川西晚三叠世深水复理石相藻管迹组合的比较遗迹学研究

COMPARATIVE STUDY IN ICHNOLOGY, AN EXAMPLE OF DEEP WATER FLYSCH PHYCOSIPHON ASSEMBLAGE FROM THE LATE TRIASSIC STRATA OF WESTERN SICHUAN

四川西部白玉地区上三叠统以Ｐｈｙｃｏｓｉｐｈｏｎ为优势属的深水复理石遗迹相，与菲律宾苏禄海的现代浊积序列中Ｐｈｙｃｏｓｉｐｈｏｎ遗迹群落特征最为相似，显示了构造活动带深海环境的贫氧和高沉积速率的特点。这些Ｐｈｙｃｏｓｉｐｈｏｎ遗迹化石因沉积速率差异而有Ａ，Ｂ，Ｃ，Ｄ４种不同的形态特征，其中ＰｈｙｃｏｓｉｐｈｏｎＡ型是后浊积遗迹相，代表相对高沉积速率，ＰｈｙｃｏｓｉｐｈｏｎＤ和Ｃ型是前浊积遗迹相，代表相对稳定和低沉积速率的环境，而ＰｈｙｃｏｓｉｐｈｏｎＢ型可能为过渡类型。这个Ｐｈｙｃｏｓｉｐｈｏｎ组合产生于晚三叠世弧后扩张盆地。遗迹化石古生态研究表明，晚三叠世白玉海盆的古地理特征和现代苏禄海盆在诸多方面可以类比，它曾是陆坡陡峭，浊积活动频繁，具有高沉积速率（至少大于１００ｃｍ／ｋａ），海盆四周被火山岛环绕，和外海交流受限，海底含氧量处于贫氧带（ｅｘａｅｒｏｂｉｃｚｏｎｅ），水深４０００－４５００ｍ之间的深水滞流盆地。

A deep water flysch trace assemblage dominated by Phycosiphon has been found from the Late Triassic of the Baiyu area, western Sichuan Province. The trace a ssemblage is analogous to the recent Phycosiphon community in the turbidite sequences in Sulu Sea, Philippines, indicating a high sedimentary rate and exaer obic oceanic bottom of active tectonic zones. Accorrding to the changes of sedim entary rate, the specimens of Phycosiphon could be distinguished as four mor photypes. Among them, Phycosiphon A refers to the post depositional traces , suggesting a higher rate; while Phycosiphon D, C are considered to be pre de positional traces, indicating a stable depositional environment with low sedimen tary rate, and Phycosiphon B may represent a transitional morphotype betwee n Phycosiphon A and Phycosiphon D. Taking into account the ecological similarity with the recent Phycosiphon community of Sulu Sea, the paleogeogr aphic aspect of the Baiyu Sea, a volcanic islands arc tensional basin during th e Late Triassic, could be well comparable with the case of the recent Sulu Sea B asin, therefore the Baiyu Basin might have been characterized by steep slope, fr equent turbidite, high depositional rate more than 100cm/ka, and sedimentary bot tom in exaerobic zone; the paleo sea seems to have been a depositional basin si lled by volcanic islands.