[meteorite-list] An Evaluation of the Proposed Spratly Islands Impact Structure

[Paul H.]

In November 3, 2013, on the “Cosmic Tusk,” Hermann G W 
Burchard proposed that the region underlying the Spratly Islands 
is the center of a multi-ring circular to oval impact structure, 
informally called “Crater Burchard,” that has a diameter of 
about 275 km (175 miles). Given that crater are not normally 
named after people, but after geographic locations, this proposed 
impact structure will be referred to as the “Spratly Islands 
Impact Structure” for purposes of discussion after the Spratly 
Islands in the South China Sea. The center of this proposed 
275 km (175 miles) in diameter impact structure is an atoll 
called Union Reefs, or Union Bank at Latitude 9.788666° and 
Longitude 114.351768°. Burchard speculates that the Union 
Reefs atoll might lie on top of the top of the central uplift of
such an impact crater. he further speculates that this proposed 
crater might be the long searched for Australasian tektite impact 
crater Burchard (2013). The existence of this impact structure 
is based entirely upon hypothetical circular features found by 
the visual examination of bathymetry as portrayed by Google 
Earth.

The Spratly Islands is part of a larger area called the "Dangerous 
Ground." The Dangerous Ground is a part of southeast South 
China Sea that is characterized numerous low islands, reefs, 
submerged banks, shoals, and atolls that often rise abruptly from
the depths of the South China Sea. Because this area is poorly 
and inconsistently charted, it was, and in part still is, a dangerous 
place for navigation. Tropical depression, typhoons, unpredictable 
squalls, modern day pirates, and armed naval vessels involved in 
various international jurisdictional disputes are additional hazards 
found within this region (Anonymous 2011).

Burchard (2013) is right about there being significant information 
(“news”) about the geology of the Spratly Islands and adjacent 
Dangerous Ground having been collected because of the oil and 
gas potential of the area. Contrary to what he assumed, specifics 
about the geology of region were quite easy to locate and were 
collected in only a few hours of effort. In addition to geological 
research associated with oil and gas studies, detailed geological 
data for this part of the South China Sea was gathered during 
Ocean Drilling Program (ODP) Leg 184 (Shipboard Scientific 
Party 2000a). Thus, the published data available for the Spratly 
Islands and adjacent Dangerous Ground includes seismic lines 
that cut across the proposed impact structure and an ODP drillhole, 
ODP Site 1143 of Leg 184, that lies just within the alleged rim 
of the proposed Spratly Islands Impact Structure. The drillhole 
at ODP Site 1143 was continuously cored to from the sea floor 
at a depth of 2772 m below sea level to a depth of  512.4 m 
(1,680 feet) below the sea bottom (Shipboard Scientific Party, 
2000b).

Because of their potential oil and gas potential and the multiple 
and contentious international claims and jurisdictional disputes 
concerning the Spratly Islands and adjacent Dangerous Ground 
region, they have been the subject of intensive and repetitive 
geological studies from a wide variety of governmental and 
nongovernmental agencies and private corporations of various 
nationalities. Although much of the data, including seismic lines 
and drillhole data, remain proprietary, scientifically significant 
and revealing data, including regional multi-channel seismic 
data, and their interpretations, have been published in sufficient 
number to provide a clear picture of their geology as discussed 
in Blanche and Blanche (1997), Hutchison (2004, 2010), 
Hutchison and Vijayan (2010), Hinz and Schlueter (1985), 
Metcalfe (2010), Wei-Weil and Jia-Biao (2011), Zhen et
al (2011) and various other publications.

The above research found that at the surface the Spratly Islands 
consist of reefs, banks, and shoals that are composed of 
biogenic carbonate that have accumulated on the higher crests 
of major sea-floor seafloor ridges. These ridges consist of a 
series of uplifted fault-blocks, called horsts, which are part of
a series of parallel and en echelon, half-grabens and rotated 
fault-blocks. The axes of the ridge crests (horsts) and their
associated grabens form well-defined linear trends that lie
parallel to magnetic anomalies of the contiguous oceanic crust 
of the adjacent South China Sea. These fault-blocks consist of 
Triassic, Jurassic, and Cretaceous strata that include calcalkalic 
extrusive rocks, intermediate to acid intrusive rocks, sandstones, 
siltstones, dark-green claystones, and metamorphic rocks 
that include biotite-muscovite-feldspar-quartz migmatites or 
gamet-micaschists (Blanche and Blanche 1997, Hutchison 2004, 
2010, Hutchison and Vijayan 2010, Hinz and Schlueter 1985, 
Wei-Weil and Jia-Biao 2011).

These horsts and grabens are the result of two distinct periods 
of tectonic stretching of continental crust along underlying 
deeply-rooted detachment faults. The early period of tectonism 
occurred during the Late Cretaceous and Early Oligocene and 
resulted in the formation of horsts, half-grabens, and rotated 
fault-blocks. This tectonism was associated with the rifting 
and stretching of continental crust that corresponded with the
initial sea-floor spreading within the South China Sea. Further 
stretching and block faulting of continental crust occurred
within the Spratly Islands and adjacent Dangerous Ground area
during the Late Oligocene-Early Miocene and eventually halted 
afterwards. After tectonic activity had ceased, the crest of the 
horsts that lay in shallow water were colonized and biogenic 
carbonates accumulated on them to form reefs, shoals and 
cays known as the Spratly Islands (Wei-Weil and Jia-Biao 
2011, Zhen et al. 2011)

The history of faulting and related tectonism within the Spratly 
Islands and adjacent Dangerous Ground region can be confidently 
reconstructed on the basis of regional unconformities that can be 
clearly seen and identified in regional and local seismic sections. 
Because they have been dated using biostratigraphy in drillholes 
that intersect them, they form timelines that can be traced using 
seismic across the entire Dangerous Ground region, including 
the Spratly Islands. The most important of these unconformities 
is known as either the “Mid-Miocene,” "Breakup," or “T60" 
unconformity (Hutchison 2004, Hutchison and Vijayan 2010, 
Wei-Wei and Jia-Biao 2011, Zhen et al. 2011). This unconformity 
is an angular unconformity that separates syn-rift strata, which 
accumulated during the faulting that formed these regional half-
grabens and rotated blocks, from post-rift strata, which 
accumulated after the regional tectonism had ceased during the 
Early Miocene. The T60 unconformity clearly demonstrates that 
faulting within Spratly Islands and Dangerous Ground had 
ended by Early Miocene (Hutchison and Vijayan 2010, Wei-Wei 
and Jia-Biao 2011, Zhen et al. 2011). Thus, there is complete
absence of either any significant faulting or any other tectonism 
that can be associated with a 0.78 Ma extraterrestrial impact. The 
relatively undisturbed and intact nature of post- Early Miocene 
sediments within the Spratly Islands and Dangerous Ground region 
completely refutes any hypothesis about they being the site of a 
relatively large 0.78 Ma extraterrestrial impact being associated 
with the Spratly Islands and Dangerous Ground region.

Equally revealing are the cores recovered from drilling at ODP 
Site 1143. The examination of these cores by Shipboard Scientific 
Party (2000b) found only one recognizable lithologic unit, which 
is subdivided into two subunits, Subunits, IA and IB, within the 
512 m-long (1,780 foot-long) core. The upper 160 m (525 feet) 
of the sedimentary sequence, Subunit 1A, consists of typically 
massive, olive-gray, light grayish green, hemipelagic, calcareous 
clay with abundant nannofossils and foraminifera. Distinct green 
clay layers are present. Foraminifer ooze turbidites were also occur 
within this subunit. The turbidites are normally graded. They 
often exhibit a scoured basal contact. The part of the sedimentary 
sequence that is below 160 m (525 feet), Subunit 1B, consists 
of are clayey nannofossil mixed sediment, nannofossil clay, and 
nannofossil ooze with clay. This subunit has a higher carbonate 
content; more turbidites; and fewer green clay layers then 
Subunit 1A. In addition, it contains infrequent dark gray volcanic 
ash layers and volcanic breccias. Subunit 1B also exhibits trace 
fossils, such as Zoophycos and Chondrites, and sedimentary 
structures associated with slumps and turbidites (Shipboard 
Scientific Party 2000b).

These sediments can be readily dated from the abundant 
microfossils, including nannofossils and foraminifera. These 
fossils demonstrate that the Pleistocene/ Pliocene boundary is 
located between 93.5 and 94.3 m (307 and 309 feet) below the 
sea bottom and the Pliocene/Miocene boundary is located 
between 213.0 and 200.6 m (699 and 658 feet) below the sea 
bottom. In addition, a clear paleomagentic declination change 
of nearly 180° at 43.2 m (142 feet) below sea bottom and in the 
middle of Core 184-1143C-5H was interpreted to represent the 
Brunhes/Matuyama reversal at about 0.78 Ma. The sedimentary 
sequence cored at ODP Site 1143 clearly shows that hemipelagic 
sedimentation of fine-grained terrigenous material and calcareous 
nannofossils occurred essentially uninterrupted from the late 
Miocene to present at this site (Shipboard Scientific Party 
2000b).

Being located just within the rim of the proposed Spratly Islands 
Impact Structure, this core, as does published seismic sections, 
demonstrates the lack of any significant Pleistocene-age 
extraterrestrial impact structure being associated with the Spratly 
Islands. The ODP Site1143 cores, seismic data, and other 
published research effectively refute the existence of the 
proposed Spratly Islands Impact Structure and relegates it to a 
long of imaginary extraterrestrial impact structures that have 
been proposed solely on the basis of remote sensing data. It 
shows how dubious a methodology using Google Earth alone 
to identify extraterrestrial impact craters. 

Note: For other examples of the dubious use of Google
Earth to identify extraterrestrial impact structures, go read

1. The Manuel Benavides Craterwrong and Cratermania
http://www.mail-archive.com/meteorite-list@meteoritecentral.com/msg92117.html

2. Preliminary Evaluation of a Proposed “Younger Dryas 
Impact” Crater
https://www.mail-archive.com/meteorite-list@meteoritecentral.com/msg102013.html

References,

Anonymous, 2011, Sailing Directions (Enroute): South China 
Sea and the Gulf of Thailand, Publication 161, 13th edition, 
National Geospatial-Intelligence Agency, Bethesda, Maryland.

Blanche, J. B. and J. D. Blanche, 1997, An Overview of the 
Hydrocarbon Potential of the Spratly Islands Archipelago 
and its Implications for Regional Development. in A. J. 
Fraser, S. J. Matthews, and  R. W. Murphy, eds., pp. 293-310,
Petroleum Geology of South East Asia. Special Publication
no. 126, The Geological Society, Bath, England 436 pp.

Burchard, H. G. W., 2013, Crater Burchard? The Cosmic
Tusk. November 3, 2013 http://cosmictusk.com/crater-burchard/

Hinz K., and H. U. Schlueter, 1985, Geology of the Dangerous 
Grounds, South China Sea, and the continental margin off 
southwest Palawan: results of SONNE Cruises SO-23 and 
SO-27. Energy. vol. 10, no. 3-4, pp. 297-315.

Hutchison, C. S., 2004, Marginal basin evolution; the southern 
South China Sea. Marine and Petroleum Geology. vol. 21, 
no. 9, pp. 1129–1148

Hutchison, C. S., 2010, The North-West Borneo Trough Marine 
Geology. vol. 271, pp. 32–43

Hutchison, C. S., and V. R. Vijayan, 2010, What are the 
Spratly Islands? Journal of Asian Earth Science. vol. 39, 
no. 5, pp. 371–385.

Metcalfe, I., 2011, Tectonic framework and Phanerozoic 
evolution of Sundaland. Gondwana Research. vol. 19, pp. 3–21

Wei-Wei1, D., and L, Jia-Biao, 2011, Seismic Stratigraphy, 
Tectonic Structure and Extension Factors Across the Dangerous 
Grounds: Evidence from Two Regional Multi-Channel Seismic 
Profiles. Chinese Journal of Geophysics. vol. 54, no. 6, 
pp. 921–941.

Shipboard Scientific Party, 2000a, Volume 184 Initial Reports. 
(South China Sea) Proceedings of the Ocean Drilling Program, 
Initial Reports. vol. 184, Ocean Drilling Program, Texas A&M 
University, College Station, Texas.

Shipboard Scientific Party, 2000b, 4. Site 11431. Proceedings 
of the Ocean Drilling Program, Initial Reports. vol. 184, Ocean 
Drilling Program, Texas A&M, University, College Station, 
Texas.

Zhen, S., Z. Zhong-Xian, L. Jia-Biao, Z. Di, and W. Zhang-
Wen, 2013, Tectonic Analysis of the Breakup and Collision 
Unconformities in the Nansha Block. Chinese Journal of 
Geophysics. vol. 54, no. 6, pp. 1069-1083.

Yours,

Paul H.