Late Paleozoic strata along the Appalachians may consist of as many as 50 vertic
ID: 801619 • Letter: L
Question
Late Paleozoic strata along the Appalachians may consist of as many as 50 vertically stacked cyclotherms. Cyclotherms record a comparable number of sea-level cycles with an estimated average during approximately 100,000 to 400,000 years each. These strata were deposited when continent-continent collision (the Appalachian or Alleghenian orogeny) was building the Appalachian and Ouachita Mountains, and when large areas of the Gondwanaland were covered by extensive glaciation. Speculate on the possible mechanisms responsible for the short-term sea-level cycles recorded in the North American cyclotherms.
Explanation / Answer
The cyclothem of late Pennsylvanian period in North America record a widespread succesion of marine beds and the widespread overlying paleosol in the terrestrial beds. This is due to extensive marine transgression as well as regression taking place in the area.
The typical sequence of these cyclothems consists of thin transgressive limestone and thin offshore dark phosphatic shale at the bottom. This sequence was followed upwards by the thick regressive limestone and other nearshore terrestrial as well as marine detrital facies and paleosols. Cyclothems which are of intemediate scale lack the black shale facies whereas the minor scale cyclothems lack much differentiation of facies.
The formation of Gondwana glacial deposits during this time, Milankovich's earth orbital parameter which determine or control the variation of solar heating in mid latitude, glacial eustacy were mainly responsible for these short term sea level cycles recorded in these cyclothems rather than the orogenic movements.
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