Shallowing-upward Carbonate Cycles Research Articles

Multiple scales of mechanical stratification and décollement fold kinematics, Sierra Madre Oriental foreland, northeast Mexico

Regional- to outcrop-scale stratigraphic relationships within Mesozoic shallow marine carbonates and clastics at Sierra del Fraile anticlinorium in northeast Mexico play an important role in controlling the deformation distribution, strain history and kinematics during folding. Structural analyses of meso- and microscopic deformation features from all stratigraphic and structural positions within the anticlinorium allow for the delineation of five regional-scale lithotectonic units. Kilometer- to decameter-scale stacking patterns of the preorogenic succession and the meter-scale stacking patterns of individual shallowing-upward carbonate cycles are shown to influence deformation kinematics in predictable ways. Mesoscopic faults and cleavage patterns along with penetrative strain from anisotropy of magnetic susceptibility (AMS) fabrics constrain fold kinematics as progressive limb rotation about pinned anticlinal and synclinal hinges with constant limb length and a mobile basal décollement horizon within the evaporites of the Minas Viejas Formation that core the anticlinorium. AMS fabrics are shown to be a useful proxy for nascent penetrative strain orientations in sedimentary rocks. Macroscopic differences in strain suggest strong lithologic facies control responding to differences in bed thickness, grain size and carbonate content. At the regional scale, variation in deformation between the lithotectonic units identifies décollement horizons coincident with lithotectonic boundaries in the Minas Viejas, upper Taraises, and Parras Formations.

Shallowing-Upward Carbonate Cycles in the Belingwe Greenstone Belt, Zimbabwe: A Record of Archean Sea-Level Oscillations

ABSTRACT Shallowing-upward carbonate cycles in the 2650 Ma Cheshire Formation, Belingwe greenstone belt (Zimbabwe), closely resemble their Proterozoic and Phanerozoic counterparts. The cycles form part of a karstified carbonate-ramp sequence that is overlain by, and grades basinward into, siliciclastic turbidites. A single section of 74 cycles (1.5 m average thickness) was studied in detail. Two basic cycle types are recognized, both with an asymmetric facies stacking pattern. One cycle type contains open marine, subtidal shale at the base. Shale is intercalated with storm-generated sandstone and grainstone beds that become more common and thicken upward, indicating progressive shallowing. Wave-rippled ooid-intraclast grainstone beds and bedsets overlie shale or form the base of the second cycle type. Grainstone formed at or above fair-weather wave base as shoreface sand sheets in an agitated, shallow subtidal setting. Microbial laminites constitute the top of both cycle types and are interpreted as peritidal deposits. In the upper part of the studied section, microbial boundstones with aragonite pseudomorphs are intercalated with, or overlie, laminites and formed in a supratidal environment. The vertical facies distribution within a cycle is indicative of rapid submergence followed by gradual shallowing of relative sea level. High-frequency eustatic sea-level changes are favored over an autocyclic mechanism and tectonically induced allocyclicity as the controlling mechanism for the cyclicity. Hierarchies of stratigraphic cyclicity occur on different scales and may be a result of the combined effects of several orders of sea-level oscillations. Cycle recurrence ratios correspond well to the Milankovitch frequencies calculated for the Late Archean, suggesting that orbital climatic forcing may have been in operation in Archean times.

Cyclic sedimentation across a Middle Ordovician carbonate ramp (Duwibong Formation), Korea

The Middle Ordovician Duwibong Formation (about 100 m thick), Korea, comprises various lithotypes deposited across a carbonate ramp. Their stacking patterns constitute several kinds of meter-scale, shallowing-upward carbonate cycles. Lithofacies associations are grouped into four depositional facies: deep- to mid-ramp, shoal-complex, lagoonal, and tidal-flat facies. These facies are composed of distinctive depositional cycles: deep subtidal, shallow subtidal, restricted marine, and peritidal cycles, respectively. The subtidal cycles are capped by subtidal lithofacies and indicate incomplete shallowing to the peritidal zone. The restricted marine and peritidal cycles are capped by tidal flat lithofacies and show evidence of subaerial exposure. These cycles were formed by higher frequency sea-level fluctuations with durations of 120 ky (fifth order), which were superimposed on the longer term sea-level events, and by sediment redistribution by storm-induced currents and waves. The stratigraphic succession of the Duwibong Formation represents a general regressive trend. The vertical facies change records the transition from a deep- to mid-ramp to shoal, to lagoon, into a peritidal zone. The depositional system of the Duwibong Formation was influenced by frequent storms, especially on the deep ramp to mid-ramp seaward of ooid shoals. The storm deposits comprise about 20% of the Duwibong sequence.

Lithostratigraphic classification and depositional history of the Permian rocks in Al Qasim Province, Saudi Arabia

Surface and subsurface investigations on the Permian rocks (Khuff Formation) in Al Qasim Province, Saudi Arabia led to the subdivision of these rocks into two formal rock units. The lower is the Sark Formation and the upper is the Al Watah Formation. The Sark Formation consists of carbonates with interbeds of claystones and marl. Its type locality lies south of Unayzah (lat. 26° 02′ N and long.44° 00′ E). The Al Watah comprises two members, the lower is the Midhnab Shale Member and the upper is the Khartam Limestone Member. The type section of the Al Watah Formation lies at Jal Al Watah (lat. 26° 30′N and long. 44° 02′ E).The Sark Formation exhibits facies change along the strike of the Arabian basin. Southeastwards at Al Arid, the environment was coastal marine, while at Al Mulayh the environment was quiet marine shelf, where the facies are fine-grained wackestones. In Al Qasim Province, the environment is open marine platform where the sequence consists of shallowing-upward carbonate cycles which were deposited under subtidal-supratidal conditions. The Al Watah Formation also shows gradual transition from one environment to another along southeast-northwest direction. At Al Arid, the depositional environment is coastal marine which changes northwestwards at Al Mulayh to lagoonal shelf since the facies are mostly of fine-grained dolostones. In Al Qasim Province, deeper open marine is recognized depositing the Midhnab Shale Member in low sea level and the Khartam Limestone Member in submerged platform (subtidal zone).

Three-Dimensional Architecture of Shallowing-Upward Carbonate Cycles: Middle and Upper Cambrian Waterfowl Formation, Canmore, Alberta

ABSTRACT Peritidal carbonates of the Middle and Upper Cambrian Waterfowl Formation are 32 m thick near Canmore, Alberta, where they are exposed in a nearly continuous, 5 km long outcrop belt. The formation comprises eight facies here: thin bedded dolomite mudstone; peloidal grainstone; thrombolites-stromatolites in grainstone; crinkly laminated dolomite mudstone; planar laminated dolomite mudstone; wavy bedded grainstone-mudstone; mudcracked, brecciated dolomite mudstone, and shale. Closely spaced measured sections, photomosaics, and walking out beds established the later variability of these facies in the lower 21 m of the outcrop belt. Here there are 14 fining-upward sequences 1 to 2.5 m thick and two intervals of finer grained facies 0.7 and 2.5 m thick all arranged in a laterally traceable, layer-cake arrangement. Many of the fining-upward sequences contain lateral accretion bedding and channel fill deposits in the basal grainstone. Thrombolites-stromatolites, crinkly laminites, and planar laminites generally cap sequences. Four mound-like thickenings of either ooid grainstone or stromatolite are found within fining-upward sequences or the thicker mudstone interval. Salt casts occur in rocks to the west-northwest of the mounds. Grainstones that constitute the bases of the fining-upward sequences represent the deposits of laterally migrating tidal channels. Channel-fills represent abandoned channels and the finer-grained, cryptmicrobial upper portions of sequences are analogous to overbank deposits. The mounds are interpreted as beach and stromatolitic barriers behind which pond deposits and channel deposits accumulated by staggered offlap. RESUME Les roches carbonatees peritidales de la formation Waterfowl du Cambrien moyen et superieur ont une epaisseur de 32 m pres de Canmore, Alberta, ou elles sont exposees dans une ceinture d'affleurements presque continue et longue de 5 km. La formation consiste ici en huit facies: pelite dolomitique finement stratifiee; grainstone fait de pellets; thrombolites-stromatolites dans un grainstone; pelite dolomitique en laminations froissees; pelite dolomitique en laminations planes; grainstone-pelite en lits ondules; pelite dolomitique brechique et fissuree par dessication, et schiste argileux. Des coupes mesurees en espacement serre, des photomosaiques, et le jallonnement des lits etablirent la variabilite de ces facies dans les 21 m inferieurs de la ceinture d'affleurements. On trouve ici 14 sequences dont la granulometrie diminue vers le haut de l a 2,5 m d'epaisseur, et deux intervalles de facies a grain plus fin epais de 0,7 a 2,5 m, tous disposes de facon a etre retrouve lateralement en couches superposees. Plusieurs des sequences dont la granulometrie diminue vers le haut remferment des lits formes par accretion laterale et des alluvions sedimentes dans le chenal, dans le grainstone a la base. Des thrombolites-stromatolites, des laminites froissees, et des laminites planes couronnent generalement les sequences. Quatre epaississements a l'apparence de monticules, composes soit de grainstone a oolite ou de stromatolites se trouvent dans les sequences dont la granulometrie diminue vers le haut ou dans les intervalles de pelite plus epais. Des moules de sel se retrouvent dans des roches en direction ouest-nord-ouest des monticules. Les grainstones qui composent la base des sequences dont la granulometrie diminue vers le haut represent les depots de migration laterale de chenaux de maree. Les alluvions de chenal representent des chenaux abandonnes et les parties superieures a grain plus fin et crypto-microbiennes des sequences sont analogues a des depots alluviaux d'inondation. On interprete les monticules comme etant des cordons littoraux ou des barrieres stromatolitiques derriere lesquelles des depots d'etang et de chenal s'accumulerent en >.

Mixed Siliciclastic and Carbonate Sedimentation Within Spar Mountain Member of Ste. Genevieve Limestone, Hamilton County, Illinois: ABSTRACT

The Spar Mountain Member of the Ste. Genevieve Limestone (middle Mississippian) in Hamilton County, Illinois, consists of 40-60 ft (12-18 m) of interbedded limestones, shales, and sandstones. Five cores and 1,400 electric logs were used to delineate two shallowing-upward carbonate cycles and 2 major clastic pulses within the Spar Mountain. Eight lithofacies representing 6 depositional environments were identified. They are: (A) echinoderm-brachiopod dolomicstone to packstone (outer ramp), (B) ooid-peloidal grainstone (intermediate ramp), (C) skeletal grainstone (intermediate ramp), (D) ooid-molluscan-intraclastic wackestone to grainstone (inner ramp), (E) pelletal-skeletal wackestone (inner ramp), (F) quartzarenite (channelized nearshore), (G) quartz-sublithic arenite to acke (delta platform), and (H) quartz mudstone (prodelta, delta platform). Deposition occurred on a southwest-dipping carbonate ramp, with siliciclastic sediments originating from the northeast. The sequence of facies and their inferred depositional environments record 2 major progradational episodes. Oolitic facies are interpreted to be of tidal-bar belt origin and quartzarenite facies are interpreted to be of delta-distributary channel origin. Their distribution is partially controlled by antecedent and syndepositional topography. Many of these paleotopographic highs are positive features today and yield pinch-out stratigraphic relationships. Paleogeographic reconstructions demonstrate that the primary control on facies distribution was the position of the delta proper along strike. However, depositional topography also influenced sedimentation, particular y in the sand-sized fraction. Using this concept, better prediction of underlying porous buildups (ooid shoals) is possible if thickness of the overlying siliciclastic is known. Within buildups, a complex diagenetic history complicates the distribution of porosity. End_of_Article - Last_Page 301------------