Sandstones that have high porosity and permeability at great burial depth and high temperatures are of economic importance because a significant amount of hydrocarbons have been discovered in such reservoirs. The Sawan gas field, with an expected ultimate recovery of more than 1 tcf, lies in the middle Indus Basin. The reservoir rocks, Cretaceous volcaniclastic sandstones of the lower Goru Formation, show very high porosities at a reservoir temperature of 175°C and depths of 3000 to 3500 m (9842 to 11,483 ft). The sandstones are mostly feldspathic litharenites. Strongly altered volcanic rock fragments are the most important lithic component. The clay fraction consists of Fe-rich chlorite (chamosite) and illite. Diagenetic features such as compaction, quartz overgrowths, carbonate cements, and feldspar dissolution are observed. The most distinguishing feature is a double layer of authigenic chlorite, lining the pores of the sandstones. Chlorite additionally occurs as a pore-filling cement and as chloritized detrital components, all having similar chemical composition. The pore-lining cement clearly developed in two stages: an earlier, poorly crystallized, and a later, better crystallized growth. Missing rims at grain contacts show that precipitation occurred after an initial stage of compaction but early relative to other diagenetic phases. Both chlorite rims grew by direct precipitation from pore waters, using products derived

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The moat of the 85-km-diameter and 35.3-Ma-old Chesapeake Bay impact structure (USA) was drilled at Eyreville Farm in 2005-2006 as part of an International Continental Scientifi c Drilling Program (ICDP)-U.S. Geological Survey (USGS) drilling project. The Eyreville drilling penetrated postimpact sediments and impactites, as well as crystalline basement-derived material, to a total depth of 1766 m. We present petrographic observations on 43 samples of suevite, impact melt rock, polymict lithic impact breccia, cataclastic gneiss, and clasts in suevite, from the impact breccia section from 1397 to 1551 m depth in the Eyreville B drill core. Suevite samples have a fi ne-grained clastic matrix and contain a variety of mineral and rock clasts, including sedimentary, metamorphic, and igneous lithologies.Six subunits (U1-U6, from top to bottom) are distinguished in the impact breccia section based on abundance of different clasts, melt particles, and matrix; the boundaries between the subunits are generally gradational. Sedimentary clasts are dominant in most subunits (especially in U1, but also in U3, U4, and U6). There