Final answer:
Geologic conditions needed to initiate the formation of a sedimentary basin include rapid drop of the seafloor caused by the weight of mountains, accumulation of sediments in the basin, and compaction and cementation of the sediments to form sedimentary rock.
Step-by-step explanation:
To initiate the formation of a sedimentary basin, certain geologic conditions are needed. One important condition is a rapid drop of the seafloor caused by the massive weight of mountains, leading to the creation of a concave basin. This drop in seafloor creates space for the accumulation of sediments in the basin. Another condition is the accumulation of sediments on top of previously deposited material, leading to compaction and cementation of the sediments, which ultimately turns them into sedimentary rock.