CAJ | 학술논문

介绍地质记录中在不稳定的沉积环境下，由于生活条件的恶化(盐度的变化，严酷的温度，低含氧量及移动的沉积基底等)以及沉积事件(浊流沉积和风暴沉积)所产生的机会(r-选择)遗迹化石和均衡(K-选择)遗迹化石及其特点以及机会行为方式的古生物证据。对现代底栖生物的生态学研究，揭示现代机会生物和均衡生物的生态特征(居群策略)，描述由于破坏事件导致动物群消除后重新移居的现代实例，有助于了解地质记录中机会(r-选择)遗迹化石和均衡(K-选择)遗迹化石的成因及其古生态特征。
개소지질기록중재불은정적침적배경하，유우생활조건적악화(염도적변화，엄혹적온도，저함양량급 이동적침적기저등)이급침적사건(탁류침적화풍폭침적)소산생적궤회(r-선택)유적화석화균형(K-선택)유적화 석급기특점이급궤회행위방식적고생물증거。대현대저서생물적생태학연구，게시현대궤회생물화균형생물적생 태특정(거군책략)，묘술유우파배사건도치동물군소제후중신이거적현대실례，유조우료해지질기록중궤회(r-선 택)유적화석화균형(K-선택)유적화석적성인급기고생태특정。
The opportunistic (r-selected) trace fossils pro duced under the unstable depositional environments and serious ecological conditions (the fluctuating salinity and temperature, low-oxygen and shifty sub strates et al. ) and the equilibrium (K-selected) trace fossils produced under the stable and predictable de positional conditions in the geological histories have attracted much attention from ichnologists and sedi mentologists for a long time. Seilacher noted that the trace fossils in the black shale of lower Jurassic Pasi donienschiefer are mainly composed of highly branched Chondrites which is related to the low-oxy gen sedimentary environments. The pellet-walled burrow Ophiomorpha and Granularia are considered to be opportunistic trace fossils in relation to the shifty sandy substrate and the sedimentary conditions with high depositional rate. Miller and Johnson (1981) described an opportunistic burrow Spirophy ton deposited under environmentally harsh fluvial tidal conditions, where temperatures, salinities and even intervals of subaerial exposures were quite vari able and unpredictable. The opportunistic (r-selected) trace fossils with respect to event deposits (turbidite and tempestites) have also been noticed. Seilacher (1962) and Kern (1980) recognized the pre-turbidite equilibrium (K selected) trace fossils consisting of Palaeodictyon, Desrnograpton , Cosrnorhaphe , Spirohaphe , Nereties and regular Scolicia and the post-turbidite opportunistic (r-selected) trace fossils consisting of Granularia, Phycosiphon and irregular Scolisia. The trace fossil assemblages in the terrigenous tem pestites of the Upper Cretaceous Cardium Formation are described by Pemberton et al. (Pemberton and Frey, 1984; Pemberton et al., 1992; Pemberton et al. in press). The opportunistic (r-selected) trace fossils consisting of Skolithos ichnofacies members in clude Arenicolites , Diplocraterion , Ophiomorpha , Palaeophycus and Skolithos. The equilibrium (K slected) trace fossils consisting of Cruziana ichnofa cies members include Anconichnus, Asterosoma, Chondrites , Helminthopsis , Palaeophycus , Plano lites, Rosselia, Teichichnus, Terebellina and Tha lassinoides. The trace fossil assemblages in the storm influenced carbonate deposits found in the Gushan Formation of the Upper Cambrian from eastern North China Platform are somewhat similar to those men tioned above in the Cardium Formation. The pre storm equilibrium ( K-selected ) trace fossils Phy codes, Thalassinoides , Palaeophycus and Planolites are composed of Cruziana ichnofacies memebers. The post-storm opportunistic (r-selected) trace fossils Diplocraterion, Arenicolites and Skolithos are com posed of Skolithos ichnofacies members ( Zhou Zhicheng et al. , in press). The characteristics of an opportunistic body fossil assemblage were summarized by Pemberton and Frey (1984) as (1) of limited aerial distribution (Waage, 1968); (2) occurring in a continuous, thin iso choronous horizon (Waage, 1968); (3) abundant in several otherwise distinct faunal assemblages (Levin ton, 1970);(4) having great abundance in a facies with which it is not generally associated (Levinton, 1970); and (5) numerical domination of one species within the fossil assemblage (Levinton, 1970). In recent ecological studies of benthic organisms, equilibrium (K-selected) species have been distin guished from opportunistic (r-selected) species. The studied results are important for understanding the paleoecologic characteristics of opportunistic (r-select ed) trace fossils and equilibrium (K-selected) trace fossils in the geological histories. In general, oppor tunistic species can respond rapidly to an open or un exploited niche and are characterized by (1) a lack of equilibrium population size, (2) a density-dependent mortality, (3) the ability to increase abundance rapidly, (4) a relatively poor competitive ability, (5) high dispersal ability, and (6) a high proportion of resources devoted to reproduction (Glassle and Grassle, 1974). Opportunistic organisms display a r strategy in population dynamics, emphasizing rapid growth rate (r), whereas equilibrium species adopt a K-strategy, based on the carrying capacity of the en vironment (K) (Boesch and Rosenberg, 1981 ). Short generation span is the most important mecha nism for increasing population size in a r-strategy; therefore life spans of opportunistic species are short er, and sexual maturation is reached earlier (Rees et al., 1977). Broad environmental tolerance and gen eralized feeding habits facilitate rapid colonization of open niches (Pianka, 1970; Wolff, 1973). Currently, ecologists involving organisms are re alizing the importance of hydrodynamics in larval set tlement, and a new hypothesis, termed passive depo sition, is gaining wide acceptance. Butman (1987) summarized the two main points of view regarding passive deposition as the following: either (1) larvae are deposited over broad areas but differently survive only in hospitable abult habitats or (2) species-speci fic larval fall velocities correspond with particular sed iment fall velocities, such that hydrodynamically sim ilar particles and larvae are deposited in the same en vironment. Episodic depositional events, like storms and turbidites, therefore can have a powerful effect on the redistribution of the larvae of benthic organ isms. In most event deposits, initial larval settle ment, initial larval settlement may be a function of the hydrodynamics of the event bringing both larvae and sediment into the area. At present, most biologists believe that larval settlement involves a complex interaction between ac tive and passive processes. Competent planktonic lar vae initially reach the seafloor at sites where passively sinking particulate, having fall velocities similar to the larvae, initially settle (Hannan, 1984). Other biological or physical processes may then redistribute them. In most event deposits, therefore, initial larval settlement may be a function of the hydrodynamics of the event bringing both larvae and sediment into the area. After initial settlement, exploitation of the open niche becomes more a function of the reproductive characteristics of the individual species. In most cas es, because of their efficient reproductive cycles, op portunistic species quickly dominate the initial stages of recolonization. Studies of recolonization rates of stable and un stable (e. g. fluctuating ecological parameters, such as salinity, sedimentation rate, and temperature) mod ern environments show that organisms in stable envi ronments are more adversely affected by physiological stress. Species present in unpredictable environments (e. g. , estuaries and river-dominated deltas), usually have broad environmental tolerance and can recover from disturbances quickly (Jenelov and Rosenberg, 1976). For instance, the benthic population of rela tively stable deep-sea environments can take more than 2 years to recover completely, while the benthic population of relatively unstable estuarine environ ments may recover in less than 11 months (Dauer and Simon, 1976; Grassle, 1977).