Monthly Archives: April 2013

Mixon Limestone Pebble (large file size)

The picture below of a polished face of a Mixon Alveolina Limestone pebble has been achieved by stitching together about 60 photomicrographs at X20 magnification taken with a USB microscope.  The file size is large to allow zooming in (three successive clicks on the image eventually brings up a highly zoomed in high resolution image).  Some digital enhancement has also been used, and other pictures of this pebble on this website give a truer, more natural colour rendition.

The alveolines are taken to be Alveolina fusiformis (Sowerby), and their wide morphological variation has previously been noted by C.G. Adams in Alveolina from the Eocene of England (1962).  Adams left open in that publication the possibility that Alveolina elongata (d’Orbigny) was actually a variant of fusiformis.

Mixon Alveolina Limestone pebble max dimension 55mm.

Mixon Alveolina Limestone pebble max dimension 55mm (multiple stitches and considerable digital adjustments)

A Foraminifera Rich Mixon (Alveolina) Limestone Pebble

An unidentified foram with alveolina in Mixon Limestone

An unidentified foram with alveolina in Mixon Limestone

This blog post is about an examination of a foramaniferal rich Mixon (Alveolina) Limestone pebble originally dredged from the English Channel about 7 miles off the West Sussex coast.

Mixon Limestone is thought to date to the Eocene epoch, Bartonian age (37.2 – 40.4 million years ago), and to relate to a Tethys Sea shallow benthic zone (SBZ 17) at its far north western edge in the Hampshire Basin of England.

The examination is mainly done with a USB micropscope offering magnifications of X20 and X400 under reflected light.

Grinding and polishing is done with diamond sharpening stones of grit sizes 200, 300, 400, 600.  Further polishing is sometimes done using up to 2400 grit emery paper.

Some digital enhancement is sometimes done in Photoshop, usually restricted to cropping and adjusting brightness/contrast with the “Levels” tool.

Also, sometimes a stitching programme is used to combine multiple photos together.

Sometimes a scanner or digital camera are used for the pictures.

Foraminiferal rich limestone pebble.

Foraminiferal rich limestone pebble.

A gallery of photomicrographs of the forams in this pebble can be found in the link on the right to the page titled “Examining a Mixon Alveolina Limestone Pebble”.  Some scans and photos are also included.