ABSTRACT The mid-Cenozoic succession in the northeast limb of the Mount Diablo anticline records the evolution of plate interactions at the leading edge of the North America plate. Subduction of the Kula plate and later Farallon plate beneath the North America plate created a marine forearc basin that existed from late Mesozoic to mid-Cenozoic times. In the early Cenozoic, extension on north-south faults formed a graben depocenter on the west side of the basin. Deposition of the Markley Formation of middle to late? Eocene age took place in the late stages of the marine forearc basin. In the Oligocene, the marine forearc basin changed to a primarily nonmarine basin, and the depocenter of the basin shifted eastward of the Midland fault to a south-central location for the remainder of the Cenozoic. The causes of these changes may have included slowing in the rate of subduction, resulting in slowing subsidence, and they might also have been related to the initiation of transform motion far to the south. Two unconformities in the mid-Cenozoic succession record the changing events on the plate boundary. The first hiatus is between the Markley Formation and the overlying Kirker Formation of Oligocene age. The succession above the unconformity records the widespread appearance of nonmarine rocks and the first abundant appearance of silicic volcanic detritus due to slab rollback, which reversed the northeastward migration of the volcanic arc to a more proximal location. A second regional unconformity separates the Kirker/Valley Springs formations from the overlying Cierbo/Mehrten formations of late Miocene age. This late Miocene unconformity may reflect readjustment of stresses in the North America plate that occurred when subduction was replaced by transform motion at the plate boundary. The Cierbo and Neroly formations above the unconformity contain abundant andesitic detritus due to proto-Cascade volcanism. In the late Cenozoic, the northward-migrating triple junction produced volcanic eruptive centers in the Coast Ranges. Tephra from these local sources produced time markers in the late Cenozoic succession.

This paper describes 127 species, subspecies, and varieties of Radiolaria all of which are new and which came from two shale members of the Upper Eocene series, north and northeast of Mount Diablo, Middle California. Both these shales are typical radiolarites, very similar in lithologic character to the well-known Oceanic beds of Barbados Island. The lower of these two shale members, the Kellogg shale, has a thickness of about 130 feet and lies just below the Markley formation and, in the western portion of the area under consideration, forms the upper portion of a series of sands and shales which have been locally known as the “Nortonville” shales and which have been included in the upper portion of the Domengine formation by the senior writer (1926). The higher of the two members, the Sidney shale, has a thickness of about 700 feet and belongs to the Markley formation; it is a little more than 2000 feet above its base. A comparison of the radiolarian assemblages of the Kellogg shale with those of the Sidney shale shows a considerable difference. Sixty-three per cent of the Kellogg species have not been found in the Sidney shale, and a little more than 58 per cent of the Sidney shale species have not been found in the Kellogg shale. The paper gives a brief description of the stratigraphic relationships of the Tertiary formations in the area under consideration and discusses in considerable detail the lithology of the two shales and its probable significance. The writers’ conclusion is that these shales were deposited in fairly deep marine waters under tropical or semi-tropical conditions.

ABSTRACT During the early Tertiary, in what is now the Sacramento Valley, four submarine canyons successively fed sediments into a deep remnant of the Mesozoic trough that formed the western margin of the North American continent. The Markley Valley is the youngest of these “canyons” having formed after deposition of the Sidney Shale Member of the Eocene Markley Formation. Cross sections show truncation of rocks as old as Cretaceous in the northern reaches of the valley but show that erosion of Tertiary rocks predominates in the southern end of the valley. The valley fill ranges from about 1.2 miles (2 km.) wide at its outcrop near Wheatland in Yuba County to greater than 12 miles (20 km.) wide west and southwest of Sacramento. In its thickest axial portion the valley fill is greater than 2000 feet (600 m.) thick. The Markley Valley is 67 miles (110 km.) long. The Markley Valley trends generally S10°W but north of Rio Vista it abruptly turns westerly to its presumed outlet. Structure contour maps of the base of the valley fill show the feature to be surprisingly irregular with reentrants that suggest tributaries and occasional highs which appear as monadnocks. Along much of its length the filling of the Markley Submarine Valley was the last marine event and the fill is overlain by continental sediments of the late Tertiary Tehama Formation. The Markley Valley Fill is dominated by shales and as such is less prospective for gas exploration than areas outside the valley. However, the Green’s Lake Gas Field 3 miles (5 km.) southwest of Sacramento gained a small portion of its production from what is locally called the Markley Valley Sandstone, clearly within valley filling sediments. This sand and others that are similar are thin and discontinuous compared to reservoir rocks outside of the valley fill. The Markley Valley more importantly impacts gas exploration as its fine-grained fill material truncates and seals thicker, more permeable reservoirs outside the valley. In as many as twelve gas fields including the Catlett, Conway Ranch, Fremont Landing, Karnak, Liberty Cut, Liberty Island, Maine Praire, Millar, Rio Jesus, Sacramento Airport, Todhunters Lake, and Winchester Lake fields, a significant amount of the gas trapped is attributable to valley-filling sediments truncating and sealing older gas reservoirs.

ABSTRACT The Kirby Hill Fault Zone (KHFZ), which crops out on the Kirby Hill gas field in Section 30, T4N - R1E and in Section 25, T4N - R1W (MDB&M), was first recognized by surface mapping in the 1930’s. Kirby Hill, which is 40 miles northeast of San Francisco, geologically and topographically reflects a faulted structural high that is nearly surrounded by lowlands of the alluviated tideland and marshland of the Sacramento River delta and associated bays and sloughs. Strata ranging in age from late Eocene (Nortonville and Markley formations) to Miocene and Pliocene (nonmarine deposits) are exposed at Kirby Hill. Dips vary widely, but mostly east dips ranging from 30°to 80° are predominant. Early exploration and gas discoveries, evolving structural interpretations, the projection of the Kirby Hill Fault northward and southward of the Kirby Hill gas field, and the imprint of Neogene compressional tectonics on the older arc-trench extensional tectonics that persisted throughout the Paleogene are examined. Fault displacement of 7500 ft. has been documented, with recurrent movementfrom Late Cretaceous through late Eocene. Neogene lateral movement across the KHFZ appears negligible, based on the mapped distribution of the “Black Diamond Coal Seam” in the Eocene Domengine Formation.

This paper lists and describes radiolarian assemblages obtained from the Kreyenhagen shales along the west side of the San Joaquin Valley in the Charleston School quadrangle near Los Banos, California. These deposits have a thickness of about 700 feet and consist mostly of organic shales. The samples were obtained from 12 stratigraphic horizons. These assemblages contain 104 species, a considerable number of which were originally described from the Sidney and Kellogg shales from the Mount Diablo and Byron quadrangles. The conclusion is that the zone represented by the Sidney shale is not represented in this section. The faunas from the lower assemblages suggest relationship to those in the Kellogg shales just below the Markley formation of the Mount Diablo area and that the other assemblages are probably intermediate between the Kellogg and the Sidney shales.

ABSTRACT The Markley Canyon is a large, ancient erosional feature in the Sacramento Valley which has truncated Eocene through Cretaceous sediments. Erosion of the canyon was post-middle Eocene CP14a (and probably CP14b) Subzone based on calcareous nannofossils, post-A-1 Zone based on benthic foraminifera, and occurred primarily during the late-Eocene (CP15 Zone) early to early late Refugian benthic foraminiferal Stage. Filling of the canyon began in the earliest Oligocene CP16a Subzone, latest Refugian Stage, and continued into the early Oligocene upper CP16 Zone, early Zemorrian Stage. Samples studied from the lower part of the Markley Canyon Fill and from other widespread areas in California demonstrate that the late Refugian, Uvigerina vicksburgensis benthic foraminiferal Zone is in part correlative to the early Oligocene Coccolithus subdistichus (CP16a) calcareous nannofossil Subzone, with no evidence of diachroneity.

ABSTRACT The gently dipping (3-5° SW), complexly faulted, homoclinal structure of the Todhunters Lake Gas Field is deeply incised by a southwest trending tributary of the Markley Submarine Canyon. Formed during late Eocene, the canyon eroded Eocene Nortonville Shale through upper Cretaceous Starkey sands. Hemipelagic sediments infilled the canyon during early Oligocene creating an impervious barrier to hydrocarbon migration. Faulting is an equally important trapping mechanism, particularly in sediments not affected by the incisement of the Markley Canyon, i.e., lower Starkey and Winters sands. A series of subparallel, NW trending, normal faults traverse the field creating isolated dry gas reservoirs. With offsets usually less than 80 feet, faults are generally not recognizable on available seismic lines. Some controversy exists over the age of faulting, but subsurface data suggests that it predates canyon incisement. No discontinuities are seen in the structure of the base of the Markley Canyon fill and well data in the canyon indicates no offset. Since the discovery of the field in 1967, gas has been successfuly produced from the upper Cretaceous First, Second and Third Massive sands of the Mokelumne River Formation as well as the Starkey One through Five sands. Significant production has also been obtained in the upper Cretaceous Winters sands in the western half of the field. Cumulative production to 1982 is estimated by the Division of Oil and Gas to be 79,761 MMCF. Future development of the field will depend largely upon the identification of subtle traps controlled by faulting.

ABSTRACT Paleogene marine strata in the eastern San Francisco Bay area are exposed in discontinuous outcrops in the various tectonic blocks. Although there are many missing intervals, the strata were previously thought to span most of the Paleocene and Eocene. Revision of biochronology and calibration to the international time scale as well as to the global oxygen isotope curve and sea-level curves indicate that the strata are latest Paleocene through middle Eocene in age and contain faunal changes that are linked to the overall global climate trends and hyperthermals of that time. The Paleocene-Eocene thermal maximum, third Eocene thermal maximum, early Eocene climatic optimum, and middle Eocene climatic optimum are all identified in the eastern San Francisco Bay marine strata. The dominance of smoothly finished, dissolution-resistant agglutinated benthic foraminiferal species corresponds with a rapid shoaling and rapid deepening (overcorrection) of the calcium compensation depth associated with the Paleocene-Eocene thermal maximum. The benthic foraminiferal extinction event was a dramatic turnover of benthic foraminiferal species that occurred shortly after the onset of the Paleocene-Eocene thermal maximum. Opportunistic species such as Bulimina , which indicate environmental stress and lower oxygen conditions, are commonly associated with the Paleocene-Eocene thermal maximum. Environmental changes similar to those observed during the Paleocene-Eocene thermal maximum also characterize the third Eocene thermal maximum, based on the agglutinated and opportunistic species. The early Eocene climatic optimum is noted by the presence of foraminiferal assemblages that indicate a stable, warmer water mass, abundant food, and an influx of terrigenous material. The onset and end of the middle Eocene climatic optimum are recognized by the dominance of siliceous microfossils. This research updates the age and environmental interpretations of the Paleogene formations occurring in the vicinity of Mount Diablo, eastern San Francisco Bay area. The revised interpretations, which are based on foraminifers and calcareous nannoplankton, make it possible to identify various global climatic and biotic events.

Abstract Patterns of plant distribution by palaeoenvironment were examined across the Pennsylvanian–Permian transition in North–Central Texas. Stratigraphically recurrent packages of distinct lithofacies, representing different habitats, contain qualitatively and quantitatively different macrofloras and microfloras. The species pools demonstrate niche conservatism, remaining closely tied to specific habitats, during both short-term cyclic environmental change and a long-term trend of increasing aridity. The deposits examined principally comprise the terrestrial Markley and its approximate marine equivalent, the Harpersville Formation and parts of lower Archer City Formation. Fossiliferous deposits are lens-like, likely representing fill sequences of channels formed during abandonment phases. Palaeosols, represented by blocky mudstones, comprise a large fraction of the deposits. They suggest progressive climate change from minimally seasonal humid to seasonal subhumid to seasonal dry subhumid. Five lithofacies yielded plants: kaolinite-dominated siltstone, organic shale, mudstone beds within organic shale, coarsening upward mudstone–sandstone interbeds and channel sandstone. Both macro- and microflora were examined. Lithofacies proved compositionally distinct, with different patterns of dominance diversity. Organic shales (swamp deposits), mudstone partings (swamp drainages) and coarsening upward mudstone–sandstone interbeds (floodplains) typically contain Pennsylvanian wetland vegetation. Kaolinite-dominated siltstones and (to the extent known) sandstones contain taxa indicative of seasonally dry substrates. Some kaolinite-dominated siltstones and organic shales/coals yielded palynomorphs. Microfloras are more diverse, with greater wetland–dryland overlap than macrofloras. It appears that these two floras were coexistent at times on the regional landscape.

This report discusses the geography, systematic geology, structure, and economic deposits in the Coast Ranges of Central California involving nine quadrangles with an area of approximately 2215 square miles of which about a fifth is water. The hills of the Coast Ranges immediately north of San Francisco occupy three north-westward-trending areas which are separated by the San Andreas fault and northern extension of the Haywards fault system. Each area is composed of distinct groups of rock formations. The oldest formations investigated, perhaps of Paleozoic age, consist of metamorphosed sediments, volcanic rocks, and quartz diorite and are exposed in Point Reyes Peninsula. They form a small residual mass of what was probably an extensive coastal land that lay west of the present coast of California but which late in the Tertiary or early in the Pleistocene foundered beneath the Pacific Ocean. This former land area is believed to have furnished many of the sediments laid down during Mesozoic and Tertiary time that are now exposed in the mountains between the San Andreas fault and the Sacramento Valley. The next younger rocks are a thick series of sandstones and associated basic igneous rocks which are widely distributed throughout the Coast Ranges of California and southern Oregon and are known as the Franciscan group. They constitute the surface rock exposures in most of the area between the San Andreas fault and the northern extension of the Haywards fault zone. The Franciscan has a thickness of 7000 feet or more. It contains no fossils except poorly preserved radiolarians in the cherts and Foraminifera in the limestones, which do not permit of an exact age determination. Recently discovered ichthyosaur head bones and teeth from cherts thought to belong to the Franciscan group are closely allied to a species from the lower Portlandian of Europe. From evidence obtained within the mapped area the Franciscan is younger than the time of intrusion of the quartz diorite into the Sur series which may have been during the late Paleozoic. Its upper age limit is uncertain because of fault contacts with the Knoxville formation. It has been considered by other writers from evidence obtained outside of the mapped area as in part contemporaneous with the Knoxville. The area between the Petaluma-Cotati Valley trough and the Sacramento Valley is composed of more than 30,000 feet of Jurassic to Quaternary marine and fresh-water sediments, together with about 1200 feet of Pliocene andesites, rhyolites, and tuffs. These sediments probably accumulated in structural troughs whose areas and physical environments changed greatly during the Cretaceous and Tertiary. The lower portion consists of clay shales and subordinate amounts of sandstone and conglomerate as much as 17,000 feet thick, containing a marine fauna of ammonites, pelecypods, and gastropods. These rocks include the Jurassic and Lower Cretaceous portions of the Knoxville formation and the Upper Cretaceous Chico. Several faunal zones may be distinguished in the Knoxville, but the formation in the mapped area cannot be subdivided on a lithologic basis. The Chico formation consists of interbedded shales and sandstones about 7000 feet thick. The Paleocene is represented by the Martinez formation, and the Eocene in ascending order by the Capay shale and the Domengine and Markley sandstones. The formations of the Paleocene and Eocene series consist of marine sediments ranging in thickness from 2000 to 5000 feet that were deposited in embayments far more restricted in area than the seas of the Upper Jurassic and Cretaceous time. The marine sedimentary formations of the Oligocene and lower part of the Miocene series occupy still more restricted areas than those of the Paleocene and Eocene, and near Carquinez Strait are more than 5000 feet thick. The upper Miocene sand-stones of the San Pablo group are far more widely distributed and are nearly 2500 feet thick. They are characteristically coarse-grained and were deposited in moderately shallow water which locally was brackish or fresh. The Pliocene rocks crop out extensively in the north-central part of the area and consist largely of alternating flows of andesite, basalt, dacite, and rhyolite together with associated tuffs and agglomerates, whose total thickness is 100 to 1200 feet. In Santa Rosa and Petaluma quadrangles marine sandstones contain invertebrate fossils closely allied to those of the Merced formation in San Francisco. The beds in Marin and Sonoma counties are about 250 feet thick and rest unconformably upon the Franciscan group. Near Petaluma Valley they interfinger with tuffs. Before the Pliocene volcanics accumulated the entire area east of the San Andreas fault was folded and faulted, after which it was deeply eroded. The Pliocene volcanics were laid down on the beveled surface of the older rocks and later were moderately folded and broken by normal faults and locally overturned and broken by thrust faults. During the Quaternary period the Coast Ranges in Middle California, in common with areas to the north and south, were undergoing crustal deformation by differential elevation and depression of the numerous fault blocks, some of which at times were temporarily beneath sea level. Stream erosion adjusted to the differentially elevated blocks and left a somewhat obscure record of the complex Quaternary history. Igneous activity was confined mainly to three widely separated epochs. The pre-Knoxville was characterized by intrusions of quartz diorite. The peridotites, gabbros, and basalts associated with the Franciscan group formed during the second epoch of activity in the early part of the late Jurassic. The third was characterized by extrusion of andesitic and rhyolitic materials during the middle and late Pliocene. Volcanoes may have been active during the intervening periods in areas not far from that studied, as tuflaceous products are present in the Oligocene and Miocene sediments. Important associated mineral resources include mercury, magnesite, limestone, road metal, building stone, clays, and surface and ground water.

ABSTRACT Two spatially separated areas of Neogene volcanic rocks are located on the northeast limb of the Mount Diablo anticline. The southernmost outcrops of volcanics are 6 km east of the summit of Mount Diablo in the Marsh Creek area and consist of ~12 hypabyssal dacite intrusions dated at ca. 7.8–7.5 Ma, which were intruded into the Great Valley Group of Late Cretaceous age. The intrusions occur in the vicinity of the Clayton and Diablo faults. The rocks are predominantly calc-alkaline plagioclase biotite dacites, but one is a tholeiitic plagioclase andesite. Mercury mineralization was likely concomitant with emplacement of these late Miocene intrusions. The northernmost outcrops of Neogene volcanic rocks occur ~15 km to the north of Mount Diablo in the Concord Naval Weapons Station and the Los Medanos Hills and are probably parts of a single andesite flow. A magnetometer survey indicates that the flow originated from a feeder dike along the Clayton fault. The lava flow is flat-lying and occupies ancient stream channels across an erosional surface of tilted Markley Sandstone of middle Eocene age. New radiometric dates of the flow yield an age of 5.8–5.5 Ma, but due to alteration the age should be used with caution. The flow is a calc-alkaline andesite rich in clinopyroxene and plagioclase. What appear to be uplifted erosional remnants of the flow can be traced northeastward in the Los Medanos Hills across a surface of tilted Cenozoic rocks that eventually rest on formations as young as the Lawlor Tuff dated at 4.865 ± 0.011 Ma. This stratigraphic relationship suggests that the andesite flow is probably late Pliocene in age and was impacted by the more recent uplift of the Los Medanos Hills but postdates the regional folding and faulting of the rocks of Mount Diablo. In terms of timing, location, and composition, the evidence suggests these two areas of dacitic and andesitic volcanics fit into a series of migrating volcanic centers in the California Coast Ranges that erupted following the northward passage of the Mendocino Triple Junction.