Question

fill in the blank question
blank sediments are those located a long distance from river mouths and were deposited thousands of years ago when sea level was lower.

Explanation:

The question is about a type of sediment related to their location (far from river mouths) and deposition time (thousands of years ago when sea level was lower). In geology (a subfield of Natural Science, specifically Geography or Earth Sciences which can be under Geography here), "relict" sediments fit this description as they are sediments that were deposited in the past under different environmental conditions (like lower sea levels) and are now in a different setting (far from river mouths due to sea - level changes or other geological processes).

Answer:

Relict