Summary of Jurassic Stratigraphy of Alaska: ABSTRACT

Abstract

Jurassic rocks are fairly wide-spread in Alaska and occur in southeastern, southcentral, and southwestern Alaska. They are also extensively exposed on the Alaska Peninsula and in northern Alaska. The Lower Jurassic deposits consist predominantly of a volcanic sequence of submarine volcanic flows, agglomerates, and tuffs with associated interbedded clastic sediments and some impure limestones and marls. The Middle Jurassic deposits are characterized by siltstones and, to less extent, sandstones with some conglomerates. The Upper Jurassic deposits consist of siltstones, sandstones, and conglomerates. Most of the Jurassic deposits contain molluscan fossils, particularly ammonites. The ammonite faunas contain genera and, in some instances, species which are identical with forms from the classic type sections of Europe. Correlation of the Alaska faunas with those of the European type sections indicates the presence in Alaska of all the European stages with the exception of the Bathonian. Within parts of the Middle Jurassic, it has been possible to recognize a number of the European zones. The later Upper Jurassic contains few diagnostic ammonites. The chronology of this part of the section has been worked out by means of a study of the ubiquitous pelecypod, Aucella (= Buchia). End_of_Article - Last_Page 260------------