I believe it's mechanical because mechanical affects rock using heat and cold causing it to expand and contract.
Here are the definitions of Chemical and Mechanical weathering for future references:
Chemical- Chemical weathering is caused by rain water reacting with the mineral grains in rocks to form new minerals (clays) and soluble salts. These reactions occur particularly when the water is slightly acidic.
Mechanical- Mechanical weathering is the process of breaking big rocks into little ones. This process usually happens near the surface of the planet. Temperature also affects the land. The cool nights and hot days always cause things to expand and contract.
