Gyrolithes:边缘海沉积的特征遗迹化石

Gyrolithes为螺旋形垂直居住潜穴,是具成对附肢的两侧对称甲壳类所建造,出现在近海泻湖和河口湾等边缘海和极浅海环境中,常与半咸水条件有关。塔里木盆地塔中地区诸多钻井的下志留统塔塔埃尔塔格组上部大量发育有此类潜穴,在局部层位可形成强烈的扰动构造。伴生的遗迹化石很少,只有极个别的Beaconites。根据沉积学、地球化学和古生态学特征,这类潜穴形成在半咸水的泻湖环境中。这类潜穴外壁基本平直,在泥质沉积物中掘穴深度大而不变形,而且其充填物与围岩完全不同,这些特点表明Gyrolithes为固底控制的遗迹化石。

Gyrolithes: A Characteristic Trace Fossil in Marginal Marine Sediments

Gyrolithes , a kind of vertical dwelling burrow, may be formed by ilaterally symmetrical animals with paired appendages and often had a brackish water origin. Abundant trace fossils of Gyrolithes were occurred in the upper part of Tataaiertage Fm.Lower Silurian of many wells from Central Tarim basin, where the sediments were extensively bioturbated by Gyrolithes animals and contained very rare trace fossils like Beaconites . Based on the sedimentological, geochemical and paleoecological features, Gyrolithes from Lower Silurian of Central Tarim basin is formed in brackish lagoon environment. This kind of trace is generally very sharp walled and unlined, reflecting the stable, cohesive nature of the substrate at the time of colonisation and burrow excavation. It remained open after the tracemaker vacated the burrow, thus allowing material from the succeeding depositional event to passively fill the open structure. If the burrow had been excavated in mud, the domicile would have collapsed upon burrow vacation, unless lined. All these features indicate that Gyrolithes is a kind of firmground controlled trace fossil.