The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Massachusetts Office of Coastal Zone Management (MA CZM), is producing detailed geologic maps of the coastal sea floor. Sidescan-sonar imagery, originally collected by NOAA for charting purposes, provide a fundamental framework for research and management activities along this part of the Massachusetts coastline, show the composition and terrain of the seabed, and provide information on sediment transport and benthic habitat. While acceptable for charting purposes, the original data contained numerous tonal artifacts due to environmental conditions (such as sea state), variable system settings (such as gain changes), attitude variations in the flight path of the towfish, or processing (such as lack of line to line normalization). Many of these artifacts have now been removed by enhancing the imagery to provide a more continuous grayscale GeoTIFF that enhances the true backscatter character and trends of the sea floor.

The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Massachusetts Office of Coastal Zone Management (MA CZM), is producing detailed geologic maps of the coastal sea floor. Sidescan-sonar imagery, originally collected by NOAA for charting purposes, provide a fundamental framework for research and management activities along this part of the Massachusetts coastline, show the composition and terrain of the seabed, and provide information on sediment transport and benthic habitat. While acceptable for charting purposes, the original data contained numerous tonal artifacts due to environmental conditions (such as sea state), variable system settings (such as gain changes), attitude variations in the flight path of the towfish, or processing (such as lack of across-track normalization). Many of these artifacts have now been removed by enhancing the imagery to provide a more continuous grayscale GeoTIFF that enhances the true backscatter character and trends of the sea floor.

The last five to seven years have seen a major revision in our understanding of the geology of central Australia, with advancements in the field of geochronology redefining the geological framework and history of this area. Prior to about 1995, the eastern Arunta region was thought to consist of moderate to high grade metamorphic Palaeoproterozoic rocks with a complex geological history. This basement was interpreted to be overlain by low grade, mainly sedimentary rocks of the Georgina and Amadeus Basins, which are part of the extensive Neoproterozoic to late Palaeozoic Centralian Superbasin (Walter et al., 1995). However, workers at Adelaide, La Trobe, Australian National and Monash Universities found that rocks of the Harts Range Group (also referred to as the Irindina Supracrustal Assemblage) have a Neoproterozoic to early Palaeozoic depositional age, and were intensely metamorphosed and deformed during the Ordovician (e.g. Miller et al., 1998, Mawby et al., 1999). Subsequent work by the Northern Territory Geological Survey (NTGS) and Geoscience Australia (GA) indicates that the Palaeoproterozoic part of the Arunta region can itself be divided into two discrete provinces: (1) the older (1840-1760 Ma) Aileron Province, and (2) the younger (1680-1610 Ma) Warumpi Province. Further work by the two geological surveys and the Australian National University suggests that in the eastern Arunta region, the Aileron Province can be divided into two sequences, the older (1820-1800 Ma) Strangways Metamorphic Complex and the younger (~1760 Ma) Oonagalabi Assemblage. Definition of these sequences became possible only because of the availability of a critical mass of geochronological data.

One of the purposes of this field trip is to illustrate the characteristics of the Palaeoproterozoic basement and the overlying Neoproterozoic to Palaeozoic rocks, with emphasis on the role of modern geochronology in resolving the newly defined terrains. The rocks of the eastern Arunta region have also undergone multiple deformation and metamorphic events that are now being unravelled. This complex history will also be illustrated during the excursion. The second aspect that will be illustrated in this field trip is the metallogeny of the eastern Arunta region. The region is characterised by a large variety of mineral deposits, including lode gold, volcanic-hosted massive sulphide (VHMS), carbonate replacement Zn-Cu, iron-oxide Cu-Au (IOCG), skarn W-(Mo-Cu-Au), carbonatite and aeolian/alluvial garnet deposits. However, most of the known deposits are small, with only the Molyhil W(-Mo-Cu-Au?) deposit, the Mud Tank vermiculite and the White Range Au deposits mined in recent times. Potentially the most economically important deposits are the garnet deposits and the Nolans Bore rare-earth-element (REE)-phosphate-U deposit. This excursion will visit examples of all of these deposit types.

The magmatic, tectonic, and topographic evolution of what is now the northern Great Basin remains controversial, notably the temporal and spatial relation between magmatism and extensional faulting. This controversy is exemplified in the northern Toiyabe Range of central Nevada, where previous geologic mapping suggested the presence of a caldera that sourced the late Eocene (34.0 mega-annum [Ma]) tuff of Hall Creek. This region was also inferred to be the locus of large-magnitude middle Tertiary extension (more than 100 percent strain) localized along the Bernd Canyon detachment fault, and to be the approximate _location of a middle Tertiary paleodivide that separated east and west-draining paleovalleys. Geologic mapping, 40Ar/39Ar dating, and geochemical analyses document the geologic history and extent of the Hall Creek caldera, define the regional paleotopography at the time it formed, and clarify the timing and kinematics of post-caldera extensional faulting. During and after late Eocene volcanism, the northern Toiyabe Range was characterized by an east-west trending ridge in the area of present-day Mount Callaghan, probably localized along a Mesozoic anticline. Andesite lava flows erupted around 35?34 Ma ponded hundreds of meters thick in the erosional low areas surrounding this structural high, particularly in the Simpson Park Mountains. The Hall Creek caldera formed ca. 34.0 Ma during eruption of the approximately 400 cubic kilometers (km3) tuff of Hall Creek, a moderately crystal-rich rhyolite (71?77 percent SiO2) ash-flow tuff. Caldera collapse was piston-like with an intact floor block, and the caldera filled with thick (approximately 2,600 meters) intracaldera tuff and interbedded breccia lenses shed from the caldera walls. The most extensive exposed megabreccia deposits are concentrated on or close to the caldera floor in the southwestern part of the caldera. Both silicic and intermediate post-caldera lavas were locally erupted within 400 thousand years of the main eruption, and for the next approximately 10 million years sedimentary rocks and distal tuffs sourced from calderas farther west ponded in the caldera basin surrounding low areas nearby. Patterns of tuff deposition indicate that the area was characterized by east-west trending paleovalleys and ridges in the late Eocene and Oligocene, which permitted tuffs to disperse east-west but limited their north-south extent. Although a low-angle fault contact of limited extent separates Cambrian and Ordovician strata in the southwestern part of the study area, there is no evidence that this fault cuts overlying Tertiary rocks. Total extensional strain across the caldera is on the order of 15 percent, and there is no evidence for progressive tilting of 34?25 Ma rocks that would indicate protracted Eocene?Oligocene extension. The caldera appears to have been tilted as an intact block after 25 Ma, probably during the middle Miocene extensional faulting well documented to the north and south of the study area.

The Central Transportation Planning Staff updated and enhanced railroad linework distributed by the United States Geological Survey (USGS) as 1:100,000 Digital Line Graphs (DLGs). The original 1:100,000 DLG data were conflated to the orthophoto-derived 1:5,000 Centerline linework now used in this layer. CTPS added several attributes pertaining to type of service, MBTA Commuter Rail status, rail line ownership, and freight and passenger operation.