Stratigraphic architecture of the Cenozoic succession in the McMurdo Sound region, Antarctica: An archive of polar palaeoenvironmental change in a failed rift setting

Abstract

The Victoria Land Basin forms part of the failed West Antarctic Rift, and preserves a Cenozoic succession up to 4 km thick that records the onset of Cenozoic glaciation, and the history of Antarctic glaciation over the past 34 Myr. This succession is relevant both to investigations of modern climate change and to studies of long-term palaeoclimate change in general. This study provides a sedimentological and stratigraphic review of the Victoria Land Basin succession, based on analysis of several continuous drillcores acquired since the 1970s, and supported by seismic stratigraphic analysis of a large array of seismic reflection data. An array of fifteen lithofacies is recognized within the Victoria Land Basin Cenozoic succession, including fossiliferous and diversely bioturbated mudrocks and diatomites, texturally mature sandstones and conglomerates, mixed mudstones and sandstones with dispersed gravel with restricted bioturbation, and diamictites and associated lithologies. These facies record a variety of marine, glaciomarine, proglacial and subglacial environments. Locally, volcanic and volcaniclastic deposits are interbedded in the succession. Lithofacies are arranged in repetitive vertical stacking patterns (depositional sequences) that record glacial advance-retreat cycles with attendant relative sea-level changes. Seven varieties of depositional sequences (stratigraphic motifs) are recognized within the succession as a whole, and interpreted to record a range of depositional settings from rifts unaffected by glacial ice (Motif 7), through varying degrees of glacial influence with abundant meltwater contributions (Motifs 6 to 3), to cold, polar glaciated environments such as that of today (Motifs 2 and 1). Overall, there is a gradual trend upward through the succession from Motif 7 at the base towards Motif 1 at the top, but the trend is not monotonic. A significant conclusion of this work is that a record of dynamic climate and glacial conditions is preserved through the entire 34 Myr period of the Cenozoic icehouse, at least in the Victoria Land Basin. Intervals characterized by consistent stratigraphic style (motifs) are recognized throughout the Victoria Land Basin succession. These intervals are of 1 to 6 Myr duration, each containing numerous depositional sequences; they are one to two orders of magnitude longer than glacial-interglacial cycles, and record periods during which environmental conditions varied in an internally consistent manner. These intervals are considered to reflect convolutions of orbital parameters that remained stable for periods of 10 6 a, and then switched to alternative configurations. Such intervals are directly analogous to 1 to 8 Myr intervals characterized by glaciogenic strata that are preserved within the late Palaeozoic of eastern Australia among other areas, and may be a recurring stratigraphic response to icehouse climate regimes through geological time.1

Post Middle Miocene Tectonomagmatic and Stratigraphic Evolution of the Victoria Land Basin, West Antarctica

“…The Cenozoic strata thin and onlap onto the Coulman High on the east side of the basin and onto the Western Shelf bordering the west flank of the basin Cooper, Davey, & Behrendt, 1991;Decesari, Sorlien, et al, 2007;Fielding et al, 2008). Drilling on the western flank of the basin (Cenozoic Investigations in the Ross Sea [CIROS]-1; Cape Roberts Project [CRP]-1, -2A, and -3; and McMurdo Sound Sediment and Tectonic Studies boreholes) and in the southern part of the basin on the east and west sides of Ross Island (Antarctic Drilling Program AND-1B and AND-2 boreholes) encountered Late Eocene through Holocene marine, glaciomarine, and volcaniclastic sedimentary strata composed of stacked unconformity bounded packages that seismic data show to thicken toward the basin axis (Cooper & Davey, 1985;Cooper, Davey, & Behrendt, 1987;Davey et al, 2000;Fielding, 2018;Fielding et al, 2006Fielding et al, , 2008Henrys et al, 2000). Fielding et al (2008) recognized 11 regional unconformities (named R a through R k ) in seismic reflection profiles spanning the VLB (Table 2).…”

Origin of blocky aragonite cement in Cenozoic glaciomarine sediments, McMurdo Sound, Antarctica

“…Stratigraphic log of the CIROS ‐1 succession showing age distribution and interpreted glacial intensity (after Fielding, ). A 9 Myr unconformity at ca 366 mbsf divides the succession into a lower ( ca 366 to 702 mbsf) and an upper ( ca 27 to 366 mbsf) section.…”

“…The basal unit ( ca 702 to 688 mbsf) consists of interbedded mudrocks, sandstones and sandy‐matrix conglomerates that contain bioturbation, coaly traces, soft‐sediment deformation and current‐generated cross‐bedding (Fielding et al ., ). Accordingly, this unit is interpreted as deposition on the delta front and prodelta of shallow water deltas that were unaffected by glacial processes (Fielding, ). The basal unit is abruptly overlain by an interval of marine mudstone, which is interpreted as a flooding event associated with isostatic loading of the Antarctic continental margin during the onset of the Oi‐glaciation ( ca 33·7 Ma; Stocchi et al ., ).…”

“…The most recent chronology, based on magnetostratigraphy and biostratigraphy, suggests that the upper section accumulated over ca 24 to 22 Ma (Roberts et al ., ). A basal interval ( ca 23 m thick) of graded conglomeratic sandstone beds that overlies the 9 Myr unconformity at ca 366 mbsf represents the last period of glaciomarine deposition without direct glacial influence in the succession (Fielding et al ., ; Fielding, ). With the commencement of the Mi‐1 glaciation event, glacial influence on sedimentation became more prominent and frequent (Hambrey et al ., ; Fielding, ).…”

“…A basal interval ( ca 23 m thick) of graded conglomeratic sandstone beds that overlies the 9 Myr unconformity at ca 366 mbsf represents the last period of glaciomarine deposition without direct glacial influence in the succession (Fielding et al ., ; Fielding, ). With the commencement of the Mi‐1 glaciation event, glacial influence on sedimentation became more prominent and frequent (Hambrey et al ., ; Fielding, ). As a result of repeated advances of grounded ice into McMurdo Sound, the depositional sequences between ca 343 m and 27 mbsf are incomplete and severely top‐truncated (Fielding, ).…”