The possibility of commercial natural gas production from gas hydrates has been tested by researchers and industry for more than ten years. Depressurisation of gas hydrates in porous and permeable sandstones has successfully produced water and natural gas. However long term sustainable production is still elusive. Catastrophic sand production into the wellbore has terminated at least three of the significant depressurisation trials including the 2013 trial at the Daini-Atsumi knoll, Nankai Trough, offshore Japan. Sand production is generally thought to be the result of mechanical and hydrodynamic instability, however it appears the failure mechanism is not the same for all reservoirs and the location of reservoir porosity and pressure on the normal compression line for sands could be a controlling factor. Sand production in reservoirs at shallow depths and low confining stresses (less than 10 MPa) are likely to be influenced by fluid flow effects like those described by the Shields (1936) diagram. The relative density of the formation may also affect the nature of the sand production in these reservoirs. The Daini-Atsumi knoll is a structural high on the outer ridge of the Kumano forearc basin, offshore Japan. Hydrate saturations of 50 to 80 % occur within three geological units of the Middle Pleistocene Ogasa group. This group is made up of deep water sediments including sediment gravity flow deposits distinguished by alternating silt and sand layers. The presence of these alternating layers could have influenced the sand production seen during the trial. This reservoir heterogeneity at the 2013 Daini-Atsumi knoll gas hydrate production trial site was characterised using the descriptions of geological units, analogues and statistical techniques. Scenarios of this heterogeneity were tested in a high pressure plane-strain sand production apparatus. The results of these tests suggest the boundary shear stress of the fluid on the grains is a significant control on sand production for the Daini-Atsumi Knoll reservoir and the layering and grainsize structure of the sediments encourages sand production. Relative density of the sediments appears to impact the nature of the sand production where denser sediments show more localised movement. These results indicate that even minor weaknesses in sand control devices will result in uncontrollable sand production rates from the Daini-Atsumi Knoll gas hydrate reservoir. Managing the fluid flow rate in the reservoir and selectively completing coarser grained zones at the base of sand layers could help limit sand production in future trials.

O Campo de Miranga, localizado no Compartimento Central da Bacia do Recôncavo, é um importante produtor de óleo e gás. As rochas reservatório portadoras de hidrocarbonetos aqui apresentadas constituem-se de corpos arenosos gerados por fluxos gravitacionais subaquosos intercalados por folhelhos e pertencem a Formação Maracangalha (depositada no Cretáceo Inferior). Com a descrição de 775 m de testemunhos, definiu-se 8 fácies deposicionais e 6 deformacionais para o intervalo estudado. O agrupamento de fácies em conjuntos que apresentam feições estruturais e genéticas similares permitiu a proposição de Associações de Fácies cujas interpretações são: AF1 - lobos turbidíticos distais; AF2 - canais e/ou lobos turbidíticos arenosos; AF3 - franjas de sistemas turbidíticos conglomeráticos; AF4 - deslizamentos ou regiões proximais de escorregamentos; AF5 - porções mais deformadas de corpos de deslizamentos a escorregamentos; AF6 - escorregamentos altamente móveis, plásticos a fluxos de detritos. Foi definido um datum na porção intermediária da formação constituído por uma espessa seção pelítica. Depósitos distais da AF6 dominam a porção basal do intervalo estudado e são sucedidos verticalmente (em direção ao datum) por intercalações entre turbiditos (AF2) e escorregamentos (AF5). Imediatamente acima do datum ocorrem níveis conglomeráticos (AF3) que são sucedidos verticalmente por um domínio onde se intercalam deslizamentos (AF4), escorregamentos (AF5) e turbiditos (AF2), definindose uma grande sucessão progradacional para a Formação Maracangalha na área estudada. O disparo desses fluxos provavelmente associa-se a movimentação de falhas durante estágio sin-rifte responsáveis por intensa sismicidade e remobilização de frentes deltaicas. Um mecanismo auxiliar associa-se ao intenso diapirismo argilocinético. A conectividade lateral rastreada em seções sísmicas é baixa e os melhores reservatórios do campo são os representantes da AF4 e AF2. Por critérios preditivos é possível determinar os intervalos mais propícios para a ocorrência desses corpos. / The Miranga Field, which is located in the Central Compartment of Reconcavo Basin, is an important oil and gas producer. The bearing hydrocarbon reservoirs presented here are composed of sand bodies generated by subaqueous gravity flows inserted between shales, belonging to the Maracangalha Formation (deposited during the Lower Cretaceous). Through the description of 775 m well cores, 8 depositional and 6 deformational facies were defined for the interval studied. These facies were grouped together according to structural and genetic characteristics making it possible to define Facies Associations with the following interpretations: AF1 - distal portions of turbidite lobes; AF2 - channels and/or sandy turbidite lobes; AF3 - borders of conglomeratic turbidite systems; AF4 - slides or proximal parts of slumps; AF5 - distal portions of the slides bodies or slumps; AF6 - highly mobile slumps to debris flows. A datum was chosen in the middle portion of Maracangalha Formation which consists of thick layer of shale. Distal deposits (AF6) dominate the basal portion of interval studied and they are succeeded vertically (toward to the datum) by layers interbedded between turbidites (AF2) and slump deposits (AF5). Immediately above the datum, conglomeratic intervals (AF3) occur and they are succeeded vertically by layers interbedded between slides (AF4), slumps (AF5) and turbidites (AF2), defining a great progradational succession to Maracangalha Formation in the studied area. Trigger mechanisms responsible for the genesis of gravitational flows are probably associated with faults activities during the syn-rift stage which led to intense seismic activity and caused the destabilization of sediments in delta fronts. An alternative cause for triggering may have been intense diapiric shale movements. The lateral connectivity traced in seismic sections is low and the sand bodies that should constitute the best reservoirs in this field belong to AF4 and AF2 categories. It is possible to determine the most favorable intervals for the occurrence of these sand bodies using predictive criteria.

O Campo de Miranga, localizado no Compartimento Central da Bacia do Recôncavo, é um importante produtor de óleo e gás. As rochas reservatório portadoras de hidrocarbonetos aqui apresentadas constituem-se de corpos arenosos gerados por fluxos gravitacionais subaquosos intercalados por folhelhos e pertencem a Formação Maracangalha (depositada no Cretáceo Inferior). Com a descrição de 775 m de testemunhos, definiu-se 8 fácies deposicionais e 6 deformacionais para o intervalo estudado. O agrupamento de fácies em conjuntos que apresentam feições estruturais e genéticas similares permitiu a proposição de Associações de Fácies cujas interpretações são: AF1 - lobos turbidíticos distais; AF2 - canais e/ou lobos turbidíticos arenosos; AF3 - franjas de sistemas turbidíticos conglomeráticos; AF4 - deslizamentos ou regiões proximais de escorregamentos; AF5 - porções mais deformadas de corpos de deslizamentos a escorregamentos; AF6 - escorregamentos altamente móveis, plásticos a fluxos de detritos. Foi definido um datum na porção intermediária da formação constituído por uma espessa seção pelítica. Depósitos distais da AF6 dominam a porção basal do intervalo estudado e são sucedidos verticalmente (em direção ao datum) por intercalações entre turbiditos (AF2) e escorregamentos (AF5). Imediatamente acima do datum ocorrem níveis conglomeráticos (AF3) que são sucedidos verticalmente por um domínio onde se intercalam deslizamentos (AF4), escorregamentos (AF5) e turbiditos (AF2), definindose uma grande sucessão progradacional para a Formação Maracangalha na área estudada. O disparo desses fluxos provavelmente associa-se a movimentação de falhas durante estágio sin-rifte responsáveis por intensa sismicidade e remobilização de frentes deltaicas. Um mecanismo auxiliar associa-se ao intenso diapirismo argilocinético. A conectividade lateral rastreada em seções sísmicas é baixa e os melhores reservatórios do campo são os representantes da AF4 e AF2. Por critérios preditivos é possível determinar os intervalos mais propícios para a ocorrência desses corpos. / The Miranga Field, which is located in the Central Compartment of Reconcavo Basin, is an important oil and gas producer. The bearing hydrocarbon reservoirs presented here are composed of sand bodies generated by subaqueous gravity flows inserted between shales, belonging to the Maracangalha Formation (deposited during the Lower Cretaceous). Through the description of 775 m well cores, 8 depositional and 6 deformational facies were defined for the interval studied. These facies were grouped together according to structural and genetic characteristics making it possible to define Facies Associations with the following interpretations: AF1 - distal portions of turbidite lobes; AF2 - channels and/or sandy turbidite lobes; AF3 - borders of conglomeratic turbidite systems; AF4 - slides or proximal parts of slumps; AF5 - distal portions of the slides bodies or slumps; AF6 - highly mobile slumps to debris flows. A datum was chosen in the middle portion of Maracangalha Formation which consists of thick layer of shale. Distal deposits (AF6) dominate the basal portion of interval studied and they are succeeded vertically (toward to the datum) by layers interbedded between turbidites (AF2) and slump deposits (AF5). Immediately above the datum, conglomeratic intervals (AF3) occur and they are succeeded vertically by layers interbedded between slides (AF4), slumps (AF5) and turbidites (AF2), defining a great progradational succession to Maracangalha Formation in the studied area. Trigger mechanisms responsible for the genesis of gravitational flows are probably associated with faults activities during the syn-rift stage which led to intense seismic activity and caused the destabilization of sediments in delta fronts. An alternative cause for triggering may have been intense diapiric shale movements. The lateral connectivity traced in seismic sections is low and the sand bodies that should constitute the best reservoirs in this field belong to AF4 and AF2 categories. It is possible to determine the most favorable intervals for the occurrence of these sand bodies using predictive criteria.

O Campo de Miranga, localizado no Compartimento Central da Bacia do Recôncavo, é um importante produtor de óleo e gás. As rochas reservatório portadoras de hidrocarbonetos aqui apresentadas constituem-se de corpos arenosos gerados por fluxos gravitacionais subaquosos intercalados por folhelhos e pertencem a Formação Maracangalha (depositada no Cretáceo Inferior). Com a descrição de 775 m de testemunhos, definiu-se 8 fácies deposicionais e 6 deformacionais para o intervalo estudado. O agrupamento de fácies em conjuntos que apresentam feições estruturais e genéticas similares permitiu a proposição de Associações de Fácies cujas interpretações são: AF1 - lobos turbidíticos distais; AF2 - canais e/ou lobos turbidíticos arenosos; AF3 - franjas de sistemas turbidíticos conglomeráticos; AF4 - deslizamentos ou regiões proximais de escorregamentos; AF5 - porções mais deformadas de corpos de deslizamentos a escorregamentos; AF6 - escorregamentos altamente móveis, plásticos a fluxos de detritos. Foi definido um datum na porção intermediária da formação constituído por uma espessa seção pelítica. Depósitos distais da AF6 dominam a porção basal do intervalo estudado e são sucedidos verticalmente (em direção ao datum) por intercalações entre turbiditos (AF2) e escorregamentos (AF5). Imediatamente acima do datum ocorrem níveis conglomeráticos (AF3) que são sucedidos verticalmente por um domínio onde se intercalam deslizamentos (AF4), escorregamentos (AF5) e turbiditos (AF2), definindose uma grande sucessão progradacional para a Formação Maracangalha na área estudada. O disparo desses fluxos provavelmente associa-se a movimentação de falhas durante estágio sin-rifte responsáveis por intensa sismicidade e remobilização de frentes deltaicas. Um mecanismo auxiliar associa-se ao intenso diapirismo argilocinético. A conectividade lateral rastreada em seções sísmicas é baixa e os melhores reservatórios do campo são os representantes da AF4 e AF2. Por critérios preditivos é possível determinar os intervalos mais propícios para a ocorrência desses corpos. / The Miranga Field, which is located in the Central Compartment of Reconcavo Basin, is an important oil and gas producer. The bearing hydrocarbon reservoirs presented here are composed of sand bodies generated by subaqueous gravity flows inserted between shales, belonging to the Maracangalha Formation (deposited during the Lower Cretaceous). Through the description of 775 m well cores, 8 depositional and 6 deformational facies were defined for the interval studied. These facies were grouped together according to structural and genetic characteristics making it possible to define Facies Associations with the following interpretations: AF1 - distal portions of turbidite lobes; AF2 - channels and/or sandy turbidite lobes; AF3 - borders of conglomeratic turbidite systems; AF4 - slides or proximal parts of slumps; AF5 - distal portions of the slides bodies or slumps; AF6 - highly mobile slumps to debris flows. A datum was chosen in the middle portion of Maracangalha Formation which consists of thick layer of shale. Distal deposits (AF6) dominate the basal portion of interval studied and they are succeeded vertically (toward to the datum) by layers interbedded between turbidites (AF2) and slump deposits (AF5). Immediately above the datum, conglomeratic intervals (AF3) occur and they are succeeded vertically by layers interbedded between slides (AF4), slumps (AF5) and turbidites (AF2), defining a great progradational succession to Maracangalha Formation in the studied area. Trigger mechanisms responsible for the genesis of gravitational flows are probably associated with faults activities during the syn-rift stage which led to intense seismic activity and caused the destabilization of sediments in delta fronts. An alternative cause for triggering may have been intense diapiric shale movements. The lateral connectivity traced in seismic sections is low and the sand bodies that should constitute the best reservoirs in this field belong to AF4 and AF2 categories. It is possible to determine the most favorable intervals for the occurrence of these sand bodies using predictive criteria.

L’intérêt scientifique porté depuis plusieurs décennies au développement des plateformes carbonatées tropicales s’explique par la complexité des facteurs de contrôle de la sédimentation, qui montre une influence de la tectonique, du climat, de l’eustatisme, de l’hydrodynamisme etc… Les plateformes carbonatées ne sont pas seulement des environnements enclins à accumuler des sédiments, mais sont aussi de prolifiques « usines » à carbonates qui produisent davantage que ce qu’elles peuvent stocker. Les sédiments en excès sont transférés vers le bassin profond. Ainsi, les transitions plateforme – bassin illustrent les interactions entre production carbonatée in-situ, transfert, et accumulation sédimentaire issue de la re-sédimentation. Dans le sud-ouest de l’Albanie, la série carbonatée du Crétacé Supérieur est composée de dépôts sédimentaire de plateforme et de bassin. Ces successions sont à présent intégrées dans le système chevauchant de la chaîne Dinarides - Hellénides, dont la mise en place est contemporaine d’une phase de déformation orogénique Plio-Holocène. La paléogéographie de la région péri-Adriatique au Crétacé Supérieur révèle une juxtaposition de méga-plateformes et de bassins adjacents dont le remplissage est en partie conditionné par la remobilisation gravitaire des sédiments de la bordure de plateforme. Les investigations sont menées sur cinq zones d’étude. Elles intègrent des descriptions faciologiques macro- et microscopiques pour chacune des huit successions étudiées. Les unités définies font l’objet d’une cartographie à l’échelle de la zone d’étude qui précise l’architecture stratigraphique du système. La datation des dépôts repose sur une étude biostratigraphique, elle est renforcée par les données chronostratigraphiques des isotopes du strontium. Sur la plateforme, les descriptions faciologiques sont appuyées par des méthodes complémentaires de pétrographie (cathodoluminescence, épifluorescence, microscopie électronique à balayage), de pétrophysique (porosimétrie à injection mercure) et de géochimie (isotopes stables du carbone et de l’oxygène) visant à révéler la dynamique de sédimentation et les propriétés réservoir de la succession.Les conditions de sédimentation sont précisées, i) sur la plateforme, dix faciès spécifiques sont identifiés, représentatifs de contidions de dépôt supra-, inter-, et subtidales. Ils s’intègrent dans des motifs d’empilement distinctifs (small-scale sequences) qui attestent le caractère cyclique de la sédimentation, contrôlé par des fluctuations haute-fréquence et basse amplitude du niveau marin relatif; ii) dans le bassin, quatorze faciès sont classés suivant le mécanisme de transport sédimentaire dominant. La répartition spatiale des dépôts permet d’identifier la provenance et les sources préférentielles du matériel calci-clastique. L’évolution tectono-sédimentaire plateforme – bassin au Crétacé Supérieur est déterminée par deux séquences: i) du Cénomanien au Turonien, la sédimentation de plateforme est caractérisée par l’aggradation plus de 700 mètres de faciès intertidaux organisés en séquences (small-scale sequences) émersives ou sub-émersives. Aucun transfert significatif n’est attesté dans le bassin adjacent, témoignant d’une relative stabilité du système évoluant dans un contexte subsident ; ii) l’intervalle Coniacien – Santonien marque l’installation d’une plateforme à rudistes favorable au transfert sédimentaire. Ce dernier se traduit par une progradation marquée des dépôts gravitaires dans le bassin pendant le Campanien. Cette dynamique de transfert est accentuée par la mise en place de slumps résultants du démantèlement tectonique de la bordure de plateforme au Campanien Supérieur et Maastrichtien. / The evolution of tropical carbonate platforms depends on complex interacting factors influencing the sedimentation, such as tectonism, climate, eustacy, hydrodynamism etc… Due to this complexity, it has been of scientific interest for decades. Carbonate platforms are not only prone to accumulate sediments, but also represent prolific carbonates “factories” producing more than they can store on their tops. Excess sediments are shed basinward. Platform-to-basin transitions exemplify interactions between in-situ carbonate production, transfer and sedimentary accumulations resulting from re-sedimentation. In south-west Albania, the Upper Cretaceous carbonate series are made up of platform and basinal deposits. Sedimentary successions are presently integrated in the Dinarides-Hellenides fold-and thrust belt that originate from a Plio-Holocene phase of the Alpine Orogeny. The paleogeographic setting during the Late Cretaceous reveals a juxtaposition of mega-platforms and adjacent basins, partly filled with sediments derived from the shelf edge. Our scientific investigations focused on five study areas. Macro- and microfacies descriptions are provided for eight platform and basin successions. Sedimentary units are defined and mapped on each study area, supporting the stratigraphic reconstruction of the system. Dating is based on biostratigraphy and supported by strontium-isotope data. Regarding platform deposits, facies descriptions are seconded by complementary methods of petrography (cathodoluminescence, epifluorescence, scanning electron microscopy), petrophysics (mercury intrusion porosimetry), and geochemistry (stable carbon and oxygen isotopes), aiming to precise the sedimentation dynamics and reservoir properties of the succession. The sedimentation conditions are specified: i) within the platform, ten specific facies are identified, precising the depositional setting that comprise supra-, inter- and subtidal environments. These facies are integrated in distinctive stacking patterns (small-scale-sequences) pointing to a cyclic sedimentary dynamic controlled by high-frequency and low-amplitude sea level changes; ii) the basinal deposits comprise fourteen facies classified according to the dominant grain-support mechanism. Spatial distribution of the deposits allowed identifying the provenance and preferential sources of calciclatic sediments. The tectono-sedimentary evolution of the platform-to-basin system during the Late Cretaceous can be subdivided into two sequences: i) from the Cenomanian to the Turonian, the platform sedimentation is characterized by a substantial aggradation (700 meters) of intertidal small-scale sequences. No significant transfer was evidenced in the adjacent Ionian Basin, pointing to stable conditions in a subsiding context; ii) the Coniacian-Santonian interval evidences the establishment of a rudist platform massively shedding sediments basinward during the Campanian. A clear progradation of gravity-flow deposits is attested during this period. During the Upper Campanian and Maastrichtian, this transfer is accentuated by the setting of tectonically-triggered slumps resulting from the dismantling of the platform edge.

A basin analysis was conducted at the Conway Flat coast (Marlborough Fault Zone, South Island, New Zealand) to investigate the interaction of regional and local structure in a transpressional plate boundary and its control on basin formation. A multi-tiered approach has been employed involving: (i) detailed analysis of sedimentary deposits; (ii) geomorphic mapping of terraces, fault traces and lineaments; (iii) dating of deposits by 14C and OSL and (iv) the integration of data to form a basin-synthesis in a sequence stratigraphy framework. A complex thrust fault zone (the Hawkswood Thrust Fault Zone), originating at the hinge of the thrust-cored Hawkswood anticline, is interpreted to be a result of west-dipping thrust faults joining at depth with the Hundalee Fault and propagating eastwards. The faults uplift and dissect alluvial fans to form terraces along the Conway Flat coast that provide the necessary relief to form the fan deltas. These terrace/fan surfaces are ~9 km long and ~3 km wide, composite features, with their upper parts representing sub-aerial alluvial fans. These grade into delta plains of Quaternary Gilbert-style fan deltas. Uplift and incision have created excellent 3D views of the underlying Gilbert-style fan delta complexes from topsets to prodelta deposits. Erosive contacts between the Medina, Rafa, Ngaroma and modern Conway fan delta deposits, coupled with changes in terrace elevations allow an understanding of the development of multiple inset terraces along the Conway Flat coast. These terraces are divided into five stages of evolution based on variations in sedimentary facies and geomorphic mapping: Stage I involves the uplift of the Hawkswood Range and subsequent increased sedimentation rate such that alluvial fans prograded to the sea to form the Medina fan delta Terrace. Stage II began with a period of incision, from lowering sea level or changes in the uplift and sedimentation rate and continued with the deposition of the Dawn and Upham fan deltas. Stage III starts with the incision of the Rafa Terrace and deposition of aggradational terraces in the upper reaches. Stage IV initiated by a period of incision followed by deposition of estuarine facies at ~8ka and Stage V began with a period of incision and continues today with the infilling of the incised valley by the modern fan delta of the Conway River and its continued progradation. New dates from within the Gilbert-type fan deltas along the Conway Flat coast are presented, using OSL and 14C dating techniques. Faulting at the Conway Flat coast began ~ 94 ka, based on the development of the Medina Terrace fan delta with uplift rates ~1.38~1.42 m/ka. The interplay of tectonics and sea level fluctuations continued as the ~79 ka Rafa Terrace fan deltas were created, with uplift rates calculated at ~1.39 m/ka. Detailed 14C ages from paleoforest (~8.4-~6.4 ka) in the Ngaroma Terrace and from the mouths of smaller streams have established uplift rates during the Holocene ~1-3 m/ka, depending on sea level.

La mer Ionienne est une zone à la géodynamique active en raison de la convergence entre les plaques Nubie et Eurasie. Elle correspond aux derniers stades de vie d’un océan, la Téthys. De ce fait, la tectonique et la sédimentation y sont très réduites ; et les faibles flux sédimentaires permettent ainsi d’enregistrer une multiplicité de processus sédimentaires.Néanmoins, c’est une zone encore peu étudiée d’un point de vue sédimentaire, notamment sur les échelles de temps de l’ordre de la centaine de milliers d’années. Ce travail est basé sur une étude sédimentologique d’archives marines complétée par des données acoustiques (bathymétrie et multi-faisceau) issue de campagnes océanographiques du SHOM. L’analyse détaillée des faciès et des séquences sédimentaire a permis, dans un premier temps, d’établir un calendrier des risques naturels (séismes, tsunamis, volcanisme), leurs sources et leurs processus de dépôt dans le bassin pour les derniers 330 000 ans. Puis, dans un second temps, de retracer l’évolution sur les derniers 400 000 ans de la circulation et de l’oxygénation des eaux de fond dans le bassin ionien et l’influence du détroit de Sicile, et notamment de la plate-forme de Malte, sur les échanges entre les bassins occidental et oriental. L’intégration des données sédimentologiques dans un modèle géoacoustique développé par le SHOM a finalement permis de déterminer l’impact des variations sédimentaires (distribution spatiale, lithologie, stratification) sur la propagation des ondes acoustique pour différentes gammes de fréquences (300 Hz - 3000 Hz) et d’angle d’incidence (0 -90°) et d’établir une cartographie de la réponse sédimentaire du le signal acoustique. / The Ionian Sea is an active geodynamic area because of the convergence between theNubia and the Eurasia plate. It corresponds to the last stage of the Tethys ocean life. Therefore,the tectonics and the sedimentation are much reduced; and the low sedimentary supply enables torecord a multiplicity of sedimentary processes. Nevertheless, this area still poorly studied from asedimentary point of view, in particular on timescales on the order of hundred thousand years.This work is based on a sedimentological study of marine archives supplemented by acoustic data(bathymetry and multibeam imagery) recovered during oceanographic campaign leaded by theSHOM. The detailed sedimentary analysis of facies and sequences allows, at first, to established acalendar of the natural hazard (earthquakes, tsunamis, volcanism), their origins and theirdepositional processes into the basin over the last 330 000 years. Then, secondly, to reconstructthe evolution over the last 400 000 years of the circulation and the oxygenation of bottom waterthrough the Ionian basin and the influence of the strait of Sicily, in particular of the Malta Plateau,on the exchanges between the western and the eastern basins. The integration of thesedimentological data in a geoacoustic modelling developed by the SHOM finally allowed todetermine the impact of the sedimentary variability (special distribution, lithology, stratification)on the acoustic waves propagation for various frequency bands (300 Hz - 3000 Hz) and incidentangle (0 - 90°) and to established a mapping of the sedimentary answer of the acoustic signal.