Exploiting a very-high-resolution Archean surface record

Barberton绿岩带(南非)的Moody群可能保存了冲积相、河流相、海岸相、潮汐相和浅海相的罕见的、非常高分辨率的太古宙表面记录，因此可能对太古宙环境动力学提供前所未有的见解。莫迪群底部火山岩的沉积年龄与夹杂河流相砂岩的薄凝灰岩的沉积年龄重叠，地层高度约2.5公里(3227 Ma/-4 Ma对3231 Ma/-6 Ma)，这与持续较高但平衡的沉降和沉积速率的几个地质标志相一致。高精度测年的初步结果也表明，需要/-1 mA的分辨率才能可靠地区分可能仅相隔几Ma的可测年太古宙事件，这是可行的。因此，穆迪群中推断的总体平均时间分辨率可能在~1毫米/年的数量级，并保存了太古宙极短期环境动力学的档案，如气候、季节和潮汐变化。本提案中要求的基金将主要用于野外工作，以检验这一假说的各个方面。目标包括：(1)重新采样可测年地点并扩大其数量；(2)识别和采样古土壤位置，包括Moody Lava顶部的一个突出的古土壤；以及(3)调查厚交错层理和生物分层沉积中的潮汐节律。

The Moodies Group of the Barberton Greenstone Belt (South Africa) likely preserves a rare, very-high-resolution Archaean surface record in alluvial, fluvial, shoreline, tidal and shallowmarine facies and may therefore offer unprecedented insights in Archean environmental dynamics. Depositional ages from volcanic strata at the base of the Moodies Group overlap those of thin tuffs interbedded with fluvial sandstones stratigraphically ~2.5 km higher (3227 +/-4 Ma vs. 3231+/-6 Ma), consistent with several geologic indications of continuously high but balanced subsidence and sedimentation rates. Preliminary results from highprecision age dating also show that +/- 1Ma resolution, required to reliably distinguish between datable Archean events possibly only a few Ma apart, is feasible. The inferred overall mean temporal resolution in the Moodies Group may thus be on the order of ~1 mm/year and preserve an archive of very short-term Archean environmental dynamics such asclimatic, seasonal, and tidal changes.Funds requested in this proposal will be used primarily for field work to test various aspects of this hypothesis. Objectives include (1) resampling datable locations and expanding their number; (2) identifying and sampling paleosol locations, including a prominent paleosol at the top of the Moodies Lava, and (3) investigating tidal rhythmicity in thick cross-bedded and biolaminated deposits.