The Oligocene–Miocene of East Java is characterized by multiple stages of isolated carbonate mound growth surrounded by deeper marine off-mound sediments or by shallow-marine siliciclastics. Three stratigraphic intervals are recognized: Kujung (carbonate mound and off-mound), Tuban (mixed carbonate-siliciclastic), and Ngrayong (siliciclastic). Exposures of the Kujung unit (∼28–22 Ma) are limited to a few isolated outcrops. At the base, the Kujung is represented by a high-energy, extensive, shallow-marine carbonate facies that grades laterally into deep-marine off-mound sediments of calcareous mudstone and chalk (lower Kujung). In other locations, shallow-water carbonate deposition was restricted to faulted topographic highs in the middle–upper Kujung. The shallow-marine sediments of the lower Kujung were covered by thick chalk and marl sediments of the middle–upper Kujung. The Tuban unit (∼22–15 Ma) consists of widely exposed shallow-marine mixed carbonate and siliciclastic and poorly exposed open-marine shale and chalk facies. The Tuban consists of at least six stacked cycles that reflect deltaic deposition with episodes of shallow-marine carbonate mound growth. The Ngrayong unit (∼15–12 Ma) represents a period of regional siliciclastic influx and progradation of tidally influenced deltas and grades into turbidites, basinal shale, mudstone, and chalk. Ngrayong beds are truncated by Bulu carbonates (Serravallian–Tortonian). This is consistent with the tectonic evolution of the region.

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