Regional stratigraphic units and structural features of the Lake Mead region are presented as a 1:250,000 scale map, and as a Geographic Information System database. The map, which was compiled from existing geologic maps of various scales, depicts geologic units, bedding and foliation attitudes, faults and folds. Units and structural features were generalized to highlight the regional stratigraphic and tectonic aspects of the geology of the Lake Mead region. This map was prepared in support of the papers presented in this volume, Special Paper 463, as well as to facilitate future investigations in the region. Stratigraphic units exposed within the area record 1800 million years of geologic history and include Proterozoic crystalline rocks, Paleozoic and Mesozoic sedimentary rocks, Mesozoic plutonic rocks, Cenozoic volcanic and intrusive rocks, sedimentary rocks and surficial deposits. Following passive margin sedimentation in the Paleozoic and Mesozoic, late Mesozoic (Sevier) thrusting and Late Cretaceous and early Tertiary compression produced major folding, reverse faulting, and thrust faulting in the Basin and Range, and resulted in regional uplift and monoclinal folding in the Colorado Plateau. Cenozoic extensional deformation, accompanied by sedimentation and volcanism, resulted in large-magnitude high- and low-angle normal faulting and strike-slip faulting in the Basin and Range; on the Colorado Plateau, extension produced north-trending high-angle normal faults. The latest history includes integration of the Colorado River system, dissection, development of alluvial fans, extensive pediment surfaces, and young faulting.

Geological mapping of the island of Lipari at 1:10,000 scale was performed by adopting a stratigraphic approach based on the integrated use of lithostratigraphic units, lithosomes, and unconformity-bounded units. This approach allows the geological peculiarity of this volcanic area to be reproduced through documention and interpretation of the different rock types (using lithostratigraphic units), and definition of the geometry of rock bodies (using lithosomes), with emphasis on unconformities in the volcano-sedimentary architecture (using unconformity-bounded units). In particular, by concentrating on accurate tephrostratigraphy and deposits formed during periods of prolonged volcanic quiescence (e.g., marine deposits and epiclastic products), unconformity-bounded units provide the main stratigraphic constraints at a regional level. Two first-order unconformities (U I and U II ), represented by surfaces of erosion bounding marine deposits emplaced during marine oxygen isotope stage (MIS) 5, can be correlated across most of the Aeolian archipelago. Furthermore, four second-order and seven third-order unconformities represented by erosion and non-deposition surfaces formed during main periods of dormancy or minor sea-level fluctuations of MIS 5 are introduced. The reconstructed unconformity-bounded stratigraphy, together with other rock-stratigraphic units, provides an effective reconstruction of the geological evolution of Lipari, ranging between ca. 220 ka and the present time, as the result of the interplay among volcanic activity of local and external provenance, sea-level fluctuations, and regional fault systems. In this framework, Lipari's eruptive history encompasses five successive eruptive epochs characterized by distinctive centers of eruption (eastwards shifting), eruption type (from mainly strombolian to hydromagmatic), and chemical composition (from calc-alkaline basalt-andesite to high-K calc-alkaline rhyolite).

A new geological map of the island of Stromboli at a scale of 1:10,000 is here presented based on 1:5000 scale field mapping, carried out in the years 1991–2001, by applying exclusively lithostratigraphic criteria and unconformity-bounded stratigraphic (UBS) units. The application of UBS units proved to be very effective, especially in such a complex succession of volcanic rocks. In total, 45 lithostratigraphic units and eight synthems, as well as various subsynthems, lithosomes, and units representing the most recent sedimentary deposits, were recognized. The resulting legend for the 1:10,000 map has been elaborated in such a way as to distinguish the lithostratigraphic units occupying a well-defined stratigraphic position from the ones for which stratigraphic attribution is uncertain; furthermore, the range of possible stratigraphic positions is also indicated. Other problems are discussed and solutions proposed, such as: (1) representing and distinguishing historic deposits that do not have any lithologic or geometric variations with respect to the recent deposits above which they have been emplaced, (2) representing units, or boundaries between units, that crop out only on vertical cliffs, (3) possible scale reduction, and (4) the cartographic problems related to structural features. Finally, the main differences from previous modern maps are described in terms of the geological evolution of Stromboli volcano, one of the best-documented examples of a multiple-collapse edifice.

In this work, unconformity-bounded stratigraphic (UBS) units are applied to a complex volcanic terrain. UBS units allow us to summarize the spatial-temporal relationships between the cartographic units of a volcanic district or complex, and identify individual successions of volcanic deposits and their probable connection with morphogenetic and/or tectonic phases. The UBS unit approach for the interpretation of significant preserved unconformity surfaces is supported by data from geomorphology, sedimentology, petrology, tectonics, and volcano-tectonics. The result is a stratigraphic scheme that combines the recognized lithostratigraphic units into a series of synthems, in which several phases of geological evolution of Ustica Island are recognized. The emplacement in the early Pleistocene of the basaltic Monte Guardia dei Turchi lithosome, which represents the emerged part of the volcanic seamount, was followed by hydromagmatic activity and construction of a tuff cone that is part of the Monte Costa del Fallo synthem. Following a period of quiescence, volcanism on the island resumed with a Plinian eruption that deposited a thick sequence of trachytic pumice breccias and was accompanied by a caldera collapse. Subsequently, marine terracing occurred in the southwest, while extrusive volcanics filled the caldera in the northern part of the island. Lava flows associated with this volcanism are present on the western flank of the volcano, whereas along the sublittoral zones, dike swarms provide evidence of phreatomagmatic activity. This volcanic activity was followed by repeated alluvial deposition and marine erosion. Finally, recent subaerial monogenetic centers produced shallow subvolcanic bodies, scoria and tuff cones, and lava flows.

Modern stratigraphic studies and field mapping of Quaternary volcanic terrains require a multidisciplinary approach for the reconstruction of the time-space history of a volcanic area (e.g., activity phases, eruptive sources, compositional changes, volcano build-up and collapse events) within the framework of concomitant and/or genetically related geological events acting on regional to global scales (e.g., tectonism, climate changes, glacio-eustatism). Here, we report recent results on the stratigraphy, structure, and evolution of the southern part of the Vulsini volcanic district (0.6–0.1 Ma), Roman Province, in the light of a new geological survey for the 1:50,000 map of Italy (CARG Project). We focus on the integration of different kinds of stratigraphic units, including lithostratigraphic, lithosomatic, and unconformity-bounded stratigraphic (UBS) units, to define and group mappable volcanic bodies. Lithostratigraphic units are characterized in terms of textural features, indicative of eruptive and emplacement scenarios, and rock-type compositions. The intervening stratigraphic discontinuities are defined in terms of nature, position, and areal extent, and they are attributed to local depositional processes versus significant temporal hiatuses in the eruptive activity or regional and interregional geological events. The mapped volcanic units are thus correlated to lithosomatic units, corresponding to volcanic source edifices, as well as to the local and regional UBS unit settings recently defined for the Tyrrhenian coast nearby. On these grounds, we illustrate the geological evolution of the study area as the interplay of constructional and destructional volcanic activity, erosion, pedogenesis, secondary volcaniclastic sedimentation during intereruptive periods, and sea-level fluctuations.

Las Cañadas caldera complex, on Tenerife, Canary Islands, truncated the construction of Las Cañadas edifice, a central composite volcanic complex formed after a main period of basaltic shield construction. The origin of the present Las Cañadas caldera complex is still a matter of considerable debate between two contrasting hypotheses, vertical (caldera forming) or lateral (landslide) collapse. However, there is increasing evidence that a long history of explosive phonolitic volcanism, including several caldera episodes, characterized the construction of Las Cañadas edifice. Los Roques de García forms a large spur that divides the Las Cañadas caldera complex into two morphological depressions. The sequence of rocks exposed along the spur consists of several formations that from base to top include: Los Roques de García Formation, Los Azulejos Formation, and the lower part of the Ucanca Formation. Los Roques de García Formation occupies the main part of Los Roques de García spur and includes proximal facies of pyroclastic (Lower Member) and sedimentary (epiclastic) (Upper Member) deposits, predominantly breccias, all of which are intruded by a dense network of phonolitic dikes and necks. Pyroclastic deposits mostly correspond to coignimbrite lag breccias, lithic-rich ignimbrites, and minor surge and ash-fall beds. Epiclastic rocks mainly include poorly to well-stratified, proximal debrisflows breccias deposited in an alluvial-fan environment, with some interbedded pyroclastic and epiclastic sandstone and conglomerate units. The central sector of Los Roques de García spur is highly fractured due to the movement of several normal faults, thus conferring a chaotic aspect to that zone. Strong hydrothermal alteration also has affected some sectors of Los Roques de García spur, enhancing this chaotic appearance. New detailed mapping and stratigraphic logging have been crucial to interpreting the nature and stratigraphy of Los Roques de García rocks, which represent two fundamental aspects for the interpretation of the origin and evolution of Las Cañadas caldera. Los Roques de García spur exhibits a stratigraphy that is concordant with the rest of Las Cañadas caldera wall and corresponds to the lower part (Lower Group) of Las Cañadas edifice, without having any relation to latter explosive episodes responsible for the deposition of its upper part (Upper Group). Lithological, sedimentological, and volcanological characteristics of Los Roques de García rocks allow them to be interpreted either as a former Las Cañadas intracaldera sequence or as the apron of an older stratovolcano, in contrast with previous interpretations, which have suggested that they correspond to the products of a major debris avalanche event that contributed to the formation of the present caldera.

During the past 15 yr, volcanological studies in Mexico have been mostly focused on the pyroclastic stratigraphy and petrologic evolution of the volcanoes, with very little attention paid to detailed mapping of volcanic areas. In this study, we present a geologic map of the Colima volcanic complex, which covers ~3780 km 2 . The Colima volcanic complex is made of El Cántaro, Nevado de Colima, Paleofuego, and Colima volcanoes, totaling 422 km 3 in volume. The activity of the Colima volcanic complex started at El Cántaro with the emission of lava flows and domes ca. 1.7 Ma. About 0.53 Ma, 15 km southward, the formation of Nevado began with the emission of lava flows. Nevado produced at least four collapses that generated debris avalanches, debris flows, and pyroclastic-flow deposits. During late Pleistocene (>>38,500 yr B.P.), the formation of Paleofuego began 5 km further south with the emission of lava flows. Paleofuego collapsed at least five times, producing debris avalanches and pyroclastic-flow deposits. The last collapse of Paleofuego, at 2505 yr B.P., produced a 5-km-wide caldera, inside of which grew Colima volcano. Colima is the most active volcano in Mexico, with 45 eruptions during the past 426 yr, representing a potential hazard for the surrounding population of ~0.9 million people. From the geological mapping, it is clear that volcanic activity and collapses of the Colima volcanic complex have been controlled by the active Tamazula fault, which generated the NE-SW Alceseca-Atenquique graben.

Abstract This collection of papers addresses the issues surrounding communication of environmental geoscience. Geologists whose research deals with environmental problems such as landslides, floods, earthquakes and other natural hazards that affect people’s health and safety, must communicate their results effectively to the public, policy makers and politicians. There are many examples of geological studies being ignored in policy and public action; this is in due in part to geoscientists being poor communicators. These papers document issues in communicating environmental geoscience, outline successes and failures through case studies, describe ways in which geoscientists can improve communication skills and show how new methods can make communication more effective.

Abstract “The new Geologic Map of North America covers ~15% of Earth’s surface and differs from previous maps in several important respects: It is the first such map to depict the geology of the seafloor, the first compiled since the general acceptance of plate-tectonic theory, and the first since radiometric dates for plutonic and volcanic rocks became widely available. It also reflects enormous advances in conventional geologic mapping, advances that have led to a significant increase in the complexity of the map. The new map, printed in 11 colors, distinguishes more than 900 rock units, 110 of which are offshore. It depicts more than seven times the number of on-land units as are shown on its immediate predecessor, as well as many more faults and additional features such as volcanoes, calderas, impact structures, small bodies of unusual igneous rocks, and diapirs. When displayed at earth science institutions and libraries, this map is sure to impress viewers with the grand design of the continent and may inspire some to pursue the science of geology. The new Geologic Map of North America is also a “thinking map,” a source for new interpretations of the geology of North America, insights into the evolution of the continent, new exploration strategies for the discovery of mineral and energy resources, and the development of better ways to assess and mitigate environmental risks and geologic hazards.3 sheets (North, South, and Legend), approximately 74 x 40 inches.”

Abstract DNAG Transect A-3. Part of GSA’s DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.

Abstract DNAG Transect E-4. Part of GSA’s DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.

Abstract Transect H-3 extends 460 krn across southern Mexico from the Pacific Ocean to the Gulf of Mexico, far south of cratonic North America. The transect has two segments: one trending N7°E from the axis of the Acapulco Trench to central Oaxaca and another extending N53°W from central Oaxaca to the Gulf of Mexico. The cross sections lie near the middle of the transect and coincide with a line connecting Puerto Escondido at the Pacific coast, the city of Oaxaca, and San Martin Tuxtlas Volcano near the NE end of the transect The mosaic of geologic provinces along the corridor made it convenient to use a tectonostratigraphic approach for the analysis of the geologic history. Terrane nomenclature in this report is derived from names of pre-Hispanic cultures dominant in each respective region. The geologic description of terranes and the bases of their discrimination are given below.

Abstract DNAG Transect H-3. Part of GSA’s DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.

Abstract DNAG Transect H-1. Part of GSA’s DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.

Abstract DNAG Transect C-1. Part of GSA's DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.