Neogene paleoclimatic evolution in Northwestern Luzon, Philippines: Insights from Lower Miocene to Lower Pliocene sedimentary records

Geochemical analyses of Neogene clastic sediments overlying the Zambales Ophiolite Complex (ZOC) in northwestern Luzon, Philippines provide insights into paleoweathering and paleoclimatic conditions. This study examines the Early Miocene Cabaluan Formation and Late Miocene to Early Pliocene Santa Cruz Formation using weathering proxies, such as the Chemical Index of Alteration (CIA), Revised Chemical Index of Alteration (CIX), Chemical Index of Weathering (CIW), and dual-elemental ratios (e.g., Al/Ti, Sc/Ti, Na/Al). Elevated CIA, CIX, and CIW values in the Cabaluan Formation indicating intense weathering suggests warm and wet conditions during the Early Miocene. Conversely, lower values and reduced Al/Ti and Sc/Ti ratios in the Santa Cruz Formation reflect a shift to cool and dry conditions at the onset of the Late Miocene period. 

These findings align with regional patterns derived from similar geochemical proxies and δ18-O values in the northern South China Sea and global climatic cooling trends during the Neogene. They also highlight the influence of the East Asian Summer Monsoon (EASM) on the prevailing local weathering regime, supported by mobility indices (αᴬˡE) showing distinct elemental depletions and enrichments linked to climatic variations.

This study contributes to the scarce but growing paleoclimate studies in the Philippines using geochemical signatures in the sedimentary record. It provides a pioneering view into the Neogene paleoclimatic shift from a warm to cool climate in northwestern Luzon, Philippines, underscoring the influence of the EASM in the local and regional climatic evolution since the Early Miocene.