Magnetostratigraphy of Borehole PGZ05 in Southern Daxing Uplift, Beijing Plain

doi:10.19657/j.geoscience.1000-8527.2019.01.06

Abstract

Abstract:

Quaternary deposits in the southern Daxing uplift in the Beijing Plain provide an important archive for Quaternary stratigraphic changes. Here we present the magnetostratigraphic results of borehole PGZ05 (255 m). A total of 440 undisturbed samples were collected from the borehole at a 0.2-0.5 m interval except for the sand and gravel lay. The results show that the Brunhes/Matuyama and Matuyama/Gauss boundaries occur at 75.60 m and 181.35 m deep, respectively. The Gauss normal polarity chron occurs at 181.35 to 255.00 m deep. The 75.60 to 181.35 m interval is fairly correlative with the Matuyama reversal in the geomagnetic polarity timescale, with two normal polarity zones corresponding to the Jaramillo (90.90-100.60 m) and Olduvai (149.70~165.50 m) subchrons, respectively. The AMS¹⁴C age of (2,370±30) a BP and (23,190±100) a BP were obtained from the samples at 12.20 m and 31.45 m deep. The lithologic section of the borehole PGZ05 includes the entire Pleistocene and Holocene sequences and part of the Pliocene sequence. According to the M/G boundary and lithologic section of the borehole, we suggest that the N/Q boundary is located at 181.35 m deep, and it represents an important lithological interface. We propose that the sediments below 181.35 m depth belong to the Upper Pliocene series. The Lower Pleistocene sequence occurs at 75.60-181.35 m deep and were deposited during 0.78-2.58 Ma. The boundary between the Middle and Upper Pleistocene sequence is located at 57.20 m deep, whilst the Holocene-Upper Pleistocene boundary is located at 17.35 m deep.

Key words: magnetostratigraphy, Quaternary, southern Daxing uplift, AMS¹⁴C dating

CLC Number:

P539
P548

ZHAO Yong, LI Ruijie, WEI Bo, WANG Chunjun, SUN Yonghua, FANG Tongming. Magnetostratigraphy of Borehole PGZ05 in Southern Daxing Uplift, Beijing Plain[J]. Geoscience, 2019, 33(01): 56-62.

Figures/Tables 5

Fig.1 Schematic structural map of the Beijing Plain and the location of borehole PGZ05

Fig.2 Lithological column, natural gamma and step resistivity logging curves, and sedimentary environment interpretation of borehole PGZ05

Fig.3 Orthogonal (Zijderveld) vector plots of representative samples from borehole PGZ05

Fig.4 Magnetostratigraphic map of borehole PGZ05

Table 1 14C dating data of samples from borehole PGZ05

样品号	深度/m	岩性	年龄/a BP
Beta-428054	12.20	含有机质黏土	2 370±30
Beta-440037	31.45	含有机质硬黏土	23 190±100

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