Lithostratigraphical units/ lithostratigraphy Flashcards
What are geological unit and phenomena dated using?
Relative methods (comparison)
Absolute methods (exact time)
What is a brief description of rock movement through the rock cycle?
Start igneous rock melting (subduction)
ejected or uplifted
weathering erosion transportation
deposition
burial
What is the trend for rock movement?
Upland to low land areas
Why is there less geological evidence the further back we go?
The earth has had more time to degrade it
What is deep time?
4.55 billion years of earth gives enormous temporal range for past processes
What processes might have occured in the range of deep time?
rock cycle
Plate tectonics
evolution
What is stratigraphy?
study of rock record of geological events through time; relative order and position of Strata and their relationship with geological timescale
What is strata?
geological units
What are the 3 eras?
Cenezoic (youngest)
Mesozoic
Paleozoic (oldest)
What periods/ epoch are in the cenezoic?
Pleistocene
Pilocene
Miocene
Oligocene
Eocene
Paleocene
What are the epochs/ periods in the mesozoic?
Cretaceous
Jurassic
Triassic
What are the epochs/periods of the paleozoic?
Permian
Carboniferous (1. Pennsylvanian 2. Mississippian)
Devonian
Silurian
Ordovician
Cambrian
What came before the cambrian epoch?
Pre-cambrian
What is the pull of the recent?
On a graph showing showing the age of different epochs the most recent young have smaller more refined gaps but the gap between epochs not linear due to destruction of old material by the rock cycle
What are lines of stratigraphical evidence used to determine?
the sequence or order of events and allow correlation with other locations
What does lithos mean?
Rock
What are the key characteristics to look for in rocks?
composition
Grain/ mineral size
colour
distinctive feature within unit
other reliable physical properties
How can rocks be defined and distinguished?
characteristics and stratifigraphic position
What are the change in lithostratigraphic characteristics like vertically?
change vertically in layering of various rock type
What are the changes in lithostratigraphic characteristics laterally?
reflecting changing environment or mode of formation
What are Facies?
set of characteristics that characterise environment in which rock formed
What is an example of a facie?
Red sandstone- desert or sand facie
Are lithostratigraphic units 1 or multiple layers of rock?
they can be either
What are some problems related to lithostratagraphic units?
no set scale/ definition
can be subjective
What is the abbreviation for formation?
FM.
What is formation? (field skills- geology)
Based on strata with comparable lithology facies (how deposited) or properties
What will formations of sedimentary rock be like?
will typically be multiple beds
What is a bed? (rock geology)
A single layer of sedimentary rock separated from other units by bedding planes
What type of sedimentary rocks will form multiple beds?
those formed near the surface by accumulation and lithification of sedimentary grain
What are some examples of sedimentary grains?
sand
silt
mud
What is the lithostratigraphic hierarchy?
Supergroup
Group (Gp)
Formation (Fm)
Member (Mbr)
Bed
What is the general trend when moving up the lithostratigraphic hierarchy?
2 or more beds make a member (this translate with 2 of one group making the next largest)
What is convention 3 of field skills? (lithostratigraphy)
First letter of lithostratigraphical unit always capitalised when using name but not for plural
What is convention 4 of ithostratigraphy?
Formally recognised stratigraphic divisions must have capital first letter (Systems, Periods)
What are the 3 marines of land sea transition?
Proximal (close to shore)
Medial marine
Distal marine (deep water)
What is the generalised characters of distal marine? (relative energy and grain size)
Very low
Very fine (mud)
What is the generalised characters of proxial marine? (relative energy and grain size)
very high
coarse (sand)
What is another term for sea level fall?
regression
What could be the reason for sea level fall/ relative change?
sea level fall
base level (land) rising
volume of water in ocean reduced
What happens to the environment when regression occurs? (sea level change)
previous shelf environment exposed to aerial weathering and oxidation leading to a facies change
loss of marine erosional processes on shelf
What is the land to sea transition of rock naming?
Land
shelf
Slope
Rise
Abyssal
What will a regression do to a proxial marine?
it will shirt it further out to sea from its original location
What is another term for sea level rise?
Transgression
What could be the reason for the relative change of sea level with a transgression?
sea level rise
base level (land) fall
ocean volume expanded
What is the environmental change after a transgression?
inland shift of medial marine
previous land areas are now flooded
and exposed to marine processes
What is it called when different environments occur at the same time?
synchronous
What will the facies be like shifting from proxial to medial?
Grain in facie will get finer grained further from land
What can happens to facie boundaries over time?
due to transgression and regression facies will migrate this can cause them to become interdigitated
What does interdigitated mean? (facies)
become interlocked together
Will facies vary laterally or vertically?
Laterally
What at facies like at the time of deposition?
essentially stratigraphically contemporaneous (= isochronous)
What is comfortable formation ? (lithostratigraphic units)
beds and formations formed without interruption or significant disruption
What is uncomfortable formation ? (lithostratigraphic units)
beds and formations formed with
interruption between them with subsequent disruption
What is Walthers law?
The vertical succession of facies reflects lateral migrations in environment
How can comfortable formation be inputted to Walthers law?
sediments that lie conformably adjacent to each other stratigraphically, must
occur adjacent to each other in original depositional environment
Where will facies migrate with regression?
seawards
What will the facies look like with regression? (in layering for answer)
Terrestrial - most coarse
Sandstone
Shale
Limestone -least coarse
How will facies migrate with transgression?
will migrate inland
What will the facies look like with transgression? (in layering for answer)
Limestone - least coarse
Shale
Sandstone
Terrestrial - most coarse
What is diachronous?
units vary in age across their extent
What is isochronous?
units are the same age through their extent
What will cause facie boundaries to migrate spatially?
Regression and transgression cycles
Why are diachronous units used in the sedimentary record?
they build up a picture of the evolution of an area through time
What is Chronostratigraphy?
when you combine lithostratigraphical units into larger groupings
Why is Chronostratigraphy done?
to establish a hierarchy of units
What will the upper and lower boundaires by like when you create your own lithostatigraphical unit?
broadly isochronous
What are Stages? (unit hierarchy)
Groups of formations
What is an example of a Stage/ group of formations? (unit hierarchy)
Carnian Stage
What is a Series? (unit hierarchy)
Groups of stages
What is an example Series/ group of Stages? (unit hierarchy)
Late Triassic Series
What are Systems ? (unit hierarchy)
Group of series
What is an example of a System? (unit hierarchy)
the Triassic System
