Dense shelf water cascading and Messinian Canyons: A new scenario for the Mediterranean salinity crisis

Abstract

The salt giant beneath the deep Mediterranean seafloor is the impressive record of the “Messinian salinity crisis,” a dramatic event that occurred about 6Ma ago following the reduction of the connections with the Atlantic Ocean. According to the shallow-water deep-basin model, developed for these deposits (Hsu¨ and others, 1973a, 1973b, 1978a, 1978b), the Messinian evaporites formed in a deep but desiccated Mediterranean, while shelves and slopes underwent subaerial erosion due to fluvial rejuvenation triggered by a 1500 m sea level drawdown. Deeply incised Messinian canyons in the continental slopes surrounding the Mediterranean are the main argument supporting this scenario. Using a state of the art model and idealized but realistic numerical simulations, here we demonstrate that the activation of downslope flows of hypersaline, dense waters, in a process similar to present-day “dense shelf water cascading,” but much more energetic, may account for both slope erosion and progressive salinity rise leading to the formation of deep-seated supersaturated brines. Our findings support a deep-water deep-basin model (Schmalz, 1969, 1991; De Benedetti, 1976, 1982; Dietz and Woodhouse, 1988), thus implying that evaporite deposition may have occurred in a non-desiccated basin with strongly reduced ocean connections

A deep palaeovalley in the floor of Polish Carpathian Foredeep Basin near Pilzno and its control on Badenian (Middle Miocene) evaporite facies

“…Only the deep-wa ter sce narios of evaporite de po si tion (cf. e.g., Roveri et al, 2014;Lugli et al, 2015) in the palaeo valley seem thus to be ac cept able in our case, in line with the sea level drop not ex ceed ing 100 m in the Carpathian Foredeep dur ing the Badenian sa lin ity cri sis assessed by other au thors from re gion ally more com pre hen sive stud ies (Oszczypko, 1998;B¹bel, 2004;Peryt, 2006;Bukowski, 2011). The deep -wa ter sce nar ios are, more over, ca pa ble of com bin ing si mul ta neous shal low-wa ter evaporite de po si tion on the pla teaux and sed i men ta tion in deep-wa ter con di tions on the palaeovalley floor.…”

“…In gen eral, as re gards the palaeovalleys in Po land, no at tempts have been made to as cribe their or i gin fully to ma rine pro cesses, in con trast to some hy poth e ses put for ward to ex plain the sce nario of the Messinian sa lin ity cri sis (cf. e.g., Roveri et al, 2014;Lugli et al, 2015). This at ti tude seems to be cor rect, tak ing into ac count the im por tant con trasts be tween the geo log i cal set tings of the Med i ter ra nean and the Carpathian Foredeep: a deep ma rine ba sin, partly un der lain by oce anic crust and con tain ing no ar eas ex pected to be much uplifted prior to and dur ing the sa line de po si tion in the for mer case, com pared with an orogenic foredeep ba sin rest ing en tirely on con ti nen tal crust and un der go ing more or less sub stan ti ated and sig nif i cant ver ti cal mo tions due to the con ti nen tal-scale end-Cre ta ceous compressional event, to flex ural bend ing of the Carpathian fore land loaded with the orogenic wedge and to an ex pected sub se quent iso static re bound in the lat ter case.…”

“…1.5 km due to evap o ra tion in an iso lated ma rine ba sin, lead ing to subaerial ex po sure of the ba sin slopes and shelves and to local ised deep flu vial in ci sion. Al ter na tive mod els of "deep-wa ter deep-ba sin" (DWDB; Schmalz, 1969Schmalz, , 1991De Benedetti, 1982;Dietz and Woodhouse, 1988) do not re quire sea level fall and as sume a submerged po si tion of eroded ba sin slopes dur ing per sis tent sea level highstand con di tions, while re fer ring to such mech a nisms of sub aque ous ero sion, can yon in ci sion and sed i ment trans port in can yons, as tur bid ity cur rents, storms, hyperpycnal flows from river floods, ma rine sa line underflows and dense shelf water cas cad ing (Lugli et al, 2013;Roveri et al, 2014 and ref erences therein).…”

The Roussillon Basin (S. France): A case-study to distinguish local and regional events between 6 and 3 Ma

“…For example, Roveri et al (2009) acknowledged a clearly demarcated inland (necessarily subaerial) MES in the peripheral Sorbas Basin. On the contrary, the same authors defended a submarine MES in the entire Mediterranean Basin but restricted to the continental slope, thereby denying its fluvial origin (Roveri et al, 2014b). However, the development of the MES during the peak of the MSC is generally widely accepted (see for example: CIESM, 2008; Roveri et al, 2014a) because it has been observed all around the Mediterranean Basin .…”

The Messinian salinity crisis: open problems and possible implications for Mediterranean petroleum systems

“…However, the 'shallow-water deep-basin' model (SWDB: Hsü et al 1973), with its highamplitude sea-level oscillations (>1500 m) up to its desiccation, is the current MSC paradigm (Roveri & Manzi 2006;Roveri et al 2014c). This model is usually considered as a fact, with obvious implications in many related fields including hydrocarbon exploration, but such a view could lead to possible misinterpretation.…”