Exploiting a very-high-resolution Archean surface record

巴伯顿绿岩带（南非）的穆迪群可能保存了罕见的、非常高分辨率的太古宙冲积、河流、海岸线、潮汐和浅海相的表面记录，因此可能为太古宙环境动力学提供前所未有的见解。moody群底部火山地层的沉积年龄与薄凝灰岩与河流砂岩互层的沉积年龄重叠~2.5 km (3227 +/-4 Ma vs 3231+/-6 Ma)，与持续高但平衡的沉降和沉积速率的几个地质指示相一致。高精度年龄测年的初步结果也表明，+/- 1Ma的分辨率是可行的，这需要可靠地区分相隔几Ma的太古宙事件。因此，穆迪群推断的总体平均时间分辨率可能在1毫米/年左右，并保存了太古宙非常短期的环境动态档案，如气候、季节和潮汐变化。本提案所要求的资金将主要用于实地工作，以检验这一假设的各个方面。目标包括：(1)重新采样数据位置并扩大其数量；(2)确定古土壤位置并取样，包括穆迪斯熔岩顶部的一个突出的古土壤；(3)研究厚交叉层状和生物层状沉积物的潮汐节律性。

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.