AbstractThis The last glacial maximum (LGM) occurred in

AbstractThis report views the Bonaparte Gulf
Basin and the British-Irish Ice sheet during the Last Glacial Maximum. It views
the sedimentation in the areas during the late Quaternary, and correlates these
sediments with the environmental changes that were occurring at that time. The
results find that the massive volume of ice produced from the Last Glacial Maximum
extends into affecting sedimentation globally. From the eustatic sea level
changes to the isostatic subsidence/uplift, the British-Irish Ice Sheet and
Bonaparte Gulf Basin were reviewed to form a timeline of the environmental
changes occurring after ~22 Ka BP up to the Heinrich event 1. The report shows
clear links between two areas that are found on different hemispheres; and the contemporaneous
environmental change that occurred.  BackgroundEnvironmental
changes lead to, if relevant to an area, alteration in the original sedimentation
processes of that area. The factors that cause this can be hugely variable,
from climate change to tectonic activity. Throughout geological time there has
always been a constant shift of these variables. The Neogene and the Quaternary
are the two most recent periods of this geological time (Fig.1). Split into the
Miocene and Pliocene, the Neogene borders the Pleistocene of the Quaternary
which is followed by the Holocene. The last glacial maximum (LGM) occurred in
the Pleistocene, ~20Ka, where the amount of global ice peaked, and as a result
lowered the global sea-level by roughly 135 m (Yokoyama et al., 2000). Most of
the time an environmental change is found via research into sedimentation of an
area. Consequently, to find the effects to sedimentation that environmental
variation has, the rocks affected must be researched first. The LGM will be the
focus, and the effects the glaciers of that time had on sedimentation. More
specifically, the first area looked at will be the Bonaparte Gulf, Australia
and then followed by the Britain-Irish Ice Sheet. Finally, the Heinrich event 1
will be reviewed, resulting in an evaluation of the environmental events of the
LGM and attempts to link everything together.     Areas Of
Study­­­Bonaparte Gulf, Australia The Bonaparte gulf is a continental shelf
found in the North-West of Australia. It is a particularly wide shelf; however,
the average sea level rarely exceeds 200 meters (Bourget et al. 2013, 2014).
The structure of the area is that of a basin surrounded by carbonate terraces
and platforms (Fig.2). Scars within said carbonate
reach at least 100 meters deep and connect the Timor sea to the basin (Fig.2;
Courgeon, Bourget and Jorry, 2016). The gulf consists of sediments that
reach over 15,000m thick, the oldest parts coming from the early Palaeozoic
(Laws & Kraus, 1974). The late quaternary contributions of these sediments
have been studied in relation to past sea level changes. Ishiwa et al studied the sediments via
radiocarbon dating, XRF core scanning and geochemical analysis (2016). The
results showed an inverse relationship between the Calcium counts and the siliciclastic-related
element, Titanium counts (Fig.3; Ishiwa et al., 2016; Gingele, De Deckker &
Hillenbrand, 2001). The variation in Calcium is thought to be the changes in
biogenic carbonate flux from the previously mentioned carbonate terraces
(Ishiwa et al., 2016). Alongside this, it was known that during the last
glacial maximum, ~20 Ka, there was a drop in eustatic sea-level by about 120 m (De Deckker & Yokoyama, 2009). The dip in the sea
level resulted in a much higher area of the carbonate terraces being revealed
above the sea level (Ishiwa et al., 2016). Figure 4 shows that the percentage
of area of the terraces and platforms exposed ranges from at least 90% when the
sea-level is -100 m, to just 25% at a eustatic sea-level of -60 m (Ishiwa et al., 2016). These correlate with the
increase of carbonate flux. As exposure to carbonate increases, a more
carbonaceous sediment reaches the basin, as more sediment is transported
fluvially along the carbonate terranes.Britain And
IrelandBritain and Ireland are
areas which environmental change affected greatly, during the LGM. During the
Late Quaternary, a large ice sheet (the British-Irish Ice Sheet) existed
(Fig.5). More specifically, using Beryllium and Chlorine exposure ages,
Ballantyne confirmed that all the low ground in Scotland and most of Ireland
was covered in ice (2009). The area covered by the Ice sheet reached a maximum
of 0.72 km2­, covering both the land and surrounding sea (Sejrup et
al., 2005). The Volume estimates reach just under 800,000 km3 (Clark
et al., 2012). Radiocarbon dating starts the retreat of the sheet in the south
at ~22 Ka (Bowen et al., 2002). Additionally, however, ages of exposed rock on
peaks of Scotland and Ireland predated the BIIS (Ballantyne, 2009). This is
thought to be because the ice was frozen to the substrate at these higher
elevations, preventing glacial based erosion (Ballantyne, 2009). The BIIS had
multiple outlet glaciers/ice streams, with some extending onto the continental
shelf, cutting into the Atlantic (Fig.5; Stoker, Hitchen and Graham, 1993). McCabe
and Clark conducted research on the North Irish sea basin to develop the
history of the BIIS (1998). The basin is a particularly good area to study, as
unlike the North-East Area of the Ice sheet, preservation of sediment is
strong, and it is known that The North Irish Sea Basin was a large major
channel for BIIS flow (McCabe and Clark, 1998).  McCabe, Clark and Clark studied an area called
Kilkeel Steps (Fig. 6), and found stacked sets of laminated deglaciation
sediment cut by marine infilled channels (2005). Radiocarbon dating found the
marine infilled channels to be ~16,700 14C yr BP (McCabe, Clark and Clark, 2005). The estimated beginning of deglaciation of
this northern part of the BIIS is ~18,000 14C yr BP (McCabe, Clark
and Clark, 2005). This area is representative of deglaciation followed by consequent
isostatic rise and then a eustatic rise in sea level (McCabe, Clark and Clark,
2005). The isostatic rise caused the previously mentioned channels to cut
through the deglaciation sediment, but the rise in eustatic sea level was
rapid; the influx of marine sediment infilled the channels (McCabe, Clark and
Clark, 2005). This Glacial retreat is thought to have reduced the BIIS by about
two thirds (McCabe, Knight and McCarron, 1998). This deglaciation even was
shortly followed by a readvancement at ~14.2 14C kyr BP (McCabe,
Knight and McCarron, 1998). Aptly named the Killard Point Stadial, Killard
Point signifies the said readvancement of the BIIS (McCabe, Clark and Clark,
2005). The stratigraphy at Killard Point is akin to a terminal outwash of a
glacier interbedded with marine mud (McCabe, Clark and Clark, 2005). utilising
the Accelerator Mass Spectrometer, McCabe, Clark and Clark dated marine
microfauna within the beds at 13,87514C yr BP and 13,99514C
yr BP: terminal outwash and marine mud respectively (2005). As the Ice
advanced, low lying parts of the North Irish Sea Basin were affected with
typical glacial deposits such as drumlins; which end at moraine-type areas such
as Killard Point (Fig. 6; McCabe, Knight and McCarron, 1998). The restraint to
the end of the readvancement is that of rough island; marine mud dated at ~12,700
14C yr BP (McCabe, Knight and McCarron, 1998). Post-readvancement, a
deglaciation event occurred, with the marine muds of rough island (Fig.6) representing
a high relative sea level (RSL) (McCabe, Clark and Clark, 2005). The high RSL
correlates with melting ice, and is often associated with the Heinrich Event 1 (McCabe,
Knight and McCarron, 1998). Heinrich Event 1Heinrich events are
processes wherein a massive number of icebergs break off ice sheets and proceed
to travel the Atlantic Ocean (Heinrich, 1988). The events are tracked in the
sediment record through ice rafted debris deposits (IRD) and a total of 6
layers of this debris was seen in Atlantic Ocean Cores (Heinrich, 1988). The
results of melting such large cold fresh water is the disturbance of the
thermohaline circulation of the North Atlantic Deep Water (Keigwin and Lehman,
1994). The relevant Heinrich event of the 6 known is Heinrich event 1 (H1). H1
is thought to have been caused by the advance of the Laurentide Ice Sheet (LIS),
once located across America and Canada (McCabe, Knight and McCarron, 1998). H1
occurred ?14.5 14C ka BP;
sediments from the Hudson strait Show the LIS participated in this event (Fig.
7; Dyke et al., 2002). Additionally, however, utilisation of the Fast Met
Office/UK Universities Simulator Global Climate Model and the Glimmer Ice Sheet
Model has produced new research (Smith, Gregory and Osprey, 2008; Rutt et al.,
2009; Roberts, Valdes and Payne, 2014). Roberts, Valdes and Payne discovered
that the resultant climatic change from H1 could not be due to the instability
of the LIS alone, and suggest that the resultant mass loss of the LIS could
play a part (2014). Separate models of freshwater input and topography change
of the LIS did not fit expected results; the cause of H1 must be due to both
factors (Roberts, Valdes and Payne, 2014). DiscussionThe relationship between the LGM
and sedimentation worldwide far exceeds what has been discussed, however
correlations can still be drawn from what has been reviewed. The gradual
Eustatic change of sea level within the Bonaparte Gulf sediments correlate to
glaciation events; more water trapped on land results in a drop in overall sea
water level. This altered the sediments being deposited in the Bonaparte Gulf
Basin: growing more carbonaceous. This is perhaps a result of the connecting
scars between the Basin and Timor sea, through the carbonate terraces; acting
as conduits during the Low sea level. The presence of terrigenous sediment
still shows fluvial sediment from the continent, but the increase in
Carbonaceous sediment shows a change in the major sediment origin. However,
within the BIIS for example, deglaciation was first recorded before the LGM
peaked. Deglaciation typically results in Eustatic sea level rise, not fall.
This could perhaps be attributed to the two areas being near opposite ends of
the earth; the Bonaparte Gulf near Australia, and the BIIS near the northern
Atlantic?  More likely is the conclusion Eyles and
Marshall McCabe found; the deglaciation of the BIIS is likely a result of
relative isostatic subsidence age (1989). The later deglaciation of the Irish
Sea Basin was followed by isostatic rise and eustatic sea level rise. From
glacial deposits, into fluvial deposits and then marine infill: the area of
Kilkeel Steps suffered an extensive change in sedimentation due to the
deglaciation. Similarly, as the BIIS re-advanced, the sediment located at
Killard Point shows significant change; with terminal glacial outwash
interbedded with marine muds. This moraine-type setting is backed up by the
Drumlins further up. The marine muds being slightly older means the glacial
outwash occurred due to the readvancement of the BIIS. Heinrich event 1 can be
seen to relate to the sedimentation of rough island. The icebergs created and
consequent fresh water flux into the Atlantic resulted in this high relative
sea level seen at rough island. The marine muds point towards this massive
influx of water into the ocean, as the inverse of what caused Bonaparte Gulf’s
sediments. The less water on land locked up in ice, means more water in the
oceans; raising the eustatic sea level. One issue could be that the relative
sea-level rise found at rough island might instead be from glacial subsidence
near the island. This however does not correlate with the data, as it would
imply a longer than expected advance of the BIIS; which the Killard point
sediments do not allow for (as they are the limit of the ice extent). One point
to be raised in this report is the consequence of the rise in sea level to the
Bonaparte Gulf. Another issue would be the lack of on land based data there is
for this report: simply put, the glaciers of the LGM provide larger volumes of
information of their extent, alteration and effects on sedimentation, in the
marine environments of that time. Conclusions

The late quaternary, or the end
of the Pleistocene, is an epoch in which sedimentation was dominated by
mass-glacial related deposits. This shows significant relation between the
environmental change that was occurring during this time (the LGM, H1), which
was largely caused by huge amounts of ice located on the land, and
sedimentation. From looking at the Bonaparte gulf, changing sea-levels play a
significant part in changing sedimentation, completely changing siliciclastic
dominated to carbonaceous dominated sediments. Whereas in Britain and the BIIS,
the relation between glacier behaviour (deglaciation or readvancement) and
Sedimentation results in more than one method of alteration i.e. during
deglaciation, isostatic uplift occurs as the weight of the glacier is removed
from land, changing the relative sea level without altering it eustatically.
This results in a complex system of sediment deposition all related to certain
events during the LGM. Furthermore, the extent of environmental change in one
area can result in larger changes worldwide. This is evident through the LIS,
as even just topographical changes in height could have resulted in global
climate changes. But included with event H1, the resultant stoppage of deglaciation
affected most of the world, sedimentation-wise. 

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