Silurian noncalcified macroscopic algal fossils from the Kalana Lagerstätte, Estonia
Date
2018-12-03
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Abstract
Inimkonna teadmised meie planeeti kunagi asustanud organismidest pärinevad fossiiliandmestikust, milles on suure ülekaaluga esindatud eluajal tugevat skeletti omanud loomad. Üliharva on kivististena säilinud nn pehmekehalised organismid, nt ilma mineraliseerunud kudedeta selgrootud või lubistumata vetikad. Kesk-Eestis, Jõgevamaal, Kalana (Otisaare) karjääris päevavalgele tulnud vetikafossiilid on nii oma anatoomilise detailsuse kui ka liigilise mitmekesisuse poolest ainulaadsed, võimaldades laiendada meie teadmisi Siluri ajastu merelistest ökosüsteemidest.
Käesoleva uurimistöö eesmärgiks oli selgitada Kalana Lagerstättes (e. erakordse säilivusega fossiilide leiukohas) leiduvate vetikafossiilide süstemaatiline kuuluvus, anda ülevaade Siluri ladestu vetikate levikust Eestis ja kogu maailmas, ning interpreteerida keskkonnatingimusi (vee sügavus, temperatuur, põhja iseloom), kus need organismid kunagi elasid ning mattusid. Doktoritöös detailselt kirjeldatud kolmest vetikaliigist kaks (Palaeocymopolia silurica ja Kalania pusilla) kuuluvad rohevetikate (Chlorophyta) seltsi Dasycladales. Kolmas Kalanast kirjeldatud liik on Leveilleites hartnageli, mis morfoloogiliste tunnuste ja paljunemisstruktuuride paiknemise järgi kuulub punavetikate (Rhodophyta) hulka, klassi Florideophyceae.
Uurimistöös jõuti järeldusele, et Kalana peaaegu terviklikuna säilinud vetikatallused on mattunud in situ normaalsoolsusega, lainetuse eest kaitstud laguunikeskkonnas, kus vee sügavus ulatus kuni 15 meetrini ning temperatuur võis püsida umbes 20 °C juures.
Eestis on üksikuid sarnaseid vetikafossiile leitud veel mitmest karjäärist ning puursüdamikust, kinnitades, et vetikad olid Siluri ajastu algul (ligikaudu 440 Ma tagasi) levinud üle kogu praeguse Eesti territooriumi. Siluri-vanuselisi lubistumata vetikate leiukohti on maailmast kokku kirjeldatud 37, neist suur osa asuvad Baltica või Laurentia paleokontinentidel.
Humanity’s knowledge of organisms our planet’s past organisms, come from fossil record, which is predominated by animals who possessed some kind of skeleton. Soft-bodied organisms, like invertebrates without mineralized tissues or non-calcified algae have only rarely been preserved as fossils. The Kalana (Otisaare) quarry in Central Estonia has revealed unique algal fossils, which show anatomical details and species diversity, which widen our knowledge about marine ecosystems in the Silurian times. The aim of the present research was to study systematics of the algal fossils in Kalana, to give an overview of algal fossils in Estonia and the whole world and to interpret the environment conditions (water depth, temperature, bottom conditions) where the algae lived and were buried. Among the species described in the present thesis, two (Palaeocymopolia silurica and Kalania pusilla) belong to green algal (Chlorophyta) order Dasycladales. The third species described from the Kalana Lagerstätte is Leveilleites hartnageli, which according to external morphology and position of reproductive structures belongs to red algae (Rhodophyta), class Floridophyceae. The algal thalli were buried in situ, probably in a lagoonal environment with normal salinity, which was protected from wave action and where water depth did not exceed 15 meters and temperature was around 20 °C. In addition to the Kalana quarry, in Estonia, noncalcified algal material has been discovered from some other quarries and drillcores, proving that noncalcified algae were widespread all over the present territory of Estonia in the early Silurian marine environments ca. 440 Ma. World-wide, 37 localities with noncalcified macroscopic algal fossils have been described from the Silurian strata, most of them have been discovered from Baltica and Laurentia palaeocontinents
Humanity’s knowledge of organisms our planet’s past organisms, come from fossil record, which is predominated by animals who possessed some kind of skeleton. Soft-bodied organisms, like invertebrates without mineralized tissues or non-calcified algae have only rarely been preserved as fossils. The Kalana (Otisaare) quarry in Central Estonia has revealed unique algal fossils, which show anatomical details and species diversity, which widen our knowledge about marine ecosystems in the Silurian times. The aim of the present research was to study systematics of the algal fossils in Kalana, to give an overview of algal fossils in Estonia and the whole world and to interpret the environment conditions (water depth, temperature, bottom conditions) where the algae lived and were buried. Among the species described in the present thesis, two (Palaeocymopolia silurica and Kalania pusilla) belong to green algal (Chlorophyta) order Dasycladales. The third species described from the Kalana Lagerstätte is Leveilleites hartnageli, which according to external morphology and position of reproductive structures belongs to red algae (Rhodophyta), class Floridophyceae. The algal thalli were buried in situ, probably in a lagoonal environment with normal salinity, which was protected from wave action and where water depth did not exceed 15 meters and temperature was around 20 °C. In addition to the Kalana quarry, in Estonia, noncalcified algal material has been discovered from some other quarries and drillcores, proving that noncalcified algae were widespread all over the present territory of Estonia in the early Silurian marine environments ca. 440 Ma. World-wide, 37 localities with noncalcified macroscopic algal fossils have been described from the Silurian strata, most of them have been discovered from Baltica and Laurentia palaeocontinents
Description
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Keywords
Silurian, algae, fossils, opencast mines, Kalana (Hiiu County), Estonia