High-resolution early Mesozoic Pangean climatic transect in lacustrine environments

Abstract

Analysis of 6700 m of core from the Newark rift basin in New Jersey, USA provides a high-resolution astronomically calibrated magnetic polarity time scale for the Late Triassic and Early Jurassic spanning about 33 million years. This time scale, and its application elsewhere, allows a significant simplification of the pattern of climate-sensitive facies in the early Mesozoic basins of the central and north Atlantic margins. Coals and deep-water lacustrine deposits were produced at the paleoequator (Richmond-type sequenc­ es), while strikingly cyclical lacustrine and playa deposits were produced \00 to the north and south (Newark-type lacustrine sequences). At 10-30 ON, eolian dunes, playas sedi­ ments and evaporites were deposited (Fundy-type sequences). Farther north, shallow-water lacustrine red beds were deposited (Fleming Fjord-type sequences), while yet farther north (-40°), perennial-lake black mudstones and coals again dominated in the humid temperate zone (Kap Stewart-type sequences). Central Pangea drifted north about 10° during the Late Triassic, and the vertical sequence of climate-sensitive facies in individual basins changed as the basins passed through different climate zones. This simple zonal climate pattern explains most first-order changes in overall lacustrine sequences seen in the rift zone. Lake­ level cycles of Milankovitch origin change in a predicable way with the latitudinal shifts in climate and lacustrine style. Roughly \0 ky precessional cycles dominate within a few degrees of the equator, while -20 ky precessional cycles are dominant northward to about 30 ON where -40 ky obliquity cycles become evident in lake-level records.