Petrologija in organska geokemija karnijskih karbonatnih plasti na Drenovem Griču in Liburnijske formacije na krasu : doktorska disertacija

Malenšek Andolšek, Neža (author), Vrabec, Mirijam (mentor)

V svetu poznamo številne primere kamnin, ki vsebujejo prevladujočo, pomembno, značilno ali le pojavno vsebnost organske snovi. Še posebno zanimive za preučevanje so z organsko snovjo primarno bolj ali manj obogatene sedimentne kamnine, ki lahko predstavljajo tudi izvorne kamnine za nastanek zemeljske nafte in/ali plina. Osrednja tema doktorske disertacije je obravnava karbonatnih kamnin, ki vsebujejo organsko snov v različnih deležih. Te kamnine so dobro poznane v slovenskem prostoru, vendar v tem smislu niso podrobno preučene. Kot predmet raziskave smo izbrali geološko dobro poznane plasti, ki so nastajale na Jadranski (Dinarski) karbonatni platformi (AdCP) v mezozoiku, in sicer črne karbonatne kamnine karnijske starosti, ki izdanjajo na Drenovem Griču in krednopaleogensko Liburnijsko formacijo na Krasu. Odvzetih je bilo 155 vzorcev, od tega 38 karnijskih karbonatnih kamnin in 117 vzorcev Liburnijske formacije iz dveh profilov. V izbranih vzorcih preučujemo vsebnost skupnega organskega ogljika (TOC), parametre dobljene z Rock-Eval pirolizo, maceralno sestavo, odsevnost vitrinita, indeks termičnega spreminjanja (TAI), fluorescenco, biomarkerje na izbranih vzorcih ter geokemično sestavo s poudarkom na elementih redkih zemelj in slednih elementih, ki so občutljivi na oksidacijsko-redukcijske pogoje. Na podlagi teh parametrov lahko določimo vrsto in izvor organske snovi, termično zrelost, ki jo je organska snov dosegla ter kakovost organske snovi in potencial za nastanek ogljikovodikov. Poleg tega smo analizirali še sedimentna okolja odlaganja izvornih kamnin. Ugotovili smo, da je organska snov v preučevanih kamninah predvsem kopenskega izvora (kerogen III – vitrinit) in iz morskega detritusa. Povprečna vsebnost organske snovi v karnijskih plasteh znaša 0,7 ut.%, kar kaže na dobro izvorno kamnino iz katere bi lahko ob ustreznih pogojih nastajali ogljikovodiki. Vendar je organska snov prezrela (>3 %RO), zato nima potenciala za nastajanje ogljikovodikov in karnijski apnenci tako predstavljajo slabo izvorno kamnino. Pogojno bi lahko nastajale le manjše količine suhega plina. Nasprotno je organska snov v Liburnijski formaciji ustrezne zrelosti, saj je znotraj naftnega okna (~1 %RO), vendar je vsebnost organske snovi premajhna (v povprečju le 0,12 ut.%) in zato velja za slabo izvorno kamnino, ki nima nobenega potenciala za nastajanje ogljikovodikov.

• Language: Slovenian
• Keywords: disertacije, geologija, grajeno okolje, organska snov, organska geokemija, Rock-Eval piroliza, petrografija, macerali, termična zrelost, odsevnost vitrinita
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FGG - Faculty of Civil and Geodetic Engineering; NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: [N. Malenšek Andolšek]
• Year: 2023
• Number of pages: XXXVIII, 172 str., A-1-D-1
• PID: 20.500.12556/RUL-148292-5de99a69-6662-d2e0-70b2-31f7f1eaa488
• UDC: 55
• COBISS.SI-ID: 161008387
• Publication date in RUL: 10.08.2023

Secondary language

• Language: English
• Title: Petrology and organic geochemistry of Carnian carbonate rocks from Drenov Grič and the Liburnia formation in kras : doctoral dissertation

Abstract

In the world, there are many examples of rocks that contain a dominant, significant, characteristic, or just incidental content of organic matter. Sedimentary rocks that are primarily more or less enriched in organic matter are particularly interesting to study, and they can be source rocks for petroleum and/or gas generation. The aim of this dissertation is to study carbonate rocks containing organic matter in different proportions. These rocks are well known in the Slovenian region but have not yet been studied in detail. As the object of study, we chose geologically well-known strata formed in the Mesozoic on the Adriatic (Dinaric) carbonate platform (AdCP), namely the Carnian dark limestone in the Drenov Grič and the Cretaceous-Paleogene Liburnian Formation in the Kras area. 155 samples were taken, 38 from the Carnian carbonate rocks and 117 samples from the Liburnian Formation, from two sections. In the selected samples we investigated total organic carbon (TOC) content, parameters from Rock-Eval pyrolysis, maceral composition, vitrinite reflectance, thermal alteration index (TAI), fluorescence, biomarkers in the selected samples, and geochemical composition with a focus on rare earth elements and redox sensitive trace elements. These parameters allowed us to determine the type and origin, thermal maturity, and quality of the organic matter, as well as the potential for hydrocarbon generation. In addition, we also analyzed the sedimentary environment in which the source rocks were deposited. We found that the organic matter in the studied rocks is mainly of terrestrial origin (kerogen III – vitrinite) with the add of marine detritus. The average total organic carbon (TOC) content in the Carnian beds is 0.70 wt.%, indicating a good source rock from which hydrocarbons could be generated under suitable conditions. However, the organic matter is too mature (>3 %RO) and therefore has no potential for hydrocarbon generation, therefore the Carnian limestones represent a poor source rock. Only small amounts of dry gas could be generated. In contrast, the organic matter in the Liburnian Formation is of appropriate maturity (~1 %RO) and is within the oil window, but the organic matter content is too low (only 0.12 wt.% on average) and is therefore considered a poor source rock with no potential for hydrocarbon generation.

• Keywords: doctoral thesis, geology, built environment, organic matter, organic geochemistry, Rock-Eval pyrolysis, petrography, macerals, thermal maturity, vitrinite reflectance