The rover recently drilled two samples at rock targets called "Aberlady" and "Kilmarie" in a region of Mars called the "clay-bearing unit".
Both drill targets were unveiled in a new selfie taken by the rover on May 12, the 2,405th Martian day, or sol, of the mission, Nasa said in a statement.
This clay-enriched region, located on the side of lower Mount Sharp, stood out to Nasa orbiters before Curiosity landed in 2012, the US space agency said.
Curiosity is exploring Mount Sharp to see if it had the conditions to support life billions of years ago. Clay often forms in water, which is essential for life.
The rover's mineralogy instrument, called CheMin (Chemistry and Mineralogy), provided the first analyses of rock samples drilled in the clay-bearing unit.
CheMin also found very little hematite, an iron oxide mineral that was abundant just to the north, on Vera Rubin Ridge.
Other than proof that there was a significant amount of water once in Gale Crater, what these new findings mean for the region is still up for debate, according to the US space agency.
It is likely that the rocks in the area formed as layers of mud in ancient lakes- something Curiosity also found lower on Mount Sharp, NASA said.
Water interacted with sediment over time, leaving an abundance of clay in the rocks there, it said.