Microfacies analysis of the Late Maastrichtian- Danian Phosphatic Succession in the H3-Trebeel district, Western Desert of Iraq

The Late Maastrichtian–Danian phosphatic succession prevails as a deposit to the west of Rutbah region, Western Iraq. This is manifested through the lithostratigraphic sections of boreholes (K.H5\6 and K.H 5\8) drilled previously in the area. The succession is mainly composed of phosphate, shale, porcelanite, oyster and foraminiferal carbonate lithofacies belonging to Digma and Akashat formations. Three facies associations are distinguished during the study: the phosclast planktonic (FA1) that dominates the outer ramp, the phosclast foraminiferal (FA2) that dominates the mid ramp, and the quartz dolomitic phosclast (FA3) present in the inner ramp. These facies’ associations are differentiated into seventeen microfacies types. Microfacies analysis and fauna contents have shown gradual facies variation grading from a high energy inner ramp environment in the east to a low energy deep water ramp environment in the west.

Mid-Cenozoic SHRIMP U-Pb detrital zircon ages from metasedimentary rocks in the North Patagonian Andes of Aysén, Chile

Previously undated low-grade metamorphic rocks from the Puerto Cisnes-Queulat area (44°30’ S) contain detrital zircons of mid-Oligocene age (ca. 28 Ma). Their outcrops represent the easternmost occurrence of the late Oligocene to early Miocene marine volcano-sedimentary Traiguén Formation; previous correlation with the Paleozoic metamorphic basement of this sector of the North Patagonian Andes is thus refuted. A similar age and provenance were obtained for a paraconglomerate bed of the La Junta Formation ca. 80 km to the north, which is thought to represent a high-energy lateral facies variation of the Traiguén Formation. Miocene plutonic rocks of the North Patagonian Batholith intruded these metasedimentary rocks, generating a contact metamorphic aureole that reaches biotite grade and overprints a previous metamorphic fabric probably formed during closure of the Traiguén Basin. Similar young ages for metamorphic rocks located immediately west of the Liquiñe-Ofqui Fault Zone 300 km north, near Ayacara, suggest a regional pattern of earliest Neogene metamorphism and rapid exhumation in this segment of the Patagonian Andes.

Quantitative analysis of facies variation using ground-based lidar and hyperspectral imaging in Mississippian limestone outcrop near Jane, Missouri

Ground-based hyperspectral imaging is useful for geologic mapping because of its high spectral and spatial resolutions at a millimeter to centimeter scale. We have used hyperspectral and terrestrial laser scanner (TLS) data collected in close range to a roadcut near Jane, Missouri, that contains a subvertical outcrop of Lower Mississippian limestone. The outcrop consists of the Compton, Northview, and Pierson Formations, which we evaluated for facies heterogeneity. The sequence near Jane, Missouri, was deposited in shelf margin with high-frequency sea-level fluctuations. These fluctuations introduced lithologic and geometric heterogeneity to the facies, and debris flows brought in carbonate mounds referred to as outrunner blocks. These are important to interpret accurately because of their equivocal depositional origin, which is highly debated by previous workers. We combined hyperspectral data with TLS for an integrated spatial analysis of geometric and compositional variations in facies by accurate, point cloud-registered mineralogical mapping. We mapped several carbonate facies based on spectral signatures of calcite, silt, and clay particles and distinguished pure limestone outrunner blocks from surrounding mud-prone limestone facies with various proportions of silt and clay (a total of approximately 60%). By tracing the classified facies from combined hyperspectral and TLS imagery, we produced a lithostratigraphic framework, which indicates rapid changes in lithology and the presence of shale baffles that vary the character of the Compton through Pierson interval and contribute to heterogeneity in this outcrop. The data suggest a lower energy depositional environment and support the hypothesis of transported outrunner blocks in a distally steepened ramp system. The information that we have evaluated in our study could help to explain reservoir heterogeneity in equivalent carbonate fields.

Lithology of the Upper Jurassic-Lower Cretaceous deposits of the eastern part of the Myrgovaam and Rauchua depressions, Western Chukotka

Upper Jurassic-Lower Cretaceous deposits were formed on the South-Western margin of the Chukotka terrane in active tectonic environment. Their stratigraphic units characterized by sedimentary structures and lithology similarities, facies variation and scarcity of reliable fauna findings. Detailed lithological studies are necessary due to the absence of a unified approach to the stratigraphic division of deposits. The paper presents petrographic, geochemical, and isotope-geochemical characteristics of Upper Jurassic-Lower Cretaceous rocks. The stages of changing the sedimentation conditions and sources, which determined the differences in sedimentological features and the composition of the studied strata, are reconstructed. The Oxford-Kimmeridgian section is composed of sandy debris flow deposits with an arcosic composition of psammitic differences. Among their sources, ancient granitoids dominated, while siliciclastic rocks, volcanites and metamorphic complexes were secondary. Volgian-valanginian interval is characterized by the accumulation of sediments in various parts of the submarine fan. In Volgian sequences fine -, medium - and coarse-grained turbidites with lenses of small-pebble conglomerates are identified. A large number of simultaneous pyroclastic material in the Volgian deposits indicates the synchronous volcanic activity. In the Volgian period, the province was dominated by volcanites, mainly of the basaltic and andesitic composition, siliciclastic rocks were present in smaller amount. The Berriasin section is composed of fine-grained turbidites with single horizons of medium-grained turbidites and gravelitic lenses, as well as slope deposits in the form of rhythmically interbedded sandstones and mudstones with slump structures. Sandstones have greywacke composition and contain an admixture of ash material in the matrix. The main sources for Berriasian deposits were siliciclastic rocks and felsic volcanic complexes. The Valanginian section is represented by fine and medium-grained turbidites with horizons of amalgamated sandstones. Sandstones are classified as arkoses by the ratio of rock-forming components. The dominant source in the Valanginian time was ancient granitoids, while siliciclastic rocks and volcanites were secondary.

Chapter 6 Jubaila–Arab–Hith sequences

During deposition of the Jubaila-Arab-Hith sequences, the most important Arab-D reservoir, the Arab-C to A reservoirs and the Arab and Hith anhydrite seals were formed. The Kimmeridgian Jubaila-Arab-D transgression (MFS J70) restored and expanded the intrashelf basin geometry. The restored basin was filled by deeper subtidal Jubaila facies, which graded upwards to the Arab-D reservoir facies. In the late stages the Arab-D facies included both basin rim shoal facies and at least one large isolated shoal surrounded by ‘lagoonal’ intrashelf basin remnants interconnected by accessway channels. This differentiation was facilitated by local structural growth of a few metres. The Arab-D reservoir is overlain by the Arab-D anhydrite, deposited initially as gypsum in broad salinas, which blanketed the intrashelf basin region, forming the first major seal. By the end of Arab-D anhydrite deposition, the entire intrashelf basin area had been filled and transformed into a broad evaporite platform. Atop this platform, the Arab-C to -A (MFS J80-100) alternating shallow water carbonate and anhydrite (initially gypsum) intervals were deposited, ending regionally with the thick Hith Anhydrite Formation. The depositional setting for each of the main Jubaila-Arab-Hith sequences is reviewed and illustrated. The evolution of Jubaila-Arab-D reservoir models is discussed. Different interpretations of Jubaila-Arab-D-Hith sequences are compared, including the issue of whether the Arab carbonate-evaporite depositional sequence boundaries should be taken at the top of the carbonate intervals or the top of the anhydrites. Examples are included which illustrate how easterly palaeowind directions were an important factor controlling Arab-D facies variation. A scenario is presented to show how the Late Jurassic Tethys shelf uplift and low angle unconformity coupled with westward structural tilt were important. An alternating balance developed between the evolving land barrier and eustatic sea-level change during deposition of the Arab carbonate–evaporites and the Hith Anhydrite. Carbonates were deposited when the barrier was inundated and evaporites when the barrier was exposed and the area restricted and hypersaline. A major late Tithonian flooding event (MFS J110) formed the top-Hith Manifa carbonate reservoir and brought open marine carbonate mud-rich deposition to the area, continuing without hiatus into the Early Cretaceous.

Formation evaluation challenges in Pliocene gas-bearing reservoirs from the Romanian Western Black Sea shelf

This paper addresses some formation evaluation challenges and petrophysical particularities regarding two gas fields of Early Pliocene age, belonging to the biogenic hydrocarbon system of Western Black Sea Basin - Romanian continental shelf. Although these structures are located at the same depth and only 15 km apart, the wells that intercepted the sands and silts gas-bearing reservoirs indicate an important lateral facies variation and different reservoir qualities. We analyzed and interpreted data from exploration and appraisal wells that targeted these reservoirs, showing that: (1) there is a limited radioactivity contrast between the reservoir and nonreservoir intervals, so a clay volume determination based solely on the gamma ray log is not practical; (2) the reservoirs are characterized by high capillary-bound water contents, leading sometimes to abnormally low resistivity readings; (3) an additional resistivity suppression might be caused by the limited vertical resolution of the electrical logging tools, in the presence of thinly laminated sand - shale intervals; (4) the identification of gas-water contacts based exclusively on pressure gradients may be inaccurate and should be checked against the results of conventional geophysical logs interpretation and of nuclear magnetic resonance logs, for delineating the intervals with bound water or with movable fluids.