层内砾岩
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层内砾岩(英语:Intraformational conglomerate)是碎屑颗粒为卵石大小的沉积物之一种。砾岩可根据砾石颗粒的来源分类[1], 如果这些砾石碎屑的矿物组成,与基质显著不同,因此可能来自更古老的地层或来自沉积盆地之外地区 , 该砾岩被称为层外砾岩。 如果这些碎屑与基质的岩性相同的矿物组成,则是来自准同生沉积盆地内的岩石,则该砾岩被称为层内砾岩[2]。
鉴定层内砾岩的两种公认指标是根据卵石颗粒的组成及形状。若卵石颗粒是由泥屑组成,不论其形状,代表其搬运距离短,因为泥屑颗粒在搬运途中,易于被破坏,不易保存[3]。第二种鉴定指标是卵石颗粒的的形状。若是扁平的卵石颗粒,也代表短途搬运[4]。经短途搬运而形成的沉积物,其碎屑颗粒的矿物组成与基质相似。
形成
[编辑]层内砾岩在准同生期尚处在半结固状态时,经侵蚀破坏和再沉积而成的砾石沉积物。通常是在浅水环境中形成[5]。由泥屑卵石颗粒组成的层内砾岩,通常实在河道内或湖边等环境中的侵蚀作用形成。由扁平卵石组成的层内砾岩则是在浅海底部或潮汐流沿海岸线地区,经由风暴或海啸侵蚀潮滩而形成的。在这地区,海底为平坦的半固结的石灰泥碎屑岩。当强流通过时,这些半固结的石灰泥碎屑岩被破坏而掀起[6]。
在加拿大Nova Scotia宾夕法尼亚世的河流相砂岩地层中有很多的侵蚀结构,在泥岩面上留下多处侵蚀面。指出曝露水面的证据。坍塌及层内砾岩都与侵蚀面有关[7]。层内砾岩在海进的初期也能形成。 在法国Haute-Savoie 地区,其白垩纪的砾岩层由不同形状的卵石构成。卵石颗粒是由海底的石灰质泥岩在半固结状态被断裂和重新沉积而形成层内砾岩[8]。
海底侵蚀亦可形成层内砾岩。在波兰的三叠纪Gogolin 的砾岩层,其卵石颗粒多为扁平状,由化学沉积的微晶石构成,很少碎屑物。这些卵石颗粒是当风暴来临时,波浪基底下降,而造成水下侵蚀,并掀起海底的半固结沉积物[9]。
波兰发现同为上泥盆纪的砾岩层,卵石颗粒为扁平状钙质和泥晶质卵石,因为位于潮间带,经由风暴潮或海啸造成海底沟流,而分裂海底半固结沉积物,形成层内砾岩,其中卵石颗粒的位移很少[10]。层内砾岩也在美国怀俄明州和蒙大拿州南部也被发现[11]。
参考文献
[编辑]- ^ Friedman, G.M. (2003) Classification of sediments and sedimentary rocks. In Gerard V. Middleton, ed., pp. 127-135, Encyclopedia of Sediments & Sedimentary Rocks, Encyclopedia of Earth Science Series. Kluwer Academic Publishers, Boston, Massachusetts. 821 pp. ISBN 978-1-4020-0872-6
- ^ Friedman, G.M. (2003) Classification of sediments and sedimentary rocks. In Gerard V. Middleton, ed., pp. 127-135, Encyclopedia of Sediments & Sedimentary Rocks, Encyclopedia of Earth Science Series. Kluwer Academic Publishers, Boston, Massachusetts. 821 pp. ISBN 978-1-4020-0872-6
- ^ Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ISBN 0-922152-76-4
- ^ ucker, M. E. (2003) Sedimentary Rocks in the Field, 3rd ed. John Wiley & Sons Ltd,West Sussex, England. ISBN 0-470-85123-6
- ^ Williams, G. D. (1966) Origin of Shale-Pebble Conglomerate. American Association of Petroleum Geologist Bulletin. vol. 50, no. 3, pp. 573–577
- ^ Boggs, S. (2006) Principles of Sedimentology and Stratigraphy., 2nd ed. Prentice Hall, New York. 662 pp. ISBN 0-13-154728-3
- ^ PLINT, A.G. (1986), Slump blocks, intraformational conglomerates and associated erosional structures in Pennsylvanian fluvial strata of eastern Canada. Sedimentology, 33: 387-399. https://doi.org/10.1111/j.1365-3091.1986.tb00543.x
- ^ Albert Carozzi; An intraformational conglomerate by mixed sedimentation in the upper Cretaceous of the Roc-de-Chere, autochthonous chains of High Savoy, France. Journal of Sedimentary Research 1956;; 26 (3): 253–257. doi: https://doi.org/10.1306/74D705F6-2B21-11D7-8648000102C1865D
- ^ Chudzikiewicz, Leszek. "Intraformational conglomerates in the Gogolin beds (Middle Triassic, southern Poland)." Annales Societatis Geologorum Poloniae. Vol. 45. No. 1. 1975.
- ^ Kaźmierczak, J., & Goldring, R. (1978). Subtidal flat-pebble conglomerate from the Upper Devonian of Poland: A multiprovenant high-energy product. Geological Magazine, 115(5), 359-366. doi:10.1017/S0016756800037377
- ^ Paul M. Myrow, Lauren Tice, Bonny Archuleta, Bryn Clark, John F. Taylor and Robert L. Ripperdan(2004)Flat-pebble conglomerate: its multiple origins and relationship to metre-scale depositional cycles。Sedimentology, Volume 51, Number 5, Page 973。DOI: 10.1111/j.1365-3091.2004.00657.x