The Importance of Ecological Accommodation Space and Sediment Supply for Cold-Water Coral Mound Formation, a Case Study From the Western Mediterranean Sea

The formation of cold-water coral (CWC) mounds is commonly seen as being the result of the sustained growth of framework-forming CWCs and the concurrent supply and deposition of terrigenous sediments under energetic hydrodynamic conditions. Yet only a limited number of studies investigated the complex interplay of the various hydrodynamic, sedimentological and biological processes involved in mound formation, which, however, focused on the environmental conditions promoting coral growth. Therefore, we are still lacking an in-depth understanding of the processes allowing the on-mound deposition of hemipelagic sediments, which contribute to two thirds of coral mound deposits. To investigate these processes over geological time and to evaluate their contribution to coral mound formation, we reconstructed changes in sediment transport and deposition by comparing sedimentological parameters (grain-size distribution, sediment composition, accumulation rates) of two sediment cores collected from a Mediterranean coral mound and the adjacent seafloor (off-mound). Our results showed that under a turbulent hydrodynamic regime promoting coral growth during the Early Holocene, the deposition of fine siliciclastic sediments shifted from the open seafloor to the coral mounds. This led to a high average mound aggradation rate of >130 cm kyr–1, while sedimentation rates in the adjacent off-mound area at the same time did not exceed 10 cm kyr–1. Thereby, the baffling of suspended sediments by the coral framework and their deposition within the ecological accommodation space provided by the corals seem to be key processes for mound formation. Although, it is commonly accepted that these processes play important roles in various sedimentary environments, our study provided for the first time, core-based empirical data proving the efficiency of these processes in coral mound environment. In addition, our approach to compare the grain-size distribution of the siliciclastic sediments deposited concurrently on a coral mound and on the adjacent seafloor allowed us to investigate the integrated influence of coral mound morphology and coral framework on the mound formation process. Based on these results, this study provides the first conceptual model for coral mound formation by applying sequence stratigraphic concepts, which highlights the interplay of the coral-framework baffling capacity, coral-derived ecological accommodation space and sediment supply.

Introduction to the volume, and definition and use of the term ‘tectono-sedimentary element’

The present volume is rooted in a map of sedimentary successions of the Arctic Region by Grantz et al. (2011), and contains a brief, but comprehensive compilation of geological and geophysical data characterizing all significant sedimentary successions in the Arctic, which cover 57% of the polar area north of 64°N. Two main goals have been designated: (i) to provide, based on the present-day knowledge and data, a characterization of all Arctic sedimentary successions (or sedimentary accumulations), and (ii) to supply a snapshot of hydrocarbon-related exploration in the Arctic at the end of the second decade of this millennium. To achieve these goals, we represent sedimentary successions as consisting of one or several “Tectono-Sedimentary Elements” (TSE). This concept allows delineation, mapping, and characterization of 9 categories of TSEs based of main tectonic regimes that formed accommodation space.A TSE characterization template has been developed as an efficient method of organising and presenting the most important information about stratigraphy, structure, and petroleum geology of a TSE, including most significant exploration facts. This organizational architecture is the backbone of the volume and is a key feature that distinguishes it from other similar works about the sedimentary basins.

Forward Stratigraphic Modeling of Kuwait Formation, Linking Facies Architecture to Hydrocarbon Occurrence

The objective of this study is to perform forward stratigraphic modeling on the Kuwait Formation (also known as Kuwait Group) exposed stratigraphic succession along the Jal Az-Zor escarpment to explain the enigmatic occurrence of an elongated NW-SE geobody mapped from subsurface data at northern Kuwait. Outcrop measurements such as; stratigraphic successions, facies distribution, critical facies trends, and paleocurrent analysis have been collected along the 60 km length of the Jal Az-Zor escarpment. Such measurements were combined with thin section lab analysis to reveal the various sedimentary processes such as wave activity, grain size distribution, sediment supply sources, accommodation space, and erosional rates. These measurements were combined with subsurface data such as seismic attributes to reconstruct the paleography of the area and run a forward stratigraphic model simulation. The vertical succession was also utilized to reconstruct the relative sea-level fluctuation through time to develop an accurate model. Forward stratigraphic modeling resulted in building a robust and reliable facies distribution 3D model for the Jal Az-Zor escarpment that demonstrates the complex facies architecture. The model shows the various stacking patterns of several depositional sequences that are observed in the field as well as the subsurface. The enigmatic geobody mapped from seismic as a channel system in previous publications turned out to be a paleoshoreline. This shoreline is composed of high-quality sands as a result of an elevated level of wave activity. Reworking of barrier island sands was also found to be responsible for the enhanced reservoir quality. Consequently, regardless of the subsurface structure, the main driver of successful hydrocarbon accumulation is directly linked to the NW-SE trending paleoshoreline. To the best of the authors’ knowledge, this is the first time forward-stratigraphic modeling is performed along the Jal Az-Zor escarpment in north Kuwait and using such an approach to unravel Kuwait Formation heavy hydrocarbon subsurface occurrences.

Significance in the Integration of Facies Analysis, Stable Isotopes and Diagenetical Results for the High-Resolution Sequence Stratigraphy Characterization in the Shallow Platform of Shuaiba Formation, Lower Cretaceous, Abu Dhabi Onshore, UAE

The study presents the sequence stratigraphy of the carbonate platform focused in lower part of Shuaiba Formation, as well as the organization of the arrangement formed by the cyclical sedimentological evolution at high-resolution scale, through the facies analysis, diagenetical imprints and finally, significance of stable carbonate isotope results in the building up of carbonate platform in southeast Abu Dhabi. Interpreted stratigraphic surfaces from integration of depositional facies reviewed in all available cored data within studied area and stable carbon isotope results allowed that four small-scale regression-transgression depositional cycles can be discriminated which are stacked into a medium-scale sequence, that may record a 600 kyr Milankovitch signal. The small-scale sequences were correlated within the studied area using both conventional well logs and stable isotope records. Transgression hemicycles represent the increasing of accommodation space and can be identified in direct evidence, such as 25-40 ft. thickness of lithocodium/bacinella floatstones and skeletal peloidal packstones facies, association of facies interpreted within upper slope sub-environment. Likewise, in δ13C profiles, the rise/fall turnarounds of small-scale sequences are marked by negative δ13C peaks and associated with characteristics patterns: (1) proportion decrease of shallower sub-environments facies is interpreted as an rising relative sea-level and (2) decreasing δ13C trends interpreted to be related to decreasing nutrient supply. The medium/big pores of floatstones poorly connected in packstone matrix are expressed in the medium/high porosity with low permeabilities. In contrast, regressive hemicycles represent the reduction in accommodation space and can be characterized in direct evidence, such as the growing up of persistent 10-20 ft. thickness with thousands of meters of correlation of stromatoporoids and rudist facies, association of facies interpreted within shelf-margin complex sub-environment. In addition, the fall/rise turnarounds are marked by positive δ13C peaks, associated with the stromatoporoids/rudists mounds with characteristic patterns: (1) proportion increase of shallower sub-environments facies is interpreted as falling relative sea-level and increase in proximity and (2) increasing δ13C values interpreted to reflect increasing nutrient supply. Unusually very high permeability is attributed to the present of fractures and dissolution events that is enhanced where proportion of stromatoporoids facies are more pronounced. The described characterization resulted in the identification of genetic cycles that reproduce the sedimentological evolution, which are presented in small-scale sequences. In addition, the δ13C values enabled to understand the internal organization and the development of the carbonate building up in the Shuaiba shallow platform evolution. This study provides update and understanding on sedimentary facies, depositional pattern, and expands on previous published works, using new approach from semi-regional to local scales. Finally, results help to understand the laterally extensive water break-through thin intervals, which are directly related to the regressive hemicycles described previously.

Regional Tectonics to Basin Fill Architecture from Aptian Shuaiba Fm to Miocene Fars Gp of Abu Dhabi

Objectives/Scope Aptian (Shuaiba-Bab) and Cenomanian (Mishrif-Shilaif) intra-shelf basins were extensively studied with their genesis focused on environmental/climatic disturbances (Vahrenkamp et al., 2015a). Additionally, local tectonic events can also affect the physiography of these basins, especially the Cenomanian intra-shelf basin subjected to NE compressional regime. As this ongoing regime increased at Late-Cretaceous and Miocene, it led to more tectonic-driven basin physiography. This paper investigates the areal extent, interaction, and commonalities between the extensional Aptian intra-shelf basin, compressional Late-Cretaceous intra-shelf basin, Late-Cretaceous-Paleogene foreland basin, and Late Oligocene-Miocene salt basin. Methods, Procedures, Process To understand the genesis, driving forces, and distribution of these basins, we used a combination of several large-scale stratigraphic well correlations and seismic, together with age dating, cores, and extensive well information (ADNOC proprietary internal reports). The methodology used this data for detailed mapping of 11 relevant time stratigraphic intervals, placing the mapped architecture in the context of the global eustatic sea level and major geodynamic events of the Arabian Plate. Results, Observations, Conclusions Aptian basin took place as a consequence of environmental/climatic disturbances (Vahrenkamp et al., 2015a). However, environmental factors alone cannot explain isolated carbonate build-ups on salt-related structures at the intra-shelf basin, offshore Abu Dhabi. Subsequently, the emplacement of thrust sheets of Tethyan rocks from NE, and following ophiolite obduction (Searle et al., 1990; Searle, 2007; Searle and Ali, 2009; Searle et al., 2014), established a compressional regime in the Albian?-Cenomanian. This induced tectonic features such as: loading-erosion on eastern Abu Dhabi, isolated carbonate build-ups, and reactivation of a N-S deep-rooted fault (possibly a continuation of Precambrian Amad basement ridge from KSA). This N-S feature was probably the main factor contributing the basin axis change from E-W Aptian trend to N-S position at Cenomanian. Further compression continued into the Coniacian-Santonian, leading to a nascent foreland basin. This compression established a foredeep in eastern Abu Dhabi, separated by a bulge from the northern extension of the eastern Rub’ Al-Khali basin (Ghurab syncline) (Patton and O'Connor, 1988). Numerous paleostructures were developed onshore Abu Dhabi, together with several small patch-reefs on offshore salt growing structures. Campanian exhibits maximum structuration associated to eastern transpression related to Masirah ophiolite obduction during India drift (Johnson et al., 2005, Filbrandt et al., 2006; Gaina et al., 2015). This caused more differentiation of the foredeep, onshore synclines, and northern paleostructures, which continued to cease through Maastrichtian. From Paleocene to Late-Eocene, paleostructure growth intensity continued decreasing and foreland basin hydrological restriction began with the Neotethys closure. Through Oligocene until Burdigalian this situation continued, where the Neotethys closed with the Zagros Orogeny (Sharland et al., 2001), causing a new environmental/climatic disturbances period. These disturbances prevented the continued progradation of the carbonate factory into the foredeep, leading to conspicuous platform-basin differentiation. Additionally, the Zagros orogeny tilted the plate northeastward, dismantling the paleostructures generated at Late-Cenomanian. Finally, during an arid climate in the Burdigalian to Middle-Miocene, the confined Neogene sea filled the foredeep accommodation space with massive evaporites. Novel/Additive Information Little has been published about the outline and architecture of these basins in Abu Dhabi and the detailed circumstances that led to their genesis using subsurface information.

New Insights on the Lower Lekhwair Formation offshore Abu Dhabi: Understanding the Key Role of Lithocodium/bacinella Floatstones on Large Scale Reservoir Quality Variations

The Lower Cretaceous Lekhwair Formation is one of the most prolific oil reservoirs in onshore and offshore UAE, yet the available literature on this interval remains limited. Based on a recent study carried out in collaboration with ADNOC Offshore, the present paper provides new insights into the comprehension of the interplay between primary depositional and secondary diagenetic controls on the reservoir performance, which is of crucial importance for the refinement of the static and dynamic models. In offshore Abu Dhabi, the Lower Lekhwair Formation is characterised by an alternation of relatively thick argillaceous (dense zones) and clean limestones (reservoir zones). Reservoir zones consist of basal, low to moderate energy inner ramp deposits, grading upward into thick inner and mid-ramp sediments. Lithocodium/Bacinella is the volumetrically dominant skeletal allochem and can form m-thick, stacked floatstone units. Such Lithocodium/Bacinella-rich floatstones are interpreted to originate from a mid-ramp depositional setting as a result of an increase in the accommodation space. By contrast, the contribution of Lithocodium/Bacinella floatstones is significantly reduced in inner ramp settings where these tend to form cm- to dm-scale, laterally discontinuous interbeds. The combination of sedimentological findings with diagenetic data provided an enhanced understanding of the origin and variations of the reservoir quality across the Lower Lekhwair Formation. In more detail, the best reservoir quality occurs within poorly cemented, Lithocodium/Bacinella-rich floatstones with grain-supported matrices, which favoured the preservation of a macropore-dominated pore system allowing an effective fluid flow. By contrast, the mud-supported textures with only rare and localised occurrence of mm- to cm-scale Lithocodium/Bacinella clumps, present the poorest reservoir quality due to the isolated nature of the macropores and the relatively tight micrite matrix surrounding them. At the large scale, the Lower Lekhwair shows an upward increase in reservoir quality, consistently with the upward increase in abundance and thickness of the Lithocodium/Bacinella-rich floatstones. The integration of depositional features with diagenetic overprint in the Lower Lekhwair Formation shows the fundamental role played by Lithocodium/Bacinella-rich floatstones with grain-supported matrices on the reservoir quality distribution. The impact of the Lithocodium/Bacinella floatstone matrices on the reservoir performance was never investigated before and hence represents an element of innovation and a powerful tool to predict the distribution of the areas hosting the best reservoir properties.

Flexural strike-slip basins

Strike-slip faults are classically associated with pull-apart basins where continental crust is thinned between two laterally offset fault segments. We propose a subsidence mechanism to explain the formation of a new type of basin where no substantial segment offset or syn-strike-slip thinning is observed. Such “flexural strike-slip basins” form due to a sediment load creating accommodation space by bending the lithosphere. We use a two-way coupling between the geodynamic code ASPECT and surface-processes code FastScape to show that flexural strike-slip basins emerge if sediment is deposited on thin lithosphere close to a strike-slip fault. These conditions were met at the Andaman Basin Central fault (Andaman Sea, Indian Ocean), where seismic reflection data provide evidence of a laterally extensive flexural basin with a depocenter located parallel to the strike-slip fault trace.

Air Contaminants in an Underwater Vehicle Cabin During Navigation

The purpose of this study is to study the air contaminants in the cabins of underwater vehicle. The basic data help for the better research of the underwater vehicle cabin environment standard and the control strategy. Pretreatment and analysis method of volatile organic compounds was preconcentration combined with gas chromatography under the condition of liquid nitrogen and detected by chromatography-mass spectrometry. The pollution of particles, carbon monoxide and carbon dioxide during the underwater vehicle voyage were monitored by online monitoring instrument. Altogether 34 kinds of pollution components were detected, most of which were low in concentration. Some are low olfactory threshold or high toxic components, such as dimethyldisulfide, benzene, carbon disulfide, trichloromethane, and several reached to ppm level. The contamination of the particles was mainly fine particles and part cabins exceeded the national standard of indoor air quality. The highest concentration of carbon dioxide in accommodation space exceeded the permissible concentration of atmosphere composition aboard diesel underwater vehicle compartments. The increase submerged time made the environment in the cabins deteriorate. The concentration of trace contaminants may close to or beyond the relevant standards with the prolonged time. The volatile organic compounds, particles, carbon monoxide and carbon dioxide aggravated the air circumstance in the cabins. It should be determined the permissible concentration of air contaminants in underwater vehicle as soon as possible.

Estuarine morphodynamics and development modified by floodplain formation

Rivers and estuaries are flanked by floodplains built by mud and vegetation. Floodplains affect channel dynamics and the overall system's pattern through apparent cohesion in the channel banks and through filling of accommodation space and hydraulic resistance. For rivers, effects of mud, vegetation and the combination are thought to stabilise the banks and narrow the channel. However, the thinness of mudflats and salt marsh in estuaries compared to channel depth raises questions about the effects of floodplain as constraints on estuary dimensions. To test these effects, we created three estuaries in a tidal flume: one with mud, one with recruitment events of two live vegetation species and a control with neither. Both mud and vegetation reduced channel migration and bank erosion and stabilised channels and bars. Effects of vegetation include local flow velocity reduction and concentration of flow into the channels, while flow velocities remained higher over mudflats. On the other hand, the lower reach of the muddy estuary showed more reduced channel migration than the vegetated estuary. The main system-wide effect of mudflats and salt marsh is to reduce the tidal prism over time from upstream to downstream. The landward reach of the estuary narrows and fills progressively, particularly for the muddy estuary, which effectively shortens the tidally influenced reach and also reduces the tidal energy in the seaward reach and mouth area.