SULU SEA BASIN PLUS SPRATLY ISLANDS MULTI-RING BASIN: DOUBLET CRATER RESULTING FROM A MIDDLE MIOCENE BINARY OBLIQUE IMPACT?

The ophiolite rimmed Sulu Sea basin and the Spratly Island multi-ring structure have nearly identical aspect ratios and long axis orientations, suggesting low angle oblique impact of a large binary object approaching from SW to NE or from NE to SW. Interpretation of the Reed Bank as an impact debris flow rampart, originating from the Spratly Island structure, favors a SW to NE approach. Middle Miocene ophiolite emplacement and coeval ophiolitic mélange formation (in Sabah and Palawan) suggest an impact age similar to Nordinger Ries crater and the Middle Miocene Disruption (extinction) event. The Sulu and Negros trenches may constitute incipient subduction zones associated with boundaries of the parent basin.

Problems include:

1) A global Middle Miocene impact layer/spherule bed has not been identified. Spherule layer should be tens of cm thick based on conventional rock vapor scaling [1,2].

2) The Middle Miocene Disruption should have been a severe (not minor) extinction event [3].

3) Impact basins of Sulu Sea Basin size are not expected in the Phanerozoic [4].

To confirm or rule out impact origin search for and identify:

1) global impact layer in continuous Middle Miocene sedimentary sequences.

2) Middle Miocene course ejecta layer proximal to these structures in oil and exploratory well cores from the South China and Celebes seas.

3) impactites in exploratory drill cores from the Spratlys.

4) high pressure and/or shocked mineral phases in Sulu Sea basin rim ophiolites: Can ophiolitic diamonds be found in chromitites from Palawan and Sabah [5]?

References: [1] Grieve R.A.F. and Cintala M.J. 1992 Meteoritics 27: 526–538. [2] Pierazzo E. et al. 1997 Icarus 127/2:408-423. [3] Sleep N.H. and Zahnle K., 1998. JGR Planets (103(E12) 28529-28544. [4] Ivanov B.A. et al. 2002 Asteroids III 89-101. [5] Yang J.-S., Robinson P. T., and Dilek Y. 2014 Elements, 10/2:127-130.