Recent Sediments of Makirina Cove (Northern Dalmatia, Croatia): Their Origin Viewed Through a Multidisciplinary Approach

Geologia Croatica

卷:58

Stanislav Bergant¹  Mirko Belak¹  Georg Koch¹  Haris Ibrahimpašić¹  Marko Šparica¹  Martina Šparica-Miko¹  Slobodan Miko¹  Sonja Lojen²  Tadej Dolenec³  Matej Dolenec³  Damir Viličić⁴  Polona Vreča⁵  Nives Ogrinc⁵ 

[1] Croatian Geological Survey;

[2] Department of Environmental Sciences, “Jožef Štefan” Institute;

[3] University of Ljubljana, Faculty of Natural Sciences and Technology;

[4] University of Zagreb, Faculty of Science, Department of Biology;

[5] “Jožef Štefan” Institute, Department of Environmental Sciences;

关键词: Recent sediments;    Geological setting;    Sedimentology;    Mineralogy;    Geochemistry;    O and C stable isotopes;    Palynofacies;    Depositional environment;    Makirina Cove;    Northern Dalmatia;    Croatia;   

DOI  :  10.4154/GC.2005.02

来源: DOAJ

【 摘 要 】

Makirina Cove was formed by the Holocene sea-level rise which

caused a marine ingression into the depression formed within Albian–

Cenomanian dolomites at approximately 4.5 ka B.P. At present, Makirina

Cove represents an restricted, stressed, shallow-marine (<2 m)

ecosystem characterized by varying seawater temperatures (0–35°C)

as well as fluctuating salinities (up to 41‰) affected by seasonally

enhanced evaporation, continuous freshwater supply through on-shore

and submarine springs associated with the coastal karst area and surface run-off episodes. These environmental conditions have been

conducive to high primary production of organic matter resulting in

the formation of organic-rich deposits which contain up to 5 wt.% of

organic carbon. Up to the present times, 3.5 m of sediments have been

deposited indicating a relatively high sedimentation rate estimated at

0.75 m/1.0 ka in the northern central part of the Cove.

The sediments are being deposited mostly as poorly sorted

clayey–sandy silts. The distribution and concentration of most of the

chemical elements is dependant on the mineralogical composition and

granulometric features of the Makirina sediments, which show values

more or less similar to those from the Central Adriatic. Accordingly,

there is a positive correlation with Al and K concentrations increasing

off-shore and with the depth being associated with increasing concentrations of clay minerals within the clay fraction. The same holds

true for concentrations of some trace elements, especially Mo and Se

which is consistent with the distribution pattern of sulphides.

Selenium is preferentially enriched in authigenic pyrite and it

is probably the major source of Se in the Makirina Cove sediments.

The concentrations of Ca, Mg and Sr decrease off-shore and they are

linked to the composition of the surrounding carbonate rocks. The

saturation indices show that the water is supersaturated with respect

to carbonates enabling the precipitation of authigenic amorphous or

crystalline carbonate phases from the pore water in the upper segment

of the sediment column. According to the oxygen isotopic (δ18O) composition,

molluscs precipitated their carbonate shells mostly during

warmer periods (May to November) at or near isotopic equilibrium

with their ambient waters. The carbon isotopic δ13C composition of

mollusc carbonate shells is environmentally affected due to oxidation

and decomposition of organic matter as well as influxes of fresh water

into the Cove, indicating their formation out of the predicted isotopic

equilibrium with atmospheric CO2. Palynological and organic carbon

isotopic (δ13C) composition shows that the sedimentary organic matter

(SOM) is 70–90% lipid- and hydrogen-rich and on average 2/3 marine

derived (mainly phytoplankton, bacteria and marine macrophytes) and

1/3 terrestrially derived (mainly woody tissue). The variations in composition of SOM have been noted as a function of the distance from

the shore. The type and the preservation state of SOM and pyrite as

well as the measurements of Eh, pH, total alkalinity, dissolved inorganic

carbon (DIC) and the enrichment of redox-sensitive trace elements,

indicate oxygen-depleted depositional conditions and that the

sediment is highly reductive even in the uppermost segment at the

sediment/water interface. According to the results obtained from the

applied methods, the features of Makirina sediments strongly reflect

the given depositional conditions within this restricted, stressed, shallow-

marine environment where these organic-rich sediments originate,

and may therefore serve as a calibration standard in further investigations

【 授权许可】

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