The Galaxy Mass Assembly ultra-deep Spectroscopic Survey samples a part of the CDFS to unprecedented depth .
The resulting distribution of 150 z > 1.4 redshifts reveals a significant peak at z = 1.6 , part of a larger overdensity found at this redshift .
The 42 spectroscopic members of this structure , called Cl 0332-2742 , form an overdensity in redshift of a factor 11 \pm 3 and have a velocity dispersion of 450 km s ^ { -1 } .
We derive a total mass for Cl 0332-2742 of \sim 7 \times 10 ^ { 14 } M _ { \odot } .
The colours of its early-type galaxies are consistent with a theoretical red sequence of galaxies with stars formed at z = 3.0 .
In addition , there are more massive , passive and older , but less star forming galaxies in CL 0332-2742 than in the field .
We conclude that this structure is a cluster under assembly at z = 1.6 .