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The recognition and correlation of stratigraphic surfaces which represent changes in depositional trends in sedimentary rocks. Such changes were generated by the interplay of sedimentation, erosion, and oscillating base level and are now determined by sedimentological analysis and geometric relationships.
- Three dimensional assemblages of lithofacies, genetically linked by active or inferred processes and environments.
- they represent the sedimentary product of associated depositional environments. They grade laterally into coeval systems, forming logical associations of paleo-geomorphic elements.
- A linkage of contemporaneous depositional systems, forming the subdivision of a sequence.
- includes all strata accumulated across the basin during a particular stage of shoreline shifts.
- interpreted based on stratal stacking patterns, position within the sequence, and types of bounding surfaces. The timing of systems tracts is inferred relative to a curve that describes the base-level fluctuations at the shoreline.
- A relatively conformable succession of genetically related strata bounded by unconformities or their correlative conformities.
- Correspond to full stratigraphic cycles of changing depositional trends. The conformable or unconformable character of the bounding surfaces is not an issue in the process of sequence delineation, nor the degree of preservation of the sequence.
Sequences and systems tracts are bounded by what?
Key stratigraphic surfaces that signify specific events in the depositional history of the basin. Such surfaces may be conformable or unconformable, and mark changes in the sedimentation regime across the boundary.
A mappable body of rock that is defined and identified on the basis of its bounding discontinuities.
=Significant hiatus +/- erosion (usually with erosion). A substantial break or gap in the geological record. It normally implies uplift and erosion with loss of the previously formed record. Relationship between rock strata in contact, characterized by a lack of continuity in deposition, and corresponding to a period of nondeposition, weathering, or esp. Erosion prior to the deposition of the younger beds.
- an unconformity in which the bedding planes above and below the break are essentially parallel, including a significant interruption in the orderly sequence of sedimentary rocks, generally by a considerable interval of erosion, and usually marked by a visible and irregular or uneven erosion surface of appreciable relief.
- =hiatus+/-erosion (no discernible erosion)
- An obscure or uncertain unconformity in which no erosion surface is discernible, and in which the beds above and below the bread are parallel.
- =Hiatus, erosion, and tilt.
- An unconformity between two groups of rocks whose bedding planes are not parallel or in which the older, underlying rocks dip at a different angle (usually steeper) than the younger, overlying strata.
- =top of basement rock.
- An unconformity developed between sedimentary rocks and older igneous or metamorphic rocks that had been exposed to erosion before the overlying sediments covered them.
- =short hiatus+/-erosion (a minor paraconformity)
- A relatively short interruption in sedimentation, involving only a brief interval of time, with little or no erosion before deposition is resumed; a depositional break of lesser magnitude than a paraconformity, or a paraconformity of very small time value.
- =no hiatus
- Undisturbed relationship between adjacent sedimentary strata that have been deposited in orderly sequence. True stratigraphic continuity in the sequence of beds.