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.

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 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 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 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 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.

ABSTRACT The Mount Diablo region has been located within a hypothesized persistent corridor for clastic sediment delivery to the central California continental margin over the past ~100 m.y. In this paper, we present new detrital zircon U-Pb geochronology and integrate it with previously established geologic and sedimentologic relationships to document how Late Cretaceous through Cenozoic trends in sandstone composition varied through time in response to changing tectonic environments and paleogeography. Petrographic composition and detrital zircon age distributions of Great Valley forearc stratigraphy demonstrate a transition from axial drainage of the Klamath Mountains to a dominantly transverse Sierra Nevada plutonic source throughout Late Cretaceous–early Paleogene time. The abrupt presence of significant pre-Permian and Late Cretaceous–early Paleogene zircon age components suggests an addition of extraregional sediment derived from the Idaho batholith region and Challis volcanic field into the northern forearc basin by early–middle Eocene time as a result of continental extension and unroofing. New data from the Upper Cenozoic strata in the East Bay region show a punctuated voluminous influx (>30%) of middle Eocene–Miocene detrital zircon age populations that corresponds with westward migration and cessation of silicic ignimbrite eruptions in the Nevada caldera belt (ca. 43–40, 26–23 Ma). Delivery of extraregional sediment to central California diminished by early Miocene time as renewed erosion of the Sierra Nevada batholith and recycling of forearc strata were increasingly replaced by middle–late Miocene andesitic arc–derived sediment that was sourced from Ancestral Cascade volcanism (ca. 15–10 Ma) in the northern Sierra Nevada. Conversely, Cenozoic detrital zircon age distributions representative of the Mesozoic Sierra Nevada batholith and radiolarian chert and blueschist-facies lithics reflect sediment eroded from locally exhumed Mesozoic subduction complex and forearc basin strata. Intermingling of eastern- and western-derived provenance sources is consistent with uplift of the Coast Ranges and reversal of sediment transport associated with the late Miocene transpressive deformation along the Hayward and Calaveras faults. These provenance trends demonstrate a reorganization and expansion of the western continental drainage catchment in the California forearc during the late transition to flat-slab subduction of the Farallon plate, subsequent volcanism, and southwestward migration of the paleodrainage divide during slab roll-back, and ultimately the cessation of convergent margin tectonics and initiation of the continental transform margin in north-central California.