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339226

Depositional environment and paleoclimate of the Middle Jurassic sedimentary rocks in Matruh Basin, Northwestern Desert, Egypt

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Last updated: 28 Dec 2024

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Abstract

This study investigates the depositional environment and paleoclimate conditions of the Middle Jurassic Khatatba Formation in Matruh Basin, northwestern Egypt, which represents an important regional gas producer in the East Mediterranean province. Khatatba Fm is marked by in situ dual source and reservoir characteristics, where fluctuations of fine and coarse clastics form intra-formational sources (lithology: shale and argillaceous siltstones), where TOC wt%: 0.88–12.98, avg. 2.95, in Matruh-5 and TOC wt%: 0.80–6.99, avg. 2.26, in Matruh-6 wells, respectively. Yet, reservoir rocks (Lithology: sandstone) were deposited during semi-arid and semi-humid conditions. This in situ dual performance is related to Tethyan sea level oscillations and climate changes during the Middle Jurassic. The Tethyan rifting that occurred during the Late Jurassic and Early Cretaceous caused subsidence events, which were accordingly associated with source rock maturation. Studying the provenance and sedimentation conditions responsible for the accumulation of organic-rich and organic-poor deposits in the Khatatba Formation in the Matruh Basin. Therefore, inorganic geochemical and geophysical data were used to interpret the depositional environment. Clastics of the Khatatba Formation were sourced by moderate weathering in the target wells of the current study (chemical index of alteration = CIA: avg. 70 and avg. 59, index of chemical variability = ICV: avg. 1.1 and avg. 1.8, chemical index of weathering = CIW: avg. 77.8 and avg. 64.7) for Matruh-5 and Matruh-6 wells, respectively. Moreover, the Rb/Sr ratios (avg. 0.36, 0.29 in Matruh-5 and Matruh-6 wells, respectively) have been used to figure out how much chemical weathering happened in the sediments' source area, which is classified as moderate weathering. The K2O/Al2O3 elemental ratios (avg. 0.14 in both wells) are below 0.4, which suggests sediment maturation. Besides, the K2O/Al2O3 ratios were also utilized to infer chemical weathering in the target wells, where values suggest a moderate level of weathering in the area where the parent rocks were situated as well. Within the Matruh-5 and Matruh-6 wells, there is a strong correlation between high levels of strontium (Sr) and low levels of calcium (Ca) in this particular sediment type of Khatatba Fm. This explains why these deposits were accumulated in tide-dominated deltaic environments based on salinity, where Sr/Ca ratios have been used as an indicator of salinity. Moreover, the negative correlations of Ti with Al in the Matruh-5 well (R2= 0.1139 U.Safa; R2=0.0007 L.Safa) suggest no association with aluminosilicate clay minerals. While the strong positive correlations of Ti with Al in Matruh-6 well (R2= 0.858 in U.Safa; R2= 0.946 in L.Safa) indicate the association of the aluminosilicate minerals. Khatatba Fm Deposition occurred during relatively semi-arid conditions (Sr/Cu: avg. 10.03; 11.33; Rb/Sr: avg. 0.36; 0.29), which were characterized by higher terrigenous inputs (sediment influx (Al/Ca): avg. 4.47, Matruh-5 well; 3.87, Matruh-6 well). Normal salinity conditions accumulated under mostly oxic to suboxic-anoxic settings, where (100*MgO/Al2O3: avg. 8.48, Matruh-5 well; 11.37, Matruh-6 well), (V/(V + Ni): avg. 0.58 in Matruh-5 well; avg. 0.32 in Matruh-6 well), and Cu/Zn: avg. 0.34 Matruh-5 well; avg. 0.27 Matruh-6 well).

DOI

10.21608/egjg.2024.256634.1066

Keywords

Depositional Environment, Paleoclimate, XRF elemental analysis, source rocks, Khatatba Formation, Matruh Basin

Authors

First Name

Walaa

Last Name

Ali

MiddleName

Awaad

Affiliation

Petroleum Geology Department, Faculty of Petroleum and Mining Sciences, Matrouh University.

Email

walaa.ali@mau.edu.eg

City

Matrouh

Orcid

0000-0002-9610-7165

Volume

67

Article Issue

1

Related Issue

40290

Issue Date

2023-12-01

Receive Date

2023-12-06

Publish Date

2023-12-30

Page Start

299

Page End

319

Print ISSN

0022-1384

Online ISSN

2805-2617

Link

https://egjg.journals.ekb.eg/article_339226.html

Detail API

https://egjg.journals.ekb.eg/service?article_code=339226

Order

18

Type

Original Article

Type Code

2,013

Publication Type

Journal

Publication Title

Egyptian Journal of Geology

Publication Link

https://egjg.journals.ekb.eg/

MainTitle

Depositional environment and paleoclimate of the Middle Jurassic sedimentary rocks in Matruh Basin, Northwestern Desert, Egypt

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Article

Created At

28 Dec 2024