Can Occurrence of Hyperpycnal Flows Be Linked to Hyperthermals?

Piret Plink-Bjorklund
Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO

Basin-floor and slope turbidites in the Eocene Central Basin of Spitsbergen (Ypresian) consist of hyperpycnal flow deposits. The high abundance of tree leaves and coal on the coastal plain, and in turbidites, bear a vestige of an ice-free and subtropical North Pole. Indeed, an array of geological records, supported by climate modeling, indicate a profound shift in global climate in the beginning of Eocene. The Paleocene/Eocene thermal maximum (PETM), ca 55 MA ago, was a period of extreme warming, associated with higher than modern greenhouse gases. The PETM had sea surface temperatures of over 23C near the North Pole. Moreover, episodic fresh surface waters have been reported from the Eocene Arctic Ocean.

This paper explores if the frequency of hyperpycnal flows could be increased during extremely warm periods, as these are accompanied by a shift towards higher humidity, more intense chemical weathering and runoff, increase in river discharge, intensified seasonality, and an intensified hydrological cycle. Intensified chemical weathering increases availability of sediments, and particularly clay particles, for seaward transport. Increasing humidity and runoff enables the rivers to carry larger sediment volumes and overcome the needed concentrations for initiation of hyperpycnal flows, especially with fresh surface waters. Larger proportion of clay enables the turbidity currents to ignite, and transport sandy sediments to the basin floor. Consequently, large volumes of hyperpycnal flow deposits may indicate extremely warm climatic conditions.

Other hypothermals than the PETM occurred in Eocene, ca 53 and ca 52 Myr ago respectively. The Spitsbergen system has more than 30 basinward-migrating shelf-margin clinoforms, but only 3 basin-floor fans, i.e. when significant hyperpycnal flows were transported to the basin floor. Are they associated with the hypothermals?

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas