Detecting Sedimentary Cycles using Autocorrelation of Grain size

Abstract

Detection of sedimentary cycles is difficult in fine-grained or homogenous sediments but is a prerequisite for the interpretation of depositional environments. Here we use a new autocorrelation analysis to detect cycles in a homogenous sediment core, E602, from the northern shelf of the South China Sea. Autocorrelation coefficients were calculated for different mean grain sizes at various depths. The results show that sediments derived from rapid depositional events have a better autocorrelation. Analysis of two other cores confirms this result. Cores composed of sediments deposited quickly under stable and/or gradually changing hydrodynamic conditions, have higher autocorrelation coefficients, whereas, those composed of sediments deposited during calm periods have relatively low autocorrelation coefficients. It shows that abrupt changes in autocorrelation coefficients usually indicate the existence of a boundary between adjacent sedimentary cycles, with each cycle beginning with a high positive autocorrelation coefficient of grain size and ending with a low negative one.

Holocene evolution of the shelf mud deposits in the north-western South China Sea

“…Combining the water depth at the coring site and sea-level positions, a paleo-water depth of 30-35 m is estimated when this transgressive sand bed accumulated between 8,300 and 7,300 years of BP. Similar transgressive sandy deposits overlying the Pleistocene terrestrial mud were also found on the middle and outer shelf of the northern SCS (Yim et al, 2006;Xiao et al, 2013;Xiong et al, 2018). These transgressive sands are inferred to be deposited in the inner and middle shelf environments (Figures 6A, B).…”

“…In the winter, north-easterly waves have an average height of 0.5-4.0 m. High waves are mainly produced by typhoons, which occur during summer and autumn and have a maximum height of over 10 m (Wang, 2007). Typhoon waves in this study area can cause the re-suspension of sea-bottom sediments on the shelf, even on the outer shelf (Xiao et al, 2013;Zhou, 2014).…”

“…In the north-western SCS, the Holocene sediments on the shelf, such as in cores YX03 and E602, mainly consist of transgressive sands (Figures 1A, 6B). Xiao et al (2013) conducted a detailed analysis on grain size of E602 and pointed out that transgressive sands were reworked by high frequent tropical storms. The narrow range of 14 C dates in transgressive sands from cores YX03 and E602 suggests they were not associated with the rapid accumulation but were produced by repeated reworking.…”

“…(C) Sea-level changes since 11 ka BP according to Xiong et al (2018). Reference cores were published by Xiao et al (2013); Huang et al (2018); Xiong et al (2018) and Yim et al (2006). The location of cores can be found in Figure 1A.…”

Late-Holocene high-frequency East Asia Winter Monsoon variability inferred from the environmentally sensitive grain size component in the distal shelf mud area, East China Sea

“…ESGSC, or end-members, were extracted from the grain size data to identify paleoenvironment and paleoclimate variations. Sediment transport processes and sedimentary environment changes have been previously inferred using the proportions and ranges of grain size components of sediments from the South China Sea (Boulay et al, 2004; Wang et al, 1999; Xiao et al, 2013) and the Arabian Sea (Prins et al, 2000). End-member modelling of grain size data was used to calculate the number of end-members from ESGSC extraction in sediments of the Arabian Sea (Prins et al, 2000).…”