Plus: Special Features on “the Future of Sepm” President’s Observations—nsf Paleoclimate Workshop Comments from Council—hand Lens

Detailed sedimentological study of Devonian black shales from the eastern USA shows that these rocks contain valuable textural clues to their depositional history, clues that hitherto have gone mostly unrecognized. Cryptic bioturbation and subtle erosional features suggest the presence, originally, of much more benthic life and bottom current activity than is commonly assumed for these deposits. Sedimentary features observed in black shales can provide prima facie evidence of depositional processes at a resolution that is hard to match with geochemical approaches. No geochemical study of black shales should be conducted without careful sedimentological evaluation because subtle sedimentary features may have a direct bearing on the applicability of proposed genetic models. Knowledge of sedimentary features is required to guide geochemical sampling so as to avoid averaging intervals of dissimilar origins, and to provide critical constraints for the interpretation of geochemical data sets. The Sedimentary Record September 2003 | 5 Lobza and Schieber (1999) demonstrated through a combination of experiments and textural studies how some traces in black shales (Figs. 1, 2) were formed. Many of the “burrows” illustrated in Figure 1A formed when worms “swam” or “wiggled” through a soft-soupy substrate with high water content (~70-75%). Rather than being sediment-filled tunnels, these “burrows” represent instead mixing structures produced by worms that dragged mud of one color into adjacent mud layers of different color (Figs. 1B, 1C). From a process perspective, they are biodeformational structures (e.g., Wetzel, 1991a; Wetzel and Uchman, 1998) and, for lack of a better name, we called them “mantle and swirl” traces (Lobza and Schieber, 1999). Now, as long as mud of contrasting color is dragged along by moving worms, these traces show up nicely (Fig. 1). Yet, if a worm moves only in one layer, its trace will be filled with similar material and there will be no color contrast (Fig. 2). This kind of “black on black” trace will be essentially “invisible” (Fig. 2). Likewise, after some distance from crossing the color boundary (e.g., gray to black), the gray mud that the worms dragged behind will run out and there will be no more color contrast. Proper identification of “sediment swimmer” traces matters. It tells us that the erstwhile black muds contained benthic life at the time of deposition, and not at some unspecified later time. Experiments on self-compaction of freshly deposited muds (Barrett and Schieber, 1999) indicate that it will take from a few days to weeks of consolidation to arrive at a water content of around 70%. Therefore, the organisms that produced the traces in Figures 1 and 2 must have done so shortly after deposition of these muds. They actually lived in carbonaceous surface muds, and that makes it highly unlikely that anoxic conditions were the norm when the black shale layers were deposited. Thus, recognizing “sediment swimmer” traces in these black shales mitigates against the prevalent assumption of anaerobic conditions. Example 2: Counterintuitive lessons from pyrite – not so anoxic after all Round to elliptical pyritic features ( Fig. 3A) are common on broken or cut surfaces of black shales, and are commonly interpreted as concretionary in origin. Pyrite concretions are not only common in black shales, but they also evoke images of anoxic conditions, especially when associated with a laminated appearance. In combination, these features of black shales (pyritic, laminated) are often thought to indicate anoxic conditions and an absence of benthos. In our example, however, X-radiographs reveal a more interesting story. What looked like concretions in cross section turns out to be pyritic trails in plan view (Fig. 3C). These trails may follow chaotic loops, turn sharply through 360 degrees, and rise and fall through the sediment (Fig. 3B). The traces, which resemble Spirophycos or Nereites, were evidently produced by small organisms that zigzagged their way through the mud in search of food. This forces us to rethink our initial assumptions of anoxic conditions for certain black shale deposits. Such pyritic trails may be much more common in black shales than we currently appreciate. While deducing oxygenated bottom waters from pyritic trails (Fig. 3) does not require a great leap of faith, proposing that pyrite concretions in black shales may actually be indicators of oxygenated bottom waters probably would meet considerable resistance. Yet, from a geochemical perspective, oxygenated waters above the seabed seem to be a prerequisite for forming localized pyrite concentrations in the bottom sediments. This is so because under fully anoxic conditions, with an excess of H2S in the sediment, all the iron that was released from terrigenous grains would be precipitated immediately in the form of disseminated and tiny iron sulfide grains. Under oxic bottom waters, however, anoxic, organic-rich sediments are typically non-sulfidic in the surface layer (Berner, 1981), and thus allow for localized accumulation of pyrite. In such settings, iron oxyhydroxide coatings on terrigenous grains of the surface sediment would be a ready source of easily solubilized iron that would keep pore waters free of H2S via pyrite formation (Canfield and Raiswell, 1991; Canfield et al., 1992). Simultaneously, bacterial decay of organic matter would remove downwardly diffusing oxygen from the pore waters. Under the ensuing combination of anoxic and non-sulfidic conditions, iron should be able to migrate through the sediment, making possible the localized accumulaFigure 1: (A) Cut and ground (1000 grit) surface of shale that consists of alternating black and greenish-gray beds. Note the downwarddiminishing abundance of gray burrow fills in the central black bed. (B) Close-up of “mantle and swirl” traces in the upper portion of the black bed. These traces are produced when worms move/swim through the soft watery substrate (~70% water content) and drag gray mud downwards into black muds. (C) Close-up of equivalent traces (white arrows) that were produced when worms moved into the underlying gray layer and dragged black mud behind them. Figure 2: (A) Seemingly undisturbed black mud with some silt laminae (white arrows). (B) the same image with serious image enhancement applied (contrast enhancement with Adobe PhotoshopTM). With contrast enhancement, lighter colored oval-shaped features (white arrows) turn out to be compressed “mantle and swirl” traces. Under normal conditions they are “invisible” because they are filled with black mud. (C) Thin-section photomicrograph illustrating the subtle nature of black shale filled traces. Gray shale-filled traces (blue arrows) are easily be observed on ground surfaces (Fig. 1); yellow arrows outline a black shale filled trace that has little color contrast with the surrounding black shale. tion of pyrite. Thus, various kinds of pyrite aggregates present in black shales (pyrite nodules, pyritized burrows, pyritized fossils, etc.) actually carry a counterintuitive message – oxygenated waters were present above the seabed. Example 3: More counterintuitive stuff – Burrowing produces laminated black shales Most black shale researchers consider laminated black shales that lack evidence of disturbance of bedding as reliable indicators of anaerobic or anoxic conditions (e.g., Wignall, 1994). A safe assumption supposedly, but what if one were to introduce a way by which burrowing could result in a laminated black shale fabric? Work on the New Albany Shale (Devonian of Indiana) has uncovered evidence for just such a mechanism at work. Figure 4 shows a fairly typical specimen of New Albany black shale. Horizontal streaks of silt (Fig. 4A) extend in many instances across the width of a thin section, giving it a laminated character that compares well to many other laminated black shales (O’Brien and Slatt, 1990). On initial inspection, this specimen appears to represent a laminated black shale from an anoxic setting. However, silt streaks and laminae that were slightly non-parallel and showed variable orientation across the specimen surface cast doubt on this interpretation. Enhancing Fig. 4A with Adobe Photoshop highlighted the silt streaks and laminae (Fig. 4B), and furthermore revealed subtle discontinuities and disruptions of laminae (Fig. 4C). Were these features due to scouring by bottom currents, or were they due to bioturbation? Lateral tracing of these features would have been helpful, but large study specimens are rarely available. Drill core material is too narrow, and in outcrop specimens, even the slightest weathering completely obscures the features in question. Persistence, however, uncovered several specimens that established that the type of black shale shown in Figure 4 (“black shale with silty streaks”) was actually a product of bioturbation (Fig. 5). Figure 5 shows “black shale with silty streaks” penetrating and crosscutting a preexisting black shale with homogenous appearance (Fig. 5D). The burrowers seem to have moved through the sediment more or less horizontally, producing “sheets” of reworked material that usually extend beyond the diameter of the core (~10 cm). In so doing, the burrowers produced what one might call a “burrow-laminated” fabric, causing grain segregation (silty streaks). Lamina disruptions (Figs. 4, 5D) suggest that burrowers reworked the sediment more than once, possibly a reflection of the high organic matter content. In the New Albany Shale, black shale intervals ranging up to four meters in thickness may show pervasive “burrow-laminated” fabric (Fig. 4), indicating almost complete reworking (Fig. 5) of an organic-rich mud. In places where gray shale beds are intercalated, other burrows, most commonly Zoophycos, penetrate downwards into “burrow-laminated” black shale. Apparently, the bioturbation that gave rise to “burrow-laminated” fabric occurs early in the depositional history when the sediment still has a high water content. The horizontal mining habit of the burrowers, combined with substantial subsequent compaction (down to 30-40% of original thickness), produced a horizontally laminated fabric. The Zoophycos traces observed in “burrowlaminated” black shales consist of closely spaced horizontal sheets. One may speculate whether the organisms that produced the “burrow-laminated” fabric also produced the subsequent Zoophycos burrows, and whether the difference in appearance reflects a lower water content of the sediment at the time of Zoophycos emplacement. Bioturbaters produce different burrows depending on substrate consistency (e.g., Bromley, 1996). The notion that “burrow-laminators” may be related to the organisms that produce Zoophycos style traces also receives support from a study of Devonian shales in the Catskill Delta of New York. There, gray mudstones are completely reworked by Zoophycos, yet the Zoophycos morphology is largely subsumed by the now “burrow-laminated” character of the sediment (Schieber, 1999). Example 4: Erosive features in black shales suggest bottom currents, water column mixing, and a stratigraphic record littered by gaps Erosive features in black shales are recognizable from the outcrop scale down to the microscopic scale (e.g., Baird, 1976; Baird and The Sedimentary Record 6 | September 2003 Figure 3: (A) Thin section of faintly laminated black shale with mm-scale, round-elliptical pyrite concretions (arrows). Sample is from the New Albany Shale, Indiana. (B) X-radiograph from same sample (note change in scale, view perpendicular to bedding). Laminae do not have enough contrast to show up, only pyritic structures produce sufficient contrast. Irregular pyritic trails occur obliquely through the sediment (arrows). Bright spots are localized pyrite accumulations that nucleated on the trails. (C) Xradiograph from a slab of comparable lithology (Chattanooga Shale from Tennessee; view perpendicular to bedding). Pyritic trails with erratic and sharp turns are present. Intensity varies because pyritization is not uniform along trail. Figure 4: Laminated black shale from the New Albany Shale, Indiana. (A) Black shale sample as it would appear to the unaided eye. (B) Same sample after contrast enhancement with Adobe Photoshop: silty streaks are more clearly visible, and laminae are non-parallel, undulose, and terminated in places. (C) Tracing of some laminae to highlight lamina characteristics. Black arrow indicates where one lamina (from right) terminates against an overlying lamina. Lamina directly to the left has been cut by whatever produced the lamina coming from the right. Black arrow is reproduced in the same position in (A) and (B). The Sedimentary Record September 2003 | 7 Brett, 1991; Schieber, 1998). Yet while larger scale features, such as macroscopic scours and truncation surfaces, are gradually accepted as indicators of strong bottom currents with attendant implications for water column mixing and oxygenation, small scale erosion features still go largely unrecognized. Figure 6 illustrates how we can decipher depositional history from the context of burrows, burrow fills, and erosion surface morphology. At first, Figure 6 seems to show just another black shale-gray shale couplet like the one illustrated in Figure 1, except that Chondrites burrows, in addition to “mantle and swirl” traces, are present. Things change when the image is contrast enhanced: what appeared initially to be a single black shale layer is actually a succession of two layers (Fig. 6A). The lower black layer (#1) is cut by an irregular erosion surface (Fig. 6B) that reflects a cm-scale pre-compaction relief, and the grayshale-filled Chondrites burrows within that layer are truncated at the erosion surface (Fig. 6B). The gray fill of the Chondrites burrows thus predates erosion (ES1) and subsequent deposition of the black layer (#3) that overlies erosion surface ES1. This relationship requires that the lower black shale layer (#1) was once overlain by a gray shale layer (#2) that supplied the fill for the Chondrites burrows. Erosion of this gray layer preceded deposition of the next black layer (#3). The burrows in the second black layer (#3) reveal a comparable story (Fig. 6C). They are cut by erosion (ES2) and have a gray fill that differs in composition from the gray shale above. As above, this indicates yet another gray shale layer (#4) that was eroded prior to deposition of the gray shale layer that we see now (#5). Basically, although we can recognize only three layers of shale, we have to conclude that there were at least five (or more) layers originally. Erosive interludes as revealed in Figure 6 suggest that powerful bottom currents may have been much more common in black shale settings than commonly assumed. This reinforces the conclusions drawn from prior examples: namely that water column mixing and oxygenation of bottom waters was the norm rather than the exception. The surface relief of these erosion surfaces (ES1 and ES2) indicates that what was eroded were semiconsolidated muds, “stiff ” enough to resist eroding currents. The degree of compaction observed in Chondrites burrows, suggesting a water content of about 45% (cover art), confirms this assessment. Because the Chondrites burrows occur next to “mantle and swirl” traces that were emplaced at water contents of around 75% (cover art), they were obviously emplaced later in the depositional history and probably at a greater depth in the sediment. Judging from studies of deep sea muds (Ekdale et al., 1984; Wetzel, 1991a), the organisms that produce Chondrites may penetrate to depths of about 35 cm. In our example, the mud had a water content of about 45% at the time Chondrites was emplaced; thus those 35 cm would be reduced to a 20 cm layer of consolidated shale. In Figure 6, all that remains of two such mud layers are the bottom portions with Chondrites burrows. If these two layers are essentially what is missing from the specimens in Figure 6, then our 5cm-thick sample (Fig. 6) may be all that is left of nearly 50 cm of potential rock record. In the context of other examples of intermittent erosion in black shales and marine mudstones (e.g., Baird, 1976; Baird and Brett, 1991; Schieber, 1998, 1999) it may well be that, just like it is true for sandstones and carbonates, the shale portion of the sedimentary record is dominated by gaps rather than by record. IMPLICATIONS Because it is commonly assumed that oxygen content or organic productivity of marine waters exerts the main control on black shale formation, discussion of their origin has largely been dominated by geochemical arguments (e.g., Beier and Hayes, 1989; Calvert et al., 1996). Geochemists have devised geochemical proxies that may provide insight into the formative conditions of black shales (notably, indices that allow us to determine the oxygenation state of the water column and the presence of anoxia; Jones and Manning, 1994). Although I have no problem with geochemistry (indeed, it is an integral part of my studies of Devonian black shales), it is clear from information summarized here that there are many conflicts between what sedimentary features tell us and what geochemical proxies would suggest. For example, the most widely employed anoxia proxy, degree of pyritization (DOP; Raiswell et al., 1988), indicates anoxic conditions for most of the samples that we analyzed. This interpretation is not supported by the erosive features and various intensities of bioturbation that these same samples contain. Sedimentological and petrographical study of the samples reveals that intermittent erosion and reworking caused hydraulic pyrite enrichment in silty laminae and lag deposits, causing artificially high DOP values (Schieber, 2001). Comparable problems exist with regard to other proxies. As the DOP example illustrates, uncritical reliance on geochemical data and proxies is risky. Sedimentological aspects of shale deposition need to be considered in the formulation of realistic geochemical models. Another inherent problem is that geochemical models for black shale formation are typically based on bulk analyses of homogenized samples representing stratigraphic intervals ranging from centimenters to tens of centimeters in thickness. In distal Devonian black shales a 10 cm interval of shale may represent a time span of as much as 100,000 years (Schieber, 1998), and much can happen to an original deposit over such a long time span. Sedimentological evaluation is a necessary prerequisite for successful geochemical studies because prima Figure 5: Image-enhanced, laminated black shale from the New Albany Shale, Indiana. (A) The black shale with silty streaks cuts across (white arrow) an earlier black shale that appears more homogenous and darker. (B) Line drawing to highlight lamina characteristics and crosscutting relationship in A. Penetration of the laminae is “burrow style” (black arrow). (C) X-radiograph of same sample. The arrows in A, B, and C all point to the crosscutting bioturbation. (D) Photomicrograph of thin section from same interval (note scale change) showing that the pre-bioturbation black shale is homogeneous, and that silty laminae and streaks are typical for the bioturbated portions. More abundant pyrite in silty streaks (white arrows) makes them show up better in X-radiographs (C). We also see lamina disruptions in the bioturbated portions (black arrows). facie knowledge of depositional processes places critical constraints on the interpretation of geochemical data sets, and is a requirement for sensible geochemical sampling (e.g., in order to avoid averaging intervals of dissimilar origins). CONCLUSIONS Black shales may seem to be largely featureless initially, but careful study can reveal a wealth of sedimentological detail that has a direct bearing on which genetic models are permissible, and which ones are unacceptable. As illustrated in the four examples above, careful examination of black shales can help to: (1)establish whether bioturbation features are syngenetic with a black shale horizon (example 1); (2)extract information about paleo-oxygenation from pyrite aggregates (example 2); (3) resolve whether laminated fabric is a primary depositional feature or a secondary feature due to bioturbation (example 3); (4) reveal erosive features that provide information about bottom currents, water-column mixing, and oxygenation, as well as information about the completeness (or lack thereof ) of the stratigraphic record in shales (example 4). Although this list is necessarily incomplete, it serves to make my main point – it pays to look at your shales. A sedimentological inventory of a black shale succession, developed through study of outcrops, hand specimens, core samples, and thin sections, can greatly advance our understanding of these rocks. Such an inventory should be conducted before the decision is made to engage in costly and time-consuming geochemical studies. ACKNOWLEDGMENTSOver the past 15 years I have benefited fromdiscussions with numerous colleagues on arange of issues related to shale sedimentology.I would like to thank in particular P. Potter,D. Krinsley, K. Bohacs, H. Blatt, N. O’Brien,F. Ettensohn, G. Retallack, M. Reed, P. Binda,G. Baird, C. Brett, K. Grimm, K. Milliken, J.Comer, J. Macquaker, and A. Wetzel for gen-erously sharing their perspectives and insightson a broad range of questions. In addition, Iwould like to thank A. Basu and E. Kauffmanfor constructive criticism of an earlier draft ofthis contribution, and reviewers G. Baird andM. Miller for suggesting improvements to themanuscript. L. Babcock, S. Leslie, andK.Polak provided editorial advice. Research onshale sedimentology over the years has beensupported through grants and logistical sup-port provided by NSF, ACS-PRF,ExxonMobil, and ChevronTexaco. REFERENCESBAIRD, G.C., 1976, Coral Encrusted Concretions; a Key to Recognitionof a “Shale on Shale” Erosion Surface. Lethaia, v. 9, p. 293-302.BAIRD, G.C., and BRETT, C.E., 1991, Submarine erosion on the anoxicsea floor; stratinomic, palaeoenvironmental and temporal significanceof reworked pyrite-bone deposits, in Tyson, R.V., and Pearson, T.H.,eds., Modern and ancient shelf anoxia. Geological Society ofLondon, London, p. 233-257.BARRETT, T., and SCHIEBER, J., 1999, Experiments on the Self-Compaction of Fresh Muds: Implications for Interpreting the RockRecord. Geological Society of America Abstracts with Programs, v.31-7, p. 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Journal of SedimentaryResearch, v. 69, p. 909-925.SCHIEBER, J., 2001, Ways in which organic petrology could contribute toa better understanding of black shales. International Journal of CoalGeology, v. 47, p. 171-187.SEILACHER, A., and MEISCHNER, D., 1964, Fazies-analyse imPaläozoikum des Oslo-Gebietes. Geologische Rundschau, v. 54, p.596-619.WETZEL, A., 1991a, Ecologic interpretation of deep-sea trace fossil com-munities. Palaeogeography, Palaeoclimatology, Palaeoecology, v. 85, p.47-69.WETZEL, A., 1991b, Stratification in black shales: depositional modelsand timing – an overview, in Einsele, G., Ricken, W., and Seilacher,A., eds., Cycles and Events in Stratigraphy, Berlin: Springer Verlag, p.508-523.WETZEL , A., and UCHMAN, A., 1998, Biogenic sedimentary structures inmudstones – an overview, in Schieber, J., Zimmerle, W. and Sethi, P.,eds., Mudstones and Shales (vol. 1): Characteristics at the Basin Scale.Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, p. 351-369.WIGNALL, P.B., 1994. Black Shales. Geology and GeophysicsMonographs, 30, Oxford, Oxford University Press, 130 p. Manuscript received 4 June 2003; accepted 6 August 2003.The Sedimentary Record 8 | September 2003Figure 6: Multiple erosion surfaces and missing layers in a black shale(layers numbered 1 through 5 in ascending order). (A) Strongly contrastenhanced image of black shale-gray shale couplet. Two dark layers areactually present. The lower one is truncated by erosion surface ES1(orange arrows). The second dark layer is truncated by erosion surfaceES2 (yellow arrows). (B) shows detail of ES1 (orange arrows) withirregular surface topography. The burrow fill in layer 1 is lighter incolor than the material from the layers that cover the erosion surface(red arrow), indicating that the gray layer (layer 2) that supplied the fillhas been eroded. (C) Detail of ES2 (yellow arrows), illustrating thatburrow fill of the second dark layer (layer 3) differs compositionallyfrom the material of the overlaying gray layer (red arrow). (D)Sediment accumulation vs. time diagram illustrating the succession ofevents that lead to the observed rock record. The Sedimentary Record September 2003 | 9A Muddied Perspective on theFuture of Sedimentary Research Shales, claystones, and mudrocks: these wordsmay make many of us uncomfortable... butwhy? Early in my studies I was impressed bythe diverse array of environments representedin the record by “shale”. Subsequent experi-ence, however, left me perplexed about howanything could ever be resolved meaningfullyby looking at the stuff. Although their charmsmay be subtle, mudstones refuse to be ignored.Mudstones are the source rocks for the bulk ofthe natural fuels. Many mudstone depositsrecord relatively continuous sedimentationwith minimal influence of reworking, erosion,or winnowing. Fossils in mudstones are oftenfound in situ, unsorted, and well preserved.The ubiquitous actions of microbes leave diag-nostic suites of early diagenetic minerals andassociated chemical signals that can help refineconditions of the depositional or early diage-netic environment. Perhaps most importantly,mudstones represent a more disparate spec-trum of depositional environments than anyother lithofacies. Nevertheless, fine-grainedsediments remain grossly under-appreciated bygeoscientists. The reasons for this are not alto-gether mysterious: sedimentary geologists tendto enjoy interpreting rocks in the field.Upon first glance, mudstones can be a bitbaffling. Typically, fine-grained sediments suf-fer the effects of weathering more drasticallythan coarser lithofacies and they are the firstrocks to fail when tectonic stresses are applied.Thus, mudstone outcrops are rare, and areoften of poor quality. Even upon close outcropinspection, sedimentary structures generallyremain elusive. Pioneering studies of mud-stones in a stratigraphic context (summarizedin Potter, et al., 1980) recognized many keyfeatures that allowed a broad-scale subdivisionof mudstones based key attributes such as color,associated lithologies, and macroscopic diage-netic features. These studies have proven vitalfor interpreting relative depositional settings,but offer little insight into mode of deposition,depositional dynamics within a facies, or bed-to-bed scale environmental changes that haveproven so important in rigorous study of otherlithofacies. Indeed, the information locked inmudstones is not easily extracted. I find that mudstones are best understoodthrough a combined approach, using the ben-efits of laboratory analysis in combinationwith the indispensable information gainedfrom studying rocks in their field context.Below, I review some exciting recent develop-ments, with far-reaching implications, derivedfrom new field-lab integrative approaches tomuds. Breakthroughs like these have enhancedmy appreciation of fine-grained rocks thatcomprise the bulk (>60%) of the sedimentaryrecord (Potter et al., 1980), but comparativelyfew pages of sedimentology textbooks.An enormous amount of time, energy, andmoney has been poured into research seekingthe causes of, and controls on, organic carbonpreservation, leading ultimately to oil forma-tion. In recent decades, debate has focused ontwo primary factors: 1. effects of anoxia, and 2.rates of productivity, sedimentation and burial.A new model (Kennedy et al., 2002) suggeststhat there is a relationship between preservationof organic carbon and surface area of the reac-tive interlayers of clay minerals. Clay minerals,especially smectites, apparently adsorb amor-phous organic matter from the water column,storing it safely from the action of microbes.The study showed that much of the organicmatter in the Cretaceous Pierre Shale is boundwithin smectite interlayers, and that this amor-phous organic matter is far more abundantthan the particulate organic matter retained inthe rock. While other factors are clearly impor-tant in the genesis of organic-rich mudstones,this model proposes that trends in detrital claymineralogy exert a first-order control on stor-age of organic carbon in marine rocks.Driven in no small part by the fact that theyare the most important petroleum sourcerocks, black shales have been the focus of adisproportionate amount of attention.Traditionally they have been regarded as repre-sentative of deposition under sustained anoxicconditions. Abundant black shales are charac-teristic of certain intervals of time (e.g., LateDevonian, Cretaceous), and have been sug-gested to signify “oceanic anoxic events,” aconcept which would, if correct, have radicalimplications for the biosphere-ocean systemduring these times. Schieber (1994) threat-ened the anoxic paradigm by demonstratingthat macroscopic bioturbation, representingthe activities of aerobically metabolizing meta-zoans, is common in some black shales. Thisstraightforward finding indicates that thesedeposits do not necessarily represent episodesof basin-wide stagnation. Furthermore,macroscopic bioturbation has been document-ed in black shale horizons bearing preservationof originally nonmineralized fossil tissues (bypyrite replacement; Sutcliffe et al., 1999).Preservation of nonmineralized tissues in blackshales has long been considered to requireanoxia. Thus, this finding has important pale-oecological implications, most importantly,that such fossils may be preserved in situunder habitable (oxic) benthic conditions, anddo not require transport.In recent years, basinal mudstones have beenthe focus of an increasing body of paleoceano-graphic research that has tapped into the high-resolution record they provide. Throughoutthe last decade, increasing analytical precisionhas allowed isotopic analysis of ever-smallersamples. One of the most startling ramifica-tions of such study has been the recognitionthat profound climate change is not necessarilya slow, steady process, but can operate ontimescales ranging down to the decadal scale.Such rapid change may involve multiple feed-back mechanisms. One such mechanism is thedestabilization of methane hydrates, which arestored in solid form in organic-rich sedimentsunder cool conditions, but which release(greenhouse) methane gas when oceanic warm-ing occurs (Kennett et al., 2003).Importantly, some mudstones may now bedated directly. Until recently, siliciclastic rockswere dated using either detrital zircons, whichcome with their own set of problematicassumptions, or using rare intercalated ashbeds or lava flows and various means of strati-graphic correlation. Recent work by Creaser etal. (2002) has demonstrated that some organ-ic-rich mudstones may be dated using the rhe-nium-osmium trace element isotope system asa geochronometer.These are only a few examples of recentbreakthroughs from the mudstone record thatserve to remind me of the wealth of informa-tion locked in mudrocks. Although wadinginto thixotropic paleoenvironments can seemdaunting, the effort can clearly be rewarding,and I think it’s safe to assume that we will behearing a great deal from this part of the sedi-mentary record in coming years. Robert R. Gaines; Geology Department,Pomona College, Claremont, CA, [email protected] REFERENCESCREASER, R. A., SANNIGRAHI, P., CHACKO, T., and SELBY, D., 2002. Furtherevaluation of the Re-Os geochronometer in organic-rich sedimentaryrocks: a test of hydrocarbon maturation effects in the Exshaw Formation,Western Canada Sedimentary Basin. Geochimica et Cosmochimica Acta,v. 66, p. 3441-3452.KENNEDY, M. J., PEVEAR, D. R., and HILL, R. J., 2002. Mineral surface con-trol of organic carbon in black shale. Science, v. 295, p. 657-660.KENNETT, J. P., CANNARIATO, K. G., HENDY, I. L., and BEHL, R. J., 2003,Methane hydrates in Quaternary climate change. American GeophysicalUnion, Washington D.C., 216 p.POTTER, P. E., MAYNARD, J. B., and PRYOR, W. A., 1980. Sedimentology ofShale: Springer-Verlag, New York, 306 p.SCHEIBER, J., 1994, Evidence for high-energy events and shallow-water depo-sition in the Chattanooga Shale, Devonian, central Tennessee, USA.Sedimentary Geology, v. 93, p. 193-208.SUTCLIFFE, O. E., BRIGGS, D. E. G., and BARTELS, C., 1999. Ichnological evi-dence for the environmental setting of the Fossil-Lagerstätten in theDevonian Hunsrück Slate, Germany. Geology, v. 27, p. 275-278.The Hand Lens—a student forum The Sedimentary Record 10 | September 2003SEPM has been a global organization formany years. Currently there are more than1100 international members in over 70countries around the world. Despite thislarge international membership, many ofSEPM’s activities are concentrated in NorthAmerica. The Society has a goal to increaseits global activities to benefit its membersand to increase its global membership. Thereare several ways in which this can be done,but it demands engagement from our mem-bers everywhere. Therefore, both interna-tional members and US members areencouraged to propose ideas to increaseSEPM activities in the global scene. Suchactivities could include:• Research conferences, organized by SEPMalone or jointly with other organizations.Cooperation with local geological organi-zations is strongly encouraged.• Sessions sponsored or cosponsored bySEPM at international conferences.Thematic sessions on subjects in sedimen-tary geology are organized at most geologymeetings and SEPM, through its interna-tional membership, should be a key playerin organizing such sessions.• Production of SEPM Special Publications.SEPM has a great record of publishing the-matic publications on important topics. ASpecial Publication should be the end goalof a thematic session at a conference or aResearch Conference. Field trips are per-haps the best way of creating enthusiasmamong geologists. There is nothing like thevaried discussions on a challenging out-crop. Field trips are often combined withResearch Conferences and conventions.• Student activities, which can be field trips,student sessions at conferences or work-shops. The SEPM Foundation has made ita special issue to help students attendSEPM events.• Contribution of papers to Journal ofSedimentary Research, PALAIOS andSpecial Publications on topics from inter-national localities. • More international sections. SEPM has twointernational sections, one in Venezuela(Latin America section) and one inGermany (Central European section).Another section is currently being organ-ized in the Asia area. The aim of an inter-national section is to organize and increasesedimentary geology activities within theirregion, with the help of the overall society’sname recognition, headquarters staff andfinancial support. However, it is alsoimportant that the international sectionspartner with other organizations to benefitsedimentary geology in the most appropri-ate way in that specific region. SEPM’s aimis to have more international sections withtime, which will work to increase interna-tional sedimentary geology activities suchas those listed above. Therefore, do not hesitate to contact meor any other member of the SEPM councilor Headquarters staff if you have ideas forSEPM international activities! Ole J. MartinsenInternational [email protected] geoscientists, including a healthycontingent of sedimentologists, sedimentarygeochemists and paleontologists in addition toclimate modelers, converged on Arlington, VAin May (2003) to discuss the status and futureof research on Earth’s “deep-time” (pre-Quaternary) climate record.Earth’s deep-time geologic record preservesthe results of multiple large-scale experimentsin environmental change. Although studies ofrecent climate states can capture a resolutioncommonly lacking in deep-time studies, theyfail to capture the full range of climate-systembehavior. In contrast,deep-time studiesshowcase environ-mental disturbancesunknown from therecent, as well asfeedbacks that occuron longer time scalesand in response toperturbations thatare different fromthose observable inthe recent. Althoughsome of the processesthat can be studied in deep time may exceedhuman time scales, through feedbacks andthresholds, they can affect those climateprocesses that do operate on human timescales. Until we can understand these process-es, gaps in our ability to understand climateon shorter time scales will remain, contribut-ing to climate-prediction uncertainty.Workshop discussions highlighted the fol-lowing key points: ●Study of the Earth’s climate record at allspatial and temporal scales is needed in orderto comprehend the full range of variability rep-resented in the climate system. The deep-timegeologic record preserves numerous examplesof past climate transitions between states moreextreme than those represented in instrumentaldata, in historical records, or even byQuaternary standards. Critically, some of thesetransitions show evidence of having occurredabruptly, a major societal concern in light ofthe large changes that are now occurring in ourcurrent climate system. Understanding thedetails of large-scale climate transitions and,more importantly, the processes involved couldvery well be critical to an informed assessmentof future climate change. ●Major science themes and issues thatrequire attention in order to achieve a holisticunderstanding of Earth’s climate systeminclude the following: ◆Time issues, especially greenhouse-icehouse-hothouse transitions, interaction of climatecomponents at different time scales, andprediction of climate thresholds ◆The various forcings and feedbacks that linkgreenhouse gases, particularly carbon diox-ide and methane, as well as water vapor, toclimate change COMMENTS FROM THE COUNCIL SEPM International ActivitiesNSF-SponsoredWorkshop onDeep-TimePaleoclimatology Continued on next page The Sedimentary Record September 2003 | 11◆The ecosystem-climate relationship, e.g.,co-evolution of the biosphere and atmos-phere ◆Tectonic-climatic and climatic-eustaticinteractions ◆Multi-component coupling in climatemodels ◆The effects of solar and orbital controls onclimate at all scales ●The use of climate models to study paleo-climate is critical because models allow us totest hypotheses, particularly regarding interac-tions and feedbacks among Earth’s climatesystem components. Unfortunately, mostmodels have been constructed based on thevery different constraints of modern instru-mental data and are, therefore, difficult to setup for paleoclimate simulations. Model out-put, geared towards atmospheric diagnostics,is also difficult to compare to geologicrecords. ●High-quality proxy data on past climatestates are equally critical, for accurate recon-structions, as input to climate models, and forindependently testing model-derived interpre-tations. However, the community needsdecreased ambiguity in existing proxies, andcontinued development of new and moreaccurate proxies for past climatic parameters,especially for deep-time slices. ●The paleoclimate research communityneeds new and better means to facilitate com-munication and collaboration, and to developsynergy between those who model paleocli-mate and those who collect and analyze deep-time paleoclimate data. Closing the currentgap between these two subdisciplines will cat-alyze rapid progress in the study of Earth’sdeep-time climate record.Critical to progress in deep-time paleocli-matology is community feedback to helpchart future directions, and approaches to theimpasses listed above. To this end, please visithttp://geoclimate.ou.edu to register feedbackuseful for guiding future research efforts andinitiatives. The full workshop report is avail-able on the geoclimate website.Funding was provided by the NationalScience Foundation (grant #0323841)through the Geology and PaleontologyProgram (Earth Sciences Division), thePaleoclimate Program (Atmospheric SciencesDivision), and the Division of PolarPrograms.Organizers: G.S. (Lynn) Soreghan,University of Oklahoma; Judith T. Parrish,University of Arizona; Christopher G.Maples, Indiana UniversityIt has been just a few months since I assumedoffice as your President. Fortunately for me, Ifollow on the heels of Peter McCabe, whoput our society on a solid course during histerm. My biggest job will be to keep the shipon a steady course. Perhaps the greatestaccomplishment of Peter’s administrationwas the creation of The Sedimentary Record.This new publication will hopefully establisha stronger link between our members and thesociety.One of the biggest challenges currentlyfacing us is that of declining membership.This decline is, in large part, due to thedemographics of the geoscience profession.Many of us are getting older. To offset thedecline we must encourage student member-ship and become a truly global society.Council has spent many hours discussingstudent involvement in SEPM and has done anumber of things to encourage student mem-bership. We now have a $25 student member-ship that includes online access to both of ourjournals, as well as, our regular member dis-counts on publications and the semi-annualfree books to students events. With all ofthese efforts, I must confess that I am stillpuzzled by the relatively low numbers of stu-dent members in the society, given the factthat sedimentary geology is still very much aprinciple component of the Earth Sciences. Iwas encouraged by my advisors to join profes-sional societies and did so as a student. Fromthat time on I began to feel more connectedwith the profession. I continue this importanteffort with my own students and even go sofar as to purchase their first year’s membershipfor them (at $25 it is a real bargain for me).Today, with low membership costs and highbenefits for students, I can’t see why more stu-dents are not taking advantage of societymembership. Maintaining a strong, dynamicand young membership is vital to our societyand to the science. We must all work harder atincreasing membership. Let me know if youhave suggestions in this area. This past year one of my graduate studentsand I attended the SEPM Incised ValleyResearch Conference in Casper, Wyoming.This was an excellent conference, wellattended, packed with high quality talks,wonderful field trips and opportunities tointeract with colleagues and friends. We bothcame away with new ideas and were ener-gized for addressing our own research proj-ects. In my opinion, research conferences areone of the greatest services our society offers.I have attended several over the years andhave, without exception, had experiencessimilar to those of the Casper meeting.I would like to see us doing more confer-ences on a greater range of themes.Did you know that there are SEPM staffwho are dedicated to helping with the organ-ization and running of research and fieldconferences? Have you ever thought aboutrunning such a conference? It is probablyeasier than you think and the rewards aregreat. Check out the SEPM web site to findout how you can propose a conference, orcontact Judy Tarpley at SEPM headquartersand get one started.One of the other great benefits of our soci-ety is the Special Publications program. TheSociety is always looking into ways to expandand hasten the turn-around time for specialpublications. Our web site now providesinformation to authors of special publicationarticles that allow them to track their papersthrough the system (http://www.sepm.org/publishing/upcoming.htm). We are workinghard to speed up the review, editing andprinting process. We are currently investigat-ing using online submission and review. Ourgoal is to reduce the turn around time to aslittle as possible. Ranging from the tradition-al print to electronic media, advanced levelcompendium to college level course material,I would encourage anyone to think aboutpublishing with SEPM. If you are interestedin proposing a special publication, contactLaura Crossey ([email protected]) at theUniversity of New Mexico, who is SEPM’sSpecial Publications Editor.The sedimentary geology community willplay a key role in the future of the EarthSciences and our society must remain strongor the science will suffer. I encourage you allto take a more active role in the society. Joina committee, attend annual meetings andresearch conferences and encourage newmembers. This is a great society of fascinat-ing people with a common interest in thesedimentary record of Earth’s history. John AndersonPresident, [email protected]’S OBSERVATIONS