Terrestrial Source Areas Research Articles

Unscrambling the source kitchen and hydrocarbon prospect information of the ultra-deepwater area in southern Pearl River Mouth basin, South China Sea: Insights from the first ultra-deepwater exploration well W21

Recent breakthroughs in Pearl River Mouth basin (PRMB) regarding offshore hydrocarbon exploration have shifted the focus from deepwater area to ultra-deepwater area (>1500 m water depth), and the southern sub-sag of Baiyun sag, Liwan sag, and the Shunhe Uplift between them constitute the front area for PRMB ultra-deepwater hydrocarbon exploration. This study investigated the source-rock strata (i.e., Eocene Wenchang Formation and Enping Formation) and reservoir fluids (mainly CO2 with small amounts of oil and alkane gas) in the first exploratory well (namely W21, drilled at Shunhe Uplift), aiming to unscramble the source kitchen and hydrocarbon prospect information in this ultra-deepwater area. Biomarker and transgressive history analysis of source-rock strata jointly determined the Wenchang Formation and Enping Formation to be marine sediments in the Liwan sag, while marine and lacustrine sediments in the Baiyun southern sub-sag, respectively. The oil biomarkers and isotopes of alkane gas evidenced prospect for mature oil and oil-associated gas in this ultra-deepwater area, and the correlated source analysis determined the source rocks in the two sags have an advantage of aquatic organic input, indicating a good hydrocarbon-generating potential. Additionally, the regional distribution of terrestrial source-specific biomarkers (i.e., oleanane and bicadinanes) in PRMB deep to ultra-deep water areas traced the terrestrial source area and revealed a significant less input of terrigenous organic matter at the two ultra-deepwater sags. The isotopic analysis of reservoir non-hydrocarbon gases determined the CO2 to be mantle-derived magmatic origin. The present reservoirs are a result of displacement of early charged oils by posterior migrated CO2. In conclusion, this PRMB ultra-deepwater area has a considerable prospect for mature oil; however, the frequent volcanism since the Pliocene poses great risks to hydrocarbon exploration.

Paleoenvironmental variations in a sedimentary Jurassic sequence from Lusitanian Basin (Portugal)

Gaiteiros-1 borehole, located in the central Lusitanian Basin (Portugal), drilled a continuous Jurassic (Hettangian to Kimmeridgian) sedimentary sequence. Forty-one samples were selected for this study to characterize the dispersed organic matter and its vertical variation along Gaiteiros-1 borehole and to evaluate the environmental changes based on palynofacies and bulk geochemistry analyses.Gaiteiros-1 borehole lithological sequence is characterized by a low organic carbon content, which varies between 0.10 wt% and 0.83 wt%, in Candeeiros carbonates and Lower Jurassic Coimbra Formation, respectively. The insoluble residue content indicate a carbonated character in almost the entire sequence, except for Kimmeridgian samples. The palynofacies analysis evidences the presence of the main groups of kerogen (Phytoclats, Amorphous and Palynomorphs) with a dominance of the amorphous group in the carbonated samples and phytoclasts in Kimmeridgian detritic samples. Different types of amorphous particles were identified, suggesting periods of reworking by bacterial activity and primary bioproductivity in depleted oxygen environments. Despite the dominance of amorphous particles, the kerogen groups vertical variation provides information that reveals changes in the depositional environment. The kerogen assemblage of the Candeeiros facies suggests a stratified water column, with well-oxygenated layers, responsible for high primary productivity periods, which allowed for the development of zooplankton, preserved in the form of zooclasts fragments and foraminiferal test-linings. The contribution of the Palynomorph group is scarce during the Lower-Middle Jurassic but increases in the Upper Jurassic. This modification in the kerogen assemblage reflects changes in the sea level, oxygenation conditions, climate and proximity to the terrestrial source area. The presence of Coleochaete-like freshwater algae was detected for the first time in the Lusitanian Basin, suggesting more restrictive conditions during the Late Oxfordian. During the Kimmeridgian, the amorphous material disappears and phytoclasts, mainly opaque phytoclasts, come to dominate the kerogen assemblage, as a result of terrigenous sediments input, due to the great proximity to the terrestrial source area.

Architecture and development of the Magdalena Submarine Fan (southwestern Caribbean)

Submarine fans are the largest sediment accumulations on Earth and are key to study the sediment-transfer zone between terrestrial source area and deep-sea depositional sink. They provide information of past climate, tectonics, carbon global inventory, and can be prolific hosts for oil/gas resources. In this paper, we present, for the first time, an analysis of the entire Magdalena Submarine Fan (MSF), from the shelf break to the distal domain, based on ~224,000 km2 of multibeam bathymetry, as well as backscatter, subbottom profiler and regional/local seismic reflection data recently acquired in southwestern Caribbean Sea. The aim is to describe in detail the MSF morphology and depositional architecture, propose a fan segmentation landform assemblage, and determine its extent within the deep basin. Three fan segments are identified: upper, middle and lower fans. The upper fan extends from the coastline to a depth of ~3000 m. Its eastern sector is characterized by a canyon system off the present-day mouth of the Magdalena River, through which most of the sediments are transported downslope to be deposited in intra-slope basins bounded by structural highs of the South Caribbean Deformed Belt. The western upper fan is characterized by distinct channel-levee complexes that are partially removed by mass transport complexes that originated near the continental shelf edge. The upper to middle fan transition is marked by a decrease in regional gradient from 1° to about 0.3° and local relief, a change from large, irregular sediment waves to more regular waves that slowly decrease in amplitude downslope, and the appearance of erosional megascours. The middle fan bedform assemblage evidences the presence of a channel-lobe transition zone in this sector of the MSF, separating well-defined, upper fan channels from lower fan depositional lobes. The middle to lower fan transition occurs between ~3800 and ~3950 m and is defined by a further decrease in gradient and by a change from sediment waves to planar parallel-bedded reflectors on subbottom profiles. The lower fan extends to a maximum depth of ~4250 m and is characterized by an almost flat seabed (slope of 0.05°), interrupted by a few isolated bathymetric highs and low-relief channels (<5 m deep). The entire area of the lower fan is interpreted as an area of turbidity current deposition, with relatively sandy sediments in the south and west giving way to muddier sediments in the northeast, which could correspond to distal fan lobes. The identification of four regional seismic facies related to MSF sedimentation allowed us to constrain the fan extent in the southwestern sector of the Caribbean. Distally, within the Colombia Basin the fan terminates against areas of elevated seafloor (Kogi-Coyaima and Quimbaya seamounts, Aruzi and Ticuna hills, and Beata Ridge), which have acted as barriers to sedimentation. Nevertheless, it was determined that the MSF extends beyond the Colombia Basin and locally reaches the Lower Nicaraguan Rise. In this new scenario, we established that the MSF is much more extensive than previously recognized, with an area of ~237,000 km2, which puts it among the World's largest submarine fans.

Organic facies variability during the Toarcian Oceanic Anoxic Event record of the Grands Causses and Quercy basins (southern France)

The early Toarcian is marked worldwide by major environmental changes that resulted in organic-rich black shale deposition, the Toarcian Oceanic Anoxic Event (T-OAE). This organic-rich sedimentation is particularly recorded in the Grands Causses (GCB) and Quercy (QB) basins. The main objectives of this study are the characterization, through organic petrology and geochemistry techniques, of the organic matter (OM) of the late Pliensbachian – early Toarcian sedimentary successions of these basins and the definition of the organic facies, assessing their implications in the evolution of depositional paleoenvironments.In the GCB sedimentation occurred, during the late Pliensbachian, in a well oxygenated water body (Total Organic Carbon - TOC 0.6wt.% and low Amorphous Organic Matter - AOM) proximal to the terrestrial source area (high terrestrial contribution) with marine influence. In the lattermost Pliensbachian a shallowing of the water column is observed with decrease of marine influence and separation from the terrestrial source area (TOC 0.9wt.%, AOM and zooclasts co-dominate) under an arid climate (Classopollis ssp.). From the Tenuicostatum to early Serpentinum chronozones a restricted and stagnated environment (TOC 5.7wt.%, AOM dominates) is implemented. From middle to late Serpentinum Chronozone the reestablishment of the oxygen levels (decrease in TOC and AOM) takes place, as well as paleoceanographic circulation patterns.In the QB, the late Pliensbachian to earliest Toarcian is characterized by low TOC (0.2wt.%) with sedimentation occurring in a shallow oxygenated proximal water body (amorphous Hydrozoans dominate) separated from the terrestrial source area with arid climate (Classopollis ssp.), and with episodes of emersion. From the Semicelatum Subchronozone to Serpentinum Chronozone the development of dysoxic to anoxic conditions (TOC 4.2wt.%) takes place, associated with water column stratification and more effective non-carbonate sedimentation, and with an increase in water level. For the lattermost Serpentinum Chronozone shallowing of a more oxidizing water body, with some oxygen depletion still present is proposed.The differences in these paleoenvironmental depositional contexts further demonstrate that, although the T-OAE has a global character, local control mechanisms in these basins play a pivotal role. Furthermore, the first occurrence of Hydrozoans, namely its free-swimming medusoid forms, is described in organopalynological preparations of sediments from the Pliensbachian–Toarcian and their first paleoenvironmental application in a palynofacies based study is made.

Grain size and mineralogy of Al Batinah beach sediments, Sultanate of Oman

The nature of Al Batinah coast beach sediments in the Sultanate of Oman was investigated by the analysis of grain size and mineralogy. The beach sediments, mostly light-medium gray green, were predominantly fine sands, with the average grain size of all samples about 200 μm. Some of the particles were gravel (2–16 mm), and some were even larger pebble-size particles (16–256 mm). Some mud (sediment <63 μm) was present, mostly in the sub-tidal sediments. The majority of the samples were skewed to the coarse size with coarse tail partly due to the presence of shell fragments. Approximately 50 % of the beach sediments were quartz with different varieties based on shape and size. The second major component of beach sediment was calcium carbonate which varied from 10 to 65 %. The other components in decreasing order consisted of microbreccia, feldspar, pyroxene, igneous rock fragments, biotite flakes, and heavy minerals. The levels of carbonate were lower in NW Al Batinah coast from Harmul to Al Khaburah but were higher in the SE from Al Khaburah to Al Ghubrah. This could be attributed to either lower carbonate production or more sediment input by wadis along the north-western part of Al Batinah coast. The unique and complex nature of these sediments is largely due to the geology of the terrestrial source area in the Hajar Mountains which contains the famous Samail ophiolite complex and the weak sorting along the shoreline in these tide-modified beaches.

Terrestrial source to deep-sea sink sediment budgets at high and low sea levels: Insights from tectonically active Southern California

AbstractSediment routing from terrestrial source areas to the deep sea influences landscapes and seascapes and supply and filling of sedimentary basins. However, a comprehensive assessment of land-to-deep-sea sediment budgets over millennia with significant climate change is lacking. We provide source to sink sediment budgets using cosmogenic radionuclide–derived terrestrial denudation rates and submarine-fan deposition rates through sea-level fluctuations since oxygen isotope stage 3 (younger than 40 ka) in tectonically active, spatially restricted sediment-routing systems of Southern California. We show that source-area denudation and deep-sea deposition are balanced during a period of generally falling and low sea level (40–13 ka), but that deep-sea deposition exceeds terrestrial denudation during the subsequent period of rising and high sea level (younger than 13 ka). This additional supply of sediment is likely owed to enhanced dispersal of sediment across the shelf caused by seacliff erosion during postglacial shoreline transgression and initiation of submarine mass wasting. During periods of both low and high sea level, land and deep-sea sediment fluxes do not show orders of magnitude imbalances that might be expected in the wake of major sea-level changes. Thus, sediment-routing processes in a globally significant class of small, tectonically active systems might be fundamentally different from those of larger systems that drain entire orogens, in which sediment storage in coastal plains and wide continental shelves can exceed millions of years. Furthermore, in such small systems, depositional changes offshore can reflect onshore changes when viewed over time scales of several thousand years to more than 10 k.y.

Rapid Climatic Signal Propagation from Source to Sink in a Southern California Sediment‐Routing System

Abstract Terrestrial source areas are linked to deep‐sea basins by sediment‐routing systems, which only recently have been studied with a holistic approach focused on terrestrial and submarine components and their interactions. Here we compare an extensive piston‐core and radiocarbon‐age data set from offshore southern California to contemporaneous Holocene climate proxies in order to test the hypothesis that climatic signals are rapidly propagated from source to sink in a spatially restricted sediment‐routing system that includes the Santa Ana River drainage basin and the Newport deep‐sea depositional system. Sediment cores demonstrate that variability in rates of Holocene deep‐sea turbidite deposition is related to complex ocean‐atmosphere interactions, including enhanced magnitude and frequency of the North American monsoon and El Nino–Southern Oscillation cycles, which increased precipitation and fluvial discharge in southern California. This relationship is evident because, unlike many sediment‐routi...

Depositional environments and hydrocarbon potential of the Middle Jurassic Los Molles Formation, Neuquén Basin, Argentina: palynofacies and organic geochemical data

A multidisciplinary analysis of palynofacies in a sequence-stratigraphical framework, TOC (total organic carbon) and TAI (thermal alteration index) analyses, has been applied to outcrop samples of the uppermost Los Molles Formation (Middle Jurassic), Neuquen Basin, Argentina, in order to characterise the palaeoenvironmental and palaeo-climatic conditions during the deposition of this unit. Five types of palynofacies (P-l to P-5) have been identified and are interpreted to indicate a restricted marine to inner neritic environment. In P-1 and P-4, a marine environment close to the terrestrial source area with moderate oxidizing conditions and energy, is suggested. In P-2, the assemblage of freshwater algae, acritarchs and prasinophytes suggest a marginal marine environment influenced by fluvial discharge. In P-3, the marine microplankton content reflects conditions ranging from a marginal-marine (sub-normal salinity) to an inner neritic environment. In P-5, a dysoxic marine environment (probably marginal) is suggested. Warm and relatively humid (abundance of Cheirolepidiaceae in association withAraucariaceae) and locally humid (presence of swamps or ponds, on the alluvial plains) conditions are inferred. TOC content (65% of the analyzed samples reach TOC values over 1%), TAI values (2 to 2+, transitional between an immature phase and the window of liquid petroleum generation) and kerogen type (P-1, P-2 and P-5 show transitional characteristics between kerogen type II and III, while P-3 and P-4 show characteristics of kerogen type III and occasionally type IV), suggest that, in the studied area, the Los Molles Formation has some hydrocarbon potential. However, kerogen state suggests that the anoxic-dysoxic conditions of the site of deposition were not optimum for its preservation.

Depositional environments and hydrocarbon potential of the Middle Jurassic Los Molles Formation, Neuquén Basin, Argentina: palynofacies and organic geochemical data.

A multidisciplinary analysis of palynofacies in a sequence-stratigraphical framework, TOC (total organic carbon) and TAI (thermal alteration index) analyses, has been applied to outcrop samples of the uppermost Los Molles Formation (Middle Jurassic), Neuqu&eacute;n Basin, Argentina, in order to characterise the palaeoenvironmental and palaeo-climatic conditions during the deposition of this unit. Five types of palynofacies (P-l to P-5) have been identified and are interpreted to indicate a restricted marine to inner neritic environment. In P-1 and P-4, a marine environment close to the terrestrial source area with moderate oxidizing conditions and energy, is suggested. In P-2, the assemblage of freshwater algae, acritarchs and prasinophytes suggest a marginal marine environment influenced by fluvial discharge. In P-3, the marine microplankton content reflects conditions ranging from a marginal-marine (sub-normal salinity) to an inner neritic environment. In P-5, a dysoxic marine environment (probably marginal) is suggested. Warm and relatively humid (abundance of Cheirolepidiaceae in association withAraucariaceae) and locally humid (presence of swamps or ponds, on the alluvial plains) conditions are inferred. TOC content (65% of the analyzed samples reach TOC values over 1%), TAI values (2 to 2+, transitional between an immature phase and the window of liquid petroleum generation) and kerogen type (P-1, P-2 and P-5 show transitional characteristics between kerogen type II and III, while P-3 and P-4 show characteristics of kerogen type III and occasionally type IV), suggest that, in the studied area, the Los Molles Formation has some hydrocarbon potential. However, kerogen state suggests that the anoxic-dysoxic conditions of the site of deposition were not optimum for its preservation.

Latitudinal distribution of terrestrial lipid biomarkers and n-alkane compound-specific stable carbon isotope ratios in the atmosphere over the western Pacific and Southern Ocean

We investigated the latitudinal changes in atmospheric transport of organic matter to the western Pacific and Southern Ocean (27.58°N–64.70°S). Molecular distributions of lipid compound classes (homologous series of C 15 to C 35 n-alkanes, C 8 to C 34 n-alkanoic acids, C 12 to C 30 n-alkanols) and compound-specific stable isotopes (δ 13C of C 29 and C 31 n-alkanes) were measured in marine aerosol filter samples collected during a cruise by the R/V Hakuho Maru. The geographical source areas for each sample were estimated from air-mass back-trajectory computations. Concentrations of TC and lipid compound classes were several orders of magnitude lower than observations from urban sites in Asia. A stronger signature of terrestrial higher plant inputs was apparent in three samples collected under conditions of strong terrestrial winds. Unresolved complex mixtures (UCM) showed increasing values in the North Pacific, highlighting the influence of the plume of polluted air exported from East Asia. n-Alkane average chain length (ACL) distribution had two clusters, with samples showing a relation to latitude between 28°N and 47°S (highest ACL values in the tropics), whilst a subset of southern samples had anomalously high ACL values. Compound-specific carbon isotopic analysis of the C 29 (−25.6‰ to −34.5‰) and C 31 n-alkanes (−28.3‰ to −37‰) revealed heavier δ 13C values in the northern latitudes with a transition to lighter values in the Southern Ocean. By comparing the isotopic measurements with back-trajectory analysis it was generally possible to discriminate between different source areas. The terrestrial vegetation source for a subset of the southernmost Southern Ocean is enigmatic; the back-trajectories indicate eastern Antarctica as the only intercepted terrestrial source area. These samples may represent a southern hemisphere background of well mixed and very long range transported higher plant organic material.

Sedimentary patterns in the late Quaternary Southern Ocean

The spatial and temporal distribution of biogenic and lithogenic sediments in the late Quaternary Southern Ocean reflects the zonal character of the Antarctic Circumpolar Current and is basically controlled by glacial dynamics in Antarctica, sea-ice distribution, temperature gradients, wind patterns, and thermohaline ocean circulation. Carbonate patterns in most places reveal a decline in biogenic carbonate preservation during glacial periods, mainly attributed to a reduced influx of North Atlantic Deep Water and increased ocean stratification, which modified deep-water chemistry towards more corrosivity. An important lithological feature of the Southern Ocean is the Circumpolar Opal Belt, which today is situated between the Polar Front and the seasonal sea-ice limit to the south. During the glacial periods the opal belt shifted to the north in response to a wider sea-ice extension that reduced light availability and diatom productivity to the south. Biosiliceous productivity to the north likely was fueled by detrital iron supplied by aeolian dust input and/or hemipelagic processes. Lithogenic fluxes generally increased during the glacial periods. Provenance studies on the origin and dispersal of detrital materials suggest combined effects of low sea-level stands, increased glaciogenic input, and enhanced current transport to have caused elevated detrital fluxes. The relative and absolute contribution of aeolian dust is difficult to decipher and awaits further clarification by integrated provenance studies of both marine sediments and more reference materials from the potential terrestrial source areas. Ice-rafted debris (IRD) represents a minor fraction of lithogenic sediments, but can be used to infer both Antarctic ice-sheet dynamics and the fate of both sea-ice and iceberg survival in the distal Southern Ocean. Future work should be concentrated on a better identification of IRD origin in terms of volcaniclastic influences, the distinction of east and west Antarctic sediment sources, and sea-ice versus iceberg transportation.

Differing Eocene floral histories in Southeastern North America and Western Europe: Influence of paleogeography

Pollen data show that in southeastern North America, the Eocene angiosperm flora attained its maximum relative diversity some 8 m.y. after the late early Eocene to earliest middle Eocene climatic maximum. Increasing diversity resulted in part from the flora's position on a large continent which allowed easy migration. In western Europe, the floral diversity began decreasing even before the climatic maximum. Paleogeography played large roles in this diversity decrease. In western Europe, terrestrial floras were on islands and peninsulas in the sea, so that the floras underwent increasing isolation and partial local extermination. Temperate plants generally did not migrate to western Europe, because of a lack of nearby uplands, lack of northern terrestrial source areas for these plants, and presence of the Turgai Straights barrier. The Eocene climate of western Europe cooled at least partly because of decreasing contact with the warm Tethys Seaway.

Early-Diagenetic Sheet-Crack Cements of Guadalupian Shelf, Yates and Tansill Formations, New Mexico--a Field and Chemical Study: ABSTRACT

Tepee-associated sheet-crack structures and carbonate cements that largely fill them are developed in the carbonate facies of the back-reef Capitan Reef complex, Guadalupe Mountains, New Mexico. Sheet cracks, their cements, and associated teepee structures were studied to better understand the timing, nature of precipitating waters, and environment of deposition of the sheet-crack cements. Sheet-crack cements were field classified into 8 morphologic fabrics. Contrary to previous work, this study found that sheet-crack fillings developed symmetrically from roofs and floors. Sheet-crack cements, the sheet cracks, and associated teepee structures developed repeatedly and episodically. Most are erosionally truncated and cross-cut by overlying surfaces. Most cements show isopachous growth indicative of precipitation under phreatic conditions. Some pendant cements suggest precipitation in a vadose environment, indicating occasional exposure of the outer-shelf and shelf-crest facies. Calcite-cement fabrics (39 samples) were analyzed for Sr, Mg, Fe, ^dgr13C, and ^dgr18O. Chemical compositions range from: Sr = 116 to 5,244 ppm; Mg = 215 to 9,188 ppm; Fe = 7 to 758 ppm; ^dgr18O = -5.6 to + 0.4^pmil; and ^dgr13C = +4.9 to 7.5^pmil (PDB). Sr exhibits distinct groupings of more than 2,000 ppm and fewer than 500 ppm. Samples with high Sr are associated with lower ^dgr13C, ^dgr18O, and Mg compositions. The converse is true for the low Sr values. Isotopically heavier samples are interpreted as precipitated from restricted marine waters. Isotopically lighter samples are interpreted as precipitated from mixed meteoric and marine waters. The meteoric water is inferred to have originated from shelfward, terrestrial source areas. It is hypothesized that these waters traveled through an aquifer system and percolated upward as springs to the sheet-crack area. End_of_Article - Last_Page 302------------

Palynology of the Monterey formation (Miocene) phosphatic facies at Lions head, Santa Maria area, California

Abstract A rich palynomorph assemblage of early Miocene age was obtained from the phosphatic facies mudstone samples of the lower Monterey Formation exposed in the basal Lions Head section in the Santa Maria area, California. Angiosperm pollen of Acer, Achillea, Bombacaceae, Carya, Ericaceae, Onagraceae, Salix, and Ulmus occurs commonly. Among conifers, bisaccate Pinus pollen is well represented. Azolla glochidia and spores of Selaginella, Sphagnum, and Polypodium are sparse. Marine algae are represented abundantly by Pterospermella, Tytthodiscus, and several dinocysts, including Leptodinium, Operculodinium centrocarpum, Spiniferites, and Tuberculodinium vancampoae. The dinocyst assemblage, unstructured amorphous organic debris, and the lack of large spores support an offshore deep marine deposition under a prevailing warm temperate climate with an annual summer rainy season. The terrestrial source area encompassed freshwater pools and ponds in a marsh/swamp environment. Pine vegetation was present in elevated areas.

Skewness as a Paleoenvironmental Indicator

ABSTRACT Because it has been suggested by many sedimentologists that skewness characteristics of recent sediments can be applied to the interpretation of paleoenvironments of unconsolidated and diagenetically unaffected sediments, we have compared skewness to both other textural features and compositional variations of the unconsolidated, uppermost Miocene sediments of central Delaware. Previous studies have indicated a lagoonal or bay environment for these silts and sands. Analysis of samples from 22 wells revealed a lignite-bearing, poorly sorted, dark gray, silty central region almost surrounded by shell fragment-bearing, poorly sorted, relatively heavy mineral-rich, gray, silty, subangular quartz sands. In the central silty region, clay (up to 20 percent) is more abundant to the north where a terrestrial source area was located. In the surrounding sandy region, the best sorted sediments, containing frosted quartz grains, occur to the south, indicating a possible transition into an offshore barrier island complex with windblown sands carried northward into the oceanward margin of the lagoon. Plotting the skewness values revealed a nearly identical central region with negative skewness almost surrounded by a marginal region of positive skewness, mimicking the bulls-eye distributional patterns of the other textural and compositional data. Comparison with recent environmental studies of skewness suggests that the central region probably represents proximity to a river mouth or tidal estuary where winnowing may have dominated over deposition, whereas the surrounding region may represent sands deposited in an adjacent shallow, sheltered lagoonal area dominated by deposition. This study supports the suggestion that the sign of skewness, coupled with lithologic and other textural analyses, is potentially useful in identifying ancient sedimentary environments. However, further work is necessary to fully evaluate its usefulness.