Age and environment of Miocene–Pliocene glaciomarine deposits, James Ross Island, Antarctica

Abstract

Knowledge of the late Miocene–Pliocene climate of West Antarctica, recorded by sedimentary units within the James Ross Island Volcanic Group, is still fragmentary. Late Miocene glaciomarine deposits at the base of the group in eastern James Ross Island (Hobbs Glacier Formation) and Late Pliocene (3 Ma) interglacial strata at its local top on Cockburn Island (Cockburn Island Formation) have been studied extensively, but other Neogene sedimentary rocks on James Ross Island have thus far not been considered in great detail. Here, we document two further occurrences of glaciomarine strata, included in an expanded Hobbs Glacier Formation, which demonstrate the stratigraphic complexity of the James Ross Island Volcanic Group: reworked diamictites intercalated within the volcanic sequence at Fiordo Belén, northern James Ross Island, are dated by 40Ar/39Ar and 87Sr/86Sr at c. 7 Ma (Late Miocene), but massive diamictites which underlie volcanic rocks near Cape Gage, on eastern James Ross Island, yielded an Ar–Ar age of <3.1 Ma (Late Pliocene). These age assignments are confirmed by benthic foraminiferal index species of the genus Ammoelphidiella. The geological setting and Cassidulina-dominated foraminiferal biofacies of the rocks at Fiordo Belén suggest deposition in water depths of 150–200 m. The periglacial deposits and waterlain tills at Cape Gage were deposited at shallower depths (<100 m), as indicated by an abundance of the pectinid bivalve ‘Zygochlamys’ anderssoni and the epibiotic foram Cibicides lobatulus. Macrofaunal and foraminiferal biofacies of glaciomarine and interglacial deposits share many similarities, which suggests that temperature is not the dominant factor in the distribution of late Neogene Antarctic biota. Approximately 10 m.y. of Miocene–Pliocene climatic record is preserved within the rock sequence of the James Ross Island Volcanic Group. Prevailing glacial conditions were punctuated by interglacial conditions around 3 Ma.

Insight into the latest Messinian (5.7–5.2Ma) palaeoclimatic events from two deep-sea Atlantic Ocean ODP Sites

“…Jonkers et al, (2002)). Why a warming and the observed hydrographic changes should occur in the Southern Ocean at that time is uncertain.…”

“…Evidence from Antarctica currently suffers from dating uncertainties, but terrestrial outcrops are available from this period. These are of great (Jonkers et al, 2002), (Pirrie et al, 1997) (Smellie et al, 2006), (Hambrey et al, 2008) (Smellie et al, 2008). In the Northern Hemisphere, in addition to long marine sequences recovered through ODP drilling (Jansen and Sjoholm, 1991) (Larsen et al, 1994),the best exposed outcrop repository of late Cenozoic glaciomarine rocks is the Yakataga Formation (Gulf of Alaska), which dates the earliest marine tidewater glacier incursions to no older than the late Miocene (Lagoe et al, 1993).…”

Late Cenozoic Foraminifera from Diamictites of Cape Lamb, Vega Island, Antarctic Peninsula

“…This assemblage was detailed by Bertels-Psotka et al (2001) and Concheyro et al (2007). Jonkers et al (2002) and Lirio et al (2003) described the foraminifera and ostracod assemblages of several localities of the James ross Island, particularly the late miocene Belén Formation, the late Pliocene Gage Formation and the late Pliocene-early Pleistocene microfauna of the Terrapin Formation.…”

“…Taking into account that the Belén Formation is late miocene in age (Jonkers et al, 2002;Lirio et al, 2003;Concheyro et al, 2007) based on the presence of Globigerinita glutinata (Egger), and the 87 sr/ 86 sr dating that indicates 6.8+1.3 -0.5 ma obtained on Zygochlamys anderssoni (Jonkers, 1998), the oldest record of G. biora could span the late Pliocene (Quilty, 2010) to the late miocene.…”

Fossil proxies of near-shore sea surface temperatures and seasonality from the late Neogene Antarctic shelf

“…These are contained within the interglacial marine Cockburn Island Formation (CIF), and include abundant large molluscs, especially Austrochlamys ('Zygochlamys' of Jonkers et al 2002;see Jonkers (2003) for a detailed taxonomic appraisal). The formation consists of rusty-brown sandstone and conglomerate containing clasts exclusively derived from the JRIVG (Jonkers 1998).…”