Western Istrian Anticline as an ideal natural laboratory for the study of the regional unconformities in carbonate rocks

 

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Team members
Regional uncorfomities and quartz-rich diagenetic sediments
Dissemination
Conferences
Published papers
Field campaigns

 

Western Istrian Anticline as an ideal natural laboratory for the study of the regional unconformities in carbonate rocks-WianLab

Funding source: Croatian Science Foundation
Duration: 1.4.2020 – 31.3.2024
Principal investigator: Prof. Dr. Goran Durn
Budget: 1.218,060.00 HRK
Project no.: 8054
Call for project proposals: IP-2019-04

https://www.researchgate.net/project/Western-Istrian-Anticline-as-an-ideal-natural-laboratory-for-the-study-of-the-regional-unconformities-in-carbonate-rocks-WIANLab

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Project goal and hypothesis

Project goal

The project goal is to investigate palaeosols (ps) related to the four regional unconformities in the shallow marine carbonate successions within the Western Istrian Anticline as indicators of palaeoenvironments, palaeoclimates and provenance. The work will be organized with the focus on (a) ps related to the Lowermost Kimmeridgian–Upper Tithonian regional unconformity (ru), (b) ps related to the Upper Aptian–Upper Albian ru, (c) ps related to the Upper Cenomanian/Upper Santonian–Lower Eocene ru, (d) ps related to the Upper Eocene–Recent ru and (e) quartz-rich diagenetic sediments within the Upper Albian carbonate rocks.

Hypothesis

Investigation of palaeosols (ps) related to carbonate successions is a global endeavour in geosciences, with active work that presents a variety of new and developing applications such as the utility of ps for reconstructing palaeoenvironments and paleoclimates, the transformation and alteration of pedogenic minerals, and the establishment of geochronology within terrestrial sedimentary strata. The project goal is to investigate ps related to the four regional unconformities in the shallow marine carbonate successions within the Western Istrian Anticline (WIA) as indicators of palaeoenvironments, palaeoclimates and provenance. Ps and deposits around them (palaeokarstified bedrock and immediate cover) as a unique package that only as a whole gives complete information on the ps genesis will be studied. The work will be organized with the focus on (a) ps related to the Lowermost Kimmeridgian–Upper Tithonian regional unconformity (ru), (b) ps related to the Upper Aptian–Upper Albian ru, (c) ps related to the Upper Cenomanian/Upper Santonian–Low er Eocene ru, (d) ps related to the Upper Eocene–Recent ru and (e) quartz-rich diagenetic sediments (qrds) within the Upper Albian carbonate rocks. Each ru and qrds will be represented with three to four locations. High-resolution approach to investigation of ps including detailed analysis of 15 attributes will be applied. After all attributes are accomplished, ps will be classified and their formation interpreted. Combination of favourable depositional environments resulting in well-defined stratigraphic hiatuses of long duration and very gentle post-depositional tectonics in the WIA enabled formation of the ideal natural laboratory (NLab) for multidisciplinary study of ru in carbonate rocks. We find that WIANLab results will be an important contribution to the research topic and that they also have a good potential for the applied investigations (e.g. REE in bauxites, concept of terroir).

Team members

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1

Full Prof. Goran Durn, PhD - project leader

University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia

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2

Assist. Prof. Uroš Barudžija, PhD

University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia

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3

Assist. Prof. Maja Martinuš, PhD

University of Zagreb, Faculty of Science, Croatia

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4

Full Prof. Marta Mileusnić, PhD

University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia

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5

Curator Ivan Razum, PhD

 

Croatian Natural History Museum, Croatia

 

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6

Assist. Prof. Vedran Rubinić, PhD

University of Zagreb, Faculty of Agriculture, Croatia

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7

Assoc. Prof. Stanko Ružičić, PhD

University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia

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8

Researcher Nadia Sabatino, PhD

Institute for Anthropic Impacts and Sustainability in the marine environment (IAS-CNR), Italy

 

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9

Full Prof. Ivan Sondi, PhD

University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia

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10

Assist. Prof. Branimir Šegvić PhD

Texas Tech University, Department of Geosciences, USA

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11

Scientific councilor Srečo Davor Škapin, PhD

Jožef Stefan Institute, Slovenia

 

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12

Full Prof. Blanka Cvetko Tešović, PhD

University of Zagreb, Faculty of Science, Croatia

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13

Full Prof. Igor Vlahović, PhD

University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia

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Regional uncorfomities and quartz-rich diagenetic sediments

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Istria

 Schematic map of the study area showing four large-scale sequences and larger outcrops of Quaternary deposits (marked by different colours on the map), as well as positions of 10 localities planned for investigation of significant unconformities (1–7 and 10–12), two localities for study of quartz-rich diagenetic deposits (8 and 9) and three localities for study of Quaternary deposits (13–15).

Lowermost Kimmeridgian–Upper Tithonian unconformity

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Bauxite deposit Rovinj-1. Lowermost Kimmeridgian–Upper Tithonian unconformity is accompanied with bauxites.

Lowermost Kimmeridgian–Upper Tithonian unconformity was of a relatively long duration (at least 6 Ma – Velić et al., 2003), resulting in a highly differentiated relief. This unconformity is accompanied with bauxites. The uppermost 20 to 30 cm of the bauxite is heavily altered: its colour is greenish-grey to yellowish-white with vertical to subvertical extensions penetrating the underlying deep red bauxite (Durn et al., 2003). The nature of the alteration of Fe-minerals is clearly redox-based and is closely related to environmental change associated with the deposition of the cover-beds. Three localities (1-3) are planned for the investigation. The rationale behind the selection of localities is to get the highest possible diversity of (a) unconformity surfaces, (b) unconformity-forming events, and (c) palaeosol profiles (in general, for all the materials related to regional unconformities as a group phrase, a common term palaeosol is used; once selected material is elaborated individually, the precise terminology will be applied). In order to reconstruct palaeoenvironmental changes that preceded and followed the periods of main subaerial exposure and to determine the beginning and the end of terrestrial phases, detailed bed-by-bed logs (several metres thick) in the rocks underlying and overlying the unconformities will be made. Depositional facies and early diagenetic alterations will be determined.

References:

Durn, G., Ottner, F., Tišljar, J., Mindszenty, A. and Barudžija, U., 2003. Regional subaerial unconformities in shallow-marine carbonate sequences of Istria: sedimentology, mineralogy, geochemistry and micromorphology of associated bauxites, palaeosols and pedo-sedimentary complexes. In: Vlahović, I., Tišljar, J. (Eds.), Evolution of Depositional Environments from the Paleozoic to the Quaternary in the Karst Dinarides and the Pannonian Basin. 22nd IAS Meeting of Sedimentology, Opatija, September 17–19, 2003, Field Trip Guidebook, 207–254.

Velić, I., Tišljar, J., Vlahović, I., Matičec, D., Bergant, S., 2003. Evolution of Istrian part of the Adriatic Carbonate Platform from the Middle Jurassic to the Santonian and formation of the flysch basin during the Eocene: main events and regional comparison. In: Vlahović, I., Tišljar, J. (Eds.), Evolution of Depositional Environments from the Paleozoic to the Quaternary in the Karst Dinarides and the Pannonian Basin. 22nd IAS Meeting of Sedimentology, Opatija, September 17–19, 2003, Field Trip Guidebook, 3–18.


Upper Aptian–Upper Albian unconformity

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Greenish-gray palaeosol in the Tri Jezerca quarry. Upper Aptian–Upper Albian unconformity is accompanied with greenish-grey clays, mainly in palaeokarst pits and coarse brecciated regolith.

Upper Aptian–Upper Albian unconformity in Istria had variable duration (11–19 Ma; Vlahović et al., 2005), and is accompanied with greenish-grey clays, mainly in palaeokarst pits and coarse brecciated regolith (Durn et al., 2003). Clays associated with this emersion range in thickness from several centimetres up to 1 metre. Transitional zones between the shallow-water carbonates and emerged parts of the platform are characterized by clay and marl deposition or by extensive coastal marshes with reductive conditions and deposition of black sediments (black pebbles). Preliminary field, mineralogical and chemical analyses gave only initial ideas about the formation and alteration of those clays (Durn et al., 2003). Weakly developed soil structure, presence of root remains, burrows and channels, now mainly filled with pyrite framboids, nests of the faecal products of soil dwelling fauna and nodular pedofeatures indicate that they were pedogenetically altered. Therefore, the colour of palaeosols, the presence of root remains only in the upper part of the profile and high abundance of pyrite framboids may imply that those were probably seasonally marshy soils or permanently waterlogged soils (Durn et al., 2003). Four localities (4-7) are planned for the investigation. The rationale behind the selection of localities is to get the highest possible diversity of (a) unconformity surfaces, (b) unconformity-forming events, and (c) palaeosol profiles (in general, for all the materials related to regional unconformities as a group phrase, a common term palaeosol is used; once selected material is elaborated individually, the precise terminology will be applied). In order to reconstruct palaeoenvironmental changes that preceded and followed the periods of main subaerial exposure and to determine the beginning and the end of terrestrial phases, detailed bed-by-bed logs (several metres thick) in the rocks underlying and overlying the unconformities will be made. Depositional facies and early diagenetic alterations will be determined.

References:

Durn, G., Ottner, F., Tišljar, J., Mindszenty, A. and Barudžija, U., 2003. Regional subaerial unconformities in shallow-marine carbonate sequences of Istria: sedimentology, mineralogy, geochemistry and micromorphology of associated bauxites, palaeosols and pedo-sedimentary complexes. In: Vlahović, I., Tišljar, J. (Eds.), Evolution of Depositional Environments from the Paleozoic to the Quaternary in the Karst Dinarides and the Pannonian Basin. 22nd IAS Meeting of Sedimentology, Opatija, September 17–19, 2003, Field Trip Guidebook, 207–254.

Vlahović, I., Tišljar, J., Velić, I., Matičec, D., 2005. Evolution of the Adriatic Carbonate Platform: palaeogeography, main events and depositional dynamics. Palaeogeography, Palaeoclimatology, Palaeoecology 220, 333–360.


Upper Cenomanian/Upper Santonian–Lower Eocene unconformity

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In the area of Minjera the footwall of bauxites are Upper Cenomanian limestones (see geological hammer) and hangingwall are Palaeogene deposits. Upper Cenomanian/Upper Santonian–Lower Eocene unconformity is accompanied with bauxites.

Upper Cenomanian/Upper Santonian–Lower Eocene unconformity was of a very long duration (from c. 25 Ma in southern Istria and Mt. Učka to 40 Ma in northern Istria). However, in the western Istria at several localities erosional remnants of Middle Eocene foraminifera limestones covering the Lower Cretaceous limestones have been found, indicating a possible stratigraphic hiatus of up to c. 87 Ma (Matičec et al., 1996). During such a long hiatus part of the succession could have been chemically weathered, so aforementioned duration of hiatuses is probably somewhat overestimated. Although this stratigraphical hiatus was extremely long relatively thin deposits were formed, mostly bauxite in the lowest parts of the palaeorelief. As in the case of the Jurassic bauxites, the cover sequence also normally begins with transitional palustrine/lacustrine facies. When related to the initial transgression, the introduction of stagnant pore waters into the soil-derived sediment takes place at a stage when diffuse porosity is still unobstructed throughout the deposit, and iron oxide phases are still partly mineralized, so the bauxite may thoroughly react with reducing fluids resulting in a large-scale alteration. This is the case for the majority of bauxite deposits in the area of Minjera. The famous pyritic bauxites, in which whole bauxite bodies are thoroughly grey due to the finely disseminated eogenetic pyrite, clearly indicate that in the case of some deposits the above prerequisites were fulfilled, since marine pore waters came into contact with unconsolidated bauxite (Šinkovec et al., 1994). Three localities (10-12) are planned for the investigation. The rationale behind the selection of localities is to get the highest possible diversity of (a) unconformity surfaces, (b) unconformity-forming events, and (c) palaeosol profiles (in general, for all the materials related to regional unconformities as a group phrase, a common term palaeosol is used; once selected material is elaborated individually, the precise terminology will be applied). In order to reconstruct palaeoenvironmental changes that preceded and followed the periods of main subaerial exposure and to determine the beginning and the end of terrestrial phases, detailed bed-by-bed logs (several metres thick) in the rocks underlying and overlying the unconformities will be made. Depositional facies and early diagenetic alterations will be determined.

References:

Matičec, D., Vlahović, I., Velić, I. & Tišljar, J., 1996. Eocene limestones overlying Lower Cretaceous deposits of western Istria (Croatia): did some parts of present Istria form land during the Cretaceous? Geol. Croatica, 49(1), 117–127.

Šinkovec, B., Sakač, K., Durn, G., 1994. Pyritized bauxites from Minjera, Istria, Croatia. Natura Croatica 3, 41–65.


Upper Eocene–Recent unconformity

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Savudrija loess-palaeosol sequence. Upper Eocene–Recent unconformity is accompanied with various sediments and soils/palaeosols among which terra rossa, loess–palaeosol sequences and pedo-sedimentary complexes predominate.

Upper Eocene–Recent unconformity was of a very long duration even in the areas characterized by the longest deposition – up to the flysch in the latest Eocene (resulting in stratigraphic hiatus of approximately 35 Ma). However, on the limbs of the Western Istrian Anticline due to the synsedimentary tectonics hiatus was longer since there was probably no younger deposits than Middle Eocene foraminifera limestones (40–45 Ma), while it is possible that in the apical part there was no carbonate deposition since the Lower Cretaceous times, so duration of stratigraphic hiatus could be more than 100 Ma. This unconformity is accompanied with various sediments and soils/palaeosols among which terra rossa, loess–palaeosol sequences and pedo-sedimentary complexes predominate. Zhang et al. (2018) investigated ∼8-m-thick loess-palaeosol sequence located near the town of Savudrija, on the northernmost cape of the Istrian Peninsula. Based on luminescence dating and palaeomagnetic age constraint they concluded that the Savudrija loess–palaeosol sequence was formed between ∼70 and ∼9 ka, correlated to the time span from the last glacial to early Holocene. Furthermore, the magnetic susceptibility record suggests that the age of ∼70 ka of the terra rossa-like soil (palaeosol) at the bottom of the section might be still ambiguous and needs further study. Three localities (13-15) are planned for the investigation. The rationale behind the selection of localities is to get the highest possible diversity of (a) unconformity surfaces, (b) unconformity-forming events, and (c) palaeosol profiles (in general, for all the materials related to regional unconformities as a group phrase, a common term palaeosol is used; once selected material is elaborated individually, the precise terminology will be applied).

References:

Zhang, J., Rolf, C., Wacha, L., Tsukamoto, S., Durn, G., Frechen, M., 2018. Luminescence dating and palaeomagnetic age constraint of a last glacial loess-palaeosol sequence from Istria, Croatia. Quat. Int. 494, 19–33.

 


Quartz-rich diagenetic sediments

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Contact of the quartz diagenetic sediments layer in Gortan Cove with the overlying limestone, hammer for scale.

In addition to palaeosols/carbonate sediments related to the four regional unconformities the quartz-rich diagenetic sediments will also be studied. Namely, within the Upper Albian shallow-marine limestone sequences in Istria, there are also some dolomites, silicified deposits and clays. Through the analysis of these deposits, significant proxies for the interpretation of the Late Albian sea-level changes, palaeoclimate, duration of subaerial exposures, and the sources of the material incorporated could be obtained. A study of the silicified material will ensure that through the proposed project all non-carbonate materials will be analysed within the thick carbonate succession of the Western Istrian Anticline.


Dissemination

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Conferences

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Published papers

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Field campaigns

Introduction

Proper interpretation and classification of palaeosols related to regional unconformities in the shallow marine carbonate successions implies looking at both the palaeosols and deposits around them (palaeokarstified bedrock and immediate cover) as an unique package that only as a whole gives complete information about the palaeosol genesis. PALAEO and GEO groups will work together in the field at the beginning of each field campaign. GEO group will stay longer in the field to undertake a detailed sampling of (palaeo)karstified bedrock (from 5 m below the contact with palaeosol) and palaeosol immediate cover (up to 10 m from the palaeosol/carbonate rock transition). Each regional unconformity will be represented with three to four locations where detailed sampling will be performed (13 locations in total, see Map of Istria). Locations were carefully selected based on previous field experience and are situated mainly in quarries (open pits) and along roads (artificial outcrops). The rationale behind such selection was to get the highest possible diversity of (a) unconformity surfaces, (b) unconformity-forming events, and (c) palaeosol profiles. NOTE For all the materials related to regional unconformities as a group phrase, a common term palaeosol will be used; once selected material is elaborated individually, the precise terminology will be applied.

Field campaign 1 – 2nd unconformity