The oldest rocks in Greater Lincolnshire lie to either side of the River Trent and were formed during a period called the Triassic. They consist of dark reddish brown and green coloured limey mudstones and siltstones, often called marls. These were laid down on a coastal plain close to the shoreline of a very shallow sea, in a very hot climate – we were about 23 degrees north of the equator at that time.
A great deal of evaporation was taking place from shallow saline lakes, leading to the formation of thin layers of a mineral called gypsum. Salt crystals were also formed, but these dissolved again later when more water gently flooded the area, leaving cubic moulds that became filled in with sediment, to form little cubic features called pseudomorphs.
These features along with ripple marks and very rare reptile footprints from adjacent parts of Nottinghamshire lead us to believe that during the late Triassic (about 230 million years ago) the area would have been similar to the modern day coastal plains of Saudi Arabia.