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We present a sequence-stratigraphically based reappraisal of sea-level variations for the Paleogene, Neogene, and early Quaternary Periods (66.0-1.5 Ma) that is biochronostratigraphically controlled and then fine-tuned through oxygen-isotopic (d18O) calibrations, with a higher-frequency, mostly isotopically calibrated curve for the last 1.5 m.y. of the Quaternary Period. Depositional sequences that form the basis of sea-level curves are largely third-order cycles (~0.5-2.5 m.y. in duration) for the Paleogene-Neogene interval and fourth- and fifth-order cycles (~400-100 k.y.) for the Quaternary. The availability of betterresolved, astronomically tuned Cenozoic chronostratigraphy and new sequence-stratigraphic studies in the past three decades makes this update timely. In this major revision, the ages of the depositional surfaces (i.e., sequence boundaries and maximum flooding surfaces, which form the basis of the sea-level curves) have been calibrated to marine benthic foraminiferal oxygen-isotopic data, thereby improving their chronologic precision. The amplitudes of sea-level highs and lows have been reevaluated based on global averaging of stratigraphic estimates, aided by isotopic data, where we also discuss the many inherent issues that reduce the efficacy of both methodologies. The global-mean data suggest that the shorter-term highs and lows are extremely variable during the Cenozoic Era, ranging from ~150 to a few tens of meters of change. Refined ages of the sequence boundaries and the resultant durations of third-order sequences imply their strong linkage to the longperiod modulations of the obliquity and eccentricity cycles and, thus, to climatic variations. [ABSTRACT FROM AUTHOR]

River deltas occupy only ~0.65% of Earth's land surface, but collectively house ~4.5% of the global population and account for more than 6% of the global GDP. Because of ongoing human interventions in the past century (river diversions, groundwater and petroleum extraction, and urbanization), deltas are coming under additional and intense threat from climate change and the impending sea-level rise. Many highlatitude and tropical deltas where population pressure is low and human modification is minimal face less peril for the foreseeable future, but densely populated deltas, especially those in Asia with extreme urbanization and environmental pressures, will be more susceptible to land loss and drowning. Here we consider six key deltas--Mississippi, Yangtze, Niger, Bengal, Nile, and Indus--emphasizing recent findings and consensus as to their health and how human activities have brought these vulnerable ecosystems perilously close to or beyond the point of no return. [ABSTRACT FROM AUTHOR]

Documentation of eustatic variations for the Triassic is limited by the paucity of the preserved marine stratigraphic record, which is confined mostly to the low and middle paleolatitudes of the Tethys Ocean. A revised sea-level curve based on reevaluation of global stratigraphic data shows a clear trend of low seastands for an extended period that spans almost 80 m.y., from the latest Permian to the earliest Jurassic. In the Early and Middle Triassic, the long-term sea levels were similar to or 10-20 m higher than the present-day mean sea level (pdmsl). This trend was reversed in the late Ladinian, marked by a steady rise and culminating in peak sea levels of the Triassic (~50 m above pdmsl) in the late Carnian. The trend reverses again with a decline in the late Norian and the base level remaining close to the pdmsl, and then dipping further in the mid-Rhaetian to ~50 m below pdmsl into the latest Triassic and earliest Jurassic. Superimposed upon this long-term trend is the record of 22 widespread third-order sequence boundaries that have been identified, indicating sea-level falls of mostly minor (<25 m) to medium (25-75 m) amplitude. Only six of these falls are considered major, exceeding the amplitude of 75 m. The long interval of Triassic oceanic withdrawal is likely to have led to general scarcity of preserved marine record and large stratigraphic lacunae. Lacking evidence of continental ice sheets in the Triassic, glacio-eustasy as the driving mechanism for the third-order cyclicity can be ruled out. And even though transfer of water to and from land aquifers to the ocean as a potential cause is plausible for minor (a few tens of meters) sea-level falls, the process seems counter-intuitive for third-order events for much of the Triassic. Triassic paleoenvironmental scenarios demonstrate a close link between eustasy, climates, and biodiversity. [ABSTRACT FROM AUTHOR]

An accurate chronostratigraphy of the timing and magnitude of global sea-level trends and their short-term variations is an indispensable tool in high-resolution correlations, exploration, and paleoenvironmental and geodynamic models. This paper is a reappraisal of the Jurassic sea-level history in view of recent updates in time scales and a large body of new chronostratigraphic data accrued since 1998, when the last such synthesis was presented. A review of the Jurassic sea-level history has also been keenly awaited by explorationists given that the Jurassic continues to be a major exploration target for the industry. As in previous eustatic models of this period, the updated Jurassic sea-level curve remains largely Eurocentric due to the limitations imposed by biostratigraphic correlation criteria (provinciality of ammonite and microfossil zones), though it can now be extended to some parts of the Tethys toward the east. The updated long-term curve indicates that there was a general rise of sea level through the Jurassic that began close to a level similar to or below the present-day mean sea level (pdmsl) in the early Jurassic, culminating in the peak high in the late Kimmeridgian-early Tithonian interval, before stabilizing in the earliest Cretaceous at ~110 m above pdmsl. Within this long-term trend are relative second-order highs in the Toarcian and Aalenian, and at Bathonian-Callovian and Kimmeridgian-Oxfordian boundaries. Superimposed are 64 third- and fourth-order fluctuations of which 15 are considered major with base-level falls of more than 75 m, although precise amplitudes of drawdowns are often difficult to establish. Higher resolution fourth-order cyclicity (~410 k.y.) is also observable in many Jurassic sections whenever sedimentation rates were high. Causes for the third-order cyclicity, in the absence of major ice sheets in the Jurassic, remains enigmatic. [ABSTRACT FROM AUTHOR]