classification of sediments by size; boulder, cobble, pebble, granule, VCS, CS, MS, FS, VFS, silt, clay

Chemical Sedimentary Rocks

Formed by direct precipitation of minerals from solution, typical of arid environments

Classifying sedimentary rocks

Grain size, sorting, angularity

Sorting

Poorly sorted (close to source to very well sorted (far from source)

Angularity

Very angular (close to source) to well rounded (far from source)

Bedload

Gains moving in continuous or intermittent contact with the bed

Saltation

Jumping movement of grains along the bed

Traction

Rolling or sliding movement of grains along the bed

Suspended load

Sediment carried in fluid without coming into contact with the bed

Bedform

Topographic features on the bed

Types of bedform

Very low flow velocity - plane bed

Low flow velocity - ripples

Moderate flow velocity - dunes

High flow velocity - plane bed

Symmetrical ripples

Formed by oscillatory currents (waves)

Asymmetrical ripples

Formed by unidirectional currents

Wave base

Depth at which water movement is negligible

Carbonate sediments

Created through biological activity (skeletal fragments of CO3 secreting organisms), accounting for 20-25% of sedimentary rock

Carbonate sediment examples

Limestone (>50% calcite or aragonite)

Dolostone (>50% dolomite)

Chalk

Chert (silica)

Environment of carbonate sediments

Tropical carbonate reefs

Parts of the "Carbonate factory"

Subtidal: reefs and lagoons

Intertidal: beaches and tidal flats

Supratidal: Algal marsh, sabkha

Carbonate reef environment

Needs salinity between 25-35% and temperature between 25-29 degrees, which was probably the same in the past, meaning anytime we find carbonate fossils outside those conditions we know that land must have been nearer the equator at one time

Reefs in the cenozoic

Predominantly hermatypic corals

Ordovician - Silurian - Devonian reefs

Stromatoporoid reefs

Cambrian reefs

Calcimicrobes

Proterozoic reefs

Stromatolite reefs

Allochems

Calcium carbonate grains that are transported and deposited to form carbonate rocks

Types of allochems

Skeletal particles, Ooids, Stromatolites, Peloids, Intraclasts

Skeletal particles

Average size of >2mm, i.e coquina

Ooids

Spherical coates grains

Stromatolites

Laminations of sediment formed by vertical growth of cyanobacteria

Peloids/Pellets

Silt to sand sized mudballs which mostly originate as fecal pellets

Intraclasts

Irregularly shaped carbonate grain formed when clasts are ripped apart during erosion and relithified

Classification of carbonate rocks

Mudstone, Wackestone, Packstone, Grainstone, Boundstone (KNOW THE TABLE FROM SLIDE 72)

Evaporites

Evaporation of sea water, leaving behind precipitates (Halite, gypsum, anhydrite)

Paleoenvironmental analysis

Obtaining paloenvironmental information from sediments/ sedimentary rock by interpreting facies - tells us about energy levels and distance of transport

Facies

A body of sediment or rock with particular characteristics that distinguish it from other rock bodies - describes depositional process and depositional environment

Facies code

First letter is grain size, second letter is structure, i.e sand with ripples = Sr

Facies associations

Groups of facies that occur together and record a specific depositional environment

Walther's Law

states that the vertical succession of facies reflects environments that were laterally connected in the past