The Mendel Formation: Evidence for Late Miocene climatic cyclicity at the northern tip of the Antarctic Peninsula

Abstract

A detailed description of the newly defined Mendel Formation is presented. This Late Miocene (5.9–5.4Ma) sedimentary sequence with an overall thickness of more than 80m comprises cyclic deposition in terrestrial glacigenic, glaciomarine and marine environments. Subglacial till was deposited by a thick grounded Antarctic Peninsula ice stream advancing eastwards through the Prince Gustav Channel, crossing the northernmost part of present-day James Ross Island, with most of the material carried actively at the base of the warm-based glacier. The form of the Prince Gustav Channel originated before the late Miocene and its present glacial over-deepening resulted in multiple grounded glacier advances during the Neogene and Quaternary. The sea prograded from the east and the glacier margin became buoyant, building a small ice shelf, below and in front of which glaciomarine and marine sediments were deposited. These sedimentary deposits are composed of material that was transported mostly by small glaciers and subsequently by the floating ice shelf and by calving icebergs towards the open sea. These environmental and glaciological conditions differ strongly from the present cold-based local glaciers of James Ross Island and the Antarctic Peninsula. These changes were triggered by the global sea level fluctuation connected with climatic changes due to Antarctic ice sheet build up and decay. This reveals Late Miocene obliquity-driven cyclicity with a ~41ka period. The Mendel Formation sedimentary sequence is comprised of at least two glacial periods and one interglacial period. Sea level rise at the northern tip of the Antarctic Peninsula between glacial lowstand and interglacial highstand was more than 50m during the late Miocene and was followed by a subsequent sea level fall of at least the same magnitude. The presence of well-preserved, articulated pectinid bivalves support “interglacial” open sea conditions. The re-deposition of palaeontological material was shown to be important for the Mendel Formation. Reworked pectinid shells revealed an open marine “interglacial” condition in this part of the Antarctic Peninsula during the Early to Mid Miocene (20.5–17.5Ma). Unfortunately, relevant sedimentary deposits have not been found on land.