In order to better define the late Eocene clinopyroxene-bearing (cpx) spherule layer and to determine how the ejecta vary with distance from the presumed source crater (Popigai), we searched for the layer at 23 additional sites. We identified the layer at six (maybe seven) of these sites: Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) Holes 592, 699A, 703A, 709C, 786A, 1090B, and probably 738B. The cpx spherule layer occurs in magnetochron 16n.1n, which indicates an age of ca. 35.4 ± 0.1 Ma for the layer. We found the highest abundance of cpx spherules and associated microtektites in Hole 709C in the northwest Indian Ocean, and we found coesite and shocked quartz in the cpx spherule layer at this site. We also found coesite in the cpx spherule layer at Site 216 in the northeast Indian Ocean. This is the first time that coesite has been found in the cpx spherule layer, and it provides additional support for the impact origin of this layer. In addition, the discovery of coesite and shocked quartz grains (with planar deformation features [PDFs]) supports the conclusion that the pancake-shaped clay spherules associated with quartz grains exhibiting PDFs are diagenetically altered cpx spherules. An Ir anomaly was found associated with the cpx spherule layer at all four of the new sites (699A, 709C, 738B, 1090B) for which we obtained Ir data. The geometric mean of the Ir fluence for the 12 sites with Ir data is 5.7 ng/cm 2 , which is ~10% of the fluence estimated for the Cretaceous-Tertiary boundary. Based on the geographic distribution of the 23 sites now known to contain the cpx spherule layer, and 12 sites where we have good chronostratigraphy but the cpx spherule layer is apparently absent, we propose that the cpx spherule strewn field may have a ray-like distribution pattern. Within one of the rays, the abundance of spherules decreases and the percent microtektites increases with distance from Popigai. Shocked quartz and coesite have been found only in this ray at the two sites that are closest to Popigai. At several sites in the Southern Ocean, an increase in δ 18 O in the bulk carbonate occurs immediately above the cpx spherule layer. This increase may indicate a drop in temperature coincident with the impact that produced the cpx spherule layer.

Abstract Shallow-water carbonate sediments deposited in tropical and subtropical settings form thick and spatially extensive accumulations referred to as “carbonate platforms.” Carbonate platforms typically have life spans of millions of tens of milliions of years, and their birth, growth, and demise are governed by a combination of factors such as tectonics, eustasy, environmental conditions, and climate. Carbonate platforms contain an archive of variations of these factors through time in its sedimentary record. These changes can then be extracted from this record, providing insight into our understanding of sedimentary processes and enhancing our knowledge of earth’s history. This study examines the stratigraphy and evolution of the Maldives isolated carbonate platform, in the equatorial Indian Ocean. The Maldives platform is unique because of its enormous size (800 x 130 km). It is the second-largest modern isolated carbonate platform (after the Bahamas). Established in the early Eocene and now more than 3 km thick, the platform contains a sedimentary record which spans more than 50 million years. This study is based on interpretation of the regional 2-D seismic data set and data from one deep exploration well that resulted from Royal Dutch/Shell during its exploration campaign in 1989-1991. The excellent quality and the vast volume (6000km of seismic data) allowed the authors to conduct a detailed study of the Maldives platform.