See previous posts on the speed of tectonic transition in SE Asia
South East Asia is famous for carbonate reefs. But these are mostly in the subsurface. A very simple overview would be that reefal systems increased as Sundaland subsided, while clastic supply decreased and the area of shallow shelf increased. Generally this lasted until about the middle Early Miocene, but locally, as around the Bunguran Trough in the SW South China Sea, it continued for a few million years more. After this, reefs declined and became patchy. Uplift in Borneo increased slilciclastic supply and some depositional areas were also uplifted, while in others subsidence decreased or was less regular.
A modern map of reefal systems makes it clear, carbonate reefs and siliciclastics don’t coexist. When the “Ngimbang” carbonates (early Late Eocene; J30 Sequence, Lunt, 2019) of East Java / south Makassar Straits were abruptly terminated and subsided they were almost immediate overlain by a new siliciclastic unit, with no appreciable time gap! However the new siliciclastics were probably just as much, or more, responsible for the demise of the J30 reefs as the subsidence to bathyal conditions in which the J40 clays were deposited. Many carbonates in SE Asia seem to have been killed off by siliciclastic influx (see this review of the E Java reefs).
At rare times there was no increase in siliciclastic influx, and it is known that basement subsidence accelerated considerably. At the base Cycle IV “Doust MMU”; Lunt and Madon, 2017) most of the Luconia Province offshore Sarawak subsided and reefs formed (and reefs of the Terumbu Limestone on the symmetrical margin across the Bunguran Trough). However, stepping down, across normal faults, into the edge of the Bunguran Trough it can be seen that reefs disappear. At first they rapidly diminished, showing the conditions were shallow enough to seed reefs (Hutchison, 2004; see this link) but these reefs could not keep up (drilled and proven by the Tuntong-1 well). This indicates a sudden acceleration in subsidence (see the North Luconia geohistory) with sufficient magnitude to outpace reefal growth.
In the south of Java and Makassar Straits multiple wells and outcrops have reefal complexes and pinnacles (Rajamandala Limestone, Jembaran-1, Agung-1, Baluran-1, JS 53B-1, Sultan-1, Snorkel Sea Mount, and Bravo-1, see Luan and Lunt 2021a) that have reefs which survived until the end of the J70 sequence, end Oligocene times, based on Letter Stage Te4 larger foraminifera and Sr dating. All these reefs became extinct near the Te4 to Te5 boundary. That so many reefs terminated in the same short time interval, to be followed by bathyal conditions (the Sultan-1 geohistory plot is at the end of this post), suggests that they subsided at a rate with which reefal growth could not keep up. It is unlikely that so many reefs would have coincidentally become extinct at the same time and, as Luan and Lunt (2021a, 2021 b and 2021c) pointed out, the basalmost Miocene around these reefs was exceptionally condensed or a deep marine hiatus (all siliciclastics being trapped in the newly subsided basin to the west).
How fast is fast?
So what is this high rate of subsidence? Bear in mind that fault development is usually fastest in its earliest stages and it then declines exponentially, so the high numbers implied here for fault-driven subsidence should not be extrapolated for millions of years.
Many reefs around the world survived the sea-level rise after the end of the last ice-age. This included sea-level rise of one to two metres per century (see figure below). Webster et al. (2009) examined reefs around Papua and Hawaii and suggested that if tectonism was superimposed on eustatic changes this was enough to kill scleractinian coral-based reefs. Their estimates of tectonic subsidence in the Gulf of Huon, Papua was 2 to 6 m/ka, or as much as an additional 0.6 metres per century. This very approximate estimate suggests an order of magnitude of 2.6 (say 2½ to 3 m/100 yrs) is enough to outpace reef growth. This is an incredible 25 to 30 km/Ma, but no one expects the accelerated subsidence to have lasted that long. Just a decade would place a reef at the base of the euphotic zone and preclude recovery, after which the rate of tectonic displacement would have rapidly faded (Allen and Allen, 2013).
In preceding posts on the speed of tectonic change (post 1 & post 2) there are other indications for very rapid rates of tectonostratigraphic change. The data from reef drowning gives a high end estimate for the rate of change of at least some of the extensional tectono-stratigraphic events.
So think of this. A few years ago we believed that tectonic change was ponderously slow, upon which glacio-eustatic sea-level cycles would imprint a distinct stratigraphic signature. Now we are identifying multiple times when the basinal configuration over wide areas, sometimes multiple depocentres at the same time, rapidly changed, not just at a rate comparable to glacio-eustatic change but to much higher magnitudes. Not just subsidence. I remember chatting with Robert Hall some years ago, who mentioned standing on young Pleistocene reefs now elevated to hundreds of meters above sea-level on east Indonesian islands. These tectonic changes might have been at a rate fast enough for a single generation of humans to observe. Tectonism has a much older history in the region than the acme of glacio-eustatic changes that really began only in mid Pliocene times (see this post).
References
Allen, P.A., Allen, J.R., 2013. Basin Analysis: Principles and Application to Petroleum Play Assessment. Wiley-Blackwell.
Luan, X., Lunt, P., 2021a. Latest Eocene and Oligocene tectonic controls on carbonate deposition in eastern Java and the south Makassar Straits, Indonesia. Journal of Asian Earth Sciences
Luan, X., Lunt, P., 2021b. Controls on Early Miocene carbonate and siliciclastic deposition in eastern Java and south Makassar Straits, Indonesia. Journal of Asian Earth Sciences
Luan, X., Lunt, P., 2021c. Occurrence in space and time of the Globigerina-sands of eastern Java; their stratigraphy, and controls on reservoir quality. Marine and Petroleum Geology
Lunt, P., 2019. The origin of the East Java Sea basins deduced from sequence stratigraphy. Marine and Petroleum Geology 105, 17-31
Lunt, P., Madon, M.B.H., 2017. A review of the Sarawak Cycles: History and modern application. Geological Society Malaysia Bulletin 63, 77-101
Stanford, J.D., Hemingway, R., Rohling, E.J., Challenor, P.G., Medina-Elizalde, M., Lester, A.J., 2011. Sea-level probability for the last deglaciation: A statistical analysis of far-field records. Global and Planetary Change. Rapid climate change: lessons from the recent geological past 79(3), 193-203
Webster, J.M., Braga, J.C., Clague, D.A., Gallup, C., Hein, J.R., Potts, D.C., Renema, W., Riding, R., Riker-Coleman, K., Silver, E.A., Wallace, L.M., 2009. Coral reef evolution on rapidly subsiding margins. Global and Planetary Change 66, 129-148
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