Hornblende alteration and fluid inclusions in Kärdla impact crater, Estonia: Evidence for impact-induced hydrothermal activity

The well-preserved Kärdla impact crater, on Hiiumaa Island, Estonia, is a 4-km diameter structure formed in a shallow Ordovician sea about 455 Ma ago into a target composed of thin (~150 m) unconsolidated sedimentary layer above a crystalline basement composed of migmatite granites, amphibolites and gneisses. The fractured and crushed amphibolites in the crater area are strongly altered and replaced with secondary chloritic minerals. The most intensive chloritization is found in permeable breccias and heavily shattered basement around and above the central uplift. Alteration is believed to have resulted from convective flow of hydrothermal fluids through the central areas of the crater. Chloritic mineral associations suggest formation temperatures of 100-300 degrees C, in agreement with the most frequent quartz fluid inclusion homogenization temperatures of 150-300 degrees C in allochthonous breccia. The rather low salinity of fluids in Kärdla crater (<13 wt% NaCleq) suggests that the hydrothermal system was recharged either by infiltration of meteoric waters from the cater rim walls raised above sea level after the impact, or by invasion of sea water through the disturbed sedimentary cover and fractured crystalline basement. The well developed hydrothermal system in Kärdla crater shows that the thermal history of the shock heated and uplifted rocks in the central crater area, rather than cooling of impact-melt or suevite sheets, controlled the distribution and intensity of the impact-induced hydrothermal processes.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Deliverable 2.3.2. Seabed geological inventories: acoustic profiling and sediment survey

Eesti merealade geodiversiteet on mitmekesine. Peamised tegurid, mis määravad geoloogilise ehituse eripära, on aluskorra kristalsete kivimite ja aluspõhja settekivimite pinnamood, mandriliustiku kulutus ja kuhje ning pärastjääaegne settimine ja kulutus (Lutt ja Raukas, 1993). Eesti kui mereriigi kohuseks on kindlustada meie territooriumile kuuluva Läänemere keskkonnasäästlik ja jätkusuutlik haldamine, tagada merealade loodusväärtused, elurikkus ja säilitada olemasolevad ökosüsteemid. Samas on Eesti riigil tekkimas üha suurenev vajadus kasutada merepõhja ressursse. Tegelikkuseks on saanud või saamas mitmed merepõhja kasutust hõlmavad projektid: sadama-alade ja veeteede käigushoidmine, mereala süvendusja kaadamistööd, avamere tuulepargid, pumphüdroelektrijaamad, gaasi- ja sidekaablid, Saaremaa püsiühendus, Tallinna-Helsinki tunnel, avamere kala-, vetika- ja karbikasvatused, vajadus merepõhja maavarade järele. Seega on tekkinud reaalne vajadus Eesti mere- ja rannaalade ruumilise planeeringu koostamisele. Kõik see süvendab tarvidust usaldusväärsete meregeoloogiliste andmete järele, mis annaksid vajalikke alusteadmisi nii merepõhja elupaikade kaardistamiseks, merepõhja ressursside otsimiseks, kaardistamiseks ja kasutamiseks ning avamererajatiste projekteerimiseks ja riskijuhtimiseks (Tuuling jt, 2021). Tehnoloogia arenguga on toimunud kiire geofüüsikaliste kaugseire meetodite arendamine ja uue aparatuuri kasutuselevõtt, võimaldades koguda merepõhja geoloogilisi andmeid oluliselt efektiivsemalt. Geofüüsikalised andmemudelid on alusinformatsiooniks erinevatele valdkondadele nagu merepõhja kaardistamiseks, mere- ja rannikualade planeerimiseks, kasutamiseks ja kaitsmiseks, merepõhja ressursside otsimiseks, avamererajatiste projekteerimiseks ning riskijuhtimise kaardistamiseks. Oluline on siinjuures andmete kogumise automatiseerimine ja standardiseerimine ning andmete koondamine rahvusvahelistele standarditele vastavatesse andmebaasidesse. Uuringutöös kasutati komplekselt erinevaid geofüüsikalisi meetodeid merepõhja efektiivseks ja innovaatiliseks kaardistamiseks. Seismoakustilised mõõdistamised pilootalal ja andmete interpreteerimise teostas Eesti Geoloogiateenistus (EGT). Merepõhja geoloogilise läbilõike kaardistamiseks kasutati üheaegselt erinevaid setteprofilaatoreid ning merepõhja pindalaliseks kaardistamiseks erinevaid sonareid (külgvaate- ja lehviksonar). Uuringu pilootalal kasutati geofüüsikalisi meetodeid koos põhjasette proovidest analüüsitud granulomeetrilise koostise tulemustega, et interpreteerida erinevaid merepõhja substraadi tüüpe ja setete litodünaamilisi protsesse. Rakendatud innovatiivne metoodika on sobilik merepõhja kaardistamiseks ja aitab efektiivselt koguda uusi alusandmeid, mis on vajalikud mereala keskkonnasäästlikuks ja jätkusuutlikuks kasutamiseks, tagades olemasolevate ökosüsteemide säilimise

Rapid Magnetic Susceptibility Characterization of Coastal Morphosedimentary Units at Two Insular Strandplains in Estonia

Coastal archives of changing hydrometeorological conditions include mineralogical anomalies, such as heavy-mineral concentrations (HMCs) of variable thickness and intensity, which contain varying ferrimagnetic (e.g., magnetite) fractions. As an effective alternative to laborious mineralogical and granulometric analysis, we present the first set of bulk-volume low-field magnetic susceptibility (MS) databases from beach and dune lithosomes in the Western Estonian archipelago: Harilaid cuspate foreland (westernmost Saaremaa Island) and Tahkuna strandplain (northernmost Hiiumaa Island). Readings were conducted both in situ from trench walls and on core subsamples. At the Tahkuna site, late Holocene beach ridges reveal substantially lower values: quartz-dominated dune sequences grade from 5&ndash;20 &mu;SI downward to diamagnetically dominated (&minus;1&ndash;7 &mu;SI) beach facies. Values are higher (20&ndash;140 &mu;SI) in historically reactivated parabolic dunes that are encroaching southward over the strandplain. At the Harilaid site, four beach dune ridges (height: 2&ndash;3 m) that span the past 250&ndash;300 years show a general increase in mean MS from 320&ndash;850 &mu;SI with decreasing age, with peaks of 1000&ndash;2000 &mu;SI below the dune crests (depth: ~0.3&ndash;0.6 m) likely related to contemporary wind acceleration during ridge aggradation. The highest mineralogical anomalies range from 2000&ndash;5500 &mu;SI in the historic dune sections and exceed 8000 &mu;SI along the actively eroding upper-berm segments, typical of HMCs generated by moderate storms. MS anomalies are likely correlated with high-amplitude electromagnetic signal responses in georadar records and provide useful information for optical luminescence sampling strategies. Our study demonstrates that magnetic susceptibility trends provide a useful means of rapidly assessing relative temporal changes in overall wave/wind climates, help identify and correlate discrete anomalies related to extreme events, serve as local beach/dune boundary indicators, and represent potentially quantifiable paleo-energy indices

Morphology‐Dependent Magnetic Properties in Shallow‐Water Ferromanganese Concretions

Ferromanganese concretions commonly occur in shallow-water coastal regions worldwide. In the Baltic Sea, they can record information about past and present underwater environments and could be a potential source for critical raw materials. We report on their microstructural characteristics and magnetic properties and link them to their formation mechanisms and environmental significance. Microstructural investigations from nano- and micro-computed tomography, electron microscopy, and micro-X-ray fluorescence elemental mapping reveal diverse growth patterns within concretions of different morphologies. Alternating Fe- and Mn-rich growth bands indicate fluctuating redox conditions during formation. Bullet-shaped magnetofossils, produced by magnetotactic bacteria, are present, which suggests the influence of bacterial activity on concretion formation. Spheroidal concretions, which occur in deeper and more tranquil environments, have enhanced microbial biomineralization and magnetofossil preservation. Conversely, crusts and discoidal concretions from shallower and more energetic environments contain fewer magnetofossils and have a greater detrital content. Our results provide insights into concretion formation mechanisms and highlight the importance of diagenetic processes, oxygen availability, and bacterial activity in the Baltic Sea.peerReviewe

Picking Up the PiecesHarmonising and Collating Seabed Substrate Data for European Maritime Areas

The poor access to data on the marine environment is a handicap to government decision-making, a barrier to scientific understanding and an obstacle to economic growth. In this light, the European Commission initiated the European Marine Observation and Data Network (EMODnet) in 2009 to assemble and disseminate hitherto dispersed marine data. In the ten years since then, EMODnet has become a key producer of publicly available, harmonised datasets covering broad areas. This paper describes the methodologies applied in EMODnet Geology project to produce fully populated GIS layers of seabed substrate distribution for the European marine areas. We describe steps involved in translating national seabed substrate data, conforming to various standards, into a uniform EMODnet substrate classification scheme (i.e., the Folk sediment classification). Rock and boulders form an additional substrate class. Seabed substrate data products at scales of 1:250,000 and 1:1 million, compiled using descriptions and analyses of seabed samples as well as interpreted acoustic images, cover about 20% and 65% of the European maritime areas, respectively. A simple confidence assessment, based on sample and acoustic coverage, is helpful in identifying data gaps. The harmonised seabed substrate maps are particularly useful in supraregional, transnational and pan-European marine spatial planning