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).

HISTORICAL BACKGROUND Until the second world war no general work had been published on the geology of French Guiana. Systematic study of the subsoil began only in 1946, under the auspices of the Office of Overseas Scientific Research. In 1949 the first study of the northern part of the country was published (B. Choubert, 1949). The southern part has been explored by M. E. Aubert de la Rüe who has just published the account of his traverses (Aubert de la Rüe, 1953). Starting in 1950, periodical contacts were established between the three Guianas, with the object of establishing correlations between the various formations. One of the results of this collaboration was the presentation, at the Nineteenth International Geological Congress in Algiers, in 1952, of the first geologic map of the three Guianas, on a scale of 1:2,000,000 and accompanied by an explanatory text (Choubert, Schols, and Bracewell, 1954). In 1952 the permanent geologic mission of the Office of Overseas Scientific Research in French Guiana became one of the branches of a multiple research organization: l’Institut Français d’Amerique Tropicale. Finally, in 1953, the preparation of a regular geologic map was begun. The first sheet (Cayenne region) is now in press. GEOLOGY Naturally, in this country covered with almost impenetrable forests, the preparation of a geologic map faces numerous obstacles. The most difficult to surmount is the scarcity of outcrops away from the river valleys. A serious study is nevertheless possible, thanks to complete coverage with vertical aerial photographs geologic mission of

Several process-based models of river incision have been proposed in recent years that attempt to describe fluvial landform development. Although some field tests have been performed, more data are required to test the ability of these models to predict the observed evolution of fluvial landforms. We have investigated several tens of rivers located in the French western Alps that flow across folded sedimentary rocks with strongly contrasting rock strengths. These rivers record significant variations in some of the parameters controlling river incision, notably bedrock lithology, stream power, incision rate, and sediment flux, potentially allowing discrimination between existing models. Variations in incision rates are driven by variations in the amount of disequilibrium introduced in the river profiles during the last glaciation. We use diagnostic indices to investigate transport- and detachment-limited conditions, which include the channel morphology, the occurrence of lithogenic knickpoints, the continuity of alluvial and bedrock reaches, and the slope-area scaling of the river long profile. We observe transitions from detachment-limited to transport-limited conditions with increasing discharge/drainage area and decreasing incision rate. Bedrock strength influences the location of the transition predictably. The formation of transport-limited rivers coincides with the development of a valley flat wider than the active channel, which accommodates variations in bedrock strength, stream power, and incision rate along the transport-limited reaches. We propose and calibrate a model for the development of valley flats along transport-limited rivers and explore some properties of landscape development in mountain ranges controlled by transport-limited rivers.

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.

ABSTRACT Heads of submarine canyons may occur anywhere on continental margins, from river mouths to continental slopes, producing a distinctive interface between shallow- and deep-marine environments. Inception of most canyons is subaerial, fluvially cut during lowered sealevel. Submarine mass flow also commences canyon formation. Submarine erosion shapes all canyons, and is especially effective in the headward region. Sliding and slumping are volumetrically most important as erosive agents, but sand spillover, bioerosion, sand flow, sand creep, and debris flow all play a part. Fluctuating channelized currents and low-velocity turbidity currents also erode and transport sediments. Canyons alter shelfbreak circulation and sedimentation. They remove detritus from fluvial outflow, longshore transport, and cross-shelf drift, and may influence the position of rip currents. On narrow shelves, surface waves diverge over canyon heads, providing a transport corridor for the return of turbid water. Suspensates downwell along canyons as high-density nepheloid layers. Channelized currents winnow fines in upper canyon heads; focused internal tides and waves may actually break, producing more extensive erosion. Although research on modern canyon systems has rapidly increased, detailed studies of ancient canyons remain sparse. An Eocene example from Southern California contains a tripartite fill representing progressive detachment from a nearshore source during a eustatic sealevel rise. Suspensate fallout, tractional flow, and mass-flow processes formed a basal amalgamated pebbly sandstone overlain by planar- to convolute-laminated sandstone, topped by variegated cut-and-fill mudstone channels. This tributary system fed the main canyon, filled with fining- and thinning- upward complexes. The Pigeon Point and Carmelo Formations of coastal California and Tethyan submarine canyons of Czechoslovakia display similar fining-upward canyon fills. Contrasting Fill sequences include coarse-grained units that dominate French Maritime Alps and New Zealand canyon complexes, and shales that plug canyons in the Gulf Coast, Sacramento Valley, and Israel. Shelf size and gradient, rates of eustacy, tectonism, and subsidence, and sedimentary-source input and migration interact to create this diversity of fills in ancient submarine canyons. Quantified analyses of canyon formation, maintenance, and Fill, and application of sedimentary hydrodynamics to observed mass transport processes and their resultant ancient counterparts, are still needed.

ABSTRACT The Bowman Road pool is an Upper Cretaceous Lathrop gas discovery drilled in September, 1994 by Nahama and Weagant Energy Company. It is located in the northernmost San Joaquin Valley, approximately five miles south of the city of Stockton. The pool, currently operated by Enron Oil and Gas Company, lies on the upthrown side of the Stockton fault one mile east of the large Lathrop gas field which has produced in excess of 350 Bcf from Lathrop sandstones. The Bowman Road discovery was based on regional studies and detailed subsurface geology tied to a one-half mile grid of CDP seismic. It targeted stacked Lathrop sandstones in a small faulted anticlinal closure. The exploration concept was a deeper pool test of the western structure of the French Camp gas field. This faulted, south-plunging anticline produced gas from the Second Starkey Sandstone and it was believed that deeper Lathrop sandstones had not been tested at a crestal position because of offset of the structural axis with depth. The crestal migration is caused by westward thinning of the section overlying prospective Lathrop sandstones. Nearly 500 feet of regional thinning occurs parallel to the Starkey shelf edge because of thicker Starkey shelf sand deposition to the east and greater compaction of coeval slope shale to the west. The interpretation proved to be correct and the well was completed from selected intervals between 7532' and 7678' at a rate of 3200 Mcf/D of 733 Btu gas on a 16/64" choke. Production sales began in January, 1996 and development of the pool is currently underway.