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Stratigraphy, sedimentology and geophysical assessment of the early Silurian Halla and Klinteberg formations, Altajme core, Gotland, Sweden

Artursson, Christopher LU (2018) In Dissertations in Geology at Lund University GEOR02 20181
Department of Geology
Abstract
The Altajme drillcore was recovered from near Buttle in central Gotland in 2015. The core was drilled in
outcrop belt of the late Wenlock (Silurian) Klinteberg Formation as a result from an international drilling campaign
between the Department of Geology at Lund University and Iowa University, USA. The coring continued to the top
of the underlying Ordovician strata at a depth of ca 330 m. In this MSc thesis the carbonate sedimentology and
gamma ray log-motifs of the top 137 m of the core has been investigated. The aim was to measure, document and
analyze the core by means of core slabs, thin sections and geophysical log measurements, including natural gamma
ray, and to perform microfacies analysis. These methods have been used to... (More)
The Altajme drillcore was recovered from near Buttle in central Gotland in 2015. The core was drilled in
outcrop belt of the late Wenlock (Silurian) Klinteberg Formation as a result from an international drilling campaign
between the Department of Geology at Lund University and Iowa University, USA. The coring continued to the top
of the underlying Ordovician strata at a depth of ca 330 m. In this MSc thesis the carbonate sedimentology and
gamma ray log-motifs of the top 137 m of the core has been investigated. The aim was to measure, document and
analyze the core by means of core slabs, thin sections and geophysical log measurements, including natural gamma
ray, and to perform microfacies analysis. These methods have been used to subdivide the strata into different depositional
environments such as the outer, middle and inner ramp and to study the relative sea level evolution. The
lower parts of the core, between -137 and -50 m, consists of a successive transition from outer ramp to middle ramp
carbonate microfacies associations. Based on literature and comparison to outcrops on Gotland, these strata can be
assigned to the Halla Formation. The overlying strata, between -50 and the surface are pure reef limestone is interpreted
to be a part of the Klinteberg Formation.
Natural gamma ray measurements show a successively higher CPS (counts per second) downhole, mirroring
the downhole transition from inner ramp (Klinteberg Formation) to outer ramp depositional environments (Halla
Formation). The combined geophysical data and carbonate sedimentology of the Altajme core implies a relative sea
level lowering from bottom to the top of the core. The geophysical data has furthermore been used to correlate data
from the nearby well Ala-Fjäle (5 km northeast from Altajme). The Ala-Fjäle and Altajme wells are situated in the
same facies belt and are expected to have a similar stratigraphic succession. The natural gamma ray data show a
clear similarity between the wells log-motifs. (Less)
Popular Abstract (Swedish)
Altajmeborrkärnan togs upp i närheten av Buttle centrala Gotland 2015. Projektet är ett resultat
av en internationell borrkampanj mellan geologiska institutionen vid Lunds universitet och Iowa universitet, USA.
Borrningen gick ned till den underliggande ordoviciska lagerföljden på ett djup av ca 330 m. I denna masteruppsats
har karbonatsedimentologin och gamma ray-loggen från de översta 137 m av borrkärnan undersökts. Syftet var att
mäta, dokumentera och analysera borrkärnan med olika metoder t.ex. genom tunnslip och geofysiska log-mätningar
inklusive gamma ray samt mikrofaciesanalys. Nämnda metoder har sedan använts till att beskriva de olika depositionsmiljöer
som är representerade i kärnan, såsom yttre, mellersta och inre rampen... (More)
Altajmeborrkärnan togs upp i närheten av Buttle centrala Gotland 2015. Projektet är ett resultat
av en internationell borrkampanj mellan geologiska institutionen vid Lunds universitet och Iowa universitet, USA.
Borrningen gick ned till den underliggande ordoviciska lagerföljden på ett djup av ca 330 m. I denna masteruppsats
har karbonatsedimentologin och gamma ray-loggen från de översta 137 m av borrkärnan undersökts. Syftet var att
mäta, dokumentera och analysera borrkärnan med olika metoder t.ex. genom tunnslip och geofysiska log-mätningar
inklusive gamma ray samt mikrofaciesanalys. Nämnda metoder har sedan använts till att beskriva de olika depositionsmiljöer
som är representerade i kärnan, såsom yttre, mellersta och inre rampen samt att bedöma den relativa
havsnivåförändringen. De undre delarna av borrkärnan mellan –137 och –50 m består av en successiv övergång
från yttre till mellan-ramps-microfacies-associationer. Baserat på litteratur och jämförelse av blottningar på Gotland
så har de tolkats att vara en del av Hallaformationen. Det överliggande intervallet mellan –50 m och markytan består
av ren kalksten och representerar en del av Klintebergformationen.
Gamma ray-loggen visar på successivt högre CPS-värden (counts per second) med djupet. Det speglar en
övergång från en inre ramp (Klintebergformationen) till en yttre ramps depositionssystem (Hallaformationen). Den
kombinerade geofysiska datan och karbonatsedimentologin i Altajmeborrkärnan visar på en relativ havsnivåsänkning
från botten till toppen av borrkärnan. Den geofysiska datan används också för korrelation med den närliggande
Ala-Fjäleborrningen (5 km nordöst från Altajme). Borrningarna Ala-Fjäle och Altajme är gjordes i samma faciesbälte
och förväntas därför ha en liknande stratigrafisk succession. Gamma ray-kurvorna från dessa borrningar uppvisar
stora likheter. (Less)
Please use this url to cite or link to this publication:
author
Artursson, Christopher LU
supervisor
organization
alternative title
Stratigrafi, sedimentologi och geofysisk analys av Halla- och Klintebergformationen från tidig Silur, Altajmeborrkärnan, Gotland, Sverige
course
GEOR02 20181
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Gotland, gamma ray, stratigraphy, carbonate sedimentology, drill core, Altajme, Ala-Fjäle, Klinteberg Formation, geophysical survey
publication/series
Dissertations in Geology at Lund University
report number
548
language
English
id
8959404
date added to LUP
2018-09-25 18:33:04
date last changed
2018-10-11 09:17:24
@misc{8959404,
  abstract     = {The Altajme drillcore was recovered from near Buttle in central Gotland in 2015. The core was drilled in
outcrop belt of the late Wenlock (Silurian) Klinteberg Formation as a result from an international drilling campaign
between the Department of Geology at Lund University and Iowa University, USA. The coring continued to the top
of the underlying Ordovician strata at a depth of ca 330 m. In this MSc thesis the carbonate sedimentology and
gamma ray log-motifs of the top 137 m of the core has been investigated. The aim was to measure, document and
analyze the core by means of core slabs, thin sections and geophysical log measurements, including natural gamma
ray, and to perform microfacies analysis. These methods have been used to subdivide the strata into different depositional
environments such as the outer, middle and inner ramp and to study the relative sea level evolution. The
lower parts of the core, between -137 and -50 m, consists of a successive transition from outer ramp to middle ramp
carbonate microfacies associations. Based on literature and comparison to outcrops on Gotland, these strata can be
assigned to the Halla Formation. The overlying strata, between -50 and the surface are pure reef limestone is interpreted
to be a part of the Klinteberg Formation.
Natural gamma ray measurements show a successively higher CPS (counts per second) downhole, mirroring
the downhole transition from inner ramp (Klinteberg Formation) to outer ramp depositional environments (Halla
Formation). The combined geophysical data and carbonate sedimentology of the Altajme core implies a relative sea
level lowering from bottom to the top of the core. The geophysical data has furthermore been used to correlate data
from the nearby well Ala-Fjäle (5 km northeast from Altajme). The Ala-Fjäle and Altajme wells are situated in the
same facies belt and are expected to have a similar stratigraphic succession. The natural gamma ray data show a
clear similarity between the wells log-motifs.},
  author       = {Artursson, Christopher},
  keyword      = {Gotland,gamma ray,stratigraphy,carbonate sedimentology,drill core,Altajme,Ala-Fjäle,Klinteberg Formation,geophysical survey},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Stratigraphy, sedimentology and geophysical assessment of the early Silurian Halla and Klinteberg formations, Altajme core, Gotland, Sweden},
  year         = {2018},
}