Abstract Ordered pyrolytic graphite was shock compressed by weak shock waves. Macroscopic characterization by scanning electron microcopy and X-ray diffraction analysis revealed that the shock pressure was enhanced by interaction and convergence of plane and oblique shock waves and the shock pressures and shock temperatures in the sample were highly heterogeneous. The heterogeneous conditions allowed the coexistence of fullerene, α-carbyne, turbostratic graphite, γ-carbon, and diamond-like carbon phase quenched in the precursor state of cubic diamond (p-diamond). The phase transformation processes of these carbon allotropic forms were investigated by high-resolution electron microscopy together with energy-dispersive X-ray spectroscopy. It was proposed that fullerene, turbostratic graphite and γ-carbon were formed through a solid–vapour–solid sequence of phase transformations, while α-carbyne and p-diamond were formed via a solid–solid sequence of phase transformations.