Microscopy of microfossils and rock formations from Scarborough

These slides were purchased from SDFossils on ebay Sept 2017.

They compose of a five slide set of thin sections – one is of shelly limestone showing fossils. The others show rock structure – including oolites which look for all the world like fossils but aren’t!

All photos on Zeiss IM microscope with Bresser MikrOkular camera. For this post only x4 and x20 objectives were used.

 

Shelly Limestone

Shelly Limestone x4 objective – microfossils are seen within the stone

For comparison purposes the following photo is from the Museum of Wales, showing fossils within limestone:

Oolites

Oolite or oölite (egg stone) is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. The name derives from the Ancient Greek word ??? for egg. Strictly, oolites consist of ooids of diameter 0.25–2 mm; rocks composed of ooids larger than 2 mm are called pisolites. The term oolith can refer to oolite or individual ooids. Some exemplar oolitic limestone, a common term for an oolite, was formed in England during the Jurassic period, and forms the Cotswold Hills, the Isle of Portland, with its famous Portland Stone, and part of the North Yorkshire Moors. A particular type, Bath Stone, gives the buildings of the World Heritage City of Bath their distinctive appearance (Wikipedia).

x4 objective:

Laminated sandstone & mudstone

The following are photographs of microscopy of two laminated rock sections (sandstone and mudstone) from Scarborough.

In geology, lamination is a small scale sequence of fine layers (so called laminae) that occurs in sedimentary rocks. Laminations are normally smaller and less pronounced than bedding. Lamination is often regarded as planar structures one centimetre or less in thickness, whereas bedding layers are greater than one centimetre. However, structures from several millimetres to many centimetres have been described as laminae. A single sedimentary rock can have both laminae and beds. Lamination consists of small differences in the type of sediment that occur throughout the rock. They are caused by cyclic changes in the supply of sediment. These changes can occur in grain size, clay percentage, microfossil content, organic material content or mineral content and often result in pronounced differences in colour between the laminae. Weathering can make the differences even more clear. Lamination can occur as parallel structures (parallel lamination) or in different sets that make an angle with each other (cross-lamination). It can occur in many different types of sedimentary rock, from coarse sandstone to fine shales, mudstones or in evaporites. Lamination is a fine structure and hence it is easily destroyed by bioturbation (the activity of burrowing organisms) shortly after deposition. Lamination therefore survives better under anoxic circumstances, or when the sedimentation rate was high and the sediment was buried before bioturbation could occur. Lamination develops in fine grained sediment when fine grained particles settle, which can only happen in quiet water. Examples of sedimentary environments are deep marine (at the seafloor) or lacustrine (at the bottom of a lake), or mudflats, where the tide creates cyclic differences in sediment supply. Laminations formed in glaciolacustrine environments (in glacier lakes) are a special case. They are called varves. Quaternary varves are used in stratigraphy and palaeoclimatology to reconstruct climate changes during the last few hundred thousand years. Lamination in sandstone is often formed in a coastal environment, where wave energy causes a separation between grains of different sizes (Wikipedia).

Laminated sandstone x4 objective:

Laminated sandstone x20 objective:

Laminated mudstone x4 objective:

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