Distribution and Implications of Sponge Spicules in Surficial Deposits in Ohio

Microscopic examination of biogenic opal isolated from the 0.05-0.02-mm total mineral fraction of 12 upland soil profiles indicates that fragments of sponge spicules are minor but ubiquitous constituents of Ohio soils, with major concentrations in the upper 10 to 15 inches of the profile. Quantities range from about 30 to 2000 parts per million biogenic opal or 1 to 65 parts per 10 million parts soil. Spicules are absent or extremely rare in calcareous Wisconsin-age till deposits. Their correlation with horizons high in silt content (50-75%), and their size and depth distribution in landscape positions which preclude an authigenic origin, indicate their aeolian transport from aquatic source areas with other loessial materials. Identification of spicules thus provides direct evidence that these horizons have been derived from loess or loess-till admixtures. This microscopic technique may serve useful for the identification of loess when field or laboratory particle-size analysis yields inconclusive evidence. INTRODUCTION Many kinds of opaline (hydrated, amorphous SiO2) constituents of biogenic origin occur in soils. Recently, Siever and Scott (1963), Smithson (1956), and Jones and Handreck (1967) have comprehensively reviewed the various forms of silica found in soils and geologic materials, considering their origins and their identification. Both plants and animals secrete various quantities of silica that may become subsequently a part of the silica fraction of a soil. Aquatic animals which secrete significant quantities of silica include radiolarians, silicoflagellates, and sponges (Vinogradov, 1953). Within the plant kingdom, monocotyledons and diatoms have been considered most important. Opal which is found in characteristic shapes, sizes, and forms localized in the aerial portion of vascular and epidermal tissues of plants is termed opal phytoliths. Opal phytoliths and siliceous sponge spicules are minor, but ubiquitous constituents of many soils. The former are by far the more abundant of the two components, but with detailed fractionation and careful microscopic observation, sponge spicules may also be readily identified. Numerous investigators have reported the occurrence of fresh-water and marine sponge spicules in soils, but different theories have been advanced to explain their presence. In sites subject to wetness or ponding, Brewer (1955, 1956) and Smithson (1959) have interpreted the rich abundance of mostly unfragmented spicules as evidence of their authigenic origin from sponges which once inhabited the area. On the other hand, in positions where topography precludes an authigenic origin, Carroll (1932), Jones and Beavers (1963), and Leeper (1955) have invoked an aeolin transport mechanism from aquatic source areas to explain their presence. The possibility that some spicules may be transported from a close source area by the feet of birds and mammals also has been suggested by Smithson (1959). For most fragmented and widely disseminated spicules, it is not possible from morphological features alone to positively identify whether they have been derived from marine or fresh-water sponges. This uncertainty, combined with the misidentification of opal phytoliths for sponge spicules in certain cases, has resulted in some confusion in the literature concerning the significance of these microfossils in soils. Previous investigations have been primarily incidental or cursory in scope, Contribution of the Agronomy Department, Ohio Agricultural Research and Development Center. Project No. State 371. Journal Paper No. 109-66. Columbus, Ohio. Manuscript received June 10, 1967. THE OHIO JOURNAL OF SCIENCE 68(2): 92, March, 1968. No. 2 SPONGE SPICULE DISTRIBUTIONS IN SOILS 93 the emphasis being placed on the documentation of presence or absence of spicules in a particular deposit. This paper presents quantitative data for the depth distribution of sponge spicules in well and moderately well drained soil profiles in Ohio. The following possible origins have been considered in evaluating the presence and distribution of spicules in surficial deposits of these soils: (1) an indigenous origin of spicules from calcareous till deposits underlying these soils; (2) an authigenic origin of spicules from sponges which may have inhabited such sites at some former time; (3) an allogenic origin of spicules that were transported with other loessial materials from adjacent local or regional aquatic source areas favorable for sponge inhabitation.