No abstract

No abstract

Αβστραχτ: Μανψ mασσ τρανσπορτ χοmπλεξεσ (ΜΤΧσ) χονταιν υπ το κιλοmετρε−σχαλε (mεγα)χλαστσ ενχασεδ ιν α δεβριτιχ mατριξ. Αλτηουγη mανψ mεγαχλαστσ αρε σουρχεδ φροm ηεαδωαλλ αρεασ, τηε ιρρεγυλαρ βασαλ σηεαρ συρφαχεσ οφ mανψ ΜΤΧσ ινδιχατεσ mεγαχλαστ εντραινmεντ δυρινγ τηε πασσαγε οφ φλοωσ ιντο τηε δεεπερ βασιν ισ αλσο χοmmον. Ηοωεϖερ, τηε mεχηανισmσ ρεσπονσιβλε φορ εντραινmεντ οφ λαργε βλοχκσ οφ συβστρατε, ανδ τηειρ ινφλυενχε ον τηε λονγιτυδιναλ βεηαϖιουρ οφ τηειρ ασσοχιατεδ φλοωσ, ηαϖε νοτ βεεν ωιδελψ χονσιδερεδ. Wε ηερε πρεσεντ εξαmπλεσ οφ mεγαχλαστσ φροm εξηυmεδ ΜΤΧσ (Νευθυν Βασιν, Αργεντινα, ανδ Καροο Βασιν, Σουτη Αφριχα) ανδ ΜΤΧσ ιmαγεδ ιν 3D σεισmιχ ρεφλεχτιον δατα (Μαγδαλενα Φαν, οφφσηορε Χολοmβια ανδ Σαντοσ Βασιν, οφφσηορε Βραζιλ) το ινϖεστιγατε τηεσε προχεσσ−προδυχτ ιντεραχτιονσ. Wε σηοω τηατ ηιγηλψ σηεαρεδ βασαλ συρφαχεσ αρε ωελλ−δεϖελοπεδ ιν δισταλ λοχατιονσ, σοmετιmεσ εξτενδινγ βεψονδ τηειρ ασσοχιατεδ δεποσιτ. Τηισ ποιντσ το δεφορmατιον ανδ ωεακενινγ οφ τηε συβστρατε αηεαδ οφ τηε φλοω, συγγεστινγ πρεχονδιτιονινγ οφ τηε συβστρατε βψ διστριβυτεδ σηεαρ αηεαδ οφ, ανδ το τηε σιδε οφ, α mασσ φλοω χουλδ ρεσυλτ ιν εντραινmεντ οφ λαργε φραγmεντσ. Αν ιmπροϖεδ υνδερστανδινγ οφ τηε ιντεραχτιονσ βετωεεν φλοω εϖολυτιον, σεαβεδ τοπογραπηψ, ανδ εντραινmεντ ανδ αβρασιον οφ mεγαχλαστσ ωιλλ ηελπ το ρεφινε εστιmατεσ οφ ρυνουτ διστανχεσ, ανδ τηερεφορε γεοηαζαρδ ποτεντιαλ, οφ συβmαρινε λανδσλιδεσ.

Although the effects of interactions between turbidity currents and the seabed have been widely studied, the roles of substrate and bathymetry on the emplacement of mass-transport complexes (MTCs) remain poorly constrained. This study investigates the effect of bathymetric variability and substrate heterogeneity on the distribution, morphology, and internal characteristics of nine MTCs imaged within a 3D seismic volume in the southern Magdalena Fan, offshore Colombia. The MTCs overlie substrate units composed mainly of channel-levee-complex sets, with subsidiary deposits of MTCs. MTC dispersal was influenced by tectonic relief, associated with a thinskinned , deep-water fold-and-thrust belt, and by depositional relief, associated with the underlying channel-levee-complex sets; it was the former that exerted the first-order control on the location of mass-transport pathways. Channel-levee-complex sets channelized, diverted, or blocked mass flows, with the style of response largely controlled by their orientation with respect to the direction of the incoming flow and by the height of the levees with respect to flow thickness. MTC erosion can be relatively deep above channel-fill deposits, whereas more subtle erosional morphologies are observed above adjacent levee units. In the largest MTC, the distribution of the seismic facies is well imaged, being influenced by the underlying bathymetry, with internal horizontal contraction occurring updip of bathymetric highs, erosion and bypass predominating above higher gradient slopes, and increased disaggregation characterizing the margins. Hence, bathymetric irregularities and substrate heterogeneity together influence the pathways, geometries, and internal characteristics of MTCs, which could in turn influence flow rheology, runout distances, the presence and continuity of underlying reservoirs, and the capacity of MTCs to act as either hydrocarbon seals or reservoirs.

Mass wasting is an important process in the degradation of deep‐water fold‐and‐thrust belts. However, the relationship between mass‐transport complex (MTC) emplacement and the timing and spatial progression of contractional deformation of the seabed have not been extensively studied. This study uses high‐quality, 3D seismic reflection data from the southern Magdalena Fan, offshore Colombia to investigate how the growth of a deep‐water fold‐and‐thrust belt (the southern Sinú fold belt) is recorded in the source, distribution and size of MTCs. More than nine distinct, but coalesced MTCs overlie a major composite basal erosion surface. This surface formed by multiple syn‐ and post‐tectonic mass‐wasting events and is thus highly diachronous, thereby recording a protracted period of tectonism, seascape degradation and associated sedimentation. The size and source location of these MTCs changed through time: the oldest ‘detached’ MTCs are relatively small (over 9–100 km2 in area) and sourced from the flanks of growing anticlines, whereas the younger ‘shelf‐attached’ MTCs are considerably larger (more than 200–300 km2), are sourced from the shelf, and post‐date the main phase of active folding and thrusting. Changes in the source, distribution and size of MTCs are tied to the sequential nucleation, amplification and along‐strike propagation of individual structures, showing that MTCs can be used to constrain the timing and style of contractional deformation, and seascape evolution in time and space.