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The course of the biotic recovery after the impact-related disruption of photosynthesis and mass extinction event at the Cretaceous-Paleogene boundary has been intensely debated. The resurgence of marine primary production in the aftermath remains poorly constrained because of the paucity of fossil records tracing primary producers that lack skeletons. Here we present a high-resolution record of geochemical variation in the remarkably thick Fiskeler (also known as the Fish Clay) boundary layer at Kulstirenden, Denmark. Converging evidence from the stable isotopes of carbon and nitrogen and abundances of algal steranes and bacterial hopanes indicates that algal primary productivity was strongly reduced for only a brief period of possibly less than a century after the impact, followed by a rapid resurgence of carbon fixation and ecological reorganization.

This review paper provides a synopsis of ongoing research and our understanding of the fundamentals of sea-level change today and in the geologic record, specially as illustrated by conditions and processes during the Cretaceous greenhouse climate episode. We give an overview of the state of the art of our understanding on eustatic (global) versus relative (regional) sea level, as well as long-term versus short-term fluctuations and their drivers. In the context of the focus of UNESCO-IUGS/IGCP project 609 on Cretaceous eustatic, shortterm sea-level and climate changes we evaluate the possible evidence for glacio-eustasy versus alternative or additional mechanisms for continental water storage and release for the 3 Cretaceous greenhouse and hothouse phases during which the presence of larger continental ice shields is considered very unlikely. Increasing evidence in the literature suggests a correlation between long-period orbital cycles and depositional cycles that reflect sea-level fluctuations, implying a globally synchronized forcing of (eustatic) sea level. Fourth-order depositional sequences seem to be related to a ~405 ka periodicity, which most likely represents long-period orbital eccentricity control on sea level and depositional cycles. Thirdorder cyclicity, expressed as time-synchronous sea level falls of ~20 to 110 m on ~0.5 to 3.0 Ma timescales in the Cretaceous are increasingly recognized as connected to climate cycles triggered by long-term astronomical cycles that have periodicity ranging from ~1.0 to 2.4 Ma. Future perspectives of research on greenhouse sea-level changes comprise a high-precision timescale for sequence stratigraphy and eustatic sea-level changes and high-resolution marine to non-marine stratigraphic correlation.

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Sequence stratigraphy is one of the primary tools for the evaluation of sea-level change throughout Earth history and provides a powerful framework for regional and global correlation on multiple time scales (Haq et al. 1987, Hardenbol et al. 1998, Simmons et al. 2007). However, the global correlation of stratigraphic sequences in the Mesozoic, specifically 3 rd-order (assigned in the literature to differing time intervals of~0 .5 to 3 Myr) sequences and shorter, has proven problematic for three reasons: (A) limitations of geochronology and chro no stratigraphic correlation, (B) differences in sequence stratigraphic approaches and concepts of sequence-orders between locations, and (C) uncertainties regarding the two main drivers of sea-level in platforms, local tectonics and eustasy. Regarding the last point, understanding large Cretaceous eustatic fluctuations is problematic given a presumed ice-free Earth, and alternatively, tectonics may repre-Newsletters on Stratigraphy Fast Track Article

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