Sedimentology of Miocene Mixed Siliciclastic-Carbonate Systems, East Java, Indonesia: Implications for the Tectonic Evolution of Southeast Asia

Jennifer Tang, University of Wisconsin-Madison, Department of Geology & Geophysics, Madison, WI, [email protected]

The East Java Basin (EJB), Java, Indonesia, lies on the southeastern Sunda Shelf directly north of the present Java Arc.  It has a uniquely complex tectono-stratigraphic history that challenges conventional basin models: Early-Middle Miocene compression from the rotation of Borneo to the north and the subducting plate to the south precludes extensional backarc basin and loaded retroarc foreland basin models.  This period of compression introduced siliciclastics to the shallow carbonate system and generated the mixed siliciclastic-carbonate Tuban Formation and the quartz-rich Ngrayong Formation.  Subsequent Plio-Pleistocene uplift exposed large sections of this Miocene sequence, which presents a unique opportunity to correlate subsurface 2D seismic and well-log interpretations of the succession with sedimentologic, petrographic, and isotopic analyses of outcrop samples. Preliminary seismic interpretations image Miocene clinoforms that prograde from the north and the south, which suggests a mixed provenance and changing drainage patterns.  These clinoforms occur at a seismic scale of 300 ms, and their interpretation in the literature ranges from tidal deposits to contourites, indicating the sustained confusion. This project’s integrated approach will examine and map in detail the provenance, paleocurrent directions, seismic architecture, age distribution, lithofacies, and environmental facies of the Tuban and Ngrayong clinoforms.  The tectonic, stratigraphic, and paleoclimatic implications derived from these results will clarify the impact of Miocene compressional tectonics on the geologic evolution of Southeast Asia and the supply of sediment to the EJB as well as modify tectonic reconstructions and basin models beneficial to the scientific and economic exploration of Java.