Sedimentologists study the constituents, textures, structures, and fossil content of the deposits laid down in different geographic environments.
The most useful indication of time equivalence is similar fossil content, provided of course that such remains are present.
Any feature, including colour variations, textures, fossil content, mineralogy, or any unusual combinations of these can be used.
Jurassic limestone and marl with rich fossil content are the characteristic rocks that dip below the Mittelland and appear again in the pre-Alps.
However, as previously noted, times of volcanism and metamorphism, which are both critical parts of global processes, cannot be correlated by fossil content.
Pinpointing the exact depositional setting for an ancient carbonate deposit requires detailed analysis of its texture, composition, sedimentary structures, geometry, fossil content, and stratigraphic relationships with modern carbonate depositional sites.
The precision with which geologic time can be measured leaves much to be desired no matter what means are used (radiometric, paleomagnetic, or the more traditional measuring of fossil content of stratigraphic layers).
In order to accomplish this, geologists attempt to measure the absolute ages of rock strata using techniques such as radioisotope dating, or they attempt to establish relative ages of strata by comparing their mineralogy, fossil content, and other attributes.
Evidence based on geologic description, fossil content, and absolute and relative ages leave no doubt that these rocks were all part of a single mountain belt before the Atlantic Ocean opened in stages from about 200 million years ago.
Amanz Gressly, (born July 17 , 1814 Bärschwil, Switz. died April 13 , 1865 Bern) Swiss geologist who originated the study of stratigraphic facies when he discovered lateral differences in the character and fossil content of strata in the Jura Mountains, reflecting a variation of the original environment of deposition.
