Nīkrāces ridas veidošanās apstākļu rekonstrukcijas
Date
2006
Authors
Indāns, Ints
Journal Title
Journal ISSN
Volume Title
Publisher
Latvijas Universitāte
Abstract
Maģistra darba mērķis ir detalizēti raksturot Nīkrāces ridas nogulumu uzbūvi un sastāvu, kā arī izdarīt secinājumus par to veidošanās apstākļiem. Šī mērķa sasniegšanai tika veikti šādi uzdevumi: apkopoti citu pētnieku iepriekš iegūtie dati par Nīkrāces ridas nogulumiem Latvijā; iepazīta ģeoloģiskā literatūra par karbonātu garozu uzbūvi, sastāvu un veidošanās apstākļiem pasaulē; uzzīmēti un aprakstīti Nīkrāces ridas dolomītu slāņkopas ģeoloģiskie griezumi; pagatavoti un aprakstīti plānslīpējumi un sagatavotas to mikrofotogrāfijas.
Pētījumu rezultātā tika iegūti šādi secinājumi: dolomītu šūnveida tekstūra, kompleksas uzbūves pizolīti, pizolīti ar karenu lejas daļu un tiltveida cementu, pizolītu izkārtojums apgrieztajā gradācijas slāņojumā un citas pazīmes liecina, ka Nīkrāces ridā ir plaši sastopamas dolomīta sastāva karbonātu garozas (dolokrēti). Nīkrāces ridas dolokrēti veidojušies areācijas zonā, par ko liecina subvertikālās kavernas, pizolītu karenā forma un tiltveida saaugumi. Domājams, ka karbonātu garozas lielā mērā veido visu Nīkrāces ridu un liecina par plašu subaerālo apstākļu attīstību devona perioda pašā beigu daļā tagadējā Latvijas teritorijā. Dažos slāņos tika novērotas arī muldas, kuras, iespējams, liecina par paleokarsta darbību.
Aim of the Master’s paper is to characterise in details geological structure and composition of deposits of the Nīkrāce Member and to draw conclusions on their origin. Following tasks have been carried out: data of previous researchers about deposits of the Nīkrāce Member in Latvia have been summarised; geological literature on geological structure, composition and origin of carbonate crusts in World have been studied; there are compiled geological sections of the Nīkrāce Member dolostone beds; thin-sections of studied deposits have been prepared and investigated. Following results are achieved in the Master’s paper: cellular structure, pisoids of complex fabric, pisoids with hanging lower part and meniscus cement, reverse grading of pisoids and other features indicate that the Nīkrāce Member is rich in dolomitic carbonate crusts (dolocretes). Dolocretes of the Nīkrāce Member have been formed in vadose zone, which is indicated by subvertical vugs, hanging lower part of pisoids and their meniscus cement. It is supposed that the carbonate crusts are largely forming all the Nīkrāce Formation and indicate about wide development of subaerial environment at the very end of Devonian period at the present area of Latvia. In some beds troughs have been found, which probably gives information about palaeokarst processes.
Aim of the Master’s paper is to characterise in details geological structure and composition of deposits of the Nīkrāce Member and to draw conclusions on their origin. Following tasks have been carried out: data of previous researchers about deposits of the Nīkrāce Member in Latvia have been summarised; geological literature on geological structure, composition and origin of carbonate crusts in World have been studied; there are compiled geological sections of the Nīkrāce Member dolostone beds; thin-sections of studied deposits have been prepared and investigated. Following results are achieved in the Master’s paper: cellular structure, pisoids of complex fabric, pisoids with hanging lower part and meniscus cement, reverse grading of pisoids and other features indicate that the Nīkrāce Member is rich in dolomitic carbonate crusts (dolocretes). Dolocretes of the Nīkrāce Member have been formed in vadose zone, which is indicated by subvertical vugs, hanging lower part of pisoids and their meniscus cement. It is supposed that the carbonate crusts are largely forming all the Nīkrāce Formation and indicate about wide development of subaerial environment at the very end of Devonian period at the present area of Latvia. In some beds troughs have been found, which probably gives information about palaeokarst processes.
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