Miocene Syn-rift Research Articles

Geophysical appraisal of the Abu Madi gas reservoir, Nile Delta Basin, Egypt: Implications for the tectonic effect on the lateral distribution of petrophysical parameters

The tectonic deformation has a significant influence on the hydrocarbon reservoirs properties. The effect of this process focuses on the lateral distribution of the petrophysical parameters characterizing the hydrocarbon reservoirs. The main objective of the current study is to perform a petrophysical examination of the Abu Madi gas reservoir which is the greatest gas-bearing reservoir at Nile Delta Basin in order to examine how far the Messinian tectonics affected the lateral variations of these petrophysical parameters. This petrophysical evaluation was performed based on the wireline log data acquired for five wells, namely, Abu Madi-2, Abu Madi-7, El Qara-3, Nidoco-7, and Nidoco-9 drilled within the Abu Madi Paleo-Valley. The petrophysical assessment for the most promising zone intervals within the Abu Madi sandstones in the inspected wells show that the total porosity varies between 17% and 22%, the effective porosity ranges from 7% to 19%, the shale volume fluctuates between 16% and 30%, hydrocarbon saturation varies from 37% to 76%, and the bulk volume of water varies between 0.02 and 0.09. These significant variations in the petrophysical properties of the Abu Madi reservoir are attributed to the tectonic influence during the deposition of the Abu Madi Formation as a part of the Late Miocene syn-rift megasequence in the Nile Delta Basin. This conclusion confirms that the petrophysical properties of sandstone reservoirs are function of tectonic and structural deformation.

Miocene syn-rift evolution of the North Croatian Basin (Carpathian–Pannonian Region): new constraints from Mts. Kalnik and Požeška gora volcaniclastic record with regional implications

Mts. Kalnik and Požeska gora volcaniclastic sequences hold valuable information concerning the Miocene syn-rift evolution of the North Croatian Basin, and the evolution of the Carpathian–Pannonian Region and the Central Paratethys. We present volcanological, high-precision geochronological, and compositional data of volcanic glass to constrain their tephrochronology, magmatic provenance, and timing of the initial Central Paratethys flooding of the North Croatian Basin. Based on CA-ID-TIMS U–Pb zircon ages (18.060 ± 0.023 Ma for Mt. Kalnik and 15.345 ± 0.020 Ma for Mt. Požeska gora) and coeval 40Ar/39Ar sanidine ages (18.14 ± 0.38 Ma and 18.25 ± 0.38 Ma for Mt. Kalnik and 15.34 ± 0.32 Ma and 15.43 ± 0.32 Ma for Mt. Požeska gora), Mt. Kalnik rhyolitic massive ignimbrites and Mt. Požeska gora rhyolitic primary volcaniclastic turbidites are coeval with Carpathian–Pannonian Region Miocene post-collisional silicic volcanism, which was caused by lithospheric thinning of the Pannonian Basin. Their affiliation to Carpathian–Pannonian Region magmatic activity is supported by their subduction-related geochemical signatures. Although Mts. Kalnik and Požeska gora volcaniclastics are coeval with the Bukkalja Volcanic Field Csv-2 rhyolitic ignimbrites, North Alpine Foreland Basin, Styrian Basin, Vienna Basin, and Dinaride Lake System bentonites and volcaniclastic deposits, reliable tephrochronological interpretations based on comparison of volcanic glass geochemical composition are not possible due to a lack of data and/or methodological discrepancies. Our new high-precision geochronology data prove that the initial Middle Miocene (Badenian) marine flooding of parts of the North Croatian Basin occurred at least ~ 0.35 Ma (during the NN4 Zone) before the generally accepted ~ 15 Ma maximum flooding age at the basin scale, calibrating the timing of the onset of the widespread “mid-Langhian” Central Paratethys flooding.

Facies analysis and depositional environments of the Miocene syn-rift carbonate–siliciclastic rock packages in the northwest Gulf of Suez, Egypt

The Miocene sedimentary successions in the northwest Gulf of Suez allow insight into the syn-rift deposition. These rocks are subdivided into three formations, namely the Sadat Formation coeval with the Gharra Formation (Early Miocene), the Hommath Formation (Middle Miocene), and the Hagul Formation (Late Miocene). The Miocene rocks in the study area are dominated by carbonate-siliciclastic packages. Detailed microfacies analysis permit discrimination of 14 sedimentary microfacies types, which are represented by continental quartz-arenites and sandy siltstones, as well as shallow-marine gypsiferous laminated shales, litharenites, dolomicrites, wackestones, wacke-/packstones, packestones, pack-/grainstones, ooidal/pelloidal pack-/grainstones, grainstones, rudstones, framestones, and bindstones. These microfacies types are stacked into four facies associations that represent fluvial, and inner ramp, shallow marine environments (facies associations for the later are restricted lagoonal/tidal flat, shoal bar, and open-lagoonal/reefal). In terms of sequence stratigraphy, it is possible to distinguish five depositional sequences in the studied Miocene succession. The retrograditional package displays predominance of open lagoon/reefal facies. The aggradational package shows increase in restricted lagoon tidal flat and shoal bar facies. The progradational package marks occurrence of continental (fluvial) facies. The regional tectonic activity related to the rifting of the Gulf of Suez was the leading control of the Miocene sedimentation in the study area.

Geochemical signatures of pervasive meteoric diagenesis of Early Miocene syn-rift carbonate platform, Red Sea, NW Saudi Arabia

Different diagenetic environments have been recognized in the Early Miocene carbonate platform of Musayr Formation in the Red Sea rift area. Early marine diagenesis includes micritisation that occurs as thin envelope around skeletal and non-skeletal grains in low-energy mud dominated facies and isopachous fibrous calcite in high-energy grain-dominated facies. Pervasive meteoric water diagenesis resulted in cementation of the carbonates by coarse-crystalline blocky-drusy calcite and meniscus cements. Depletion of oxygen (avg. –9.08‰), carbon (avg. –1.6‰) isotopes and trace elements concentrations (avg. values of Fe: 1387 ppm; Mn: 1444 ppm; Sr: 419 ppm; Na: 1194 ppm) in conjunction with negative correlation between Mn2+ and oxygen isotope data suggest variable degrees of fluid-rock interactions and pervasive meteoric diagenesis. The formation of meteoric diagenesis in the Musayr Formation can be explained by two subsequent mechanisms: (1) the presence of meteoric lenses during the time of deposition might have been associated with active freshwater input from the hinterland (NE) due to fall in the relative sea level; (2) later uplift episode during Plio-Pleistocene may have also contributed to the pervasive meteoric diagenetic alterations of the carbonates of the Musayr Formation. The first mechanism is supported by the cement stratigraphy where the blocky-drusy cements postdate the meniscus cement. The latter mechanism seems to have more pronounced effect on the alteration of Musayr carbonate sequence by observing the occurence of late cements such as blocky calcite in most of the samples. The impact of meteoric diagenesis on the studied samples suggest that dissolution is less severe than cementation, hence the visible porosity is very low. Understanding the timing of meteoric diagenesis provides useful information about the reservoir quality distribution in syn-rift carbonate sequences.

Submarine slope processes in rift-margin basins, Miocene Suez Rift, Egypt

New, high-resolution lithofacies data from hanging-wall Miocene synrift (Rudeis Formation) exposures of the eastern Suez Rift margin, Egypt, reveal a submarine slope depositional system dominated by coarse-grained (pebble), heterogeneous, lenticular beds, formed by coalescing turbidity currents, slumps, and debris flows deposited on deforming submarine substrate. Flows include prerift clasts and contemporaneous shallow-marine fossil fragments originating from an uplifted eastern hinterland. Multiple terrestrial drainages debouched onto faulted offshore slopes or fed small fan deltas on narrow shelves ( 360 m Rudeis Formation is divided into stratigraphic units R1 and R2, which exhibit upward-coarsening and unordered vertical motifs. Ongoing faulting influenced synrift deposition by controlling the locus of subsidence and gravity base level. Mesoscale faults became inactive during Rudeis Formation times, with strain localized on the large rift border fault system, leading to a wider basin with time. We compare 16 subaqueous rift-margin basin fills from various tectonic and geographic settings and show they generally represent proximal gravity-flow deposits dominated by nongraded beds. We find little commonality in vertical grain-size trends, highlighting the diversity of stratal architectures. Most basin fills show an inverse relationship between maximum clast size and shelf width. We propose a new model to capture the spectrum of sedimentary responses to rifting within rift-margin basins, varying as a function of shelf width, slope gradient, maximum grain size, and textural maturity. Rudeis Formation strata at north Wadi Baba represent a particularly coarse-grained end member, deposited on steep slopes, with a narrow shelf.

Anatomy of a submarine channel system and related fan in a foramol/rhodalgal carbonate sedimentary setting: a case history from the Miocene syn-rift Sardinia Basin, Italy

During Aquitanian–Burdigalian times, thick mixed carbonate–siliciclastic successions were deposited in basins located on the grabens and half-grabens along the Oligo-Miocene Sardinia Rift Basin. Locally active tectonics, sea level variations and ecological factors combined to control the development and distribution of foramol carbonate factories as well as the remobilisation and the redeposition of carbonate sediments into the adjacent deeper areas. In the Isili Basin, foramol/rhodalgal carbonate factories developed on submerged structural highs which resulted from pre- and syn-sedimentary tectonics. These carbonate factories were periodically shaved mainly during negative sea level oscillations and the sediments removed were funnelled towards the basin through a complex submarine channel network which included a tributary belt, one main channel (Isili Channel) and the related fan. The Isili Channel is up to 1 km wide, 60–100 m deep and includes two stacked channel complexes each built up by several minor-order channel units. Complex strata geometries characterise the Isili Channel and its related architectural elements (e.g., overbank, levee, margin and channel thalweg) which also include up to 15 m high bedforms. Individual channel complexes were temporally related to individual fan systems whose spatial distribution and internal geometry were strongly controlled by the type and rate of sediment accumulation and, in turn, by relative sea level oscillations. Facies associations include sandy to cobble-sized gravity flow and bottom current deposits as well as megabreccias characterised by impressive displaced and tilted blocks which resulted from major channel margin collapses. Detailed analysis has led to the reconstruction of the internal geometry and depositional architecture of these carbonate bodies and to the determination of the main controlling factors. The dimension and distribution of channel and channel-related depositional bodies have been accurately determined. This information provides a useful tool to analyse less extensively exposed analogues and to model foramol shelf to basin transitions and related channel and fan systems.

Miocene carbonate factories in the syn-rift Sardinia Graben Subbasins (Italy)

Miocene syn-rift carbonate production areas are exposed in south-eastern Sardinia (Italy) along the eastern side of the Plio-Pleistocene Campidano Graben. Here the downfaulted margins of the Oligo-Miocene Sardinia rift-basin crop out with a complex alignment of smaller subbasins. Carbonate factories developed during the Aquitanian times in these tectonically controlled small depositional subbasins, where terrigenous input might be high due to the erosion of the uplifted pre-Neogene substrata. Terrigenous deposits generally acted as passive substratum for pioneer communities of rhodalgal-type (red algae, ostreids, bryozoans) and locally evolved into coral-dominated assemblages. Carbonate production areas occur on tilted, uplifted blocks as well as along basement margins. These have varying organic communities and facies characteristics strongly dependent on different environmental conditions. In footwall areas, devoid of (or with a very reduced) terrigenous supply, open foramol carbonate factories occur with aggradational-progradational stratigraphic geometries. The resulting pure calcareous successions are organized in sequences, bounded by tectonically driven discontinuity surfaces. In sectors close to the hinterland area, with a higher freshwater input and a consequent significant clastic input, coral-dominated assemblages grew during long periods of quiescence between flash floods. Repeated coral-rich communities developed on thick wedges of terrigenous debris. Carbonate facies composition and distribution were mainly controlled by local syn-sedimentary tectonics and eustasy as well as by climate. However, although the inception of the carbonate factories was presumably not synchronous, their growth represented the response to a relative regional sea level rise subsequent to episodes of significant clastic supply: the expression of an early syn-rift stage. During the Burdigalian (N6 zone) a hemipelagic cover uniformly sealed the neritic successions. This basin wide drowning event appears to correspond to the transgressive system tract of the TB2.1 cycle ofHaq et al. (1987) but it can also be interpreted as the expression of an evolved syn-rift stage passing to late syn-rift and quiescence stages. Beneath the hemipelagic cover in some areas, ?late Aquitanian-early Burdigalian deep erosive surfaces, terrigenous clastics and paleosoils have been recognized. These suggest a relative sea level fall and may relate to the global sea level drop at the TB1-TB2 boundary (seeHaq et al., 1987) or to diacronous uplift of different fault blocks.

Lithostratigraphy and Depositional History of Part of the Midyan Region, Northwestern Saudi Arabia

ABSTRACT The Midyan region provides a unique opportunity in which to examine exposures of the Upper Cretaceous and Neogene sedimentary succession. Recent investigations have yielded new interpretations of its depositional environments, stratigraphic relationships, and structure. In this paper, all the lithostratigraphic units of the Midyan succession are considered to be informal in advance of an on-going process of formalization. The region is bounded to the north and northeast by mountains of Proterozoic rocks and to the west and south by the Gulf of Aqaba and the Red Sea, respectively. The Wadi Ifal plain occupies most of the eastern half of the region, beneath which is a thick sedimentary succession within the Ifal basin. The oldest sedimentary rocks are the fluviatile Upper Cretaceous Adaffa formation and marine siliciclastics and carbonates of the lower Miocene Tayran group, unconformable on the Proterozoic basement. The Tayran group is unconformably overlain by the deep-marine lower Miocene Burqan formation that, in turn, is overlain by marine mudstones, carbonates, and evaporites of the middle Miocene Maqna group. The poorly exposed middle Miocene Mansiyah and middle to upper Miocene Ghawwas formations consist of marine evaporites and shallow to marginal marine sediments, respectively. The youngest rocks are alluvial sands and gravels of the Pliocene Lisan formation. A complex structural history is due to Red Sea Oligocene-Miocene extension tectonics, and Pliocene-Recent anti-clockwise rotation of the Arabian Plate relative to Africa on the Dead Sea Transform Fault. The Upper Cretaceous succession is a probable pre-rift unit. The Oligocene?-Miocene syn-rift 1 phase of continental extension caused slow subsidence (Tayran group). Syn-rift 2 was an early Miocene phase of rapid subsidence (Burqan formation) whereas syn-rift 3 (early to middle Miocene) was another phase of slow deposition (Maqna group). The middle to late Miocene syn-rift 4 phase coincided with the deposition of the Mansiyah and Ghawwas formations. The Lower Pliocene to Recent succession is related to the drift (post-rift) phase during which about 45 kilometers of sinistral movement occurred on the Dead Sea Fault. The structural control on sedimentation is evident: the Ifal basin was formed by east-west lithospheric extension; pull-apart basins occur along major left-lateral faults on the eastern coast of the Gulf of Aqaba; and basin-bounding faults controlled deposition of the Burqan, Ghawwas, and Lisan formations. Pliocene to Recent earth movements may be responsible for activating salt diapirism in the Ifal basin. Extensive Quaternary faulting and regional uplift caused the uplift of coral reefs to at least 6 to 8 meters above sea level.

Rift Basin Sequence Stratigraphy Models: Parts A and B, Gulf of Suez Miocene Syn-Rift Deposits : ABSTRACTS

Rift Basin Sequence Stratigraphy Models: Parts A and B, Gulf of Suez Miocene Syn-Rift Deposits : ABSTRACTS

The Red Sea — Gulf of Aden: re-assessment of hydrocarbon potential

The results and conclusions of the UNDP/World Bank Red Sea — Gulf of Aden Regional Hydrocarbons Study Project (June 1989 – January 1992) are summarized. These derive from detailed examination of pooled public sector data provided to the project by the participating bordering states in the region; these included samples and logs from about 56 wells drilled in the two basins (out of a total of 71) and about 30 000 line km of reflection seismic data (selected from 110 000 km available). Well logs were digitized and correlated, and basinwide biostratigraphic, lithostratigraphic and palaeoenvironmental studies, source rock organic richness, quality and maturity studies and sedimentological analyses studies were performed by contracted specialist staff in the UK and France. These were integrated with basinwide seismic structural and isopach mapping for selected regional reflectors/intervals by national task forces in Cairo under project supervision; academically acquired crustal seismic and other geophysical data and oil industry velocity and other borehole data were also integrated for the Red Sea. Modelling utilizing recently acquired geophysical data indicates crustal asymmetry for the Red Sea rift with oceanic crust of pull-apart basin type flooring some portions of offshore Egypt and Sudan on the west and stretched continental crust underlying the eastern Arabian flank. These interpretations furthermore suggest that sinistral strike-slip processes controlled the initial break up of the Arabian plate, shaping the African flank as a sharp plate boundary; similar processes appear to have initially shaped the Somalia flank of the Gulf of Aden rift. Only later did true seafloor spreading propagate; in the eastern Gulf of Aden 10–12 Ma, about <5 Ma in the western Gulf of Aden, Afar and the southern/central Red Sea. Biostratigraphic work shows that deep subsidence and ocean water inundation commenced in the late Middle Oligocene in the Gulf of Aden, in the Late Oligocene in the southern Red Sea and in the Early Miocene in the Central Red Sea/Gulf of Suez. A regional lithostratigraphic nomenclature scheme for the Miocene-Recent syn- and post-rift Red Sea successions keyed to detailed biostratigraphical distribution charts and microfaunal assemblage characteristics was erected, tied to the well documented and understood petroliferous Gulf of Suez basin scheme; this allows facies variations within the basin to be compared and allows consistent interpretation and correlations across the basin to which local informal nomenclature can be related. Pre-rift (pre-Oligocene) marine sediments are present in most of the Gulf of Aden (Jurassic-Eocene) but only incompletely on the basin margins in the Red Sea (Jurassic in the south, Upper Cretaceous — Early Palaeogene in the north). Significant pre-rift oil/gas prone Upper Jurassic, Cretaceous and Palaeogene source rocks occur in Gulf of Aden sub-basins initiated by Late Jurassic — Early Cretaceous tensional tectonics, with maturity levels ranging from early-late to post-mature, whereas early synrift source rocks are generally immature. In the Red Sea good quality pre-rift source rocks outcrop in the north and south but are probably overmature for oil in the basin except in the extreme south (if present). Good syn-, pre- and post-salt and post-rift source levels occur throughout the basin but in the central/southern sectors only the post-salt remains within the oil window because of high geothermal gradients. Both basins are little explored. Attractive pre-rift Jurassic-Eocene exploration plays in rotated fault and horst blocks in predominantly carbonate but subordinate sandstone reservoirs are present in the Gulf of Aden (confirmed by an important undeveloped Eocene light oil discovery in offshore Yemen) with subordinate synrift potential where maturity is established. Relative continental shelf narrowness is economically limiting, but wider sectors occur. In the Red Sea the principal exploration plays are in Miocene synrift, pre- and post-salt successions. Rotated fault blocks occur in the pre-salt, but maturity for oil in the deeper levels is restricted to the northern sector. These levels in the central and southern sectors are overmature except in the southernmost portion but excellent potential exists in the synrift post-salt and early post-rift sequences with a number of attractive play types. Reservoirs for synrift plays are mainly sandstones and potential is confirmed by several undeveloped gas and condensate discoveries and numerous oil seepages throughout the basin; relatively wide continental shelves occur in the south and along much of the eastern flank.