Final answer:
The time period where marine chemical sedimentation was prevalent in the western US was the Paleozoic era, evidenced by significant limestone and shale deposits originating from that era which are still visible today.
Step-by-step explanation:
The time period during which the dominant sedimentary process in the western interior of the United States was marine chemical sedimentation, such as lime, in a shallow sea is the Paleozoic era. During the Permian period, which is the last period of the Paleozoic era, significant marine chemical sedimentation occurred.
The sedimentary rocks formed during this time, including limestones and shales, are still present in areas such as the Midwest. These sedimentary rocks are indicative of a shallow marine environment and can include extensive cave systems like those found in Mammoth Cave, Kentucky.
Following the Permian, the Mesozoic era begins with the Triassic period, which saw a shift in sediment types and significant extinction events, marking the end of one era and the beginning of another.
The paleoenvironments of these times were favorable for fossil preservation, especially in marine settings where limestones and shale were common deposits.