It doesn't form strata IN THE GEOLOGIC COLUMN which is made up of sedimentary rock.
The traps referred to in this image are layers of basalt originating from a series of volcanic eruptions which gave rise to the Deccan Traps in India which cover an area of 500,000 km2 and are 2000m deep. In between the two layers of igneous basalt in the picture is a 9m deep sedimentary layer of shallow marine origin.
Edited by Malcolm, : Trying for a sensible size