Previous studies suggested the multi-millennial scale changes of Australian-Indonesian monsoon (AIM) rainfall, but little is known about their mechanism. Here, AIM rainfall changes since the Last Deglaciation (~18 ka BP) are inferred from geochemical elemental ratios (terrigenous input) and palynological proxies (pollen and spores). Pollen and spores indicate drier Last Deglaciation (before ~11 ka BP) and wetter Holocene climates (after ~11 ka BP). Terrigenous input proxies infer three drier periods (i.e., before ~17, ~15–13.5, and 7–3 ka BP) and three wetter periods (i.e., ~17–15, ~13.5–7, and after ~3 ka BP) which represent the Australian-Indonesian summer monsoon (AISM) rainfall changes. Pollen and spores were highly responsive to temperature changes and showed less sensitivity to rainfall changes due to their wider source area, indicating their incompatibility as rainfall proxy. During the Last Deglaciation, AISM rainfall responded to high latitude climatic events related to the latitudinal shifts of the austral summer ITCZ. Sea level rise, solar activity, and orbitally-induced insolation were most likely the primary driver of AISM rainfall changes during the Holocene, but the driving mechanisms behind the latitudinal shifts of the austral summer ITCZ during this period are not yet understood.

The northern region of East Java is known as Indonesia's largest oil and gas producer. The southern region also exhibits several potential petroleum system manifestations, such as shale outcrops that extract biogenic hydrocarbons in Dongko District, Trenggalek Regency. Identification of palynofacies/palynomacerals can be determined based on the kerogen composition of sedimentary rocks. This is crucial for more detailed exploration of hydrocarbon potential. The kerogen composition of samples K4 and K5 was analyzed from surface outcrop profiles. Previous research indicates that samples K4 and K5 are Middle Miocene in age and were deposited in a mangrove environment. Palynofacies identification from kerogen analysis indicates that sample K4 was deposited in an environment farther from the source of organic material, or in a mangrove environment in the lower deltaic plain, characterized by fine-to-very-fine carbonate sandstone. Conversely, sample K5 was deposited in an environment closer to the source of organic material, or in a mangrove environment in the upper deltaic plain, characterized by black shale with launau-clay lithology. Samples K4 and K5 have the same organic material composition, namely inertinite, vitrinite, and exinite, although the material sizes are different.