Reconstructing chemical weathering, physical erosion and monsoon intensity since 25 Ma in the northern South China Sea; a review of competing proxies

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doi: 10.1016/j.earscirev.2014.01.002
Author(s): Clift, Peter D.; Wan Shiming; Blusztajn, Jerzy
Author Affiliation(s): Primary:
Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA, United States
Other:
Chinese Academy of Sciences, Institute of Oceanology, China
Woods Hole Oceanographic Institution, United States
Volume Title: Earth-Science Reviews
Source: Earth-Science Reviews, Vol.130, p.86-102. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-8252 CODEN: ESREBW
Note: In English. Includes appendices. 103 refs.; illus., incl. 1 table, sketch map
Summary: Reconstructing the changing strength of the East Asian summer monsoon has been controversial because different proxies, many being indirect measures of rainfall, tell contrasting stories about how this has varied over long periods of geologic time. Here we present new Sr isotope, grain-size and clastic flux data and synthesize existing proxies to reconstruct changing chemical erosion in the northern South China Sea since the Oligocene, using the links between weathering rates and monsoon strength established in younger sediments as a way to infer intensity. Chemical proxies such as K/Rb, K/Al and the Chemical Index of Alteration (CIA), together with clay proxies like kaolinite/(illite+chlorite) show a steady decline in alteration after a sharp fall following a maximum at the Mid Miocene Climatic Optimum (MMCO; 15.5-17.2 Ma), probably as a result of cooling global temperatures. In contrast, physical erosion proxies, including bulk Ti/Ca and clastic mass accumulation rates (MAR), show peaks at 21-23 Ma, ≈19 Ma and 15.5-17.2 Ma, implying faster run-off in the absence of drainage capture. Rates increase again, likely driven by slightly increased run-off after 13 Ma, but decrease after 8 Ma, which is identified as a period of summer monsoon weakening. Sr isotope composition correlates with hematite/goethite and the spectral proxy CRAT to show stronger weathering linked to more monsoonal seasonality. These proxies argue for a strengthening of the East Asian Monsoon after 22-23 Ma, followed by an extended period of monsoon maximum between 18 and 10 Ma, then weakening. There is some suggestion that the summer monsoon may have strengthened since 3-4 Ma after reaching a minimum in the Pliocene. Abstract Copyright (2014) Elsevier, B.V.
Year of Publication: 2014
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Absolute age; Alkaline earth metals; Cenozoic; Chemical composition; Chemical ratios; Chemical weathering; Clastic sediments; Clay minerals; Dates; Erosion; Geochemistry; Geomorphology; Isotope ratios; Isotopes; Leg 184; Metals; Middle Miocene Climatic Optimum; Mineral assemblages; Mineral composition; Miocene; Monsoons; Neogene; North Pacific; Northwest Pacific; ODP Site 1144; ODP Site 1146; ODP Site 1148; Ocean Drilling Program; Pacific Ocean; Paleo-oceanography; Paleoclimatology; Physical weathering; Reconstruction; Sedimentary petrology; Sediments; Sheet silicates; Silicates; South China Sea; Sr-87/Sr-86; Stable isotopes; Strontium; Tertiary; Weathering; West Pacific
Coordinates: N192724 N192724 E1161622 E1161622
Record ID: 2015010688
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands