Since the seminal works of Wegener and Darwin the notion that things evolve, and the how and the why of it, has generated intense debate. The surface of the Earth, and the creatures that live on it, are not static entities. Landscapes evolve. Organisms evolve. Understanding the how and the why requires a firm understanding of a myriad of interdependent and complex variables such as (but not limited to) climate, ecology, and tectonics. Unravelling the complexities though which landscapes and ecosystems evolve requires a broad interdisciplinary approach, where multiple investigative tools are simultaneously brought to bear on a given question. The study of old lake sediments, or paleolimnology, is a marquee example of a powerful interdisciplinary methodology that has been used extensively in reconstructing the Earth's past. This work showcases two examples where the discipline of paleolimnology advances our understanding of evolution on a landscape scale and on a human scale. In the southwestern United States, a record of the processes involved during the late Miocene and early Pliocene (~ 5 Ma) evolution of a major continental river drainage - the Colorado River – is partially preserved along the southern border of Arizona and California as the enigmatic Bouse Formation. And in southern Kenya, nearly 170 meters of lake and wetland sediments that have accumulated in the Koora Plain preserve a one-million-year long record of the environmental conditions against which our species, Homo sapiens, evolved. My research allows me to conclude that the depositional environment of the Bouse Formation was lacustrine; a fully marine interpretation that has been previously proposed is untenable. I also demonstrate that over the past 1.0 Ma, Homo sapiens in southern Kenya evolved against a backdrop of increasing regional aridity.

Many conceptual models have been proposed to explain the fluid-flow mechanism responsible for the origin of carbonate-hosted lead-zinc deposits such as those in the Mississippi Valley and at Pine Point. This study is devoted to the quantitative investigation of one ore-genesis mechanism gravity-driven groundwater-flow systemso Numerical modeling techniques are used to develop a self-contained computer code for two-dimensional simulation of regional transport processes along cross sections through sedimentary basins. The finite-element method is applied to solve the steady-state, fluid-flow and heat-transport equations, and a movin6-particle random-walk model is developed to predict the dispersion and advection of aqueous components. The program EQ3/EQ6 is used to compute possible reaction-path scenarios at the ore-forming site. Full integration of geochemical calculations into the transport model is currently impractical because of computer-time limitations. Results of a sensitivity analysis indicate that gravity-driven ground water-flow systems are capable of sustaining favorable fluid-flow rates, temperatures, and metal concentrations for ore formation near the thin edge of a basin. Dispersive processes render long-distance transport of metal and sulfide in the same fluid an unlikely process in the genesis of large ore deposits, unless metal and sulfide are being added to the fluid along the flow path. The transport of metal in sulfate-type brines is a more defensible model, in which case the presence of reducing agents control the location of ore deposition. Hydrodynamic conditions that could result in ore formation through mixing of two fluids are rare. The theoretical approach is a powerful tool for gaining insight into the role of fluid flow in ore genesis and in the study of specific ore districts. A preliminary model of the Pine Point deposit suggests paleoflow rates on the order of 1.0 to 5.0 m3/m2 yr, paleoconcentrations of zinc on the order of 1.0 to 5.0 mg/kg• H 2 O, and paleotemperatures in the range 60°C to 100°c. Under these conditions, the time required for the formation of Pine Point would be on the order of 0.5 to 5.0 million years.

Lower Mesozoic strata in the northern Cache Creek terrane range in age from Ladinian to Pliensbachian as shown by conodont and radiolarian collections from chert. Chert beds are interlayered with argillite that has ε(Nd)(t) values of -8.8 to -7.4, indicating detritus eroded from Precambrian source areas. These ε(Nd)(t) values are similar to those of fine-grained Middle Triassic sedimentary strata of the miogeocline (-10.5 to -6.7) and to sediments of the modern Pacific Ocean floor. Volcanic-lithic sandstone interbedded with the chert and argillite is petrographically similar to coeval sandstone from the northern Stikine terrane. ε(Nd)(t) values for northern Cache Creek sandstone are -1.1 to +5.8, similar to most coeval northern Stikine strata (-0.4 to +4.7). These observations, coupled with limited paleocurrent indicators, suggest that northern Cache Creek sandstone was deposited in the distal parts of clastic fans derived from the Late Triassic northern Stikine arc. Quartzofeldspathic sandstone layers in northern Stikine have ε(Nd)(t) values of -8.1 to -1.8 and are associated with conglomerate containing metasedimentary clasts similar to rocks of the Nisling terrane. Nisling rocks have ε(Nd)(t) values of -4.6 to +0.5 (Boundary Ranges suite) and -20.6 to -15.6 (Florence Range suite). These data and existing sedimentologic evidence corroborate interpretations that northern Stikine clastic rocks were derived in part from the Nisling terrane in Late Triassic time. Stacks of thrust sheets containing Cache Creek strata are floored by the Nahlin and King Salmon faults, and are bound on the north by the Squanga-Crag Lake tear fault system which has at least 90 km of right-lateral slip and 2.2 km of south-side-up slip. These strata were thrust southwestward over northern Stikine between Middle Jurassic and mid-Cretaceous time. North and west of this nappe, Stikine and Cache Creek strata are shortened by open, upright folds and only minor thrust faults. Structural, stratigraphic and isotopic data are consistent with a minimum-displacement model for development of the western Canadian Cordillera, in which terranes located east of the Coast Mountains batholith developed and remained in the eastern Pacific Ocean throughout their histories.

The cosmogenic radionuclide ¹⁰Be from a marine sediment core was studied to help understand late Quaternary variations in the geomagnetic field and cosmic rays. The primary objective of this study was to see if the ¹⁰Be anomalies observed in polar ice cores could be observed in mid-latitude marine sediments. A partly-varved sediment core from the upper 50 meters of Leg 64 (DSDP) in the Gulf of California was determined to be ideal. A chronology of the core was determined by radiocarbon analysis, sedimentation rates, and oxygen-isotope stratigraphy. It was found that radiocarbon analysis of total carbon content was reliable only for the sediments younger than 16,000 B.P. Older sediments contain a modern ¹⁴C component added during diagenesis. Radiocarbon analysis of the Holocene sediments showed that the laminations in the sediments formed yearly. Thus, a reasonably reliable chronology for the lower sections of the core was determined from the relatively constant and high sedimentation rate. In addition, data from the authigenic fraction of the sediments were gathered for aluminum, iron, manganese, calcium, magnesium, and beryllium. From these data, the determination of the history of the waters of the Gulf of California was possible. Hydrothermal activity, glacial meltwater events, and the changing water masses in the Gulf of California possibly have left a record in the core studied. Analysis of the ¹⁰Be data along with the elemental data shows that the ¹⁰Be concentrations in the authigenic fraction of the sediments tracked the production rate of this isotope in the atmosphere. The ¹⁰Be concentrations at this site were little affected by diagenesis, hydrothermal activity, and terrigenous input. Most of the ¹⁰Be deposited at site 480 originated from the open sea. The changing geomagnetic dipole moment for the Holocene is seen in the ¹⁰Be data. The production rate for ¹⁰Be during the late Pleistocene tracked the changing dipole moment of the Earth as shown in other studies. Two ¹⁰Be anomalies correspond with the Mono Lake and Laschamp geomagnetic excursions. It was determined that the geomagnetic excursions could not have produced these anomalies. The data for the ¹⁰Be anomalies are consistent with a previous hypothesis for supernovae shock waves and the generation of cosmic rays. It is proposed that a series of such shock waves compress the heliosphere and affect the magnetosphere of the Earth. For such a mechanism to produce the observed geomagnetic excursions, either an enhanced interplanetary magnetic field must be externally imposed on the magnetosphere, or external forcing creates a corresponding non-linear response from the magnetodynamo of the Earth.

Hell Canyon and Sycamore Canyon are major ungaged tributaries in the upper Verde River basin of central Arizona. Gage data implies that the record discharge of 1507 cms occurred on February 20, 1993 measured at the Verde River gage near Clarkdale, Arizona was derived primarily from these tributaries. 1993 flow reconstructions measure 800-900 cms in Sycamore Canyon and 600-700 cms in Hell Canyon. Historic and pre-historic units were exposed in various stratigraphic exposures in these canyons; as many as 11 floods are recorded at any one site. The 1993 floodwaters typically overtop all prior stratigraphy; however, dendrochronology suggests that similar floods occurred prior to the gage record. These results confirm that Hell Canyon and Sycamore Canyon are major contributors to floods on the Verde River in both the historic and paleoflood record.

El Alacran, northern Sonora, Mexico, is a high-level, Laramide porphyry copper deposit encompassing an east-west elongated altered and mineralized area of 2.7 by 6 km. A small quartz latite porphyry plug forcefully intrudes comagmatic(?) Late Cretaceous or Early Tertiary andesitic to quartz latite volcaniclastic rocks.Veinlet-controlled and pervasive potassic, Type I phyllic, and transition type alteration with related base-metal mineralization postdates pervasive propylitic alteration and is related in space and time to the intrusive and its associated intrusion-breccia annulus. Potassic alteration is dated by K-Ar at 55.4 +- 1.2 m.y. Later pervasive and veinlet-controlled Type II phyllic and minor advanced argillic alteration is associated with intrusive breccia dikes and pipes which are genetically related to degassing of the system. Minor veinlet-controlled late-stage alteration followed. Hypogene zoning is exhibited by alteration, mineralization, total sulfide volume, mineralized fracture density, and geochemistry with zoning being centered over or to the east of the exposed intrusive. Supergene enrichment processes have modified hypogene sulfides, oxides, and silicates and have formed a copper enriched blanket which underlies a leached cap. The blanket is characterized by a chalcocite zone which grades downward into a bornite-digenite-covellite zone and then into low-grade protore. Although the enriched blanket appears to be subeconomic, this study indicates potential for a deep, high-grade protore zone.