Evidence for distal transport of reworked Andean tephra: Extending the cryptotephra framework from the Austral volcanic zone

Abstract

Cryptotephra deposits (non-visible volcanic ash beds) may extend thousands of kilometres and provide valuable chronological isochrons. Here, we present a Lateglacial-early Holocene (c. 16,500 cal yr BP-6,000 cal yr BP) tephrostratigraphy from Hooker's Point, East Falkland, South Atlantic. This period spans the last glacial termination across the southern mid-latitudes, a time period during which the palaeoenvironmental record is poorly resolved in southern South America and the South Atlantic. The development of a regional tephrostratigraphy will provide chronological constraint for palaeoenvironmental records from this period. Two cryptotephra deposits from Hooker's Point are linked with Mt. Burney, including the early-Holocene MB 1 tephra, while a third is likely to be derived from the R 1 eruption of Reclus volcano. The high shard abundance of these cryptotephra deposits suggests they extend further into the Southern Ocean, and may act as regional stratigraphic markers during the Lateglacial. Further peaks in shard abundance are composed of detrital glass (tephra not derived from primary air fall events), with mixed shard morphologies and geochemically heterogeneous glass populations. This detrital glass is likely to have been repeatedly reworked by wind action in the Patagonian Steppe before final deposition in the Falkland Islands. The high abundance of detrital glass in the Hooker's Point sequence suggests long distance transport of reworked tephra is common in this region, and highlights the need to carefully analyse cryptotephra deposits in order to avoid incorrectly describing reworked tephra as new isochrons. A temporal pattern of shard abundance is apparent in the Hooker's Point sequence with a reduction /absence of shards between 14,300-10,500 cal yr BP.

Supplemental Material: Late glacial–Holocene record of Southern Hemisphere westerly wind dynamics from the Falkland Islands, South Atlantic Ocean

“…The methodology and results of cryptotephra (non-visible volcanic ash), pollen and plant macrofossil analyses from Hooker's Point, including volcanic-glass chemical compositions (Reclus Volcano R1 and Mt. Burney MB1), are presented by Monteath et al (2019) and Scaife et al (2019).…”

“…Two 14 C dates were placed directly beneath cryptotephra deposits associated with the Reclus Volcano R1 and Mt. Burney MB1 volcanic eruptions in order to provide more precise age constraints for these regional isochrons (Monteath et al, 2019).…”

“…Radiocarbon dates placed immediately beneath cryptotephra deposits linked with the Reclus Volcano R1 and Mt. Burney MB1 volcanic eruptions (Monteath et al, 2019) place the ash falls between 13.8-13.5 ka and 9.5-9.0 ka, respectively. The date beneath the Reclus R1 is substantially younger than previous estimates (16.1-14.3 ka, Stern 2008;15.5-14.4 ka, McCulloch et al, 2005;14.5-14.1 ka, Smith et al, 2019) and would require an unlikely shift in peat-accumulation rates to be accurate.…”

The Volcanic-Rich Layer of the “Camporotondo (Marche, Italy)” Section: Petrography and Sedimentation of an Unknown Distal Messinian Eruption

“…Conversely, pyroclastic flows tend to form un-sorted thick deposits (ignimbrites) up to distances ranging from few to tens of km from the vent [6][7][8][9][10]. Tephras, i.e., loose pyroclastic materials of any origin [9,11,12] and lithified tephras labelled here volcanic-rich layers (VRL), can be the unique witnesses of dismantled volcanoes, erased by tectonic or erosive processes [9,[13][14][15][16][17][18][19]. Finally, there are cryptotephras, i.e., sedimentary levels hosting volcanic materials [9,20].…”

Distal ash fall from the mid-Holocene eruption of Mount Hudson (H2) discovered in the Falkland Islands: New possibilities for Southern Hemisphere archive synchronisation

“…Only a limited number of cryptotephra deposits originating from Patagonian explosive volcanism have previously been reported in peat bogs across the Southern Atlantic, including the Falkland Islands and South Georgia (Hall et al, 2001;Oppedal et al, 2018), with the most recently identified linked to eruptions at Mt. Burney (MB1; 8.85-9.95 ka cal BP) and the Reclus Volcano (R1; 14.76 ± 0.18 ka cal BP (Monteath et al, 2019;Stern et al, 2011).…”