The Cerithium limestone Member at Stevns Klint reflecting the carbonate production recovery after the K/Pg mass-extinction
(2024) In Dissertations in Geology at Lund University GEOR02 20232Department of Geology
- Abstract
- The Cerithium limestone Member (Mb) at Stevns Klint holds an invaluable record in understanding the marine recovery after the K/Pg mass extinction. The Cerithium limestone Mb constitutes a pale yellow limestone including several different microfacies and a large boxwork of Thalassinoides burrows and flint nodules. This paper aims to describe these microfacies in detail and document their vertical and lateral distribution. To achieve these goals, two sites were sampled along the cliff of Stevns Klint, one at Kulstirenden locality and one at Rødvig. Twenty-eight thin sections were made from 16 samples from both sites; the thin sections were classified petrographically using Dunham classification. Representative samples were point-counted and... (More)
- The Cerithium limestone Member (Mb) at Stevns Klint holds an invaluable record in understanding the marine recovery after the K/Pg mass extinction. The Cerithium limestone Mb constitutes a pale yellow limestone including several different microfacies and a large boxwork of Thalassinoides burrows and flint nodules. This paper aims to describe these microfacies in detail and document their vertical and lateral distribution. To achieve these goals, two sites were sampled along the cliff of Stevns Klint, one at Kulstirenden locality and one at Rødvig. Twenty-eight thin sections were made from 16 samples from both sites; the thin sections were classified petrographically using Dunham classification. Representative samples were point-counted and further analyzed with SEM. Following the observations, the Cerithium limestone Mb was subdivided into subunits A-D with unit D being unique to Kulstirenden. Subunit A shows at both sites a bryozoan-dominated bioclastic rich wackestone/packstone associated with crinoids. The subunit B consists of a foraminiferal-dominated bioclastic-poor wackestone/mudstone with an increasing amount of sponge spicules up section. Subunit B at Kulstirenden contains more sponge spicules than at Rødvig and is more condensed. Subunit C shows a bioclastic-poor wackestone dominated by sponge spicules and calcispheres. Subunit D shows a mudstone with rare bioclasts dominated by echinoderm spines and foraminifera as well as a bioclastic-poor wackestone (15% bioclast content). As subunit D is unique to Kulstirenden and exists above the Thalassinoides marker horizon, it could represent strata missing at Rødvig. Such erosion is possibly marked by the hardground at the top of the Cerithium limestone Mb at both sites, which therefore may have some topographic relief. In some instances, bioturbation causes gradual but sometimes sharp boundaries between the microfacies, except for subunit A, which is consistent at both sites. The distribution of the microfacies from subunits B-D appears to show a slight increasing trend in bioclast content but is not significant enough to suggest a change in energy regime. On a microscale there are bioturbation traces separating the mud and wackestone. Because of this the Cerithium limestone Mb heterogeneity is probably not a change in energy regime but is more likely caused by extensive bioturbation. However, some thin-sections show varying degrees of sorting and fragmentation that could indicate that some level of sea-floor current transport did occur. More research is needed to clarify the lateral and vertical facies variation of the Cerithium limestone Mb at Stevns Klint. (Less)
- Popular Abstract
- The Cerithium Limestone in Denmark or how to recover from the Cretaceous/Paleogene mass extinction
66,1 Ma the Cretaceous-Paleogene mass extinction wiped out 75% of all marine life and 50% of all life on land. Archives telling us how the Earth recovered from such a massive mass extinction are important for understanding the Earth's ecosystems. One of these archives is located at Stevens Klint, south of Copenhagen in Denmark. The site is of importance as it contains both the clay layer recording the extinction (Fiskeler Member (Mb)) and the layer showing the recovery time, the Cerithium Limestone Mb. The Cerithium Limestone is a pale yellow, loosely consolidated limestone with a dense network of burrows and numerous flint nodules. It is an... (More) - The Cerithium Limestone in Denmark or how to recover from the Cretaceous/Paleogene mass extinction
66,1 Ma the Cretaceous-Paleogene mass extinction wiped out 75% of all marine life and 50% of all life on land. Archives telling us how the Earth recovered from such a massive mass extinction are important for understanding the Earth's ecosystems. One of these archives is located at Stevens Klint, south of Copenhagen in Denmark. The site is of importance as it contains both the clay layer recording the extinction (Fiskeler Member (Mb)) and the layer showing the recovery time, the Cerithium Limestone Mb. The Cerithium Limestone is a pale yellow, loosely consolidated limestone with a dense network of burrows and numerous flint nodules. It is an archive of a deep marine post-extinction environment where you can observe a progressive return of the fauna and flora, and in peculiar carbonate rock-forming organisms. The Cerithium Limestone was for a long time thought to be a homogenous or single characteristic unit. However, the Cerithium limestone is now considered heterogeneous, constituted by several elements in different proportions forming an ensemble called microfacies. Classifying and describing microfacies is crucial for reconstructing past environments as they show us glimpses of the depositional environment of the area.
My thesis aims to expand our knowledge of these microfacies and be the first to catalog their horizontal and vertical distribution. This was done by making thin-sections from samples taken at two different sites at Stevens Klint. One near the town of Rødvig in the south and a second site in the north at Kulstirenden. Microfacies were classified using a classification called Dunham which measures the amount of grain with biological origin like fossils (bioclast) within a limestone. In this paper only three classifications were utilized mudstone (<10% bioclasts content), wackestone (10% -50%), and packstone (>50%). However, the wackestone was further divided into bioclastic poor and bioclastic rich wackestone to increase the detail of our descriptions. The bioclastic content was measured using point counting on thin-sections where 250 points were selected on each thin-section at random. These points are then classified as either different fossils or matrix for the fine-grained middle mass between fossils.
The results showed that the Cerithium limestone contains a bryozoan-dominated packstone layer at both sites. At Rødvig it transitions into a foraminifera-dominated mudstone with a large amount of ostracods and bivalve fragments. The limestone then gradually changes to bioclastic poor wackestone with an increasing amount of siliceous sponge. For Kulstirenden, the lower levels are thicker, and the middle section is more condensed. The Cerithium limestone has a continuation in Kulstirenden not visible at Rødvig, a bioclastic poor wackestone with varying degrees of bioclasts containing a mix of sponge spicules foraminifera, as well as some bryozoans. Normally changes in limestones are often linked to either changes in the fauna or changes in water depth. These changes usually present as larger-scale systematic changes. Since the changes in the Cerithium Limestone are only visible on a microscopic scale and appear to have a random distribution pattern at both sites, the difference in the amount of bioclasts is most likely due to the burrowing of the deposited sediments by diverse organisms of different sizes. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9166209
- author
- Andersson, Jacob LU
- supervisor
-
- Sylvain Richoz LU
- Mikael Calner LU
- organization
- course
- GEOR02 20232
- year
- 2024
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Bioturbation, Point-counting, Dunham classification, Bioclasts, Lithostratigraphy, Bryozoans, Foraminifera
- publication/series
- Dissertations in Geology at Lund University
- report number
- 692
- language
- English
- id
- 9166209
- date added to LUP
- 2024-06-23 17:26:36
- date last changed
- 2024-06-23 17:26:36
@misc{9166209,
abstract = {{The Cerithium limestone Member (Mb) at Stevns Klint holds an invaluable record in understanding the marine recovery after the K/Pg mass extinction. The Cerithium limestone Mb constitutes a pale yellow limestone including several different microfacies and a large boxwork of Thalassinoides burrows and flint nodules. This paper aims to describe these microfacies in detail and document their vertical and lateral distribution. To achieve these goals, two sites were sampled along the cliff of Stevns Klint, one at Kulstirenden locality and one at Rødvig. Twenty-eight thin sections were made from 16 samples from both sites; the thin sections were classified petrographically using Dunham classification. Representative samples were point-counted and further analyzed with SEM. Following the observations, the Cerithium limestone Mb was subdivided into subunits A-D with unit D being unique to Kulstirenden. Subunit A shows at both sites a bryozoan-dominated bioclastic rich wackestone/packstone associated with crinoids. The subunit B consists of a foraminiferal-dominated bioclastic-poor wackestone/mudstone with an increasing amount of sponge spicules up section. Subunit B at Kulstirenden contains more sponge spicules than at Rødvig and is more condensed. Subunit C shows a bioclastic-poor wackestone dominated by sponge spicules and calcispheres. Subunit D shows a mudstone with rare bioclasts dominated by echinoderm spines and foraminifera as well as a bioclastic-poor wackestone (15% bioclast content). As subunit D is unique to Kulstirenden and exists above the Thalassinoides marker horizon, it could represent strata missing at Rødvig. Such erosion is possibly marked by the hardground at the top of the Cerithium limestone Mb at both sites, which therefore may have some topographic relief. In some instances, bioturbation causes gradual but sometimes sharp boundaries between the microfacies, except for subunit A, which is consistent at both sites. The distribution of the microfacies from subunits B-D appears to show a slight increasing trend in bioclast content but is not significant enough to suggest a change in energy regime. On a microscale there are bioturbation traces separating the mud and wackestone. Because of this the Cerithium limestone Mb heterogeneity is probably not a change in energy regime but is more likely caused by extensive bioturbation. However, some thin-sections show varying degrees of sorting and fragmentation that could indicate that some level of sea-floor current transport did occur. More research is needed to clarify the lateral and vertical facies variation of the Cerithium limestone Mb at Stevns Klint.}},
author = {{Andersson, Jacob}},
language = {{eng}},
note = {{Student Paper}},
series = {{Dissertations in Geology at Lund University}},
title = {{The Cerithium limestone Member at Stevns Klint reflecting the carbonate production recovery after the K/Pg mass-extinction}},
year = {{2024}},
}