Unconformity relative

The oldest profile (CBAC 215) was preserved beneath Paleocene lake sediments. The least weathered saprock in this profile (59 m beneath the unconformity) has a REE pattern very similar to North American shale composite (NASC). The light REE show marked relative depletion in the upper part of the profile and enrichment near the weathering front. Cerium shows marked enrichment at depth (Fig. 2). 

A third profile (BRAC 1) was examined beneath Late Miocene alluvial sands and ferruginous gravels. This profile is considered to be mid Cenozoic in age and has been partly eroded. The upper part of this profile below the unconformity has a similar REE pattern to NASC. Deeper in the profile there is relative enrichment in all the REE, but slightly more marked in the light REE (Fig. 4). 

Improved magnetotelluric methods have detected deep conductors and shallow alteration zones in the search for deep unconformity-related deposits (Farqu-harson Craven 2008). Clay-rich, quartz-corroded quartz-arenite has relatively low resistivity, whereas quartz-rich silicified zones are characterized by high resistivity. Although expensive, 3D seismic has been used to image details of basement topology and more favourable areas for drilling. 

Intermediate subsystem of burial-induced groundwater flow Lateral flow of groundwater is away from the depocentre and focussed along unconformities and through relatively permeable, sandy, silty and limestone units... 

There are only a few Archaean cratons which preserve late Archaean sedimentary basins, which are unconformable on the craton. These sedimentary basins are very different from greenstone belts, for they are not strongly deformed, nor do they have the elongate shape and the abundance of basalts frequently associated with greenstone belts. Basins of this type have previously been described as "late Archaean cover successions" (Nisbet, 1987). In the past, their relatively undeformed state has misled workers into thinking that they were Proterozoic, rather than Archaean in age,... 

The relatively small number of late Archaean basins may reflect a low preservation potential, but may also indicate that relatively few cratonic nuclei had stabilized before the end of the Archaean. Examples of late Archaean basins include the (3.1-2.7 Ga) Witwatersrand basin in South Africa (Robb Meyer, 1995), and its correlative the 3.0-2.67 Ga Pongola Supergroup in Swaziland (Walraven. Pape, 1994 Gold von Veh, 1995), both unconformable upon the Kaapvaal Craton. In western Australia the 2.77-2.71 Ga Fortescue Group is unconformable upon older Archaean rocks of the Pilbara Craton (Blake et al., 2004). 

The theoretical subsidence in various areas over time can be reconstituted with reference to the Hercynian unconformity taken for a zero level by adding successive layers of Mesozoic sedimentary layers. Since the Silurian source rocks (and, occasionally, the Devonian) closely underlie the Hercynian unconformity in the northern Sahara, the subsidence depth relative to the Hercynian surface (the bottom of a Triassic reservoir) is in fact the depth of source rock subsidence for a given area. 

An unconformity represents a break in the stratigraphical record and occurs when changes in the palaeogeographical conditions lead to a cessation of deposition for a period of time. Such a break may correspond to a relatively short interval of geological time or a very long one. An unconformity normally means that uplift and erosion have taken place, resulting in some previously formed strata being removed. The beds above and below the surface of unconformity are described as unconformable. 

The Tambaredjo field prodnces from the Paleocene age Saramacca formation. These coastal plain sandstones are locally identified as the T-unit and were deposited on top of a Cretaceous unconformity. The sands pinch out updip, south of the field, providing stratigraphic traps for the oil. The pilot area, located in the Tambaredjo field, has imdergone very little structural deformation and minimal diagenesis since the deposition of the Paleocene T-reservoirs consequently the sediments are relatively unconsolidated. This type of sedimentary processes of coastal plain deposition resnlted in reservoir compartmentalization, which is demonstrated by the pressure distribution along the area. 

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