My guess (without being able to crawl around through the cigarette butts and lick the floor) is that this is a mudstone or siltstone. The difference between the red and grey does not look like a primary deposition structure of different sediment layers but seems to be an oxidation-reduction (also called redox) 'front' between areas of orange oxidised iron and grey reduced iron. The front would have formed in the sediments after being formed - probably related to groundwater of different chemical composition moving through the material. Sometimes the redox change can be induced by different components in the rock - even fossils but that doesn't seem to be the case here.
Note the darker red line right at the interface between the two colours. The banding in the orange, oxidised area mostly parallels the interface in a way that couldn't happen in sedimentary deposition. The banding appears similar to Liesgang rings.