Ice loading and its effects on sedimentary basins and the carbon cycle

Amberg, Sebastian Christoph; Littke, Ralf (Thesis advisor); Back, Stefan (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

Glaciations during the Pleistocene profoundly influenced the Earth’s system, e.g., the morphology, the climate, and the subsurface. This thesis investigates the influence of Pleistocene glaciations on parts of the subsurface in Central and North Europe. Two sedimentary systems, the Netherlands and the northern Barents Sea, were selected as the main study areas because they are regarded as two end members of glacial ice coverage and duration. Numerical basin modeling is used as the main tool in this study to enhance the understanding of glacial-related influences on different parameters in the subsurface, e.g., temperature distribution, rock properties, and fluid migration. Chapter 2 presents an integrated 3D numerical basin modeling and seismic interpretation study of the onshore northeastern Netherlands, where burial and temperature histories were reconstructed for four different geological structural elements (Groningen Platform, Lauwerszee Trough, Friesland Platform, and Lower Saxony Basin). Temperature and vitrinite reflectance data from 28 wells were used to evaluate burial and temperature histories. Seismic interpretation was used to assist in identifying erosion events throughout the area. This combined approach resulted in modeled burial and maturity histories for each of the four structural elements. Additionally, the hydrocarbon generation in major source rock intervals of Carboniferous, Jurassic, and Cretaceous sedimentary layers was simulated. Modeling results indicate the highest present-day temperatures and maturities of the Paleozoic sedimentary succession in the Lauwerszee Trough and the Lower Saxony Basin, where the deepest burial occurred. Two major phases of deep burial and subsequent uplift occurred in Carboniferous to Permian and Triassic to Jurassic times. Both intervals govern the maturation and transformation of kerogen from Paleozoic source rocks. The highest modeled present-day maturities of Mesozoic sediments is calculated in depressions between salt diapirs in the Lower Saxony Basin. The Cretaceous Wealden Shale generated hydrocarbons since Late Cretaceous times. This numerical 3D model was extended and refined in chapter 3 to study the influence of low surface temperatures and the mechanical loading of ice sheets on the subsurface during the Pleistocene. Ice sheets covered parts of the study area during two glacial stages, the Elsterian and Saalian stages. Overall, Pleistocene glacial stages substantially impact the temperature and pressure distribution in the subsurface. Subsurface temperatures are significantly reduced during glacial stages, leading to lowered present-day temperatures and a low geothermal gradient in the shallow subsurface. In sedimentary formations, pressures build up with every glacial advance resulting in overpressures in deeply buried, non-permeable formations at the present day. A loss of Coevorden Formation-sourced hydrocarbons to the surface was calculated for the Lower Saxony Basin during the glacial stages, indicating an influence of glacial loading on the Mesozoic petroleum system. In chapter 4, glacial advances during the Pleistocene were implemented into a 2D basin model transecting the Olga Basin in the northern Norwegian Barents Sea. The model incorporated ice sheet advances, glacial erosion, and low temperatures during the Pleistocene. In addition to the influence on the temperature and pressure conditions, this study focused on the impact of fault systems on the migration of carbon-bearing fluids from microbial and thermogenic sources to the surface and the development of gas hydrate stability zones in the area. Faults in the 2D model were introduced in two scenarios: closed and partially open for fluid migration during ice retreat. Results show that temperatures within the sedimentary rock column were significantly lowered due to erosion and low surface temperatures, and cyclic pressure increases were calculated due to vertical stress from ice shields. In the second scenario, faults acted as effective conduits for fluid migration, providing pathways for hydrocarbons ascending from deep-seated source rocks generating thermogenic hydrocarbons. Both fault-model scenarios showed that hydrocarbon leakage to the sea floor on the southwestern margin of the Olga Basin mainly depends on outcropping permeable layers. Shallow source rocks for microbial gas were added to the model with temperature-dependent generation rates to evaluate depth zones for the generation of Pleistocene microbial methane. During glacial stages, the methane-hydrate stability zone below the ice sheet expanded due to the high pressure and low basal ice sheet temperatures. Any thermogenic ethane and propane contribution to the gas present as hydrate enhanced its stability.

Institutions

• Division of Earth Sciences and Geography [530000]
• Institute for Geology and Geochemistry of Petroleum and Coal [532410]