The Eastern belt of the Sierra Nevada comprises an Ordovician(?) to Devonian(?) succession of psammites and pelites belonging to the Shoo Fly Complex, and is overlain by three Paleozoic to Mesozoic arc volcanic sequences. The northern part of the belt, the subject of this chapter, is divided into a series of discrete blocks by steeply dipping faults, considered to be eastward-directed thrusts. The metamorphic history of this region has been little investigated previously. It has been argued that low-grade metamorphism of the Eastern belt is a Nevadan orogenic effect; in contrast, it has also been suggested that metamorphism of the arc volcanic rocks was a result of burial effects in the arc environment. In this study the metamorphic grade of the area has been established using mineral assemblages in metabasites and pelites, combined with illite crystallinity and b 0 data from pelitic rocks. The Shoo Fly Complex underwent epizonal metamorphism under Barrovian-type conditions prior to the earliest arc volcanism. Metamorphic grade in the overlying arc volcanic rocks ranges from pumpellyite-actinolite facies in the strongly foliated rocks of the (westernmost) Butt Valley and Hough blocks, through prehnite-pumpellyite facies in the Keddie Ridge and Genesee blocks, to low anchizone to diagenetic grade in Jurassic rocks of the (easternmost) Mt. Jura and Kettle Rock blocks. There is evidence for at least three discrete regional metamorphic events in these arc rocks; one is interpreted as being related to the burial of the arc volcanic rocks, which reached prehnite-pumpellyite facies; this event was followed by deformation and pumpellyite-actinolite facies metamorphism during the Nevadan orogeny; a final episode of static, low-grade metamorphism, possibly due to tectonic loading effects, probably also resulted in pumpellyite-actinolite facies. Subsequently, rocks exposed in the extreme east of the region were affected by contact metamorphism during the emplacement of Sierra Nevada batholith granitoids.

Abstract A vital lesson of plate tectonics is that there is no validity to any assumption that the simplest and therefore most acceptable interpretation demands a proximal rather than a distant origin. (Coombs, 1997 , p. 763). This field trip steps back to provide the very long term and large-scale tectonic history that one might call the broader tectonic context of the 1906 San Francisco earthquake. In effect, the field trip follows a cross section of northern California, with stops that illustrate the geologic history of the region. The field guide also discusses several archaeological stops of significance to California's prehistory. The entire field trip is meant to be taken over a period of four days, with overnight stops in Davis and in Quincy. Day one comprises Stops 1–9; Day 2, Stops 10–18; Day 3, Stops 19–28; and Day 4, Stops 29–33. Northern California geology is the result of an extended history of active plate margin interactions spanning some 500 million years (m.y.). Over the course of this period, countless numbers of large earthquakes of different types no doubt accompanied tens of thousands of kilometers of movement between tectonic plates and microplates that eventually came together to form the rocks of northern California as we see them today. From ca. 500–18 million years ago (Ma), subduction, a process still active north of Cape Mendocino, dominated the geologic history of northern California. During this period, several subduction zones and volcanic arcs were active, and subduction zones, whose former positions we will see on our trip, consumed ocean basins thousands of kilometers wide, sweeping together a vast collage of rocks from far-flung locations in the process. Remnants of the most ancient of these subduction zones and collided blocks (typically called terranes) are preserved in the Sierra Nevada. The most recent subduction history along the North American margin involved the Farallon plate, a plate that lay east of the Pacific plate and was separated from it by a spreading mid-oceanic ridge. The products of this subduction episode are preserved in the rocks of the Coast Ranges, and in the granitic and younger volcanic rocks of the Sierra Nevada ((Figs. 1) and 2). For the past 18 m.y., the plate margin has been dominated by right-lateral faults of a transform plate margin, the most famous of which, the San Andreas fault, produced the 1906 earthquake. The present plate boundary between the Pacific plate on the west and stable North America on the east is a broad one consisting of two active zones: (1) the San Andreas fault system, whose right-lateral faults occupy the California Coast Ranges; and (2) a zone east of the Sierra Nevada including the right-lateral faulting associated with the Walker Lane and the Eastern California Shear Zone, and, east of the Walker Lane, the extensional faults of the Basin and Range province (Fig. 3). These zones of active faults, shown in Figure 3 , are responsible for generating most of the earthquakes in the area traversed by our field trip. The preexisting complexity of the crust resulting from the earlier tectonic history probably influenced the development and location of these more recent fault zones, in addition to giving us some exceedingly interesting and complex geology to examine on our trip. This long and complex history requires a great deal of discussion for complete understanding. In this guide, we present first the stops in sequence, including brief descriptions for each site. To augment these brief discussions, we follow the field trip guide with an Appendix in which we discuss the tectonic development of northern California more fully.

Abstract Volcanism and tectonism are the dominant endogenic means by which planetary surfaces change. This book, in general, and this overview, in particular, aim to encompass the broad range in character of volcanism, tectonism, faulting and associated interactions observed on planetary bodies across the inner solar system – a region that includes Mercury, Venus, Earth, the Moon, Mars and asteroids. The diversity and breadth of landforms produced by volcanic and tectonic processes are enormous, and vary across the inventory of inner solar system bodies. As a result, the selection of prevailing landforms and their underlying formational processes that are described and highlighted in this review are but a primer to the expansive field of planetary volcanism and tectonism. In addition to this extended introductory contribution, this Special Publication features 21 dedicated research articles about volcanic and tectonic processes manifest across the inner solar system. Those articles are summarized at the end of this review.

Abstract The separation of South America from Africa during the Early Cretaceous isolated equivalent stratigraphic sequences on both continents. This is well established for rock sequences, including flood basalts, which were deposited prior to oceanic onset; however, earlier extensional events are also recorded by the resulting intracontinental basins. Of these, the depositional area containing the Late Permian-earliest Triassic Gai-As Lake is a prime example. The aims of this paper are (1) to record facies generated within and outside the lake body and (2) to compare them with correlative bodies on the other side of the present-day South Atlantic Ocean, and (3) to record the controls of fault structures on facies architecture and lake margins. The advantages of good exposures produced by river dissection of the continental margin in northern Namibia allows good access for identifying synsedimentary fault controls on theGai-As Lake. We suggest that these can be extrapolated to correlative sequences at the conjugate South American side where exposure and thus the potential for recognition of synsedimentary structural activity is limited; consequently, the Parana "basin," commonly dealt with as an intracratonic sag basin, may be underlain by a complex of stacked rift and thermal subsidence-controlled depositional centers.

An outcrop of the Mississippian Hartselle Sandstone in north-central Alabama preserves in situ, erect cormose lycopsids, assigned to Hartsellea dowensis gen. and sp. nov., in association with a low diversity bivalve assemblage dominated by Edmondia . The isoetalean lycopsids are rooted in a silty claystone in which the bivalve assemblage occurs, representing the transition from tidal flat and tidal channel regime into a poorly developed inceptisol. Two paleosols are preserved in the sequence and each is overlain by a fine-grained quartz arenite, responsible for casting aerial stems and cor-mose bases of the entombed plants. The massive quartz arenites are in sharp contact with interpreted O-horizons of the paleosol, and the lower sandstone displays a lobate geometry. The plant assemblages are interpreted as back-barrier marshes, the first unequivocal marshlands in the stratigraphic record, preserved by overwash processes associated with intense storm surges in a Transgressive Systems Tract. A sample suite curated in the National Museum of Natural History, collected by David White at the turn of the last century in the Greenbrier Limestone of West Virginia, preserves rooting structures, leaves and sporophylls, and sporangia and megaspores of H. downensis in a mixed carbonate mud (micrite). The presence of isoetalean lycopsids in both siliciclastic and carbonate peritidal environments within nearshore shelf settings of the Early Carboniferous indicates that adaptation to periodic brackish water, if not tolerance to infrequent fully marine-water inundation during storm surges, had evolved in these marsh plants by the late Paleozoic.

Abstract Paleoenvironmental signatures deduced from the sedimentary record of the Upper Permian Madumabisa Formation in the Mid-Zambezi Basin indicate moderate climate and positive hydrologic balance in continental interiors of Gondwana (50-60° S) during the Late Permian. The inferred climate conditions are congruent with the prolific Late Permian terrestrial ecosystems that characterized south-central Africa and equivalent latitudes in Gondwana. Our results do not support the severe aridity and extreme seasonal temperature variations simulated by numerical climate models. The Madumabisa Formation is a lacustrine sequence that represents the maximum extensional phase of the Mid-Zambezi Rift basin. The basin preserves > 5 km of continental sedimentary rocks, of which the Upper Permian Madumabisa Formation comprises freshwater lacustrine deposits up to 700 m thick. Deposition occurred in a fault-controlled asymmetric half graben formed by passive rifting driven by plate boundary stresses that originated from the southern edge of Gondwana. The sedimentary sequence is dominated by black and dark greenish gray mudstones and limestones interbedded with minor gray siltstones and sandstones. The mudstones are predominantly internally massive or bioturbated, but thin-bedded and thinly laminated dark shales with moderate quantities of organic matter and carbonate occur in the lower part of the sedimentary sequence. Laminated limestones are interbedded with the mudstones and comprise fossil-rich beds and inorganic micrite beds precipitated from lake waters, most likely during periods of low clastic supply. Minor current-rippled siltstones and sandstones indicate that silt-laden flows reached deep parts of the basin. Judging from the distribution of the remains of the Madumabisa Formation, the ancient “Madumabisa Lake” covered 140,000 km 2 , and was larger than most modern lakes. The mainly dark color of the rocks and thinly laminated shales and carbonate content suggest that the lake was deep and experienced periodic, perhaps seasonal, thermal stratification. Abundant biogenic remains including conchostracods, bivalves, fish, and algae indicate a highly productive freshwater lake. Lack of features indicative of emergence and desiccation, such as evaporites, soil features, mudcracks, or cavities, suggests that the lake was perennial. Preserved plant debris including leaves and wood logs indicate that uplands in the watershed were vegetated. For most of the history of the lake system, the perennial lake remained hydrologically closed because of a steady subsidence and moderate axial sediment supply. At the end of the Permian, pulses of basinal shortening caused shallowing of the lake. Basin uplift associated with postulated basin inversion led to changes in sediment supply patterns from axial to rift flanks, as shown by paleocurrent directions. The lake sediments were eroded and buried rapidly, as indicated by the lack of paleosol features, and the lake was filled by thick, red conglomeratic sandstones of the Lower Triassic Escarpment Grit Formation. Contrary to predictions of numerical climate models, abundant moisture and cool (to moderately warm) temperatures would have been essential to sustain a large, perennial, freshwater lake such as “Madumabisa Lake” was, deep within the continental interior of south Gondwana.