Sea level change through geological time and other features relevant to fieldwork Flashcards by Andrew Jeavons

What are the main sea level change principles?

Eustacy
Isostasy
Thermal expansion

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What is eustacy?

Global change in amount of water in oceans due to climate and/or changing
basin geometry/volume due to tectonics changing the volume of water oceans can hold

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What is isostacy?

Changes in relative height of the Earth’s crust due to loading (buoyancy,
subsidence)

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What is thermal expansion?

changes in volume in relation to temperature change; warmer water has a
larger volume

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What is regression?

sea levels fall and facies migrate seawards

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What is transgession?

sea level rise facies migrate inland

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What can regression and transgression identify?

when sea level has changed but not absolute height

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What is a geological proxy?

natural recorder of direct measurement for environmental or climate variability

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What are some examples of proxy data?

tree rings, ice cores, fossil pollen and spores, ocean sediments, corals and
historical data

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Is there any reliable proxy for water depth?

only generalities and relative estimates

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What is faunal proxy evidence?

fossil with eyes suggest organisms lived within photic zone

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What is the photic zone?

depth light penetrates the water column

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What are the problems with faunal evidence?

Fossil not ubiquitous
Eyes maybe not reserved
Photic zone depth varies (up to 200m)
Dont know eyes functional or relict
Was fossil in photic zone or transported

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What can cause the photic zone to vary?

salinity, sediment levels/turbidity, biological
composition

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What 2 ways can depositional water depth in the rock record be split?

proximal and Distal

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What will proximal sediment composition be like?

High energy
Siliciclastic minerals
Coarse grain size
Rapid deposition
Frequent sedimentary structures

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What will distal sediment composition be like?

Low energy
Mud dominated
Fine grain size
Slow deposition
Sedimentary structures less common

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What will normal conditions be like for wave form and wave base?

Fair weather wave base (FWWB)

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What can crest to crest length tell us above the waves?

depth of water displaced

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What will conditions be like above FWWB in normal conditions?

water column and sediment affected by wave action and in coastal areas tides. May
also be influenced by currents

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What will conditions be like below FWWB in normal conditions?

water column and sediment unaffected by affected by waves and tides, but may be
influenced by currents

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What will the depth of the FWWB be?

varies between 5 and 15m

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What does FWWB define in sedimentary environments?

upper shore face

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What is SWB?

Storm Wave Base

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What is the affect of larger wavs in SWB?

affect water column to a deeper level

How will SWB occur in relation to FWWB?

SWB will be below FWWB but not at same time

What is the depth of SWB?

15-40m but deeper in extreme events (hurricane, typhoon)

What does SWB define in depositional environments?

lower shore face

What will conditions be like above SWB?

water column and sediment: water interface affected by storm wave action agitating and re-working the sediment.

What will conditions be like below SWB?

water column and sediments not affected by storm wave action – currents may occur

What will be the cause for sedimentation below SWB?

current activity or from muddy sediment settling from suspension

What will the duration of background sedimentation for FWWB?

significantly longer longer than SWB

How will the water column be affected FWWB?

at this height not affected by wave or tidal action

What sort of energy condition is FWWB?

low energy - no wave agitation

What is the sedimentation rate of FWWB like?

very low- sediment as mud falling from suspension

What might have a potential to introduce high energy conditions/ sediments?

perhaps current activity

How would frequency of event sedimentation be described?

infrequent

What is the duration of event sedimentation?

short duration

How will the water column be affected in event sedimentation?

affected by wave action

What will the energy conditions be like in event sedimentation?

high- mixing sediment and agitating sea floor if at this depth

What will the sediment be like in event sedimentation?

coarse grained poorly sorted rapidly deposited

What sediment structures are present in event sedimentation?

cross bedding ripples lenticular bedding

What is the sedimentation rate be like event sedimentation?

high sedimentation rate

What are the requirements with ripples?

Unconsolidated sand sized sediment particles Current moving over the sediment (wind, water, ice)

What is key observation of ripple shape in cross section?

symmetrical or asymmetrical

What is key observation of ripple shape in plan view?

parallel sinuous bifurcating

What is key observation of ripple wavelength?

distance crest-crest, or trough to trough

What is key observation of ripple height/amplitude?

height from bottom of trough to top of crest

What is key observation of ripple orientation?

orientation on ripple plane (plunge)

What processes can exacerbate weathering?

Heating/cooling Wetting/drying Physical contact (abrasion) including wind and water transported debris Biological weathering Chemical weathering (often through water)

What are the major physical properties of rock that affect susceptibility to weathering?

Composition Hardness Planes of weakness

What are some examples of planes of weakness?

faults fractures joints cleavage

What is competent rock?

not easily broken or fragmented

What are some examples of competent rock?

granite, gneiss, basalt, some sandstone, some limestone

What can competent rock be used for?

building stone or aggregate

What is incompetent rock?

easily broken or fragmented susceptible to weathering

what are some examples of incompetent rock?

mudrocks (mudstone, siltstone, claystone), some sandstones, some limestone

What are some ways you can tell a rock has been weathered?

orange colours honeycomb texture joints and faults

What will orange colour in rock suggest?

iron content oxidised

What will honeycomb texture indicate with weathering?

heterogeneous calcium carbonate cement careous weathering

What will fresh rock surfaces allow for?

identification of original features grain/crystal size, shape and colour fabrics and textures within the rock

What will weathered surfaces allow you to identify?

alteration products changes in mineralogy (shape, size, colour) additional fabrics within the rock

When will baked and chilled margins occur?

when hot igneous body intruded into or extruded onto pre-existing and cooler rock strata

What is a baked margin?

altered by contact metamorphism (hot rock affecting cold rock)

What rock often present at baked margins?

hornfels

What is a chilled margin?

when got intrusion cooled by country rock with smaller sized crystals

What is sill?

igneous rocks intruded into existing strata

What is lava flows?

igneous rocks extruded onto Earth’s surface

What are ammonites?

linage of molluscs within class Cephalopoda

What is distinctive about ammonites?

whorled shell with internal divisions into chambers

Where are ammonites extensively found in fossil record?

Jurassic and cretaceous

What are the positives of using ammonites?

Diverse and species/genera/families readily identified Exclusively in marine rocks Geographically widespread Biostratigraphic applications (biozone 1Ma)

What are trace fossils?

Physical evidence of fossil organisms in the absence of body fossils Feeding, movement and habitation traces

What is diagenesis?

Physical and chemical changes that occur in the transition of sediment to a sedimentary rock

What are some examples of diagenesis?

Dewatering Compaction Dissolution Cementation Lithification

What are diagenetic concretions (nodules) form?

Rounded mineral masses (typically calcium carbonate, iron carbonate or pyrite) that form after the host rock was deposited by diagenesis

What can form if diagenetic concretions fracture?

fracture and recrystallise forming septarian nodules)

What is taphonomy?

The science of death and decay; controls what and how organisms enter into the fossil record

What are the key elements of taphonomy?

Life cycles of organisms Physical transportation Preservational biases Mineralisation and geochemistry Diagenesis Decay zones and processes