I have been asked: "is a marine sedimentary rock earier to be located on a geological time period than one of terrestrial origin? Is that relative to fossil finding?"


The answer I have found:
Marine sedimentary rocks containing fossils as a rule can be more easily dated relative to terrestrial sedimentary rocks which contain fewer fossils. Rocks containing a great number of fossils can be positioned in geologic time easily based on the fossils and their position in the stratigraphic column relative to other formations. This is quick. Terrestrial sedimentary rocks barren of fossils must be dated by relative position alone and this can at time require quite a bit of jigsaw puzzle like problem solving depending on the extent of deformation. At times as luck and plate tectonics will have it, the sedimentary succession is uninterrupted like those rocks exposed in the Grand Canyon. More often successive events of deformation and erosion makes the dating less clear.

Absolute dating methods used on igneous rocks are more time consuming and expensive. So in this regard, yes, marine sedimentary rocks are cheaper and easier to date than terrestrial rocks of either igneous or sedimentary origin.