Geologia Croatica 58/1 21–72 14 Figs. 12 Tabs. 9 Pls. ZAGREB 2005 Recent Sediments of Makirina Cove (Northern Dalmatia, Croatia): Their Origin Viewed Through a Multidisciplinary Approach Marko ŠPARICA1, Georg KOCH1, Mirko BELAK1, Slobodan MIKO1, Martina ŠPARICA-MIKO1, Damir VILIČIĆ2, Tadej DOLENEC3, Stanislav BERGANT1, Sonja LOJEN4, Polona VREČA4, Matej DOLENEC3, Nives OGRINC4 and Haris IBRAHIMPAŠIĆ1 Key words: Recent sediments, Geological setting, Selenium is preferentially enriched in authigenic pyrite and it Sedimentology, Mineralogy, Geochemistry, O and C 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 stable isotopes, Palynofacies, Depositional environ- linked to the composition of the surrounding carbonate rocks. The ment, Makirina Cove, Northern Dalmatia, Croatia. 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 Abstract of the sediment column. According to the oxygen isotopic (δ18O) com- Makirina Cove was formed by the Holocene sea-level rise which position, molluscs precipitated their carbonate shells mostly during caused a marine ingression into the depression formed within Albian– warmer periods (May to November) at or near isotopic equilibrium 13 Cenomanian dolomites at approximately 4.5 ka B.P. At present, Maki- with their ambient waters. The carbon isotopic δ C composition of rina Cove represents an restricted, stressed, shallow-marine (<2 m) mollusc carbonate shells is environmentally affected due to oxidation ecosystem characterized by varying seawater temperatures (0–35°C) and decomposition of organic matter as well as influxes of fresh water as well as fluctuating salinities (up to 41‰) affected by seasonally into the Cove, indicating their formation out of the predicted isotopic enhanced evaporation, continuous freshwater supply through on-shore equilibrium with atmospheric CO2. Palynological and organic carbon and submarine springs associated with the coastal karst area and sur- isotopic (δ13C) composition shows that the sedimentary organic matter face run-off episodes. These environmental conditions have been (SOM) is 70–90% lipid- and hydrogen-rich and on average 2/3 marine conducive to high primary production of organic matter resulting in derived (mainly phytoplankton, bacteria and marine macrophytes) and the formation of organic-rich deposits which contain up to 5 wt.% of 1/3 terrestrially derived (mainly woody tissue). The variations in com- organic carbon. Up to the present times, 3.5 m of sediments have been position of SOM have been noted as a function of the distance from deposited indicating a relatively high sedimentation rate estimated at the shore. The type and the preservation state of SOM and pyrite as 0.75 m/1.0 ka in the northern central part of the Cove. well as the measurements of Eh, pH, total alkalinity, dissolved inor- The sediments are being deposited mostly as poorly sorted ganic carbon (DIC) and the enrichment of redox-sensitive trace ele- clayey–sandy silts. The distribution and concentration of most of the ments, indicate oxygen-depleted depositional conditions and that the chemical elements is dependant on the mineralogical composition and sediment is highly reductive even in the uppermost segment at the granulometric features of the Makirina sediments, which show values sediment/water interface. According to the results obtained from the more or less similar to those from the Central Adriatic. Accordingly, applied methods, the features of Makirina sediments strongly reflect there is a positive correlation with Al and K concentrations increas- the given depositional conditions within this restricted, stressed, shal- ing off-shore and with the depth being associated with increasing con- low-marine environment where these organic-rich sediments originate, centrations of clay minerals within the clay fraction. The same holds and may therefore serve as a calibration standard in further investiga- true for concentrations of some trace elements, especially Mo and Se tions. which is consistent with the distribution pattern of sulphides. 1. INTRODUCTION The markedly indented coastline of both mainland and islands along the Eastern Adriatic has formed numerous bays and coves, mostly representing restricted, shallow marine depositional environments within which Recent 1 Institute of Geology, Sachsova 2, HR-10000 Zagreb, Croatia; (Holocene) sediments accumulate. Some of these sedi- e-mail: [email protected] ments have been investigated from a specific viewpoint 2 University of Zagreb, Faculty of Science, Department of Biology, Rooseveltov trg 6, HR-10000 Zagreb, Croatia; dealing with a particular problem. A number of papers e-mail: [email protected] on Holocene sediments from NE Adriatic sites have 3 University of Ljubljana, Faculty of Natural Sciences and been published based on investigation or material of the Technology, Department of Geology, Aškerčeva 12, SLO-1000 Göttingen working group (D. Meischner). Accordingly, Ljubljana, Slovenia; e-mail: [email protected] investigations have been carried out dealing with sedi- 4 “Jožef Štefan” Institute, Department of Environmental Sciences, Jamova 39, SLO-1000 Ljubljana, Slovenia; mentology (FÜTTERER, 1969; PAUL, 1970; MEISCH- e-mail: [email protected] NER, 1972; RANKE, 1974; FÜTTERER & PAUL, 22 Geologia Croatica 58/1 1976), benthic foraminiferal dynamics (DANIELS ing all implied problems, a working group has been 1971; MEISCHNER, 1971; PAUL, 1971) and ostra- convened at the Institute of Geology, Department of cod assemblages (UFFENORDE, 1971, 1975), pollu- Geology, Zagreb, in order to conceptualise a project for tion problems (STIRN et al., 1974), interstitial water further investigation of the Recent sediments within the composition (CESCON et al., 1975), heavy metal research project “Basic Geological Map of the Republic composition (PAUL & MEISCHNER, 1976), vege- of Croatia, Scale 1:50.000”. Consequently, the project tation development (BEUG, 1977), geochemistry and “Recent sediments of the coast and the islands of the microbiology (GOLUBIĆ et al., 1977), and sea-level Republic of Croatia” has been established in order to changes based on sedimentology, fossil biota and geo- study the sediments, on the one hand, in all aspects by chemistry (MEISCHNER, 1995). During the last two using the concept of a multidisciplinary approach and, decades, investigations of Recent sediments have inten- on the other hand, to apply the results obtained from sified and have also included a number of sites from these investigations to a wide range of interests. This other regions of the Eastern Adriatic. The study of the means that many types of standards have to be com- Recent sediments of the Krka river estuary has yield- piled within the calibration of the reference sites which ed information on heavy metal distribution (PROHIĆ can then be correlated with other sites, and to apply the & JURAČIĆ, 1984, 1989; PROHIĆ & KNIEWALD, actualistic principles while studying and interpreting 1987), organic matter and sediments (JEDNAČAK- various aspects of recent and fossil sedimentary bod- BIŠĆAN & JURAČIĆ, 1987), approach to pollution ies of similar origin. As all depositional environments problems (PRAVDIĆ & JURAČIĆ, 1988), suspended are characterised by the complex interaction of bio- matter and sediments (JURAČIĆ & PRAVDIĆ, 1991) logical, physical and chemical processes, any variation and sedimentology (JURAČIĆ & PROHIĆ, 1991). may then be interpreted in terms of environmental, i.e. Similarly, the papers dealing with the Raša river estuary ecological changes which have been caused by natural Recent sediments have reported on pollution problems and/or anthropogenic influences, in Recent sediments (JURAČIĆ et al., 1992), particulates and trace metals and natural influences in fossil sediments. Therefore, (VDOVIĆ & JURAČIĆ, 1993; SONDI et al., 1994) and the main objectives of this project are to: (1) define the sedimentology (SONDI et al., 1995; BOGNER et al., origin of the sediments, especially regarding formation 2003). The Recent sediments of Kaštela Bay have been processes, (2) apply the results of the investigation into investigated in order to define heavy and trace metal every potentially interesting field, (3) evaluate the eco- distribution (BOGNER et al., 1998) and in Pirovac Bay nomic value of the sediments, (4) estimate the degree selenium distribution (MIKO et al., 1998). The results of anthropogenic pollution, and (5) publish the obtained of the study of the Morinje Bay sediments have includ- results as far as possible within the frame of the pre- ed some consideration of kerogen precursor formation sented investigation objectives. processes (KOCH et al., 2000) and pollution problems The investigation of sediments of Makirina Cove, (KOCH et al., 2002). Recent sediments of the Croatian Morinje Bay and Velike Soline has recently been car- islands have also been a matter of scientific interest for ried out in terms of the concept of a multidisciplinary quite a long time. For example, the study of the Mljet approach, providing a better insight into the complex- lakes sediments has provided information on sedimen- ity of their origin. The results of this investigation have tology (SEIBOLD & WIEGERT, 1960; JURAČIĆ et opened some new perspectives concerning the process- al., 1998; GOVORČIN et al.,