LANDING AND WEBSTER A5 -1 IAPETAN RIFT‒PASSIVE MARGIN TRANSITION IN NE LAURENTIA AND EUSTATIC CONTROL ON CONTINENTAL SLOPE OXYGENATION, TACONIC SLATE COLORS, AND EARLY PALEOZOIC CLIMATE By Ed Landing1, New York State Museum, 222 Madison Avenue, Albany, NY 12230 Mark Webster2, Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637 Email addresses:
[email protected], 2mwebster@geosci,uchicago.edu INTRODUCTION This excursion along the eastern margin of the New York Promontory was prepared for the combined meeting of the New England Intercollegiate Geological Conference and the New York State Geological Association (October 2018). Parts of this guide have been modified from reports by EL and MW and are so indicated. There are two purposes of the trip: (1) The oldest rocks of the Taconic allochthon (originally deposited on the east Laurentian margin of the Iapetus Ocean and at least 75 km east of its present location) and coeval shelf margin rocks in the Green Mountain anticlinorium (not seen on this trip) indicate a surprisingly late persistence or rejuvenation of Iapetan rifting. Although Iapetan rifting began in the later Ediacaran, the oldest record of sedimentary rocks deposited on the middle Proterozoic basement of the Grenvillian orogen in NE Laurentia is late Early Cambrian, with immature sandstone (arkose) deposition continuing well into the Middle Cambrian in the eastern Ottawa-Bonnechere aulacogen (Landing et al., 2009, In press; Figure 1). (2) The second purpose of this trip emphasizes the relationship of major eustatic changes to macroscale alternations in oxygenation on the east Laurentian continental slope as exhibited in the Lower Paleozoic of the Taconic allochthon.