Carboniferous coprolites from Qinhuangdao, North China

Abstract

Here we reported the coprolites that are preserved in the dark grey silty shale of the Carboniferous Benxi Formation from Shimenzhai, Qinhuangdao, North China. The coprolites occur in a sinusoidal and ribbon-like aggregate. A coprolite granule is sesame-shaped, roundish at the terminals, equidimensional and equimorphic. It is 2.2 mm long and 0.6 mm wide. Its ventral surface appears flat, and its dorsal surface is slightly convex and has an axial furrow consisting of a string of bead-shaped pits. The coprolite granule has a directional arrangement and general equality in distribution within the aggregate. Its long axis is commonly perpendicular to the margins of the aggregate. The undigested food remains of animals and plants and the organomineral calcites with heteromorphology can be seen within the coprolite granule under photomicroscope and SEM. We deduced that a tracemaker of coprolites may be a tiny polyphagia animal similar to a modern loach or a tiny fish and that the tracemaker defecated and moved in synchronization below the interface between water and sediment. The coprolites may have a high viscidity and intensity while they were defecated. Diagenesis of feces may take place earlier and quicker than the host strata because of microbes. The lagerstatte of coprolites described herein may result from the combination of many factors, such as the high content of oxygen in the Carboniferous atmosphere, the brackish lagoon in humid and tropic climate background, the low water energy, and the anoxic taphonomic environment that was lack of other animals. Further we suggested that the deoxidized color (dark grey) of host strata of coprolites may be formed in the sedimentary environment rich in oxygen and the early anoxic diagenetic environment.