A review on palaeogeographic implications and temporal variation in glaucony composition  

作　　者：Santanu Banerjee Udita Bansal Anup Vilas Thorat 

机构地区：[1]Department of Earth Sciences,Indian Institute of Technology Bombay

出　　处：《Journal of Palaeogeography》2016年第1期43-71,共29页古地理学报（英文版）

基　　金：Department of Science and Technology,Government of India for financial support through Grant IR/S4/ESF-16/2009(2);DST-IITB National Facility for EPMA,Department of Earth Sciences,Indian Institute of Technology Bombay

摘　　要：This study presents a review on palaeogeographic implications and temporal variations of giaucony coveringboth modern and ancient records. Phanerozoic giaucony preferably forms in a shelf depositional setting. Deep marine conditions and low seawater temperature discourage formation of glaucony. Around 75% of glaucony is recorded from the Cretaceous to the Holo- eene sediments, which are related to the abundance of the most common substrates, faecal pellets and bioclasts. TFe203 （total）, A1203, K20 and MgO contents of glaucony vary appreciably through geological time. IMhile TFe203 content of most Mesozoic and Cenozoic giaucony ex- ceeds 20%, it is always less than 20% in Precambrian varieties. High K20, A1203, MgO and low TFe203 distinguish the Precambrian glaucony from its Phanerozoic counterpart. Precambrian glaucony, preferably formed within a K-feldspar substrate, is always rich in potassium irre- spective of its degree of evolution, while high K-content in Phanerozoic evolved glaucony in- dicates significant stratigraphic condensation. K20 iJs. TFe203 relationship of glaucony exhibits three different evolutionary trends corresponding to three common modes of origin. Depositional conditions may influence the composition of glaucony as slightly reducing conditions favour Fe enrichment, whereas oxidising conditions cause Fe depletion in giaucony.This study presents a review on palaeogeographic implications and temporal variations of giaucony coveringboth modern and ancient records. Phanerozoic giaucony preferably forms in a shelf depositional setting. Deep marine conditions and low seawater temperature discourage formation of glaucony. Around 75% of glaucony is recorded from the Cretaceous to the Holo- eene sediments, which are related to the abundance of the most common substrates, faecal pellets and bioclasts. TFe203 （total）, A1203, K20 and MgO contents of glaucony vary appreciably through geological time. IMhile TFe203 content of most Mesozoic and Cenozoic giaucony ex- ceeds 20%, it is always less than 20% in Precambrian varieties. High K20, A1203, MgO and low TFe203 distinguish the Precambrian glaucony from its Phanerozoic counterpart. Precambrian glaucony, preferably formed within a K-feldspar substrate, is always rich in potassium irre- spective of its degree of evolution, while high K-content in Phanerozoic evolved glaucony in- dicates significant stratigraphic condensation. K20 iJs. TFe203 relationship of glaucony exhibits three different evolutionary trends corresponding to three common modes of origin. Depositional conditions may influence the composition of glaucony as slightly reducing conditions favour Fe enrichment, whereas oxidising conditions cause Fe depletion in giaucony.

关 键 词：Glaucony Glauconite Evolutionary trend Substrate Palaeogeography Faecal pellet 

分 类 号：P531[天文地球—古生物学与地层学] P315.7[天文地球—地质学]