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The programme is strongly linked with the Course Unit on Surface Processes. Dr. Wilson, Senior Lecturer in the Department of Earth Sciences at the Open University, examines some thin sections of l...imestones under a polarising microscope which is coupled to a television camera. The texture and the packing of grains is discussed. A model is used to demonstrate grain-packing. Oolitic sediments are forming around the edges of the Bahama Banks today. These are studied from the air, on the ground where the banks are exposed at low tide, and underwater. Sedimentary structures such as ripples and cross-bedding are seen as they are forming, and there is evidence for burrowing organisms. Dr. George Farrow, Lecturer in Geology at the University of Glasgow, demonstrates the shape of similar burrows which he has filled with resin. They are made by burrowing crustaceans. Armed with this evidence for present day conditions of oolite deposition the programme goes on to look at an ancient sedimentary environment - in the Upper Jurassic rocks of Dorset. Trace fossils, thin sections, cross-bedding and so on are used to build up a picture of what conditions of deposition of those sediments must have been like some one hundrad and fifty million years ago.
Metadata describing this Open University video programme
Item code: S23-; 09
First transmission date: 20-05-1972
Published: 1972
Rights Statement:
Restrictions on use:
Duration: 00:24:35
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Producer: Peter Clarke
Contributors: George Farrow; Chris Wilson
Publisher: BBC Open University
Keyword(s): 150 million years ago; Bahama Banks; Burrowing crustaceans; Limestone; Oolitic sediments; Packing of grains; Polarising microscope; Surface processes; Texture; Thin sections
Footage description: Shots of two thin sections of calcium carbonate under the microscope. Wilson adds the analyser and rotates the stage to show the crystals. Wilson shows a model (made of balls in a plastic column) which distinguishes the phenomena of grain support and matrix support in sediments. Wilson shows a sedimentary rock specimen which contains a number of visible shells. This specimen shows grain support. Film shots of an amphibious aircraft (probably a Catalina) taking off from water, Aerial film shots of the Bahaman oolite sand banks. Commentary by Wilson gives the background. lson with a map of the sandbanks points out their main features. More aerial photographs. Shots of Shell Oil Company geologists examining the sandbanks at low tide. Commentary by Wilson. Underwater shots of the sand banks at high tide. Ripples are seen forming in the oolitic sediment. Wilson's commentary explains how the ripples are formed. Underwater shots of the sandbank front. The sediment here is unstable and the bank 'advances' over the meadows of marine grass. Shots of mounds and coils of sediment passed out by burrowing creatures. Two burrows are disturbed. A crab and a marine worm are dug up. Wilson introduces George Farrow. George Farrow explains his method for studying burrow systems on Aldabra Island. (He makes resin casts). Farrow shows the cast of one such system and points out its major features. (This is the burrow of a ghost shrimp). Farrow demonstrates how the animal was able to respond to sedimentation by modifying the burrow. Farrow shows the cast of the burrow of a community of snapping shrimps. Wilson with a cross section model of Upper Jurassic oolitic sediment (Corallian Beds) in Dorset. He points out the major features in the model. Series of still shots showing Jurassic sediment layers in cliffs in Dorset. Commentary by Wilson discusses the various features. Several fossilised burrows can be seen. These are similar to the burrow casts shown earlier. Shots of thin sections taken from the deposits. More shots of sediment layer; showing evidence of water currents durirg their formation. More shots of fossilised burrows. Wilson with a sedimentary rock specimen showing fossilised U-shaped burrows. Animated diagram thows a hypothetical burrow dweller making the characteristic burrow shape as found in the fossil record. Wilson sums up the programme by comparing the Jurassic limestone of Dorset with the new oolitie sandbanks in the Bahamas. He goes back to the model of the Upper Jurassic sediment, discusses its features and explains how the present sedimentary rock was formed from this.
Master spool number: 6HT/70523
Production number: 00522_3111
Videofinder number: 1717
Available to public: no