They are only likely to be effaced by igneous or high-grade metamorphic processes, or by erosion once they reach the surface. As with shallow and surface phenomena, anthroturbation fabrics will reach the surface if the crust is eroded following tectonic uplift. Uplift and denudation rates vary considerably, depending on the tectonic setting, but typically do not exceed a couple of millimetres a year (e.g. Abbott et al., 1997 and Schlunegger and Hinderer, 2002); structures a few kilometres

deep will not break the surface for millions to tens of millions of years. Structures on currently stable or descending crust may of course remain preserved below the surface for very much longer, or even permanently. The expression of deep mines and boreholes (particularly once they reach the surface, in

the far geological CCI-779 cell line future) will differ. PD98059 datasheet Mines – particularly those, such as coalmines that exploit stratabound minerals – will show stratigraphically-related patterns of occurrence. Thus, in each of many coal-fields, that today have substantial outcrops and subcrops in many parts of the world (Fig. 2 for the UK), there can be up to several tens of coal seams exploited to depths that may exceed a kilometre. Each of these seams, over that lateral and vertical extent, will be largely replaced by a horizon marked by little or no remnant coal, but considerable brecciation of adjacent strata (while fossilized examples of, say pit props or mining machinery (or the skeletons of pit ponies or even miners) might occasionally be encountered). In between these intensely worked units there will be thick successions of overlying and underlying strata that are effectively pristine, other than being penetrated in a few places by access shafts and exploration boreholes. Boreholes into present-day oilfields are abundant globally (the total length of oil

boreholes), the great majority drilled since the mid-20th century, has been estimated at 50 million km (J.P.M. Syvitski, personal communication), roughly equivalent to the 4��8C length of the present-day global road network or the distance from the Earth to Mars. For each human on Earth today there is thus a length of oil borehole of some seven metres – their share (on average) in the provision of the liquid energy that helps shape their lives. The density of boreholes in oilfields may be seen, for instance, in the map showing the 50,686 wells drilled to date in American waters of the Gulf of Mexico (see http://robslink.com/SAS/democd33/borehole.htm). Boreholes are structures that in reality penetrate long crustal successions. However, once exhumed in the far future, they may only rarely be encountered in typical rock exposures as lengths of (usually) vertical disruption at decimetre to metre scale in width.