The unusual dark pool activity looks to be selling IMO. Check out the volume candle chart on December 9, 2019.
This is a bit like reading tea leaves so I could be totally wrong here but notice how IWM went down following the dark pool order. When price conclusively breaks to either the upside or downside immediately following a large dark pool print, it suggests the print was either a buy or sell. In this case, because IWM dropped after the posting of the dark pool order, it suggests that it might be a sell order BUT no one really knows but the insiders and market makers.
This is tax selling week where, seasonally speaking, it’s usually a sideways to down week for markets.
Not only does seasonally support a pullback this week but look at the daily chart of IWM. We have two days of upper-shadow candlesticks at the top of uptrend channel resistance which also favors a pullback.