Mud Volcano

The salt waters from the Emilia-Romagna sector of the Northern Apennine Foredeep have been investigated using major and trace element and stable isotope (δ2H, δ18O, δ37Cl, δ81Br and 87Sr/86Sr ratio). Ca, Mg, Na, K, Sr, Li, B, I, Br and SO4 vs. Cl diagrams suggest the subaerial evaporation of seawater beyond gypsum and before halite precipitation as primary process to explain the brine’s salinity, whereas saline to brackish waters were formed by mixing of evaporated seawater and water of meteoric origin. A diagenetic end-member may be a third component for mud volcanoes and some brackish waters. Salinization by dissolution of (Triassic) evaporites has been detected only in samples from the Tuscan side of the Apennines and/or interacting with the Tuscan Nappe. In comparison with the seawater evaporation path, Ca–Sr enrichment and Na–K–Mg depletion of the foredeep waters reveal the presence of secondary processes such as dolomitization–chloritization, zeolitization–albitization and illitization. Sulfate concentration, formerly buffered by gypsum-anhydrite deposition, is heavily lowered by bacterial and locally by thermochemical reduction during burial diagenesis. From an isotopic point of view, data of the water molecule confirm mixing between seawater and meteoric end-members. Local 18O-shift up to +11‰ at Salsomaggiore is related to water–rock interaction at high temperature (≈150°C) as confirmed by chemical (Mg, Li, Ca distribution) and isotopic (SO4–H2O) geothermometers. 37Cl/35Cl and 81Br/79Br ratios corroborate the marine origin of the brines and evidence the diffusion of halogens from the deepest and most saline aquifers toward the surface. The 87Sr/86Sr ratio suggests a Miocene origin of Sr and rule out the hypothesis of a Triassic provenance of the dissolved components for the analyzed waters issuing from the Emilia-Romagna sector of the foredeep. Waters issuing from the Tuscan side of the Apennines and from the Marche sector of the foredeep show higher 87Sr/86Sr ratios because of the interaction with siliciclastic rocks.

Mud volcanoes are important conduits for deep fluids to migrate upward, providing an important window to study fluid/sediment interactions at depth in accretionary prisms. Fluids emitting from mud volcanoes in southern and eastern Taiwan were analyzed for dissolved chemical composition and B isotopes to delineate the sources and chemical alteration occurring during fluid migration. Concentrations of dissolved major elements (Cl, Na, K, Ca, Mg, and SO4) in most of the mud volcano fluids were lower than seawater concentrations, except for the high Ca samples in eastern Taiwan, which were probably affected by fluids/igneous rock interactions. The high concentrations of B, Ba, and Li in the mud volcano fluids are consistent with a scenario that involves intense sediment alteration and clay dehydration at depth. The reaction temperatures estimated using chemical thermometers fall within the range of 70–170 °C, with some variation by location. In nearby mud volcano sites, the concentration of dissolved major elements varied little, but the B stable isotope compositions varied by as much as 20‰, supporting the argument that dissolved B concentrations were over-printed with effects of sediment adsorption. This explains the occurrence of B enriched and heavy δ11B fluids at moderate depths in subduction zones. It is probable that the fluids in mud volcanoes in Taiwan originated from 2 to 5 km depth and are influenced by processes involving tectonic shortening, sediment alteration, and clay dehydration, and subsequent retrograde adsorption during fluid migration.► Large B enrichment with heavy d11B was detected in mud volcano fluids. ► d11B ratios are inversely correlated B concentrations in mud volcano fluids. ► Sedimentary B desorption at the fluid source region is crucial. ► Significant B re-adsorption has occurred during fluid migration.

The Florence Rise is a submarine feature extending from the island of Cyprus in the southeast to the Anaximander Mountains which form the northwestern end of the Cyprus Arc south of western Turkey. The eastern Florence Rise includes a topographic high near Cyprus while its central domain displays relatively low relief. Most of the major elements of relief appear to be bounded by faults, in the light of new geophysical data. An underlying ‘core’ ridge, likely made of pre-Pliocene nappes emplaced from the north, separates relatively undeformed sediments to the northeast from actively shearing sediments and seismic basement, to the southwest. A dextral arc-parallel wrench zone, at least 15 km wide, has created a lineated seafloor texture and accompanying flower structures within the central Florence Rise. Apparent Riedel type conjugate shears within this system cut across the Florence Rise and mark changes in the relief along the arc. Several mud volcanoes are observed within the wrench zone and along associated faults, indicating that overpressuring at depth is relieved by these faults. There is no evidence for any typical subduction along this arcuate trend, which is considered to act as the present boundary between the African and Anatolian–Aegean plates. In contrast, both the nature of faulting and the morphology of the Florence Rise seem to indicate some degree of transpressional coupling between the two plates, even though they appear disconnected by a tectonic boundary in the form of a major shear zone.

The first high-resolution mapping of mud volcanoes and mud domes of the Central Mediterranean Ridge (Eastern Mediterranean) presented here is based on successive in situ observations from the Nautile submersible [MEDINAUT (1998) and NAUTINIL (2003) surveys] and near-bottom side-scan sonar data (MEDINETH cruise, 1999). Data were obtained over two types of clay-kinetic-related features previously identified south of Crete: the Olimpi field mud volcanoes and the Southern belt mud domes, characterized by highly contrasting morpho-acoustic characteristics. Using the new data we can better define the morphological and backscatter characteristics of both mud volcanoes and mud domes and illustrate their similarities and differences; and establish ground truth, in terms of the presence or not of mud flows, diagenetic carbonate pavements, active seepage and macro-and microbiology. This study reveals strong contrasts between: (1) large mud volcanoes, made of successive mud flows, and associated with diagenetic carbonates and fluid venting activity, and (2) smaller mud domes, characterized by steep slopes affected by sedimentary instabilities, and without any evidence of mud flow, specific fluid seepage activity, authigenic carbonate pavement, or biologic communities. From these results we demonstrate a strong variability of clay-kinetic structures from the central domain of the Mediterranean Ridge accretionary complex to its northern thrust boundary against the Cretan continental backstop. From an integration of the high-resolution results to the Mediterranean Ridge geologic and structural settings, a qualitative model is finally proposed to explain the mud volcano and mud dome emplacement.

In order to collect adequate data for the evaluation of the soil liquefaction hazard during seismic events in Italy, a preliminary investigation was carried out aimed at identifying the phenomena that can be attributed to possible soil liquefaction associated with historical earthquakes. The more important works on historical seismicity were examined, mainly seismic catalogues and specific studies of the main earthquakes. The analysis of the data collected so far indicates that soil liquefaction is generally characterized by limited phenomena that occurred within the epicentral areas of events having intensity I ⩾ IX MCS at the site.

Based on a recent marine geophysical data set, including swath bathymetry, acoustic imagery and six-channel seismics, recorded over a large area of the Mediterranean Ridge (MR) in early 1998 during the Prismed 2 survey, this paper presents a study of the various relationships observed between tectonic features cutting across the Central Mediterranean Ridge accretionary wedge and massive mud expulsions (known as mud volcanoes), identified over large areas of the ridge.Regional mapping of two of the mud volcano fields previously only partly investigated (Olimpi and United Nations Rise) revealed the presence of many new mud expulsion centres and a third new mud volcano field has been identified. All the mud features show great variability in morphology, size and backscatter strength of their surrounding mud flows. Based on their contrasting morpho-acoustic characteristics, we propose a classification into three main groups of mud construction: (1) “mud volcanoes”, these consist of subcircular and prominent reliefs, often associated with high backscatter mud flows; (2) “mud domes”, similar to mud volcano, but smaller, these occurrences correspond to weakly reflective mud constructions; (3) “mud plateaus” represent a third category which appears as wide, often highly reflective and rather flat mud extrusions. From all available data, an attempt to explain the different mud ascent processes and driving forces is discussed, in relation to the initial collision structural setting of the Central Mediterranean Ridge. Within this area, most of the mud constructions have been observed to be associated with tectonic features and, in particular, with strike-slip faulting for the first time. As a hypothesis, we propose in this paper two different ascent processes to explain the contrasting mud constructions: (1) “extrusion” for the mud volcanoes and plateaus and (2) “intrusion” for the mud domes, connected to two different mud levels controlled by the crustal geometry of this pre-collision area and especially the southwards extension of the Cretan continental crust below the Mediterranean Ridge accreted sediments.

In order to understand gas hydrate related seafloor features in the near shore area off SW Taiwan, a deep-towed sidescan sonar and sub-bottom profiler survey was conducted in 2007. Three profiles of high-resolution sub-bottom profiler reveal the existence of five gas seeps (G96, GS1, GS2, GS3 and GS4) and one pockmark (PM) in the study area. Gas seeps and pockmark PM are shown in lines A and C, while no gas venting feature is observed along line B. This is the first time that a gas-hydrate related pockmark structure has been imaged off SW Taiwan. The relatively high backscatter intensity in our sidescan sonar images indicates the existence of authigenic carbonates or chemosynthetic communities on the seafloor. More than 2,000 seafloor photos obtained by a deep-towed camera (TowCam) system confirm the relatively high backscatter intensity of sidescan sonar images related to bacteria mats and authigenic carbonates formation at gas seep G96 and pockmark PM areas. Water column gas flares are observed in sidescan sonar images along lines A and C. Likewise, EK500 echo sounder images display the gas plumes above gas seep G96, pockmark PM and gas seep GS1; the gas plumes heights reach about 150, 100 and 20 m from seafloor, respectively. Based on multichannel seismic reflection (MCS) profiles, an anticline structure trending NNE-SSW is found beneath gas seep G96, pockmark PM and gas seep GS2. It implies that the gas venting features are related to the anticline structure. A thermal fluid may migrate from the anticline structure to the ridge crest, then rises up to the seafloor along faults or fissures. The seafloor characteristics indicate that the gas seep G96 area may be in a transitional stage from the first to second stage of a gas seep self-sealing process, while the pockmark PM area is from the second to final stage. In the pockmark PM area, gas venting is observed at eastern flank but not at the bottom while authigenic carbonates are present underneath the pockmark. It implies that the fluid migration pathways could have been clogged by carbonates at the bottom and the current pathway has shifted to the eastern flank of the pockmark during the gas seep self-sealing process.

Mud volcanoes distributed in the southern part of Taiwan are believed to be sourced from an accretionary prism located along the collision boundary between the Philippine Sea plate and the Asian Continental plate. Fluid and mud samples have been collected from Wushanting and Hsiaokunshui mud volcanoes during October 2004, March and June 2005, and analyzed for major ions, trace elements, and stable isotopes. The results show that the mud volcano fluids are enriched in Na+ and Cl− but are depleted in Ca2+ and Mg2+. The chemical composition and oxidation state of the fluids fluctuate seasonally, with ionic contents being notably higher during the dry pre-monsoon period. The enriched ionic (e.g., Na+, NH4+, K+, Mg2+ and Cl−) compositions of the exchangeable fractions indicate that the muds were sourced from a marine depositional environment. δD and δ18O values indicate that the mud volcano fluids may have been modified by chemical exchange with 18O-rich crustal rocks and possibly originated from mixing of deep brines with circulating meteoric water. The spatial and temporal distribution of ions in the muds suggests a varied mixing regime within the mud volcanoes. Incubation study of the muds shows the leaching of soluble salts under aerobic conditions, which is generally consistent with the fluid geochemical characteristics. Moreover, elevated trace element (e.g., As, Zn, Cu and Mn) concentrations are also observed in the fluids and muds. Geochemical correlations between As, Zn and Cu in the muds suggest prevailing SO4-reducing conditions at depth. The relatively low Eh values (range: −50 to −30 mV) of the fluids near the surface would favor bacterial Fe reduction and mobilization of As. The dewatering of mud volcanoes may represent a significant source of groundwater As in the nearby Chianan plain.

Submersible observations and seafloor mapping over areas of mud volcanism in the eastern Mediterranean Sea reveal an abundance of methane-rich fluid emissions, as well as specific seep-associated fauna (e.g. tubeworms, bivalves and chemosynthetic bacteria) and diagenetic deposits (i.e. carbonates crusts). Cold seeps characterized by abundant chemosynthetic bivalves, bacterial mats, and reduced sediments are the surface manifestations of present-day expulsion of methane-rich fluids, whereas massive carbonate crusts with clusters of tubeworms indicate long-term seeping that might be dormant at present. The surface characteristics of the mud flows (roughness of the surface, gas escape features, presence of hemipelagic dust, colonization by benthic fauna, development of carbonate crusts) present a high variability related to the intensity and age of seepage, and can be correlated to the observed backscatter variations. The repartition of the mud flows and active seeps is organized concentrically around the centre of the mud volcanoes and potential parasitic cones. Sidescan sonar backscatter patterns are thus indirectly related to spatial and temporal variation of mud volcanic activity.

The Neogene stratigraphic series is characterized by predominant clayey facies alternated by other sand layers. The outcrop and subsurface studies show varied and complex styles of deformations and lead to relate the structures to paleoseismic events. The seismicity of eastern onshore and offshore Tunisian margin follows the master fault corridors oriented globally N–S, E–W, and NW–SE that correspond to the bordering faults of grabens and syncline corridors and associated faulted drag fold structures oriented NE–SW. Epicenters of magnitudes between 3 and 5 are located along these border fault corridors. The Neogene strata record brittle structures, including numerous and deep faults and fractures with straight and high-angle dipping planes. The structuring of NE–SW en echelon folds and synclines inside and outside NW–SE and E–W right lateral and N–S and NE–SW left lateral tectonic corridors indicates the strike-slip type of bordering faults and their seismogenic nature. Wrench fault movements that induce mud and salt diapirs, mud volcanoes, and intrusive ascensions are related to seismic shocks. Seismic waves caused by activity along one, or most likely, several tectonic structures would have propagated throughout the Quaternary cover producing seismites. The similarity of deposits, structuring, and seismites between the Tunis-Bizerte to the North and Hammamet-Mahdia to the South accredits the hypothesis that the seismic episodes might have affected sedimentation patterns along the Sahalian large geographic area. The paleoseismic events in northeastern Tunisia might be related to tectonic fault reactivations through time. This hypothesis is consistent with the geomorphologic context of the study area, characterized by several morphostructural lineaments with strong control on the sediment distribution, as well as uplifted and subsiding terrains. The estimated magnitude of the seismic events and the great regional tectonically affected areas demonstrate that the northeastern Tunisia experienced stress through the last geological episodes of its evolution. This Neogene kinematic reconstruction highlights the neotectonic system inducing the actual seismicity on this margin. Therefore, there is a straight relationship between deepseated faults and seismicity. تتميز ستراتيغرافيا العهد النيوجيني (Neogene) بطبقات طينية سميكة تتخللها طبقات أخرى من الرمل. وتظهر الدراسات الميدانية و تحت سطح الأرض (جيوفيزيائية) أنماط متنوعة ومعقدة من التشوهات، تؤدي إلى ربطها بأحداث زلزالية قديمة. تبدو الزلازل في شرق البلاد قد اتبعت ممرات الصدوع الرئيسية والمتجهة عموما شمال-جنوب، شرق-غرب و شمال غرب-جنوب شرق توافقا مع الصدوع المتاخمة للهياكل المنخفضة و المقعرة (grabens) وما يرتبط بها من طيات ذات اتجاه شمال شرق-جنوب غرب. ويتراوح مركز الزلزال بين 3 و 5 درجات على مقياس ريشترRichter))، على امتداد ممرات الصدوع. تظهر طبقات النيوجين هياكل هشة تحتوي على صدوع عديدة وعميقة ذات زاويا مرتفعة. كما أن هيكلة الطيات و المنخفضات المتجهة شمال شرق-جنوب غرب داخل وخارج الممرات التكتونية ذات التحرك الجانبي الأيمن والمتجهة شمال غرب-جنوب شرق و شرق-غرب والأخرى ذات التحرك الجانبي اليساري والمتجهة شمال-جنوب و شمال شرق-جنوب غرب، تشير إلى نوعية الصدوع و طبيعة السيسموجينية (seismogenic) المرافقة لها. إن التحركات الجانبية للصدوع والتي رافقتها هياكل نتيجة تحركات و صعود الطين (mud diapirs) والملح (salt diapirs) والبراكين، قد ارتبطت بالصدمات الزلزالية. و يبدو أن الموجات الناجمة عن نشاط واحد أو العديد من الهياكل التكتونية قد انتشرت عبر طبقات العصر الرباعي منتجة بذالك العديد من السايسميت (seismites). إن تشابه الترسبات والهياكل و السايسميت بين جهتي تونس-بنزرت من الشمال والحمامات-المهدية من الجنوب، يدعم فرضية أن الحلقات الزلزالية قد أثرت على أنماط الترسيب على مساحة جغرافية واسعة من الساحل التونسي. تبدو الأحداث الزلزالية القديمة (paleoseismic events) في شمال شرق البلاد التونسية ذات صلة بعودة النشاط التكتونى للصدوع (tectonic fault reactivations) عبر الزمن. و تتلاءم هذه الفرضية مع الإطار الجيومورفولوجي (geomorphologic) لمنطقة الدراسة و الذي يتميز بعدة عناصر مورفو بنيوية (morphostructural) تتحكم في توزيع الرواسب والتضاريس المرتفعة و المنخفضة. إن حجم الأحداث الزلزالية وأهمية التكتونية الإقليمية تثبت أن شمال شرق البلاد التونسية قد تعرض لضغوط خلال الحلقات الجيولوجية الأخيرة من تطوره. وتبين نماذج التغير الديناميكي للعهد النيوجيني أهمية التكتونية الحديثة (neotectonic) في تحفيز الأحداث الزلزالية في الوقت الحالي. لذالك توجد علاقة مباشرة بين توزيع الصد وع العميقة و نوعيتها وتحركاتها عبر الزمن، و الأحداث الزلزالية المسجلة.

... 1). It extends for ca. 300 km and is characterized by a complex geological evolution entailing several phases of rifting, convergence, and strike-slip motions since the Triassic ([Srivastava et al., 1990], [Maldonado et al., 1999] and [Maldonado and Nelson, 1999]). ...