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

From: Paul H. <inselberg_at_meteoritecentral.com>
Date: Thu, 5 Dec 2013 10:14:50 -0500
Message-ID: <20131205101450.SVDSW.383296.imail_at_eastrmwml214>

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 at meteoritecentral.com/msg92117.html

2. Preliminary Evaluation of a Proposed ?Younger Dryas
Impact? Crater
https://www.mail-archive.com/meteorite-list at 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.
Received on Thu 05 Dec 2013 10:14:50 AM PST