Paleoenvironmental Trends Research Articles

Tracing the latest Jurassic–earliest Cretaceous paleoenvironment evolution in swell carbonate facies: a case study of the High-Tatric succession (Central Western Carpathians, Tatra Mts, Poland)

This paper presents an interpretation of sedimentologic, paleomagnetic, and geochemical data collected in the Upper Kimmeridgian–Valanginian carbonates of the Giewont series (Giewont and Mały Giewont sections, High-Tatric succession, Western Tatra Mountains, Poland). The studied succession provides insight into the sedimentary conditions prevailing in the South Tatric Ridge (Tatricum), a submarine elevation located between the Zliechov Basin (Fatricum) and the Vahic (=South Penninic) Ocean. The sedimentary sequence includes micrites, pseudonodular limestones, cyanoid packstones, lithoclastic packstone, and encrinites. The results are discussed with regards to their significance for detrital input, paleoclimate, and paleoproductivity, which in turn are considered in the context of both local and regional paleoenvironmental trends and events. The greatest depositional depths during the latest Kimmeridgian–earliest Tithonian are documented by the occurrence of pseudonodular limestones. A Tithonian shallowing trend is demonstrated via the increasing size and roundness of cyanoids, while the final (?)emergence and erosion in the South Tatric Ridge is documented by earliest Cretaceous disconformities. This process might have been related to both falling sea-level during the major eustatic regressive cycle and tectonic uplift caused by the mutually related (re)activation in the Neotethyan Collision Belt and rifting in the Ligurian-Penninic-Vahic Oceans. The highest lithogenic influx (although still low; max 0.5% of Al content) during the Late Kimmeridgian is considered as associated with relatively humid climate conditions, whereas a subsequent decreasing trend is thought to result from aridification during the latest Kimmeridgian–earliest Tithonian. Ultimately, deposition in the High-Tatric zone was affected by both large-scale environmental perturbations characteristic of the latest Jurassic (climate changes, variations in seawater pH, monsoonal upwelling, lithogenic input, etc.), as well as local sedimentary controls, predominantly the oxygenation state of bottom waters and tectonic movements. Supplementary Material 1

Relationship between cyclic patterns of organic matter concentrations and their paleoenvironmental controls in the Upper Cretaceous rocks in Abu El Gharadig basin, Egypt: Cyclo-sequence stratigraphic framework

Abu El Gharadig Basin includes active petroleum systems that produce petroleum in many fields such as Abu El Gharadig Field. The hydrocarbon source rocks in the Upper Cretaceous of Bahariya and Abu Roash formations play an important role in such petroleum systems. The organic matter concentration is very important parameter to determine the potentiality of source rock occurrences. The understanding of cyclic changes of the organic matter enrichments measured in total organic carbon (TOC) is targeted in the present study together with the paleoenvironmental trends that control their distribution. The paleoenvironmental conditions are determined using the statistical analysis of palynofacies by applications such as cluster and correspondence analyses. These analyses are used to identify the palynofacies types (A, B, C, D and E) with distinctive paleoenvironmental conditions. The correspondence analysis is used to determine the paleoenvironmental trends including proximal-distal trend in axis 2 and oxygenation conditions on axis 1. The palynofacies type D and E are characterized by anoxic to suboxic distal conditions. The measured total organic carbon values are generally low (3.3 wt%) in the studied wells and the higher values have tendency to associate the distal anoxic environment of palynofacies type D. The succession was divided into 15 stratigraphic sequences using the palynofacies analysis which enabled the basinal correlations through the studied wells. Additional trace elements measurements are used to confirm the paleoenvironmental characteristics indicated by the palynofacies analysis. The G-ray log in addition to the proximal-distal trend represented by correspondence axis 2 and organic matter concentrations are subjected to time series analysis by spectral and wavelet transform applications. The analysis revealed similar ratios of the resulted periodicities that indicate existence of a common cyclic pattern. This cyclic pattern is connected to the oscillation orbitallly induced climate changes.

Verification of regional-to-global scale environmental factors in paleosol stable carbon isotope ratios through the lower Permian succession of north-central Texas, U.S.A.

Upper Paleozoic (~300 Ma) rocks in the Midland Basin of Texas (USA) record a transition from icehouse (glaciated) to greenhouse (non-glaciated) conditions in low latitudes, western Pangea. This work revisits the stratigraphic interval that records stable carbon isotopic compositions of paleosol materials from previous studies and uses newly collected paleosol samples to test the reproducibility of paleosol stable carbon isotopic values, and assesses paleoclimate and paleoatmospheric pCO 2 changes across the global climate transition. Thirty upper Wolfcampian (Nacona Formation) to upper Leonardian (Clear Fork Group) paleosol profiles were measured and described in detail. Detailed petrographic analysis of paleosol carbonate nodules was used to identify the best representatives of pristine pedogenic microcrystalline calcite cements and separate them from later diagenetic or altered calcite cements. The best candidates for pedogenic micritic calcite cement were drilled, and organic-rich fractions of acid-treated residues co-existing within carbonate nodules were collected. The δ 13 C values of 23 paired, pristine pedogenic micritic calcite samples (δ 13 C cc ) and associated, occluded organic matter from carbonate nodules and calcareous rhizoliths (δ 13 C om ) range from −6.5‰ to −3.3‰ and −25.3‰ to −20.5‰, respectively. The stratigraphic trends in paleopedogenic micritic calcite δ 13 C cc values are essentially no different from results published in previous studies, which supports the reproducibility of paleosol carbonate as a reliable proxy for the carbon isotopic composition that reflects the regional-to-global paleoclimatic and paleoenvironmental trends. However, δ 13 C om values measured here are consistently more negative than previously reported for fossilized plant compressions preserved within strata associated with these paleosol profiles ( Montañez et al., 2007 ). We suggest that the coexisting organic matter from acid-treated residues in paleosol carbonate is a better material to assess original soil δ 13 C om values that was contributing toward soil CO 2 than the fossilized components of above-ground, photosynthesizing vascular plant parts as was utilized in previous studies. The isotopic differences between the paleosol micritic calcite δ 13 C cc values and associated organic-rich-residue δ 13 C om values were used in conjunction with a two-component CO 2 mixing model to yield atmospheric pCO 2 estimates. The estimates are different and with opposite excursions, ranging from 1.7 to 2.7 times pre-industrial atmospheric levels (PIAL) and from 2.3 to 4.2 times of PIAL, when applying the relationships of modern soil pCO 2 (S z )-mean annual precipitation (MAP) and Sz-pedotype, respectively, to assess the S z of paleosols. The different approaches result in different assumed S z of paleosols at the time of calcite crystallization and lead to lower estimates of atmospheric pCO 2 than previously reported. These results suggest that the icehouse-to-greenhouse climate transition was associated with much lower pCO 2 thresholds than previously thought. • The carbon isotope compositions of pedogenic calcite from microsamples are repeatable. • The carbon isotope compositions of pedogenic calcite can record regional processes. • Only limited increase in atmospheric pCO 2 across icehouse-to-greenhouse transition.

Benthic foraminifera and Neogene sea level changes in the Pelotas Basin, offshore south Brazil

The Neogene benthic foraminiferal ecostratigraphy of offshore Pelotas Basin has not yet been researched. The benthic foraminifera were examined in twenty-nine ditch cuttings samples from Well 1-SCS-3B, present water depth 200 m. These samples ranged from the Lower Miocene Catapsydrax dissimilis planktonic foraminiferal Zone to the Pliocene Globigerinoides trilobus fistulosus Zone. Only ditch cuttings were available, which allowed us to present just broad paleoenvironmental trends within the studied section. Benthic foraminifera indicate deposition mostly between outer neritic to upper bathyal paleodepths. A peak in uvigerinid relative abundance marks a possible flooding surface or condensed section with a high nutrient flux, low diversity (marked by the Shannon Function H), and sluggish circulation within the Globorotalia mayeri Zone. This peak is bracketed by high abundances of Cibicidoides, which indicate stronger current action than within the condensed section. Biostratigraphic hiatuses within these Cibicidoides-rich intervals are concluded not to indicate subaerial exposure, but to reflect current action sufficiently strong to induce either non-deposition or seafloor scouring. A second possible flooding surface occurs at the top of the section, indicated by a decline in Cibicidoides associated with upticks in Sphaeroidina and Bolivina and a dip in H. The top of this younger maximum flood was not encountered, probably occurring above the studied section. That the timing of these floods differs from those recorded elsewhere in the Pelotas Basin implies that they were tectonically induced, perhaps as distal effects associated with the interaction between the South American and Nazca tectonic plates. Future studies with better quality core samples will add detail to this picture; such studies can incorporate eustatic sea-level changes into the model presented.

Seasonal patterns of pollen sedimentation in Lake Montcortès (Central Pyrenees) and potential applications to high-resolution paleoecology: a 2-year pilot study

Lakes with varved sediments are especially well suited for paleoecological study, from annual to even seasonal resolution. The interpretative power of such high-resolution paleoenvironmental reconstructions relies on the availability of modern analogs with the same temporal resolution. We studied seasonal pollen sedimentation in varved Lake Montcortès, Central Pyrenees (Spain), as a modern analog for high-resolution reconstruction of Late Holocene vegetation and landscape dynamics. Seasonal samples were obtained from sediment traps that were submerged near the maximum water depth for a 2-year period (fall 2013 to fall 2015). Seasonal pollen sedimentation was compared with meteorological variables from a nearby weather station. Bulk pollen sedimentation, dominated by Pinus (pine) and Quercus (oak), followed a clear seasonal pattern that peaked during the spring/summer, coinciding with maximum temperature and precipitation, minimum relative humidity and moderate winds from the SSE. Pollen sedimentation lags (PSL) were observed for most pollen types, as substantial amounts of pollen were found in the traps outside of their respective flowering seasons. Two pollen assemblages were clearly differentiated by their taxonomic composition, corresponding to spring/summer and fall/winter. This pattern is consistent with existing interpretation of the sediment varves, specifically, that varves are formed by two-layer couplets that represent the same seasonality as pollen. We concluded that pollen sedimentation in Lake Montcortès exhibits a strong seasonal signal in the quantity of pollen, the taxonomic composition of the pollen assembalges, and relationships between the pollen and meteorological variables. Thus, varved sediments provide a potentially powerful tool for paleoecological reconstruction at seasonal resolution. This method could be used not only to identify paleoenvironmental trends, but also to identify annual layers and therefore date sediments, even in the absence of evident sediment laminations. A satisfactory explanation of PSL will require further studies that examine internal lake dynamics and pollen production/dispersal patterns.

Registro de diatomeas de los últimos 1400 años de la Laguna Pululos, Jujuy, Argentina

This paper presents high-resolution (multi-decadal) paleoenvironmental data of the last 1400 years in the northwestern sector of the dry Puna, Jujuy Province (Argentina). This information results from the analysis of the diatom assemblies recovered from sediment core samples collected at Laguna Pululos (22º32'43'' S; 66º48'25'' W), a shallow lake located at 4557 m.a.s.l. In this work we present and discuss the main results regarding the species composition of the diatom assemblages, and the observed paleoenvironmental trends related to the main characteristics and chronology of the medieval climatic anomaly (MCA) and little ice age (LIA). The results of the study indicate the onset of very arid conditions between ~800 and 1500 AD, and a sharp change to moister conditions from the latter period until the end of the XIX century. Noteworthy, two periods could be recognized, one between 600 and 800 AD (the moistest phase of the last 1400 years), and between 1366 and 1463 AD (a particularly arid phase). These periods recorded in Laguna Pululos apparently shared characteristics with the MCA and LIA, although, showing differences with chronologies found in the North Hemisphere, with an extended span of the arid conditions during the MCA in comparison with other paleoenvironmental records of the Andes.

Sedimentary development of a continuous Middle Devonian to Mississippian section from the fore-reef fringe of the Brilon Reef Complex (Rheinisches Schiefergebirge, Germany)

The Brilon-reef complex is one of the biggest Devonian carbonate buildups (*80 km 2 ) of the Rhei- nisches Schiefergebirge. The Burgberg section is located in the southeastern fore-reef area of the Brilon Reef Complex and exposes a succession of strata (117 m thick), which extends from the Middle Givetian (middle varcus conodont Zone) to the Visean (bilineatus cono- dont Zone). Field and microfacies observations led to the definition of nine microfacies that are integrated into a sedimentary model divided into off-reef, intermediate fore-reef, and proximal fore-reef sedimentary domains (SD). The off-reef domain (SD1) is the most distal set- ting observed and is characterized by fine-grained sedi- ments, dominated by pelagic biota and the local occurrence of gravity-flow deposits. The intermediate fore-reef (SD2) is characterized by a mixture of biota and sediments coming from both deeper-water and shallow-water sources and is influenced by storm and gravity-flow currents. In this domain, Renalcis mound- like structures developed locally. Finally, the proximal fore-reef (SD3) corresponds to the most proximal setting that is strongly influenced by gravity-flow currents derived from the Brilon Reef Complex. The temporal evolution of microfacies in the fore-reef setting of the Burgberg section show five main paleoenvironmental trends influenced by the onset, general development, and demise/drowning of the Brilon Reef Complex. Fore-reef to off-reef lithologies and their temporal changes are from the base to the top of the section: (U1)—fine- grained sediments with large reef debris, corresponding to the initial development of the reef building upon submarine volcaniclastic deposits during the Middle Givetian (middle varcus Zone) and first export of reef debris in the fore-reef setting; (U2)—high increase of reef-derived material in the fore-reef area, corresponding to a significant progradation of the reef from the Middle Givetian to the Early Frasnian (maximum extension of the Brilon Reef Complex to the south, disparilis to the falsiovalis conodont biozones); (U3)—progressive decrease of shallow-water derived material and increase of fine-grained sediments and deep-water biota into the fore-reef setting, corresponding to the stepwise with- drawal of the reef influence; from the Middle to the Late Frasnian (jamieae conodont Zone); (U4)—development of a submarine rise characterized by nodular and ceph- alopod-bearing limestones extending from the Late Frasnian to the Late Famennian corresponding to the demise and drowning of the Brilon Reef Complex as a result of the Late Frasnian Kellwasser events (upper rhenana and triangularis conodont biozones); (U5)— significant deepening of the Burgberg area starting in the Late Famennian, directly followed by an aggrading trend marked by pelagic shales overlying the nodular limestone deposits.

Paleoenvironmental trends in Venezuela during the last glacial cycle

This chapter summarizes and updates the main Quaternary paleoclimatic and sea-level trends recorded in Venezuela, and provides a paleoenvironmental framework for studies addressing biogeographical, ecological, and evolutionary topics. Venezuela has a number of localities that have provided paleoenvironmental sequences in the neotropical, circum-Caribbean domain, such as the Cariaco basin, Lake Valencia, the Merida Andes, and the Guayana region (e.g., Markgraf 2000). Venezuela encompasses a wide range of physiographic, climatic, and biogeographic conditions because of its geographic location. This spatial heterogeneity has led to complex, but interesting, paleoenvironmental reconstructions.

Paleosalinity history of middle Holocene lagoonal and lacustrine deposits in the Enriquillo Valley, Dominican Republic based on pore morphometrics and isotope geochemistry of ostracoda

The southwestern region of the Dominican Republic (Enriquillo Valley) contains exceptionally well-preserved, relict marine and saline lake deposits of mid-Holocne age. Abundant euryhaline ostracodes found in this deposit include Cyprideis salebrosa, C. mexicana, C. similis ,a ndC. edentata. Morphometric and geochemical analyses performed on Cyprideis spp. provide high 18 Oa nd 13 C values that are coincident with relative abundances of irregularly shaped pores that permeate the ostracode carapace. We recognize three stratigraphic intervals with distinct ostracode pore shape and stable isotope trends: (I) a 4.5-5.0m interval that contains ostracodes with highly irregular shaped pores (multiradiate) and high amplitude variability in 18 Oa nd 13 C values; (II) a 5.0-5.6m interval com- prised of ostracodes with circular pores and an overall trend towards low 18 Oa nd 13 C values; and (III) a 5.6-6.5m interval containing ostracodes with an upward increasing abundance of circular pore shapes coincident with a decreasing trend in 18 Oa nd 13 Cv alues. When the Enriquillo lagoon was first separated from the Caribbean Sea approximately 4.3 ka, an arid and evaporative climate led to hypersaline water in a restricted lagoon environment. By the middle to late-Holocene, increased precipitation in the valley resulted in a coastal lake system that became progressively oligohaline. Moderate to small amplitude variability in the salinity proxy data ( 18 O) sug- gest short-term oscillations in the precipitation-evaporation budgets at that time. At least two marine incursions likely contributed to the observed variability in ostracode 18 Oa nd 13 C values. Evidence for abrupt changes in base level indicate that climatic factors or also tec- tonic activity may have contributed to the observed paleoenvironmental trends recorded in these deposits.

Paleoenvironmental Trends in Paleocene Wilcox Tew Lake Marker Beds, LaSalle Parish, LA

ABSTRACT The Tew Lake Marker (TLM) beds are recognized on electric logs throughout east-central Louisiana by an uncommon, resistive unit within the Wilcox delta complex. This study explores how the wide distribution of this marker sequence is linked to its paleoenvironmental history. Petrographic and foraminiferal data derived from continuous, conventional cores from two wells located one mile apart are used to identify paleoenvironments and to interpret paleoenvironmental trends recorded in the TLM beds. The main discoveries of this investigation are: The resistive TLM beds consist of a shale sequence interbedded with very thin, calcareous, fossiliferous layers. The TLM beds were deposited in bay/lagoon paleoenvironments having salinities that ranged from hyposaline to normal marine. The TLM beds are divisible into lower and upper depositional sequences that are related to paleoenvironmental changes in the region. The lower depositional sequence fines upward and records normal marine and hyposaline-normal marine bay/lagoon deposits. This lower depositional sequence rests unconformably upon freshwater lignite, documenting a marine transgression inland over a freshwater swamp of the Wilcox lower delta plain. The upper depositional sequence coarsens upward and contains hyposaline-normal marine bay/ lagoon deposits that grade upward into hyposaline bay/lagoon deposits, suggesting regression in the lower delta plain. Muddy, fresh waters from nearby delta-distributary streams and stream crevasses filled lakes, inner bays and inner lagoons with sediment and reduced the salinities of water bodies and wetlands of the lower delta plain. Lateral facies between the two wells indicate marine influence during TLM deposition was greater and more persistent toward the east.

A benthic foraminiferal record of Paleocene sea level and trophic/redox conditions at Gebel Aweina, Egypt

We quantitatively analyzed benthic foraminiferal assemblages in order to reveal biotic and paleoenvironmental trends in the Paleocene section of Gebel Aweina, Egypt, on the southern Tethyan shelf. The first correspondence axis ranks taxa along an empirically derived bathymetric gradient, with neritic taxa (e.g., Discorbis duwi and Haplophragmoides walteri) opposed to bathyal taxa (e.g., Nuttallides truempyi and Gavelinella beccari(/ormis). The estimated paleodepth, as reflected by the various assemblages, was mostly ~ 200 m, but varied between ~ 50 m (P3a, NP4) and ~ 300 m (P4, N P8). The resultant four relative sea-level cycles appear to be at least of regional extent and may in part be eustatically controlled. The second correspondence axis reflects trends in trophic and redox development. Low-food, high-oxygen conditions prevailed during Biochrons Plc-P3b (NP4 NP5) and late P4 (NP8), when assemblages were mostly dominated by Cibicidoides spp. Most oligotrophic conditions coincided with maximum paleodepth. Intermediate trophic levels were established during middle P4 (NP6) and early P5 (NP9). From the level of the latest Paleocene benthic extinction event (BEE; middle P5 and NP9) onwards until Biochron P6a (NP10), assemblages dominated by buliminids marked increased trophic levels and reduced ventilation, probably resulting from enhanced surface productivity. Enhanced surface productivity along the southern Tethyan margin started during Biochron P4, and, at least on some shelves, intensified after the BEE. Increasing productivity during the latest Paleocene contrasts with global trends. This may be expected during climatic warming and an expanding trophic resource continuum, leading to regionally intensified eutrophy and oligotrophy. High productivity through upwelling along the southern Tethyan provides support for GCM predictions of intense wind-stress in this region during the warm late to latest Paleocene. © 1998 Elsevier Science B.V.

Ecospace utilization, paleoenvironmental trends, and the evolution of early nonmarine biotas

Paleozoic trace fossils evidence paleoenvironmental trends that are linked directly to progressive ecospace utilization (spatial and functional). These trends resulted in a considerable increase of ichnodiversity throughout the Paleozoic. Colonization of settings began as early as the Late Ordovician, as recorded by the presence of terrestrial burrow systems associated with ancient soils. In the other cases, the presence of nonmarine trace fossils in Cambrian and Ordovician sedimentary rocks was the result of temporary colonization by marginal marine organisms and does not reflect establishment of true fresh-water faunas. Devonian trace fossils have been reported from alluvial and alluvial-lacustrine transitional environments. Surface arthropod trackways are dominant in marginal lake settings, representing the development of true biotas. The presence of vertical burrows in fluvial deposits records the establishment of deep suspension-feeding infaunal organisms. Trace fossils from the Carboniferous reflect migration farther into the lakes. Ichnofossils have been reported from shallow and deep lake deposits and from alluvial and alluvial-lacustrine transitional environments. Lake assemblages are dominated by surface grazing trails. The Permian was characterized by the establishment of a deep deposit-feeding infauna, commonly recorded by the Scovenia ichnofacies represented by backfilled meniscate burrows.

Paleogene paleoenvironmental trends as reflected by palynological assemblage types, Salta Basin, NW Argentina

Paleogene paleoenvironmental trends as reflected by palynological assemblage types, Salta Basin, NW Argentina

Growth in encrusting cheilostome bryozoans: II. Circum-Atlantic distribution patterns

Differences in zooid skeletal ontogeny are strongly linked to the distribution of bryozoan species, even along such large-scale environmental gradients as depth and latitude. Three growth patterns broadly characterize zooid formation for encrusting cheilostome bryozoans: zooidal and intrazooidal budding, which facilitate growth in two dimensions at colony margins; and frontal budding, which also permits upward growth in the third dimension. Analyses of skeletal growth patterns of encrusting species present in 230 Recent assemblages from the North Atlantic, Mediterranean, North Sea, and Gulf of Mexico show that species with zooidal budding dominate overwhelmingly at lower latitudes and in shallower water, as assessed by percentages of species within assemblages. In contrast, patterns within moderately diverse fossil assemblages from North America indicate that within the geographic and environmental limits sampled, species with intrazooidal budding once dominated and probably originated in shallow, warm water environments. Intrazooidal budding now occurs with greater relative frequency among species from deeper and higher latitude assemblages. Patterns for frontal budding suggest a slight decrease with increasing depth, but no consistent relationship with latitude. These paleoenvironmental trends occur withn a putatively monophyletic clade and are markedly similar to onshore/offshore trends recognized in other groups of marine benthos, based on patterns of occurrence of supra-specific taxa and novel morphotypes. Results presented here are based on relative dominance of species within assemblages and thus provide a novel comparative test of these previously reported trends.

TROPICAL AMERICAN TERTIARY FLORAS AND PALEOENVIRONMENTS: MEXICO, COSTA RICA, AND PANAMA

Three Tertiary microfossil floras from northern Latin America are considered with reference to paleoenvironments and paleoenvironmental trends, especially paleotemperatures: Gatuncillo (middle (?) to late Eocene, Panama), Uscari (early Miocene, Costa Rica), and Paraje Solo (late Miocene, Veracruz, Mexico). The composition of the floras reflect lower temperatures in the late Miocene for terrestrial environments at ca. 18°N latitude, and temperatures comparable to the present for the middle (?) to late Eocene and early Miocene at ca. 9°N latitude. These values are consistent with Tertiary paleotemperature curves derived from 18O and 13C isotope studies of marine invertebrates, and show that the global drop in temperature at the end of the Miocene affected terrestrial biotas at least as far south as 18°N latitude. Comparison of the paleobotanical data with paleotemperature curves further reveals that the late Miocene was not only a likely time for the introduction of northern temperate elements into the Latin American biota (viz., establishment of the floristic and faunal relationship between eastern United States and eastern Mexico), but that earlier times were progressively less favorable because of generally rising temperatures and more tropical conditions. Information on the Tertiary history of vegetation in the Gulf/Caribbean region is also being monitored with reference to the effect of global sea level changes, although the specific influence of these fluctuations cannot as yet be detected.

Adaptation, plant evolution, and the fossil record

The importance of adaptation in determining patterns of evolution has become an important focus of debate in evolutionary biology. As it pertains to paleobotany, the issue is whether or not adaptive evolution mediated by natural selection is sufficient to explain the stratigraphic distributions of taxa and character states observed in the plant fossil record. One means of addressing this question is the functional evaluation of stratigraphic series of plant organs set in the context of paleoenvironmental change and temporal patterns of floral composition within environments. For certain organ systems, quantitative estimates of biophysical performance can be made on the basis of structures preserved in the fossil record. Performance estimates for plants separated in time or space can be compared directly. Implicit in different hypotheses of the forces that shape the evolutionary record (e.g., adaptation, mass extinction, rapid environmental change, chance) are predictions about stratigraphic and paleoenvironmental trends in the efficacy of functional performance. Existing data suggest that following the evolution of a significant structural innovation, adaptation for improved functional performance can be a major determinant of evolutionary change in plants; however, there are structural and development limits to functional improvement, and once these are reached, the structure in question may no longer figure strongly in selection until and unless a new innovation evolves. The Silurian-Devonian paleobotanical record is consistent with the hypothesis that the succession of lowland floodplain dominants preserved in the fossil record of this interval was determined principally by the repeated evolution of new taxa that rose to ecological importance because of competitive advantages conferred by improved biophysical performance. This does not seem to be equally true for Carboniferous-Jurassic dominants of swamp and lowland floodplain environments. In these cases, environmental disruption appears to have been a major factor in shaping the fossil record. This does not mean that continuing adaptation was not important during this interval, but it may indicate that adaptive evolution was strongest in environments other than those best represented in the paleobotanical record.

Upper Holocene Paleoceanography of Inner Miramichi Bay

Changes in sediment texture and in foraminiferal and molluscan assemblages observed in three vibracores collected in Miramichi Inner Boy reflect the development of a barrier island system across the mouth of the Bayt and the opening and closing of channels between the islands. The barrier island system apparently developed initially between 4400 and 3600 C14 years B.P. Opening and infilling of Buckleberry Gulley during the past 1300 years is indicated by changes in the proportions of estuarine and open bay assemblages of benthonic foraminifera. Mollusc and foraminifera data do not always suggest the same paleoenvironmental conditions at any given place and time, but they are in good agreement with respect to the direction of paleoenvironmental trends.