Methane-seep brachiopod fauna within turbidites of the Sinaia Formation, Eastern Carpathian Mountains, Romania

摘要

This study elucidates the paleoecology and paleobiogeography of the Early Cretaceous brachiopod Peregrinella known in museum collections from a few localities in Romania, supplemented with new material from a rediscovered locality first mentioned in the 1870s. Most Peregrinella fossils are enclosed in mass waste deposits, but at two sites authigenic limestones with assemblages of brachiopods preserved in life position have been recognized. Paleontological, petrographic, stable isotopic, and organic geochemical investigations of these brachiopod-bearing limestones from the Upper Sinaia Formation, Eastern Carpathian Mountains, Romania, confirm Peregrinella as having lived at methane seeps in a siliciclastic-dominated flysch basin. The seeps developed on the slope of the External Dacides Basin. The new collections of Peregrinella indicate that shells derived from contemporaneous intrabasin methane seeps and were transported downslope by turbidity currents. Previous paleoecological models that consider Peregrinella to be solely derived from transport downslope from shelf environments are questionable especially as Peregrinella has never been recovered from typical shelf faunas; in the instance documented here from the External Dacides Basin methane-seep faunas with Peregrinella are likely to be the origin of such allochthonous faunas. The Sinaia Formation was deposited in a deep-water marine basin, derived from an intracontinental rift that developed during Late Jurassic-Early Cretaceous extension. The fractured and faulted basin margin provided the backdrop for the development of the methane seepage and the associated fauna. Foraminifera from background sediments in the sequence with turbidites confirm a late Hauterivian to early Barremian age for Peregrinella within the Sinaia Formation. This is significant because it indicates that Peregrinella ranged through into the Barremian, whereas it has typically been considered to range only as high as the Hauterivian.