The K-T boundary in Nanxiong (long)

["David Marjanovic" <david.marjanovic@gmx.at>]

In my thick folders I haven't found a paper on ammonite extinction so far,
but here's something about the only Asian terrestrial K-T site I :-> know
of:

Ye Jie: Discussion on the problems of K/T boundary in the Nanxiong Basin,
Vertebrata PalAsiatica 38(1), 1 -- 9 (January 2000) (in Chinese with English
"summary", appears to be a full translation... apparently translated by the
author)

A priori: In marine and Hell Creek layers, the K-T boundary lies in the
magnetochron 29R. This appears to be lacking, therefore it looks like the
boundary and quite some strata above and below it aren't preserved in the
Nanxiong Basin. No evidence for Lazarus dinos either.
        There are no figures at all in the paper. If I've understood the
text correctly the author argues for

Nongshan Fm  T  mammals
Shanghu Fm  T  mammals
smooth fm boundary = K-T boundary
Pingling Fm  K  dino eggs
unconformity
Yuanpu Fm  K  dino eggs

"Summary

[...] Russell _et al._ examined examined the sequence of the polarity chron
established by Zhao _et al._ [1991] by calculating the depositional rates
(Russell _et al._, 1993, table 1). In their opinion the variation in
sedimentation rates of the different polarity chron[s] is quite great. The
depositional rates of the upper part of the Pingling Formation are extremely
high, even higher than those in the rapidly subsiding Triassic-Jurassic rift
valleys of Newark Group in eastern North America. Therefore Russell _et al._
modified the sequence of the polarity chrons for reducing the apparent
variation in sedimentation rates (Russell _et al._, 1993, table 2). The new
chrons are very different from older one:the [sic] original chron 31N near
the top of the Yuanpu Formation was changed into 32.2N [is that how
subchrons are written?] in New sequence [sic] and, original chron 29R was
substituted by two chrons: chron 31R for the upper part of the Pingling
Formation and chron 26R for the lower Part [sic] of the Shanghu Formation.
Hence a hiatus of ca. 6.37Ma occurs between the Shanghu Formation and the
Pingling Formation. Russell _et al._ analysed the shanghu [sic] local mammal
fauna based on the previous data and came to the conclusions: '...and it is
unlikely that the chrons identified by Zhao _et al._ (1991) near the middle
of the formation as 29N and 28N are older than 26N and 25N (see table 2)'.
The mention above indicates big divergence between Russell _et al._ and Zhao
_et al._ in the chronological framework of Nanxiong sections. It is not only
because of the different basic biostratigraphic data they possessed from
ours but also because of the differences in understanding and using of the
methods of stratigraphy. In order to promote the study of the stratigraphy
in Nanxiong Basin, I would [like to?] discuss the following problems with
[ = in that paper?] Russell _et al._ 1) How to understand the depositional
rate during geologic time. 2) how to identify polarity chrons in continental
section[s]. 3) Interrelation between K/T boundary and iridium anomaly.

[...]

[... The sediments are continental, so deposition was very complicated.]
Russell _et al._ have doubts about the depositional rate of the Pingling
Formation, which is of fluviatile deposits. According to my study in the
field the river changed the course and overflowed often and thus cutting and
filling took place alternatively during the sedimentation. So the average
depositional rate calculated by means of the measured thickness is not the
real rate and is variable. [Sounds like Bug Creek to me.]

[...]

Geomagnetic polarity reversal is global synchronous and repeated event
during the whole history of the Earth. Hence, it is difficult to identify
the paleomagnetion [sic] chrons of the strata according to only the
magnetopolarity records. We have to use other time carriers kept in the
sediment to calibrate the identified magnetic chrons.
        In Nanxiong Basin the following time records can be used: 1) The
basaltic lava near the top of Yuanpu Formation was dated 67.4Ma on an
average (Zhao _et al._ 1991, pp.3, 14), indicating late Mastrichtian [sic]
age and approximating the end of polarity chorn [sic] 31N, comparable with
109 -- 172m of C. G. Y. section (an interval of normal polarity near the top
of Yuanpu Formation). However, Russell _et al._ changed the magnetic
polarity of C. G. Y. 109 -- 172m into chron 32.2N without any new data in
order to reduce the apparent variatin in sedimentation rate (Russell _et
al._ 1993, table 2, P.142).
        [...] Russell _et al._ identified two normal polarity intervals in
Shanghu Formation based on the published data of fossil mammals and pollens.
However the biostratigraphic information they utilized of the fossils was
not certain. Some mammal-bearing beds in Nanxiong basin will be discussed
below [but not which mammals are in there!]. Near the bottom of Shanghu
Formation often exist faults and paddy fields, so it is difficult to check
up these beds described by predecessors (invertebrate paleontology). Instead
of invertebrate and pollens [I] will here [hardly] discuss the distribution
of mammal fossils.
        [...] It has also been considered by the Chinese geologists [like
Russell et al.] that an unconformity should be exist [sic] between Mesozoic
and Cenozoic rocks in Nanxiong basin -- a hiatus occurred between Pingling
Formation and Shanghu Formation. According to the careful observation of the
present author in the field, the top part of Pingling formation [...]
yielding nests of Dinosaur eggs; the bottom part of Shanghu Formation [...
has a different lithology]. The contact surface of these two formations is
clear and flat with no trace of hiatus in between. The relatively apparent
hiatus should occur in the Mesozoic between Yuanpu and Pingling formations.
[...] The haitus [sic] between Yuanpu and Pingling formations is therefore
obvious. However the haitus [sic] is short for the dinosaur eggs from above
and below the boundary are consistent.
        Furthermore, based on the previously published data on the fossil
mammals, Russell _et al._ considered that there are no lower Paleocene
sediments in the lower part of Shanghu Formation. [... But there are 5 in
the Shanghu and 2 in the overlying Nongshan Fm.] The present author has
checked the [... 2nd] fossiliferous layer in the field and confirmed that it
was 56m above the bottom of Shanghu Formation. It should be metnioned that
another fossiliferous layer [the 1st] 2m above the bottom of Shanghu
Formation has been found by the present author and his colleagues. Although
the fossils were ill-preserved and could not be identified exactly, they
were obviously different from those from the four layers above. According to
Zhai [typo for Zhao???] (oral communication) they could belong to one of the
small primitive condylarths. Wang _et al._ (1998) dated the Shanghu Fauna to
be equal to Puercan-middle Torrejonian of North American mammal Age, and
Ting (1998) considered the Shanghuan to be equal to Torrejonian. It is
therefore impossible [strong words] that 'several millions of years of the
earliest part of Paleocene record is absent' in Nanxiong basin.

[...]
        When Russell _et al._ discussed whether deposits of the Cretaceous
and Tertiary in the Nanxiong Basin were continuous they stressed iridium
anomaly record (Russell _et al._ 1993, P.143). The present author could not
understand the reason why they stressed: Did they mean that iridium anomaly
marked the K/T boundary [of course!] or iridium anomaly is a criterion of
continuous deposition. In my opinion, the reason of the last dinosaur
extinction has been being a problem is dispute [sic]. Although impact theory
is reasonable, it is not yet mature scientific conclusion because of
insufficient evidences. The nature and the influenced area of iridium
anomaly event has not been cleared. It should be careful to consider the
iridium anomaly the only criterion of K/T boundary. In addition, it is worth
considering the problem whether iridium could be deposited in running water,
because iridium kept in stratum is in form of particle. It is unreasonable
to deny the deposit continuation at Cretaceous-Tertiary boundary based only
on the absence of iridium anomaly although the iridium anomaly is very
important for deciding where the K/T boundary lies."

I'd highly appreciate any comments by geologists.

Refs (there are only 2 more; I haven't read any yet):

Russell D A, Russell D F, Sweet A R, 1993. The end of the dinosaurian era in
Nanxiong Basin. Vertebrata PalAsiatica 31(2), 139 -- 145
Ting SY, 1998. Paleocene and early Eocene land mammal ages of Asia. Bull
Carnegie Mus Nat Hist 34, 124 -- 147
Wang Y[uan?]q[ing?], Hu Y[ao?]m[ing?], Chow M C [Zhao Mingzhen?] et al. [no
more authors cited], 1998. Chinese Paleocene mammal faunas and their
correllation. Bull Carnegie Mus Nat Hist 34, 89 -- 123
Zhao Z[i]k[ui], Ye J[ie], Li HM et al., 1991. Extinction of the dinosaurs
across the Cretaceous-Tertiary boundary in Nanxiong Basin, Guangdong
Province. Vertebrata PalAsiatica 29(1), 1 -- 20 (in Chinese with English
summary)