Featured Research

from universities, journals, and other organizations

Jurassic 'burn-down' events and organic matter richness in the Kimmeridge Clay Formation

Date:
January 21, 2010
Source:
National Oceanography Centre, Southampton (UK)
Summary:
The sediments of the Kimmeridge Clay Formation were deposited during the Late Jurassic between around 160 and 145 million years ago, the age of the reptiles. They are the main oil source rock in the North Sea. However, within this unit beds rich in organic matter are interspersed with organic-poor sediments. New evidence demonstrates that organic-poor sediments were probably caused by post-depositional loss of organic matter during so-called "burn-down" events.

Monika Kodrans-Nsiah inspects an exposed section of the Kimmeridge Clay Formation on Dorset's "Jurassic Coast."
Credit: Ian Harding (NOCS)

The sediments of the Kimmeridge Clay Formation were deposited during the Late Jurassic between around 160 and 145 million years ago, the age of the reptiles. They are the main oil source rock in the North Sea. However, within this unit beds rich in organic matter are interspersed with organic-poor sediments. New evidence demonstrates that organic-poor sediments were probably caused by post-depositional loss of organic matter during so-called 'burn-down' events.

Related Articles


The Kimmeridge Clay Formation is named after the English village of Kimmeridge on Dorset's 'Jurassic Coast', a favourite haunt of fossil hunters. The sediments comprising the formation, which is particularly well exposed here, were probably deposited in shallow marine environment with an average water depth of 50-100 metres.

"We were particularly interested in the transition between organic-rich and organic-poor sediments," said Dr Ian Harding of the University of Southampton's School of Ocean and Earth Science at the National Oceanography Centre, Southampton (NOCS), and a member of the team that investigated the underlying processes.

A long-held hypothesis is that the organic-rich beds were the result of elevated planktonic productivity in sunlit surface waters, possibly accentuated by enhanced preservation of the resulting organic matter by the oxygen-depleted bottom waters resulting from this excess productivity.

A second possibility was that a cyclic rise and fall of the interface between oxygenated and oxygen-depleted waters was responsible for the transition between organic-rich and organic poor sediments. According to this theory, when oxygenated waters reached the seabed, organic matter already deposited would have been oxidised and degraded. These post-depositional 'burn down' events could have alternated with periods during which the bottom waters had little oxygen, favouring preservation of organic matter.

"The first theory emphasises changes in the amount of organic matter reaching the seabed, while the 'burn-down' theory puts more weight on the relative dominance of preservation or degradation after it has got there," said Dr Harding.

To distinguish between these two theories, he and colleagues from the University of Bremen and the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, analysed the chemical composition and organic content of a sediment core from a borehole in Swanworth Quarry in Dorset, originally drilled as part of the Natural Environment Research Council (NERC) Rapid Global Geological Events Project run by NOCS' Prof. John Marshall.

Monika Kodrans-Nsiah, a PhD student jointly supervised by Dr Harding and Dr Karin Zonneveld (Bremen) was responsible for analysing the fossilised organic cysts of various species of dinoflagellate, a group of tiny aquatic organisms, found in the sediments. Different dinoflagellate species are known to be adapted to different environmental conditions, so studying the distribution of 'dinocyst' fossils helps reconstruct past environments.

The lower part of the core was rich in organic carbon, with abundant dinocysts, and its chemical composition was indicative of anoxic conditions, implying that sediments were deposited and preserved in an oxygen-deficient environment.

However, the chemical composition of the uppermost sediments indicated the presence of oxygenated water when they were deposited. This transition was sudden, occurring at a drilling depth of 122.37 metres, but changes in organic content and dinocyst distributions were more gradual.

"It looks likely that influxes of well-oxygenated bottom water caused the oxidation and degradation of organic matter and cysts after they were deposited," said Dr Harding: "This would explain the gradual reduction in the amount of organic matter above the transition, and provide support for the idea of 'burn-down' events during the Jurassic."

The study was supported by the German Research Foundation (DFG grant EUROPROX). The investigated core was drilled as part of the Natural Environmental Research Council (NERC) Special Topic 'Rapid Global Geological Events (RGGE) Kimmeridge Drilling Project'.

The researchers are: Monika Kodrans-Nsiah, Christian März and Karin Zonneveld (University of Bremen). Ian Harding (SOES/NOCS), and Sabine Kasten (Alfred Wegener Institute for Polar and Marine Research, Bremerhaven). MKN and CM are now at the University of Szczecin and the University of Oldenburg, respectively.


Story Source:

The above story is based on materials provided by National Oceanography Centre, Southampton (UK). Note: Materials may be edited for content and length.


Journal Reference:

  1. Kodrans-Nsiah et al. Are the Kimmeridge Clay deposits affected by "burn-down" events? Palynological and geochemical studies on a 1 metre long section from the Upper Kimmeridge Clay Formation (Dorset, UK). Sedimentary Geology, 2009; 222 (3-4): 301 DOI: 10.1016/j.sedgeo.2009.09.015

Cite This Page:

National Oceanography Centre, Southampton (UK). "Jurassic 'burn-down' events and organic matter richness in the Kimmeridge Clay Formation." ScienceDaily. ScienceDaily, 21 January 2010. <www.sciencedaily.com/releases/2010/01/100119111055.htm>.
National Oceanography Centre, Southampton (UK). (2010, January 21). Jurassic 'burn-down' events and organic matter richness in the Kimmeridge Clay Formation. ScienceDaily. Retrieved December 21, 2014 from www.sciencedaily.com/releases/2010/01/100119111055.htm
National Oceanography Centre, Southampton (UK). "Jurassic 'burn-down' events and organic matter richness in the Kimmeridge Clay Formation." ScienceDaily. www.sciencedaily.com/releases/2010/01/100119111055.htm (accessed December 21, 2014).

Share This


More From ScienceDaily



More Plants & Animals News

Sunday, December 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Researchers Test Colombian Village With High Alzheimer's Rates

Researchers Test Colombian Village With High Alzheimer's Rates

AFP (Dec. 19, 2014) — In Yarumal, a village in N. Colombia, Alzheimer's has ravaged a disproportionately large number of families. A genetic "curse" that may pave the way for research on how to treat the disease that claims a new victim every four seconds. Duration: 02:42 Video provided by AFP
Powered by NewsLook.com
Monarch Butterflies Descend Upon Mexican Forest During Annual Migration

Monarch Butterflies Descend Upon Mexican Forest During Annual Migration

Reuters - Light News Video Online (Dec. 19, 2014) — Millions of monarch butterflies begin to descend onto Mexico as part of their annual migration south. Rough Cut (no reporter narration) Video provided by Reuters
Powered by NewsLook.com
The Best Protein-Filled Foods to Energize You for the New Year

The Best Protein-Filled Foods to Energize You for the New Year

Buzz60 (Dec. 19, 2014) — The new year is coming and nothing will energize you more for 2015 than protein-filled foods. Fitness and nutrition expert John Basedow (@JohnBasedow) gives his favorite high protein foods that will help you build muscle, lose fat and have endless energy. Video provided by Buzz60
Powered by NewsLook.com
Birds Might Be Better Meteorologists Than Us

Birds Might Be Better Meteorologists Than Us

Newsy (Dec. 19, 2014) — A new study suggests a certain type of bird was able to sense a tornado outbreak that moved through the U.S. a day before it hit. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins