olelog

What on earth

Graptolites and the Guangxian Orogeny, China

, ,

Graptolites are fossil colonial animals known chiefly from the Upper Cambrian through the Lower Carboniferous (Mississippian). The name graptolite comes from the Greek graptos, meaning "written", and lithos, meaning "rock", as many graptolite fossils resemble hieroglyphs written on the rock. Graptolites are common fossils and have a worldwide distribution. The preservation, quantity and gradual change over a geologic time scale of graptolites allows the fossils to be used to date strata of rocks throughout the world. They are important index fossils for dating Palaeozoic rocks as they evolved rapidly with time and formed many different species.



Apart from a reassessment of Upper Ordovician graptolites in China a recent study also recommend the studied graptolites to assess the initiation time of a tectonic event known as the Kwangsian Orogeny (orogeny = mountain building period). Well, known or known. I must admit that i have a few problems with Chinese orogenies, and tectonic plates, and (not least) their names.



The studied Ordovician graptolites (Ordovician - ca. 488-444 million years ago) were from southern Guangxi, and this region has lent its name to the Guangxian Orogeny (a synonym for the Kwangsian Orogeny, just spelt differently, transcription from Chinese to Latin characters is not straightforward). The Guangxian Orogeny was earlier seen as part of the Caledonian Orogeny (ca. 490-390 million years ago In Northern Europe and North American), because it took place in a similar time-span. Changes in water depths an depositional rates in the Period from 475-450 million years ago may indicate that the Guangxian Orogeny started in the early Katian (Katian - ca. 456-446 million years ago).

The Guangxian Orogeny would have been a result of the convergence and collision between the Cathaysian and Yangtze blocks. Now here is another confusing problem as these terms have been used differently in the literature in the past. The same is true for Yangtze Plate/Block and South China Plate/Block. For instance the terms ‘Yangtze Plate’ and ‘South China Plate’ have both been used for the modern plate shown on the following map. Yangtze Plate is the term used in ‘An updated digital model of plate boundaries’ by Peter Bird (2003).



An older discussion (from 2000) on the orogeny, we are talking about, is found in ‘Reinterpretation of the Guanxian Orogeny’ by Haoruo. This paper placed the Guanxian Orogeny at the end of Silurian ca. 460 million years ago.

Relevant full-text pdf-files:
Ordovician graptolite-bearing strata in southern Jiangxi with a special reference to the Kwangsian Orogeny
Reinterpretation of the Guangxian Orogeny
Pre-Devonian tectonic evolution of the eastern South China Block: Geochronological evidence from detrital zircons
An updated digital model of plate boundaries





Academics

Microbial Mounds at Guilin, ChinaPliocene Warm Period

Comments

MalcolmVadrosaul Saturday, January 1, 2011 10:25:22 PM

Interesting. My recent examinations of England's Cambrian system geology of the west midlands also mentioned graptolites embedded in shales.


http://pumicecastle.blogspot.com/

Write a comment

New comments have been disabled for this post.

May 2013
M T W T F S S
April 2013June 2013
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30 31