Fig. 5

a − c Cathodoluminescence microscopy revealed the common occurrence of luminescent fractures and growth lines in the collected belemnites, particularly around the apical line and the ventral invagination. Traces of bioerosion are comparatively sparse. While a considerable number of belemnite samples from the Spiti Valley contains dark areas, all rostra from the Zanskar Valley are strongly luminescent reflecting considerable alteration. Only samples from non-luminescent areas, believed to be at least moderately well-preserved, were used for palaeoenvironmental reconstructions (a: SP16-066 from the Upper member near Demul, Spiti Valley; b: SP18-022 from the Upper member near Demul, Spiti Valley; c: ZA18-003 from the Lower member near Zangla Cliff, Zanskar Valley); d, e Scanning electron microscopy demonstrates varying levels of preservation among the studied fossils. Well-preserved belemnite rostra show comparatively regular, radial calcite crystals without signs of alteration or fractures (d: SP16-069 from the Upper member near Demul, Spiti Valley). In contrast, all studied oysters are poorly preserved with abundant fractures crossing the partly recrystallized shell layers (e: SP16-023 from the Middle member near Langza, Spiti Valley)