What characterizes marine silts and clays formed after the glacial period?

The presence of marine silts and clays formed after the glacial period is primarily characterized by their deposition in marine environments, which can often be found in coastal regions and areas that were once submerged under ocean water. In the case of the Boston area, this region is known to have been affected by sea-level rise after the last glacial advance, resulting in the accumulation of soft sediments such as silts and clays in the post-glacial marine environment.

These sediments are typically fine-grained and were deposited in low-energy conditions, which leads to their characteristic properties. Therefore, this option accurately reflects the geographical and geological context of post-glacial marine deposits, especially in areas such as Boston where marine influences played a significant role in sediment accumulation. The choice suggests an understanding of both the sedimentary processes involved and their regional implications, making it the correct selection in this context.