geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...

, tectonostratigraphy is stratigraphy that refers either to rock sequences in which large-scale layering is caused by the stacking of thrust sheets, or

nappe In geology, a nappe or thrust sheet is a large sheetlike body of rock that has been moved more than or above a thrust fault from its original position. Nappes form in compressional tectonic settings like continental collision zones or on the o ...

s, in areas of

thrust tectonics Thrust tectonics or contractional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the shortening and thickening of the crust or lithosphere. It is one of the three main types of tectonic regime, ...

or to the effects of tectonics on

lithostratigraphy Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous ...

Tectonically formed stratigraphy

One example of such a tectonostratigraphy is the

Scandinavian Caledonides The Scandinavian Caledonides are the vestiges of an ancient, today deeply eroded orogenic belt formed during the Silurian–Devonian continental collision of Baltica and Laurentia, which is referred to as the Scandian phase of the Caledonian or ...

. Within the entire exposed 1800 km length of this

orogenic belt An orogenic belt, or orogen, is a zone of Earth's crust affected by orogeny. An orogenic belt develops when a continental plate crumples and is uplifted to form one or more mountain ranges; this involves a series of geological processes collec ...

the following sequence is recognised from the base upwards: * Autochthon : undisturbed foreland of the Baltic plate * Parautochthon : thrust sheets that have moved only a short distance (up to 10s of km) from their original position * Lower

allochthon upright=1.6, Schematic overview of a thrust system. The hanging wall block is (when it has reasonable proportions) called a nappe. If an erosional hole is created in the nappe that is called a window (geology)">window. A klippe is a solitary out ...

: far travelled thrust sheets derived from the Baltic plate

passive margin A passive margin is the transition between oceanic and continental lithosphere that is not an active plate margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere. Continental rifting cre ...

, mainly sediments associated with the break-up of Rodinia * Middle allochthon : also derived from the margin of the Baltic plate, Proterozoic basement and its psammitic cover * Upper allochthon : thrust sheets including

island arc Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle alon ...

and ophiolitic sequences * Uppermost allochthon : thrust sheets containing sediments with fossil assemblages indicating an origin on the margin of the Laurentian plate This vertically stacked sequence thus represents the passive margins of Baltica and Laurentia and intervening island arcs and back-arc basins telescoped together and emplaced on top of the Baltic Shield, involving hundreds of km of shortening. Within this overall stratigraphy the individual layers have their own tectonostratigraphy of stacked thrust sheets.

Effects of active tectonics on lithostratigraphy

Tectonic events are typically recorded in sediments being deposited at the same time. In the case of a

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

, for instance, the sedimentary sequence is normally broken down into three parts:Jackson, C A L ,Gawthorpe, R L, Leppard, C W , Sharp, I R 2006. Rift-initiation development of normal fault blocks: insights from the Hammam Faraun fault block, Suez Rift, Egypt. Journal of the Geological Society, 163, 165–18

/ref> * The ''pre-rift'' includes a sequence deposited before the onset of rifting, recognised by the lack of thickness and sedimentary Facies (geology), facies changes across the rift faults. * The ''syn-rift'' includes a sequence deposited during active rifting, typically showing facies and thickness changes across the

active fault An active fault is a fault that is likely to become the source of another earthquake sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,0 ...

unconformities An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

on the fault footwalls may pass laterally into continuous conformable sequences in the hanging walls. * The ''post-rift'' includes a sequence deposited after the rifting has finished, it may still show thickness and facies changes around the rift faults due to the effects of differential compaction and remnant rift topography, particularly in the earliest part of the sequence. This relatively straightforward nomenclature may become difficult to use, however, in the case of multiphase rifting with the post-rift from one event being the pre-rift to a later event.

References

{{reflist Stratigraphy Tectonics

Tectonically formed stratigraphy

Effects of active tectonics on lithostratigraphy

See also

References