LATE TRIASSIC-EARLIEST JURASSIC GEOMAGNETIC POLARITY SEQUENCE AND PALEOLATITUDES FROM DRILL CORES IN THE NEWARK RIFT BASIN, EASTERN NORTH-AMERICA

Paleomagnetic study of about 2400 samples from nearly 7 lan of core re covered at seven drill sites in the Newark continental rift basin of e astern North America provides a detailed history of geomagnetic revers als and paleolatitudinal motion for about 30 m.y. of the Late Triassic and earliest Jurassic (Carnian to Hettangian). Northward drift of onl y about 7 degrees is recorded in the continental sediments and minor i nterbedded basaltic lavas in the basin, from 2.5 degrees to 6.5 degree s north paleolatitude in the Carnian and from 6.5 degrees to 9.5 degre es north paleolatitude over the Norian-''Rhaetian'' and the early Hett angian. A total of 59 polarity intervals, ranging from about 4 m to ov er 300 m in thickness, have been delineated in a composite stratigraph ic section of 4660 m. The lateral continuity and consistent relationsh ip of lithological lake level cycles and magnetozones in the stratigra phically overlapping sections of the drill cores demonstrate their val idity as time markers. A geomagnetic polarity timescale was constructe d by scaling the composite section assuming that lithostratigraphic me mbers in the predominant lacustrine facies represent the 413-kyr orbit al periodicity of Milankovitch climate change and by extrapolating a s edimentation rate for the fluvial facies in the lower part of the sect ion; a 202 Ma age for the palynological Triassic/Jurassic boundary was used to anchor the chronology based on published concordant radiometr ic dates linked to the earliest Jurassic igneous extrusive zone. Geoma gnetic polarity intervals range from about 0.03 to 2 m.y., have a mean duration of about 0.5 m.y., and show no significant polarity bias. Th e cyclostratigraphically calibrated record provides a reference sectio n for the history of Late Triassic-earliest Jurassic geomagnetic rever sals. Correlations are attempted with available magnetostratigraphies from nonmarine sediments from the Chinle Group of the southwestern Uni ted States and marine limestones from Turkey.