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
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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
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