Palynomorphs have been recovered from the Adigrat Sandstone in the subsurface of the southeastern Ogaden region of Ethiopia. Core samples from well Abred-1 have yielded rich and well-preserved assemblages which are characterized by the dominance of the pollen genus Classopollis (average frequency 93%). Significant accessory elements are Anapiculatisporites dawsonensis, Ceratosporites helidonensis, Foraminisporis tribulosus, Nevesisporites vallatus, Retitriletes semimuris, Araucariacites australis, Callialasporites turbatus, and Perinopollenites elatoides. The microflora can be correlated with the lower part of the Corollina torosa Zone of Australia. It is concluded, therefore, that the studied section is of Hettangian or Sinemurian age. Continental deposition of the Adigrat Sandstone occurred probably under hot and dry climatic conditions. The presence of small numbers of acritarchs indicates a restricted marine influence.
Table of Contents
1. Abstract
2. Introduction
3. Source of material
4. Techniques and storage of material
5. List of taxa identified
5.1 A Spores
5.1.1 A 1 Trilete spores
5.1.1.1 A 1.1 Azonate forms
5.1.1.2 A 1.2 Cingulate forms
5.1.1.3 A 1.3 Cavate forms
5.1.2 A 2 Alete spores
5.2 B Pollen
5.2.1 B 1 Monosaccate forms
5.2.2 B 2 Disaccate forms
5.2.3 B 3 Inaperturate forms
5.2.4 B 4 Monosulcate forms
5.2.5 B 5 Rimulate forms
5.2.6 B 6 Monoporate forms
5.3 C Acritarchs
5.3.1 C 1 Sphaeromorphs
6. Composition
7. Correlation
8. Conclusions
Research Objectives and Core Themes
The primary research objective of this study is to analyze and document the Early Jurassic palynomorph assemblages recovered from the Adigrat Sandstone in the Abred-1 well, located in the Ogaden region of Ethiopia. By conducting a detailed taxonomic identification and compositional analysis, the paper aims to determine the age of the sedimentary section, investigate the paleoenvironmental conditions of deposition, and establish correlations with established palynological zonations in Australia.
- Palynological analysis and taxonomic identification of microfloral assemblages in the Adigrat Sandstone.
- Age determination of the studied section based on palynomorph correlation (Hettangian to Sinemurian).
- Reconstruction of continental depositional environments characterized by hot and dry climatic conditions.
- Evaluation of restricted marine influence based on the presence of acritarchs.
- Revision of stratigraphic terminology regarding the Bokh Shale in the Ogaden Basin.
Excerpt from the Book
Composition
The palynomorph assemblages recovered are of corresponding composition (Table I) and consist essentially of pteridophytic and bryophytic spores and gymnosperm pollen associated with small numbers of acritarchs.
Spores make up only a minor proportion of the miospore suite (4 - 7%, average 6%) and are represented mainly by acavate trilete forms. Most abundant are specimens which in this paper have been assigned to the Neoraistrickia sp. A / Retitriletes semimuris complex (cf. FILATOFF, 1975, p. 53).
The miospore suite is dominated by gymnosperm pollen (93 - 96%, average 94%). Predominant element is the genus Classopollis (92 - 95%, average 93%). This taxon is known to be produced by thermophilic and xerophytic conifers of the family Cheirolepidiaceae.
Sphaeromorph acritarchs assignable to Leiosphaeridia sp. constitute between 2 - 4% of the total assemblage (average 3%).
Chapter Summaries
Abstract: Provides a high-level overview of the recovered palynomorphs, their dominance by Classopollis, and the conclusion that the Adigrat Sandstone represents a Hettangian or Sinemurian age continental sequence.
Introduction: Outlines the geological context of the Ogaden Basin, proposes a reclassification of the Bokh Shale, and summarizes previous findings regarding the age of the local sandstone units.
Source of material: Details the drilling history of the Abred-1 well, the geographical and geological location, and the specific cored intervals selected for palynological processing.
Techniques and storage of material: Describes the laboratory processing of shale samples and explains how identified specimens were documented, photographed, and cataloged for the author’s collection.
List of taxa identified: Presents a comprehensive catalog of the spores, pollen, and acritarchs identified, systematically organized by morphological form.
Composition: Analyzes the distribution and frequency of the identified palynomorphs, noting the clear dominance of gymnosperm pollen over spore and acritarch counts.
Correlation: Compares the identified assemblages with Australian palynofloral zones, confirming the dating of the section to the Hettangian or earliest Toarcian.
Conclusions: Summarizes the key geological findings, confirming the age of the sandstone, the climate of deposition, and the need to abandon specific outdated stratigraphic terms.
Keywords
Palynomorphs, Adigrat Sandstone, Ogaden Basin, Ethiopia, Classopollis, Hettangian, Sinemurian, Cheirolepidiaceae, Palynology, Microflora, Biostratigraphy, Continental deposition, Paleoclimate, Abred-1, Corollina torosa Zone.
Frequently Asked Questions
What is the primary scope of this research paper?
The paper focuses on the palynological analysis of core samples taken from the Adigrat Sandstone in the Abred-1 well to determine the geological age and environmental conditions of the region.
What are the central themes discussed in the document?
The central themes include the taxonomy of recovered palynomorphs, the age determination through biostratigraphic correlation with Australia, and the reconstruction of the paleoenvironment.
What is the main research question or goal?
The goal is to accurately date the middle part of the Adigrat Sandstone and characterize the microfloral assemblages found within the Ogaden Basin.
Which scientific methods were applied during the study?
The author utilized standardized palynological processing techniques, involving the creation of strew slides, identification of specimens, and the preparation of single grain mounts for photography and documentation.
What topics are covered in the main body of the work?
The main body covers the geological source of the material, a detailed taxonomic list of the taxa identified, the composition of the palynomorph suites, and the correlation of these findings with the Corollina torosa Zone.
Which keywords best describe this study?
The study is best described by terms such as palynology, biostratigraphy, Adigrat Sandstone, Classopollis, Ogaden Basin, and Hettangian age.
Why is the term "Bokh Shale" considered outdated by the author?
The author argues that the term should be abandoned because the original type section in well Bokh-1 was determined to be of Early Palaeozoic age, which is inconsistent with its usage for younger deposits.
How does the author interpret the presence of acritarchs in the samples?
The presence of a small number of acritarchs is interpreted as evidence of a restricted marine influence within the predominantly continental depositional environment.
- Quote paper
- Dr. Otfried Hankel (Author), 2013, Early Jurassic palynomorphs from the Adigrat Sandstone in well Abred-1, Ogaden, Ethiopia, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/208243
