Abundant feldspar in a sedimentary rock most likely indicates:

• A. Slow deposition
• B. Volcanic ash deposition
• C. Rapid deposition caused by tectonic activity
• D. High weathering rate

Answer: (C)

Feldspar in detrital sedimentary rocks signals limited chemical weathering and short transport time before burial. Feldspar weathers relatively quickly to clays; if grains stay as feldspar, they haven’t spent long on the surface being altered. In tectonically active regions, rapid uplift and strong sediment supply produce high-rate deposition, such as in turbidity currents or fault-controlled basins, which bury material quickly and preserve feldspar grains. That rapid deposition is the best explanation for abundant feldspar in a sedimentary rock. Slow deposition or high weathering rates would destroy or convert feldspar to clay, while volcanic ash can contribute varied minerals but doesn’t as reliably indicate rapid, tectonically driven deposition.