https://wserv3.esc.cam.ac.uk/p1acollections/items/browse?tags=high+energy&output=atom <![CDATA[1A Collections]]> 2024-04-09T21:16:16+01:00 Omeka https://wserv3.esc.cam.ac.uk/p1acollections/items/show/33 <![CDATA[<h2><strong>L354<br /></strong></h2> <h2>Limestone, shelly</h2>]]>

Hand Specimen

This rock is made up of well cemented bioclasts. The bioclasts (mainly shell fragments) are poorly sorted, ranging from <1mm up to a few 10s of mm. 
Fine-grained cement fizzes with acid, indicating that it is carbonate. It has weathered to a pale yellow-grey.

Thin-section

Carbonate fossil fragment in a carbonate cement (sparite). The laminated structure of the shells is visible in places. 
Cement contains some hematite (brown regions). 
There are a few epidote grains and some opaque areas.
This is a rudstone (Dunham naming system) or biosparite (Folk naming system).

Rock History

The shells are not in life position – they have been transported. 
Deposited in moderate to high energy environment. 

Rock Name

shelly limestone
]]> 2019-07-04T09:52:11+01:00

Title

L354

Limestone, shelly

Subject

Age

Middle Jurassic

Location

Forest Marble
Near Weymouth

Description

Hand Specimen

This rock is made up of well cemented bioclasts. The bioclasts (mainly shell fragments) are poorly sorted, ranging from <1mm up to a few 10s of mm. 
Fine-grained cement fizzes with acid, indicating that it is carbonate. It has weathered to a pale yellow-grey.

Thin-section

Carbonate fossil fragment in a carbonate cement (sparite). The laminated structure of the shells is visible in places. 
Cement contains some hematite (brown regions). 
There are a few epidote grains and some opaque areas.
This is a rudstone (Dunham naming system) or biosparite (Folk naming system).

Rock History

The shells are not in life position – they have been transported. 
Deposited in moderate to high energy environment. 

Rock Name

shelly limestone
]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/21 <![CDATA[<h2><strong>L311<br /></strong></h2> <h2>Conglomerate</h2>]]>

Hand Specimen

Poorly sorted. Rounded clasts up to ~15 mm long. 
Pale yellow matrix of quartz grains. 
Cement fizzes with acid, indicating that it contains carbonate. 
This conglomerate is just clast-supported.

Thin-section

Rounded clasts of very dark red brown amorphous silica (chert) and polycrystalline quartz.

Matrix of quartz grains (typically 0.25 mm) and fine-grained carbonate cement (sparite). Dark red-brown iron staining.

Rock History

Deposited in a high energy environment.

Advanced Notes

Iron staining 
Hematite (Fe2O3) → red (blood-red, cherry-red, brown-red) iron-staining 
Limonite (FeO(OH)•nH2O) → yellow or brown iron-staining

The red-brown colour of this rock is probably produced by hematite.

Rock Name

conglomerate
]]> 2019-07-04T09:52:07+01:00

Title

L311

Conglomerate

Subject

Age

Eocene

Location

Hertfordshire

Description

Hand Specimen

Poorly sorted. Rounded clasts up to ~15 mm long. 
Pale yellow matrix of quartz grains. 
Cement fizzes with acid, indicating that it contains carbonate. 
This conglomerate is just clast-supported.

Thin-section

Rounded clasts of very dark red brown amorphous silica (chert) and polycrystalline quartz.

Matrix of quartz grains (typically 0.25 mm) and fine-grained carbonate cement (sparite). Dark red-brown iron staining.

Rock History

Deposited in a high energy environment.

Advanced Notes

Iron staining 
Hematite (Fe2O3) → red (blood-red, cherry-red, brown-red) iron-staining 
Limonite (FeO(OH)•nH2O) → yellow or brown iron-staining

The red-brown colour of this rock is probably produced by hematite.

Rock Name

conglomerate
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