dsc08825 (2)

17. INV1 Hll HKMI lUINOl.lHJY OF CONTINHNTAl FRHSHWATKR ENYIRONMKNTS

stratlfied, lim'- lo vory eonrse-grained sandstone channel deposits. Unlortunatoly, tho idonlity ot tho tracemaker and tho functional sigiiilicanco ot tho vertical burrows in lIuvi.il channel laeies aro poorly undorslood. allliough interpretation as domirilos ot suspension teodors soorns reasonable. 1'heso Iow diyersity (commonly nuMiospęcific) ichnofaunas domina ted bv simplo yortical burrows aro rogami od as frosh walor o\an\plos ot tho SkoliUio* ichnotacios (Buatois and Mangano, 1998, 2004).

In contrast, tho iohnotauna ot abaudouod or inactice channol doposits is characterized by menis-cato traoo tossils    Ttienkiiuui), vortioal to

inelmed bumnvs (Skylitlnw, Cy li minami) and simple hori/ontal burrows (Pnlmvp/iyais) (o.g.. Allen and Williams, 0)81; Graham and Pollard, 1982; Bamford ot al.. 1986; Sar kar and Chaudhuri. 1992; Miller and Gollinson. 1994; Miller. 2000; Keighley and Piekerill, 2003; Morrissoy and Braddy, 2004; Buatois ot al,, in pross a). lohnodivorsitv is almost invariablv Iow. Tracę tossils commonly occur in trough cross-bedded, planar cross-bedded, parallol stratified or current ripple cross-laminatod tino- to coarse-grained sand-stone. rhis iohnotauna reflects colonization ot sandstono doposits aftor channel diversk>n (‘abandon-mont*) or during poriods ot Iow dischargo yirtually characterized by nondoposition (*inaetive^ł) (Buatois and Mangano, 20041. Monlscate burrows most likoly rotloct tho activitv ot cagile organisms moeing into tho substrate in soarch for food, iwoaling a combinalion ot bypassing and ingostion. Yortical to inclined burrows havo socoral functions, including pormanont domicilos, somi-pormanont sholtors, nosts, and passa-goways (Stanley and Fagerstrom, 1974). Insect nosting tracę tossils may also occur, rofloeting thoir ability to eolonize ditloront substrato types tGoniso ot al.. 2000), lYaeemakers aiv inferrcd to bo behacioral gonoralists recording an opportunistic stratogy (Miller and Collinsem, 1994). Ichnofaunas ot abfmdoned or inac-ttve channel doposits aro romarkably similar to thoso from ovorbank doposits, bocause abandonod channels lo.ul to tho formation ot ponded arras (Ouatois and Manganu, 2002, 2004). Thoso ichnofaunas can bo ■ ontidontly assignod to tho Scoyt'iiiii ichnotaoios.

Iłu- most diwrse atul abmulant traco tossil assom-t'lagos in Iluvtal depositlona! system® commonly i*ił nr m owrb.mk ttoposUs (o.g. Fordyce, 1980; ŁTAIe*wwmdro ot al, 1987; Ouatois ot al., 199?a; Oualoi*. and Manganu, 2(102, 2004, Keighley atul 1’akonll, 2000 (Keibdiik sołtings ineludr a wldo v ariety ni doposits, *uu h as llmHlplains, eiwassc splays and k?vov* In stuno t a sos, although no hu maso in uhutkłiwrsify N apparonl, ovotlJa.uk rleposlts itro moro intonsoly bu>tnrbatod than tholt injulvalonl

channel doposits (Buatois ot al., in pross a). Ii j$ rolatiyoly common that tho only traco tossils in a tluyial succossion corrospond to fine-grainod over-bank horiz.ons interbedded within unbioturbated, coarsor grained stacked channel doposits. The occur-ronco ot distinct ichnofossil-boaring pond doposits within an othorwise unfossiliforous tluyial succossion may bo regarded as recording taphonomic and colonization Windows (Buatois et al., bN7a). Ratcliffo and Fagerstrom (1980) notieed a disparity betwoon tho abundanco ot biogenic structures in 1 lolocene overbank doposits and tho rolatiyoly poor recorcl ot thoir anciont counterpnrts, underscoring the importance ot taphonomic factors. In addition, Mnples and Archer (1989) outlined a number ot conditions that improvod preservation potential ot biogenic structures in ooerbank enoironments. namely deposition ot tine-grained hetomgoneous sediment, little or no roworking. and enough timo betwoon depositional evonts to allow colonization, but not so much timo that plant colonization obliterates animal traces. Thoso conditions allow pmsoryation in protocted ponded a mas not only ot tiny im ortobratc traces, but also ot delicate fish trails (e.g., Ndorrissey ot al.. 2004; Wisshak ot al., 2004a). Sonie ovorl\mk ichnofaunas reflect emplacenient ot biogenic structures in wator bodies that ha w boon subjected to pvog.ress.iye desiccation (desiccated twerbank) while others wore emplacod subaqueously in walor bodies lillod by owrbank vertical accmtion without o\perioncing desiccation (ooerfilled ocorbankl (Buatois and Mangano, 2004).

Ichnofaunas frorn dosiccatod ocorbank do;wib consist ot arthropod traekways (o.g.. Dif$ęh$itG$s hvłic/miłtv,    Ihuhoimłuhnu^. votlw

brato traekways (o.g.. l inniopus, Hyloidi<lmu<). Kuk-ftlled moniscato traces (o.g.. Sawiiw, Twudmi ornamented burrows (o.g.. Sf^n^rllionioryhi, and bil oba to traces with scratch marks (o.g.. Crjciaw. Rifsi>p/n/cus). \brtical bumnvs (o.g., SAofi/^. Cwliihlrii uni) aiv accessory eompononts. Ins^Yt aM arachnid nosting structures may also be pmsont. Inwrtebrate iclmodiyorsity is Iow to ramh nw\lorah'-but Nertebrate traces may be mlaticely diwMso IY.ua' tossils typiv.\lly occur in tnmgh cross Iwklwl planar cn'ss-bodvlevl. p^uallol stratitu\l. climbmg ripple cmss-lamlnated, or current ripple cncss-kuni* naloit. \i'r\ lino t\' mt\łium>graint\ł s*mdsMu' and uuulstono. \ssvuiati\t plwsical stuu tums aiv indicatwo ot poriodtc subaorial v'\js\sum such dosuxation ci.uk'' .nul ra ind rop imprints. bA.unpU^ Ot desiecated oiorKmk icluu't.uu\«vs havo twn o\tensivelv dwumentod in tho titt'wUm' (Bn»młe\ and Asgaan I, 1979- |(ux\n .nul Ihihul ł^t