TY - JOUR A1 - Christ, Nicolas A1 - Immenhauser, Adrian A1 - Amour, Frederic A1 - Mutti, Maria A1 - Tomas, Sara A1 - Agar, Susan M. A1 - Alway, Robert A1 - Kabiri, Lahcen T1 - Characterization and interpretation of discontinuity surfaces in a Jurassic ramp setting (High Atlas, Morocco) JF - Sedimentology : the journal of the International Association of Sedimentologists N2 - Discontinuity surfaces are widely recognized but often poorly understood features of epeiric carbonate settings. In sedimentary systems, these features often represent hiatus surfaces below biostratigraphic resolution and may represent a considerable portion of the time contained in the sediment record. From an applied perspective, discontinuities may represent horizontal flow barriers and result in reservoir compartmentalization. Here, a total of 80 condensed surfaces (S1), firmgrounds (S2) and hardgrounds (S3) from a Jurassic (Middle and Upper Bajocian Assoul Formation) ramp setting of the High Atlas in Morocco are carefully documented with respect to their morphology, their secondary impregnation by Fe and Mn oxides and phosphates and their palaeoecological record. A statistical frequency distribution of two surfaces of the S1 type, 1.1 surfaces of the S2 type and 0.4 surfaces of the S3 type per 10 section metres is observed along a 220 m long carbonate succession. Based on two stratigraphically and spatially separated study windows and correlative sections, the stratigraphic frequency distribution, the lateral extent and the nature of facies change across discontinuities are documented in a quantitative manner. Specific features of the study site include the considerable stratigraphic thickness of the Assoul Formation and the conspicuous absence of subaerial-exposure-related features. Based on the data presented here, firmground and hardground surfaces are best interpreted as maximum-regression-related features. Relative sea-level lowstand results in a lowered wave base, and wave orbitals and currents result in sea floor omission and lithification. Care must be taken to avoid overly simplistic interpretations, as differences in bathymetry and carbonate facies result in marked changes in discontinuity characteristics in proximal-distal transects. The data shown here are of significance for those concerned with the interpretation of shoal water carbonate environments and are instrumental in the building of more realistic carbonate reservoir flow models. KW - Atlas Mountains KW - carbonate ramp KW - discontinuity surfaces KW - hardgrounds KW - hydrodynamic level KW - Jurassic KW - palaeoecology KW - relative sea-level Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-3091.2011.01251.x SN - 0037-0746 VL - 59 IS - 1 SP - 249 EP - 290 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Amour, Frederic A1 - Mutti, Maria A1 - Christ, Nicolas A1 - Immenhauser, Adrian A1 - Benson, Gregory S. A1 - Agar, Susan M. A1 - Tomas, Sara A1 - Kabiri, Lahcen T1 - Outcrop analog for an oolitic carbonate ramp reservoir a scale-dependent geologic modeling approach based on stratigraphic hierarchy JF - AAPG bulletin N2 - Considerable effort has been devoted to the development of simulation algorithms for facies modeling, whereas a discussion of how to combine those techniques has not existed. The integration of multiple geologic data into a three-dimensional model, which requires the combination of simulation techniques, is yet a current challenge for reservoir modeling. This article presents a thought process that guides the acquisition and modeling of geologic data at various scales. Our work is based on outcrop data collected from a Jurassic carbonate ramp located in the High Atlas mountain range of Morocco. The study window is 1 km (0.6 mi) wide and 100 m (328.1 ft) thick. We describe and model the spatial and hierarchical arrangement of carbonate bodies spanning from largest to smallest: (1) stacking pattern of high-frequency depositional sequences, (2) facies association, and (3) lithofacies. Five sequence boundaries were modeled using differential global position system mapping and light detection and ranging data. The surface-based model shows a low-angle profile with modest paleotopographic relief at the inner-to-middle ramp transition. Facies associations were populated using truncated Gaussian simulation to preserve ordered trends between the inner, middle, and outer ramps. At the lithofacies scale, field observations and statistical analysis show a mosaiclike distribution that was simulated using a fully stochastic approach with sequential indicator simulation. This study observes that the use of one single simulation technique is unlikely to correctly model the natural patterns and variability of carbonate rocks. The selection and implementation of different techniques customized for each level of the stratigraphic hierarchy will provide the essential computing flexibility to model carbonate settings. This study demonstrates that a scale-dependent modeling approach should be a common procedure when building subsurface and outcrop models. Y1 - 2013 U6 - https://doi.org/10.1306/10231212039 SN - 0149-1423 VL - 97 IS - 5 SP - 845 EP - 871 PB - American Association of Petroleum Geologists CY - Tulsa ER - TY - JOUR A1 - Tomas, Sara A1 - Homann, Martin A1 - Mutti, Maria A1 - Amour, Frederic A1 - Christ, Nicolas A1 - Immenhauser, Adrian A1 - Agar, Susan M. A1 - Kabiri, Lahcen T1 - Alternation of microbial mounds and ooid shoals (Middle Jurasssic, Morocco) - response to paleoenvironmental changes JF - Sedimentary geology : international journal of applied and regional sedimentology N2 - The occurrence of neritic microbial carbonates is often related to ecological refuges, where grazers and other competitors are reduced by environmental conditions, or to post-extinction events (e.g. in the Late Devonian, Early Triassic). Here, we present evidence for Middle Jurassic (Bajocian) microbial mounds formed in the normal marine, shallow neritic setting of an inner, ramp system from the High Atlas of Morocco. The microbial mounds are embedded in cross-bedded oolitic facies. Individual mounds show low relief domal geometries (up to 3 m high and 4.5 m across), but occasionally a second generation of mounds exhibits tabular geometries (<1 m high). The domes are circular in plan view and have intact tops, lacking evidence of current influence on mound preferred growth direction or distribution patterns, or truncation. The mound fades consists almost entirely of non-laminated, micritic thrombolites with branching morphologies and fine-grained, clotted and peloidal fabrics. Normal marine biota are present but infrequent. Several lines of evidence document that microbial mound growth alternates with time intervals of active ooid shoal deposition. This notion is of general significance when compared with modern Bahamian microbialites that co-exist with active sub-aquatic dunes. Furthermore, the lack of detailed studies of Middle Jurassic, normal marine shallow neritic microbial mounds adds a strong motivation for the present study. Specifically, Bajocian mounds formed on a firmground substratum during transgressive phases under condensed sedimentation. Furthermore, a transient increase in nutrient supply in the prevailing mesotrophic setting, as suggested by the heterotrophic-dominated biota, may have controlled microbial mound stages. KW - Microbial mounds KW - Thrombolites KW - Ooid shoals KW - Paleoenvironment KW - Jurassic Y1 - 2013 U6 - https://doi.org/10.1016/j.sedgeo.2013.05.008 SN - 0037-0738 VL - 294 SP - 68 EP - 82 PB - Elsevier CY - Amsterdam ER -