Worbarrow Bay Questions

Field trip to introduce and aid revision of S260 units 1, 2 & 4. covering

1) Basic interpretation of geological maps and comparisons with actual field observations to determine :
Dips , strikes and true & vertical thickness of beds, with reference to scales and cross sections.

Identify different structures and faults.

Relate lithologies and structures to the overall topography of the area.

2) Identify and classify various siliciclastic, carbonate sediments and evaporites to deduce sources and depositional environments.

3) Identify fossils and study features that show their life styles and habitats.

Maps
Q1
If we were at grid reference 868795 ,where would we be and what rock would we be standing on?
Q2
How far to Mupe Rocks?
Q2a
What general trends are there for rock outcrops? (Dip, strike, patterns)
Q3
In the Worbarrow Bay area what is the actual dip?
Q4
What is the relationship between
i) the dip and relative age of rocks that outcrop here?
ii) the dip and strike?
iii) the width of the outcrops and the dips in Portland and Purbeck members?
Q5
Is this infallible ; what about the Wealden member?
Looking eastwards, what about the narrow outcrop of Portland Sand at St Aldehm's Head head? Or the wider outcrops of the succeeding Portland Stone / Lower Purbeck members?
Q6
What is the relationship of these outcrops to the contour lines?
Now have a look at the cross sections 1 & 2 - do they confirm our deductions?
Q7
Why are the dips in the cross section 1 almost double what is shown on the map?
Now look at the real geology of the area and the regional setting.
Estimate the thickness of the Wealden member.
Q8
How could you calculate the true thickness, just from the map?
Q9
Describe what is happening to the beds from Swanage to Mupe Rocks.
Q10
From the map and observations of high/low ground what can you generalise about the properties of the different outcrops.
Q11
From the outcrop patterns and dips, what geological structure could we have in this area and what is the relative age of the events causing it.
Not much faulting in the area , but look at the biggish one in Swanage
Q12
On which side of the fault are the younger beds.
Q13
What could the relative movement be. What type of fault is it?
Q14
What is relative age of the fault.
Q15
Couple of other bits from the map.- what feature can you see at grid ref 922824
Q16
What can you generalise about the V shape outcrops over at St Aldhem's in relation to direction and angle of dips?
Sedimentary Rock Types
Q17
What are the 3 main minerals making up sedimentary rocks.
Carbonates
Q18
What is the most common mineral?
Q19
What is its polymorph, secreted by seashells?
Q20
What are the 2 origins of Limestone?
Q21
Why does it fizz with hydrochloric acid?
Q22
When doesn't a limestone fizz?
Q23
How does limestone chemically weather when exposed?
Q24
Limestones can be described by 3 grain types and 2 intergranular - materials what are they?
Grains 1) 2) 3)
Matrix 1) 2)
Q25
In what circumstances will the 3 grain types accumulate.
Mudstones
Q26
What are the main mineral constituents.
Q27
What are their origins.
Q28
Why are higher current speeds required to return them to suspension.
Sandstones
Q29
What are their main mineral constituents.
Q30
What are their origins.
Q31
Draw a diagram showing how to classify sedimentary rocks by their mineral composition.
Q32
What are the most common cements of sedimentary rock?
Q33
What are their origins?
Q34
Comparable grain sizes for classification of sandstones
Q35
What 2 types of weathering are there? Where are each most intensive and why?
Q36
What are the weathering products of the following minerals and what sort of structure do they have in terms of silicate tetrahedra :
Mineral Product Silicate structure
Olivine
Pyroxine
Amphibole
Mica
Feldspar
Quartz
Q37
Which minerals generally indicate a mature sediment?
Q38
What properties do we look at in classifying sandstones?
Q39
How would you define a Greywacke?
Flow Regimes and Structures
Q40
How would you define an Arkose?
Q41
What flow rate produces
Laminar Cross Bedding
Trough Cross
Bedding Herring Bone Cross Bedding
Q42
Generally, what properties determine ripples caused by current and wave action.
Evaporites
Q43
What are the 3 most abundant in Worbarrow bay.
Q44
Why does volume change accompany a change from one calcium sulphate to another.
Q45
What are the main constituents of :
Chert
Chalk
Greensand
Fossils
Q46
What are their uses?
Q47
What makes for a good zone fossil?
Q48
What conditions makes for good preservation and where is this most likely to occur?
Q49
Draw / describe the main features of 2 types of invertebrate fossils you have seen today that give some indication to their lifestyle, feeding habits and locomotion.
Q50
Describe the geology and environment over time from Late Jurassic to present day in the Worbarrow bay area, including at least one unconformity.