Two-decked nature of the Ouachita Mountains, Arkansas

Article Abstract:

Two structural decks make up the Ouachita Mountains of Arkansas and Oklahoma. Tight to isoclinal multiple folding and low-grade metamorphism characterize the lower deck, while open folds make up the upper deck. Fold shortening in the former is estimated to be five times that of the latter. Tight folding gives way to broad folding in the Mississippian Stanley Group, due to disharmonic folding of a ductile deck underneath a stiff one. The structural differences resulted from the deposition of younger deformed foreland-basin strata over an older deck stacked in an accretionary wedge.

Geology, Stratigraphic, Stratigraphy, Rock deformation, Mountains, Ouachita Mountains

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Abiological origin of described stromatolites older than 3.2 Ga: comment and reply

Article Abstract:

The pseudocolumnar stromatolite-like structures found in the North Pole disproves the allegations that biogenic stromatolites did not exist in rocks older than 3.2 Ga. The structures, which also prove the existence of life during the Archean age, were not created through precipitation and deformation. The origin of conical stromatolite-like structures, however, may have been influenced by biological and evaporative occurences. Furthermore, geological biogenicity criteria are not very accurate in determining the biogenic features of ancient rocks.

Stromatolites, Rocks

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Structure of the Variscan belt beneath the British and Armorican overstep sequences

Article Abstract:

The opening and closure of the "Lizard ocean" between France and England is clarified by seismic, gravity and magnetic data on the buried Variscan belt. The belt is composed of a mobile and thick crust between the Midlands block, the Armorican block, and a detached northern block formerly associated with the latter. Late Carboniferous frontal collision between the two blocks produced a narrowing of the belt and the ejection of structural wedges. The data also sheds light on Precambrian terrane structure and distribution.

England

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