The Paleogeographic Significance Of Old Red Sand On The North Haitan Island,Fujian

The "Old Red Sand" is Widely distributed in the eastern coastal areas,China.It is a semi-bonded and unconsolidated sand deposists in Quaternary,with its color is red(10R4/8),palm(2.5YR4/8),reddish brown(5YR5/8)and dark yellow orange(5YR/5/8).Existing reserch shows that the foration of "Old Red Sand" requires a certain amount of iron oxide and water,as well as a stable and oxidized environment for a long time affer the deposition of primary Aeolian sand.Generally speaking,the warm-wet climate in the tropical and subtropical are suitable for rubefaction,but rubefaction is relatively slow under a cold conditions.Moreover,similar sediments are also found in the Zhejiang zhoushan islands,which is located in the north subtropical,and even in warm temperate zone of Shandong peninsula.Whether these findings show that Shandong peninsula was affected by the subtropical climate during the sedimentary period of "Old Red Sand"?Haitan Island is located in the boeder of the south Asian tropical and subtropical,and a seriers of "Old Red Sand" sediments distribution in the north of the island,which is characterized by its cyclic sedimentations and with a lagre thickness,intact sedimentary sequence.Based on its sensitive location and typical traits,we can be further discussed the paleoenvironmental significance of the "Old Red Sand".Therefore,basing on the regional differentiation regularity of natural geography and the quaternary geology(weathering crust,the ancient climate and sea level changes)theory,we select the typical section(QF,JS and LS profile)in the northern island as the research object.In this paper,we establishe a chronology framework in this study area,and focue on further researching the grain size,chromaticity,clay minerals characteristics,and its paleoenvironmental significance,and find that:(1)On the basis of the ESR and OSL dating analysis and the regional stratigraphic classification and correlation,we find that the modem coastal eolian sand belonged to late Holocene,homogeneous "Old Red Sand" mainly formed in the period of late Pleistocene,checkered "Old Red Sand" formed in the middle Pleistocene period,and even the sand layer in the bottom of the LS profile formed in the early Pleistocene.All of these sedimentary sequences form in different periods can illustrate the rise and fall of sea-level,and the change of climate in the study area during Quaternary.(2)Using high-resolution sampling and OSL dating analysis directly determine the age of QF profile,and find that the "Old Red Sand" in the study area formed in the late Pleistocene,the dating results between 107.57±11.79-51.35±5.22 ka,corresponding to the MIS5d-MIS3.Through using regional stratigraphic division and correlation,and referring to the previous research findings to determine the upper pluvial sand layer of JS section formed in the MIS 3-1 period,the "Old Red Sand" at the bottom of JS section formed in MIS 5;the homogeneous "Old Red Sand" layer of the LS profile also formed in MIS 5,and the checkered "Old Red Sand" layer formed in middle Pleistocene,the celadon homogeneous sand and red orange old red sand at the bottom of LS profile formed in the early Pleistocene.(3)The particle size composition of old red sand in the study area is given priority to with medium sand and fine sand,and contains a certain amount of clay,silt.Its sorting is moderatly sorted or poorly sorted,the skewness is negative bias category,and the kurtosis change is from flat to very sharp.The frequency distribution curves is given priority to with unimodal and contains a significant fine tail.The cumulative probability curves show three obvious characteristics in rolling-jumping-suspension.The granularity characteristics between different sand layer show that their handling power and chemical weathering intensity have significant differences.(4)The a*,RI values of "Old Red Sand" are higher than pluvial sand or sage reen sand layer,and also the palm red sand layers are higher than yellow orange sand layer,but the L*values,on the other hand.The clay minerals of QF,JS and LS profile are given priority to with quartz and calcite.The palm red sand layer contains a certain amount of hematite,shows that its weathering and reddening is stronger,reflects the sedimentary environment is relatively hot and humid.The yellow orange sand layer,alluvial sand deposition and sage green sand layer contain a certain amount of porphyry copper,corresponding a reducing environment,and the climate is relatively dry.The chromaticity parameters and mineral species in different sand layers exist difference,show that their sedimentary environment and dry-wet condition exist obvious difference.(5)The OSL ages of palm red sand layer in the QF section were corresponding to interglacial period,and the yellow orange sand layers are corresponding to ice age.The pluvial sand layer in JS profile is corresponding to the transition of ice age-interglacial stage,and the palm red sand layer in the bottom of JS section is corresponding to interglacial period.The upper old red sand layer and the lower sage green sand layers in LS section can reflect the rise and fall of sea level changes during different periods.The comparation between the ages of "Old Red Sand",which around the coast of the east,South Asia,and the characteristics of global sea level change,find that the sedimentary period and rubefaction of "Old Red Sand" mainly occurr in high water period,and in relatively low sea-level period,sedimentations form in parts of area,but the rubefaction was not obvious.(6)The special geographical position and the sedimentary sequences of the "Old Red Sand" in the study area,may reveal the southeast coastal of Fujian had experienced large-scale climatic zone north-south migration in quaternary.