Ejecta blanket deposits of the Chicxulub crater from Albion Island, Belize
Ejecta blanket deposits of the Chicxulub crater from Albion Island, Belize
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伯利兹阿尔比恩岛希克苏鲁伯陨石坑的喷出层沉积物
DOI：
10.1130/0-8137-2307-8.75
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
A. G. Fischer
中科院分区：
文献类型：
--
作者：
A. Ocampo;K. Pope;A. G. Fischer
在伯利兹北部的阿尔比恩岛，一个不整合的非凡沉积物覆盖在晚白垩世白云岩上。基底单元为1 m厚的富粘土白云岩和方解石粉砂层，含有大量直径1 ~ 20 mm的白云岩球状体和含有残余囊泡的球形至角状粘土碎屑。白云岩和粘土球体在接近基底接触面处均变平。这个球形床上覆盖着15米的二晶岩，其中包含毫米到米大小的碎屑（最大7.5米），漂浮在白云岩粉砂基质中。碎屑以白云岩为主，含早白垩世至中白垩世初生岩和有孔虫类灰岩。碎屑通常是破碎的，从圆圆的鹅卵石和鹅卵石到棱角分明的薄片。抛光的切面和单一碎屑上的多组条纹表明严重的磨损。辉长岩层中还含有丰富的含残余囊泡和泥球的粘土碎屑、方解石类球袋和自生石英。变质岩和碎屑石英仅限于在不溶性残留物中发现的罕见的砂粒大小的碎片。我们认为，阿尔比恩岛沉积物是迄今为止发现的最接近希克苏鲁伯陨石坑喷出物的暴露部分。阿尔比恩球层与墨西哥湾沿岸和加勒比海地区其他地方描述的球层相似，但白云岩球层迄今为止是独一无二的，可能是蒸发碳酸盐的陨石等价物。唯一与阿尔比恩二晶岩相对应的是在希克苏鲁伯陨石坑边缘钻出的粗糙喷出物。阿尔比恩角砾岩与里斯陨石坑的邦特角砾岩有许多共同特征。我们认为球床是由蒸汽羽流沉积而成，而辉长岩是由弹道沉积和泥石流作用共同形成的。
An extraordinary deposit disconformably overlies Late Cretaceous dolomite on Albion Island in northern Belize. The basal unit is a 1-m-thick bed of clay-rich dolomite and calcite silt containing abundant 1-to 20-mm-diameter spheroids of dolomite and spheroidal to angular clasts of clay containing relict vesicles. Both the dolomite and clay spheroids are flattened near the basal contact. This spheroid bed is overlain by 15 m of diamictite that contains millimeter-to meter-sized clasts (maximum 7.5 m) floating in a matrix of dolomite silt. The clasts are mostly dolomite but include limestones with Early to Middle Cretaceous rudists and foraminifera. Clasts are commonly fractured and range from well-rounded pebbles and cobbles to highly angular flakes. Polished facets and multiple sets of striations on single clasts indicate severe abrasion. The diamictite bed also contains abundant clay clasts with relict vesicles as well as mud balls, pockets of calcite pisoids, and authigenic quartz. Metamorphic rocks and detrital quartz are restricted to rare sand-size chips found in insoluble residues.We propose that the Albion Island deposits are the most proximal, exposed section of ejecta from the Chicxulub crater yet found. The Albion spheroid bed is similar to spherule beds described from elsewhere in the Gulf Coast and Caribbean region, but the dolomite spheroids are thus far unique and may be the tektiteequivalent of vaporized carbonates. The only correlate for the Albion diamictite is the coarse ejecta unit drilled on the rim of the Chicxulub crater. The Albion diamictite shares many characteristics with the Bunte breccia of the Ries crater. We propose that the spheroid bed was deposited by the vapor plume and the diamictite by ballistic sedimentation coupled with debris flow processes.