lecture_15 - LECTURE 15 GLACIAL RECORD OF NORTH AMERICA...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
LECTURE 15 - GLACIAL RECORD OF NORTH AMERICA LATE TERTIARY GLACIATION Traces of Miocene and Pliocene glaciations occur in southern Alaska , mainly on the Seward Peninsula, in the Wrangell Mountains and the Upper Cook Inlet. Most striking record of Miocene glaciation is in the lower part of the Yakataga Formation consisting mainly of glaciomarine sediments and covering 30,000 km 2 in the Gulf of Alaska. Planktonic foraminifera have given ages of 5-6 million years. EARLY PLEISTOCENE GLACIATIONS Classical subdivision of North American Quaternary stratigraphy dates from 19th century and includes four cold stages and three warm stages . The cold stages were based on the occurrence of different tills and the warm stages on the occurrence of paleosols . In the 1960's the two oldest cold stages, Kansan and Nebraskan, were assumed to be younger than the Matuyama/Brunhes magnetic reversal and younger then the ‘Pearlette-Ash’ which originated from the Yellowstone region. It was found later that the ash really represented three different as falls, the ages of which were older than previously supposed. They were dated to about 600 ka (Pearlette O) 1.2 Ma (Pearlette S) and 2 Ma (Pearlette B) by K/Ar and 40Ar/39Ar methods. Reexamination of some of the older tills formally associated with Kansan
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
and Nebraskan glaciations show they underlie sediments that are magnetically reversed . As a consequence, the terms “
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

lecture_15 - LECTURE 15 GLACIAL RECORD OF NORTH AMERICA...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online