Page 127 - Petrology of Sedimentary Rocks

deformation of Stille). Example: Appalachian welt during later
Paleozoic. Often caused by collision of tectonic plates, or
compression atop a subduction zone.

Dv, Vertical Deformation--block faulting, symmetrical folding, rocks
merely jostled without much squashing (“Germanotype” deforma-
tion of Stille). Example: Basin Range province, horsts and
grabens. Often caused by tensional movement accompanying
separation of crustal plates, or rifting within a single plate.

R, REJUVENATION* of source area; source region uplifted without differ-
ential deformation, little jostling or squashing takes place; source
lithology depends on past history. Transitional in “activity” between Q
and D. Common on neokraton, e.g., Gulf and Atlantic Coastal Plain
Tertiary.

X, EXTRUSIVE activity; volcanoes active during deposition of sediments,
may be independent of any other tectonics, may happen almost any
place at any time; thus associated with Dh,DVR, and sometimes even
Q. Probably most common in the island arc-subduction zone situation.

II. Paleogeology of the Source Area. There are four main divisions, namely G
(granite, gneiss, and in general plutonic igneous); M (metamorphic rocks,
schist to slate, metaquartzite); S (Sedimentary rocks, if dominantly a
carbonate terrane, can be specially designated Sc)i and X (extrusive,
volcanic rocks) whether contemporary or not. Volcanoes active at the time
of deposition of the beds in question would be shown DX.X/; erosion of old
volcanic rocks by R.X/, Dh.X/, etc. Subequal mixtures can be shown by GM,

MS, etc.; gradual changes during the unroofing of a region or burgeoning of
volcanism can be shown M - G, S -cX, etc. The rare basic plutonic source
can be designated B.

Ill. Tectonic framework of the depositional site. Krynine adopted the view that
thick prisms (p) were always associated with block-faulting (Dv); that sheet

sands (s) were always associated with Quiescent kratons (Qk); etc. It is
undoubtedly true that these are very common associations, and perhaps they
are the most common; but wemust realize that all sediments do not fit such
an ideal pattern, and should recognize existence of exceptions and not
mentally sweep them under the rug. For example, sands can be washed off a
stable kraton and accumulate in a violently subsiding neighboring trough. It
is difficult to make a logical classification of basins, but here is an attempt-
-suggestions welcome on improving it.

S Sheet or blanket, very thin and widespread

S” Sheet-wedge, basically a sheet covering a large area, but greatly
thickened at one side

b Basin, fairly equant shape, thin to moderately thick (e.g., Michi-
gan Basin)

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