Holocene climatic change on the Arabian Peninsula: a high-resolution record from the Layla Lakes, central Saudi Arabia

The Layla Lakes are a series of karst lakes located in central Saudi Arabia (300 km S of Riyadh). Their sediments were exposed in the 1980s due to groundwater drawdown. These finely laminated lacustrine sediments likely consist of seasonally alternating carbonate and sulfate layers and preserve a high-resolution archive of Holocene environmental variability in central Saudi Arabia.

Two sedimentary successions capture the transition from a more humid early Holocene to increasingly arid conditions after ~4000 cal BP. The humid phase (7500–6200 cal BP) is characterised by laminated micritic carbonates with the average sedimentation rate ~2.7 mm/year and alternating loosely and tightly packed layers. Loosely packed layers are rich in biogenic compounds, whereas tightly packed layers lack visible biological content. This alternation likely reflects summer–winter seasonality, forming seasonal laminae. Fossil-rich layers were potentially formed during summer, and biogenically poor layers during winter.

The arid phase (4400–2600 cal BP) is marked by a higher sedimentation rate ~5.1 mm/year with alternating thick gypsum and thin carbonate layers, and pollen assemblages typical of semi-desert vegetation. Gypsum layers are devoid of organic remains and likely formed during hot, dry summers with intense evaporation, whereas carbonate layers contain biogenic material (ostracods, algae, diatoms, and gastropod fragments) and may reflect cooler, wetter winters. This seasonal deposition regime appears to have persisted until recent times.

These sedimentary patterns reflect a long-term Holocene shift toward increased aridity and seasonality. Additionally, the rhythmic recurrence of carbonate and sulfate layers and variations in fossil content indicate sub-Milankovitch (centennial-scale) climatic cyclicity.