The Jurassic–Lower Cretaceous Byers Group, South Shetland Islands, Antarctica: revised stratigraphy and regional correlations
The Byers Group, exposed in the western South Shetland Islands, is a thick (at least 2.7 km) succession recording Late Jurassic–Early Cretaceous sedimentation and volcanism on the Pacific flank of the Antarctic Peninsula magnetic arc. At least 1.3 km of marine clastic rocks are overlain by 1.4 km of non-marine strata. Penecontemporaneous, mainly intrusive, igneous rocks are present in much of the succession. At the base of the Byers Group, radiolarian-rich, hemipelagic mudstones of the Kimmeridgian–Tithonian Anchorage Formation are succeeded by terrigenous, slope-apron mudstones and sandstones of the Berriasian President Beaches Formation. These deep-marine strata are overlain by shallower-marine conglomerates and mudstones of the Berriasian–Valanginian Chester Cone Formation. The upper part of the marine succession also includes the volcanic breccias of the Start Hill Formation, interpreted as part of a debris-apron flanking a substantial volcanic edifice. Finally, following a Valanginian–Aptian erosional hiatus, non-marine volcaniclastic rocks of the Cerro Negro Formation were deposited in early Aptian times. Comparison with time-equivalent successions elsewhere in the Antarctic Peninsula region suggests that within the overall regressive trend, the Byers Group records regionally significant pulses or arc uplift in Tithonian–earliest Berriasian, latest Berriasian, and late Valanginian–Earliest Aptian times.