Preliminary Integrated Chronostratigraphy of the AND-1B Core, ANDRILL McMurdo Ice Shelf Project, Antarctica

Chronostratigraphic data available for the preliminary age model for the upper 700 m for the AND-1B drill core include diatom biostratigraphy, magnetostratigraphy, 40Ar/39Ar ages on volcanic material, 87Sr/86Sr ages on calcareous fossil material, and surfaces of erosion identifi ed from physical appearance and facies relationships recognised in the AND-1B drill core. The available age data allow a relatively well-constrained age model to be constructed for the upper 700 m of the drill core. Available diatom biostratigraphic constraints and 40Ar/39Ar ages allow a unique correlation of ~70% of the AND1B magnetic polarity stratigraphy with the Geomagnetic Polarity Time Scale (GPTS). Unique correlation is not possible in several coarse diamictite intervals with closely spaced glacial surfaces of erosion and sparse microfl ora. However, the age model indicates relatively rapid (up to 1 m/k.y.) and continuous accumulation of intervening fi ner grained diatomaceous intervals punctuated by several halfto millionyear hiatuses representing more than half of the last 7 m.y. in the AND-1B record. The midto late Pleistocene is represented by superimposed diamictite units separated from upper Pliocene alternating diamictites/diatomites by a ~1 m.y. hiatus co-incident with a regionally correlated seismic refl ection surface. A c. 100 m-thick diatomite represents a signifi cant portion of the early Pliocene record in the AND-1B drill core. Strata below ~620 m are late Miocene in age; however, biostratigraphic constraints are absent below 586 m and correlation with the GPTS is relatively unconstrained. At the time of writing, the only chronostratigraphic data available below 700 mbsf include three 40Ar/39Ar ages on volcanic clasts from near 1280 mbsf affording a maximum depositional age of 13.57 Ma for the base of the AND-1B drill core. CHRONOSTRATIGRAPHIC DATA DIATOM BIOSTRATIGRAPHY The upper 586 metres (m) of the AND-1B drill core contains a varied and rich Plio-Pleistocene diatom fl ora, though abundances and preservation vary markedly with facies changes in the core. Diatomaceous-rich intervals contain multiple taxa, which provide direct correlation to Southern Ocean biostratigraphic frameworks (see Scherer et al. this volume). However, the occurrence datums throughout the AND-1B core tend to be truncated or interrupted by the rapidly varying facies, glacial/interglacial alternations, frequent hiatuses, and volcanic events recorded in the core and thus probably do not represent the full age ranges of taxa observed in the open-ocean records. On-ice diatom data are therefore subdivided into 13 facies-based units in the core and the assemblage within each unit used to constrain the age by correlation to Southern Ocean biochronology (Tab. 1). Diatom occurrences are limited above 150 metres below seafl oor (mbsf), with thin intervals containing biostratigraphically useful species occurring at 58.15-58.90, 86.92-97.08, and 116.75-118.70 mbsf, respectively (see Scherer et al. this volume). The interval between 58.15 and 58.90 mbsf (Diatom Unit 1 or DU1) contains a mixed assemblage (Diatom Unit Assemblage 1, or DUA1), which indicates significant reworking. However, age-diagnostic © Terra Antartica Publication 2007 298 G. Wilson et al. Tab. 1 Preliminary chronsotratigraphic data for the AND-01B drill core. Event Datum AND-1B Depth Age Error (-) Error (+) Sources (mbsf) (Ma) (Ma) (Ma) GSE1 Glacial surface of erosion 41.10 <0.78 This paper GSE2 Glacial surface of erosion 47.86 <0.78 This paper GSE3 Glacial surface of erosion 51.10 <0.78 This paper D1 LO R leventerae Bohaty 52.98 0.21 0.14 0.14 Cody et al. (2007). Zielinski & Gersonde (2002) GSE4 Glacial surface of erosion 56.49 <0.78 This paper D2 LO T elliptipora (Donahue) Fenner 58.15 0.68 0.38 1.13 Cody et al. (2007), Harwood & Maruyama (1992), Ramsey & Baldauf (1999), Ciesielski (1983), Baldauf & Barron (1991), Fenner (1991), Zielinski & Gersonde (2002) DUA1top A. actinochilus, A. ingens, R. leventerae, T. antarctica, T. elliptipora, T. lentiginosa, T. torokina late form 58.15 0.14 0.01 Zielinski & Gersonde (2002) DUA1bot A. actinochilus, A. ingens, R. leventerae, T. antarctica, T. elliptipora, T. lentiginosa, T. torokina late form 58.9 1.07 Zielinski & Gersonde (2002) GSE5 Glacial surface of erosion 67.10 <0.78 This paper GSE6 Glacial surface of erosion 70.37 <0.78 This paper GSE7 Glacial surface of erosion 72.48 <0.78 This paper MPR1 Magnetic polarity reversal (Normal above Reversed below) 80.03 0.781 Ogg & Smith (2004) GSE8 Glacial surface of erosion 82.74 0.80-0.97 0.05 0.04 This paper MPR2 Magnetic polarity reversal (Reversed above Normal below) 84.97 0.988 Ogg & Smith (2004) A1 Felsic Tephra 85.50 1.014 0.004 0.004 This paper D3 LO A. ingens Rattray 86.90 0.54 0.24 1.45 Cody et al. (2007), Ciesielski (1983), Baldauf & Barron (1991), Harwood & Maruyama (1992), Gersonde & Barcena (1998), Ramsey & Baldauf (1999), Winter & Iwai (2002), Zielinski & Gersonde (2002) DUA2top A. actinochilus, A. ingens, R. leventerae, T. antarctica, T. elliptipora, T. lentiginosa, T. torokina 86.92 0.73 0.3 Zielinski & Gersonde (2002) D4 FO R. leventerae Bohaty 89.2 (255.70) 2.04 0.04 0.04 Cody et al. (2007) MPR3 Magnetic polarity reversal (Normal above Reversed below) 91.13 1.072 Ogg & Smith (2004) S1 foraminifera 91.60 1.52 0.05 0.05 This paper GSE9 Glacial surface of erosion 93.00 1.1-<1.65 This paper DUA2bot A. actinochilus, A. ingens, R. leventerae, T. antarctica, T. elliptipora, T. lentiginosa, T. torokina 97.08 1.07 Zielinski & Gersonde (2002) GSE10 Glacial surface of erosion 99.20 >1.1-<1.65 This paper GSE11 Glacial surface of erosion 103.73 >1.1-<1.65 This paper GSE12 Glacial surface of erosion 109.42 >1.1-1.65 This paper D5 LO T. vulnifi ca (Gombos) Fenner (58.88) 110.39 2.17 1.57 0.93 Cody et al. (2007), Weaver & Gombos (1991), Baldauf & Barron (1991), Harwood & Maruyama (1992), Winter (1995), Gersonde & Barcena (1998), Ramsey & Baldauf (1999), Winter & Iwai (2002), Zielinski & Gersonde (2002) A2 Basaltic Tephra 112.51 1.65 0.03 0.03 This paper DUA3top A. actinochilus, A. ingens, R. leventerae, T. antarctica, T. elliptipora, T. fasciculata, T. lentiginosa, T. torokina 116.75 0.84 0.09 Cody et al. (2007), Zielinski & Gersonde (2002) DUA3bot A. actinochilus, A. ingens, R. leventerae, T. antarctica, T. elliptipora, T. fasciculata, T. lentiginosa, T. torokina 118.7 2.08 Cody et al. (2007), Zielinski & Gersonde (2002) GSE13 Glacial surface of erosion 124.22 1.66 This paper D6 LO T. fasciculata Harwood & Maruyama ( 5 8 . 4 9 ) 125.6 0.89 0.14 0.92 Cody et al. (2007), Harwood & Maruyama (1992), Gersonde & Burckle (1990), Zielinski & Gersonde (2002) D7 LO A. karstenii Van Heurck (86.90) 126.39 2.15 0.34 0.76 Cody et al. (2007), Harwood & Maruyama (1992), Zielinski & Gersonde (2002) A3 Basaltic Tephra 136.21 1.67 0.03 0.03 This paper GSE14 Glacial surface of erosion 150.23 1.75-<2.45 This paper D8 LO T. inura Gersonde (52.98) 150.7 2.54 0.66 0.56 Cody et al. (2007), Harwood & Maruyama (1992), Winter (1995), Winter & Harwood (1997), Ramsey & Baldauf (1999), Zielinski & Gersonde (2002) 299 Preliminary Integrated Chronostratigraphy of the AND-1B Core Event Datum AND-1B Depth Age Error (-) Error (+) Sources D9 LO T. kolbei (Jouse) Gersonde (86.96) 150.7 1.98 0.37 0.72 Cody et al. (2007), McCollum (1975), Ciesielski (1983), Gersonde & Burckle (1990), Baldauf & Barron (1991), Fenner (1991), Harwood & Maruyama (1992), Barron (1992), Winter (1995), Winter & Harwood (1997), Gersonde & Barcena (1998), Ramsey & Baldauf (1999), Zielinski & Gersonde (2002) GSE15 Glacial surface of erosion 150.73 >1.75-2.45 0.1 This paper D10 LO T. tetraoestrupii var. reimeri Mahood & Barron 150.80 1.33 0.01 0.28 Cody et al. (2007), Mahood & Barron (1996), Zielinski & Gersonde (2002) DUA4top A. actinochilus (rare), R. diploneides, T. elliptipora, T. inura. T. kolbei., T. oestrupii/tetraoestrupii, T. tetraoestrupii var. reimerii, T. torokina 150.87 1.46 0.15 Zielinski & Gersonde (2002) D11 LO R. diploneides Schrader 151.21 2.62 0.11 0.07 Cody et al. (2007), Harwood & Maruyama (1992) D12 FO A. actinochilus (Ehrenberg) Simonsen 153.80 2.77 0.57 0.42 Cody et al. (2007), Gersonde & Burckle (1990), Baldauf & Barron (1991), Harwood & Maruyama (1992), Ramsey & Baldauf (1999) D13 FO T. tetraoestrupii var. reimeri Mahood & Barron 159.25 (190.65) 2.36 0.01 0.3 Cody et al. (2007), Mahood & Barron (1996), Zielinski & Gersonde (2002) DUA4bot A. actinochilus (rare). R. diploneides. T. elliptipora. T. inura. T. kolbei. T. oestrupii/ tetraoestrupii . T. tetraoestrupii var. reimerii. T. torokina 159.33 2.55 Zielinski & Gersonde (2002) GSE16 Glacial surface of erosion 163.65 <2.58 0.2 This paper DUA5top A. fasciculatus, A. maccollumii, R. diploneides, T. elliptipora, T. fasciculata, T. inura, T. kolbei, T. oestrupii/tetraoestrupii, T. oliverana, T. torokina, T. vulnifi ca 164.1 2.25 Cody et al. (2007), Zielinski & Gersonde (2002) D14 LO A. fasciculatus Harwood & Maruyama 164.40 2.16 0.35 0.65 Cody et al. (2007), Harwood & Maruyama (1992) D15 LO A. maccollumii Harwood & Maruyama 177.00 2.43 0.62 0.48 Cody et al. (2007), Harwood & Maruyama (1992), Zielinski & Gersonde (2002) DUA5bot A. fasciculatus, A. maccollumii, R. diploneides, T. elliptipora, T. fasciculata, T. inura, T. kolbei, T. oestrupii/tetraoestrupii, T. oliverana, T. torokina, T. vulnifi ca 180.73 2.9 0.4 Cody et al. (2007), Zielinski & Gersonde (2002) GSE17 Glacial surface of erosion 182.99 <2.58 0.2 This paper DUA6top A. maccollumii, R. diploneides, T. elliptipora (rare), T. fasciculata, T. inura, T. kolbei, T. oestrupii/ tetraoestrupii, T. oliverana, T. torokina, T. vulnifi ca 183.42 2.54 0.82 Zielinski & Gersonde (2002), Whitehead & Bohaty (2003) D16 FO A. fasciculatus Harwood & Maruyama 185.05 2.71 0.99 0.06 Cody et al. (2007), Harwood & Maruyama (1992) GSE18 Glacial surface of erosion 190.63 <2.58 0.2 This paper MPR4 Magnetic polarity reversal (Reversed above Normal below) 191.75 2.581 Ogg & Smith (2004) D17 FO A. maccollumii Harwood & Maruyama 201.40 2.82 0.32 0.48 Cody et al. (2007), Harwood & Maruyama (1992), Zielinski & Gersonde (2002) D18 FO T. vulnifi ca (Gombos) Fenner 201.4 (256.9) 3.15 0.95 0.36 Cody et al. (2007), Ciesielski (1983), Baldauf & Barron (1991), Harwood & Maruyama (1992), Winter (1995), Ramsey & Baldauf (1999), Winter & Iwai (2002), Whitehead & Bohaty (2004) DUA6bot A. maccollumii, R. diploneides, T. elliptipora (rare), T. fasciculata. T. inura, T. kolbei, T. oestrupii/ tetraoestrupii, T. oliverana, T. torokina, T. vulnifi ca 201.59 3.12 Zielinski & Gersonde (2002), Whitehead & Bohaty (2003) D19 FO T. elliptipora (Donahue) Fenner 207.4 (286.6) 2.03 0.96 1.48 Cody et al. (2007), Baldauf & Barron (1991), Fenner (1991), Harwood & Maruyama (1992), Mahood & Barron (1996), Ramsey & Baldauf (1999) DUA7top T. fasciculata, T. elliptipora (rare), T. inura, T. oestrupii/tetraoestrupii, T. torokina 209.96 2.37 0.75 Zielinski & Gersonde (2002), Harwood & Maruyama (1992) Tab. 1 Continued. 300 G. Wilson et al.