“…Total organic carbon (TOC) values in these rocks range from 3 to 30% with increased TOC values in the lower part of the succession, the MCM (Alqudah et al ., 2015; Hakimi et al ., 2016; März et al ., 2016; Abu‐Mahfouz et al ., 2019, 2020, 2022a, 2022b, 2023; Grohmann et al ., 2021, 2023). The rocks exhibit a complex diagenetic history (Powell & Moh'd, 2012; Hooker et al ., 2017; Huggett et al ., 2017), with an abundance of different diagenetic features (for example, chert beds, chert/carbonate concretions and early diagenetic folding).…”
This paper presents an integrated petrographic-geochemical-geomechanical study of the growth mechanisms of carbonate and chert concretions observed at outcrop and core from the Upper Cretaceous to Eocene organic-rich carbonate mudrocks, central Jordan. It provides evidence for displacive and replacive concretion growth from the analysis of primary lithological characteristics, compaction strain and deformation structures associated with concretion growth. Concretions were analysed to determine the primary lithological controls on their development and the measurement of strain in the host rock to develop a method for constraining the growth mode and their paragenesis. Concretions exhibit either a replacive or displacive growth mode largely dependent on the original host lithology. Displacive concretions exhibit irregular shapes and semi-fibrous internal structures in contrast to regular shapes and microcrystalline textures observed for replacive concretions. Cement fraction is high in both carbonate concretion types, indicating early formation in high-porosity sediments at shallow burial depths. The strain field around displacive concretions is vertically asymmetrical. Conversely, it is symmetrical with uniform differential compaction for the replacive concretions. Evidence for displacive growth comes from triangular areas of chert at the lateral margins of some carbonate concretions, interpreted as areas of reduced strain. Another indicator is the forced asymmetrical folding of heterolithic host rocks around displacive concretions, with displacive carbonate units separated by trace laminae of the original (chert) beds. Enveloping chert beds exhibit early-formed radial silica fractures with increased aperture size in the areas of maximum curvature. Carbon isotopic signatures of carbonate concretions show a strong correlation between concretion centres and host rock, suggesting a relatively shallow depth (first few tens of metres) of initial growth. Carbonate concretions are interpreted to have formed at shallow depths in the presence of alkaline pore waters rich in dissolved organic carbon in the presence of Mg 2+ ions, available organic matter and redox-sensitive metals such as U and Mo. A paragenetic history for the different concretion types is presented.
“…Total organic carbon (TOC) values in these rocks range from 3 to 30% with increased TOC values in the lower part of the succession, the MCM (Alqudah et al ., 2015; Hakimi et al ., 2016; März et al ., 2016; Abu‐Mahfouz et al ., 2019, 2020, 2022a, 2022b, 2023; Grohmann et al ., 2021, 2023). The rocks exhibit a complex diagenetic history (Powell & Moh'd, 2012; Hooker et al ., 2017; Huggett et al ., 2017), with an abundance of different diagenetic features (for example, chert beds, chert/carbonate concretions and early diagenetic folding).…”
This paper presents an integrated petrographic-geochemical-geomechanical study of the growth mechanisms of carbonate and chert concretions observed at outcrop and core from the Upper Cretaceous to Eocene organic-rich carbonate mudrocks, central Jordan. It provides evidence for displacive and replacive concretion growth from the analysis of primary lithological characteristics, compaction strain and deformation structures associated with concretion growth. Concretions were analysed to determine the primary lithological controls on their development and the measurement of strain in the host rock to develop a method for constraining the growth mode and their paragenesis. Concretions exhibit either a replacive or displacive growth mode largely dependent on the original host lithology. Displacive concretions exhibit irregular shapes and semi-fibrous internal structures in contrast to regular shapes and microcrystalline textures observed for replacive concretions. Cement fraction is high in both carbonate concretion types, indicating early formation in high-porosity sediments at shallow burial depths. The strain field around displacive concretions is vertically asymmetrical. Conversely, it is symmetrical with uniform differential compaction for the replacive concretions. Evidence for displacive growth comes from triangular areas of chert at the lateral margins of some carbonate concretions, interpreted as areas of reduced strain. Another indicator is the forced asymmetrical folding of heterolithic host rocks around displacive concretions, with displacive carbonate units separated by trace laminae of the original (chert) beds. Enveloping chert beds exhibit early-formed radial silica fractures with increased aperture size in the areas of maximum curvature. Carbon isotopic signatures of carbonate concretions show a strong correlation between concretion centres and host rock, suggesting a relatively shallow depth (first few tens of metres) of initial growth. Carbonate concretions are interpreted to have formed at shallow depths in the presence of alkaline pore waters rich in dissolved organic carbon in the presence of Mg 2+ ions, available organic matter and redox-sensitive metals such as U and Mo. A paragenetic history for the different concretion types is presented.
“…Locally, the Cretaceous-Paleocene periods show a rise in sea level, which is reflected in the rock types by which the deposition of the MCM. These rises were coupled with variations in the elevation and sedimentary influx enhancing the preservations in several sites along Jordan and neighboring countries [47][48][49].…”
Section: Stratigraphy and Structural Modelmentioning
Local geological and tectonic processes have been pivotal in shaping the diverse sedimentation patterns observed in Jordan, forming sub-basins characterized by elevated organic matter content (TOC). This study aims to characterize the Maastrichtian basin, focusing on sedimentation rates using calcareous nannofossils and understanding paleoecological and paleo-oceanic conditions. It offers insights into the paleoenvironmental factors impacting oil shale deposition in the late Maastrichtian–Paleocene period. It employs classical biostratigraphical, semi-quantitative, and statistical methodologies to achieve its objectives of age determination and paleoecological insights. A total of 116 smear slides from two sites were obtained: the first, consisting of WA-1 (23 samples), WA-2 (18 samples), and WA-3 (11 samples), and the second, with 60 samples. Notably, the sites exhibit varying topography. WA-1 and WA-2, situated at lower elevations, have the highest Total Organic Carbon (TOC) levels, while areas with higher elevations in section four are visually identified by a light color. The study revealed varying patterns of calcareous nannofossil richness in the two investigated sites. These patterns were instrumental in defining biozones, with the utilization of marker species such as Lithraphidites quadratus, Micula murus, Micula prinsii, and Cruciplacolithus tenuis. Chronologically, these sections were classified as Maastrichtian–Paleogene, encompassing the following biozones in sequential order: UC-20a, UC-20b, UC-20c, UC-20d, and NP-2. Furthermore, the study identified two hiatus intervals, observed in sections WA-1 and KAS-1. The absence of certain biozones in the analyzed sections suggests that these sections correspond to distinct geological blocks within the basin, underscoring the role of tectonic forces during the deposition period. The sedimentation rate initially commenced at low levels but gradually increased due to topographic alterations. Notably, the biozone UC-20c demonstrated a clear trend toward warming and enhanced nutrient availability. In this context, the abundance and diversity of species were associated with increased continental influx into the sub-basin, resulting in rising nutrient levels and the number of calcareous nannofossils. This study enhances the understanding of the local and global effects such as tectonic and climates of the continuity of basins by deciphering calcareous nannofossil patterns and their correlation with sedimentation factors.
“… Figure 1 Stress distribution modelled around the kerogen body as a function of overpressure. The figure shows the magnitude of tangential stress acting at any location along the kerogen boundary in a radial coordinate (from [1] ). …”
Section: Stress Distribution Around Kerogen Bodymentioning
confidence: 99%
“…For a normal stress regime dominated in Oligocene to Miocene during bitumen generation [ 1 , 2 ], the maximum principal stress is the overburden load while the horizontal stress is the least. The effective principal stresses acting on the kerogen boundary can be approximated as follows: where is the far-field overburden/vertical stress, is the hydrostatic pore pressure, and is the biot-Willis coefficient [6] .…”
Section: Stress Distribution Around Kerogen Bodymentioning
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