Miocene And Oligocene Calcareous Nannofossils

Author : Jarrett W. Cruz
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (134 download)

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Download or read book Utilizing Indian Ocean Calcareous Nannofossil Biostratigraphy of Miocene Sediments to Investigate Tectonic and Climatic Forcing During the Evolution of the Himalayas written by Jarrett W. Cruz and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The geological history of Himalayans and Tibetan Plateau is important for understanding how our planet evolves, and how geological structures can have local and global effects on climate and floral and faunal evolution of a system. This thesis presents how biostratigraphy of calcareous nannofossils can be a vital tool when attempting to identify timing of sedimentological events captured within cores recovered from deep below the ocean floor. Here I utilize nannofossil biostratigraphy from International Ocean Discovery Program Expedition 354 Sites 1451 and 1450 drilled in the Eastern Bengal Fan to investigate the paleogeographic setting and evolution of the Himalayans. This is done by linking autogenetic characteristics of calcareous nannofossils to allogenic and autogenic processes directed by tectonic and climatic forcing. More specifically, this study uses biostratigraphy to identify nannofossils observed in sediments collected to produce a data set for assigning a biostratigraphic zonal scheme. The biostratigraphy is used as a baseline for calculating sedimentation rates and errors, relate sedimentation rates and turbidite frequencies to tectonic and climatic forcing and understanding the paleo environment. Biostratigraphy is a vital tool for identifying events directed by tectonic and climatic forcing and in turn, to test and support or reject other groups of researchers' hypotheses. Expedition 354 Site 1451 was successful at recording nannofossil markers from the Holocene (0 Ma) to the Miocene-Oligocene boundary (23 Ma). The Gradstein and others (2012) Time Scale was utilized to assign ages to the Martini (1971) and Okada and Bukry (1980) nannofossil zonal schemes. Sixty-one biostratigraphic events assigned by sixty-five marker species were observed delineating sixty-one zones/subzones discussed herein. The ages range from recently deposited (Holocene) to older than 57.4 million years (Paleogene). I utilize the biostratigraphic ages to analyze seven events representing pulses in turbiditic activity throughout the Miocene. Once the events were outlined, I compared each one to proposed tectonic and climatic events outlined in current published research in order to see whether they can be supported or rejected. Three of these events indicate the influence of significant tectonic forcing displaying nearly double the average sedimentation rate. The first event occurred around 6.1-8.2 Ma in the central Himalayans and has a strong source signal from the Ganges river system. The second and third events occurred around 8.3-10.9 Ma in the Eastern Tibetan Plateau and projects a strong source signal from the Brahmaputra river system. The fourth and fifth events can be linked to a monsoon activity and occurred around 10.8-13.5 Ma. The sixth event occurred around 14.1-14.91 Ma during the Middle Miocene cooling event and may have been influenced by a long-term sea level low. The seventh event occurred around 15.80-17.95 Ma during the Early to Middle Miocene climate optimum during a long-term sea level high. Site 1451 Holes A and B were drilled from sea floor to 1181.3 m below the sea floor with 86% recovery from Hole A and 29% recovery from hole B resulting in 628.9 m of total sediment collected. There were 245.1 meters of turbiditic sediment identified within the cores. This accounts for 38.9% of the total collected sediment. The lowermost turbidite sequence is assigned an age range of 15.80 to 17.95 Ma. Radiolarian blooms are identified in 18.2 m of sediment before any recorded turbidites. There are 5.47 m of volcanic ash layers denoting 8 identifiable volcanic events. There were also 40.85 m of plant fragment inclusions observed within the cores. These plant fragment inclusions were deposited between 0.29-1.26 Ma and 8.68+ Ma, leaving a gap in plant-fragment inclusions from 1.26-8.68 Ma. The commencement of significant plant fragment deposition correlates with the onset of the monsoons and activity of crustal thickening around 15-18 million years ago. In order to get a better understanding of the variation in depositional characteristics, 125 post cruise samples were analyzed from Site 1450 to correlate Pleistocene and Pliocene depositional patterns to Site 1451. Site 1450 biostratigraphy highlights a more expanded Pleistocene and Pliocene sections than Site 1451 with different sedimentation rates during the Pliocene/Pleistocene interval. This analysis highlights the variation in depositional characteristics from the two locations across the Bengal Fan head and hints to a possible reorganization of depositional patterns from source river systems around 5 Ma. This research has increased the resolution of proposed tectonic and climatic forcing events during the evolution of the Himalayan and Tibetan Plateau. Tectonic uplift in the central Himalayas initiated around 7.42+ Ma, and around 9.69-10.97 Ma in the Tibetan Plateau. Climatic forcing occurred around 14.91 to 15.8 Ma, altering sedimentation patterns in the Indian Ocean. Onset of turbidite deposition at site 1451 around 15.8 to 17.95 Ma confirms Early Miocene evolution of the Himalayas.