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Results of apatite fission track analyses on 29 Ordovician through Permian sandstones from the Appalachian Basin in Pennsylvania are presented. Ages range from 111±17 to 184±10 Ma. Mean track lengths of 10.71±0.29 to 13.10±0.17 μm with unimodal, negatively skewed length distributions are indicative of slow cooling. The data separate into two groups on an age versus mean length plot. The younger group (111–144 Ma) is found in the structural depressions of the Anthracite Basin and the Broad Top Basin and adjacent Appalachian Plateau. The older group (144–184 Ma) is found in the structurally higher southwestern Appalachian Plateau and Juniata Culmination and adjacent central plateau. Fission track data suggest that the basin cooled slowly after the Alleghanian Orogeny, with culminations cooling earlier than depressions. Cooling histories modeled from apatite fission track data, with maximum temperatures constrained by vitrinite reflectance, indicate cooling beginning soon after the Alleghanian Orogeny except in the Juniata Culmination, which apparently experienced synorogenic cooling and unroofing during formation of the underlying duplex. Model cooling histories and available geologic information indicate that the foreland basin did not experience Mesozoic reheating. Unroofing histories were modeled from fission track cooling histories using heat flow estimates and burial depths derived from vitrinite reflectance profiles. The models suggest that the unroofing history of the Appalachian Basin in Pennsylvania can be divided into three episodes. An initial episode of relatively rapid cooling and unroofing (Late Permian‐Early Jurassic) is attributed to flexural rebound of the foreland in response to erosional removal of Alleghanian topographic load. Initial unroofing rates are higher in eastern Pennsylvania than in the west, consistent with a flexural model. An episode of little to no unroofing (Middle Jurassic‐late Oligocene) began contemporaneously with the inception of drift at the Atlantic continental margin. At this time, unloading of the orogen was replaced by subsidence and sedimentation on the new margin. Without flexural rebound the driving force for unroofing of the basin was removed and unroofing slowed greatly. An episode of rapid unroofing over the full width of the basin occurred from the Miocene to the present. Although the driving mechanism for unroofing at this time has not been identified, it is consistent with increased sedimentation rates in the middle Atlantic offshore basins for the same period.

The Manson impact structure is a 36.5-km-wide, well-preserved crater centered 130 km northwest of Des Moines, Iowa, that formed about 74 Ma. Its diverse lithologies (sandstone, shale, carbonate; leucogranite, gabbro/diabase, gneiss, amphibolite) contain a wide range of shock damage. Seventy-six samples from drill hole 2-A (1953, drilled to a total depth of 144 m) and M-1 (1991, to 212 m depth), located on the upper eastern flank of the 12 km (at base) central peak, were analyzed by optical petrography to determine shock index values useful for determining several key aspects of shock level distribution and modes of emplacement. Core samples from the upper half of hole 2-A consist of breccia with clasts comprised mainly of biotite granites, granodiorites, and gneisses; these lithologies also dominate the crystalline basement blocks that make up the lower half of the 2-A core. Planar deformation features (PDFs) in quartz (2-6 sets/crystal) and feldspars occur at all depths; biotite is readily kinked and variably decomposed. A diagnostic shock feature in quartz (uncommon in feldspars), referred to descriptively as "toasting," may be an optical rather than a compositional phenomenon. Subdivision of larger quartz crystals into numerous polygonal interlocked domains (commonly with thin boundaries of clear, post-impact quartz) produces a distinctive polycrystalline texture; individual domains contain PDF sets, many having no continuity of orientations with neighbors. Feldspars may show internal melt flow and recrystallization; alternate albite twins are selectively more shock disordered and subsequently altered.Shock levels are higher in the upper 38 m of the 2-A core, decreasing downward over the next 81 m as the drill hole passed through the lower impact melt breccia into the crystalline rock megablock zone. M-1 units (distinguished overall by fewer PDFs in quartz) are mostly shales (with a few possibly melted clasts) and quartz sandstone (uncommonly with PDFs) in the upper 57 m; below this a 34 m interval of breccia with mainly leucogranite clasts having high shock indexes, characterized by extensive clast recrystallization and matrix glass; then 18 m of light and dark igneous and metamorphic clasts (variably shocked) with a few clasts of shocked sandstones and shales and some devitrified glass; and bottomed by 49 m of amphibole-rich suevite breccias with less obvious shock damage.

27We present new biostratigraphic analyses of approximately 200 outcrop samples 28 across western New Guinea. These data were used to reconstruct palaeogeography

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