Calibrating the Southern Hemisphere Glacio-Eustasy Record


Tapia Orellana, Claudio Andrés


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The late Neogene evolution of the Antarctic ice sheet is argued to have been relatively stable since the middle Miocene in response to progressive tectonic and palaeoceanographic isolation of the continent. The primary data set used to support the stability theory is the marine <5180 record. However, the stable isotopic system does not allow discrimination between water temperature and ice volume/ eustatic sea level controls. In this thesis, calibration of the global sea level record is proposed from three different continental margin marine records (Chile, New Zealand and Antarctica).
Five late Neogene, shallow marine records from two main locations of northern Chile (Mejillones Peninsula and Caldera), are investigated in order to compare them to the existing Antarctic and New Zealand marine sedimentary records. The aim is to find common sea level components that are presumably glacial in origin. Magnetostratigraphic models are integrated with biostratigraphic and radiometric data to construct high- resolution chronologies for the studied sections.
Sedimentology and sequence stratigraphic studies reveal facies associations of continental shelf and submarine fan environments in the Chilean records. Textural and faunal variations indicate that coarsening and fining up of the successions are due to shallowing and deepening of the continental margin, respectively.
Paleomagnetic studies indicate that the northern Chile marine sediments retain a three component remanent magnetization: a low unblocking temperature (Tb), recent thermo viscous component; an intermediate Tb component which is the primary detrital magnetization; and a high Tb component, considered to be diagenetic in origin. Rock magnetism studies indicate that the magnetic carriers of remanence are most likely to be detrital magnetite, hematite, titanomagnetite and/or low titanium maghemite.
The chronologic models constrain: Caleta Herradura section between 18.5 and 4.7 Ma, with two unconformities (16.2-14.9 and 8.9-7.3 Ma); Tiburon Basin lower section between 4.2 and 2.8 Ma; Bahia lnglesa succession between 7.5 and 4.2 Ma, with one unconformity (5.5-5.1 Ma); Quebrada Playa Chorrillos section between 7.23 and 6.03 Ma, with two unconformities (7.1-6.74 and 6.44- 6.26 Ma); and the Quebrada La Higuera section between 15.52 and 14.2 Ma., with two unconformities (15.04-14.9 and 14.72-14.58 Ma).
Correlation of the northern Chile records with the Wanganui Basin (New Zealand), the AND-1B core (Antarctica) and the oxygen isotope curve reveals that: 1) During the mid- late Miocene, cyclothems from Caleta Herradura, Quebrada La Higuera and AND-1B core are likely to be controlled by sea level variation with orbital periodicities of eccentricity and obliquity; 2) During the late Miocene- early Pliocene, cyclothems from Bahia Inglesa, Caleta Herradura, Quebrada Playa Chorrillos, Wangafmi Basin and AND-1B are likely to be controlled by sea level fluctuation with orbital frequencies of eccentricity and obliquity; 3) During the early- late Pliocene, cyclothems from Tiburon Basin, Rangitikei, Tangahoe and AND-1B core are likely to be controlled by sea level change with orbital periodicities of obliquity, and; 4) between 3.2 and 2.9 Ma, records from the three continental margins showed synchronous, high- amplitude sea level fluctuations interpreted to represent phases of climatic deterioration of greater extent, implying an variable behavior of the Antarctica ice sheet .

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xiv, 370, LXVI pages : illustrations, maps ; 30 cm.


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Tapia Orellana, Claudio Andrés, “Calibrating the Southern Hemisphere Glacio-Eustasy Record,” Otago Geology Theses, accessed December 4, 2021,

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