Author : Evin P. Maguire
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (139 download)
Book Synopsis The Effect Of Volcanic Ash Deposition On Marine Environments, Invertebrate Ecosystems And Fossil Preservation by : Evin P. Maguire
Download or read book The Effect Of Volcanic Ash Deposition On Marine Environments, Invertebrate Ecosystems And Fossil Preservation written by Evin P. Maguire and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation contains 6 chapters which examine the effects of volcanic ash deposition on paleoenvironment, sedimentology, fossil preservation, and paleoecology. It includes field-based research and experimental data which demonstrate that volcanic ash deposition can play an important role in shaping the nature of the sedimentary and fossil records in marine settings at both distal and proximal localities. Chapters 1 and 2- Summary and introduction. Chapter 3 - This chapter discusses two Cenozoic marginal marine settings which occur proximal (within 100 km) to prominent volcanic centers; one in the Pacific Northwestern United States, and one in the south of the Patagonian Cordillera, Argentina. The Oligocene Lincoln Creek Formation in Washington contains an exceptionally well-preserved marine fauna dominated by crustaceans and mollusks, and the late Miocene-early Oligocene Estancia 25 de Mayo Formation in southern Patagonia, Argentina, contains a similar exceptionally preserved fauna. In both settings, evidence shows that exceptional fossil preservation was facilitated by the deposition of mass quantities of volcanic ash via marine hyperpycnal flows following large volcanic eruptions. Chapter 4 - As discussed in the previous chapter, volcanic sediments can facilitate exceptional fossil preservation. The rapid deposition of fine-grained material in marine settings can preserve fossil material which may otherwise not be preserved. One such example of preservation in volcanic ash is a new species of isopod from the above-described Estancia 25 de Mayo Formation. In this chapter, Cirolana centinelensis n. sp. is described as the first known occurrence of the Isopoda in the fossil record of Argentina. The chapter discusses the recalcitrance of fossil isopods with respect to preservation and elucidates how the rapid deposition of volcanic ash facilitated the preservation of this exceptionally rare fossil specimen. Also discussed are the vagaries of the fossil record of the Isopoda, the difficulties in placing them systematically, and a brief review of the fossil record of isopods in South America. Chapter 5 - As discussed in the previous chapters, deposition of volcanic ash in localities proximal to eruptive centers is an important process in fossil preservation and sedimentary processes in marine settings. This chapter details how volcanic processes can be important even in distal marine basins, hundreds to thousands of kilometers from eruptive centers. The distance at which volcanic eruptions can have profound impacts on sedimentary basins is of importance not only for understanding the geologic history of North America, but also predicting future impacts of large-scale eruptions. This chapter discusses the sedimentary mechanisms and possible provenance of a prominent volcanic ash layer in the late Cretaceous (Maastrichtian) Fox Hills Formation in Emmons County, North Dakota. The locality studied is 600-1,000 km from any possible volcanic source, yet ash is recorded at thicknesses of up to 9 m across Emmons County. A volume of 7.8 km3 was calculated using data from two previous studies, which used measured sections and well logs to create isopach maps of the ash body. Geochemical data of the ash is also presented, as well as interpretation of the depositional mechanisms and paleoenvironment. Chapter 6 - This chapter discusses early taphonomic processes associated with burial in volcanic ash via an experiment designed to observe the first 10 months of post-burial in fine, glass-rich volcanic ash. After 10 months, it was observed that specimens of Penaeus sp. were exceptionally well-preserved, with soft tissue such as gills and musculature preserved, as well as delicate cuticular structures like antennae and distal appendage elements. Observation of volcanic glass shards with petrographic and scanning electron microscopy showed that alteration of the ash did not occur after 10 months in acidic decay fluids surrounding the shrimp. Portions of specimens were observed to be encapsulated in a biofilm intercalated with flat, glassy ash shards, which may play a role in their preservation.
