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Geochemical and sedimentary signatures of Phanerozoic events.

Wigforss-Lange, Jane LU (2007) In LITHOLUND theses
Abstract (Swedish)
Popular Abstract in Swedish

Populärvetenskaplig sammanfattning



Dramatiska händelser har inträffat regelbundet under jordens historia. Primära, kortvariga katastrofer som t ex asteroidnedslag, omfattande vulkanism eller kraftiga jordskalv kan ge långvariga miljöeffekter, som t ex global uppvärmning eller nedkylning, förändringar i havsnivå och cirkulationsmönster, syrefria oceanbottnar mm. Alla dessa händelser lämnar spår efter sig i de sediment som är avsatta under respektive skede och tecknen kan ses som anomalier i den geokemiska sammansättningen, särskilda sedimentära strukturer och förändringar i flora och fauna.



Denna avhandling behandlar sedimentologiska och geokemiska spår av... (More)
Popular Abstract in Swedish

Populärvetenskaplig sammanfattning



Dramatiska händelser har inträffat regelbundet under jordens historia. Primära, kortvariga katastrofer som t ex asteroidnedslag, omfattande vulkanism eller kraftiga jordskalv kan ge långvariga miljöeffekter, som t ex global uppvärmning eller nedkylning, förändringar i havsnivå och cirkulationsmönster, syrefria oceanbottnar mm. Alla dessa händelser lämnar spår efter sig i de sediment som är avsatta under respektive skede och tecknen kan ses som anomalier i den geokemiska sammansättningen, särskilda sedimentära strukturer och förändringar i flora och fauna.



Denna avhandling behandlar sedimentologiska och geokemiska spår av specifika händelser som inträffat under jordens senaste 500 miljoner år (fanerozoikum) och syftet är att dokumentera och tolka de olika företeelserna och deras bakomliggande orsaker. Studien omfattar tre olika tidsintervall; slutet av silur, gränsen mellan jura och krita samt gränsen mellan krita och paleogen. Blottningar och utgrävningar i Skåne från sen silur och jura-krita undersöktes, dokumenterades och provtogs, medan krita-paleogengränsen provtogs från blottningar i Mexiko-Belize, nära nedslagskratern Chicxulub på Yucatanhalvön. Den gemensamma nämnaren för dessa avsättningar är att de återspeglar sedimentologiska och/eller geokemiska avvikelser i förhållande till bakgrundsvärden.



Under slutet av silurperioden förändrades sammansättningen av kol- respektive syreisotoperna i havsvattnet. Det avspeglas som en kraftig ökning av den tyngre isotopen 13C, och ?13C värden i marina kalkstenar stiger från ca +1 ? till >+10 ?. Liknande höga värden har registrerats i samtida karbonater från andra platser i världen. Denna förändring i den marina kolisotop-sammansättningen framstår som den största under fanerozisk tid, med global signifikans. Många teorier till bakomliggande orsaker har lagts fram, men magnituden på anomalin gör den svårförklarlig med nuvarande globala kolcykelmodeller. I denna avhandling föreslås multipla orsaker. De högsta värdena kan förklaras med en regional, kraftig ökning av fotosyntetiserande aktivitet, vilket påvisas av den plötsliga massförekomsten av cyanobakterier i grunda miljöer. Vid dessa bakteriers fotosyntes förbrukas CO2 och det är framförallt den lätta isotopen 12C som tas upp medan den tyngre isotopen 13C koncentreras i vattenmassan. Denna 13C ökning lades ovanpå en redan globalt förändrad ?13C (ca +3 ? till +5 ?) sammansättning i havsvattnet. Men frågan kvarstår om vilken mekanism som kan ha orsakat den initiala globala ökningen av 13C i havsvattnet. Det är möjligt att det finns ett samband mellan massförekomsten av cyanobakterier och koldioxidhalten i atmosfären (som var extremt hög under perioden) och vidare till den globala förhöjningen av ?13C i marina karbonater. Under samma period sker också en förändring i ?18O sammansättningen, till en ökning av den tyngre isotopen 18O. Avsättningarna i Skåne påvisar en evaporitisk miljö, bland annat genom förekomsten av cerebroida ooider som bildas i vatten med hög salthalt. Avdunstning och avgasning av H2O och CO2 från vattenmassan anses ha orsakat förändringen i syreisotopsammansättningen. Avgasning av CO2 medför högre koncentration av den tunga isotopen 13C i vattenmassan, vilket kan förklara ?13C ökningen i sediment som inte har direkt anknytning till cyanobakterier.



De sedimentära gränslagren från jura-krita vid Eriksdal i Skåne innehåller en sekvens som visar en plötslig och snabb förändring i vattenenergin. Vitabäckslerorna består framförallt av gröna till mörkt grå-svarta leror, avsatta under lugna förhållanden. Den avvikande sekvensen består av grövre material, den har en skarp erosiv basyta och innehåller växtfragment och en blandning av marina och kontinentala fossil. Med hänvisning till de sedimentologiska och paleontologiska särdragen har tsunamiavsättning föreslagits för den relativt korta sekvensen (ca 1.5 m). Den bakomliggande orsaken som skapande tsunamivågor kan vara jordskalv och/eller asteroidnedslag där en möjlig aspirant är Mjølnirkratern i Barents Hav.



Den mer välkända nedslagskratern Chicxulub på Yucatanhalvön i Mexico är ett typexempel på katastrofala händelser i jordens historia. Kratern med en diameter på 200 km visar magnituden av nedslaget. Tiden för nedslaget anses vara gränsen mellan krita-paleogen (K-T) eftersom detta gränslager, globalt, har förhöjda iridiumhalter och innehåller kvartskorn som utsatts för extremt tryck och temperatur. Det finns emellertid avvikande meningar angående tidsaspekten, som hävdar att Chicxulub nedslaget skedde innan K-T och att ett senare nedslag gav upphov till gränslagret. De geokemiska undersökningarna utförda inom detta projekt visar emellertid ett genetiskt samband mellan den närliggande ejekta-avsättningen (ca 330-360 km från kratern) och bergarterna på nedslagsplatsen och vidare till det globala gränslagret. Detta får anses som en bekräftelse på att nedslaget i Chicxulub verkligen gav upphov till K-T gränslagret. (Less)
Abstract
Geological and biological catastrophic events have occurred repeatedly in the Earth's history, leaving traces in the global stratigraphical record in the form of sedimentary features, geochemical anomalies and biotic turnovers. This thesis focuses on the sedimentological and geochemical signatures of several key events in the Phanerozoic stratigraphical record, and aims to interpret the different signals and the causal mechanisms behind each of these events.



Three intervals are investigated; the Upper Silurian (late Ludfordian), Jurassic-Cretaceous and the Cretaceous-Paleogene (K-T) boundaries. Sedimentological investigations coupled with analyses of major and trace element concentrations and of carbon and oxygen... (More)
Geological and biological catastrophic events have occurred repeatedly in the Earth's history, leaving traces in the global stratigraphical record in the form of sedimentary features, geochemical anomalies and biotic turnovers. This thesis focuses on the sedimentological and geochemical signatures of several key events in the Phanerozoic stratigraphical record, and aims to interpret the different signals and the causal mechanisms behind each of these events.



Three intervals are investigated; the Upper Silurian (late Ludfordian), Jurassic-Cretaceous and the Cretaceous-Paleogene (K-T) boundaries. Sedimentological investigations coupled with analyses of major and trace element concentrations and of carbon and oxygen isotopic compositions were undertaken on drillcore and outcrop samples of Late Silurian age from central Scania, Sweden. Sedimentological and trace element analyses were performed on samples from the Jurassic-Cretaceous transition from Scania, Sweden and on ejecta sediments from the K-T transition along the Mexico-Belize border, close to the Chicxulub impact site. The common characteristic of these successions is that they represent special depositional environments related to exceptional short-lived events.



The geochemical event in the Upper Silurian sedimentary rocks is marked by carbon and oxygen isotope anomalies in marine carbonates. The ?13C values increase from ca +1 ? to +10 ?, which represent the heaviest values recorded in this interval from Baltica. The ?18O values rise from ca -10 ? to -5 ? and show a somewhat unstable pattern. None of the conventional mechanisms for 13C enrichment can independently cause a ?13C shift in the oceanic dissolved inorganic carbon (DIC) that would answer to the observed magnitude of change. Thus, multiple causes are suggested herein. The isotopic excursions coincide with a mass occurrence of cyanobacteria, and the most extreme ?13C values may be explained by 13C enrichment in DIC through regional increases in photosynthetic activity, probably superimposed on an already 13C enriched (ca +3 ? to +5 ?) ocean. This initial anomaly still lacks a reasonable explanation. In the Scanian deposits an evaporitic environment is confirmed by the presence of e.g. cerebroid ooids, which form in highly saline waters and it is suggested that evaporation is responsible for the 18O enrichments. Degassing of CO2 may also explain the 13C enrichment in deposits that are not closely associated with cyanobacteria. It is, however, arguable whether evaporation, although prolonged and widespread, could modify the carbon isotope composition in deep marine settings. Still, it is possible that the pCO2atmos and cyanobacteria-stromatolites may be linked in some way that in turn links to the ?13C anomaly. However, the causes of the event remain enigmatic and further analyses of ?13C and ?18O from various environments (e.g. paleosols and lake sediments) and from different parts of the world are required.



Sedimentary beds reflecting an atypical event were identified in the Jurassic-Cretaceous transition (within the Vitabäck Clays) at Eriksdal, Sweden. Samples were selected from an excavated ditch for geochemical, mineralogical and palynological analyses. Additional sedimentological studies where performed in field. Well-preserved assemblages of miospores and for the first time, dinoflagellates were identified in the Vitabäck Clays. The palynological assemblage corroborates an Early Cretaceous (Berriasian) age. The Vitabäck Clays consist predominantly of greenish to dark grey clays, but a coarse-grained unit is enclosed within the homogenous fine-grained sediments and these beds are also recognized by anomalous sedimentary structures and fossil content. The relatively short succession (ca 1.5 m) documents a change in energy of the transport media by the sharp erosive base, coarse-grained lithology, the incorporation of plant fragments and a fauna of mixed terrestrial and marine origin. This anomalous succession is herein interpreted to represent a tsunami deposit, possibly generated by tectonic activity or by an asteroid impact, the Mjølnir impact in the Barents Sea being a possible candidate.



The Cretaceous-Paleogene boundary event relates to the Chicxulub impact in Mexico. The Upper Cretaceous Barton Creek Dolomite and the overlying two-layered ejecta deposit, collectively spanning the K-T boundary, were sampled at several sites along the Mexico-Belize border. The employed sedimentological and geochemical investigations document the chaotic circumstances following the impact. The geochemical analyses provided a genetic link between the proximal ejecta, the target rocks and K-T boundary deposits at other sites. There has been considerable debate as to whether this particular impact in fact took place at the K-T boundary. The results of this study envisage that the Chicxulub impact produced the global K-T boundary layer. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Associate professor Munnecke, Axel, Institute of Palaeontology, Erlangen University, Tyskland
organization
publishing date
type
Thesis
publication status
published
subject
keywords
geokemi, Sedimentology, Petrology, mineralogy, geochemistry, Petrologi, mineralogi, Carbon and oxygen isotopes, Jurassic-Cretaceous boundary, K-T boundary, Late Silurian, Events, Trace elements, Sedimentologi
in
LITHOLUND theses
pages
58 pages
publisher
Department of Geology, Lund University
defense location
PANGEA, Geologiska inst. Sölvegatan 12, Lund
defense date
2007-09-25 10:00
ISSN
1651-6648
ISBN
978-91-86746-96-4
language
English
LU publication?
yes
id
69786381-751f-4cee-af1d-0b395b5b44f0 (old id 548994)
date added to LUP
2007-09-07 11:41:49
date last changed
2016-09-19 08:44:53
@phdthesis{69786381-751f-4cee-af1d-0b395b5b44f0,
  abstract     = {Geological and biological catastrophic events have occurred repeatedly in the Earth's history, leaving traces in the global stratigraphical record in the form of sedimentary features, geochemical anomalies and biotic turnovers. This thesis focuses on the sedimentological and geochemical signatures of several key events in the Phanerozoic stratigraphical record, and aims to interpret the different signals and the causal mechanisms behind each of these events.<br/><br>
<br/><br>
Three intervals are investigated; the Upper Silurian (late Ludfordian), Jurassic-Cretaceous and the Cretaceous-Paleogene (K-T) boundaries. Sedimentological investigations coupled with analyses of major and trace element concentrations and of carbon and oxygen isotopic compositions were undertaken on drillcore and outcrop samples of Late Silurian age from central Scania, Sweden. Sedimentological and trace element analyses were performed on samples from the Jurassic-Cretaceous transition from Scania, Sweden and on ejecta sediments from the K-T transition along the Mexico-Belize border, close to the Chicxulub impact site. The common characteristic of these successions is that they represent special depositional environments related to exceptional short-lived events.<br/><br>
<br/><br>
The geochemical event in the Upper Silurian sedimentary rocks is marked by carbon and oxygen isotope anomalies in marine carbonates. The ?13C values increase from ca +1 ? to +10 ?, which represent the heaviest values recorded in this interval from Baltica. The ?18O values rise from ca -10 ? to -5 ? and show a somewhat unstable pattern. None of the conventional mechanisms for 13C enrichment can independently cause a ?13C shift in the oceanic dissolved inorganic carbon (DIC) that would answer to the observed magnitude of change. Thus, multiple causes are suggested herein. The isotopic excursions coincide with a mass occurrence of cyanobacteria, and the most extreme ?13C values may be explained by 13C enrichment in DIC through regional increases in photosynthetic activity, probably superimposed on an already 13C enriched (ca +3 ? to +5 ?) ocean. This initial anomaly still lacks a reasonable explanation. In the Scanian deposits an evaporitic environment is confirmed by the presence of e.g. cerebroid ooids, which form in highly saline waters and it is suggested that evaporation is responsible for the 18O enrichments. Degassing of CO2 may also explain the 13C enrichment in deposits that are not closely associated with cyanobacteria. It is, however, arguable whether evaporation, although prolonged and widespread, could modify the carbon isotope composition in deep marine settings. Still, it is possible that the pCO2atmos and cyanobacteria-stromatolites may be linked in some way that in turn links to the ?13C anomaly. However, the causes of the event remain enigmatic and further analyses of ?13C and ?18O from various environments (e.g. paleosols and lake sediments) and from different parts of the world are required.<br/><br>
<br/><br>
Sedimentary beds reflecting an atypical event were identified in the Jurassic-Cretaceous transition (within the Vitabäck Clays) at Eriksdal, Sweden. Samples were selected from an excavated ditch for geochemical, mineralogical and palynological analyses. Additional sedimentological studies where performed in field. Well-preserved assemblages of miospores and for the first time, dinoflagellates were identified in the Vitabäck Clays. The palynological assemblage corroborates an Early Cretaceous (Berriasian) age. The Vitabäck Clays consist predominantly of greenish to dark grey clays, but a coarse-grained unit is enclosed within the homogenous fine-grained sediments and these beds are also recognized by anomalous sedimentary structures and fossil content. The relatively short succession (ca 1.5 m) documents a change in energy of the transport media by the sharp erosive base, coarse-grained lithology, the incorporation of plant fragments and a fauna of mixed terrestrial and marine origin. This anomalous succession is herein interpreted to represent a tsunami deposit, possibly generated by tectonic activity or by an asteroid impact, the Mjølnir impact in the Barents Sea being a possible candidate.<br/><br>
<br/><br>
The Cretaceous-Paleogene boundary event relates to the Chicxulub impact in Mexico. The Upper Cretaceous Barton Creek Dolomite and the overlying two-layered ejecta deposit, collectively spanning the K-T boundary, were sampled at several sites along the Mexico-Belize border. The employed sedimentological and geochemical investigations document the chaotic circumstances following the impact. The geochemical analyses provided a genetic link between the proximal ejecta, the target rocks and K-T boundary deposits at other sites. There has been considerable debate as to whether this particular impact in fact took place at the K-T boundary. The results of this study envisage that the Chicxulub impact produced the global K-T boundary layer.},
  author       = {Wigforss-Lange, Jane},
  isbn         = {978-91-86746-96-4},
  issn         = {1651-6648},
  keyword      = {geokemi,Sedimentology,Petrology,mineralogy,geochemistry,Petrologi,mineralogi,Carbon and oxygen isotopes,Jurassic-Cretaceous boundary,K-T boundary,Late Silurian,Events,Trace elements,Sedimentologi},
  language     = {eng},
  pages        = {58},
  publisher    = {Department of Geology, Lund University},
  school       = {Lund University},
  series       = {LITHOLUND theses},
  title        = {Geochemical and sedimentary signatures of Phanerozoic events.},
  year         = {2007},
}