ALBERT

Description: The early Eocene (ca. 56–47.8 Ma) was an interval of exceptional warmth with reduced pole-to-equator temperature gradients. Climate proxies indicate mean annual air temperatures (MATs) and sea-surface temperatures (SSTs) exceeding 8–18 °C and frost-free, mild winters in polar areas, features that have proven difficult to reproduce with the most elaborate climate models. A full appraisal of the early Eocene polar climate has been, however, limited by possible seasonal biases associated with geochemical proxies and the lack of data from the vast Eurasian Arctic. Here we present multiproxy data from lower-middle Eocene coastal plain sediments of the New Siberian Islands (Russia) showing that taxodioid Cupressaceae, palms, and the mangrove Avicennia grew in Arctic Siberia above 72°N under air temperatures averaging 16–21 °C annually and 5.5–14 °C in winter. Kaolinite contents are exceptionally high (up to 60% of clay assemblages) and comparable to those found in present-day subtropical soils formed under high mean annual precipitation (MAP 〉1000 mm) and warm (MAT 〉15 °C) conditions. The Avicennia pollen records the northernmost mangrove growth ever documented and indicates early Eocene SSTs exceeding 13 °C in winter and 18 °C in summer. Considering the high MAP estimated for Arctic Siberia and other pan-Arctic landmasses, we propose that the heat from warm river waters draining into the Arctic might have amplified early Eocene polar warmth. Our results provide the first climate constraints for the early Eocene of Arctic Siberia and support the view that most climate models underestimate polar warming in greenhouse conditions.

Description: This study illustrates a basin-scale sequence stratigraphic framework based on wireline well-logs, cores and outcrops from the Early Triassic Montney Formation in the Western Canada Sedimentary Basin. A very dense and well-constrained database (2200 wells, 18 cores and 4 outcrops) derived from petroleum exploration made it possible to implement and test common workflows and terminologies used for sequence stratigraphic analysis along an ancient wave-dominated margin. Following facies definition from cores and outcrops and recognition of associated well-log patterns, a two-step approach allows for the reconstruction of large-scale geometries: 1) the model-independent definition of surfaces and units; and 2) the interpretation of the sequence boundaries and systems tracts based on a depositional sequence model. The typical facies association and log pattern of different sedimentary environments including tidal, as well as wave-dominated foreshore, shoreface and offshore settings are presented. The spatial distribution of characteristic sedimentary environments associated with stratigraphic surfaces and systems tracts is also detailed at the basin scale. Among other results, this study highlights the differences in the sedimentary facies geometries across two different types of sequence boundaries: the facies geometries of the first sequence boundary are quite similar to Haq et al. (1988) sequence model, whereas the geometries of the second are similar to the Hunt and Tucker (1992) sequence model. This work shows that during a rapid, high amplitude base level fall on a high gradient slope, turbidites are more likely to occur, whereas, during slow, low amplitude base level fall on a low gradient topography, forced regressive shoreface will be more likely to occur.