Hardgrounds and the Flood

Hard Facts About Hardgrounds
Taxonomic Survey of Known Marine Borers
Petrology of Carbonate Hardgrounds
Taphonomy of Trace Fossils at Omission Surfaces [PDF]

Dan Wonderly on Hardgrounds: Excerpts from 'Neglect of Geologic Data,' p. 24-27

In many of the carbonate rock layers of the world we find 'hardground surfaces.' In such cases the layers of rock have visible characteristics on their upper surfaces which show that each such surface was exposed to at least some scouring, dissolution, or other alteration after it was lithified and before the succeeding layer of limestone was added above it.

Since these hardground layers are marine in origin, many of them have an abundance of marine fossil shells embedded in the limestone. Commonly, in such a layer, the shells which are at the upper surface are extensively eroded (truncated) so that only one half or less of the shell remains -- solidly embedded in the hard limestone. Since this rock layer was lying in water while the erosion was going on, encrusting-type, lime-secreting, marine animals (such as oysters) are frequently found on the eroded surfaces. Also many of the eroded surfaces have been 'bored' by sponges and other types of marine animals which bore holes in the rock by a process in which they secrete acid which dissolves the carbonate rock. The inner surfaces of these 'bored' holes frequently contain the truncated remainder of compoenent grains of the rock which where cleanly cut off by the animal as it advanced deeper into the rock (Bathurst, 1975, pp. 373 and 395-397; Wilkinson, et al., 1985, pp. 171-173).

It is very evident that all of these processes of change in the upper surface of the layer required several years of time. And on must not forget that an extended period of time wa required for cementation of the carbonate grains into the form of a hard layer before thees processes of erosion, encrusting, and boring could begin. . .

Some of the best examples of older carbonate hardgrounds which have been formed in ancient rock systems on the continents are the following. (1) a formation of Jurassic limestones in Lorraine in France containing 30 to 40 hardgrounds, with many encrusting and boring organisms represented (Jaanusson, 1961, p. 228; compare Bathurst, 1975, p. 396, Fursich, 1979m p. 27, and Purser, 1969). Fursich (1979, pp. 3-9) lists pver 30 locations in Europe where Jurassic hardgrounds are located, and gives references for the descriptions of them. (2) A Devonian formation in Russia in which hardgrounds with 'a rich epifauna . . . occur at many different levels' (Jaanusson, 1961, p. 227). (3) An Ordovician formation in Sweden, slightly over 6 meters thick, containing a succession of fossiliferous hardgrounds, with the beds being from 2 to 20 cm thick, with marl of shale between them (Bathurst, 1975, pp. 397-399). (4) Hardgrounds of Middle Ordovician limestone sequences in southwest Virginia (Read and Grover, 1977, p. 961-963). These exhibit encrustation by bottom-dwelling marine organisms such as bryozoans. Also most of the hardground surfacers are impregnated by brown to black opaque minerals which obviously accumulated on them by precipitation before they were covered over by the next succeeding layer. . . (5) An excellent example of a Jurassic carbonate hardground sequence here in the United States which has been carefully described and studied in detail is that found in the Sundance Formation of southeastern Wyoming . . . A thorough study of the petrology, inferred depositional environments, and cement types of this formation has recently been made by Wilkinson, Smith, and Lohmann (1985). This latter study carefully investigated the cement crystals which were formed during early lithification (i.e. before erosion and burial) of at least 9 of the hardgrounds in the vertical sequence found in this part of Wyoming. One particular layer of these hardgrounds was identified at several widely-seperated sites covering an area of approximately three thousands square miles.

The hardgrounds in Wyoming are composed mainly of identifiable biogenic particles and are an unusually good example of how such layers were bored and encrusted after having been well lithified by early cement. Many of the borings made clean-cut truncations, not only of the well-formed grains of the early carbonate cement, but also of the ooids and fragments of fossils which had been cemented into the layer. . . After burial, pore-filling carbonate cement filled in most of the holes and other cavities which has been made by boring endolithic fauna and also formed 'late cement' layers over many of the shells of animals which has encrusted the hardgrond layers. . . Wilkinson and his colleagues summarize these events as follows:

Macroscopic features demonstrate that sandstone and limestone units were repeatedly lithified during deposition of the Sundance Formation. Boring by endolithic mollusks as well as encrustation by oysters and serpulid worms requires the formation of well-lithified substrates prior to deposition of overlying units. Rounding of sandstone and limestone clasts further attests to the repeated development of well-indurated units during deposition (p. 179).

 

Letter from Mark Wilson to Answers in Genesis

(See also Tas Walker's laughable rebuttal. It is a a true gem of pseudogeology. I especially like the "squeezed plum" explanation of marine borings!)

To the Editorial Team at AiG:

The following is designed to be published in your “feedback” section. As you will see soon, it is “negative”. This letter has not been submitted elsewhere. I agree to transfer copyright to Answers in Genesis. You may use my full name and address when the letter is posted on your website.

I am a geologist at The College of Wooster in Ohio. I have long followed the creation/evolution debate, and I am very familiar with Answers in Genesis and other creationist organizations. I respect your courage and enthusiasm, but I believe you are very wrong about evolution, the fossil record, and the age of the Earth.

Part of my geological research involves the development of carbonate hardgrounds and their associated fossil communities in the sedimentary record. Hardgrounds and their fossils show that many limestones formed over long intervals of time, at least hundreds if not thousands of years. I believe, of course, that the sedimentary rock column was formed over hundreds of millions of years, but with this letter I simply want to demonstrate that many rocks could not possibly have formed during the few days or months allocated to them in your ”flood geology” model. I have supported my comments below with citations of work I have done so that there can be no confusion as to the nature of the evidence.

A carbonate hardground is a synsedimentarily-cemented carbonate seafloor (see, for examples and further references, Lethaia 25:19–34, 1992, and Geology 26:379–381, 1998). Under certain conditions on the floor of a shallow tropical sea, usually a reduction in sedimentation rate, increased circulation of seawater through pore space, and elevated carbon dioxide levels, calcium carbonate will crystallize between sedimentary grains and cement them together. In a real sense, then, this process is the lithification of the sediment on the seafloor prior to burial. Forming a hardground probably takes years, but we do not yet have any direct way to estimate the duration of the process.

After the sediment is lithified into a hardground, many animals and plants colonize this hard substrate. They have particular adaptations for living on hard surfaces. Many bryozoans, for example, produce a modular calcitic skeleton which adheres tightly to the surface and grows laterally and, often, upward into mounds or stout branches. Some crinoids attach themselves with special disks (holdfasts) which allow them to extend their long crown-topped stalks into food-bearing currents above the hardground.

Oysters cement themselves onto the substrate, as do other organisms such as cornulitids, barnacles, sponges and algae. Many of these creatures have easily-fossilized skeletons, so they are often found encrusting ancient hardgrounds (see, for examples, Palaeontology 42:887–895, 1999; Ichnos 3:79–87, 1994; Journal of Paleontology 67:1011–1016, 1993; Nature 335:809–810, 1988).

In addition to these encrusting organisms, many other animals drill holes directly into hardgrounds and other hard substrates to build dwelling spaces. These boring organisms include bivalves, sponges, barnacles and worms of various sorts. Most use a combination of chemicals (such as acids) and skeletal devices to excavate their holes. Many of these borings show the growth of the drilling animal as the hole was deepened (see Journal of Paleontology 72:769–772, 1998; Palaios 13:70–78, 1998). Bivalves, for example, drill holes which start with a small diameter for the juvenile bivalve, and then they increase in diameter with depth as the bivalve grows. The result is a hole with a bivalve in it far too large to get out the restricted opening. This is not a problem, of course, because the animal is a filter-feeder with no need to leave its rocky home. Hardgrounds and other hard substrates are often riddled with several generations of these borings (see Palaeontology 29:691–703, 1986).

The problem for creationists comes when these carbonate hardgrounds and their faunas are forced into a “flood geology” framework where they must have formed in just a few days or months. Fossiliferous hardgrounds are found throughout the geological record, from the Cambrian through the Recent, so they are not restricted to any particular level (The Paleontological Society Special Publication 5:137–152, 1990). A hardground community is preserved in place (not transported) because the organisms either encrusted the substrate or had bored into it. The encrusters had to land as larvae on the hardground after it was lithified, and then they developed into adults. It is clear from the size and distribution of many of these fossils that this development took years and was often halted and restarted by physical disturbances (see Science 228:575–577, 1985). How could this have happened many times during the course of a massive, short-lived flood?

In addition, the boring animals also show the length of time required for these hardground communities to mature. The borings themselves were formed during the lifespans of individuals, which was usually years. The borings often cut into other borings from previous generations, many of which are filled with cemented sediment. The borings are sometimes overgrown by encrusters, again showing the depth of time available for this community development (see Palaios 13:70–78, 1988, for a good example). Again, this biological process happened dozens and dozens of times through the sedimentary rock record. Again, this cannot be explained within the flood model, but it is entirely consistent with a rock record hundreds of millions of years old.

I am anxious to see how you respond to this challenge from hardgrounds and their fossils. I cannot conceive of a creationist model which can account for them in the context of a single global flood. They are instead one of many indicators of an Earth millions of years old with a history long preceding that of humanity.