What was one consequence of John Marshall's excavation approach in the Harappan Civilisation?

The grouping of artefacts from the same unit, regardless of their stratigraphic layers.

The correct answer is Option 3 - The grouping of artefacts from the same unit, regardless of their stratigraphic layers

In fact, John Marshall’s stint as Director-General of the ASI marked a major change in Indian archaeology. He was the first professional archaeologist to work in India, and brought his experience of working in Greece and Crete to the field. More importantly, though like Cunningham he too was interested in spectacular finds, he was equally keen to look for patterns of everyday life. Marshall tended to excavate along regular horizontal units, measured uniformly throughout the mound, ignoring the stratigraphy of the site. This meant that all the artefacts recovered from the same unit were grouped together, even if they were found at different stratigraphic layers. As a result, valuable information about the context of these finds was irretrievably lost.

It was R.E.M. Wheeler, after he took over as DirectorGeneral of the ASI in 1944, who rectified this problem. Wheeler recognised that it was necessary to follow the stratigraphy of the mound rather than dig mechanically along uniform horizontal lines.

Stratigraphy- In archaeology, stratigraphy refers to the study of the layers of soil or sediment that make up an archaeological site.  Generally, the lowest layers are the oldest and the highest are the most recent.