Andrew Horbury - Academia.edu (original) (raw)

Papers by Andrew Horbury

Sedimentary Geology, Dec 1, 1989

... Meteoric phreatic diagenesis in cyclic late Dinantian carbonates, northwest England ANDREW D.... more ... Meteoric phreatic diagenesis in cyclic late Dinantian carbonates, northwest England ANDREW D. HORBURY 1 and ANTHONY E. ADAMS ... these represent periods of rapid tectonically-controlled subsidence fol-lowed by upwards shoaling in response to sedi-mentary processes ...

Sedimentary Geology, Aug 1, 1992

Abstract Early lithified peloid cementstone-palaeoberesellid buildups of a previously undescribed... more Abstract Early lithified peloid cementstone-palaeoberesellid buildups of a previously undescribed type of Late Asbian (Late Dinantian) age occur near Carnforth in North Lancashire. One of these buildups formed a 1–2 m topographic feature and accreted a total thickness of 11 m before growth stopped. The buildup occurs near to a windward shelf margin which is grainstone shoal dominated. The buildup and associated sediments comprise three main facies: (1) core facies of the palaeoberesellid Kamaenella and marine peloidal cements; (2) flanking crinoidal-bryozoan facies comprising grainstone, packstone and conglomeratic textures in which reworked core facies intraclasts are present; and (3) shoal-lagoonal facies typical of the shelf margin. During the Asbian, Kamaenella was a successful coloniser of shallow, moderate- to low-energy, shelf environments subject to frequent and rapid sea-level changes, but it appears to have been only an opportunistic bioherm builder. The presence of rounded core-facies clasts in the flanking facies indicates that peloidal cementation lithified the buildup. These cements probably developed in response to microbial activity in low- to moderate-energy settings where framebuilder growth and sedimentation rates were low. Vertical growth of the buildup suggests that deposition kept pace with a rise in relative sea level.

Proceedings, 2015

The Triassic-Early Jurassic stratigraphy of the Arabian Plate is notably different to all underly... more The Triassic-Early Jurassic stratigraphy of the Arabian Plate is notably different to all underlying and overlying units. Several unique features include an often thick, very strongly vertically heterogeneous and often thin-bedded stratigraphy dominated by evaporites, restricted facies carbonates, and paralic siliciclastics. MFS are marked by open marine carbonates, and may be traced laterally across the plate. In general these record very low energy environments that are faunally impoverished; carbonates dominate intrabasinal and basin flank highs. Evaporites are concentrated in depocentres and are dominated by sulphates. Siliciclastics fringe the basin system. This is the least prospective of the post-Carboniferous units; sporadic carbonate reservoirs are usually thin, high-energy dolomitized oolites. Other reservoirs are thicker continental clastics. Source rocks have an evaporitic to locally lacustrine signature and yield generally light oils, but are mostly localised in depocentres where reservoir rocks are often lacking; whilst sealing evaporites are also often restricted to basinal areas whilst being absent on paleohighs. Future success within this stratigraphy will mainly depend upon our ability to predict the distribution and thicknesses of reservoir units within areas of reasonable burial depth; whilst the complex stratigraphy and regional thickness changes offer the possibility of locating stratigraphically trapped reserves.

Seventh Arabian Plate Geology Workshop: Pre-Cambrian to Paleozoic Petroleum Systems in the Arabian Plate, 2018

Only a few wells were drilled through the Pre-Khuff section in Kuwait and therefore limited data ... more Only a few wells were drilled through the Pre-Khuff section in Kuwait and therefore limited data is available. A composite pre-Khuff stratigraphic section is attempted from this data by utilizing age dating data, the distinctive heavy mineral assemblages and by correlating with regional analogues. In north Kuwait, the oldest sediments encountered are evaporites overlain by carbonates likely belonging to the Hormuz Group of Infra-Cambrian to Early Cambrian age. The Permo-Carboniferous Unayzah Formation unconformably overlies these carbonates. In south Kuwait these strata are missing and the Upper Permian Khuff Formation directly overlies on the older sediments. The oldest sediments in south Kuwait consist of deformed, varve like deposits of finely laminated siltstone and mudstone probably belonging to the Murdama Group of Lower Ediacaran age. The overlying Rubtayn / Mataar Formation of possible latest Precambrian (Ediacaran) to earliest Cambrian age is made up of polymictic conglomer...

Second Arabian Plate Geology Workshop 2010, 2010

Quarterly Journal of Engineering Geology, 1998

Abstract Freshly quarried Doulting limestone of Jurassic age differs in terms of mineralogy and p... more Abstract Freshly quarried Doulting limestone of Jurassic age differs in terms of mineralogy and porosity compared to the decayed stone of Wells Cathedral, Somerset, UK. Stones from both localities contain allochems including ooids, peloids, extraclasts (reworked Carboniferous limestone) and bioclasts. Sparry calcite cement is present as twinned, syntaxial, overgrowths nucleated onto crinoid ossicles with high Fe content due to extensive burial cementation. The Fe content in specific phases determines the weathering stability of the rock on the building. The decayed stone shows the development of porosity which is parallel to the weathered surface, mobilization of Fe into a hard layer near the surface and incidences of high concentrations of SO42-, NO3- and Cl-. Despite low concentrations of SO2 present in the atmosphere at the time of the study, the extent of stone decay and composition of crustal deposits implies that SO2 pollution may have been greater in the past, with stone currently affected by gypsum salts formed during earlier pollution episodes.

Proceedings of the Geologists' Association, 1990

Dinantian sediments south of the Lake District, northwest England, outcrop in an approximate stri... more Dinantian sediments south of the Lake District, northwest England, outcrop in an approximate strike section along the depositional surface of a tilted fault block. Using outcrop information, together with known facies distributions from other areas, it is possible to reconstruct a model for Dinantian sedimentation from north Cumbria southwards across the Lake District to northern Morecambe Bay. Two major tectono-sedimentary cycles are recognised, each characterised by three stages which can be related to tectonic activity in northern Britain as a whole. Episodes of non-deposition in Cumbria (late Chadian-early Arundian and late Holkerian-early Asbian) may relate to emergence of footwall highs and are coincident with the onset of rifting in basinal areas. These were followed by episodes of intermediate to rapid subsidence producing deepening successions in south Cumbria (mid Arundian and late Asbian-early Brigantian). During periods of tectonic quiescence, slow subsidence as a result of post-rift sag resulted in re-establishment of shallow ramp or platform facies (late Arundian-Holkerian and late Brigantian-Namurian). Thickness variations along the depositional slope in south Cumbria are attributed to variations in basement response during rifting, perhaps as a result of movement on transfer faults.

Semi-quantitative analysis of allochems from the Urswick Limestone Formation (Asbian) of the sout... more Semi-quantitative analysis of allochems from the Urswick Limestone Formation (Asbian) of the southern Lake District area of northern England has revealed a distinctive cyclicity of the microfacies. Cycle-top grainstone microfacies contain an algal flora comprising Koninckopora, Anatolipora and Polymorphocodium, with Girvanella filaments and Ortonella lumps. Other allochems include intraclasts, large peloids and thick-shelled bivalves and gastropods. The middles of cycles are mostly packstones and micro-grainstones and contain allochems dominated by small peloids and the algae Kamaena, Kamaenella and Epistacheoides, with the microproblematicum Ungdarella and relatively high abundances of micritic-walled foraminifera such as endothyrids. Cycle bases contain a diverse algal assemblage including Coelosporella and Stacheoides, with other allochems represented by trilobites, ostracodes, Saccamminopsis, foraminifera such as Archaediscidae, the base late Asbian guide Howchinia, the base ear...

Iraqi Geological Journal, 2020

The Palaeozoic basin of Jordan and Iraq occupies the NW part of the Arabian Plate. The Lower Pala... more The Palaeozoic basin of Jordan and Iraq occupies the NW part of the Arabian Plate. The Lower Palaeozoic succession is the most under-explored succession in Iraq, particularly in western Iraq where it is the most promising target for future exploration. The western Iraqi subsurface and Jordanian geology are characterized by similar major chrono-stratigraphic rock units. In western Iraq, the Akkas-1 well is the only gas and condensate discovery in sandstone reservoirs of Early Silurian and Late Ordovician age. Lower Silurian sandstones of the Akkas Formation are an oil reservoir characterized by an average porosity of 6.5% and permeability of 0.2 mD. Underlying Upper Ordovician sandstones of the upper part of the Khabour Formation are also reservoir, but for sweet gas and condensate. The latter are comparable to both the Risha and Wadi Sirhan discoveries in Jordan. Several deeper potential sandstone reservoirs (of older Ordovician and Cambrian ages) are also present across the region. Equivalent Ordovician age Jordanian reservoirs are primarily developed in homogeneous, highly mature quartz arenites of storm-dominated clastic-shelf stratigraphies. Within the Risha Field and the Wadi Sirhan area, are also end-Ordovician (Hirnantian) glaciogenic and periglacial sandstones with more variable reservoir quality characteristics compared to the underlying quartz arenites. These often comprise highly immature arkoses (as diamictites), which provide a mineralogically much less stable assemblage in which there is a possibility of developing secondary porosity. Almost similar sandstones were also reported from the upper part of the Khabour Formation in the Akkas Field of western Iraq. Sedimentological and XRD mineralogical studies suggest that diagenesis is an important factor in developing of reservoir quality. Nevertheless, reservoir quality is a major exploration risk where burial was significant that led to quartz overgrowth and clay cementation. It is notable that some sandstone reservoirs have chlorite-clay

GEO 2010, 2010

The Cenomanian-early Turonian Mishrif Formation reservoir of the Mesopotamian Basin accommodates ... more The Cenomanian-early Turonian Mishrif Formation reservoir of the Mesopotamian Basin accommodates more than one third of the proven Iraqi oil reserves within rudist-bearing stratigraphic units. Difficulty in predicting the presence of reservoir units is due to the complex palaeogeography. Extensive accumulation of rudist banks occurred along an exterior shelf margin of the basin along an axis that runs from Hamrin to Badra and southeast of that, with interior margins around an intrashelf basin. Buildups were stacked or sometimes shingled as thicker shallowing-up cycles of several smaller-scale accommodation cycles. As a result, each field shows different combinations of pay zones, barriers and seal geometries.

Sedimentary Geology, 1989

Sedimentary Geology, 1992

Proceedings of the Yorkshire Geological Society, 1989

SUMMARY Circular to elliptical pits with raised rims, up to 80 cm across, occur on a palaeokarsti... more SUMMARY Circular to elliptical pits with raised rims, up to 80 cm across, occur on a palaeokarstic surface in the Asbian Urswick Limestone near Grange-over-Sands, Cumbria. The raised rims consist of laminated micritic carbonate resembling laminar calcrete but with sub-vertical laminae. The pits and their raised rims are interpreted as structures formed by tree roots (rhizocretions). Their presence indicates subaerial exposure for sufficient time and under conditions favourable for the growth of mature trees.

Marine and Petroleum Geology, 2000

Diagenetic studies of sedimentary rocks using cold cathodoluminescence (CL) microscopy have been ... more Diagenetic studies of sedimentary rocks using cold cathodoluminescence (CL) microscopy have been severely limited because of the very low intensity of visible luminescent emissions, which required long photographic exposure times, and because of the difficulty in obtaining quantitative data from CL observations. The solution to this problem is to fit the microscope with a high-sensitivity digital colour video camera linked to a computer with image enhancement and image analysis software. The new technique described in this paper: • produces digital CL images of consistent high quality, both quickly and cheaply; • controls the capture and editing of CL images, to reveal detailed textural information even from minerals exhibiting low level luminescence such as quartz; • acquires quantitative information on pore systems and the abundance of cement zones from CL images. Examples are presented to demonstrate the high quality of images produced in this way and the range of uses to which the new technique can be applied. The ability to image exactly the same field of view in both plane polarised light and CL is a particular advantage. Image analysis techniques have been developed to give a statistical characterisation of both pore systems and cement phases that infill them. The abundance of contrasting cement zones seen in CL can be measured and the abundance of cement phases can be mapped across a reservoir. The history of porosity occlusion can be reconstructed quantitatively and integrated with burial history and hydrocarbon migration. Porosity can be measured accurately and, since the technique obtains data on pore geometry as well as abundance, the pore system can be characterised by pore size distributions and pseudo-capillary pressure curves. This also opens the possibility of estimating permeability from thin sections.

Lethaia, 1992

Palaeoberesellids are septate, tubular microfossils usually attributed to the green algae. They o... more Palaeoberesellids are septate, tubular microfossils usually attributed to the green algae. They occur widely in Upper Palaeozoic carbonate sediments, where they are normally seen in thin sections as cross-sections or short lengths of thallus. Detailed study of late Dinantian (Asbian) limestones from two areas of the UK. South Wales and northwest England, show that palaeoberesellids. particularly Kamaenelli~. are the most important carbonate-producing organisms in shallow. low to moderate energy environments and supplied grains to higher energy environments as a result of storm breakage and transport. Where palaeoberesellids were the dominant organisms they formed low-growing 'thlckets' on the sea-floor which trapped fine sediment. to create a hafflestone texture. The late Dinantian was a time of great instability with rapid sea-level changes. Palaeoberesellids were opportunistic organisms which thrived in such an environment. The volume of carbonate produced by these organisms in shallow water may have been a contributory factor in the progradation of shallow marine facies and the establishment of relatively flat-topped shelves from the ramps of the Early Dinantian. 0 Asbiun, Chlorophyta. Dinuntian, Green Algoe, KMAENA, K A M A F N E L L I , palaeohereselliiis. Airrhon)' E. Adanis. Depurrmt.nr of Geolog),. llitri~ersir~~ o/ Manche.~rer. Mnrrchesler. M 13 YPL, UK:

Journal of Petroleum Geology, 2010

$Research paper thumbnail of Stratigraphic architecture and fracture-controlled dolomitization of the Cretaceous Khami and Bangestan groups: an outcrop case study, Zagros Mountains, Iran$

Geological Society, London, Special Publications, 2010

The Barremian–Aptian upper Khami Group and Albian–Campanian Bangestan Group have been studied at ... more The Barremian–Aptian upper Khami Group and Albian–Campanian Bangestan Group have been studied at outcrop in Lurestan, SW Iran. The upper Khami Group comprises a thin deltaic wedge (Gadvan Fm) transgressively overlain by shelfal carbonates (Dariyan Fm). The Dariyan Fm can be divided into lower and upper units separated by a major intra-Aptian fracture-controlled karst. The top of the Daryian Fm is capped by the Arabian plate-wide Aptian–Albian unconformity. The overlying Bangestan Group includes the Kazhdumi, Sarvak, Surgah and Ilam formations. The Kazhdumi Fm represents a mixed carbonate-clastic intrashelf basin succession, and passes laterally (towards the NE) into a low-angle Orbitolina-dominated muddy carbonate ramp/shoal (Mauddud Mbr). The Mauddud Mbr is capped by an angular unconformity and karst of latest Albian–earliest Cenomanian age. The overlying Sarvak Fm comprises both low-angle ramp and steeper dipping (5–10°) carbonate shelf/platform systems. Three regionally extensive...