Organic Facies Variability and Source Rock Potential of the Matulla Formation (Upper Cretaceous) in the Gulf of Suez, Egypt: Insights From Geochemistry, Palynofacies and Organic Petrography

The Gulf of Suez rift basin represents one of the most prolific hydrocarbon‐producing provinces in Egypt and North Africa. Within this basin, the Upper Cretaceous (Coniacian–Santonian) Matulla Formation serves as a key pre‐rift source rock and reservoir interval; nevertheless, definitive petrographic and palynofacies constraints on its source rock quality and organic‐facies heterogeneity remain inadequately documented across different sub‐basins. To address this, an integrated evaluation combining bulk organic geochemistry (total organic carbon [TOC] and Rock‐Eval 6 pyrolysis), palynofacies analysis and incident‐light/fluorescence organic petrography was conducted on ditch‐cutting samples from four offshore exploration wells across the central and southern Gulf of Suez. Geochemical analyses demonstrate marked lateral and vertical variations in organic richness and generative potential: the central sub‐basin (well GS‐197‐2) exhibits fair‐to‐very good richness (TOC = 0.65–2.42 wt.%; S 2 = 1.22–12.40 mg HC/g rock) with hydrogen index (HI) values ranging from 161 to 516 mg HC/g TOC, corresponding predominantly to oil‐prone Type II and mixed oil/gas‐prone Type II/III kerogen. Conversely, the southern sub‐basin (well SB 357‐1) exhibits poor to very good richness (TOC = 0.41–2.10 wt.%; S 2 = 0.34–8.90 mg HC/g rock) with lower HI values (83–424 mg HC/g TOC), reflecting a pronounced terrestrial input and gas‐prone Type III kerogen. Thermal maturity appraisal based on Rock‐Eval T max values indicates early oil‐window entry in the central sector ( T max = 431°C–440°C), whereas higher maturity characterising the peak oil window is attained in the southern sector ( T max = 437°C–445°C). Palynofacies and organic petrographic observations confirm these spatial variations: the central and distal southern marine intervals (wells GS‐197‐2, GS‐173‐1 and SB 367‐1A) are dominated by structureless amorphous organic matter (AOM > 89%) along with fluorescent lamalginite and bituminite aligned with rock matrix laminations, indicative of deposition under distal, suboxic‐to‐anoxic marine ramp settings. In contrast, shallower intervals in well SB 357‐1 display a high abundance of non‐fluorescent, structured terrestrial phytoclasts and cellular vitrinite, reflecting deltaic and nearshore influx. Multivariate hierarchical cluster analysis differentiated four discrete organic facies (A1, A2, B1 and B2), documenting an environmental and maceral transition from marine alginite/bituminite‐rich to terrestrial vitrinite‐dominated assemblages. These findings refine the source rock heterogeneity and generative model of the Matulla Formation in the Gulf of Suez.