PANGANDARAN — Researchers from Universitas Pakuan have uncovered evidence that limestone exposures in Selasari, Pangandaran, record the evolution of a tropical shallow-marine carbonate platform that existed millions of years ago during the Miocene.
The study, conducted by Teti Syahrulyati and Margaretha R. Shindra Kotouki from the Geological Engineering Program, Faculty of Engineering, Universitas Pakuan, was published in the International Journal of Scientific Multidisciplinary Research (IJSMR) 2026. It focuses on microfacies analysis of the calcarenite member of the Pamutuan Formation in Selasari.
Using field observations from 53 outcrops and four stratigraphic traverses—Selasari, Bangunkarya, Cimanggu, and Kersaratu—the research reconstructs depositional environments that shaped southern West Java’s carbonate platform during the Middle to Late Miocene.
Evidence of Open and Restricted Marine Environments
Microfacies analysis identified two principal depositional settings: open marine shelf circulation (Facies Zone 7) and restricted inner platform environments (Facies Zone 8).
Facies Zone 7 is characterized by wackestone and packstone textures containing transported skeletal fragments such as foraminifera and mollusks. These features indicate moderate hydrodynamic energy typical of shallow tropical shelves with active water circulation.
Facies Zone 8 reflects quieter lagoonal or protected shelf environments. The presence of quartz and plagioclase grains suggests intermittent terrestrial influence, marking shifts in sediment supply and depositional energy.
Together, these facies provide strong evidence of fluctuating sea levels and dynamic carbonate sedimentation processes across the Pangandaran region.
A Tropical Carbonate Platform During the Miocene
Petrographic observations reveal abundant larger benthic foraminifera, calcareous algae, and molluscan fragments, indicating deposition in warm, shallow, and well-circulated marine waters.
During the Middle Miocene, reduced volcanic activity across southern Java allowed carbonate-producing organisms to thrive. Transgressive sea-level conditions further expanded shallow marine habitats, supporting extensive calcarenite deposition across the region.
These environmental conditions played a major role in shaping the carbonate stratigraphy observed today.
Structural Geology Influenced Sediment Distribution
Regional tectonic structures such as the Cikalong anticline, Cintaratu syncline, and Selasari strike-slip fault influenced the spatial distribution of carbonate deposits.
Although these structures formed later during Plio-Pleistocene compressional events, they contributed to the uplift and exposure of the limestone units now visible at the surface.
As a result, Selasari limestone exposures preserve not only depositional records but also evidence of post-depositional tectonic evolution in southern West Java.
Diagenesis Reveals a Long Geological Transformation
The Universitas Pakuan research team also identified four major diagenetic stages affecting the limestone after deposition: marine phreatic cementation, burial compaction, meteoric phreatic alteration, and meteoric vadose dissolution.
Early cementation stabilized sediments shortly after deposition. Burial processes then aligned mineral grains under pressure. Later tectonic uplift exposed the limestone to meteoric water, triggering recrystallization and microspar development.
Finally, dissolution near the surface produced vuggy cavities that remain visible today.
These processes demonstrate how carbonate rocks preserve a continuous record of environmental change from deposition to surface exposure.
A Valuable Archive of Southern Java’s Geological History
Microfacies evidence from the Pamutuan Formation provides important insights into the evolution of Neogene carbonate platforms along the southern Java margin.
Future studies integrating isotopic analysis and larger benthic foraminiferal assemblages may further refine reconstructions of paleoclimate influence, sea-level fluctuations, and carbonate platform dynamics across Southeast Asia.
The Selasari limestone thus stands as a key geological archive documenting the interaction between tropical marine systems and tectonic processes in Indonesia’s geological past.
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