Paleoenvironmental Reconstruction Using Microfossils
AdvisorWigand, Peter E.
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The impact of global climate change has reached crisis proportions. Inaction is not an option if humanity hopes to survive. The question is what should be done? Micropaleontology is providing one of the primary sources of information helping to answer these questions. In this research records of paleoenvironmental change were reconstructed using several paleoenvironmental data sources, including pollen, diatoms, foraminifera, woodrat middens, sediment grain-size, and geochemical. In first chapter pollen, benthic foraminifera, diatoms, grain size, and organic matter content from a 230-cm AMS dated piston core (Core SB-51B) were used to reconstruct paleoenvironmental changes and paleoclimatic evolution of the Seal Beach Wetland, southern California (USA), during the last ~ 2000 years. A Q-mode cluster analysis based on diatom and foraminiferal data revealed three distinct units: 1) the lowest sandy to silty-sand unit from 230 to 140 cm in depth (deposited earlier then 1838 Cal. years B.P.) is devoid of microfossils; 2) the intermediate unit between 150 to 52 cm (1838 and 513 Cal. years B.P.) is primarily composed of clay and dominated by brackish and brackish-marine diatoms and foraminifera; and 3) the uppermost unit from 52 cm to the surface (deposited after 513 Cal. years B.P.) is enriched in clay and microfossils, particularly diatoms, which typify a high salt marsh environment. Unit 2 contains strata at 105 cm, 82 cm, and 75 cm with fresh-water and salt-tolerant diatoms indicating that fresh water flowed into the wetland. This may have come from the flooding of a nearby stream, which overflowed into the marsh. Pollen analysis of the core indicates a shift in the lower portion of the core from dominance by saltmarsh plant species to increased abundance of terrestrial plant species, probably from around the marsh margins. The Artemisia/Chenopodiaceae (A/C) ratio reflects both the shift to more terrestrial species during the record, and possible infilling of the marsh. In particular, pine pollen production increases upward suggesting mean cooler and wetter climate conditions during the last 300 years. These changes share similarities with other regional pollen records that shifted from drier conditions during the last 1,800 years to the cooler, more mesic conditions of the Little Ice Age. The analyzed sedimentary sequence may also reveal three seismic events during the late Holocene: E3 and E2 that occurred before 1761 Cal. years B.P. and E1 occurred prior to 391 Cal. years B.P. In the second chapter, Late Pleistocene to late Holocene Vegetation Transition were reconstructed by using Packrat Midden and Pollen in Central Mojave Desert. The Mojave Desert of the American West is characterized by plant species that reflect a unique mixture of winter precipitation and summer monsoon climate. Today the Mojave Desert demonstrates a strong summer monsoonal pattern with weak winter precipitation. Data from pollen and packrat midden analyses have resulted in a vegetation history of the Mojave Desert during the Late Pleistocene to Late Holocene (~17500 Cal. years B.P. to ~ 1200 Cal. years B.P.) transition that highlight a summer dominated monsoonal pattern similar to those in the greater American Southwest. Here we compare pollen data from a lava tube in the Cima Volcanics in the south-central Mojave Desert with plant macrofossil data from several woodrat midden localities in the region. The Cima Volcanics record reveals a vegetation history spanning the last ~ 8300 Cal. years B.P. and data from ancient woodrat middens detail the record from ~17500 Cal. years B.P. to 7,800 Cal. years B.P. A Bryson MCM climate model for the late Pleistocene to the Late Holocene transition was created and compared to our findings determining possible relationships between climatic variations and the arrival of influential plant species within the Mojave Desert. In the third chapter, the morphology of Pseudoanacardium peruvianum (Berry) is described by nano CT-scanning from the early Oligocene Belén flora of Peru. Fossil fruits formerly described as cashews from the Oligocene of Peru, have been reinvestigated based upon the original specimens and newly collected materials. The recovery of an outer spiny layer preserved in the sedimentary molds surrounding the locule casts indicates that these disseminules do not represent Anacardium. Imagery from CT scans of the specimens document a distinctive morphology that does not resemble any fruits or seeds of Anacardiaceae. We describe the morphology in more detail and reassign the fossils to an extinct genus, Pseudoanacardium gen. nov., of uncertain familial affinity. Pseudoanacardium peruvianum (Berry) comb. nov. was a prominent member of the Belén carpoflora, which also included palms plus Annonaceae, Euphorbiaceae, Humiriaceae, Leeaceae, Icacinaceae, Rutaceae, and Vitaceae.