Mineral microbial structures in a bone of the Late Cretaceous dinosaur Saurolophus angustirostris from the Gobi Desert, Mongolia — a Raman spectroscopy study

Bones, while buried, undergo diagenetic transformations, the intensity of which depends on a variety of geochemical factors. Microbial degradation is one of the main processes acting on bones during early diagenesis. We present mineral microspheres formed during bone diagenesis from the inner walls of the left tibia of the Late Cretaceous dinosaur Saurolophus angustirostris from the Gobi Desert (Mongolia). The microspheres occur either as individual bodies, from a few micrometers to about 70 μm in diameter, or aggregated in clusters. Micro-Raman analysis shows that the microspheres are composed of various Fe-oxides – mostly hematite and goethite – that form regular reddish-brown rings, with organic matter at their cores. The bone itself is composed, for the most part, of diagenetically transformed carbonate-fluorapatite. Calcite cement was identified around the spheres and at points of contact with bone tissue. Negative Ce anomalies indicative of Ce(IV) in the diagenetic environment indicate oxic burial conditions. All the size distribution of the microspheres, their mode of occurrence, and the presence of organic matter in cores surrounded by concentric Fe-oxide envelopes indicate early diagenetic microbially-mediated mineralization in aerobic conditions. The presence of microspheres and other mineral phases in the studied bone gives evidence of at least two mineralization episodes: (1) Fe-oxide formation during an early diagenetic microbial attack on the bone, and (2) later calcite/barite/gypsum cementation.