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- Title
Shallow-water hyperpycnites in the Asara Shale, Karaj Formation, Eocene, Iran.
- Authors
Malekzadeh, Mohammad; Hosseini-Barzi, Maahboubeh; Sadeghi, Abbas; Zavala, Carlos
- Abstract
The depositional environment of Asara Shale is discussed in this paper through the detailed analysis of outcrops from the Alborz Basin, NW of Tehran, Iran. The Asara Shale is composed of fine-grained clastic and carbonate (marlstone) strata interbedded with tuff levels. Sedimentary structures include mm- to cm-scale parallel and cross laminations, basal gutter cast, Thalassinoides burrows, bioturbation, clastic/biogenic particle alignment, and normal-size grading. Facies analysis suggests an accumulation dominated by periodic flood energy fluctuations, here related to shallow-marine hyperpycnal discharges. Based on the sedimentary architecture and analysis of the facies associations, five main sedimentary facies have been defined in these outcrops, corresponding to S1, S2, S3, S4, and MM. Suspended‐load‐dominated facies (Facies S) are related to sedimentation from weak turbulent suspensions and consist of massive sandstones (S1), parallel and low-angle-laminated sandstones (S2), ripple-marked sandstones (S3), parallel‐laminated/massive siltstones and mudstones (S4), and microbial mats (MM). Ratios of redox-sensitive elements indicate that the Asara Shale accumulated in an oxygenated depositional environment. This environment is associated with the presence of parallel-crested ripple marks, microbial-induced sedimentary structures (i.e., wrinkle structures), plant fragments, and surface-grazing gastropods. Based on a variety of sedimentary textures and structures, a shallow-water depositional environment is proposed. This study offers new insights into the depositional environment of Asara Shale. Due to the oxic character of this sedimentary basin, and the lack of significant organic matter, it is interpreted that the Asara Shale is not a potential hydrocarbon source for the future explorations.
- Subjects
KARAJ (Iran); IRAN; TEHRAN (Iran); SEDIMENTARY structures; SHALE; EOCENE Epoch; MUDSTONE; MICROBIAL mats; SEDIMENTARY facies (Geology); GRAZING
- Publication
Arabian Journal of Geosciences, 2023, Vol 16, Issue 11, p1
- ISSN
1866-7511
- Publication type
Article
- DOI
10.1007/s12517-023-11725-2