Interrelations of mud volcanism, fluid venting, and thrust‐anticline folding: Examples from the external northern Apennines (Emilia‐Romagna, Italy)

Abstract

[1] The present work aims to provide an example of connection between fluid seepage and fault/fracture zones associated with compressional thrust folds. Surface fluid seepage along the Pede-Apennine margin consists of mud volcanism and methane-rich emissions showing an intimate link with thrust-related folds. Dominant gaseous or CH 4 -bearing fluid emissions characterize thrust fold settings in which fluid escape from the main reservoir and source rock (i.e., the Marnoso Arenacea flysch) is not impeded by a seal layer. Conversely, remarkable mud volcanism is closely linked to the presence of the impermeable Ligurian units sealing the Marnoso Arenacea reservoir. Structural analyses focused on selected thrust folds exhibiting clear relations between surface seepage and brittle elements associated with the fold. Various scenarios potentially explaining mud volcanism and venting over the crestal region of the thrust-related folds are discussed with respect to fluid pressure state and the development of second-order fault and fracture sets that are observed to control surface fluid expulsion. It is proposed that mud volcanism can be potentially triggered by first-order fault failure cycles during which the overpressured fluid is released during faulting events. Past anomalous eruptions associated with strong earthquakes seem to support this hypothesis. The relatively quiescent but continuous activity of the current Pede-Apennine mud volcanoes could instead reflect a short-lived leakage of overpressured fluids along permeable fractures/faults. Expansion of methane contained in the rising mud may assist this process fundamentally.

Geologic control of natural marine hydrocarbon seep emissions, Coal Oil Point seep field, California

“…This appears to demonstrate a correlation between seepage and the deformed nature of the Sisquoc and Monterey Formations, with steeper dips related to the strongest areas of seepage. This is consistent with the proposed model of Bonini (2007) that related seepage to fractures in regions of high curvature in folds (e.g., crests of anticlines).…”

“…Thus, simple geologic models-for example, based on fold curvature (Bonini 2007)-may adequately describe the seepage distribution only in part. The farthest offshore seeps are well predicted in some places, but in the southeast, these seeps are focused south away from the prominent South Ellwood Fault System and the underlying anticline crest.…”

“…Important controlling factors are tectonic; for example, mud volcanism most commonly is associated with compression settings (Kopf 2002). Foldand-thrust fault belts are a prominent setting for fluid migration from deeper layers through faults and fractures, allowing accumulation of hydrocarbons in anticlines and other traps (Bonini 2007). In some settings, geologic structures close to the seabed, such as authigenic carbonates (Boetius and Suess 2004) and low-permeability sediment (e.g., clay) layers (Naudts et al 2006), can be important factors controlling flux rates.…”

Origin and assessment of deep groundwater inflow in the Ca' Lita landslide using hydrochemistry and in situ monitoring

“…Analytical errors are in the order of ±0.2 T.U. -2007, Cremaschi (2008 found an average isotopic gradient of about −0.1 ‰ δ 18 O/100 m for the same area. This is in agreement with Longinelli et al (2006), which reported more depleted values of δ 18 O in precipitations over the Po Plain areas during years 2002, 2003 and 2004 which were characterised by high temperatures.…”

“…1a, b) affect the impermeable QM. These phenomena, which are widely observed along compressive margins around the world (Martinelli and Judd, 2004;Martinelli and Dadomo, 2005), consist of Na-Cl waters (up to 90 g l −1 ) flushing out particles of clay and entrapped connate water of the old Pliocene sea (Bonini, 2007). They originate from the buried QM-TU contact (located at a depth of more than 2000 m), whereas oilfield fluids start to rise up towards the surface following inverse faults.…”