訴說人類工業史的岩石

原文網址：www.sciencedaily.com/releases/2017/03/170327114255.htm

訴說人類工業史的岩石

研究人員正對灘岩(beachrock)進行研究。位於畢爾包河口的這種岩石其基質保存了工業革命的紀錄

「由於某些地質事件能記下一切事物，研究它們有助於重建過去的環境並且測定人類如何影響環境。它們甚至能提供寶貴的資訊讓我們得以處理氣候變遷可能造成的效應。」這篇分析灘岩(beachrock)的研究作者Nikole Arrieta如此主張。灘岩這種岩層一般形成於熱帶和副熱帶地區的潮間帶。儘管如此，在西班牙比斯開灣的海岸也能找到它們的蹤影。

他們研究的灘岩為近代才形成的岩層，其位於內維翁河-伊拜薩巴河河口的右岸，是深受人類活動影響的地區。Arrieta補充：「跟我們研究對象一樣出現在溫帶的灘岩相當稀少，全世界僅有8-10個例子。」這些沉積岩是由碳酸鹽膠結物(CaCO₃)的顆粒間沉澱作用形成。Arrieta解釋：「在眾多沉積物顆粒之間會產生膠結，使得這些沙子不會跟平常沙灘上的一樣鬆散，而是形成岩石。」但即使組成灘岩的膠結物質主要是碳酸鹽，我們這處海岸的地層也含有鐵質膠結物。包覆在膠結岩塊中的鐵屑會因為酸雨之類的大氣或降水事件而遭受溶解，還會在孔隙之間重新沉澱成不可溶的鐵鹽。

研究人員在他們發表的成果中著重於膠結物的特性。首先，為了研究膠結的種類，他們運用創新的光譜技術來徹底分析出不同的礦物相。「從顯微鏡的角度下可以看見膠結呈現出層層堆積的樣貌，其中每一層都能給出其形成的時間、環境以及其他各式資訊。」接著，他們分析了包覆在膠結中的物質。「我們在其中發現了工業革命時鑄造廠產生的鐵屑，有的廢棄物上甚至還具有歐洲企業的戳記，顯示它們曾以油輪來到此地傾倒礦渣。這就是我們為何能在海灘上找到所謂的『人工製品化石』(technofossils)，也就是人類活動的痕跡。在此案例中，國際企業傾倒的工業廢棄物有助於我們計算灘岩的年代。」

人類世的證據

這些物質都能成為「人類世」(Anthropocene epoch)地質紀錄中的案例。人類世目前正受到世界各地的專家熱切討論。根據對此名稱表示支持的科學家所言，既然人類造成的巨變已經在地層中留下痕跡，代表地球正處於一個新的地質時代，即「人類時代」。相對而言，反對者則聲稱這是一個政治議題而非科學問題。該地質年代包含了第四紀中最接近現代的時期，而全世界的專家現在都對此抱持著高度興趣。Arrieta說：「位在河口右岸的小港灣Tunelboka中的地層是這篇研究的重點，因為它提供了人類世的證據而受到全世界的學者討論。」除了在全世界的中緯度地區鮮少有地點呈現出此事件之外，「跟我們的研究對象一樣呈現出這類特徵的灘岩甚至更少，它們含有的鐵屑量實在令人極為驚訝。我跟澳洲和美國著名大學的許多研究人員合作，當他們看到研究地點的相片或樣品時無不感到十分驚奇。」

研究作者Nikole Arrieta說：「我們必須要持續研究這些特別且獨一無二的地質事件，以及我們的海岸所呈現的。因為它們在地球化學、環境科學及歷史學上令人大感興趣；可以運用於工程及復育相關領域；在界定最新的人類世上具有重要地位；當然，工業考古學也相當關注組成它們的物質。」

Rocks that tell our industrial history

Researchers are exploring beachrocks, rocks that have the record of the industrial revolution in the estuary of Bilbao preserved in their matrix

"Because certain geological events record everything, studying them helps to reconstruct the environmental past and to determine how human beings have influenced the environment. They will even be able to offer valuable information to tackle possible effects of climate change," asserted Nikole Arrieta, author of the study analysing beachrocks. They are rock formations that are produced in intertidal areas, normally in tropical and sub-tropical zones. Despite that, they can also be found on the Biscay coast.

The beachrocks studied are recent formations located on the right bank of the Nerbioi-Ibaizabal estuary where they have been severely affected by human activity. "Their presence in temperate latitudes like ours is rare, there are 8-10 cases all over the world," added Arrieta. These sedimentary formations are produced by the intergranular precipitation of carbonate cements (CaCO3). "A cement has formed between the various sediments. So the sand, instead of being loose as on normal beaches, forms these rocks," explained Arrieta. Yet even though the cements that the beachrocks are made up of are carbonates, the geological formations on our coast also have ferruginous cements. The slag trapped in the cemented blocks has undergone dissolution processes as a result of meteorization or atmospheric events, such as acid rain, and has even re-precipitated in the pores as insoluble iron salts.

The research carried out in the work published focussed on the characterisation of these cements. Firstly, to study the types of cements, innovative spectroscopic techniques were applied and which allowed the various mineral phases to be thoroughly analysed. "On a microscopic scale various layers of cement appear, and each one provides information on the moment when they precipitated, the conditions that existed, etc." Secondly, they analysed the materials trapped in these cements where "we found foundry slag from the industrial revolution, even waste bearing the seals of European companies that used to dump their slag when they arrived with their vessels. That is why we can find the so-called technofossils or traces of human activity on the beaches, in this case the industrial waste of international companies which helps to calculate the age of the beachrock."

Evidence of the Anthropocene

All this would constitute an example of the geological record of the Anthropocene epoch, currently being discussed among specialists across the world. And the fact is that according to the scientific supporters of this name, the Earth is in a new geological epoch, "the era of the human being," since human action is leading to major changes that are leaving their mark on the Earth's geological strata. Its detractors, by contrast, argue that it is a political rather than a scientific question. This geological era would include the most recent period of the Quaternary, and right now is of great interest for specialists all over the world. "The strata of the Tunelboka, a cove located on the right bank of the estuary which is the focus of the research, have been discussed across the world with a view to offering evidence of the Anthropocene," said Arrieta. And besides the fact that there are very few locations in the world in temperate latitudes that display this event, "there are even fewer that display the characteristics of ours; the quantity of slag they contain is mind-boggling. I have collaborated with various researchers of recognised prestige at universities in the United States and Australia, and they are all fascinated when they see the photos or materials of the location."

Nikole Arrieta, the author of the study, says "we have to keep alive the research into this geological event that is so special and unique and which we have on our coasts, for the geochemical, environmental and historical interest of these formations, their applications in the fields of engineering and restoration, their importance in defining the recent Anthropocene epoch and, why not, the industrial archaeological interest of the materials that form them."

原始論文：Nikole Arrieta, Ane Iturregui, Irantzu Martínez-Arkarazo, Xabier Murelaga, Juan Ignacio Baceta, Alberto de Diego, María Ángeles Olazabal, Juan Manuel Madariaga. Characterization of ferruginous cements related with weathering of slag in a temperate anthropogenic beachrock. Science of The Total Environment, 2017; 581-582: 49 DOI: 10.1016/j.scitotenv.2016.12.132

引用自：University of the Basque Country. "Rocks that tell our industrial history: Researchers are exploring beachrocks, rocks that have the record of the industrial revolution in the estuary of Bilbao preserved in their matrix." ScienceDaily. ScienceDaily, 27 March 2017.