We use a secular representation to describe the long-term dynamics of transneptunian objects in mean-motion resonance with Neptune .
The model applied is thoroughly described in [ ] .
The parameter space is systematically explored , showing that the secular trajectories depend little on the resonance order .
High-amplitude oscillations of the perihelion distance are reported and localised in the space of the orbital parameters .
In particular , we show that a large perihelion distance is not a sufficient criterion to declare that an object is detached from the planets .
Such a mechanism , though , is found unable to explain the orbits of Sedna or 2012 \text { VP } _ { 113 } , which are insufficiently inclined ( considering their high perihelion distance ) to be possibly driven by such a resonant dynamics .
The secular representation highlights the existence of a high-perihelion accumulation zone due to resonances of type 1 : k with Neptune .
That region is found to be located roughly at a \in [ 100 ; 300 ] AU , q \in [ 50 ; 70 ] AU and I \in [ 30 ; 50 ] \degree .
In addition to the flux of objects directly coming from the Scattered Disc , numerical simulations show that the Oort Cloud is also a substantial source for such objects .
Naturally , as that mechanism relies on fragile captures in high-order resonances , our conclusions break down in the case of a significant external perturber .
The detection of such a reservoir could thus be an observational constraint to probe the external Solar System .