Complex sentence: Lack of oxygen slowed bacterial decomposition and kept the usual scavengers away, so leaves of palms, ferns and sycamores, some showing the insect damage they had sustained during their growth, were covered with fine-grained silt and preserved.
Split into simpler sentences: Lack of oxygen slowed bacterial decomposition and kept the usual scavengers away. So leaves of palms, ferns and sycamores, some showing the insect damage they had sustained during their growth, were covered with fine-grained silt and preserved.