摘要:
在我国西沙群岛的石岛上,发育着一种奇特的景观，前人曾误认为鹿角珊瑚丛体组成的珊瑚礁灰岩，或群体虫孔1)。作者研究认为它们是在植物根系参与下，在珊瑚礁灰沙岛沉积里，表生成岩过程中形成的方解石岩管。我们还在海南岛西北部，白马井以南海岸找到了包围着活树根的类似的岩管，而在排浦附近海蚀崖上发现了白云化的岩管。这类岩管是在渗流带或海岸潮间带里，水流沿着植物根系渗透和溶滤而发生溶解、沉淀和交代作用的产物.我们称它为渗滤岩管。在这一过程中，植物直接控制着沉积物的石化和白云化作用。近三十年来，关于生物对碳酸盐沉积作用的巨大意义已为地质界所公认，但对于植物在成岩作用中，特别是在白云化中的作用的论著还不多。有人认为，生物在石化成岩和白云石生成方面的作用是不可忽视的，但这一作用是间接的。本文拟对这类岩管的产状、组构、形成机理、及植物在石化和白云化中的控制作用阐述如次。
Abstract:
A kind of rock- tubules(3-25 mm in diameter and 30-50cm in length)occurs in the late Pleistocene biosparites on the Shidao Island of lisha Islands，China.These tubules, whcih had been misunderstood as colony of corals species Acropora, or colony of warm pipes, have concentric stratoid structures.Its inner stratu m, having acentral tubule 5一8 mm in diameter, is made of dark brown micrite with corrosional cements but the light gray outerstratum is made of biosparites cemented by finely crystalline sparry calcites(0. 03-0. 04mm)，and locally filled up the intergranular space.Another kind of rocky tubules occurs in the Pleistocene fine sandy-silty sediments interbedded with stratoid and lenticular dolomites is the Paipu area of northwestern Hainan Island,China.These tubules have mainly vertical and horizontal occurrences with circle and oval cross section.They- also have stratoid structures.The loose and rough central area ,about 4 mm in diameter. consists of 65一75% quartz and other elastic materials and 10-15% crystalline dolomite.The fine and dense intensely dolomitized inner stratum( 5 -10 mm in thickness)consists of 90% dolomite,only 5% clastic materials and 5 % pore space.This dolomite is a euhedral rhombohedron,medium to very finely crwstalline with porphwritic testure.The silty clastic particles have relict structures caused by the infiltration and replacement.The loose cemented outer stratum consists of 40% elastic particles(medium to coarse grain size)，40%euhedral finely一medium crystalline dolomite and about 20% pore.The physiological action of plants controls the formation of these rocky tubules around the plant roots. Their formation mechanism is as follows:The transpiratio and respiration or metabolism of plants suck up moisture from below.drain，off the CO2 and organic acid on the one hand. and the vadose watr moves down along the roots on the other.Thus. in the microen}ironment near the root, the dissolution.precipitation and metasomatism of carbonate take place re-etpeatedly around the root system.and primary carbonate tubules are formed during their living time。After their death.the surface water may infiltrate along the formed tubules, the dissolution of the sediments and precipitation of crystalline calcite within the pore space mac continuously- take place.Carbonate tubules formed in such a way are called infiltration rocky tubules by the authors. In the vadose zone with fresh water, calcite rocky tubule is formed, whereas in the intertidal zone of the coast.the dolomitized infiltration rock3- tubule is formed under the influence of schizahaline condition produced by sea water alternating with fresh ground water.This unusual process of dolomite formation may- be called dolomitization of plants.The formation of infiltrated rocky tubules as a process of early diagenesis is of great sigricance for the romprehension of the direct effect of plants on the diagenesis
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