Figure 1

Palaeogeographic map, location, photomicrographs, and laminae compositions of the studied Mongolian lacustrine deposits. (A) Reconstructed mid-Cretaceous palaeoclimatic zonation and palaeo-wind patterns40. (B) Distribution of Lower Cretaceous lacustrine strata and location of study site in Mongolia39. (C) Photomicrographs of tens of micrometer-scale laminae in shale bed taken under transmitted (left) and reflected fluorescence (right) light. (D) Elemental composition of lamina couplets based on SEM–EDX analysis, consisting of micrometer-scale alternations of organic carbon (fluorescent algal OM), lenticular micritic calcite aggregates, and detrital clay mineral (less fluorescent) layers, in ascending order.