Organic and inorganic geochemical aspects of Mediterranean Late Quaternary sapropels and Messinian evaporitic deposits

H.L. Ten Haven

Research output: ThesisDoctoral thesis 1 (Research UU / Graduation UU)

Abstract

This thesis describes the results of organic and inorganic geochemical investigations obtained for samples collected from the eastern Mediterranean sea floor and from Italy. The samples vary in age from the Late Miocene up to the Holocene. The environmental conditions prevailing during deposition of the samples differ greatly. Sediment samples deposited under both marine anoxic and oxic conditions were studied as well as samples from hypersaline depositional environments. Late Quaternary eastern Mediterranean sediments are characterized by the occurrence of organic rich layers, so-called sapropels. Detailed investigations of the soluble organic matter of these sapropels indicate that the organic matter is of a mixed marine, terrigenous and bacterial origin (Chapters 2 and 3). A study of the lateral variation in concentration of organic compounds in the youngest sapropel (SI) revealed a trend of relatively increasing amounts of continentally derived organic matter going from coastal towards more seaward and deeper realms (Chapter 3). Variations in the sea-surface water temperatures during deposition of the sapropels could be inferred from the relative abundance of di- and triunsaturated C37 ketones and from the relative abundance of 27-nor-24-methylcholesta-5,22E-dien-3p-ol and cholesta-5,22E-dien-3p-ol (Chapter 4). Three samples of Holocene age from the anoxic brine-filled Tyro basin were investigated (Chapter 5). Most compounds identified in these samples were also present in the sapropels, but some compounds, such as trisnorhopan-21-one and bishomohopanoic acid, are ascribed to an input from microbiota living at the brine-seawater interface. The brine is thought to be formed by leaching of tectonically exposed Messinian evaporitic deposits, consisting of gypsum, halite and some soluble salts (Chapter 6). The interstitial water chemistry of sediments from the Tyro basin suggests that selective leaching has taken place, namely halite dissolution followed later by gypsum dissolution (Chapter 7). The intersti tial water chemistry of a core collected in the adjacent Kretheus basin, where at present the bottom salinity and oxygen content is at a normal level, is characterized by a strong downward increase of Na and Cl, indicating that conditions similar to the Tyro basin must once have prevailed in the Kretheus basin. The interstitial water chemistry of "normal" Mediterranean sediments is also discussed in chapter 7. Chapter 8 describes the occurrence and significance of hydrocarbons present in three samples from a Messinian evaporitic basin (northern Apennines). Several new compounds were detected and are discussed. A series of extended hop-17(2l)-enes maximizing at the C35 members, a very low pristane/phytane ratio, and an even over odd predominance of long chain alkanes seem characteristic for hypersaline conditions prevailing in the past. Using the biological markers described in chapter 8 it is suggested that the source rock of the Rozel Point Oil was deposited under hypersaline conditions (Chapter 9). The investigations of the samples from ancient hypersaline environments also revealed some anomalies in hopanoid and steroid maturi ty indices (Chapters 8 and 9). Extended 17a(H),21~(H)-hopanesand extended hop-17(21)-enes occur fully isomerized at C-22; 20R- and 20S-5a(H),14~(H),17~(H)steranes are relatively abundant whereas 20S-5a(H),14a(H),17a(H) steranes are virtually absent. Possible diagenetic pathways explaining these phenomena are proposed in chapter 10.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Utrecht University
Supervisors/Advisors
  • Schenck, P.A., Primary supervisor, External person
  • van der Weijden, C.H., Supervisor
  • de Leeuw, J.W., Co-supervisor
Award date15 Dec 1986
Place of PublicationUtrecht
Publisher
Publication statusPublished - 15 Dec 1986

Keywords

  • sapropel
  • evaporites
  • geochemistry
  • Mediterranean Sea
  • Italy

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