From genesis to demise: investigating the stratigraphic evolution, island dolomitisation, and drowning of the cretaceous mid-pacific isolated carbonate platforms
File(s)
Author(s)
Nourelyamani, Mahmoud
Type
Thesis or dissertation
Abstract
The Cretaceous period witnessed widespread neritic carbonate development, including isolated carbonate platforms (ICPs) which are geologically complex and economically significant for hydrocarbon exploration, as in Egypt’s Zohr Field. Despite extensive research, many questions remain about how these platforms formed, evolved, and ultimately declined. This thesis explores these gaps by focusing on Cretaceous ICPs in the Mid-Pacific (Resolution and Allison guyots), integrating core, logging, seismic reflection, and geochemical data, and tectonic reconstruction to derive broader implications.
I elucidated the sequence stratigraphic evolution of these platforms, revealing a more dynamic interplay of factors—including eustasy, subsidence, carbonate production, ocean chemistry, and magmatism—than traditional models suggest. The high-resolution 3D depositional model developed here can be applied to other Cretaceous ICPs worldwide. Karst features on these platforms show two patterns: vertically stacked flank-margin caves along steep windward margins and laterally extensive karst-horizons in the interior with sinkholes and intermittent intervals of brecciation and solution-vugs.
The dolomitisation of these platforms, long attributed to seawater circulation, appears to be driven by magmatism instead. I propose a hydrothermal model where heat flow, seawater circulation, and slight mixing with magmatic fluids altered seawater chemistry, increasing magnesium and enabling dolomite formation. A global database of Cretaceous dolostones supports my reinterpretation, challenging older models of widespread dolomitisation by the Cretaceous normal seawater.
These platforms were demised in the late-Albian to early-Cenomanian, when magmatism caused uplift and subaerial exposure, halting carbonate production. Rapid subsidence from hotspot migration and eustatic rise deepened platform tops, pushing them beyond depths suitable for carbonate growth. My findings challenge the hypothesis of “death-by-excessive-warmth-in-peri-equatorial-waters”—suggesting the heat tolerance of Cretaceous carbonate-secreting organisms.
This work provides new insights into the evolution, diagenesis, and decline of Cretaceous ICPs, improving our understanding of ancient carbonate systems and their significance for analogous platforms in frontier hydrocarbon exploration, like East Mediterranean.
I elucidated the sequence stratigraphic evolution of these platforms, revealing a more dynamic interplay of factors—including eustasy, subsidence, carbonate production, ocean chemistry, and magmatism—than traditional models suggest. The high-resolution 3D depositional model developed here can be applied to other Cretaceous ICPs worldwide. Karst features on these platforms show two patterns: vertically stacked flank-margin caves along steep windward margins and laterally extensive karst-horizons in the interior with sinkholes and intermittent intervals of brecciation and solution-vugs.
The dolomitisation of these platforms, long attributed to seawater circulation, appears to be driven by magmatism instead. I propose a hydrothermal model where heat flow, seawater circulation, and slight mixing with magmatic fluids altered seawater chemistry, increasing magnesium and enabling dolomite formation. A global database of Cretaceous dolostones supports my reinterpretation, challenging older models of widespread dolomitisation by the Cretaceous normal seawater.
These platforms were demised in the late-Albian to early-Cenomanian, when magmatism caused uplift and subaerial exposure, halting carbonate production. Rapid subsidence from hotspot migration and eustatic rise deepened platform tops, pushing them beyond depths suitable for carbonate growth. My findings challenge the hypothesis of “death-by-excessive-warmth-in-peri-equatorial-waters”—suggesting the heat tolerance of Cretaceous carbonate-secreting organisms.
This work provides new insights into the evolution, diagenesis, and decline of Cretaceous ICPs, improving our understanding of ancient carbonate systems and their significance for analogous platforms in frontier hydrocarbon exploration, like East Mediterranean.
Version
Open Access
Date Issued
2024-04-29
Date Awarded
2025-02-01
Copyright Statement
Attribution-Non Commercial-No Derivatives 4.0 International Licence (CC BY-NC-ND)
Advisor
John, Cedric
Bell, Rebecca
Sponsor
Ministry of Higher Education and Scientific Research
Egyptian Bureau for Cultural and Educational Affairs
Publisher Department
Department of Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)