STRATIGRAPHIC ANALYSIS OF TWO CORES FOR PALEOENVIRONMENTAL DATA, CAMP PENDLETON, CALIFORNIA

Two cores were collected from Camp Pendleton for the purpose of paleoenvironmental analysis of the sentiments during the month of February, 2011. R. A. Varney was present during field collection of the cores and able to make observations and assessments of the local environment. Upon receipt of these two cores, which were collected in the field with a truckmounted hydraulic corer, we proceeded to lay out all of the individual sections or drives of the cores for description and sampling. Radiocarbon dates were obtained as close to the bottom of each core as we were able to recover organic fragments. The goal was to examine to stratigraphic records of the Holocene from this basin. Potential analyses of the sentiments included pollen, phytoliths, diatoms, shells, macrofloral and faunal remains, and resistivity testing. Previous stratigraphic reconstructions of the Ysidora Basin suggest that during the Early Holocene the area could best be described as a floodplain. By approximately 9400 an estuary had developed. Then between approximately 9400 and 5400 sediments and proxy records suggest transitions back and forth between an estuary and a lagoon. Finally, at approximately 5400 a salt marsh develops and persists for approximately 400 years before resurgence of the estuary. By approximately 3500 BP waters have receded or the basin has sedimented to a level that a floodplain has developed. No evidence of estuary, salt marsh, or lagoon conditions were noted between 3500 BP and present (Pope 2005:66-73).2011年2月，为开展该区域沉积物的古环境分析，我们从彭德尔顿营（Camp Pendleton）采集了两处岩芯。野外采集岩芯期间，R·A·瓦尼（R. A. Varney）全程在场，并对当地环境进行了观测与评估。该批岩芯采用车载液压取芯器完成野外采集，收到样品后，我们随即对岩芯的各分段（或岩芯回次）进行展开，以开展描述与采样工作。我们尽可能在每处岩芯的底部附近获取有机碎屑，用于放射性碳定年。本次研究的目标是解析该盆地全新世（Holocene）的地层记录。潜在的分析测试项目包括花粉、植硅体（phytoliths）、硅藻（diatoms）、生物壳体、大植物与动物遗体，以及电阻率测试。此前针对西多拉盆地（Ysidora Basin）的地层重建研究显示，早全新世时期该区域最适宜被描述为泛滥平原（floodplain）。至约9400年前，河口湾（estuary）已然形成。随后在约9400年至5400年期间，沉积物与代用指标记录表明，该区域在河口湾与泻湖（lagoon）之间反复转换。最终，约在5400年时形成盐沼（salt marsh），并持续约400年，之后河口湾再度出现。至约距今3500年（Before Present，BP）时，水体已退去，或是盆地因沉积作用抬升至可形成泛滥平原的水位。在距今3500年至今的时段内，未发现河口湾、盐沼或泻湖环境的相关证据（Pope 2005：66-73）。