Holocēna veģetācijas izmaiņu liecības organogēnajos nogulumos Ziemeļvidzemē
Date
2013
Authors
Ozola, Ilze
Journal Title
Journal ISSN
Volume Title
Publisher
Latvijas Universitāte
Abstract
Disertācijā analizēti piecu Ziemeļvidzemes purvu nogulumu pētījumu rezultāti, kas iegūti, izmantojot lauka un laboratorijas pētījumu metodes - augu makroskopisko atlieku, sporu un putekšņu, citu mikroskopisko atlieku, kūdras sadalīšanās pakāpes un botāniskā sastāva, nogulumu karsēšanas zudumu analīzi, kā arī nosakot nogul umu absolūto vecumu ar 14 C un AMS 14 C metodēm. Pētītajos ezeru un purvu nogulumos Ziemeļvidzemē atpazītas liecības pa r būtiskām nogulumu uzkrāšanās apstākļu izmaiņām visā holocēna laikā, kas ietekmējušas nogulumu sastāvu un raksturu, tai skaitā noskaidrot a aukstā 8200 notikuma un Mazā Ledus laikmeta, kā arī holocēna termālā maksimuma apstākļu ietekme uz nogulumu uzkrāšanos. Pētīto nogulumu sastāva izmaiņas, augu makroskopisko atlieku, sporu un putekšņu, citu mikroskopisko atlieku, kā arī karsēšanas zudum u analīzes rezultāti ļauj secināt, ka pētīto Puikules purva un Pantenes griezumu nogulumos – kūdrā un gitijā ir atpazīstams 8200 notikums. To apstiprina diagrammā putekšņu spektrus raksturojošais bērzu un lakstaugu putekšņu līknes straujš un īslaicīgs kāpu ms vienlaicīgi ar izmaiņām nogulumu sastāvā. Līdzīgi, bet mazāk izteikti, zemā purva diagrammas putekšņu spektros ir konstatējams Mazais ledus laikmets. Tas labāk atpazīstams augsto purvu nogulumu sporu un putekšņu procentuālajās diagrammās, kā arī uz to n orāda kūdras uzkrāšanās intensitātes palielināšanās un sadalīšanās pakāpes samazināšanās, kamēr kūdras botāniskajā sastāvā izmaiņas šai laikā nav izteiktas. Veikto pētījumu rezultātā noskaidrotas iespējas holocēna Ziemeļvidzemes organogēno nogulumu stratif icēšanā un definētas robežas starp agro un vidējo, kā arī starp vidējo un vēlo holocēnu.
In this doctoral study, the Holocene vegetation changes have been determined by tracing their evidence in the organogenic deposits in the selected five mires in Northern Vidzeme. Field and laboratory research methods were used, such as plant macro scopic re main, spore and pollen, non - pollen, peat decomposition degree and botanical composition, and loss - on - ignition analyses, as well as determination of the absolute age of the deposits with the 14 C conventional and AMS 14 C methods. In the organogenic sediments investigated, vegetation changes during the Holocene have been recogni s ed, which indicate changes in nature conditions in Northern Vidzeme during the Holocene, including colder (the 8 . 2 event and the Little Ice Age) and warmer (the Holocene Thermal Maximu m) conditions. The changes in deposit composition, as well as the complementary results of pollen and plant macroremain and microremain composition analyses allow to recognis e the 8 .2 event in the deposits of the investigated sections of Puikule Mire and Pantene Mire. This is confirmed by a rapid short - term rise of the birch and herb pollen curve in the pollen diagram, accompanied by changes in deposit composition. The Little Ice Age is identified similarly - although to a less pronounced extent and not always with a reliable mark - in the pollen spectra from fens. This event is more recognisable in the pollen spectra of raised bog pollen diagrams as well as from the increase in peat accumulation intensity and decrease in decomposition degree, whil e changes in peat botanical composition are not pronounced. Possibilities for the Holocene organic deposit stratification at Northern Vidzeme were clarified and boundaries between the Early and Middle, as well as, between the Middle and Late Holocene were defined.
In this doctoral study, the Holocene vegetation changes have been determined by tracing their evidence in the organogenic deposits in the selected five mires in Northern Vidzeme. Field and laboratory research methods were used, such as plant macro scopic re main, spore and pollen, non - pollen, peat decomposition degree and botanical composition, and loss - on - ignition analyses, as well as determination of the absolute age of the deposits with the 14 C conventional and AMS 14 C methods. In the organogenic sediments investigated, vegetation changes during the Holocene have been recogni s ed, which indicate changes in nature conditions in Northern Vidzeme during the Holocene, including colder (the 8 . 2 event and the Little Ice Age) and warmer (the Holocene Thermal Maximu m) conditions. The changes in deposit composition, as well as the complementary results of pollen and plant macroremain and microremain composition analyses allow to recognis e the 8 .2 event in the deposits of the investigated sections of Puikule Mire and Pantene Mire. This is confirmed by a rapid short - term rise of the birch and herb pollen curve in the pollen diagram, accompanied by changes in deposit composition. The Little Ice Age is identified similarly - although to a less pronounced extent and not always with a reliable mark - in the pollen spectra from fens. This event is more recognisable in the pollen spectra of raised bog pollen diagrams as well as from the increase in peat accumulation intensity and decrease in decomposition degree, whil e changes in peat botanical composition are not pronounced. Possibilities for the Holocene organic deposit stratification at Northern Vidzeme were clarified and boundaries between the Early and Middle, as well as, between the Middle and Late Holocene were defined.
Description
Keywords
Ģeoloģija , kūdra , gitija , augu makroskopiskās atliekas , putekšņi , rizopodi , 8200 notikums , Geology , peat , gyttja , plant macro scopic remains , pollen , rhizopoda , 8.2 event