We evaluated the age of two Upper Eocene impact ejecta layers (North American microtektites linked to the Chesapeake Bay impact structure and clinopyroxene [cpx] spherules from the Popigai crater) and the global effects of the associated impact events. The reported occurrence of cpx spherules from the Popigai impact structure at South Atlantic ODP Site 1090 within the middle of magnetochron C16n.1n yields a magnetochronologic age of 35.4 Ma. We generated high-resolution stable isotope records at Sites 1090, 612 (New Jersey slope), and Caribbean core RC9-58 that show: (1) a 0.5‰ δ 13 C decrease in bulk-carbonate at Site 1090 coincident with the Popigai cpx spherule layer, and (2) a 0.4‰–0.5‰ decrease in deep-water benthic foraminiferal δ 13 C values across the Popigai impact ejecta layer at Site 612 and core RC9-58. We conclude that the δ 13 C excursion associated with Popigai was a global event throughout the marine realm that can be correlated to magnetochron C16n.1n. The amplitude of this excursion (~0.5‰) is within the limits of natural variability, suggesting it was caused by a decrease in carbon export productivity, potentially triggered by the impact event(s). North American microtektites associated with the Chesapeake Bay impact occur stratigraphically above the Popigai cpx spherules at Site 612 and core RC9-58. We found no definite evidence of a δ 13 C anomaly associated with the North American microtektite layer, though further studies are warranted. High-resolution bulk-carbonate and benthic foraminiferal δ 18 O records show no global temperature change associated with the cpx spherule or North American microtektite layers.

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Abstract The last decade has witnessed significant advances in analytic techniques and methodologic approaches to understanding earth history. It was with this in mind that we convened a research symposium at the 67th annual meeting of SEPM in New Orleans (27 April 1993) entitled Geochronology, Time Scales and Stratigraphic Correlation: Framework for a Historical Geology. In a one day (27 April) symposium, 15 (of 18 scheduled) papers were presented on all aspects of the symposium topic. Oral presentations were complemented by a half day (28 April) poster session. The present volume represents a distillation of the symposium presentations with the inclusion of two of the three that were not presented owing to unavoidable circumstances, the addition of two new papers and the elimination of two of the papers presented at the symposium. The result is the 16 papers that constitute this volume and which represent a broad spectrum of approaches to understanding earth history and the passage of (geologic) time. But let’s back off a minute and ask what is time anyway? Time has been defined as a measured or measurable period, a continuum that lacks spatial dimensions. In the 5th century A.D., the Platonist St. Augustine wrestled with the inadequacy of words to define the concept. Time is of philosophical interest to us humans not the least because we regret the past and fear the (uncertainty and inevitability of) the future. Modern physics teaches us that time cannot, in fact, be treated in isolation from space. There is an interdependence

Abstract Using replicate measurements of a homogeneous reference zircon, the discrimination of Pb + and UO + ions relative to U + observed in zircon analysis with the SHRIMP ion microprobe has been established as a power law relationship. This relationship minimizes uncertainty in comparative measurement of 206 Pb/ 238 U ages in zircons. Ages thus obtained have been compared with isotope dilution thermal ionisation mass spectrometric (1DTIMS) analysis of zircons in the Paterson Volcanics (Carboniferous, Australia) and 40 Ar/ 39 Ar dating of sanidines in the Z1 tonstein (Carboniferous, Germany). No bias can be detected between the three dating methods, confirming that SHRIMP zircon 206 Pb/ 238 U ages are accurate and comparable with other well-measured Phanerozoic ages. The age of the Westphalian B Stage of Europe is constrained by the Z1 tonstein; SHRIMP zircon analysis supports the 40 Ar/ 39 Ar age of 311 Ma and improves on its precision by a factor of two. The Paterson Volcanics mark both the Australian base of the Kiaman magnetic superchron and onset of the major, Late Palaeozoic period of Gondwana glaciation; SHRIMP and 1DTIMS zircon dating reassign these processes to the Namurian from the late Westphalian assignment used until now for global correlations.