The northern fault exposure is . . . Avoid the common grammatical mistakes. The surface was eroded. However, it was not subaerially exposed. However, that restriction has never made much sense to me.
Commas separate two independent clauses, each of which have a subject and a verb.
The grains are well-rounded and commonly have oolitic coatings. The grains are well-rounded and they commonly have oolitic coatings.