豫西济源中三叠统二马营组中、下段遗迹组构与沉积环境

Ichnofabrics and Sedimentary Environments of Middle and Lower Members of Middle Triassic Ermaying Formation in Jiyuan,West Henan Province

豫西济源中三叠统二马营组中、下段发育丰富的陆相遗迹化石,共鉴定出7属9种,包括:Skolithos linearis、Palaeophycus tubularis、Palaeophycus alternatus、Scoyenia gracilis、Planolites beverleyensis、Planolites montanus、Taenidium barretti、Didymaulichnus roualti和根迹,识别出5种遗迹组构:(1)Skolithos遗迹组构,代表泥质、细砂质的河流或滨湖环境;(2)Palaeophycus⁃Planolites遗迹组构,代表低‒中等水能河流堤岸或滨湖泥坪环境;(3)Scoyenia遗迹组构,代表周期性淹没的洪泛平原环境;(4)Taenidium遗迹组构,代表半干旱气候下的洪泛平原环境;(5)Rhizoliths遗迹组构,代表半干旱气候条件下、中‒低等水能的河流堤岸或河漫环境.二马营组中、下段遗迹组构及沉积特征反映河湖相沉积环境,自下而上相继发育辫状河‒曲流河‒滨浅湖沉积,该沉积期气候以半干旱‒温湿的多次交替为特征,同时伴随着氧化条件与还原条件的交替.

Abundant terrestrial ichnofossils were recovered from the middle and lower members of the Middle Triassic Ermaying Formation in Jiyuan area,West Henan Province.A total of 7 ichnogenera and 9 ichnospecies have been found and identified,including Skolithos linearis,Palaeophycus tubularis,Palaeophycus alternatus,Scoyenia gracilis,Planolites beverleyensis,Planolites montanus,Taenidium barretti,Didymaulichnus roualti and rhizoliths.According to the pattern,composition and distribution of ichnofossils,five kinds of ichnofabrics have been discriminated:(1)Skolithos ichnofabric represents the fluvial or shore lacustrine sedimentary environment with mud,fine sand deposits;(2)Palaeophycus⁃Planolites ichnofabric appears in the sedimentary environment of low-medium hydropower fluvial embankment or lacustrine mudflat deposits;(3)Scoyenia ichnofabric forms in the periodically submerged flood plain sedimentary environment;(4)Taenidium ichnofabric emerges from the flood plain environment under semi-arid climate;(5)rhizoliths ichnofabric preserves from embank oroverbank environment under semi-arid climate conditions.Based on the ichnofabrics and sedimentary characteristics,fluvio-lacustrine strata are dominant in the middle and lower members of the Ermaying Formation.From bottom to top,braided streammeandering river-lacustrine deposits were formed successively.It can be divided into six sedimentary subfacies:meandering channel subfacies,embankment subfacies,overbank subfacies,braided channel subfacies,floodplain subfacies and shore lacuetrine subfacies.The whole sedimentary period is characterized by alternation of humid and semi-arid,with the transformation from reduction environment to oxidation environment.