Early and middle Holocene fossil-bearing marine sediments from Potter Peninsula, King George Island (South Shetland Islands, Antarctica)

Holocene sections composed of marine sediments and glacial as well as alluvial
fan deposits are exposed on the coasts of Potter Peninsula, King George
Island/Isla 25 de Mayo, South Shetland Islands (Antarctica) (Fig. 1) (Valle et
al. 2002, 2003):

Section 1 (Fig. 2): 2.6 m-thick early-to-middle Holocene succession exposed
(1.17-3.77 m above sea level: a.s.l.) at "Pingfo II" locality (62 degrees 14
minutes S, 58 degrees 48 minutes W) (Fig. 1) composed of (from base to top): a)
Marine silty-sands (0.85 m thick: 1.17-2.02 m a.s.l.) deposited in open fjord
with Laternula sp shells in growth position, which are radiocarbon dated to c.
9600 cal yrs BP, b) Glacial-marine deposits (0.15 m thick: 2.02-2.17 m a.s.l.),
c) Marine beach sands and fine-grained gravels (0.60 m thick: 2.17-2.77 m
a.s.l.) with marine invertebrates, seaweed, and seal and penguin bones (Table
1) radiocarbon dated to c. 7500 cal yrs BP (Table 2), and d) Glacial till (1 m
thick: 2.77-3.77 m a.s.l.) covered by a thin coat of marine pebbles (Table 3).

Section 2 (Fig. 3): 2.90 m-thick middle Holocene succession exposed (14.4-17.3
m a.s.l.) at "Pingfo I" locality (62 degrees 15 minutes S, 58 degrees 37
minutes W) (Fig. 1) formed of alluvial fan gravels alternated with marine beach
sands that form three layers between 14.7-16.7 m a.s.l. The raised beach
sediments contain bones of flying birds, seals, and penguins (Table 1)
radiocarbon dated to c. 5500 cal yrs BP (Tables 2 and 3).

These data allow to reconstruct part of the Holocene history of sea level (Fig.
4) and constrain the age of early-to-middle Holocene environmental changes on
the Potter Peninsula coastal area (Table 4): The early Holocene withdrawal of
glaciers from Potter Cove (south-west King George Island) acompanied by a sea
level high stand allowed marine sedimentation in an open fjord c. 9600 years
ago (Section 1). This high stand of sea level may be related to the 10-9 ka BP
marine transgression that drowned the Maxwell Bay coasts (south-west King
George Island) (Fig. 1) down to 25-30 m depths. After a short-live episode of
glacial-marine sedimentation, an early-middle Holocene (c. 9600-7500 yr BP)
lowering of the relative sea level allowed marine beach sediments to be
deposited on the fjord sediments (Section 1). The glacial till that covers the
marine beach sediments (Section 1) is thought to be deposited during the middle
Holocene (post-7500 yr BP) glacial advance named "Pu nta Baliza" (PBGA:
Birkenmajer 1998). The thin coat of raised marine gravels, which covers PBGA
reworked glacial till at c. 3.77 m a.s.l. (Section 1), suggests that probably
during the culmination of PBGA the sea penetrated well into the coastal area of
Potter Peninsula. Additionally the raised marine beach sediments 14.7-16.7 m
dated to c. 5500 yr BP (Section 2), confirm that the sea drowned the coasts of
Potter Peninsula down c. 10-12 m depths during middle Holocene periods of open
marine water conditions.