Deformational structures

Question 1

What is deformational structures?

Answer 1

Distortion of pre-existing structures or creation of new structures.

Question 2

What is “load cast”?

Answer 2

Formed by differential compaction between two types of material (mudstone vs. sandstone).

Looks like balls pressed sidewards down into the sediment underneath

Question 3

What is “flame structure”?

Answer 3

Formed by differential compaction between two type of material (mudstone vs. sandstone).

Looks like… a flame of the sediment underneath going up into the sediment on top

Question 4

What is a slump?

Answer 4

Sedimentary folding affecting several beds.

Deposited flat –> instability (like earthquake) –> sediment starts to slide

Usually occurs in marine environments

Question 5

What are mud-cracks?

Answer 5

Sub-aerally exposed = used to be under water but is now not

Can also have frosty tracks in it

Sand is not affected -> Only in mud/clay; can swell up because of smectite that incorporates a lot of water in the structure, and when it dries out, it cracks

Question 6

What are rain drops?

Answer 6

A present-day sediment

Question 7

What is syn-sedimentary faulting?

Answer 7

Sediments being disposed —> something happened that only did something to a specific part of the sedimentary structure—> new sediment on top (or older below) not affected

Question 8

What are biologically-induced structures?

Answer 8

Carbonic, often porous

Structures due to microbial binding
- Microbes = life; the first living organisms (as far as we know)

Microbe consortium produces a slime (Exo-Polymeric Substance) that can trap and bind surrounding sedimentary materials and/or favor precipitation of early diagenetic carbonates ➙ Microbial mats

Stromatolites
Thrombolites
Oncoids

Question 9

Where does stromatolites form?

Answer 9

= Cyano bacteria

Shark Bay, Australia (best example of stromatolites from today)

Warm and salty water, not that many animals live here and thus the stromatolites aren’t grazed upon

Remember: Can have MULTIPLE looks! (i.e. not necessarily the tops seen in Shark Bay)

The white part of them is the slime binding evaporites; capturing carbon grains, eg. gypsum.

Favoured the precipitation of dolomite

Question 10

What are thrombolites?

Answer 10

Also microbial mats; microbial structures - we just don’t see the structure

Looks like nothing

Question 11

What are oncoids?

Answer 11

Spherical or less well- rounded structures, commonly up to 2-3 cm in diameter but sometimes larger.

Lamination similar to stromatolites

The binding starts around a core; something that was there before

Question 12

What is a bioherm?

Answer 12

ancient organic reef of moundlike form (positive topography over the sea floor) built by a variety of marine invertebrates, including corals, echinoderms, gastropods, mollusks, and others…

Question 13

What is a biostrome?

Answer 13

structure built by similar organisms that is bedded but not moundlike.

Question 14

What is a carbonate mud mound?

Answer 14

Mound = pile of something

carbonate mud-dominated deposits with topographic relief and few or no stromatolites, thrombolites or in place skeletons.

E.g. bryozoan mound at Stevns klint

Question 15

What is a patch reef?

Answer 15

small isolated bioherm

Reef doesn’t necessarily mean that there’s corals!

Question 16

What are the main reef-building organisms today vs. before?

Answer 16

Today = corals
Cretaceous = rudists (bivalves)
Jurassic = lithiotids (bivalves)
Before = worms (serpulids)

Question 17

What are serpulids (worms)?

Answer 17

Produces a slime around them that traps bioclasts

Looks disgustingly like a lot of holes beside each other

Not necessarily tiny

Question 18

What are bioturbations?

Answer 18

Huge variety, can be related to all behaviours of animals and plants (most common in foods looking for food, digging or walking)

Question 19

What is the most common bioturbation?

Answer 19

Thalassinoides

Shrimps, crabs digging in the sediment to form this

Looks a bit like a stick (en gren) inside the sediment, and holes on top. When many are together, it’s a mix of sticks sticking together

Question 20

What is diplocraterion?

Answer 20

Created by a worm, the ‘rings’ between the big worm-shape is from when the worm grew and pushed it’s middle down –> ergo the outermost layer is the worm, and in between there is something resembling a soft ladder; those are when the middle of the worm pushed down

Question 21

What does an alternation between sand and clay indicate?

Answer 21

An alternation between high and low energy