Forty kilometers south of Tecate, Baja California Norte, is an extensive area of pre–medial Cretaceous, greenschist-facies flysch, poorly exposed, and of unknown thickness. These rocks are lithocorrelative with the Triassic(?) French Valley and Julian Schist Formations and the Upper Triassic-Middle Jurassic Bedford Canyon Formation, north of the international border. The flysch type strata of the area consist of tabular, thin- to thick-bedded subarkosic metasandstone interbedded with metapelite. Isotopic studies on detrital zircon suggest a mixed population of discordant Middle to Late Proterozoic zircon and late Paleozoic and Triassic zircon. The flysch strata, herein named the Rancho Vallecitos Formation, is divided into a predominantly sandstone lithofacies and a predominantly shale lithofacies. Vertical sequence patterns and associations of sedimentary structures (graded bedding, outsized clasts, meniscate and diffuse laminae, etc.) indicate that the sandstones of both lithofacies were deposited by high-density turbidity currents. Rare ripple-laminated contourites of the shale lithofacies indicate deposition by northerly and southerly oriented paleocurrents. Vertical sequence patterns of sandstone beds in the sandy lithofacies suggest deposition in the outer part of a submarine fan-like system. Features of the predominantly shale lithofacies suggest a basin-plain depositional environment. Subordinate pebbly mudstone and local olistostrome/mélange deposits of the shaly lithofacies indicate proximity to slope areas. The overall fine-grained, poorly sorted, and matrix-rich character of all the sandstones suggests deposition in a large submarine fan or cone system of unrestricted open ocean basins, characteristically fed by large river/delta systems. Modal analyses of the sandstone framework indicates sediment sources of recycled orogens and possibly craton interior.

An area near Hemet in Riverside County, California, has been studied in which the sedimentology and pre-intrusive metamorphism at the site of the Southern California Batholith are well preserved. Pelitic schists of the Jurassic (?) Bedford Canyon Formation are conformably overlain by a 13,000-foot thick section of quartzite, schist, and amphibolite of the French Valley Formation (new name). These rocks were formed from a series of shales, shale-clast conglomerates, poorly sorted feldspathic, calcareous, and arkosic sandstones, and rare basaltic extrusives. Relict sedimentary textures and structures preserved at low metamorphic grade indicate a marginal basin environment; the age of deposition, formerly thought to be Paleozoic, is unknown. The sedimentary rocks were intruded by basaltic sills, folded and regionally metamorphosed at low pressures (3–5 kb) and moderate-to-high temperatures, up to 750°C, producing andalusite, cordierite, sillimanite, and garnet in the pelitic schists, and converting the basic igneous rocks to garnet-diopside-amphibolites. Four metamorphic zones are distinguished. Their boundaries trend north-south, athwart the regional strike, and bear no relation to the distribution of plutonic intrusives of the Southern California Batholith. Ultra-basic magma was intruded following the kinematic phase of metamorphism but was metamorphosed at temperatures and hydrostatic pressures comparable to those affecting the enclosing gneiss. The metamorphism is thought to have antedated emplacement of the Southern California Batholith (Late Cretaceous) and is analogous to the low-pressure andalusite-type metamorphism described by Miyashiro (1961).

Abstract This paper presents a detailed VHR seismic analysis, ground-truthed by vibracore sampling, of the middle and outer segments of two modern incised-valley fills (the Charente and the Lay–Sèvre incised valleys) located on the French Atlantic coast, about 100 km north of the well-known Gironde incised valley. Despite strong similarities between these two incised-valley systems, including (1) small river drainage basins of less than 10,000 km 2 , (2) mixed-energy wave- and tide-dominated estuaries, (3) similar valley shape, and (4) two major disconnected submarine depocenters separated by a sediment starved area, their internal architecture shows major differences. To the south, the seaward depocenter of the Charente incised valley displays a typical succession including, from base to top: high-angle, subhorizontal (mixed sand and mud unit) and high- to low-angle reflector (sandy unit) units. The shoreward depocenter of the Charente incised-valley fill consists mainly of seismic units that display subhorizontal reflectors and is composed of mixed sand and mud, draping over small seismic units that display high-angle reflectors. To the north, the Lay–Sèvre incised-valley fill exhibits a rather different internal architecture, displaying mainly high-angle clinoforms composed of sand, covered by a mud drape in the shoreward depocenter. Summarizing our results, it appears that the northern Lay–Sèvre incised-valley fill is sand-dominated, whereas the southern Charente incised-valley fill consists of mixed sand- and mud-dominated deposits. Because those two incised-valley systems are located very close together (a few kilometers), it is postulated that they have experienced similar sea-level changes, vertical crustal motions, and climate changes. As a consequence, the observed differences in sediment infill must be related to variations in sediment supply. Because the drainage-basin areas of the rivers connected to those valleys are very small, and given that sediments include marine facies, it is proposed that variations in sediment supply signify different marine sources. A greater marine sediment supply has infilled the northern incised valley (the Lay–Sèvre incised valley) more than the southern (the Charente incised valley) because this northern valley acted as a trap for marine sediments derived from the southward-oriented littoral drift. By comparison, the Charente valley contains more mud derived from the Gironde estuary, located to the south. Such comparative study between two modern incised valleys belonging to the same basin shows that, despite similar tectonic, eustatic, and hydrodynamic controls, their infill can be very different as a function of variations in the type and amount of marine-derived sediment, controlled by both physiography and littoral drift. It shows a variant model for sediment-starved margins, which we name the rocky-coast estuarine model, where hydrodynamics and sediment transport are strongly controlled by bedrock morphology.

Abstract Catastrophic deep-seated landslides (DSL) are generally considered to be the result of large slope deformations also known as deep-seated gravitational slope deformation (DSGSD). This paper aims to build a synthesis of multiple studies made in the Tinée Valley (southern French Alps) to assess the geometrical, kinematical, mechanical and chronological relationships between these two gravitational processes. At the scale of the valley, data issued from geological, geomorphological and 10 Be dating indicate a clear geometrical link between DSGSD and DSL occurring at the base of the slope and suggest that gravitational slope evolution began after the glacial retreat (13 ka BP). This is supported by the example of the well-documented La Clapière slope. A continuous evolution process is characterized geometrically and temporally from geomorphic observations and analogue modelling. Coupling structural, geomorphological, physical and chronological studies allowed us to propose a four-dimensional (4D) deformation model mechanically correlated with progressive failure concept. The validity and variability of this reference site are discussed at the valley scale (taking Isola and Le Pra slope deformation as examples). It allows a rough estimation of the state of slope deformation at the valley scale to be constructed and the slope evolution with time to be considered. This 4D model could then be considered as a reference for other deep-seated gravitational slope deformations in comparable Alpine valleys.

ABSTRACT The northern portion of the northwest-southeast trending Great Valley of California is broken in the subsurface into several distinct tectonic subunits by a number of northeast-southwest trending basement faults, the largest being the Stockton (or French Camp) fault, with over 2000 feet of reverse or thrust fault displacement in the shallower upper Cretaceous stratigraphic section. Similar features of lesser magnitude with the same geographic trend and exhibiting similar tectonic histories both to the north and south of the Stockton fault have been recognized by several explorationists and researchers but are less well documented. While the smaller of these features appear to lose structural integrity to the west with thickening sedimentary cover and deepening Sierran basement, they exhibit several common characteristics and structural history which include: (1) two distinct periods of structural movement separated by a period of apparent non-movement; (2) involvement of Sierran basement, at least on the east side of the valley; (3) early indications of tensional or tranverse movement with significant growth on the downthrown side followed by a later period of apparent compressional movement; (4) reversal of apparent throw from the early movement to the late movement withthe initially downthrown hanging wall block exhibiting thrust displacement in the later compressional stage. Between the two time periods of apparent movement seen on these faults, the dominant fault pattern in the Sacramento valley was related to the predominantly northwest-southeast trending Midland fault system with its large growth faults active from paleocene through early Eocene time. It is suggested that these three periods of faulting correspond to an early period of regional plate convergence and subduction during the upper Cretaceous, an intermediate period of plate junction during the Paleocene and lower Eocene characterized by emplacement of diapiric ophiolite sequences such as Mt. Diablo near the outcrop of the Great Valley Thrust with the large growth faults of the Midland system being associated with these diapiric serpentinite emplacements; thirdly, a post-Eocene period of faulting wherein the dominance of strike-slip movement along the San Andreas fault system is associated with a change in regional stress which placed the previously tensional cross-valley faults into a compressional regional stress pattern and reactivated the older faults in a different structural setting.