Acorn Business Centre, 1-16 Empress Road, Southampton. Archaeological Watching Brief and Geoarchaeological Evaluation (SOU1678)

The Acorn Business Centre at 1-16 Empress Road, Southampton was redeveloped in 2014-15. An archaeological condition on the application resulted in an archaeological watching brief on the ground investigations and the retrieval and analysis of a sleeved core taken through the below ground deposits, which included prehistoric peat. The lowest deposit observed in the piling was the London Clay. This was overlain from -5.27m OD by sands and gravels of the Whitecliff Sand Member. These were cut by the valley of the Itchen in the Pleistocene period. The earliest surviving river valley deposits were sand and silt that included pond weed remains indicating standing fresh water. This was followed by increased organic content suggesting vegetation encroachment leading to peat formation. The peat was a mix of sedge and alder with alder becoming more prevalent towards the top, after which tidal inundation began to affect the area. The base of the peat, which was at c.-4m OD, was radiocarbon dated to the early Mesolithic period (10225 to 10165 cal BP) and the top of the peat, which was at c.-1.55m OD, was radiocarbon dated to the mid-Mesolithic period (7715 to 7620 cal BP). This would give a total rise in relative sea level of 2.45m over approximately 2250 years being on average just over 1mm a year. The changes in lithology, vegetation and hydrology seen in the deposits undoubtedly resulted from positive relative sea-level change, well documented for the Solent. The prehistoric deposits were overlain by disturbed tidal flat deposits and 19th century made ground. The base of the peat (10225 to 10165 cal BP), is the earliest date to be obtained from a layer of peat in the Itchen valley. The Empress Road site therefore provides important new evidence for the early chronology of the river Itchen. The earliest peat (dated to the early-Mesolithic) probably lay in a narrow channel and this is the first time it has been found; the later peat ties in with the dates from two nearby sites suggesting a wider deposit of peat in the mid-to late-Mesolithic period. The archive contains text documents and raster images. The paper archive and the photographic archive; comprised of black and white negatives and prints, colour slides and digital images, was deposited with Southampton City Council Museums archaeological archive. Some environmental material was recovered from the geoarchaeological evaluation.

南安普顿皇后路1-16号的橡果商业中心（Acorn Business Centre）于2014至2015年间实施了重建工程。该项目审批申请中的考古条款要求，对现场勘探开展考古监护监测（archaeological watching brief），并对穿过包含史前泥炭（prehistoric peat）的地下堆积层的带套管岩心（sleeved core）进行取回与分析。桩基勘探中发现的最低堆积层为伦敦黏土（London Clay），该层以OD基准面（Ordnance Datum）-5.27米处为界，之上覆有怀特克利夫砂层段（Whitecliff Sand Member）的砂与砾石堆积。更新世（Pleistocene）时期，伊钦河谷（Itchen valley）侵蚀切割了这套堆积。现存最早的河谷堆积为砂与粉砂堆积，其中含有pond水草遗存（pond weed remains），表明当时存在静止淡水水域。此后堆积的有机质含量升高，指示植被逐渐侵入该区域并形成泥炭。该泥炭由莎草与桤木混合组成，其中桤木占比随层位向上逐渐增加；此后潮汐淹没开始影响该区域。该泥炭的基底位于OD基准面约-4米处，经碳十四测年（radiocarbon dating）确定为中石器时代早期（early Mesolithic period，10225~10165 cal BP）；泥炭顶部位于OD基准面约-1.55米处，测年结果为中石器时代中期（mid-Mesolithic period，7715~7620 cal BP）。据此可推算，在约2250年的时间跨度内，相对海平面总计上升了2.45米，平均年上升幅度略超过1毫米。堆积层中展现的岩性、植被与水文变化，无疑由相对海平面正升运动所致——这一现象在索伦特海峡（Solent）地区已有充分的文献记录。史前堆积层之上覆有受扰动的潮坪堆积与19世纪人工填土。该泥炭基底的测年结果（10225~10165 cal BP）是伊钦河谷泥炭层中获得的最早年代数据。因此，皇后路遗址为伊钦河的早期年代序列提供了重要的新证据。年代为中石器时代早期的最早泥炭层，大概率形成于狭窄河道中，这是该类泥炭层首次被发现；后期泥炭的测年结果与附近两处遗址的测年数据相符，表明中石器时代中晚期存在分布范围更广的泥炭堆积。该档案包含文本文件与栅格图像（raster images）。纸质档案与影像档案（含黑白负片、照片、彩色幻灯片与数字图像）已移交南安普顿市议会博物馆考古档案库保管。本次地质考古评估中还回收了部分环境样本。