Re-interpreting the Baltringer Horizont as a subtidal channel facies: Implications for a new understanding of the Upper Marine Molasse "Cycles" (Early Miocene)
Heimann, Florian U.M. Schmid; Pippèrr, Martina; Reichenbacher, Bettina
published: Oct 1, 2009
ArtNo. ESP155025401007, Price: 29.00 €
At the type-area near Baltringen in the Southwest German part of the Molasse Basin, the sediments of the so-called Second Cycle of the Upper Marine Molasse, i.e. the Baltringer Schichten and overlying Feinsandserie, were studied. Based on sedimentary features, we show that the Baltringer Horizont does not form a continuous layer at the base of the Baltringer Schichten as it is conventionally suggested. Instead, we suggest its deposition in a subtidal channel environment, which is additionally supported by microfacies and microfossils. The Feinsandserie was deposited in a shallower environment, but rhythmic sedimentation, bidirectional and herringbone cross-bedding still suggest tidal influences. Two separation planes were identified, one at the base, the second within the Feinsandserie. Drops in layer thickness and grain-sizes above these planes lead to the division of two sedimentary segments in the Feinsandserie. We suggest shallowing events at the base of both segments and a subsequent deepening trend section-upwards in an intertidal environment. A shift in the heavy mineral assemblages above the upper separation plane probably correlates with the previously described transition from a garnet-epidote (GE) to a garnet-staurolithe-apatite (GSA) mineral assemblage in the upper part of the Upper Brackish Molasse. We conclude that the Upper Marine Molasse in the Southwest German part of the Molasse Basin represents a single transgressive-regressive unit, and that its so-called First and Second Cycle just represent a continuous shallowing process.