Geology of Cape Lamb, Vega Island, Antarctic Peninsula

The first geologic map of Cape Lamb, SW Vega Island, is presented
along with their description and interpretation. The main outcrops
correspond to Late Cretaceous sedimentary rocks and neogene volcanic
rocks.

The former, mainly sandstones and mudstones deposited in shelf
environments during Maastrichtian times, are sudbivided into three
informal members (K1, K2 and K3) and assigned to the Marambio
Group. The identification and descrition of nine sedimentary facies
allowed an environmental restoration of the area and two complete
transgressive-regressive cycles (K1+K2 and K3) are identified. The
erosive surface bounding these cycles is covered by a transgressive
lag deposit and can be interpreted either as a wave ravinement surface
(transgressive erosional surface) or as a coplanar (sequence
boundary+flooding surface) surface. The Late Cretaceous rocks contain
a very abundant and diverse invertebrate marine fauna and have yielded
a unique assemblange of terrestrial and marine vertebrates
(plesiosaurs, mosasaurs, dinosaurs and birds). A list of the
vertebrates and invertebrates recognized up to now with their
stratigraphic distribution is also presented. These rocks correlate
with those cropping out at the northern part of the Cerro Nevado (Snow
Hill) and southern part of the Marambio (Seymour) islands towards the
basin center. Based on the joint occurrence of Gunnarites antarcticus
and Jacobites crofti, K2 is correlated with the Karlsen Cliff and
Haslum Crag members of the Snow Hill Island Formation, while
palynomorphs and the amonnoid Maorites densicostatus allow to link K3
with medium levels (KLB6-7) of the Lopez de Bertodano
Formation. Therefore, the lag conglomerate at the base of K3 could
represent a condensed deposit equivalent to part of the Haslum Crag
Member of the Snow Hill Island Formation and the lower, muddy, section
(KLB1-4) of the Lopez de Bertodano Formation at the Cerro
Nevado-Marambio section.

The latter, assigned to the James Ross Volcanic Group, are composed of
glaciomarine diamictites (Ta), intercalated within volcanic and
volcaniclastic depostis and basaltic dikes (Tb). The history of the
GVJRI at Cape Lamb is the result of three eruptive events. The large
thickness of pyroclastic deposits indicates a clear dominance of the
explosive facies. The presence of sedimentary structures and
compositional studies allow to relate these deposits to subacueous and
subglaciar processes. According to textural and compositioanl
characteristics, the tuffs are product of base surge whereas the
breccias may result from autobreccia of basalt flows entering the
glaciomarine environment. Subareal facies are minor participants
represented by basalt flows and subvolcanic bodies with fine columnar
jointing. The geomorphology of the area is modelled mainly by glacial,
marine and fluvial processes along with pervasive slumping.

This paper presents and describes the distribution and composition of
the different units, interpreting their origin and correlation with
other parts of the James Ross Basin.