Three-Dimensional Numerical Modelling Study of Sound Speed in the Persian Gulf

Modern cemented intervals (beachrock, firmgrounds to hardgrounds and concretionary layers) form in the lagoon and intertidal sabkha of Abu Dhabi. Seafloor lithification actively occurs in open, current‐swept channels in low‐lying areas between ooid shoals, in the intertidal zone of the middle lagoon, some centimetres beneath the inner lagoonal seafloor (i.e. within the sediment column) and at the sediment surface the intertidal sabkha. The concept of ‘concretionary sub‐hardgrounds’, i.e. laminar cementation of sediments formed within the sediment column beneath the shallow redox boundary, is introduced and discussed. Based on calibrated radiocarbon ages, seafloor lithification commenced during the Middle to Late Holocene (ca 9000 cal yr bp), and proceeds to the present‐day. Lithification occurs in the context of the actualistic relative sea‐level rise shifting the coastline landward across the extremely low‐angle carbonate ramp. The cemented intervals are interpreted as parasequence boundaries in the sense of ‘marine flooding surfaces’, but in most cases the sedimentary cover overlying the transgressive surface has not yet been deposited. Aragonite, (micritic) calcite and, less commonly, gypsum cements lithify the firmground/hardground intervals. Cements are described and placed into context with their depositional and marine diagenetic environments and characterized by means of scanning electron microscope petrography, cathodoluminescence microscopy and Raman spectroscopy. The morphology of aragonitic cements changes from needle‐shaped forms in lithified decapod burrows of the outer lagoon ooidal shoals to complex columnar, lath and platy crystals in the inner lagoon. Precipitation experiments provide first tentative evidence for the parameters that induce changes in aragonite cement morphology. Data shown here shed light on ancient, formerly aragonite‐cemented seafloors, now altered to diagenetic calcites, but also document the complexity of highly dynamic near coastal depositional environments.

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“…1. Geographical location and bathymetry of the Gulf (modified from Sadrinasab & Kenarkohi, 2009). The red box indicates the study area.…”

Section: Geographical and Geological Settingmentioning

confidence: 99%

Late Holocene to Recent aragonite‐cemented transgressive lag deposits in the Abu Dhabi lagoon and intertidal sabkha

Pederson

Lokier

et al. 2020

Sedimentology

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“…4.-Map of surface water salinity in A) fall, B) winter and spring. This map was generated using field sampling (2016 and 2017) at sites around the Qatari coast (white dots), and integration of contour trends from literature (Erftemeijer et al 2004;Sadrinasab and Kenarkohi 2009;Rezaei-Latifi 2016). Basemap: GeoEye satellite data captured in 2011 by DigitalGlobe, Inc (Esri).…”

Section: Water Chemistrymentioning

confidence: 99%

The Geochemistry of Qatar Coastal Waters and its Impact on Carbonate Sediment Chemistry and Early Marine Diagenesis

Rivers

Varghese

Yousif

et al. 2019

Journal of Sedimentary Research

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The southern margin of the Arabian Gulf is a ''classic'' shallow-water, evaporative, carbonate-producing setting. The sediments and early diagenetic products creating the ''Great Pearl Bank'' of the United Arab Emirates to the east and accumulating in the coastal regions of Qatar to the west have long been studied as modern analogs for ancient evaporitic carbonate deposits of the rock record. An integrated study measuring the chemistry of Qatar subtidal coastal waters, evaporating tidal-pond waters (to halite saturation), and meteoric pond waters was undertaken encompassing both the dry (fall) and wet (winter/spring) seasons of 2016-2017. Measured parameters included temperature, pH, dissolved oxygen, and alkalinity, as well as major-ion (Na þ , Ca 2þ , Mg 2þ , K þ , Sr 2þ , Cl -, and SO 4 2-) and stable-isotope (d 18 O and dD) composition. Initial concentration by evaporation (to~90 practical salinity units (psu)) is interpreted to drive minor diagenetic aragonite precipitation. Further evaporation initially causes minor aragonite dissolution followed by gypsum and halite precipitation. One pond showed evidence of ongoing replacive dolomitization interpreted to be driven by H 2 S formation and oxidation in association with microbial breakdown of organic matter. The stable-isotope composition of water in restricted ponds is a function of the degree of evaporation and dilution by meteoric waters during the wet season. Unexpectedly, beyond 350 psu, d 18 O and dD continue to rise reaching values greater than 12 and 60%, respectively. The slope of the d 18 O-dD regression line exhibits no differences between dry and wet seasons.During collection of coastal waters (up to~90 psu), live Pirenella cingulata (previously Cerithidea cingulata) gastropods were collected and their shells analyzed for d 18 O and d 13 C, as well as Sr 2þ and Ca 2þ concentration. The d 18 O of water and Pirenella from the same sample site exhibits a strong correlation (R 2 ! 0.85) with a slope of~1, suggesting that the shells may be a useful chemical archive for the isotopic composition of past oceans. The d 18 O and d 13 C of the shells correlate positively, likely reflecting greater sequestration of 12 C into organic matter in more restrictive evaporative settings. The intercept of the d 18 O and d 13 C correlation shifts between dry and wet seasons, and is interpreted to reflect average seawater temperature differences during recent growth. There is also a strong correlation (R 2 ! 0.85) between shell d 18 O and measured water salinity, reflecting their mutual control by degree of evaporation. The Sr 2þ content of the gastropods does not correlate well with any measured oceanographic parameter, or show evidence of systematic seasonal change.

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“… Geographical background in the study area (a) Geography and bathymetry of the Gulf (modified from Sadrinasab & Kenarkohi, 2009), and the Abu Dhabi coastal area is indicated by red frame (b) Geography and bathymetry of the Abu Dhabi coastal area, and detailed study locality (Khawr as Sadiyat, indicated by red frame) for sediment and seawater properties. The bathymetry data was sourced from United Arab Emirates‐Approaches to Abu Dhabi (Abu Zaby) (Marine Chart: SA_GB45050B), and the wind data from El‐Sayed (1999) (c) Enlargement of the Khawr as Sadiyat with proximal‐distal environmental variations seawards from Yas Lagoon, Fahid Lagoon to Al Bahyah Lagoon adjacent to open marine (d) Seawater and sediment sample distribution in the Khawar as Sadiyat.…”

Section: Geological and Geographical Backgroundmentioning

confidence: 99%

Extensive Early Marine Seafloor Cementation in a Modern Epeiric Sea Induced by Seawater Properties and a Shallow Redox Boundary Below the Seafloor

2022

Geochem Geophys Geosyst

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Extensive early marine cementation at the seafloor has important environmental implications (e.g., ocean chemistry and atmosphere pCO2), but its driver remains controversial, because many factors have been proposed to affect early marine cementation. At the Abu Dhabi coastal area of the Persian Gulf, extensive early marine cementation at the seafloor provides a good modern study case for ancient analogs. Based on petrological (thin section, cathodoluminescence and scanning electron microscope) and geochemical (e.g., δ13CDIC, alkalinity, aragonite saturation) analyses, this study investigates integrated factors from seawater to sediment properties and tests previously proposed explanations about extensive early marine cementation at the seafloor. Results suggest multiple factors involved in the early marine cementation. CaCO3 saturation, small CaCO3 saturation gradient and higher sea level in the early Holocene are consistent with former explanations. A new finding is shallow redox boundary within the seafloor sediment promoting extensive early marine cementation. The formation of shallow redox boundary is unrelated to anoxic bottom water and/or enhanced organic influx, but rather is related to: (a) high salinity under hot and arid climate, and (b) low‐energy and restricted shallow marine settings., These conditions undoubtedly occurred in past shallow and warm epeiric marine seas. This provides new insights into formation mechanism and paleoenvironmental interpretation of ancient extensive early marine cementation at the seafloor on epeiric seas.

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Three-Dimensional Numerical Modelling Study of Sound Speed in the Persian Gulf

Cited by 9 publications

References 4 publications

Late Holocene to Recent aragonite‐cemented transgressive lag deposits in the Abu Dhabi lagoon and intertidal sabkha

Late Holocene to Recent aragonite‐cemented transgressive lag deposits in the Abu Dhabi lagoon and intertidal sabkha

The Geochemistry of Qatar Coastal Waters and its Impact on Carbonate Sediment Chemistry and Early Marine Diagenesis

Extensive Early Marine Seafloor Cementation in a Modern Epeiric Sea Induced by Seawater Properties and a Shallow Redox Boundary Below the Seafloor

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