Mesozoic of the British Isles

Question 1

What systems was the Triassic initially dominated by?

Answer 1

Non-marine fluvial and aeolian systems (global warm period)

Question 2

What did the increasing influence of marine conditions lead to in the Triassic?

Answer 2

Evaporites

Question 3

What makes correlation difficult for the Permo-Trias boundary?

Answer 3

Lack of significant marine deposits (non-marine dominance till end Triassic)

Question 4

What occurred in the Carnian (230 Ma)?

Answer 4

Ongoing breakup of Pangea

Question 5

Why is the Carnian important?

Answer 5

Important rifting - with deposition of sherwood sandstone and sucession of Mercia mudstone

Question 6

What conditions were sherwood sandstone deposited under?

Answer 6

Crustal extension

Question 7

What conditions was the Mercia Mudstone deposited under?

Answer 7

Post-rift thermal subsidence

Question 8

Where is the base of the Triassic taken from?

Answer 8

First pebble bed in the Triassic Sherwood sandstone

Question 9

What are the rock groups of the Triassic? (old to young)

Answer 9

Sherwood sandstone
Mercia Mudstone
Penarth group

Question 10

What does palynology prove?

Answer 10

Facies are diachronous

Question 11

What is a suggestion of the mid-Triassic English midlands?

Answer 11

Marine influence

Question 12

What does the Penarth group mark?

Answer 12

the beginning of the significant marine influence

Question 13

What us early Triassic sedimentation like in the UK? (deposition of Sherwood sandstone)

Answer 13

Aeolian and fluvial

Question 14

Where is a major source of the Sherwood sandstone?

Answer 14

Variscan Highlands transporting many well-rounded Quartzite clasts northwards

Question 15

What are some examples of rock formations in the Sherwood sandstone?

Answer 15

Otter sandstone
Budleigh salterton pebble sands

Question 16

What are the mudstones like in the mercia mudstones?

Answer 16

Red and green mudstones

Question 17

What environment was the mercia mudstone produced in?

Answer 17

Restricted basins (salt assumulation)

Question 18

Where is 90% of the UKs Halite located?

Answer 18

Cheshire basin.
Worth £¼ Billion p.a. to the U.K.
Currently producing about 6 Million tonnes p.a

Question 19

What was the depositional environment of the Mercia Mudstone?

Answer 19

Less fluvial input.
Carbonate soils and marginal halites

Question 20

What was the depositional environment of the Sherwood sandstone?

Answer 20

Fluvial input, braided rivers.
Coarse alluvial fans with anhydrite or carbonate rich soils.

Question 21

What provides a biostratigraphic framework through the Jurassic?

Answer 21

Ammonites

Question 22

What are ammonites good biomarkers?

Answer 22

Evolve rapidly
Planktonic (widespread distribution)

Question 23

What marks the early Jurassic?

Answer 23

Global transgression

Question 24

What caused significant changes to the sedimentary system throughout the Jurassic?

Answer 24

Fluctuating eustatic sea-level change, plate tectonics and local structural factors

Question 25

What marks the end Jurassic?

Answer 25

significant global lowstand reflects global cooling

Question 26

What was the early Jurassic palaeogeography?

Answer 26

Central Atlantic Magmatic Province UK shallow shelf seas on northern Tethys

Question 27

What is the basin structure of the Jurassic outcrop in the UK?

Answer 27

Basin and swell

Question 28

What are the swell (block) features of the UK Jurassic?

Answer 28

Mendips Moreton Market Weighton

Question 29

What might the highs and basins of the Jurassic swells in the UK have been like?

Answer 29

High - potentially emergent, Thinner and condensed Basins - Thicker

Question 30

What was the early Jurassic lithostratigraphy like?

Answer 30

Almost exclusively marine (mud and shales)

Question 31

What is there evidence of near the top of the Early Jurassic?

Answer 31

Shallowing (sandstone and ironstone)

Question 32

What is found within the Blue liass formation and what does it show?

Answer 32

Ammonites, bivalves, crinoids, brachiopods, vertebrates, trace fossils (well oxygenated environment)

Question 33

What is the jet rock of whitby mudstone an example of?

Answer 33

Ocean anoxic event

Question 34

What evidence is shown in the jet rock?

Answer 34

Perturbation of carbon cycle and ocean system

Question 35

What was the result of the oceanic anoxic event on the jet rock?

Answer 35

No benthos Laminated sediments Exceptional preservation of nekton/ plankton Marked carbon isotope excursion (CIE)

Question 36

What is an example of the Toarcian and Aalenian in the UK?

Answer 36

Bridport Sands

Question 37

What are the Bridport sands?

Answer 37

Shallow marine, offshore shoal sands, on top of which are the earliest beds of the Inferior Oolite

Question 38

What rock formation marks the Aalenian to the Bathonian?

Answer 38

Inferior Oolite of S England

Question 39

What is the Oxford clay?

Answer 39

Marine clay Callovian to lower Oxfordian

Question 40

What are the characteristics of the Oxford clay?

Answer 40

Fine-grained, fissile, dark-grey shale, minor mudstones/limestones Rich in invertebrates (benthics)

Question 41

What is the economic importance of the Kimmeridge clay?

Answer 41

The source rock for much of our North Sea Oil

Question 42

What is displayed in the Kimmeridge clay?

Answer 42

Milnakovitch scale cyclicity

Question 43

How was the Kimmeridge clay deposited?

Answer 43

Under a stratified water column

Question 44

What marks the late Jurassic to earliest cretaceous?

Answer 44

Tithonian Portland Gp and Purbeck Gp

Question 45

What are the Tithonian Portland Gp and Purbeck Gp like?

Answer 45

Lagoonal limestone and shale with rich invertebrate and vertebrate and trace fossils Gypsum and palaeosols

Question 46

What does the gypsum and palaeosols of the Tithonian Portland Gp and Purbeck Gp an indicator of?

Answer 46

Indicate climatic and environmental conditions

Question 47

What was late cretaceous palaeogeography like?

Answer 47

Widening N. Atlantic & opening S. Atlantic Tethys - Atlantic - Pacific connections High sea levels - flooded continental margins

Question 48

Where can UK outcrops of the cretaceous be found?

Answer 48

Wessex and Hampshire basins, S England to East Anglia. Weald Basin of SE England. Cleveland Basin of the Yorkshire- Lincolnshire Coast. East Antrim, NE Ireland

Question 49

What is the Berriasian like?

Answer 49

‘Purbeck’ marls & Lmst in the south (alternating FW, brackish, marginal marine); sands and marine clays to the north

Question 50

What is Hauterivian like?

Answer 50

‘Wealden’ silts and clays in the south (non-marine); marine marls, clays & sands in north

Question 51

What is Aptian like?

Answer 51

Marine conditions return to the south as Mn-Fe-rich sandstones (Greensands) & clays

Question 52

What is Albian like?

Answer 52

Marine clays and sands in the south & east, iron-rich limestones in the N Sea

Question 53

What occurred in the mid to upper Albian in the wessex basin?

Answer 53

Marine transgression (Gault clay and upper green sandstone)

Question 54

What happened in the weald basin between Lower Hauterivian to the Barremian?

Answer 54

Non marine - weald clay formation

Question 55

What is found in the weald clay formation?

Answer 55

Fluvial and mudflat/overbank sediments; Main UK source of dinosaur remains (Iguanodon); FW-Brackish invertebrate fauna/flora.

Question 56

What are the characteristics of the Speeton clay?

Answer 56

Mid- to dark grey clay with horizons of concretions, glauconite and fossil concentrations.

Question 57

What is the age of the speeton clay?

Answer 57

Earlt cretaceous

Question 58

How thick is the speeton clay at coastal exposure?

Answer 58

About 100 m

Question 59

What beds are present in the Speeton clay?

Answer 59

Bssal nodular beds (phosphatic nodules)

Question 60

What do organic rich shales in the Early Barremian indicate?

Answer 60

widespread anoxic event

Question 61

How will rocks be aligned in the Gault clay formation?

Answer 61

Grey calcareous clay, generally mid-late Albian, sandwiched between Lr & Ur Greensands

Question 62

What is the late cretaceous dominated by?

Answer 62

Chalk

Question 63

What is the chalk of the late cretaceous like?

Answer 63

Pure limestone Entirely planktonic/ biogenic

Question 64

What is the result of planktonic forms having evolved on the chalk?

Answer 64

fine-grained, pure low-magnesium calcite limestone (a biomicrite)

Question 65

What distinctive feature can be found in rhythmic black nodular layers?

Answer 65

Flint

Question 66

What are the characteristics of flint?

Answer 66

Hard, brittle, siliceous; early- diagenetic remobilization of biogenic silica (mainly sponge spicules, some radiolaria)