Lower Benue Trough Research Articles

Fish remains (Elasmobranchii, Actinopterygii) from the Late Cretaceous of the Benue Trough, Nigeria

Selachian and ray-finned fish remains from various Late Cretaceous localities of Nigeria are described. Each locality has yielded only a very few specimens and the diversity is therefore very low. However, some taxa are recorded for the first time in Africa. The Ashaka locality in the Upper Benue Trough (northeastern Nigeria) has yielded a small but interesting late Cenomanian assemblage of microremains, including teeth of “Carcharias” amonensis, Rhombopterygia zaborskii sp. nov., Hamrabatis sp., “Stephanodus” sp., and a possible ionoscopiform. A large prearticular dentition coming from the early Turonian beds of this locality is assigned to the large pycnodontiform Acrotemnus, a poorly known genus here regarded as a senior synonym of Macropycnodon. In the Lower Benue Trough (southeastern Nigeria), several localities ranging in age from the late Cenomanian to the early Maastrichtian have yielded various widespread taxa such as Ptychodus, Scapanorhynchus, Squalicorax, Vidalamiinae indet., cf. Protosphyraena, and Eodiaphyodus. The seaway that occupied the Benue Trough during transgressive episodes (late Cenomanian–early Turonian and Maastrichtian) created opportunities for the dispersal of many marine fish taxa into new areas, such as the proto-South Atlantic.

An appraisal of the water related contaminants as they affect the environment around the Enugu coal mines of Enugu state, southeastern Nigeria

Enugu metropolis is within the Anambra basin, which comprises mainly sedimentary rocks of sandstone, siltstone, mudstone and shales in the Lower Benue trough and as the capital of Enugu state in Nigeria and also as one of the major municipal and industrial centers in southeastern Nigeria experiences much groundwater contamination due to coal mining activity. The Area is richly endowed with sub-bituminous three-coal seams within the Mamu Formation. It also lacks prolific and potable groundwater due to the thinning-out of the Ajali sandstone aquifer through Udi town and Ninth-mile into Enugu metropolis. Generally, the specific discharge of Ajali sandstone (17.5 m2/day) is higher than that of Mamu Formation (14.5 m2/day). This appraisal becomes necessary to acquaint the Enugu city developers on the need for the prediction and understanding of the Environmental Impact Assessment (EIA) on the future development, management and maintenance of the mine water. The study also aims at identifying various contaminants, sources, level of concentrations, effects and control measures. Many springs, streams and seepages exist on the foot of most of the hills and ridges. The springs form the headwaters of the major streams and rivers like Ekulu, Iva and Nyaba at the base of the escarpment. Out of the streams and rivers in Enugu coal city, Ekulu River is the largest and thus very important for industrial and agricultural purposes. However, the coal mines discharge their effluents and waste waters directly into the Ekulu River with toxic heavy metals like As, Cd, Cr, Fe, Mn, Ni and Pb that contaminate the water and sediments. At the mines, most of the seepages, springs and streams rise directly from the perennial flood water from the mines. The water from the coal mines with special treatment for pH and iron contents can be employed in augmenting the present inadequate water supply that comes from the Ninth Mile borehole network and Ekulu River reservoir. The pH can be treated with hydrated lime, while iron (Fe2+) can be treated with aeration and filtration. Key words: Groundwater, coal mine, Ajali sandstone, sub-bituminous, coal, rivers, seepage.

English

The lead-zinc deposit of Enyigba and its environs are localized in the cretaceous sedimentary rocks of the Albian Asu River Group in the Lower Benue Trough, Southeastern Nigeria. The Albian Asu River Group is made up of shale, siltstone, sandstone and limestone. The deposits were formed epigenetically through the crystallization of hydrothermal solutions and are localized within the fractures, hence the need to study the trend of the fractures in the rock unit where the mineral deposits are being hosted.  In order to study the fractures, two units of the formation were identified and designated as units A and B. The ore field extends to about 3.7 km strike length with an average width of 5 m. From the detailed field mapping, the identified structures that control the mineralization are fold, fault and joint/fractures in which the fractures predominate. The total measured identified fractures is 503 in number and are represented in rose diagram, histogram and stereographic net which shows that they trend NW-SE and N-S directions, and dip SW-NE direction. Key words: Mineralization, stereographic net, shale, siltstone, sandstone, limestone, deposits.

Hydrocarbon generation potentials of the EzeAku Shale, Southern Benue Trough, Nigeria

This study is a contribution to our understanding of the hydrocarbon potentials of the EzeAku Shale in the Lower Benue Trough, Nigeria. It assessed the hydrocarbon generation potentials and timing of the EzeAku Shale—source horizon encountered in Amansiodo-1 well drilled in the basin using one-dimensional Genesis Zetaware basin modelling software. This software allowed the integration of burial and thermal effects on EzeAku source rock with kinetic inputs. The result of the model indicates that the EzeAku source horizon encountered at 3,490 m in Amansiodo-1 well expelled 285 mg/gTOC of oil and 80 mg/gTOC of gas. The hydrocarbon generation began in Early Santonian but was breached as remote uplift was still taking place. Maximum expulsion occurred at the end of Santonian (83 My) at the rate of 90 mg/gTOC/My. Hydrocarbon expulsion resumed later after the Santonian inversion in the Campanian (80 My) and Palaeocene (61 My) at the rate of 30 mg/gTOC/My and 10 mg/gTOC/My, respectively. The huge volume of hydrocarbons expelled at the end of Santonian from this source horizon could be due to early maturation under increased heat during the inversion. Subsequent expulsions occurred as the uplift gave way to subsidence in the Campano–Maastrichtian time. The current seepages observed in the basin at the nose of the anticlinorium could suggest a possible migration of the generated hydrocarbons through the open unconformity and fault planes.

Stratigraphy and depositional environments of the Mamfe Formation and its implication on the tectonosedimentary evolution of the Ikom-Mamfe Embayment, West Africa

AbstractA 42 m thick outcropping portion of the Mamfe Formation is subdivided into Manyu (31 m thick) and Kesham (11m thick) Members on the basis of textural, mineralogical and structural differences. The Manyu Member (Albian) consists of folded and indurated, medium to coarse grained arkosic sandstones and thickly laminated organic-rich shales deposited in a lacustrine environment. The Kesham Member (Cenomanian) consists of subarkoses intercalated with massive green shale and mudstone deposited in a fluvial environment. The change in depositional environment was tectonically controlled. The mid Cretaceous paleogeography of the embayment was governed by the NE-SW trending “Ikom ridge” which prevented marine incursion from adjacent the Benue Sea. Evaporites found within the basin were precipitated from ocean water that was periodically spilled by strong tides and storms across the ridge into the embayment. The filling-up of the embayment to base level in the Cenomanian resulted in a shift in the depositional center downstream to adjoining lower Benue Trough. Similarity in heavy mineral composition and maturity of the Cenomanian sandstones with recent clastics in the embayment indicates their derivation from the same source terrain and relatively stable tectonic and climatic conditions at the source area since the Cenomanian time.

Aeromagnetic Study of Oil Seepage along the Basement Flanks of Part of the Lower Benue Trough, South Eastern Nigeria

Aeromagnetic Study of Oil Seepage along the Basement Flanks of Part of the Lower Benue Trough, South Eastern Nigeria

Lithostratigraphy of the Maastrictian Nsukka Formation in the Anambra Basin, S.E Nigeria.

A detailed lithostratigraphic study of the Campanian-Maastrichtian formations (Early basal Campanian to Maastrichtian) from a borehole and wells in the Anambra Basin has been undertaken. The lithofacies of the Nsukka Formation comprises shales, sandy clay and sands. The formation was encountered at several wells in the Anambra Basin. The Elf Nigeria Ltd well numbers 447/1/AAR-1, 7/4/AO-1 and 447/6/NM-1 penetrated the entire Campanian-Maastrichtian sequences of the formations. A lectostratotype has been proposed from the lithological differences between the Mamu and Nsukka Formations for the proper definition of the stratigraphic unit. This is to satisfy the code of accepted stratigraphic practice which states that stratotype should be proposed for established formations. It will also help to reduce the general assumption on similarities in the stratigraphic nomenclature of some lithofacies in the Mamu and Nsukka Formations. I. Introduction The Anambra Basin became the site of major deposition following the Santonian folding in the southeastern Nigeria (Fig. 1). Compressional uplift of the Lower Benue Trough succession (Albian to Coniacian) along a NE - SW axis was accompanied by tectonic inversion and downwarping of the Anambra platform. Estimates of total sediments thickness in the Anambra Basin from gravity measurements range from 1000 - 4500 m (Ladipo et al., 1992), out of which between 3000 - 3500 m were deposited during the late Cretaceous (Upper Campanian to Maastrichtian). The aims of this study are to provide a detailed description of the Nsukka Formation and to propose a type section for its elucidation. No type section was designated when the unit was established rather been generalized as similar to the Mamu Formation. A type section is the best means of defining a stratigraphic unit (Hedberg, 1976).

FACIES EVALUATIONS AND PALEOENVIRONMENTAL RECONSTRUCTION OF THE TURONIAN NKALAGU FORMATION, SOUTH EASTERN NIGERIA

The Turonian Nkalagu Formation exposed at NIGERCEM (Nigerian Cement Company) within the Lower Benue Trough was studied in this work in order to determine and establish the lithostratigraphic successions and reconstruct the paleoenvironment of the deposition. Two major litho-facies were delineated. The first is matrix-supported bioclastic shell lag wackestone facies which account for about 70% of the carbonates. The second is a massive fossil-poor micritic limestone. However, using the fossil contents, five distinct micro-biofacies were recognized namely: massive lithoclastic floatstone, bioclastic wakestone, siliceous fossil-poor limestone, bioclastic (bivalve debris) wackestone and bioclastic packstone. The litho-clast consists of probably shallow water transported materials while still in various degrees of lithification from shelf into deeper basin. Many of the lithoclasts are sub-angular whereas others have rounded shape. Textural gradient was upward fining and algae were completely absent which is typical of shallow calcareous marine sediments of the photic zone. The trends of the textural characteristics fall in pattern correlatable with the different facies outlined in the study. Thus, the evidence from this study has put Nkalagu Formation as a deposition in shallow marine environment but later displaced into relatively deeper water, probably that of the off-shelf zone, by some sedimentary flow mechanisms.

Sedimentological Characterization of the Pre-Santonian Siliciclastic Deposits of Lower Benue Trough, Southeastern Nigeria

The study which involves forty-one (41) sandstone samples’ collected from the area delimited by longitudes 7°00'E and 8°30'E and latitudes 5°00'N and 6°30'N, entailed evaluating and characterizing these sediments. Detailed field studies to establish the lithostratigraphy was carried out and fresh samples were subjected to petrographic, granulometric and heavy mineral analyses. Field observations revealed that the sandstones of the Awi Formation are angular to subangular, feldspathic, and generally fines upward and Amaseri are calcareous, indurated and laterally extensive. Agbani Sandstone consists of thick vertical sequences of ferruginized and indurated sandstones. Granulometric study shows medium to coarse-grained (0.78-1.30?), poorly to moderately sorted (0.87-1.19?), coarse to strongly fine skewed (-0.17-0.57?) and very platykurtic to leptokurtic (0.66-1.31?). This indicates mostly high energy condition and this is characteristic of fluvial environments. Petrographic studies for Awi samples indicate that they are texturally immature to submature, subarkosic arenites from a continental block provenance, while Amaseri Sandstones are texturally submature sublitharenites from a recycled orogen provenance. Agbani Sandstones are texturally immature to mature subarkosic arenites, sublitharenites and quartz arenites. Heavy mineral studies revealed zircon, tourmaline, rutile and hornblende to be common to all formations, sillimanite, kyanite, garnet, and staurolite are mostly common to Awi and Amaseri Sandstones while Agbani Sandstone has a dominance apatite with spinel. This suite of minerals suggests an acid igneous rock to typical dynamothermal metamorphic rock sources. The ZTR indices (74.0-94.4%) indicate mineralogically mature sediments. The study established that the pre- Santonian siliciclastic sequences of the Lower Benue Trough are texturally immature to mature and compositionally submature to supermature products of a continental block and recycled orogenic provenance under humid climates and deposited in fluvial to tidally influenced fluvial environments with high to moderate energy conditions humid climates which are deposited under high to moderate energy conditions.

Hydrocarbon potential of Cretaceous sediments in the Lower and Middle Benue Trough, Nigeria: Insights from new source rock facies evaluation

The Nigerian Benue Trough is an intracratonic rift structure which evolution is related to the Early Cretaceous opening of the South Atlantic Ocean and the Gulf of Guinea. Previous hydrocarbon potential assessments of the successions in the trough revealed a number of organic rich intervals capable of yielding significant quantities of hydrocarbons in the Cretaceous sections. Stratigraphic continuity of these intervals suggests their potentials for hydrocarbons if thermally mature and both oil and gas can be generated.The present study have expanded on some previously reported source rock data of the Cretaceous formations in the Benue Trough by detailed mapping of the stratigraphic intervals with source rock potentials on the basis of their structural setting, lithologic characteristics, and depositional environments. Further characterization of the organic matter within the Cenomanian to Coniacian on one hand and the Campanian to Maastrichtian intervals were carried out to determine the geochemical character of the organic rich zones, their maturity and effectiveness to generate and expel hydrocarbons.In the Lower Benue Trough, mature facies of the Cenomanian to Turonian Eze–Aku Formation with a predominance of Types II and III kerogen, the Turonian to Coniacian Type III dominated Awgu Formation and the Type III dominated Lower Maastrichtian sub-bituminous coals of the Mamu Formation have proven potentials as oil and gas source rocks. In the Middle Benue Basin, the preserved mature intervals of the Awgu Formation shales and coals are good gas source rocks with some oil prone units in view of the predominating Type III kerogen. Targets for hydrocarbons generated by these source rock intervals should focus on the non-emergent Cretaceous reservoirs within the pre-Santonian successions whereas, the mature equivalents of the sub-bituminous coal facies would generate and charge both Upper Cretaceous reservoirs and possibly the sub-Niger Delta successions in the sub-surface.

Mineral and trace element composition of the Lokpanta oil shales in the Lower Benue Trough, Nigeria

The concentrations of minerals and trace elements in the Lokpanta oil shale from the Lower Benue Trough, Nigeria have been determined by X-ray diffraction (XRD) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), respectively. X-ray diffraction data were evaluated using the SIROQUANT™ interactive data processing system based on Rietveld interpretation methods. A new method of trace element determination in oil shale, involving LA-ICP-MS analysis of glass beads prepared by fusing oil shale ash on an iridium strip heater was used, and the accuracy of the method was assessed by including a standard shale reference material (SGR-1b) in the analysis program.The minerals in the raw oil shales are mainly quartz, calcite and clay minerals, with the latter being represented by kaolinite and interstratified illite/smectite. Ashes of the oil shale samples prepared at 815°C have quartz and (in some cases) illite as the dominant mineral phases, along with a significant proportion of amorphous materials. The Lokpanta oil shales are highly enriched in some potentially hazardous trace elements, including V, Cr and Ni, when compared with oil shales from other deposits around the world. The results obtained for the trace elements in the reference material show that the LA-ICP-MS method described in this study is very accurate and precise for the determination of a wide range of trace elements in oil shales.

Evaluation of hydrogeochemical characteristics of groundwater in parts of the lower Benue Trough, Nigeria

The aim of this work is to evaluate the hydrogeochemical characteristics of groundwater in parts of the lower Benue Through in Nigeria as well as to evaluate the variation in groundwater chemistry data and the suitability of the groundwater for drinking and other domestic purposes. This was based on chemical analyses of 44 water samples from existing wells and boreholes in the study area. From the statistical analysis (wide ranges, median and standard deviation), it is obvious that there are significant variations in the quality/composition of groundwater in the period of sampling. The calculated SAR, Na% and RSC values indicated that the water is of excellent to good quality and is suitable for irrigation. Na and HCO3 are dominant with respect to the chemical composition of the groundwater. On the basis of water chemistry, hydrochemical indices and factor analysis the dominant controls or processes affecting the distribution of geochemical variables in the study area have been shown to be water/rock interaction which is mainly controlled by carbonate and silicate dissolution as well as anthropogenic influence to a lesser extent. Additional processes include cation exchange reactions and reverse ion exchange to a minor extent.

Geophysical investigation in the lower Benue Trough of Nigeria using gravity method

Gravity survey in parts of Akataka and the environs in Abakaliki area of the Lower Benue trough was conducted over an area between longitudes 8°42′ E to 8°47′ E and latitudes 6°35′ N to 6°45 ′ N. Ninety eight gravity stations were occupied and the data collected were reduced relative to a base station. The geometry of the buried body was determined from the interpretation of residual anomaly data. Spherical model was assumed for the anomalous body based on the local geology and the residual gravity anomaly. A density contrast of 0.32 gcm-3 was calculated for the body. The residualized and interpreted gravity profiles yielded results that reveal low Bouguer gravity anomalies with magnitudes ranging from –2.5 to 3.8 mgals and with abrupt changes at intervals thereby suggesting a fault. The low-density anomalous body suspected to be salt deposit was buried at depths of between 868 and 2618 m. Its diameter ranging between 2,126 and 3,322 m, mass ranges from 1.18 to 4.52 × 1013 kg. The low Bouguer gravity anomaly over the area suggests a zone of basic to intermediate igneous intrusions, deep basement and crustal thinning. These calculated values are in agreement with other works carried out within Abakaliki areas in particular and the Lower Benue trough in general. Key words: Gravity survey, profiles, Benue trough, intrusions, salt deposit, density.

Organic geochemical evaluation of the oil/gas-generative potential of organic matter in Cretaceous strata from the Lower Benue Trough, Nigeria

An analytical procedure involving Rock-Eval pyrolysis of whole-rocks was adopted on fresh outcrop samples covering the three lithostratigraphic units in the Afikpo Basin of the Lower Benue Trough. Three petroleum systems are present in the Cretaceous delta frame: the Asu-River Group, the Eze-Aku Group and proto-Niger Delta sequences. The Afikpo Basin has been correlated to three petroleum systems in the Lower Congo Basin, Niger Delta and the Anambra Basin.

Hydrocarbon-Generative Potential of Coal and Interbedded Shale of Mamu Formation, Benue Trough, Nigeria

Coal and its interbedded shale samples were collected from Okaba, Onyeama, and Okpara seams in the Mamu Formation, Lower Benue Trough, Nigeria. In the present study, source rock evaluation and biomarker distribution in the samples were investigated by Rock-Eval pyrolysis, vitrinite reflectance measurement, and gas chromatography–mass spectrometry (GC-MS) analysis. All of the samples analyzed contained the minimum of 0.5 wt.% and 2 mg/g of total organic carbon (TOC) and genetic potential (GP) respectively of organic matter required to serve as good source rock for oil and gas. Several plots from the Rock-Eval pyrolysis classified the organic matter in the samples as type II/III kerogen. The abundance of hopanes, homohopanes (C31–C35), benzohopanes, and C29 steranes in most of the samples indicates terrigenous materials, phytoplankton, and cyanobacteria contributions to the organic matter that formed the coal. High Pr/Ph ratio (1.73–12.47) and n-alkane distribution in the samples showed that Mamu samples consisted of terrestrial organic matter with marine incursion deposited under oxic/suboxic-oxic in lacustrine-fluvial/deltaic environments. The distribution patterns of C32–C35 benzohopanes in the samples confirmed the redox condition of organic matter deposition within the formation. The occurrence of olean-18-ene, olean-13 (18)-ene, and olean-12-ene in Okaba samples favors terrestrial organic matter deposited in lacustrine-fluvial/deltaic environment. The vitrinite reflectance values (0.48–0.60% Ro) and all the maturity parameters derived from the Rock-Eval analysis and biomarker distributions showed that Okaba samples are immature, whereas Okpara and Onyeama are at the beginning of the oil window.

Brittle deformation in the Afikpo Basin (Southeast Nigeria): Evidence for a terminal Cretaceous extensional regime in the Lower Benue Trough, Nigeria

This paper deals with the regional and structural framework of the Cretaceous rocks in the Afikpo Basin located in the southeastern part of the Lower Benue Trough. Results from regional tectonics are presented together with those of the microtectonic analysis of microfaults in the Owutu-Afikpo-Adadama area in the basin.

Origin of carbonate cements in Cretaceous sandstones from lower Benue Trough, Nigeria: Evidence from petrography and stable isotope composition

Beds of authigenic carbonates were identified from three Cretaceous lithostratigraphic units of the Lower Benue Trough, Nigeria. Three carbonate lithologies were recognized by petrographic analysis in the study area. Carbonate-cemented sandstones are dominated by ferroan calcite cements with subordinate amount of siderite and dolomite/ankerite cements formed throughout the diagenetic history of the Asu River Group, Eze-Aku Group and Campano-Maastrichtian proto-Niger Delta sequences. δ18O for the cements range from -4.22 to -6.91‰(PDB) in Asu River Group; -5.23 to 12.66‰(PDB) in Eze-Aku and -4.45 to 6.89‰(PDB) in Campano- Maastrichtian proto-Niger Delta sandstones. δ13C values averaged -5.23‰ PDB for Asu River Group; -11.03‰ PDB and -5.88‰ PDB for Eze-Aku and Campano-Maastrichtian proto-Niger Delta sandstones. Petrography and geochemical data suggest that the mixing of meteoric and marine waters in the sediments caused dolomitization in Asu River group and Eze-Aku Group sediments while deep burial diagenesis under marine depositional environment precipitated calcite cements. Both authigenic and biogenic carbonate cements with low and high δ13C values exits in the sandstones analyzed. The low δ13C values of Asu River Group, Eze-Aku and Campano-Maastrichtian cements that range from 0 to 2.98 ‰ suggest that they are shallow water carbonates. Biogenic carbonate cements were also identified in some of the sandstones. The carbonate cements were formed under the influence of both meteoric- and marine diagenetic conditions which changed in time and space. The dolomitized rocks occur just below erosion surfaces on the continental sediments and on which shallow marine facies are developed.

Magnetic anomaly trends and spacing patterns in parts of the lower Benue trough, Nogeria

Magnetic anomaly trends and spacing patterns in parts of the lower Benue trough, Nogeria

A Tectonic Implication Of The Eruption Of Pyroclastics In Uturu, Southern Benue Trough, Southeast Nigeria

The origin of the Benue Trough is linked to rifting associated with the separation of South America from Africa in the Cretaceous times. The vast igneous activities in the trough are thought to either precede the separation of the two continents or post-date Albian sediments deposited in the trough after the separation. Exposures of pyroclastics within flatland in Uturu, east of Okigwe, were studied with a view to determining the implication of the eruption that emplaced the pyroclastics on the tectonic evolution of the Lower Benue Trough. Field expressions show that the pyroclastics erupted parallel to the axial plane of the Abakiliki anticlinorium in NE-SW direction and are spatially associated with shales of the Asu River Group and Nkporo Shale. Mud fragments of diverse sizes (1cm-20cm) and shapes of the host Asu River Group are incorporated in the pyroclastics. The sizes of the fragments of the pyroclastics fall mainly within the range of tuff and lapilli composed of mainly pyroxene, plagioclase, melilite and opaque minerals. The Nkporo Shales form cover unit over the pyroclastics and do not show any effect of the volcanism on them. The stratigraphic relationship between the pyroclastics and the surrounding sedimentary units shows that the pyroclastics erupted after the deposition of Asu River Group shales (mid-Albian) but terminated before the deposition of the Nkporo Shales. This corresponds to period between Cenomanian and Santonian and suggests a link to the tectonic events that post-dated the separation of South America from Africa. Keywords : Benue Trough, Tectonism, Abakiliki anticlinorium, pyroclastics, lapilli. Global Journal of Geological Sciences Vol. 6 (2) 2008: pp. 123-128

A report on the occurrence of Albian–Cenomanian elater-bearing pollen in Nasara-1 well, Upper Benue Trough, Nigeria: Biostratigraphic and palaeoclimatological implications

Elater-bearing pollen including Elaterocolpites castelainii, Elateroplicites africaensis, Elaterosporites klaszii, Elaterosporites protensus and Senegalosporites petrobrasi were recovered from the Yolde Formation and the Bima Sandstone penetrated by the Nasara-1 well. Although some elater-bearing species have previously been documented, this is the first report of the occurrence of these particular species in the Upper Benue Trough. The assemblage is interpreted as Albian to Middle Cenomanian in age, and indicates possible arid to semi-arid palaeoclimatic conditions for these periods in the Upper Benue Trough. Earlier similar species were interpreted as Upper Albian in the Lower Benue Trough of Nigeria located to the southwest, and as Albian to Cenomanian in other localities within the Africa–South America (ASA) palynofloral province. This therefore allows a palynostratigraphic correlation of the Bima Sandstone and the Yolde Formation of the Upper Benue Trough with the Albian to Cenomanian sequences of the Lower Benue Trough and other localities within the ASA palynofloral province.