FALSIFICATION OF HYPOTHESES OF A MAJOR HIATUS IN THE NEWARK SUPERGROUP RHAETIAN (LATE TRIASSIC, US AND CA) BASED ON DATA FROM THE BRISTOL CHANNEL (UK) AND NORTH GERMANIC BASINS (DE)

Rift basins of eastern North America and Morocco arguably preserve the temporally most tightly constrained record of abrupt continental biotic change through the end-Triassic mass-extinction (ETE) based on astrochronology and U-Pb dates (1). However, two biostratigraphic hypotheses have been proposed for these sections requiring a multi-million-year hiatus or unconformity spanning most of the Rheatian that we show here are falsified.

Van Veen (2) hypothesized a hiatus based on European records where vesicate pollen (Patinasporites-Enzonalasporites-Vallisporites complex) disappear in the early Rhaetian while continuing up to the Newarkian ETE, and therefore implying the Newark succession is very condensed, consistent with a major hiatus. This is falsified by the presence of the vesicate forms in late Rhaetian strata of the Bristol Channel Basin (3). This pattern is more simply explained by a time-transgressive disappearance (in present geography) of the low-latitude vesicate pollen group as central Pangae translated north (4) prior to their ETE extirpation (5).

Similarly, Kozur & Weems (6) hypothesized that the absence of several Germanic basin clam shrimp zones in the Newark Supergroup indicate a hiatus spanning most of the Rhaetian. Their key observations are, “…the upper Norian faunas were dominated by very large conchostracans, while the Rhaetian (and Hettangian) conchostracan faunas are everywhere composed of very small forms.” The lack of these zones and the presence of the large Shipingia just below the ETE in Newark Supergroup strata led to the hypothesis of a major hiatus. This hypothesis is falsified by our discovery of abundant large cf. S. olseniin late Rhaetian, largely marine strata in the North Germanic Basin.

Both hypotheses for a significant hiatus are thus falsified; moreover, no physical evidence for a significant hiatus at this critical level exists. There is instead compelling physical and magnetostratigraphic evidence of completeness at the 20 kyr level (e.g., chron E23r). The most parsimonious interpretation is that the Newarkian records through the ETE are continuous.

1, Blackburn+ 2013 Science 340:941; 2, Van Veen 1995 Tectonopysics 245:93; 3, Bonis+ 2010 JGS Lond 167:877; 4, Kent & Tauxe 2005 Science 307:240; 5, Olsen+2011 EESTRSE 101:201; 6, Kozur & Weems 2011 NMMNHS Bull 53:295.