81-602: The Los Angeles Basin is a sedimentary basin located in Southern California , in a region known as the Peninsular Ranges . The basin is also connected to an anomalous group of east–west trending chains of mountains collectively known as the Transverse Ranges . The present basin is a coastal lowland area, whose floor is marked by elongate low ridges and groups of hills that is located on
162-473: A monotreme , appeared. The predatory South American phorusrhacids were rare in this time; among the last was Titanis , a large phorusrhacid that migrated to North America and rivaled mammals as top predator. Other birds probably evolved at this time, some modern (such as the genera Cygnus , Bubo , Struthio and Corvus ), some now extinct. Alligators and crocodiles died out in Europe as
243-634: A basal marine conglomeratic sandstone, followed by a dominantly basaltic middle layer of multiple submarine lava flows and tuffs. The youngest part of this unit is a sedimentary breccia, conglomerate, sandstone, and a siltstone . The earliest deposits of the Topanga Group appear to reflect the continuation of a shift in shoreline that can be seen in both the Sespe and Vaqueros formations. Eruptions from one or more of volcanic centers locally and temporarily interrupted sedimentation. The Puente Formation
324-408: A basin are progressively younger from the outside in, with the youngest rocks in the center. Basins are often large in areal extent, often hundreds of kilometers across. Structural basins are often important sources of coal , petroleum , and groundwater . Pliocene The Pliocene ( / ˈ p l aɪ . ə s iː n , ˈ p l aɪ . oʊ -/ PLY -ə-seen, PLY -oh- ; also Pleiocene )
405-604: A broad anticline that is truncated by the Santa Monica fault zone. The central block contains both marine and non-marine clastic rock units interbedded with volcanic rocks that are late Cretaceous to Pliocene in age. Pliocene and Quaternary strata are most visible within the central block. Structurally, there is a synclinal trough. The northeastern block contains fine to coarse grained clastic marine rocks of Cenozoic age. Locally, middle Miocene volcanics can be seen as well as Eocene to Miocene aged non-marine sedimentary rocks. There
486-524: A general timeline to categorize the sequence of depositional events in the LA Basin's evolution and they are as follows: During pre- Turonian , metamorphosed sedimentary and volcanic rocks are present that serve as the two major basement rock units for the LA Basin. Large-scale movement along the Newport–Inglewood zone juxtaposed the two bedrock units along the east and west margins. During this phase,
567-450: A higher probability of experiencing seismic activity. The region experiences earthquakes that are mostly mild (magnitude ≤2.25). However moderate earthquakes (magnitude 4.9 to 6.4) have been reported. Earthquakes of moderate magnitude are very infrequent. This fault zone is the most notable feature within the basin that is a single strand with local (fault) splays. The fault zone is also marked by low hills, scarps, and ten anticlinal folds in
648-406: A large neocortex relative to body mass and stone tool manufacture. Improvements in dating methods and in the use of climate proxies have provided scientists with the means to test hypotheses of the evolution of human ancestors. Early hypotheses of the evolution of human traits emphasized the selective pressures produced by particular habitats. For example, many scientists have long favored
729-470: A major unconformity at the base of the middle Miocene units. Emergence did not occur at the same rate or in all sections of the basin. During this time, the basin was covered by a marine embayment. Rivers sourced in the highlands brought large amounts of detritus to the northeastern edge of the basin. During this period, the Topanga formation was also being deposited. The present form and structural relief of
810-429: A particular habitat. The change to a cooler, drier, more seasonal climate had considerable impacts on Pliocene vegetation, reducing tropical species worldwide. Deciduous forests proliferated, coniferous forests and tundra covered much of the north, and grasslands spread on all continents (except Antarctica). Eastern Africa in particular saw a huge expansion of C 4 grasslands. Tropical forests were limited to
891-543: A right-stepping en echelon pattern. It is located in the southwest portion of the basin and is a strike-slip margin. There are several oil fields that run parallel to this fault. This fault lies on the eastern border of the basin and mergers with the Elsinore Fault in the canyon of the Santa Ana River, one of the upper branches of the fault. This fault is a reverse right-oblique fault. It is most known for
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#1732780476060972-544: A shallow marine environment. Tectonic instability coupled with volcanic activity in rapidly subsiding areas during the Middle Miocene set the stage for the modern basin. The basin formed in a submarine environment and was later brought back above sea level when the rate of subsidence slowed. There is much discussion in the literature about the geologic time boundaries when each basin forming event took place. While exact ages may not be clear, Yerkes et al. (1965) provided
1053-968: A tight band around the equator, and in addition to dry savannahs , deserts appeared in Asia and Africa. Both marine and continental faunas were essentially modern, although continental faunas were a bit more primitive than today. The land mass collisions meant great migration and mixing of previously isolated species, such as in the Great American Interchange . Herbivores got bigger, as did specialized predators. In North America, rodents , large mastodons and gomphotheres , and opossums continued successfully, while hoofed animals ( ungulates ) declined, with camel , deer , and horse all seeing populations recede. Three-toed horses ( Nannippus ), oreodonts , protoceratids , and chalicotheres became extinct. Borophagine dogs and Agriotherium became extinct, but other carnivores including
1134-408: A type of geological trough . Some structural basins are sedimentary basins , aggregations of sediment that filled up a depression or accumulated in an area; others were formed by tectonic events long after the sedimentary layers were deposited. Basins may appear on a geologic map as roughly circular or elliptical, with concentric layers. Because the strata dip toward the center, the exposed strata in
1215-583: Is a deep-marine formation that is characterized by pro-delta sediments and an overlapping fan system. This unit lies above the Topanga Group giving it a Late Miocene depositional age and is divided into four members. The La Vida Member is a micaceous, platy siltstone with subordinate amounts of thin-bedded feldspathic sandstone. The next member is the Soquel, which is a thick bedded to massive micaceous sandstone. Locally abundant siltstone, conglomerate, and intraformational breccia can also be seen in this member. Above
1296-552: Is a key finding of research into a lake-sediment core obtained in Eastern Siberia, which is of exceptional importance because it has provided the longest continuous late Cenozoic land-based sedimentary record thus far. During the late Zanclean, Italy remained relatively warm and humid. Central Asia became more seasonal during the Pliocene, with colder, drier winters and wetter summers, which contributed to an increase in
1377-406: Is a large decline from the almost 1 billion barrels per year produced in the late 1970s. Oil fields include: Structural basin A structural basin is a large-scale structural formation of rock strata formed by tectonic warping ( folding ) of previously flat-lying strata into a syncline fold. They are geological depressions , the inverse of domes . Elongated structural basins are
1458-520: Is a largely unconsolidated unit and is composed mostly of gravel and floodplain sediments. The sediments that mark the top of the basin can be found in modern streams/rivers and at the base of the foothills. The history of this basin begins with the subduction of Pacific plate underneath the North American plate in the beginning of the Mesozoic. During this subduction event, two smaller plates,
1539-442: Is a mid-Miocene fault block that revealed a northwest trending ridge of Paleocene age rocks. This structural feature is important because it revealed many oil traps and orientation of the beds indicate the age of subsidence in this portion of the basin. This particular anticline is the most notable subsurface feature within the basin. Deformation events such as erosion of the uplifted crustal blocks, initiation of various faults, and
1620-418: Is also an anticline in the northeastern block. Homogeneous evolution of this basin did not occur due to dynamic tectonic activity. Despite the active setting, there are over 9,100 m of strata within the basin. The dynamic setting was also responsible for the heterogeneous deposition of each formation. It is common for rock units of the same depositional event to have different names in different locations within
1701-401: Is marked by two sandstone, siltstone and shale units. There are also characteristic mollusk fossils that indicate the area was dominately shallow marine. The Topanga Group is the next major formation in the stratigraphic sequence and infills the topography on older rocks. It is a mixed sedimentary and volcanic unit whose base is an erosional unconformity. The unit consists of 3 parts: First is
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#17327804760601782-415: Is remarkable due to the relatively small size and youth of the basin. The basin currently has about 40 active oil fields that collectively have 4,000 operating wells. In 1904, there were over 1,150 wells in the city of Los Angeles alone. Tight spacing and continued pumping of the wells resulted in most of the wells to dry up. Most recent data indicates that 255 million barrels of oil were produced in 2013. This
1863-519: Is split into two sub-facies known as the Pico and Repetto Members . These members represent a distinct change in the depositional environment and are of Pleistocene age. The Repetto is the older of the two members and is composed of interbedded fine to coarse grained siltstone, mudstone, and sandstone. The Pico Member is mostly made of massive siltstones and sandstones interbedded with minor silty-sandstones. Holocene alluvium and Quaternary sediments
1944-722: Is the epoch in the geologic time scale that extends from 5.33 to 2.58 million years ago (Ma). It is the second and most recent epoch of the Neogene Period in the Cenozoic Era . The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch. Prior to the 2009 revision of the geologic time scale, which placed the four most recent major glaciations entirely within the Pleistocene,
2025-466: Is the Whittier and Newport–Inglewood faults that have dictated the seismic behavior within the basin. The Los Angeles basin is still active tectonically and the region continues to experience earthquakes as a result. Due to the number of faults and fault splays, seismic activity is not concentrated in one particular area. The cities that are overlain by the Newport–Inglewood and Whittier fault zones have
2106-522: Is the first to appear above the great unconformity and is marked by interbedded mudstones, sandstones and pebbly sandstones. This bed sequence indicates an alluvial fan, meandering stream or braided stream origin. Upward from the Sespe Formation toward the Vaqueros , the grains become finer and the beds become thinner; indicating a transition to a shallow marine environment. The Vaqueros Formation
2187-468: Is used to correlate strata throughout the basin. The record of the Cenozoic activity begins above this unconformity. The stratigraphic record for this basin indicates that it began as a non-marine environment and then transgressed to a deep ocean system. The oldest basement units of this basin are of both sedimentary and igneous origin. The sedimentary unit was metamorphosed as a result of slippage of
2268-588: The Hardangervidda plateau to 1200 m in the Early Pliocene. In Southern Sweden similar movements elevated the South Swedish highlands leading to a deflection of the ancient Eridanos river from its original path across south-central Sweden into a course south of Sweden. The Pliocene is bookended by two significant events in the evolution of human ancestors. The first is the appearance of
2349-686: The Isthmus of Panama during the Pliocene, making possible the Great American Interchange and bringing a nearly complete end to South America's distinctive native ungulate fauna, though other South American lineages like its predatory mammals were already extinct by this point and others like xenarthrans continued to do well afterwards. The formation of the Isthmus had major consequences on global temperatures, since warm equatorial ocean currents were cut off and an Atlantic cooling cycle began, with cold Arctic and Antarctic waters decreasing temperatures in
2430-571: The Netherlands the Pliocene is divided into these stages (old to young): Brunssumian C, Reuverian A, Reuverian B, Reuverian C, Praetiglian , Tiglian A, Tiglian B, Tiglian C1-4b, Tiglian C4c, Tiglian C5, Tiglian C6 and Eburonian . The exact correlations between these local stages and the International Commission on Stratigraphy (ICS) stages is not established. During the Pliocene epoch (5.3 to 2.6 million years ago (Ma)),
2511-650: The Newport–Inglewood fault and is known as the Catalina Schist . The Catalina Schist can be found on the southwestern edge of the basin and is predominantly a chlorite-quartz schist. Closer to the Newport–Inglewood fault zone, garnet -bearing schists and metagabbros occur. The Santa Monica Slate can be observed in the northwestern block of the basin. The eastern complex is characterized by Santiago Peak Volcanics. This rock unit contains andesitic breccias , flow, agglomerates and tuffs . The Sespe Formation
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2592-478: The North Atlantic and North Pacific Ocean beds. Mid-latitude glaciation was probably underway before the end of the epoch. The global cooling that occurred during the Pliocene may have accelerated on the disappearance of forests and the spread of grasslands and savannas. During the Pliocene the earth climate system response shifted from a period of high frequency-low amplitude oscillation dominated by
2673-861: The Santa Monica Mountains and Puente, Elysian, and Repetto hills. To the southeast, the basin is bordered by the Santa Ana Mountains and the San Joaquin Hills . The western boundary of the basin is marked by the Continental Borderland and is part of the onshore portion. The California borderland is characterized by northwest trending offshore ridges and basins. The Los Angeles Basin is notable for its great structural relief and complexity in relation to its geologic youth and small size for its prolific oil production. Yerkes et al. identify five major stages of
2754-497: The hominin Australopithecus anamensis in the early Pliocene, around 4.2 million years ago. The second is the appearance of Homo , the genus that includes modern humans and their closest extinct relatives, near the end of the Pliocene at 2.6 million years ago. Key traits that evolved among hominins during the Pliocene include terrestrial bipedality and, by the end of the Pliocene, encephalized brains (brains with
2835-634: The savannah hypothesis . This proposes that the evolution of terrestrial bipedality and other traits was an adaptive response to Pliocene climate change that transformed forests into more open savannah . This was championed by Grafton Elliot Smith in his 1924 book, The Evolution of Man , as "the unknown world beyond the trees", and was further elaborated by Raymond Dart as the killer ape theory . Other scientists, such as Sherwood L. Washburn , emphasized an intrinsic model of hominin evolution. According to this model, early evolutionary developments triggered later developments. The model placed little emphasis on
2916-493: The weasel family diversified, and dogs and short-faced bears did well. Ground sloths , huge glyptodonts , and armadillos came north with the formation of the Isthmus of Panama. The latitudinal diversity gradient among terrestrial North American mammals became established during this epoch some time after 4 Ma. In Eurasia rodents did well, while primate distribution declined. Elephants , gomphotheres and stegodonts were successful in Asia (the largest land mammals of
2997-469: The 41,000-year period of Earth's obliquity to one of low-frequency, high-amplitude oscillation dominated by the 100,000-year period of the orbital eccentricity characteristic of the Pleistocene glacial-interglacial cycles. During the late Pliocene and early Pleistocene, 3.6 to 2.6 Ma, the Arctic was much warmer than it is at the present day (with summer temperatures some 8 °C warmer than today). That
3078-595: The Earth's climate became cooler and drier, as well as more seasonal, marking a transition between the relatively warm Miocene to the cooler Pleistocene . However, the beginning of the Pliocene was marked by an increase in global temperatures relative to the cooler Messinian . This increase was related to the 1.2 million year obliquity amplitude modulation cycle . By 3.3-3.0 Ma, during the Mid-Piacenzian Warm Period (mPWP), global average temperature
3159-456: The Holocene is characterized by non marine gravel, sand and silt. This phase also includes the late-stage compressional deformation responsible for the formation of the hydrocarbon traps. Four major faults are present in the region and divide the basin in the central, northwest, southwest, and northeast structural blocks. These blocks not only denote their geographic location, but they indicate
3240-591: The Monterey and Juan de Fuca plates, also began to subduct underneath the North American plate. Around 20Ma, the Monterey plate attached to and followed the motion of the Pacific plate. Later, subduction of the Pacific-Monterey ceased and the plate margin was converted to a transform boundary. The North America/Pacific-Monterey transform boundary began to move north and created crustal extension. This rifting
3321-510: The Pliocene also included the Gelasian Stage, which lasted from 2.59 to 1.81 Ma, and is now included in the Pleistocene. As with other older geologic periods, the geological strata that define the start and end are well-identified but the exact dates of the start and end of the epoch are slightly uncertain. The boundaries defining the Pliocene are not set at an easily identified worldwide event but rather at regional boundaries between
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3402-628: The Pliocene contains the Dacian (roughly equal to the Zanclean) and Romanian (roughly equal to the Piacenzian and Gelasian together) stages. As usual in stratigraphy, there are many other regional and local subdivisions in use. In Britain , the Pliocene is divided into the following stages (old to young): Gedgravian, Waltonian , Pre-Ludhamian, Ludhamian, Thurnian, Bramertonian or Antian, Pre-Pastonian or Baventian, Pastonian and Beestonian . In
3483-566: The Pliocene were such proboscideans as Deinotherium , Anancus , and Mammut borsoni , ) though proboscidean diversity declined significantly during the Late Pliocene. Hyraxes migrated north from Africa. Horse diversity declined, while tapirs and rhinos did fairly well. Bovines and antelopes were successful; some camel species crossed into Asia from North America. Hyenas and early saber-toothed cats appeared, joining other predators including dogs, bears, and weasels. Africa
3564-806: The Soquel lies the Yorba Member. This member is a sandy siltstone that is interbedded with a fine-grained sandstone. The Sycamore Canyon Member contains lenses of conglomerate, conglomeratic sandstone, and sandstone. Sandy siltstone and fine-grained sandstones are interbedded with the aforementioned rock types. The Monterey Formation is characterized by abnormally high silica content compared to most clastic rocks. There are also silica-cemented rocks known as porcelanite and porcelanite shale . While this formation has distinguishable beds, there are many shale, sandstone, and mudstone beds that have normal amounts of silica. This sequence of this formation indicates an off-shore marine environment. The Fernando Formation
3645-546: The Western Atlantic, assemblages of bivalves exhibited remarkable stasis with regards to their basal metabolic rates throughout the various climatic changes of the Pliocene. The Pliocene was a high water mark for species diversity among Caribbean corals. From 5 to 2 Ma, coral species origination rates were relatively high in the Caribbean, although a noticeable extinction event and drop in diversity occurred at
3726-429: The Whittier, Brea-Olinda, Sansinena, oil fields. There is an anticline that runs parallel to the Whittier fault that is evidence for compressional deformation during the late Miocene to early Pliocene. Thinning and pinch-out of the Pliocene sandstones are evidence for uplift during this same time period. The Anaheim nose is a subsurface feature that was discovered by geophysical surveys and exploratory drilling in 1930. It
3807-544: The abundance of C 4 plants across the region. In the Loess Plateau , δ13C values of occluded organic matter increased by 2.5% while those of pedogenic carbonate increased by 5% over the course of the Late Miocene and Pliocene, indicating increased aridification. Further aridification of Central Asia was caused by the development of Northern Hemisphere glaciation during the Late Pliocene. A sediment core from
3888-588: The basin lies on the boundary of the Transverse and Peninsular Ranges, this basin experiences both compressional and strike slip tectonics. During the early Pliocene, also identified as the "Basin Disruption" phase, deformation and folding occurred as a result of fault movement and a slight rotation event. While movement along the San Andreas Fault is responsible for the placement of the basin, it
3969-402: The basin was above sea level. The hallmarks of this phase were successive shoreline transgression and regression cycles. Deposition of older marine and non-marine sediments began to fill the basin. Towards the end of this phase, the shoreline began to retreat and deposition continued. After the deposition of the pre-Turonian units, there was a large emergence and erosion that can be observed as
4050-469: The basin was largely established during this phase of accelerated subsidence and deposition which occurred during the late Miocene and continued through the early Pleistocene. Clastic sedimentary rocks from the highland areas (to the north and east) moved down the submarine slopes and infilled the basin floor. Subsidence and sedimentation most likely began in the southern portion basin. Subsidence and Deposition occurred simultaneously, without interruption, until
4131-585: The basin's evolution, which began in the Upper Cretaceous and ended in the Pleistocene . This basin can be classified as an irregular pull-apart basin accompanied by rotational tectonics during the post- early Miocene . Before the formation of the basin, the area that encompasses the Los Angeles basin began above ground. A rapid transgression and regression of the shoreline moved the area to
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#17327804760604212-399: The basin. The thickness of these oil sands range from hundreds to thousands of feet. Anticlines and faulted anticlines are the structural features that are also responsible for trapping oil. The first reported oil-producing well was discovered in 1892 on the land that is presently beneath Dodger Stadium . This basin was responsible for half of the states oil production until the (90's?). This
4293-477: The basin. This may be a result of large variation in clast size as with the upper Pliocene Pico Formation in the northwestern part of the basin and the Upper Fernando Formation in the southwest part of the basin. The Los Angeles Basin contains what is known as the " Great Unconformity " which has been interpreted as a large-scale erosional event in the basement rock unit. This unconformity
4374-735: The climate cooled. Venomous snake genera continued to increase as more rodents and birds evolved. Rattlesnakes first appeared in the Pliocene. The modern species Alligator mississippiensis , having evolved in the Miocene, continued into the Pliocene, except with a more northern range; specimens have been found in very late Miocene deposits of Tennessee . Giant tortoises still thrived in North America, with genera like Hesperotestudo . Madtsoid snakes were still present in Australia. The amphibian order Allocaudata became extinct. In
4455-568: The development of the submarine channel led to the anticline's formation. Fold initiation began in the late-Miocene to early Pliocene period of deformation. There are many other anticlines within the basin and isopach data suggests that the formation of these folds occurred mostly during the Pliocene. The La Brea Tar Pits are pools of stagnant asphaltum that have been found on the basin's surface. These "pools" are important because hundreds of thousands of late Pleistocene bones and plants have been found. These pits allowed scientists to better understand
4536-475: The early-mid Pliocene (5 Ma – 3 Ma), after three-million-year intervals with modern or glacial ice volume became longer and collapse occurs only at times when warmer global temperature coincide with strong austral summer insolation anomalies. Continents continued to drift , moving from positions possibly as far as 250 km from their present locations to positions only 70 km from their current locations. South America became linked to North America through
4617-406: The ecosystem at that particular point in the geologic past. Accumulations of oil and gas occur almost wholly within strata of the younger sequence and in areas that are within or adjacent to the coastal belt. The Puente formation has proved to be the most notable reservoir for petroleum in the basin. The primary reason for the high abundance of oil is because the oil sands are well saturated within
4698-729: The edge of the Pacific plate . The Los Angeles Basin, along with the Santa Barbara Channel , the Ventura Basin , the San Fernando Valley , and the San Gabriel Basin , lies within the greater Southern California region. The majority of the jurisdictional land area of the city of Los Angeles physically lies within this basin. On the north, northeast, and east, the lowland basin is bound by
4779-570: The end of this interval. Oceans continued to be relatively warm during the Pliocene, though they continued cooling. The Arctic ice cap formed , drying the climate and increasing cool shallow currents in the North Atlantic. Deep cold currents flowed from the Antarctic. The formation of the Isthmus of Panama about 3.5 million years ago cut off the final remnant of what was once essentially a circum-equatorial current that had existed since
4860-549: The first time since the Cretaceous , with North American rodents and primates mixing with southern forms. Litopterns and the notoungulates , South American natives, were mostly wiped out, except for the macrauchenids and toxodonts , which managed to survive. Small weasel-like carnivorous mustelids , coatis and short-faced bears migrated from the north. Grazing glyptodonts , browsing giant ground sloths and smaller caviomorph rodents , pampatheres , and armadillos did
4941-413: The influence of seasonal variation. More recent research has emphasized the variability selection hypothesis, which proposes that variability in climate fostered development of hominin traits. Improved climate proxies show that the Pliocene climate of east Africa was highly variable, suggesting that adaptability to varying conditions was more important in driving hominin evolution than the steady pressure of
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#17327804760605022-412: The initiation of the modern basin. This movement caused the southwestern block to be uplifted relative to the central basin block. The central part of the basin continued to experience sediment deposition through the Pleistocene from flooding and erosional debris from the surrounding mountains and Puente Hills. This infill was responsible for the final retreat of the shoreline from the basin. Deposition in
5103-443: The late Pliocene. Until the rate of deposition gradually overtook the rate of subsidence, and the sea level began to fall. Towards the end of this phase, the margins of the basin began to rise above sea level. During the early Pleistocene, deposition began to outpace subsidence in the depressed parts of the basin and the shoreline began to move southward. This phase also had movement along the Newport–Inglewood fault zone that resulted in
5184-555: The northern South China Sea shows an increase in dust storm activity during the middle Pliocene. The South Asian Summer Monsoon (SASM) increased in intensity after 2.95 Ma, likely because of enhanced cross-equatorial pressure caused by the reorganisation of the Indonesian Throughflow. In the south-central Andes , an arid period occurred from 6.1 to 5.2 Ma, with another occurring from 3.6 to 3.3 Ma. These arid periods are coincident with global cold periods, during which
5265-754: The now-separated Atlantic Ocean. Africa 's collision with Europe formed the Mediterranean Sea , cutting off the remnants of the Tethys Ocean . The border between the Miocene and the Pliocene is also the time of the Messinian salinity crisis . During the Late Pliocene, the Himalayas became less active in their uplift, as evidenced by sedimentation changes in the Bengal Fan . The land bridge between Alaska and Siberia ( Beringia )
5346-512: The onset of continental glaciation in the Arctic, suggesting that vegetation changes in Australia during the Pliocene behaved similarly to during the Late Pleistocene and were likely characterised by comparable cycles of aridity and humidity. The equatorial Pacific Ocean sea surface temperature gradient was considerably lower than it is today. Mean sea surface temperatures in the east were substantially warmer than today but similar in
5427-400: The opposite, migrating to the north and thriving there. The marsupials remained the dominant Australian mammals, with herbivore forms including wombats and kangaroos , and the huge Diprotodon . Carnivorous marsupials continued hunting in the Pliocene, including dasyurids , the dog-like thylacine and cat-like Thylacoleo . The first rodents arrived in Australia. The modern platypus ,
5508-628: The position of the Southern Hemisphere westerlies shifted northward and disrupted the South American Low Level Jet, which brings moisture to southeastern South America. From around 3.8 Ma to about 3.3 Ma, North Africa experienced an extended humid period. In northwestern Africa, tropical forests extended up to Cape Blanc during the Zanclean until around 3.5 Ma. During the Piacenzian, from about 3.5 to 2.6 Ma,
5589-514: The recent", referring to the essentially modern marine mollusc fauna. In the official timescale of the ICS , the Pliocene is subdivided into two stages . From youngest to oldest they are: The Piacenzian is sometimes referred to as the Late Pliocene, whereas the Zanclean is referred to as the Early Pliocene. In the system of In the Paratethys area (central Europe and parts of western Asia)
5670-499: The region was forested at irregular intervals and contained a significant Saharan palaeoriver until 3.35 Ma, when trade winds began to dominate over fluvial transport of pollen. Around 3.26 Ma, a strong aridification event that was followed by a return to more humid conditions, which was itself followed by another aridification around 2.7 Ma. From 2.6 to 2.4 Ma, vegetation zones began repeatedly shifting latitudinally in response to glacial-interglacial cycles. The climate of eastern Africa
5751-527: The scene. Bears, dogs and weasels (originally from North America) joined cats, hyenas and civets as the African predators, forcing hyenas to adapt as specialized scavengers. Most mustelids in Africa declined as a result of increased competition from the new predators, although Enhydriodon omoensis remained an unusually successful terrestrial predator. South America was invaded by North American species for
5832-498: The strata present and major structural features. The southwestern block was uplifted prior to the middle Miocene and is composed mostly of marine strata and contains two major anticlines. This block also contains the steeply-dipping Palos Verdes Hills fault zone. The middle Miocene volcanics can be seen locally within the southwest block. The northwestern block consists of clastic marine sediments of Late Cretaceous to Pleistocene age. Middle Miocene volcanics are also present. This block has
5913-400: The surrounding environment. Anthropologists tended to focus on intrinsic models while geologists and vertebrate paleontologists tended to put greater emphasis on habitats. Alternatives to the savanna hypothesis include the woodland/forest hypothesis, which emphasizes the evolution of hominins in closed habitats, or hypotheses emphasizing the influence of colder habitats at higher latitudes or
5994-514: The warmer Miocene and the relatively cooler Pleistocene. The upper boundary was set at the start of the Pleistocene glaciations. Charles Lyell (later Sir Charles) gave the Pliocene its name in Principles of Geology (volume 3, 1833). The word pliocene comes from the Greek words πλεῖον ( pleion , "more") and καινός ( kainos , "new" or "recent") and means roughly "continuation of
6075-505: The west. This condition has been described as a permanent El Niño state, or “El Padre.” Several mechanisms have been proposed for this pattern, including increased tropical cyclone activity . The extent of the West Antarctic Ice Sheet oscillated at the 40 kyr period of Earth's obliquity. Ice sheet collapse occurred when the global average temperature was 3 °C warmer than today and carbon dioxide concentration
6156-470: Was 2–3 °C higher than today, while carbon dioxide levels were the same as today (400 ppm). Global sea level was about 25 m higher, though its exact value is uncertain. The northern hemisphere ice sheet was ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 Ma. The formation of an Arctic ice cap is signaled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in
6237-430: Was accompanied with the rotation of the western Transverse Ranges. This rotation is responsible for the placement and northwest–southeast orientation of the LA Basin. Early in the Miocene, before deposition of the Topanga, high heat flow and transtension caused the extension of the basin. As the crust thinned, the basin began to subside from isostatic pressure as a result of large amounts of sediment deposition. Because
6318-511: Was at 400 ppmv. This resulted in open waters in the Ross Sea . Global sea-level fluctuation associated with ice-sheet collapse was probably up to 7 meters for the west Antarctic and 3 meters for the east Antarctic. Model simulations are consistent with reconstructed ice-sheet oscillations and suggest a progression from a smaller to a larger West Antarctic ice sheet in the last 5 million years. Intervals of ice sheet collapse were much more common in
6399-486: Was dominated by hoofed animals, and primates continued their evolution, with australopithecines (some of the first hominins ) and baboon-like monkeys such as the Dinopithecus appearing in the late Pliocene. Rodents were successful, and elephant populations increased. Cows and antelopes continued diversification and overtook pigs in numbers of species. Early giraffes appeared. Horses and modern rhinos came onto
6480-452: Was first flooded near the start of the Pliocene, allowing marine organisms to spread between the Arctic and Pacific Oceans. The bridge would continue to be periodically flooded and restored thereafter. Pliocene marine formations are exposed in northeast Spain , southern California , New Zealand , and Italy . During the Pliocene parts of southern Norway and southern Sweden that had been near sea level rose. In Norway this rise elevated
6561-545: Was very similar to what it is today. Unexpectedly, the expansion of grasslands in eastern Africa during this epoch appears to have been decoupled from aridification and not caused by it, as evidenced by their asynchrony. Southwestern Australia hosted heathlands , shrublands , and woodlands with a greater species diversity compared to today during the Middle and Late Pliocene. Three different aridification events occurred around 2.90, 2.59, and 2.56 Ma, and may have been linked to
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