Discusses on Preservational Potential of Event Bed
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摘要: 影响事件层保存潜力的主要因素有 :纯粹的沉积速率、生物成因的混合速率以及机械改造的规模,可以从时间规模 (过渡时间和消除时间 )的角度来考虑事件层保存潜力。基底的机械改造同样对于事件层和正常天气下的沉积物的保存具有重要影响。综合分析影响事件层保存潜力的各种因素表明,在近基的临滨带中、上部及滨外带下部,事件层具有较高的保存潜力,而在近基及远基两端之间的临滨带下部及滨外带上部,事件层保存潜力较低.Abstract: The increasing awareness of tcmpcstitcs in the ancient record has correspondingly led to much consideration of their prcscrvahility.The main factors influencing the prcscrvahilitv are the net sedimentation rate Tthe hiogcnic mixing rate } and the magnitude of physical reworking. Theateroft has put forward the concept of time scales to attempt to solve this problem.The terms of transit time and dissipation time arc introduced.Transit time is related to the thickness of the hiogcnic reworking zone,the thickness of event beds and sedimentation rate.The hiogcnic reworking zone is also controlled by the animal size and the behavior engaged in during its generation.The determination of transit time is difficult because of the unstcadv and unpredictable mination of dissipation time is even more complicated than that of transit time.The dissipation time is controlled by manv factors such as the size of infauna, the behavior engaged in by the organisms, the dynamic interplay between the hcnthic community and the dcpositional event itself the dcsirahilitv of the event bed as a site for colonization and as a repository of food resources and the absolute time available for burrowing ctc.Unfortu- natelv, the preceding factors appear to resist quantification and therefore severely limit the effectiveness of existing mathcmatical models to explain tcmpcstitcs preservation in the rock record. Physical reworking of the substrate has a profound effect on the preservation of both the event hcd and the fair-wcathcr deposits.On the basis of comprehensive analyses of all factors influencing prcscrvational potential of event beds and cmpirical ohservations} both proximal upper-shorcfacc and middle-shorcfacc and distal shelf and lower offshore favor prcscr-vation of tcmpcstitcs but for markedly different reasons.The lowest prcscrvational potential for tcmpcstitcs appears to occur somewhere between the proximal and distal extremes.Such zones appear to correspond to proximal Cruziana ichnofacics suite of the upper offshore and distal portion of the lower shorcfacc.
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Key words:
- event bed /
- preservational potential /
- transit time /
- dissipation time /
- physical reworking
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