A 10e13 kg bolide and a 'rain-out' of 10e17 kg displaced water vapour would leave a signal in the delicate near-continent, ocean-floor sedimentary record - most likely signs of increased influx of terrigenous sediment through continental erosion.
(displaced water vapour; would leave; a signal in the delicate near-continent)
displaced water vapour
would leave
a signal in the delicate near-continent